Fix a bunch of issues with 'hidden' DOM types.

frog/frogsh

Index: frog/frogsh
diff --git a/frog/frogsh b/frog/frogsh
index 1b9790d7c89506c6931b6ed5032d54d3a5cc7c2e..6c26c3e7645e00f2c7dc4642f633468d88f2105b 100755
--- a/frog/frogsh
+++ b/frog/frogsh
@@ -1,18 +1,26 @@
 #!/usr/bin/env node
 //  ********** Library dart:core **************
 //  ********** Natives dart:core **************
+Object.prototype.$typeNameOf = function() {
+  if ((typeof(window) != 'undefined' && window.constructor.name == 'DOMWindow')
+      || typeof(process) != 'undefined') { // fast-path for Chrome and Node
+    return this.constructor.name;
+  }
+  var str = Object.prototype.toString.call(this);
+  str = str.substring(8, str.length - 1);
+  if (str == 'Window') str = 'DOMWindow';
+  return str;
+}
 /**
  * Generates a dynamic call stub for a function.
  * Our goal is to create a stub method like this on-the-fly:
- *   function($0, $1, capture) { this($0, $1, true, capture); }
+ *   function($0, $1, capture) { return this($0, $1, true, capture); }
  *
  * This stub then replaces the dynamic one on Function, with one that is
  * specialized for that particular function, taking into account its default
  * arguments.
  */
 Function.prototype.$genStub = function(argsLength, names) {
-  // TODO(jmesserly): only emit $genStub if actually needed
-
   // Fast path: if no named arguments and arg count matches
   if (this.length == argsLength && !names) {
     return this;
@@ -71,7 +79,8 @@ Function.prototype.$genStub = function(argsLength, names) {
   return new Function('$f', 'return ' + f + '').call(null, this);
 }
 function $notnull_bool(test) {
-  return (test === true || test === false) ? test : test.is$bool(); // TypeError
+  if (test === true || test === false) return test;
+  $throw(new TypeError(test, 'bool'));
 }
 function $assert(test, text, url, line, column) {
   if (typeof test == 'function') test = test();
@@ -154,17 +163,31 @@ Clock.frequency = function() {
   return 1000;
 }
 // ********** Code for AssertError **************
-function AssertError(failedAssertion, url, line, column) {
+function AssertError() {}
+AssertError._internal$ctor = function(failedAssertion, url, line, column) {
   this.failedAssertion = failedAssertion;
   this.url = url;
   this.line = line;
   this.column = column;
   // Initializers done
 }
+AssertError._internal$ctor.prototype = AssertError.prototype;
 AssertError.prototype.toString = function() {
   return ("Failed assertion: '" + this.failedAssertion + "' is not true ") + ("in " + this.url + " at line " + this.line + ", column " + this.column + ".");
 }
-AssertError.prototype.toString$0 = AssertError.prototype.toString;
+AssertError.prototype.toString$0 = function() {
+  return this.toString();
+};
+// ********** Code for TypeError **************
+TypeError._internal$ctor = function(src, dstType) {
+  this.srcType = (src == null ? "Null" : src.$typeNameOf());
+  this.destType = destType;
+  this.toString = function() {
+    return ("Failed type check: type " + this.srcType +
+        " is not assignable to type" + this.dstType);
+  }
+}
+TypeError._internal$ctor.prototype = TypeError.prototype;
 // ********** Code for Object **************
 Object.prototype.get$dynamic = function() {
   return this;
@@ -199,6 +222,369 @@ Object.prototype.addSource$1 = function($0) {
 Object.prototype.appendByteStringToken$2 = function($0, $1) {
   return this.noSuchMethod("appendByteStringToken", [$0, $1]);
 };
+Object.prototype.assert$ArgumentNode = function() {
+  $throw(new TypeError._internal$ctor(this, "ArgumentNode"));
+};
+Object.prototype.assert$Arguments = function() {
+  $throw(new TypeError._internal$ctor(this, "Arguments"));
+};
+Object.prototype.assert$BeginGroupToken = function() {
+  $throw(new TypeError._internal$ctor(this, "BeginGroupToken"));
+};
+Object.prototype.assert$BinaryExpression = function() {
+  $throw(new TypeError._internal$ctor(this, "BinaryExpression"));
+};
+Object.prototype.assert$BlockScope = function() {
+  $throw(new TypeError._internal$ctor(this, "BlockScope"));
+};
+Object.prototype.assert$BlockStatement = function() {
+  $throw(new TypeError._internal$ctor(this, "BlockStatement"));
+};
+Object.prototype.assert$CallExpression = function() {
+  $throw(new TypeError._internal$ctor(this, "CallExpression"));
+};
+Object.prototype.assert$ClassElement = function() {
+  $throw(new TypeError._internal$ctor(this, "ClassElement"));
+};
+Object.prototype.assert$ClassNode = function() {
+  $throw(new TypeError._internal$ctor(this, "ClassNode"));
+};
+Object.prototype.assert$CodeWriter = function() {
+  $throw(new TypeError._internal$ctor(this, "CodeWriter"));
+};
+Object.prototype.assert$Collection_E = function() {
+  $throw(new TypeError._internal$ctor(this, "Collection<E>"));
+};
+Object.prototype.assert$Collection_Object = function() {
+  $throw(new TypeError._internal$ctor(this, "Collection<Object>"));
+};
+Object.prototype.assert$Collection_Type = function() {
+  $throw(new TypeError._internal$ctor(this, "Collection<Type>"));
+};
+Object.prototype.assert$Comparable = function() {
+  $throw(new TypeError._internal$ctor(this, "Comparable"));
+};
+Object.prototype.assert$Compiler = function() {
+  $throw(new TypeError._internal$ctor(this, "Compiler"));
+};
+Object.prototype.assert$ConcreteMember = function() {
+  $throw(new TypeError._internal$ctor(this, "ConcreteMember"));
+};
+Object.prototype.assert$ConcreteType = function() {
+  $throw(new TypeError._internal$ctor(this, "ConcreteType"));
+};
+Object.prototype.assert$Date = function() {
+  $throw(new TypeError._internal$ctor(this, "Date"));
+};
+Object.prototype.assert$DeclaredIdentifier = function() {
+  $throw(new TypeError._internal$ctor(this, "DeclaredIdentifier"));
+};
+Object.prototype.assert$DefinedType = function() {
+  $throw(new TypeError._internal$ctor(this, "DefinedType"));
+};
+Object.prototype.assert$Definition = function() {
+  $throw(new TypeError._internal$ctor(this, "Definition"));
+};
+Object.prototype.assert$DotExpression = function() {
+  $throw(new TypeError._internal$ctor(this, "DotExpression"));
+};
+Object.prototype.assert$DoubleLinkedQueueEntry_KeyValuePair_K$V = function() {
+  $throw(new TypeError._internal$ctor(this, "DoubleLinkedQueueEntry<KeyValuePair<K, V>>"));
+};
+Object.prototype.assert$Duration = function() {
+  $throw(new TypeError._internal$ctor(this, "Duration"));
+};
+Object.prototype.assert$Element = function() {
+  $throw(new TypeError._internal$ctor(this, "Element"));
+};
+Object.prototype.assert$Expression = function() {
+  $throw(new TypeError._internal$ctor(this, "Expression"));
+};
+Object.prototype.assert$ExpressionStatement = function() {
+  $throw(new TypeError._internal$ctor(this, "ExpressionStatement"));
+};
+Object.prototype.assert$FieldMember = function() {
+  $throw(new TypeError._internal$ctor(this, "FieldMember"));
+};
+Object.prototype.assert$FunctionDefinition = function() {
+  $throw(new TypeError._internal$ctor(this, "FunctionDefinition"));
+};
+Object.prototype.assert$FunctionElement = function() {
+  $throw(new TypeError._internal$ctor(this, "FunctionElement"));
+};
+Object.prototype.assert$FunctionExpression = function() {
+  $throw(new TypeError._internal$ctor(this, "FunctionExpression"));
+};
+Object.prototype.assert$FunctionType = function() {
+  $throw(new TypeError._internal$ctor(this, "FunctionType"));
+};
+Object.prototype.assert$FunctionTypeReference = function() {
+  $throw(new TypeError._internal$ctor(this, "FunctionTypeReference"));
+};
+Object.prototype.assert$GenericTypeReference = function() {
+  $throw(new TypeError._internal$ctor(this, "GenericTypeReference"));
+};
+Object.prototype.assert$GlobalValue = function() {
+  $throw(new TypeError._internal$ctor(this, "GlobalValue"));
+};
+Object.prototype.assert$HBasicBlock = function() {
+  $throw(new TypeError._internal$ctor(this, "HBasicBlock"));
+};
+Object.prototype.assert$HGraph = function() {
+  $throw(new TypeError._internal$ctor(this, "HGraph"));
+};
+Object.prototype.assert$HInstruction = function() {
+  $throw(new TypeError._internal$ctor(this, "HInstruction"));
+};
+Object.prototype.assert$HLiteral = function() {
+  $throw(new TypeError._internal$ctor(this, "HLiteral"));
+};
+Object.prototype.assert$HLocal = function() {
+  $throw(new TypeError._internal$ctor(this, "HLocal"));
+};
+Object.prototype.assert$HParameterValue = function() {
+  $throw(new TypeError._internal$ctor(this, "HParameterValue"));
+};
+Object.prototype.assert$HPhi = function() {
+  $throw(new TypeError._internal$ctor(this, "HPhi"));
+};
+Object.prototype.assert$HStatic = function() {
+  $throw(new TypeError._internal$ctor(this, "HStatic"));
+};
+Object.prototype.assert$HTypeGuard = function() {
+  $throw(new TypeError._internal$ctor(this, "HTypeGuard"));
+};
+Object.prototype.assert$HVisitor = function() {
+  $throw(new TypeError._internal$ctor(this, "HVisitor"));
+};
+Object.prototype.assert$HashMapImplementation = function() {
+  $throw(new TypeError._internal$ctor(this, "HashMapImplementation"));
+};
+Object.prototype.assert$HashSetImplementation = function() {
+  $throw(new TypeError._internal$ctor(this, "HashSetImplementation"));
+};
+Object.prototype.assert$Identifier = function() {
+  $throw(new TypeError._internal$ctor(this, "Identifier"));
+};
+Object.prototype.assert$IndexExpression = function() {
+  $throw(new TypeError._internal$ctor(this, "IndexExpression"));
+};
+Object.prototype.assert$InterpStack = function() {
+  $throw(new TypeError._internal$ctor(this, "InterpStack"));
+};
+Object.prototype.assert$Iterable = function() {
+  $throw(new TypeError._internal$ctor(this, "Iterable"));
+};
+Object.prototype.assert$Iterator_T = function() {
+  $throw(new TypeError._internal$ctor(this, "Iterator<T>"));
+};
+Object.prototype.assert$KeywordState = function() {
+  $throw(new TypeError._internal$ctor(this, "KeywordState"));
+};
+Object.prototype.assert$LambdaExpression = function() {
+  $throw(new TypeError._internal$ctor(this, "LambdaExpression"));
+};
+Object.prototype.assert$Library = function() {
+  $throw(new TypeError._internal$ctor(this, "Library"));
+};
+Object.prototype.assert$Link_Element = function() {
+  $throw(new TypeError._internal$ctor(this, "Link<Element>"));
+};
+Object.prototype.assert$Link_Node = function() {
+  $throw(new TypeError._internal$ctor(this, "Link<Node>"));
+};
+Object.prototype.assert$Link_Token = function() {
+  $throw(new TypeError._internal$ctor(this, "Link<Token>"));
+};
+Object.prototype.assert$Link_Type = function() {
+  $throw(new TypeError._internal$ctor(this, "Link<Type>"));
+};
+Object.prototype.assert$List = function() {
+  $throw(new TypeError._internal$ctor(this, "List"));
+};
+Object.prototype.assert$ListFactory = function() {
+  $throw(new TypeError._internal$ctor(this, "ListFactory"));
+};
+Object.prototype.assert$List_ArgumentNode = function() {
+  $throw(new TypeError._internal$ctor(this, "List<ArgumentNode>"));
+};
+Object.prototype.assert$List_Definition = function() {
+  $throw(new TypeError._internal$ctor(this, "List<Definition>"));
+};
+Object.prototype.assert$List_EvaluatedValue = function() {
+  $throw(new TypeError._internal$ctor(this, "List<EvaluatedValue>"));
+};
+Object.prototype.assert$List_GlobalValue = function() {
+  $throw(new TypeError._internal$ctor(this, "List<GlobalValue>"));
+};
+Object.prototype.assert$List_HInstruction = function() {
+  $throw(new TypeError._internal$ctor(this, "List<HInstruction>"));
+};
+Object.prototype.assert$List_Member = function() {
+  $throw(new TypeError._internal$ctor(this, "List<Member>"));
+};
+Object.prototype.assert$List_ParameterType = function() {
+  $throw(new TypeError._internal$ctor(this, "List<ParameterType>"));
+};
+Object.prototype.assert$List_String = function() {
+  $throw(new TypeError._internal$ctor(this, "List<String>"));
+};
+Object.prototype.assert$List_Token = function() {
+  $throw(new TypeError._internal$ctor(this, "List<Token>"));
+};
+Object.prototype.assert$List_Type = function() {
+  $throw(new TypeError._internal$ctor(this, "List<Type>"));
+};
+Object.prototype.assert$List_Value = function() {
+  $throw(new TypeError._internal$ctor(this, "List<Value>"));
+};
+Object.prototype.assert$List_int = function() {
+  $throw(new TypeError._internal$ctor(this, "List<int>"));
+};
+Object.prototype.assert$LiteralString = function() {
+  $throw(new TypeError._internal$ctor(this, "LiteralString"));
+};
+Object.prototype.assert$Map_Node$Element = function() {
+  $throw(new TypeError._internal$ctor(this, "Map<Node, Element>"));
+};
+Object.prototype.assert$Map_String$Member = function() {
+  $throw(new TypeError._internal$ctor(this, "Map<String, Member>"));
+};
+Object.prototype.assert$Member = function() {
+  $throw(new TypeError._internal$ctor(this, "Member"));
+};
+Object.prototype.assert$MemberSet = function() {
+  $throw(new TypeError._internal$ctor(this, "MemberSet"));
+};
+Object.prototype.assert$MethodGenerator = function() {
+  $throw(new TypeError._internal$ctor(this, "MethodGenerator"));
+};
+Object.prototype.assert$MethodMember = function() {
+  $throw(new TypeError._internal$ctor(this, "MethodMember"));
+};
+Object.prototype.assert$NameTypeReference = function() {
+  $throw(new TypeError._internal$ctor(this, "NameTypeReference"));
+};
+Object.prototype.assert$Node = function() {
+  $throw(new TypeError._internal$ctor(this, "Node"));
+};
+Object.prototype.assert$NodeList = function() {
+  $throw(new TypeError._internal$ctor(this, "NodeList"));
+};
+Object.prototype.assert$NumImplementation = function() {
+  $throw(new TypeError._internal$ctor(this, "NumImplementation"));
+};
+Object.prototype.assert$Operator = function() {
+  $throw(new TypeError._internal$ctor(this, "Operator"));
+};
+Object.prototype.assert$Parameter = function() {
+  $throw(new TypeError._internal$ctor(this, "Parameter"));
+};
+Object.prototype.assert$ParameterType = function() {
+  $throw(new TypeError._internal$ctor(this, "ParameterType"));
+};
+Object.prototype.assert$ParenthesizedExpression = function() {
+  $throw(new TypeError._internal$ctor(this, "ParenthesizedExpression"));
+};
+Object.prototype.assert$Pattern = function() {
+  $throw(new TypeError._internal$ctor(this, "Pattern"));
+};
+Object.prototype.assert$PostfixExpression = function() {
+  $throw(new TypeError._internal$ctor(this, "PostfixExpression"));
+};
+Object.prototype.assert$PropertyMember = function() {
+  $throw(new TypeError._internal$ctor(this, "PropertyMember"));
+};
+Object.prototype.assert$SendSet = function() {
+  $throw(new TypeError._internal$ctor(this, "SendSet"));
+};
+Object.prototype.assert$SourceFile = function() {
+  $throw(new TypeError._internal$ctor(this, "SourceFile"));
+};
+Object.prototype.assert$SourceSpan = function() {
+  $throw(new TypeError._internal$ctor(this, "SourceSpan"));
+};
+Object.prototype.assert$SourceString = function() {
+  $throw(new TypeError._internal$ctor(this, "SourceString"));
+};
+Object.prototype.assert$Statement = function() {
+  $throw(new TypeError._internal$ctor(this, "Statement"));
+};
+Object.prototype.assert$StringBuffer = function() {
+  $throw(new TypeError._internal$ctor(this, "StringBuffer"));
+};
+Object.prototype.assert$Token = function() {
+  $throw(new TypeError._internal$ctor(this, "Token"));
+};
+Object.prototype.assert$TreeVisitor = function() {
+  $throw(new TypeError._internal$ctor(this, "TreeVisitor"));
+};
+Object.prototype.assert$Type = function() {
+  $throw(new TypeError._internal$ctor(this, "Type"));
+};
+Object.prototype.assert$TypeAnnotation = function() {
+  $throw(new TypeError._internal$ctor(this, "TypeAnnotation"));
+};
+Object.prototype.assert$TypeDefinition = function() {
+  $throw(new TypeError._internal$ctor(this, "TypeDefinition"));
+};
+Object.prototype.assert$TypeMember = function() {
+  $throw(new TypeError._internal$ctor(this, "TypeMember"));
+};
+Object.prototype.assert$TypeReference = function() {
+  $throw(new TypeError._internal$ctor(this, "TypeReference"));
+};
+Object.prototype.assert$Types = function() {
+  $throw(new TypeError._internal$ctor(this, "Types"));
+};
+Object.prototype.assert$UnaryExpression = function() {
+  $throw(new TypeError._internal$ctor(this, "UnaryExpression"));
+};
+Object.prototype.assert$Value = function() {
+  $throw(new TypeError._internal$ctor(this, "Value"));
+};
+Object.prototype.assert$ValueSetNode = function() {
+  $throw(new TypeError._internal$ctor(this, "ValueSetNode"));
+};
+Object.prototype.assert$VarExpression = function() {
+  $throw(new TypeError._internal$ctor(this, "VarExpression"));
+};
+Object.prototype.assert$VarFunctionStub = function() {
+  $throw(new TypeError._internal$ctor(this, "VarFunctionStub"));
+};
+Object.prototype.assert$VarMember = function() {
+  $throw(new TypeError._internal$ctor(this, "VarMember"));
+};
+Object.prototype.assert$VariableDefinitions = function() {
+  $throw(new TypeError._internal$ctor(this, "VariableDefinitions"));
+};
+Object.prototype.assert$VariableElement = function() {
+  $throw(new TypeError._internal$ctor(this, "VariableElement"));
+};
+Object.prototype.assert$Visitor = function() {
+  $throw(new TypeError._internal$ctor(this, "Visitor"));
+};
+Object.prototype.assert$lang_Element = function() {
+  $throw(new TypeError._internal$ctor(this, "Element"));
+};
+Object.prototype.assert$lang_Expression = function() {
+  $throw(new TypeError._internal$ctor(this, "Expression"));
+};
+Object.prototype.assert$lang_Identifier = function() {
+  $throw(new TypeError._internal$ctor(this, "Identifier"));
+};
+Object.prototype.assert$lang_Node = function() {
+  $throw(new TypeError._internal$ctor(this, "Node"));
+};
+Object.prototype.assert$lang_Statement = function() {
+  $throw(new TypeError._internal$ctor(this, "Statement"));
+};
+Object.prototype.assert$lang_Token = function() {
+  $throw(new TypeError._internal$ctor(this, "Token"));
+};
+Object.prototype.assert$lang_Type = function() {
+  $throw(new TypeError._internal$ctor(this, "Type"));
+};
 Object.prototype.block$0 = function() {
   return this.noSuchMethod("block", []);
 };
@@ -268,9 +654,6 @@ Object.prototype.genValue$2 = function($0, $1) {
 Object.prototype.generate$1 = function($0) {
   return this.noSuchMethod("generate", [$0]);
 };
-Object.prototype.generateBody$2 = function($0, $1) {
-  return this.noSuchMethod("generateBody", [$0, $1]);
-};
 Object.prototype.getBeginToken$0 = function() {
   return this.noSuchMethod("getBeginToken", []);
 };
@@ -331,6 +714,12 @@ Object.prototype.invoke$4$isDynamic = function($0, $1, $2, $3, isDynamic) {
 Object.prototype.invoke$5 = function($0, $1, $2, $3, $4) {
   return this.noSuchMethod("invoke", [$0, $1, $2, $3, $4]);
 };
+Object.prototype.is$List = function() {
+  return false;
+};
+Object.prototype.is$SourceString = function() {
+  return false;
+};
 Object.prototype.isAssignable$1 = function($0) {
   return this.noSuchMethod("isAssignable", [$0]);
 };
@@ -465,7 +854,7 @@ Object.prototype.writeDefinition$2 = function($0, $1) {
 };
 function $assert_bool(x) {
   if (x == null || typeof(x) == "boolean") return x;
-  throw new TypeError("'" + x + "' is not a bool.");
+  $throw(new TypeError._internal$ctor(this, "bool"))
 }
 // ********** Code for IllegalAccessException **************
 function IllegalAccessException() {
@@ -600,11 +989,11 @@ Math.min = function(a, b) {
 }
 function $assert_num(x) {
   if (x == null || typeof(x) == "number") return x;
-  throw new TypeError("'" + x + "' is not a num.");
+  $throw(new TypeError._internal$ctor(this, "num"))
 }
 function $assert_String(x) {
   if (x == null || typeof(x) == "string") return x;
-  throw new TypeError("'" + x + "' is not a String.");
+  $throw(new TypeError._internal$ctor(this, "String"))
 }
 // ********** Code for Strings **************
 function Strings() {}
@@ -625,86 +1014,85 @@ function print(obj) {
   }
 }
 function _toDartException(e) {
-  {
-    function attachStack(dartEx) {
-      // TODO(jmesserly): setting the stack property is not a long term solution.
-      var stack = e.stack;
-      // The stack contains the error message, and the stack is all that is
-      // printed (the exception's toString() is never called).  Make the Dart
-      // exception's toString() be the dominant message.
-      if (typeof stack == 'string') {
-        var message = dartEx.toString();
-        if (/^(Type|Range)Error:/.test(stack)) {
-          // Indent JS message (it can be helpful) so new message stands out.
-          stack = '    (' + stack.substring(0, stack.indexOf('\n')) + ')\n' +
-                  stack.substring(stack.indexOf('\n') + 1);
+  function attachStack(dartEx) {
+    // TODO(jmesserly): setting the stack property is not a long term solution.
+    var stack = e.stack;
+    // The stack contains the error message, and the stack is all that is
+    // printed (the exception's toString() is never called).  Make the Dart
+    // exception's toString() be the dominant message.
+    if (typeof stack == 'string') {
+      var message = dartEx.toString();
+      if (/^(Type|Range)Error:/.test(stack)) {
+        // Indent JS message (it can be helpful) so new message stands out.
+        stack = '    (' + stack.substring(0, stack.indexOf('\n')) + ')\n' +
+                stack.substring(stack.indexOf('\n') + 1);
+      }
+      stack = message + '\n' + stack;
+    }
+    dartEx.stack = stack;
+    return dartEx;
+  }
+
+  if (e instanceof TypeError) {
+    switch(e.type) {
+      case 'property_not_function':
+      case 'called_non_callable':
+        if (e.arguments[0] == null) {
+          return attachStack(new NullPointerException());
+        } else {
+          return attachStack(new ObjectNotClosureException());
         }
-        stack = message + '\n' + stack;
-      }
-      dartEx.stack = stack;
-      return dartEx;
+        break;
+      case 'non_object_property_call':
+      case 'non_object_property_load':
+        return attachStack(new NullPointerException());
+        break;
+      case 'undefined_method':
+        if (e.arguments[0] == 'call' || e.arguments[0] == 'apply') {
+          return attachStack(new ObjectNotClosureException());
+        } else {
+          // TODO(jmesserly): can this ever happen?
+          // sra: Yes, seen on '$add'.
+          return attachStack(new NoSuchMethodException('', e.arguments[0], []));
+        }
+        break;
     }
-
-    if (e instanceof TypeError) {
-      switch(e.type) {
-        case 'property_not_function':
-        case 'called_non_callable':
-          if (e.arguments[0] == null) {
-            return attachStack(new NullPointerException());
-          } else {
-            return attachStack(new ObjectNotClosureException());
-          }
-          break;
-        case 'non_object_property_call':
-        case 'non_object_property_load':
-          return attachStack(new NullPointerException());
-          break;
-        case 'undefined_method':
-          if (e.arguments[0] == 'call' || e.arguments[0] == 'apply') {
-            return attachStack(new ObjectNotClosureException());
-          } else {
-            // TODO(jmesserly): can this ever happen?
-            // sra: Yes, seen on '$add'.
-            return attachStack(new NoSuchMethodException('', e.arguments[0], []));
-          }
-          break;
-      }
-    } else if (e instanceof RangeError) {
-      if (e.message.indexOf('call stack') >= 0) {
-        return attachStack(new StackOverflowException());
-      }
+  } else if (e instanceof RangeError) {
+    if (e.message.indexOf('call stack') >= 0) {
+      return attachStack(new StackOverflowException());
     }
-    return e;
   }
+  return e;
 }
 //  ********** Library dart:coreimpl **************
 // ********** Code for ListFactory **************
 ListFactory = Array;
-ListFactory.prototype.is$ListFactory = function(){return this;};
-ListFactory.prototype.is$List = function(){return this;};
-ListFactory.prototype.is$List_ArgumentNode = function(){return this;};
-ListFactory.prototype.is$List_Definition = function(){return this;};
-ListFactory.prototype.is$List_EvaluatedValue = function(){return this;};
-ListFactory.prototype.is$List_GlobalValue = function(){return this;};
-ListFactory.prototype.is$List_HInstruction = function(){return this;};
-ListFactory.prototype.is$List_Member = function(){return this;};
-ListFactory.prototype.is$List_ParameterType = function(){return this;};
-ListFactory.prototype.is$List_String = function(){return this;};
-ListFactory.prototype.is$List_Token = function(){return this;};
-ListFactory.prototype.is$List_Type = function(){return this;};
-ListFactory.prototype.is$List_Value = function(){return this;};
-ListFactory.prototype.is$List_int = function(){return this;};
-ListFactory.prototype.is$Collection_E = function(){return this;};
-ListFactory.prototype.is$Collection_Object = function(){return this;};
-ListFactory.prototype.is$Collection_Type = function(){return this;};
-ListFactory.prototype.is$Iterable = function(){return this;};
+ListFactory.prototype.assert$ListFactory = function(){return this};
+ListFactory.prototype.is$List = function(){return true};
+ListFactory.prototype.assert$List = function(){return this};
+ListFactory.prototype.assert$List_ArgumentNode = function(){return this};
+ListFactory.prototype.assert$List_Definition = function(){return this};
+ListFactory.prototype.assert$List_EvaluatedValue = function(){return this};
+ListFactory.prototype.assert$List_GlobalValue = function(){return this};
+ListFactory.prototype.assert$List_HInstruction = function(){return this};
+ListFactory.prototype.assert$List_Member = function(){return this};
+ListFactory.prototype.assert$List_ParameterType = function(){return this};
+ListFactory.prototype.assert$List_String = function(){return this};
+ListFactory.prototype.assert$List_Token = function(){return this};
+ListFactory.prototype.assert$List_Type = function(){return this};
+ListFactory.prototype.assert$List_Value = function(){return this};
+ListFactory.prototype.assert$List_int = function(){return this};
+ListFactory.prototype.assert$Collection_E = function(){return this};
+ListFactory.prototype.assert$Collection_Object = function(){return this};
+ListFactory.prototype.assert$Collection_Type = function(){return this};
+ListFactory.prototype.assert$Iterable = function(){return this};
 ListFactory.ListFactory$from$factory = function(other) {
   var list = [];
   for (var $i = other.iterator(); $i.hasNext$0(); ) {
     var e = $i.next$0();
     list.add(e);
   }
-  return (list && list.is$ListFactory());
+  return (list == null ? null : list.assert$ListFactory());
 }
 ListFactory.prototype.add = function(value) {
   this.push(value);
@@ -752,7 +1140,7 @@ ListFactory.prototype.iterator = function() {
 }
 ListFactory.prototype.add$1 = ListFactory.prototype.add;
 ListFactory.prototype.addAll$1 = function($0) {
-  return this.addAll(($0 && $0.is$Collection_E()));
+  return this.addAll(($0 == null ? null : $0.assert$Collection_E()));
 };
 ListFactory.prototype.every$1 = function($0) {
   return this.every(to$call$1($0));
@@ -792,7 +1180,7 @@ function ListIterator(array) {
   this._pos = 0;
   // Initializers done
 }
-ListIterator.prototype.is$Iterator_T = function(){return this;};
+ListIterator.prototype.assert$Iterator_T = function(){return this};
 ListIterator.prototype.hasNext = function() {
   return this._array.length > this._pos;
 }
@@ -875,7 +1263,7 @@ ImmutableList.prototype.toString = function() {
 }
 ImmutableList.prototype.add$1 = ImmutableList.prototype.add;
 ImmutableList.prototype.addAll$1 = function($0) {
-  return this.addAll(($0 && $0.is$Collection_E()));
+  return this.addAll(($0 == null ? null : $0.assert$Collection_E()));
 };
 ImmutableList.prototype.removeLast$0 = ImmutableList.prototype.removeLast;
 ImmutableList.prototype.sort$1 = function($0) {
@@ -891,8 +1279,8 @@ function ImmutableMap(keyValuePairs) {
     this._internal.$setindex(keyValuePairs.$index(i), keyValuePairs.$index(i + 1));
   }
 }
-ImmutableMap.prototype.is$Map_Node$Element = function(){return this;};
-ImmutableMap.prototype.is$Map_String$Member = function(){return this;};
+ImmutableMap.prototype.assert$Map_Node$Element = function(){return this};
+ImmutableMap.prototype.assert$Map_String$Member = function(){return this};
 ImmutableMap.prototype.$index = function(key) {
   return this._internal.$index(key);
 }
@@ -934,8 +1322,8 @@ ImmutableMap.prototype.getValues$0 = ImmutableMap.prototype.getValues;
 ImmutableMap.prototype.isEmpty$0 = ImmutableMap.prototype.isEmpty;
 // ********** Code for NumImplementation **************
 NumImplementation = Number;
-NumImplementation.prototype.is$NumImplementation = function(){return this;};
-NumImplementation.prototype.is$Comparable = function(){return this;};
+NumImplementation.prototype.assert$NumImplementation = function(){return this};
+NumImplementation.prototype.assert$Comparable = function(){return this};
 NumImplementation.prototype.isNaN = function() {
   return isNaN(this);
 }
@@ -987,7 +1375,7 @@ NumImplementation.prototype.compareTo = function(other) {
   }
 }
 NumImplementation.prototype.compareTo$1 = function($0) {
-  return this.compareTo(($0 && $0.is$NumImplementation()));
+  return this.compareTo(($0 == null ? null : $0.assert$NumImplementation()));
 };
 NumImplementation.prototype.hashCode$0 = NumImplementation.prototype.hashCode;
 // ********** Code for ExceptionImplementation **************
@@ -1008,16 +1396,16 @@ function HashMapImplementation() {
   this._keys = new ListFactory(8/*HashMapImplementation._INITIAL_CAPACITY*/);
   this._values = new ListFactory(8/*HashMapImplementation._INITIAL_CAPACITY*/);
 }
-HashMapImplementation.prototype.is$HashMapImplementation = function(){return this;};
-HashMapImplementation.prototype.is$Map_Node$Element = function(){return this;};
-HashMapImplementation.prototype.is$Map_String$Member = function(){return this;};
+HashMapImplementation.prototype.assert$HashMapImplementation = function(){return this};
+HashMapImplementation.prototype.assert$Map_Node$Element = function(){return this};
+HashMapImplementation.prototype.assert$Map_String$Member = function(){return this};
 HashMapImplementation.HashMapImplementation$from$factory = function(other) {
   var result = new HashMapImplementation();
   other.forEach((function (key, value) {
     result.$setindex(key, value);
   })
   );
-  return (result && result.is$HashMapImplementation());
+  return (result == null ? null : result.assert$HashMapImplementation());
 }
 HashMapImplementation._computeLoadLimit = function(capacity) {
   return $truncdiv((capacity * 3), 4);
@@ -1194,8 +1582,8 @@ function HashMapImplementation_E$E() {
   this._values = new ListFactory(8/*HashMapImplementation._INITIAL_CAPACITY*/);
 }
 $inherits(HashMapImplementation_E$E, HashMapImplementation);
-HashMapImplementation_E$E.prototype.is$Map_Node$Element = function(){return this;};
-HashMapImplementation_E$E.prototype.is$Map_String$Member = function(){return this;};
+HashMapImplementation_E$E.prototype.assert$Map_Node$Element = function(){return this};
+HashMapImplementation_E$E.prototype.assert$Map_String$Member = function(){return this};
 HashMapImplementation_E$E._computeLoadLimit = function(capacity) {
   return $truncdiv((capacity * 3), 4);
 }
@@ -1331,55 +1719,55 @@ HashMapImplementation_E$E.prototype.containsKey = function(key) {
 // ********** Code for HashMapImplementation_Element$HInstruction **************
 function HashMapImplementation_Element$HInstruction() {}
 $inherits(HashMapImplementation_Element$HInstruction, HashMapImplementation);
-HashMapImplementation_Element$HInstruction.prototype.is$Map_Node$Element = false;
-HashMapImplementation_Element$HInstruction.prototype.is$Map_String$Member = false;
+HashMapImplementation_Element$HInstruction.prototype.assert$Map_Node$Element = function(){$throw(new TypeError._internal$ctor(this, "Map<Node, Element>"))};
+HashMapImplementation_Element$HInstruction.prototype.assert$Map_String$Member = function(){$throw(new TypeError._internal$ctor(this, "Map<String, Member>"))};
 // ********** Code for HashMapImplementation_Element$HLocal **************
 function HashMapImplementation_Element$HLocal() {}
 $inherits(HashMapImplementation_Element$HLocal, HashMapImplementation);
-HashMapImplementation_Element$HLocal.prototype.is$Map_Node$Element = false;
-HashMapImplementation_Element$HLocal.prototype.is$Map_String$Member = false;
+HashMapImplementation_Element$HLocal.prototype.assert$Map_Node$Element = function(){$throw(new TypeError._internal$ctor(this, "Map<Node, Element>"))};
+HashMapImplementation_Element$HLocal.prototype.assert$Map_String$Member = function(){$throw(new TypeError._internal$ctor(this, "Map<String, Member>"))};
 // ********** Code for HashMapImplementation_K$DoubleLinkedQueueEntry_KeyValuePair_K$V **************
 function HashMapImplementation_K$DoubleLinkedQueueEntry_KeyValuePair_K$V() {}
 $inherits(HashMapImplementation_K$DoubleLinkedQueueEntry_KeyValuePair_K$V, HashMapImplementation);
-HashMapImplementation_K$DoubleLinkedQueueEntry_KeyValuePair_K$V.prototype.is$Map_Node$Element = false;
-HashMapImplementation_K$DoubleLinkedQueueEntry_KeyValuePair_K$V.prototype.is$Map_String$Member = false;
+HashMapImplementation_K$DoubleLinkedQueueEntry_KeyValuePair_K$V.prototype.assert$Map_Node$Element = function(){$throw(new TypeError._internal$ctor(this, "Map<Node, Element>"))};
+HashMapImplementation_K$DoubleLinkedQueueEntry_KeyValuePair_K$V.prototype.assert$Map_String$Member = function(){$throw(new TypeError._internal$ctor(this, "Map<String, Member>"))};
 // ********** Code for HashMapImplementation_String$EvaluatedValue **************
 function HashMapImplementation_String$EvaluatedValue() {}
 $inherits(HashMapImplementation_String$EvaluatedValue, HashMapImplementation);
-HashMapImplementation_String$EvaluatedValue.prototype.is$Map_Node$Element = false;
-HashMapImplementation_String$EvaluatedValue.prototype.is$Map_String$Member = false;
+HashMapImplementation_String$EvaluatedValue.prototype.assert$Map_Node$Element = function(){$throw(new TypeError._internal$ctor(this, "Map<Node, Element>"))};
+HashMapImplementation_String$EvaluatedValue.prototype.assert$Map_String$Member = function(){$throw(new TypeError._internal$ctor(this, "Map<String, Member>"))};
 // ********** Code for HashMapImplementation_String$int **************
 function HashMapImplementation_String$int() {}
 $inherits(HashMapImplementation_String$int, HashMapImplementation);
-HashMapImplementation_String$int.prototype.is$Map_Node$Element = false;
-HashMapImplementation_String$int.prototype.is$Map_String$Member = false;
+HashMapImplementation_String$int.prototype.assert$Map_Node$Element = function(){$throw(new TypeError._internal$ctor(this, "Map<Node, Element>"))};
+HashMapImplementation_String$int.prototype.assert$Map_String$Member = function(){$throw(new TypeError._internal$ctor(this, "Map<String, Member>"))};
 // ********** Code for HashMapImplementation_int$HInstruction **************
 function HashMapImplementation_int$HInstruction() {}
 $inherits(HashMapImplementation_int$HInstruction, HashMapImplementation);
-HashMapImplementation_int$HInstruction.prototype.is$Map_Node$Element = false;
-HashMapImplementation_int$HInstruction.prototype.is$Map_String$Member = false;
+HashMapImplementation_int$HInstruction.prototype.assert$Map_Node$Element = function(){$throw(new TypeError._internal$ctor(this, "Map<Node, Element>"))};
+HashMapImplementation_int$HInstruction.prototype.assert$Map_String$Member = function(){$throw(new TypeError._internal$ctor(this, "Map<String, Member>"))};
 // ********** Code for HashMapImplementation_int$String **************
 function HashMapImplementation_int$String() {}
 $inherits(HashMapImplementation_int$String, HashMapImplementation);
-HashMapImplementation_int$String.prototype.is$Map_Node$Element = false;
-HashMapImplementation_int$String.prototype.is$Map_String$Member = false;
+HashMapImplementation_int$String.prototype.assert$Map_Node$Element = function(){$throw(new TypeError._internal$ctor(this, "Map<Node, Element>"))};
+HashMapImplementation_int$String.prototype.assert$Map_String$Member = function(){$throw(new TypeError._internal$ctor(this, "Map<String, Member>"))};
 // ********** Code for HashSetImplementation **************
 function HashSetImplementation() {
   // Initializers done
   this._backingMap = new HashMapImplementation_E$E();
 }
-HashSetImplementation.prototype.is$HashSetImplementation = function(){return this;};
-HashSetImplementation.prototype.is$Collection_E = function(){return this;};
-HashSetImplementation.prototype.is$Collection_Object = function(){return this;};
-HashSetImplementation.prototype.is$Collection_Type = function(){return this;};
-HashSetImplementation.prototype.is$Iterable = function(){return this;};
+HashSetImplementation.prototype.assert$HashSetImplementation = function(){return this};
+HashSetImplementation.prototype.assert$Collection_E = function(){return this};
+HashSetImplementation.prototype.assert$Collection_Object = function(){return this};
+HashSetImplementation.prototype.assert$Collection_Type = function(){return this};
+HashSetImplementation.prototype.assert$Iterable = function(){return this};
 HashSetImplementation.HashSetImplementation$from$factory = function(other) {
   var set = new HashSetImplementation();
   for (var $i = other.iterator(); $i.hasNext$0(); ) {
     var e = $i.next$0();
     set.add(e);
   }
-  return (set && set.is$HashSetImplementation());
+  return (set == null ? null : set.assert$HashSetImplementation());
 }
 HashSetImplementation.prototype.clear = function() {
   this._backingMap.clear();
@@ -1438,7 +1826,7 @@ HashSetImplementation.prototype.iterator = function() {
 }
 HashSetImplementation.prototype.add$1 = HashSetImplementation.prototype.add;
 HashSetImplementation.prototype.addAll$1 = function($0) {
-  return this.addAll(($0 && $0.is$Collection_E()));
+  return this.addAll(($0 == null ? null : $0.assert$Collection_E()));
 };
 HashSetImplementation.prototype.contains$1 = HashSetImplementation.prototype.contains;
 HashSetImplementation.prototype.every$1 = function($0) {
@@ -1458,45 +1846,45 @@ HashSetImplementation.prototype.some$1 = function($0) {
 // ********** Code for HashSetImplementation_E **************
 function HashSetImplementation_E() {}
 $inherits(HashSetImplementation_E, HashSetImplementation);
-HashSetImplementation_E.prototype.is$Collection_E = function(){return this;};
-HashSetImplementation_E.prototype.is$Collection_Object = function(){return this;};
-HashSetImplementation_E.prototype.is$Collection_Type = function(){return this;};
-HashSetImplementation_E.prototype.is$Iterable = function(){return this;};
+HashSetImplementation_E.prototype.assert$Collection_E = function(){return this};
+HashSetImplementation_E.prototype.assert$Collection_Object = function(){return this};
+HashSetImplementation_E.prototype.assert$Collection_Type = function(){return this};
+HashSetImplementation_E.prototype.assert$Iterable = function(){return this};
 // ********** Code for HashSetImplementation_HInstruction **************
 function HashSetImplementation_HInstruction() {}
 $inherits(HashSetImplementation_HInstruction, HashSetImplementation);
-HashSetImplementation_HInstruction.prototype.is$Collection_E = function(){return this;};
-HashSetImplementation_HInstruction.prototype.is$Collection_Object = function(){return this;};
-HashSetImplementation_HInstruction.prototype.is$Collection_Type = false;
-HashSetImplementation_HInstruction.prototype.is$Iterable = function(){return this;};
+HashSetImplementation_HInstruction.prototype.assert$Collection_E = function(){return this};
+HashSetImplementation_HInstruction.prototype.assert$Collection_Object = function(){return this};
+HashSetImplementation_HInstruction.prototype.assert$Collection_Type = function(){$throw(new TypeError._internal$ctor(this, "Collection<Type>"))};
+HashSetImplementation_HInstruction.prototype.assert$Iterable = function(){return this};
 // ********** Code for HashSetImplementation_HPhi **************
 function HashSetImplementation_HPhi() {}
 $inherits(HashSetImplementation_HPhi, HashSetImplementation);
-HashSetImplementation_HPhi.prototype.is$Collection_E = function(){return this;};
-HashSetImplementation_HPhi.prototype.is$Collection_Object = function(){return this;};
-HashSetImplementation_HPhi.prototype.is$Collection_Type = false;
-HashSetImplementation_HPhi.prototype.is$Iterable = function(){return this;};
+HashSetImplementation_HPhi.prototype.assert$Collection_E = function(){return this};
+HashSetImplementation_HPhi.prototype.assert$Collection_Object = function(){return this};
+HashSetImplementation_HPhi.prototype.assert$Collection_Type = function(){$throw(new TypeError._internal$ctor(this, "Collection<Type>"))};
+HashSetImplementation_HPhi.prototype.assert$Iterable = function(){return this};
 // ********** Code for HashSetImplementation_String **************
 function HashSetImplementation_String() {}
 $inherits(HashSetImplementation_String, HashSetImplementation);
-HashSetImplementation_String.prototype.is$Collection_E = function(){return this;};
-HashSetImplementation_String.prototype.is$Collection_Object = function(){return this;};
-HashSetImplementation_String.prototype.is$Collection_Type = false;
-HashSetImplementation_String.prototype.is$Iterable = function(){return this;};
+HashSetImplementation_String.prototype.assert$Collection_E = function(){return this};
+HashSetImplementation_String.prototype.assert$Collection_Object = function(){return this};
+HashSetImplementation_String.prototype.assert$Collection_Type = function(){$throw(new TypeError._internal$ctor(this, "Collection<Type>"))};
+HashSetImplementation_String.prototype.assert$Iterable = function(){return this};
 // ********** Code for HashSetImplementation_lang_Type **************
 function HashSetImplementation_lang_Type() {}
 $inherits(HashSetImplementation_lang_Type, HashSetImplementation);
-HashSetImplementation_lang_Type.prototype.is$Collection_E = function(){return this;};
-HashSetImplementation_lang_Type.prototype.is$Collection_Object = function(){return this;};
-HashSetImplementation_lang_Type.prototype.is$Collection_Type = function(){return this;};
-HashSetImplementation_lang_Type.prototype.is$Iterable = function(){return this;};
+HashSetImplementation_lang_Type.prototype.assert$Collection_E = function(){return this};
+HashSetImplementation_lang_Type.prototype.assert$Collection_Object = function(){return this};
+HashSetImplementation_lang_Type.prototype.assert$Collection_Type = function(){return this};
+HashSetImplementation_lang_Type.prototype.assert$Iterable = function(){return this};
 // ********** Code for HashSetImplementation_int **************
 function HashSetImplementation_int() {}
 $inherits(HashSetImplementation_int, HashSetImplementation);
-HashSetImplementation_int.prototype.is$Collection_E = function(){return this;};
-HashSetImplementation_int.prototype.is$Collection_Object = function(){return this;};
-HashSetImplementation_int.prototype.is$Collection_Type = false;
-HashSetImplementation_int.prototype.is$Iterable = function(){return this;};
+HashSetImplementation_int.prototype.assert$Collection_E = function(){return this};
+HashSetImplementation_int.prototype.assert$Collection_Object = function(){return this};
+HashSetImplementation_int.prototype.assert$Collection_Type = function(){$throw(new TypeError._internal$ctor(this, "Collection<Type>"))};
+HashSetImplementation_int.prototype.assert$Iterable = function(){return this};
 // ********** Code for HashSetIterator **************
 function HashSetIterator(set_) {
   this._nextValidIndex = -1;
@@ -1504,7 +1892,7 @@ function HashSetIterator(set_) {
   // Initializers done
   this._advance();
 }
-HashSetIterator.prototype.is$Iterator_T = function(){return this;};
+HashSetIterator.prototype.assert$Iterator_T = function(){return this};
 HashSetIterator.prototype.hasNext = function() {
   if (this._nextValidIndex >= this._entries.length) return false;
   if (this._entries.$index(this._nextValidIndex) === const$1/*HashMapImplementation._DELETED_KEY*/) {
@@ -1540,7 +1928,7 @@ function HashSetIterator_E(set_) {
   this._advance();
 }
 $inherits(HashSetIterator_E, HashSetIterator);
-HashSetIterator_E.prototype.is$Iterator_T = function(){return this;};
+HashSetIterator_E.prototype.assert$Iterator_T = function(){return this};
 HashSetIterator_E.prototype._advance = function() {
   var length = this._entries.length;
   var entry;
@@ -1576,8 +1964,8 @@ function LinkedHashMapImplementation() {
   this._map = new HashMapImplementation();
   this._list = new DoubleLinkedQueue_KeyValuePair_K$V();
 }
-LinkedHashMapImplementation.prototype.is$Map_Node$Element = function(){return this;};
-LinkedHashMapImplementation.prototype.is$Map_String$Member = function(){return this;};
+LinkedHashMapImplementation.prototype.assert$Map_Node$Element = function(){return this};
+LinkedHashMapImplementation.prototype.assert$Map_String$Member = function(){return this};
 LinkedHashMapImplementation.prototype.$setindex = function(key, value) {
   if (this._map.containsKey(key)) {
     this._map.$index(key).get$element().set$value(value);
@@ -1589,13 +1977,13 @@ LinkedHashMapImplementation.prototype.$setindex = function(key, value) {
 }
 LinkedHashMapImplementation.prototype.$index = function(key) {
   var $0;
-  var entry = (($0 = this._map.$index(key)) && $0.is$DoubleLinkedQueueEntry_KeyValuePair_K$V());
+  var entry = (($0 = this._map.$index(key)) == null ? null : $0.assert$DoubleLinkedQueueEntry_KeyValuePair_K$V());
   if (entry == null) return null;
   return entry.get$element().get$value();
 }
 LinkedHashMapImplementation.prototype.remove = function(key) {
   var $0;
-  var entry = (($0 = this._map.remove(key)) && $0.is$DoubleLinkedQueueEntry_KeyValuePair_K$V());
+  var entry = (($0 = this._map.remove(key)) == null ? null : $0.assert$DoubleLinkedQueueEntry_KeyValuePair_K$V());
   if (entry == null) return null;
   entry.remove();
   return entry.get$element().get$value();
@@ -1655,24 +2043,24 @@ LinkedHashMapImplementation.prototype.isEmpty$0 = LinkedHashMapImplementation.pr
 // ********** Code for LinkedHashMapImplementation_Element$String **************
 function LinkedHashMapImplementation_Element$String() {}
 $inherits(LinkedHashMapImplementation_Element$String, LinkedHashMapImplementation);
-LinkedHashMapImplementation_Element$String.prototype.is$Map_Node$Element = false;
-LinkedHashMapImplementation_Element$String.prototype.is$Map_String$Member = false;
+LinkedHashMapImplementation_Element$String.prototype.assert$Map_Node$Element = function(){$throw(new TypeError._internal$ctor(this, "Map<Node, Element>"))};
+LinkedHashMapImplementation_Element$String.prototype.assert$Map_String$Member = function(){$throw(new TypeError._internal$ctor(this, "Map<String, Member>"))};
 // ********** Code for LinkedHashMapImplementation_Node$Element **************
 function LinkedHashMapImplementation_Node$Element() {}
 $inherits(LinkedHashMapImplementation_Node$Element, LinkedHashMapImplementation);
-LinkedHashMapImplementation_Node$Element.prototype.is$Map_Node$Element = function(){return this;};
-LinkedHashMapImplementation_Node$Element.prototype.is$Map_String$Member = false;
+LinkedHashMapImplementation_Node$Element.prototype.assert$Map_Node$Element = function(){return this};
+LinkedHashMapImplementation_Node$Element.prototype.assert$Map_String$Member = function(){$throw(new TypeError._internal$ctor(this, "Map<String, Member>"))};
 // ********** Code for LinkedHashMapImplementation_String$Keyword **************
 function LinkedHashMapImplementation_String$Keyword() {}
 $inherits(LinkedHashMapImplementation_String$Keyword, LinkedHashMapImplementation);
-LinkedHashMapImplementation_String$Keyword.prototype.is$Map_Node$Element = false;
-LinkedHashMapImplementation_String$Keyword.prototype.is$Map_String$Member = false;
+LinkedHashMapImplementation_String$Keyword.prototype.assert$Map_Node$Element = function(){$throw(new TypeError._internal$ctor(this, "Map<Node, Element>"))};
+LinkedHashMapImplementation_String$Keyword.prototype.assert$Map_String$Member = function(){$throw(new TypeError._internal$ctor(this, "Map<String, Member>"))};
 // ********** Code for DoubleLinkedQueueEntry **************
 function DoubleLinkedQueueEntry(e) {
   // Initializers done
   this._element = e;
 }
-DoubleLinkedQueueEntry.prototype.is$DoubleLinkedQueueEntry_KeyValuePair_K$V = function(){return this;};
+DoubleLinkedQueueEntry.prototype.assert$DoubleLinkedQueueEntry_KeyValuePair_K$V = function(){return this};
 DoubleLinkedQueueEntry.prototype._link = function(p, n) {
   this._next = n;
   this._previous = p;
@@ -1704,7 +2092,7 @@ function DoubleLinkedQueueEntry_E(e) {
   this._element = e;
 }
 $inherits(DoubleLinkedQueueEntry_E, DoubleLinkedQueueEntry);
-DoubleLinkedQueueEntry_E.prototype.is$DoubleLinkedQueueEntry_KeyValuePair_K$V = function(){return this;};
+DoubleLinkedQueueEntry_E.prototype.assert$DoubleLinkedQueueEntry_KeyValuePair_K$V = function(){return this};
 DoubleLinkedQueueEntry_E.prototype._link = function(p, n) {
   this._next = n;
   this._previous = p;
@@ -1733,7 +2121,7 @@ function DoubleLinkedQueueEntry_KeyValuePair_K$V(e) {
   this._element = e;
 }
 $inherits(DoubleLinkedQueueEntry_KeyValuePair_K$V, DoubleLinkedQueueEntry);
-DoubleLinkedQueueEntry_KeyValuePair_K$V.prototype.is$DoubleLinkedQueueEntry_KeyValuePair_K$V = function(){return this;};
+DoubleLinkedQueueEntry_KeyValuePair_K$V.prototype.assert$DoubleLinkedQueueEntry_KeyValuePair_K$V = function(){return this};
 DoubleLinkedQueueEntry_KeyValuePair_K$V.prototype._link = function(p, n) {
   this._next = n;
   this._previous = p;
@@ -1755,7 +2143,7 @@ DoubleLinkedQueueEntry_KeyValuePair_K$V.prototype._asNonSentinelEntry = function
 }
 DoubleLinkedQueueEntry_KeyValuePair_K$V.prototype.previousEntry = function() {
   var $0;
-  return (($0 = this._previous._asNonSentinelEntry()) && $0.is$DoubleLinkedQueueEntry_KeyValuePair_K$V());
+  return (($0 = this._previous._asNonSentinelEntry()) == null ? null : $0.assert$DoubleLinkedQueueEntry_KeyValuePair_K$V());
 }
 // ********** Code for _DoubleLinkedQueueEntrySentinel **************
 function _DoubleLinkedQueueEntrySentinel() {
@@ -1792,10 +2180,10 @@ function DoubleLinkedQueue() {
   // Initializers done
   this._sentinel = new _DoubleLinkedQueueEntrySentinel_E();
 }
-DoubleLinkedQueue.prototype.is$Collection_E = function(){return this;};
-DoubleLinkedQueue.prototype.is$Collection_Object = function(){return this;};
-DoubleLinkedQueue.prototype.is$Collection_Type = function(){return this;};
-DoubleLinkedQueue.prototype.is$Iterable = function(){return this;};
+DoubleLinkedQueue.prototype.assert$Collection_E = function(){return this};
+DoubleLinkedQueue.prototype.assert$Collection_Object = function(){return this};
+DoubleLinkedQueue.prototype.assert$Collection_Type = function(){return this};
+DoubleLinkedQueue.prototype.assert$Iterable = function(){return this};
 DoubleLinkedQueue.prototype.addLast = function(value) {
   this._sentinel.prepend(value);
 }
@@ -1875,7 +2263,7 @@ DoubleLinkedQueue.prototype.iterator = function() {
 }
 DoubleLinkedQueue.prototype.add$1 = DoubleLinkedQueue.prototype.add;
 DoubleLinkedQueue.prototype.addAll$1 = function($0) {
-  return this.addAll(($0 && $0.is$Collection_E()));
+  return this.addAll(($0 == null ? null : $0.assert$Collection_E()));
 };
 DoubleLinkedQueue.prototype.every$1 = function($0) {
   return this.every(to$call$1($0));
@@ -1896,34 +2284,34 @@ DoubleLinkedQueue.prototype.some$1 = function($0) {
 // ********** Code for DoubleLinkedQueue_ClassElement **************
 function DoubleLinkedQueue_ClassElement() {}
 $inherits(DoubleLinkedQueue_ClassElement, DoubleLinkedQueue);
-DoubleLinkedQueue_ClassElement.prototype.is$Collection_E = function(){return this;};
-DoubleLinkedQueue_ClassElement.prototype.is$Collection_Object = function(){return this;};
-DoubleLinkedQueue_ClassElement.prototype.is$Collection_Type = false;
-DoubleLinkedQueue_ClassElement.prototype.is$Iterable = function(){return this;};
+DoubleLinkedQueue_ClassElement.prototype.assert$Collection_E = function(){return this};
+DoubleLinkedQueue_ClassElement.prototype.assert$Collection_Object = function(){return this};
+DoubleLinkedQueue_ClassElement.prototype.assert$Collection_Type = function(){$throw(new TypeError._internal$ctor(this, "Collection<Type>"))};
+DoubleLinkedQueue_ClassElement.prototype.assert$Iterable = function(){return this};
 // ********** Code for DoubleLinkedQueue_E **************
 function DoubleLinkedQueue_E() {}
 $inherits(DoubleLinkedQueue_E, DoubleLinkedQueue);
-DoubleLinkedQueue_E.prototype.is$Collection_E = function(){return this;};
-DoubleLinkedQueue_E.prototype.is$Collection_Object = function(){return this;};
-DoubleLinkedQueue_E.prototype.is$Collection_Type = function(){return this;};
-DoubleLinkedQueue_E.prototype.is$Iterable = function(){return this;};
+DoubleLinkedQueue_E.prototype.assert$Collection_E = function(){return this};
+DoubleLinkedQueue_E.prototype.assert$Collection_Object = function(){return this};
+DoubleLinkedQueue_E.prototype.assert$Collection_Type = function(){return this};
+DoubleLinkedQueue_E.prototype.assert$Iterable = function(){return this};
 // ********** Code for DoubleLinkedQueue_Element **************
 function DoubleLinkedQueue_Element() {}
 $inherits(DoubleLinkedQueue_Element, DoubleLinkedQueue);
-DoubleLinkedQueue_Element.prototype.is$Collection_E = function(){return this;};
-DoubleLinkedQueue_Element.prototype.is$Collection_Object = function(){return this;};
-DoubleLinkedQueue_Element.prototype.is$Collection_Type = false;
-DoubleLinkedQueue_Element.prototype.is$Iterable = function(){return this;};
+DoubleLinkedQueue_Element.prototype.assert$Collection_E = function(){return this};
+DoubleLinkedQueue_Element.prototype.assert$Collection_Object = function(){return this};
+DoubleLinkedQueue_Element.prototype.assert$Collection_Type = function(){$throw(new TypeError._internal$ctor(this, "Collection<Type>"))};
+DoubleLinkedQueue_Element.prototype.assert$Iterable = function(){return this};
 // ********** Code for DoubleLinkedQueue_KeyValuePair_K$V **************
 function DoubleLinkedQueue_KeyValuePair_K$V() {
   // Initializers done
   this._sentinel = new _DoubleLinkedQueueEntrySentinel_KeyValuePair_K$V();
 }
 $inherits(DoubleLinkedQueue_KeyValuePair_K$V, DoubleLinkedQueue);
-DoubleLinkedQueue_KeyValuePair_K$V.prototype.is$Collection_E = function(){return this;};
-DoubleLinkedQueue_KeyValuePair_K$V.prototype.is$Collection_Object = function(){return this;};
-DoubleLinkedQueue_KeyValuePair_K$V.prototype.is$Collection_Type = false;
-DoubleLinkedQueue_KeyValuePair_K$V.prototype.is$Iterable = function(){return this;};
+DoubleLinkedQueue_KeyValuePair_K$V.prototype.assert$Collection_E = function(){return this};
+DoubleLinkedQueue_KeyValuePair_K$V.prototype.assert$Collection_Object = function(){return this};
+DoubleLinkedQueue_KeyValuePair_K$V.prototype.assert$Collection_Type = function(){$throw(new TypeError._internal$ctor(this, "Collection<Type>"))};
+DoubleLinkedQueue_KeyValuePair_K$V.prototype.assert$Iterable = function(){return this};
 DoubleLinkedQueue_KeyValuePair_K$V.prototype.addLast = function(value) {
   this._sentinel.prepend(value);
 }
@@ -1944,7 +2332,7 @@ function _DoubleLinkedQueueIterator(_sentinel) {
   // Initializers done
   this._currentEntry = this._sentinel;
 }
-_DoubleLinkedQueueIterator.prototype.is$Iterator_T = function(){return this;};
+_DoubleLinkedQueueIterator.prototype.assert$Iterator_T = function(){return this};
 _DoubleLinkedQueueIterator.prototype.hasNext = function() {
   return this._currentEntry._next !== this._sentinel;
 }
@@ -1964,7 +2352,7 @@ function _DoubleLinkedQueueIterator_E(_sentinel) {
   this._currentEntry = this._sentinel;
 }
 $inherits(_DoubleLinkedQueueIterator_E, _DoubleLinkedQueueIterator);
-_DoubleLinkedQueueIterator_E.prototype.is$Iterator_T = function(){return this;};
+_DoubleLinkedQueueIterator_E.prototype.assert$Iterator_T = function(){return this};
 // ********** Code for StopwatchImplementation **************
 function StopwatchImplementation() {
   this._start = null;
@@ -2009,7 +2397,7 @@ function StringBufferImpl(content) {
   this.clear();
   this.add(content);
 }
-StringBufferImpl.prototype.is$StringBuffer = function(){return this;};
+StringBufferImpl.prototype.assert$StringBuffer = function(){return this};
 StringBufferImpl.prototype.get$length = function() {
   return this._length;
 }
@@ -2048,7 +2436,7 @@ StringBufferImpl.prototype.toString = function() {
 }
 StringBufferImpl.prototype.add$1 = StringBufferImpl.prototype.add;
 StringBufferImpl.prototype.addAll$1 = function($0) {
-  return this.addAll(($0 && $0.is$Collection_Object()));
+  return this.addAll(($0 == null ? null : $0.assert$Collection_Object()));
 };
 StringBufferImpl.prototype.isEmpty$0 = StringBufferImpl.prototype.isEmpty;
 StringBufferImpl.prototype.toString$0 = StringBufferImpl.prototype.toString;
@@ -2074,8 +2462,8 @@ StringBase.concatAll = function(strings) {
 }
 // ********** Code for StringImplementation **************
 StringImplementation = String;
-StringImplementation.prototype.is$Pattern = function(){return this;};
-StringImplementation.prototype.is$Comparable = function(){return this;};
+StringImplementation.prototype.assert$Pattern = function(){return this};
+StringImplementation.prototype.assert$Comparable = function(){return this};
 StringImplementation.prototype.endsWith = function(other) {
   if (other.length > this.length) return false;
     return other == this.substring(this.length - other.length);
@@ -2133,10 +2521,10 @@ StringImplementation.prototype.indexOf$2 = function($0, $1) {
 };
 StringImplementation.prototype.isEmpty$0 = StringImplementation.prototype.isEmpty;
 StringImplementation.prototype.replaceAll$2 = function($0, $1) {
-  return this.replaceAll(($0 && $0.is$Pattern()), $assert_String($1));
+  return this.replaceAll(($0 == null ? null : $0.assert$Pattern()), $assert_String($1));
 };
 StringImplementation.prototype.replaceFirst$2 = function($0, $1) {
-  return this.replaceFirst(($0 && $0.is$Pattern()), $assert_String($1));
+  return this.replaceFirst(($0 == null ? null : $0.assert$Pattern()), $assert_String($1));
 };
 StringImplementation.prototype.startsWith$1 = function($0) {
   return this.startsWith($assert_String($0));
@@ -2191,8 +2579,8 @@ DateImplementation.now$ctor = function() {
   this._asJs();
 }
 DateImplementation.now$ctor.prototype = DateImplementation.prototype;
-DateImplementation.prototype.is$Date = function(){return this;};
-DateImplementation.prototype.is$Comparable = function(){return this;};
+DateImplementation.prototype.assert$Date = function(){return this};
+DateImplementation.prototype.assert$Comparable = function(){return this};
 DateImplementation.prototype.get$value = function() { return this.value; };
 DateImplementation.prototype.get$timeZone = function() { return this.timeZone; };
 DateImplementation.prototype.$eq = function(other) {
@@ -2263,10 +2651,10 @@ DateImplementation.prototype._asJs = function() {
     return this.date;
 }
 DateImplementation.prototype.add$1 = function($0) {
-  return this.add(($0 && $0.is$Duration()));
+  return this.add(($0 == null ? null : $0.assert$Duration()));
 };
 DateImplementation.prototype.compareTo$1 = function($0) {
-  return this.compareTo(($0 && $0.is$Date()));
+  return this.compareTo(($0 == null ? null : $0.assert$Date()));
 };
 DateImplementation.prototype.toString$0 = DateImplementation.prototype.toString;
 // ********** Code for TimeZoneImplementation **************
@@ -2317,7 +2705,7 @@ function joinPaths(path1, path2) {
       pieces.add$1(piece);
     }
   }
-  return Strings.join((pieces && pieces.is$List_String()), '/');
+  return Strings.join((pieces == null ? null : pieces.assert$List_String()), '/');
 }
 function dirname(path) {
   var lastSlash = path.lastIndexOf('/', path.length);
@@ -2370,11 +2758,11 @@ LinkFactory.Link$factory = function(head, tail) {
 function LinkTail() {
   // Initializers done
 }
-LinkTail.prototype.is$Link_Element = function(){return this;};
-LinkTail.prototype.is$Link_Node = function(){return this;};
-LinkTail.prototype.is$Link_Token = function(){return this;};
-LinkTail.prototype.is$Link_Type = function(){return this;};
-LinkTail.prototype.is$Iterable = function(){return this;};
+LinkTail.prototype.assert$Link_Element = function(){return this};
+LinkTail.prototype.assert$Link_Node = function(){return this};
+LinkTail.prototype.assert$Link_Token = function(){return this};
+LinkTail.prototype.assert$Link_Type = function(){return this};
+LinkTail.prototype.assert$Iterable = function(){return this};
 LinkTail.prototype.get$head = function() {
   return null;
 }
@@ -2402,62 +2790,62 @@ LinkTail.prototype.isEmpty = function() {
 LinkTail.prototype.isEmpty$0 = LinkTail.prototype.isEmpty;
 LinkTail.prototype.iterator$0 = LinkTail.prototype.iterator;
 LinkTail.prototype.printOn$1 = function($0) {
-  return this.printOn(($0 && $0.is$StringBuffer()));
+  return this.printOn(($0 == null ? null : $0.assert$StringBuffer()));
 };
 LinkTail.prototype.toString$0 = LinkTail.prototype.toString;
 // ********** Code for LinkTail_Element **************
 function LinkTail_Element() {}
 $inherits(LinkTail_Element, LinkTail);
-LinkTail_Element.prototype.is$Link_Element = function(){return this;};
-LinkTail_Element.prototype.is$Link_Node = false;
-LinkTail_Element.prototype.is$Link_Token = false;
-LinkTail_Element.prototype.is$Link_Type = false;
-LinkTail_Element.prototype.is$Iterable = function(){return this;};
+LinkTail_Element.prototype.assert$Link_Element = function(){return this};
+LinkTail_Element.prototype.assert$Link_Node = function(){$throw(new TypeError._internal$ctor(this, "Link<Node>"))};
+LinkTail_Element.prototype.assert$Link_Token = function(){$throw(new TypeError._internal$ctor(this, "Link<Token>"))};
+LinkTail_Element.prototype.assert$Link_Type = function(){$throw(new TypeError._internal$ctor(this, "Link<Type>"))};
+LinkTail_Element.prototype.assert$Iterable = function(){return this};
 // ********** Code for LinkTail_Node **************
 function LinkTail_Node() {}
 $inherits(LinkTail_Node, LinkTail);
-LinkTail_Node.prototype.is$Link_Element = false;
-LinkTail_Node.prototype.is$Link_Node = function(){return this;};
-LinkTail_Node.prototype.is$Link_Token = false;
-LinkTail_Node.prototype.is$Link_Type = false;
-LinkTail_Node.prototype.is$Iterable = function(){return this;};
+LinkTail_Node.prototype.assert$Link_Element = function(){$throw(new TypeError._internal$ctor(this, "Link<Element>"))};
+LinkTail_Node.prototype.assert$Link_Node = function(){return this};
+LinkTail_Node.prototype.assert$Link_Token = function(){$throw(new TypeError._internal$ctor(this, "Link<Token>"))};
+LinkTail_Node.prototype.assert$Link_Type = function(){$throw(new TypeError._internal$ctor(this, "Link<Type>"))};
+LinkTail_Node.prototype.assert$Iterable = function(){return this};
 // ********** Code for LinkTail_T **************
 function LinkTail_T() {
   // Initializers done
 }
 $inherits(LinkTail_T, LinkTail);
-LinkTail_T.prototype.is$Link_Element = function(){return this;};
-LinkTail_T.prototype.is$Link_Node = function(){return this;};
-LinkTail_T.prototype.is$Link_Token = function(){return this;};
-LinkTail_T.prototype.is$Link_Type = function(){return this;};
-LinkTail_T.prototype.is$Iterable = function(){return this;};
+LinkTail_T.prototype.assert$Link_Element = function(){return this};
+LinkTail_T.prototype.assert$Link_Node = function(){return this};
+LinkTail_T.prototype.assert$Link_Token = function(){return this};
+LinkTail_T.prototype.assert$Link_Type = function(){return this};
+LinkTail_T.prototype.assert$Iterable = function(){return this};
 // ********** Code for LinkTail_Token **************
 function LinkTail_Token() {}
 $inherits(LinkTail_Token, LinkTail);
-LinkTail_Token.prototype.is$Link_Element = false;
-LinkTail_Token.prototype.is$Link_Node = false;
-LinkTail_Token.prototype.is$Link_Token = function(){return this;};
-LinkTail_Token.prototype.is$Link_Type = false;
-LinkTail_Token.prototype.is$Iterable = function(){return this;};
+LinkTail_Token.prototype.assert$Link_Element = function(){$throw(new TypeError._internal$ctor(this, "Link<Element>"))};
+LinkTail_Token.prototype.assert$Link_Node = function(){$throw(new TypeError._internal$ctor(this, "Link<Node>"))};
+LinkTail_Token.prototype.assert$Link_Token = function(){return this};
+LinkTail_Token.prototype.assert$Link_Type = function(){$throw(new TypeError._internal$ctor(this, "Link<Type>"))};
+LinkTail_Token.prototype.assert$Iterable = function(){return this};
 // ********** Code for LinkTail_Type **************
 function LinkTail_Type() {}
 $inherits(LinkTail_Type, LinkTail);
-LinkTail_Type.prototype.is$Link_Element = false;
-LinkTail_Type.prototype.is$Link_Node = false;
-LinkTail_Type.prototype.is$Link_Token = false;
-LinkTail_Type.prototype.is$Link_Type = function(){return this;};
-LinkTail_Type.prototype.is$Iterable = function(){return this;};
+LinkTail_Type.prototype.assert$Link_Element = function(){$throw(new TypeError._internal$ctor(this, "Link<Element>"))};
+LinkTail_Type.prototype.assert$Link_Node = function(){$throw(new TypeError._internal$ctor(this, "Link<Node>"))};
+LinkTail_Type.prototype.assert$Link_Token = function(){$throw(new TypeError._internal$ctor(this, "Link<Token>"))};
+LinkTail_Type.prototype.assert$Link_Type = function(){return this};
+LinkTail_Type.prototype.assert$Iterable = function(){return this};
 // ********** Code for LinkEntry **************
 function LinkEntry(head, tail) {
   this.head = head;
   this.tail = tail;
   // Initializers done
 }
-LinkEntry.prototype.is$Link_Element = function(){return this;};
-LinkEntry.prototype.is$Link_Node = function(){return this;};
-LinkEntry.prototype.is$Link_Token = function(){return this;};
-LinkEntry.prototype.is$Link_Type = function(){return this;};
-LinkEntry.prototype.is$Iterable = function(){return this;};
+LinkEntry.prototype.assert$Link_Element = function(){return this};
+LinkEntry.prototype.assert$Link_Node = function(){return this};
+LinkEntry.prototype.assert$Link_Token = function(){return this};
+LinkEntry.prototype.assert$Link_Type = function(){return this};
+LinkEntry.prototype.assert$Iterable = function(){return this};
 LinkEntry.prototype.get$head = function() { return this.head; };
 LinkEntry.prototype.get$tail = function() { return this.tail; };
 LinkEntry.prototype.set$tail = function(value) { return this.tail = value; };
@@ -2466,7 +2854,7 @@ LinkEntry.prototype.prepend = function(element) {
 }
 LinkEntry.prototype.iterator = function() {
   var $0;
-  return (($0 = this.toList().iterator()) && $0.is$Iterator_T());
+  return (($0 = this.toList().iterator()) == null ? null : $0.assert$Iterator_T());
 }
 LinkEntry.prototype.printOn = function(buffer, separatedBy) {
   buffer.add(this.head == null ? 'null' : this.head);
@@ -2498,7 +2886,7 @@ LinkEntry.prototype.toList = function() {
 LinkEntry.prototype.isEmpty$0 = LinkEntry.prototype.isEmpty;
 LinkEntry.prototype.iterator$0 = LinkEntry.prototype.iterator;
 LinkEntry.prototype.printOn$1 = function($0) {
-  return this.printOn(($0 && $0.is$StringBuffer()));
+  return this.printOn(($0 == null ? null : $0.assert$StringBuffer()));
 };
 LinkEntry.prototype.toString$0 = LinkEntry.prototype.toString;
 // ********** Code for LinkEntry_T **************
@@ -2508,11 +2896,11 @@ function LinkEntry_T(head, tail) {
   // Initializers done
 }
 $inherits(LinkEntry_T, LinkEntry);
-LinkEntry_T.prototype.is$Link_Element = function(){return this;};
-LinkEntry_T.prototype.is$Link_Node = function(){return this;};
-LinkEntry_T.prototype.is$Link_Token = function(){return this;};
-LinkEntry_T.prototype.is$Link_Type = function(){return this;};
-LinkEntry_T.prototype.is$Iterable = function(){return this;};
+LinkEntry_T.prototype.assert$Link_Element = function(){return this};
+LinkEntry_T.prototype.assert$Link_Node = function(){return this};
+LinkEntry_T.prototype.assert$Link_Token = function(){return this};
+LinkEntry_T.prototype.assert$Link_Type = function(){return this};
+LinkEntry_T.prototype.assert$Iterable = function(){return this};
 // ********** Code for LinkBuilderImplementation **************
 function LinkBuilderImplementation() {
   this.head = null
@@ -2615,9 +3003,9 @@ ArrayBasedScanner.prototype.appendBeginGroup = function(kind, value) {
   this.tail.next = token;
   this.tail = this.tail.next;
   while (kind !== 60/*null.LT_TOKEN*/ && !$notnull_bool(this.groupingStack.isEmpty()) && this.groupingStack.get$head().get$kind() === 60/*null.LT_TOKEN*/) {
-    this.groupingStack = (($0 = this.groupingStack.get$tail()) && $0.is$Link_Token());
+    this.groupingStack = (($0 = this.groupingStack.get$tail()) == null ? null : $0.assert$Link_Token());
   }
-  this.groupingStack = (($0 = this.groupingStack.prepend(token)) && $0.is$Link_Token());
+  this.groupingStack = (($0 = this.groupingStack.prepend(token)) == null ? null : $0.assert$Link_Token());
 }
 ArrayBasedScanner.prototype.appendEndGroup = function(kind, value, openKind) {
   var $0;
@@ -2628,14 +3016,14 @@ ArrayBasedScanner.prototype.appendEndGroup = function(kind, value, openKind) {
     $throw(new MalformedInputException(('Unmatched ' + value)));
   }
   while (openKind !== 60/*null.LT_TOKEN*/ && !$notnull_bool(this.groupingStack.isEmpty()) && this.groupingStack.get$head().get$kind() === 60/*null.LT_TOKEN*/) {
-    this.groupingStack = (($0 = this.groupingStack.get$tail()) && $0.is$Link_Token());
+    this.groupingStack = (($0 = this.groupingStack.get$tail()) == null ? null : $0.assert$Link_Token());
   }
   if (this.groupingStack.get$head().get$kind() !== openKind) {
     if (openKind === 60/*null.LT_TOKEN*/) return;
     $throw(new MalformedInputException(('Unmatched ' + value)));
   }
   this.groupingStack.get$head().set$endGroup(oldTail.next);
-  this.groupingStack = (($0 = this.groupingStack.get$tail()) && $0.is$Link_Token());
+  this.groupingStack = (($0 = this.groupingStack.get$tail()) == null ? null : $0.assert$Link_Token());
 }
 ArrayBasedScanner.prototype.appendGtGt = function(kind, value) {
   var $0;
@@ -2643,12 +3031,12 @@ ArrayBasedScanner.prototype.appendGtGt = function(kind, value) {
   this.appendStringToken(kind, value);
   if ($notnull_bool(this.groupingStack.isEmpty())) return;
   if (this.groupingStack.get$head().get$kind() === 60/*null.LT_TOKEN*/) {
-    this.groupingStack = (($0 = this.groupingStack.get$tail()) && $0.is$Link_Token());
+    this.groupingStack = (($0 = this.groupingStack.get$tail()) == null ? null : $0.assert$Link_Token());
   }
   if ($notnull_bool(this.groupingStack.isEmpty())) return;
   if (this.groupingStack.get$head().get$kind() === 60/*null.LT_TOKEN*/) {
     this.groupingStack.get$head().set$endGroup(oldTail.next);
-    this.groupingStack = (($0 = this.groupingStack.get$tail()) && $0.is$Link_Token());
+    this.groupingStack = (($0 = this.groupingStack.get$tail()) == null ? null : $0.assert$Link_Token());
   }
 }
 ArrayBasedScanner.prototype.appendGtGtGt = function(kind, value) {
@@ -2657,16 +3045,16 @@ ArrayBasedScanner.prototype.appendGtGtGt = function(kind, value) {
   this.appendStringToken(kind, value);
   if ($notnull_bool(this.groupingStack.isEmpty())) return;
   if (this.groupingStack.get$head().get$kind() === 60/*null.LT_TOKEN*/) {
-    this.groupingStack = (($0 = this.groupingStack.get$tail()) && $0.is$Link_Token());
+    this.groupingStack = (($0 = this.groupingStack.get$tail()) == null ? null : $0.assert$Link_Token());
   }
   if ($notnull_bool(this.groupingStack.isEmpty())) return;
   if (this.groupingStack.get$head().get$kind() === 60/*null.LT_TOKEN*/) {
-    this.groupingStack = (($0 = this.groupingStack.get$tail()) && $0.is$Link_Token());
+    this.groupingStack = (($0 = this.groupingStack.get$tail()) == null ? null : $0.assert$Link_Token());
   }
   if ($notnull_bool(this.groupingStack.isEmpty())) return;
   if (this.groupingStack.get$head().get$kind() === 60/*null.LT_TOKEN*/) {
     this.groupingStack.get$head().set$endGroup(oldTail.next);
-    this.groupingStack = (($0 = this.groupingStack.get$tail()) && $0.is$Link_Token());
+    this.groupingStack = (($0 = this.groupingStack.get$tail()) == null ? null : $0.assert$Link_Token());
   }
 }
 // ********** Code for ArrayBasedScanner_SourceString **************
@@ -2689,7 +3077,8 @@ function Keyword(syntax, isPseudo) {
   this.isPseudo = isPseudo;
   // Initializers done
 }
-Keyword.prototype.is$SourceString = function(){return this;};
+Keyword.prototype.is$SourceString = function(){return true};
+Keyword.prototype.assert$SourceString = function(){return this};
 Keyword.prototype.get$syntax = function() { return this.syntax; };
 Keyword.prototype.get$isPseudo = function() { return this.isPseudo; };
 Keyword.get$keywords = function() {
@@ -2710,7 +3099,7 @@ Keyword.prototype.hashCode = function() {
   return this.syntax.hashCode();
 }
 Keyword.prototype.$eq = function(other) {
-  return !!(other && other.is$SourceString) && this.toString() == other.toString$0();
+  return !!(other && other.is$SourceString()) && this.toString() == other.toString$0();
 }
 Keyword.prototype.printOn = function(sb) {
   sb.add(this.syntax);
@@ -2723,14 +3112,14 @@ Keyword.prototype.get$stringValue = function() {
 }
 Keyword.prototype.hashCode$0 = Keyword.prototype.hashCode;
 Keyword.prototype.printOn$1 = function($0) {
-  return this.printOn(($0 && $0.is$StringBuffer()));
+  return this.printOn(($0 == null ? null : $0.assert$StringBuffer()));
 };
 Keyword.prototype.toString$0 = Keyword.prototype.toString;
 // ********** Code for KeywordState **************
 function KeywordState() {
   // Initializers done
 }
-KeywordState.prototype.is$KeywordState = function(){return this;};
+KeywordState.prototype.assert$KeywordState = function(){return this};
 KeywordState.get$KEYWORD_STATE = function() {
   if ($globals.KeywordState__KEYWORD_STATE == null) {
     var strings = new ListFactory(const$119/*Keyword.values*/.get$length());
@@ -2785,7 +3174,7 @@ ArrayKeywordState.prototype.isLeaf = function() {
 }
 ArrayKeywordState.prototype.next = function(c) {
   var $0;
-  return (($0 = this.table.$index(c - 97/*null.$a*/)) && $0.is$KeywordState());
+  return (($0 = this.table.$index(c - 97/*null.$a*/)) == null ? null : $0.assert$KeywordState());
 }
 ArrayKeywordState.prototype.get$keyword = function() {
   $throw("should not be called");
@@ -3115,8 +3504,8 @@ ElementListener.prototype.beginLibraryTag = function(token) {
 ElementListener.prototype.endClassDeclaration = function(interfacesCount, beginToken, extendsKeyword, implementsKeyword, endToken) {
   var $0;
   this.discardNodes(interfacesCount);
-  var supertype = (($0 = this.popNode()) && $0.is$Identifier());
-  var name = (($0 = this.popNode()) && $0.is$Identifier());
+  var supertype = (($0 = this.popNode()) == null ? null : $0.assert$Identifier());
+  var name = (($0 = this.popNode()) == null ? null : $0.assert$Identifier());
   this.pushElement(new PartialClassElement(name.get$source(), beginToken, endToken));
 }
 ElementListener.prototype.endInterface = function(token) {
@@ -3127,12 +3516,12 @@ ElementListener.prototype.endFunctionTypeAlias = function(token) {
 }
 ElementListener.prototype.endTopLevelMethod = function(beginToken, endToken) {
   var $0;
-  var name = (($0 = this.popNode()) && $0.is$Identifier());
+  var name = (($0 = this.popNode()) == null ? null : $0.assert$Identifier());
   this.pushElement(new PartialFunctionElement(name.get$source(), beginToken, endToken));
 }
 ElementListener.prototype.endTopLevelField = function(beginToken, endToken) {
   var $0;
-  var name = (($0 = this.popNode()) && $0.is$Identifier());
+  var name = (($0 = this.popNode()) == null ? null : $0.assert$Identifier());
   this.canceler.cancel("Cannot handle fields", null, beginToken);
 }
 ElementListener.prototype.handleIdentifier = function(token) {
@@ -3146,7 +3535,7 @@ ElementListener.prototype.endTypeArguments = function(count, beginToken, endToke
 }
 ElementListener.prototype.handleParenthesizedExpression = function(token) {
   var $0;
-  var expression = (($0 = this.popNode()) && $0.is$Expression());
+  var expression = (($0 = this.popNode()) == null ? null : $0.assert$Expression());
   this.pushNode(new ParenthesizedExpression(expression, token));
 }
 ElementListener.prototype.discardNodes = function(count) {
@@ -3171,18 +3560,18 @@ ElementListener.prototype.unexpected = function(token) {
 }
 ElementListener.prototype.pushElement = function(element) {
   var $0;
-  this.topLevelElements = (($0 = this.topLevelElements.prepend(element)) && $0.is$Link_Element());
+  this.topLevelElements = (($0 = this.topLevelElements.prepend(element)) == null ? null : $0.assert$Link_Element());
 }
 ElementListener.prototype.pushNode = function(node) {
   var $0;
-  this.nodes = (($0 = this.nodes.prepend(node)) && $0.is$Link_Node());
+  this.nodes = (($0 = this.nodes.prepend(node)) == null ? null : $0.assert$Link_Node());
   if (false/*null.VERBOSE*/) this.log(("push " + this.nodes));
 }
 ElementListener.prototype.popNode = function() {
   var $0;
   $assert(!$notnull_bool(this.nodes.isEmpty()), "!nodes.isEmpty()", "listener.dart", 406, 12);
-  var node = (($0 = this.nodes.get$head()) && $0.is$Node());
-  this.nodes = (($0 = this.nodes.get$tail()) && $0.is$Link_Node());
+  var node = (($0 = this.nodes.get$head()) == null ? null : $0.assert$Node());
+  this.nodes = (($0 = this.nodes.get$tail()) == null ? null : $0.assert$Link_Node());
   if (false/*null.VERBOSE*/) this.log(("pop " + this.nodes));
   return node;
 }
@@ -3198,10 +3587,10 @@ function NodeListener(canceler, logger) {
 $inherits(NodeListener, ElementListener);
 NodeListener.prototype.endClassDeclaration = function(interfacesCount, beginToken, extendsKeyword, implementsKeyword, endToken) {
   var $0;
-  var body = (($0 = this.popNode()) && $0.is$NodeList());
+  var body = (($0 = this.popNode()) == null ? null : $0.assert$NodeList());
   var interfaces = this.makeNodeList(interfacesCount, implementsKeyword, null, ",");
-  var supertype = (($0 = this.popNode()) && $0.is$TypeAnnotation());
-  var name = (($0 = this.popNode()) && $0.is$Identifier());
+  var supertype = (($0 = this.popNode()) == null ? null : $0.assert$TypeAnnotation());
+  var name = (($0 = this.popNode()) == null ? null : $0.assert$Identifier());
   this.pushNode(new ClassNode(name, supertype, interfaces, beginToken, extendsKeyword, endToken));
 }
 NodeListener.prototype.endClassBody = function(memberCount, beginToken, endToken) {
@@ -3210,7 +3599,7 @@ NodeListener.prototype.endClassBody = function(memberCount, beginToken, endToken
 NodeListener.prototype.endFormalParameter = function(token) {
   var $0;
   var name = new NodeList.singleton$ctor(this.popNode());
-  var type = (($0 = this.popNode()) && $0.is$TypeAnnotation());
+  var type = (($0 = this.popNode()) == null ? null : $0.assert$TypeAnnotation());
   this.pushNode(new VariableDefinitions(type, null, name, token));
 }
 NodeListener.prototype.endFormalParameters = function(count, beginToken, endToken) {
@@ -3224,7 +3613,7 @@ NodeListener.prototype.handleNoArguments = function(token) {
 }
 NodeListener.prototype.endReturnStatement = function(hasExpression, beginToken, endToken) {
   var $0;
-  var expression = (($0 = $notnull_bool(hasExpression) ? this.popNode() : null) && $0.is$Expression());
+  var expression = (($0 = $notnull_bool(hasExpression) ? this.popNode() : null) == null ? null : $0.assert$Expression());
   this.pushNode(new Return(beginToken, endToken, expression));
 }
 NodeListener.prototype.endExpressionStatement = function(token) {
@@ -3236,21 +3625,21 @@ NodeListener.prototype.handleOnError = function(token, error) {
 NodeListener.prototype.handleLiteralInt = function(token) {
   var $this = this; // closure support
   this.pushNode(new LiteralInt(token, (function (t, e) {
-    return $this.handleOnError((t && t.is$Token()), e);
+    return $this.handleOnError((t == null ? null : t.assert$Token()), e);
   })
   ));
 }
 NodeListener.prototype.handleLiteralDouble = function(token) {
   var $this = this; // closure support
   this.pushNode(new LiteralDouble(token, (function (t, e) {
-    return $this.handleOnError((t && t.is$Token()), e);
+    return $this.handleOnError((t == null ? null : t.assert$Token()), e);
   })
   ));
 }
 NodeListener.prototype.handleLiteralBool = function(token) {
   var $this = this; // closure support
   this.pushNode(new LiteralBool(token, (function (t, e) {
-    return $this.handleOnError((t && t.is$Token()), e);
+    return $this.handleOnError((t == null ? null : t.assert$Token()), e);
   })
   ));
 }
@@ -3296,7 +3685,7 @@ NodeListener.prototype.handleConditionalExpression = function(question, colon) {
 }
 NodeListener.prototype.endSend = function(token) {
   var $0;
-  var arguments = (($0 = this.popNode()) && $0.is$NodeList());
+  var arguments = (($0 = this.popNode()) == null ? null : $0.assert$NodeList());
   var selector = this.popNode();
   this.pushNode(new Send(null, selector, arguments));
 }
@@ -3308,10 +3697,10 @@ NodeListener.prototype.endFunctionBody = function(count, beginToken, endToken) {
 }
 NodeListener.prototype.endFunction = function(token) {
   var $0;
-  var body = (($0 = this.popNode()) && $0.is$Statement());
+  var body = (($0 = this.popNode()) == null ? null : $0.assert$Statement());
   var formals = this.popNode();
   var name = this.popNode();
-  var type = (($0 = this.popNode()) && $0.is$TypeAnnotation());
+  var type = (($0 = this.popNode()) == null ? null : $0.assert$TypeAnnotation());
   this.pushNode(new FunctionExpression(name, formals, body, type));
 }
 NodeListener.prototype.handleVarKeyword = function(token) {
@@ -3323,42 +3712,42 @@ NodeListener.prototype.handleFinalKeyword = function(token) {
 NodeListener.prototype.endVariablesDeclaration = function(count, endToken) {
   var $0;
   var variables = this.makeNodeList(count, null, null, ",");
-  var type = (($0 = this.popNode()) && $0.is$TypeAnnotation());
+  var type = (($0 = this.popNode()) == null ? null : $0.assert$TypeAnnotation());
   this.pushNode(new VariableDefinitions(type, null, variables, endToken));
 }
 NodeListener.prototype.endInitializer = function(assignmentOperator) {
   var $0;
-  var initializer = (($0 = this.popNode()) && $0.is$Expression());
+  var initializer = (($0 = this.popNode()) == null ? null : $0.assert$Expression());
   var arguments = new NodeList.singleton$ctor(initializer);
-  var name = (($0 = this.popNode()) && $0.is$Expression());
+  var name = (($0 = this.popNode()) == null ? null : $0.assert$Expression());
   var op = new Operator(assignmentOperator);
   this.pushNode(new SendSet(null, name, op, arguments));
 }
 NodeListener.prototype.endIfStatement = function(ifToken, elseToken) {
   var $0;
-  var elsePart = (($0 = (elseToken == null) ? null : this.popNode()) && $0.is$Statement());
-  var thenPart = (($0 = this.popNode()) && $0.is$Statement());
-  var condition = (($0 = this.popNode()) && $0.is$ParenthesizedExpression());
+  var elsePart = (($0 = (elseToken == null) ? null : this.popNode()) == null ? null : $0.assert$Statement());
+  var thenPart = (($0 = this.popNode()) == null ? null : $0.assert$Statement());
+  var condition = (($0 = this.popNode()) == null ? null : $0.assert$ParenthesizedExpression());
   this.pushNode(new If(condition, thenPart, elsePart, ifToken, elseToken));
 }
 NodeListener.prototype.endForStatement = function(beginToken, endToken) {
   var $0;
-  var body = (($0 = this.popNode()) && $0.is$Statement());
-  var update = (($0 = this.popNode()) && $0.is$Expression());
-  var condition = (($0 = this.popNode()) && $0.is$ExpressionStatement());
-  var initializer = (($0 = this.popNode()) && $0.is$VariableDefinitions());
+  var body = (($0 = this.popNode()) == null ? null : $0.assert$Statement());
+  var update = (($0 = this.popNode()) == null ? null : $0.assert$Expression());
+  var condition = (($0 = this.popNode()) == null ? null : $0.assert$ExpressionStatement());
+  var initializer = (($0 = this.popNode()) == null ? null : $0.assert$VariableDefinitions());
   this.pushNode(new For(initializer, condition, update, body, beginToken));
 }
 NodeListener.prototype.endDoWhileStatement = function(doKeyword, whileKeyword, endToken) {
   var $0;
-  var condition = (($0 = this.popNode()) && $0.is$Expression());
-  var body = (($0 = this.popNode()) && $0.is$Statement());
+  var condition = (($0 = this.popNode()) == null ? null : $0.assert$Expression());
+  var body = (($0 = this.popNode()) == null ? null : $0.assert$Statement());
   this.pushNode(new DoWhile(body, condition, doKeyword, whileKeyword, endToken));
 }
 NodeListener.prototype.endWhileStatement = function(whileKeyword, endToken) {
   var $0;
-  var body = (($0 = this.popNode()) && $0.is$Statement());
-  var condition = (($0 = this.popNode()) && $0.is$Expression());
+  var body = (($0 = this.popNode()) == null ? null : $0.assert$Statement());
+  var condition = (($0 = this.popNode()) == null ? null : $0.assert$Expression());
   this.pushNode(new While(condition, body, whileKeyword));
 }
 NodeListener.prototype.endBlock = function(count, beginToken, endToken) {
@@ -3366,13 +3755,13 @@ NodeListener.prototype.endBlock = function(count, beginToken, endToken) {
 }
 NodeListener.prototype.endType = function(count, beginToken, endToken) {
   var $0;
-  var type = new TypeAnnotation((($0 = this.popNode()) && $0.is$Identifier()));
+  var type = new TypeAnnotation((($0 = this.popNode()) == null ? null : $0.assert$Identifier()));
   this.discardNodes(count - 1);
   this.pushNode(type);
 }
 NodeListener.prototype.endThrowStatement = function(throwToken, endToken) {
   var $0;
-  var expression = (($0 = this.popNode()) && $0.is$Expression());
+  var expression = (($0 = this.popNode()) == null ? null : $0.assert$Expression());
   this.pushNode(new Throw(expression, throwToken, endToken));
 }
 NodeListener.prototype.endRethrowStatement = function(throwToken, endToken) {
@@ -3424,8 +3813,8 @@ NodeListener.prototype.handleNoFieldInitializer = function(token) {
 }
 NodeListener.prototype.endField = function(beginToken, endToken) {
   var $0;
-  var initializer = (($0 = this.popNode()) && $0.is$Expression());
-  var name = (($0 = this.popNode()) && $0.is$Identifier());
+  var initializer = (($0 = this.popNode()) == null ? null : $0.assert$Expression());
+  var name = (($0 = this.popNode()) == null ? null : $0.assert$Identifier());
   this.pushNode(null);
   this.canceler.cancel("fields are not implemented yet", name);
 }
@@ -3437,9 +3826,9 @@ NodeListener.prototype.makeNodeList = function(count, beginToken, endToken, deli
   var $0;
   var nodes = const$209/*const EmptyLink<Node>()*/;
   for (; count > 0; --count) {
-    nodes = (($0 = nodes.prepend(this.popNode())) && $0.is$Link_Node());
+    nodes = (($0 = nodes.prepend(this.popNode())) == null ? null : $0.assert$Link_Node());
   }
-  var sourceDelimiter = (($0 = (delimiter == null) ? null : new StringWrapper(delimiter)) && $0.is$SourceString());
+  var sourceDelimiter = (($0 = (delimiter == null) ? null : new StringWrapper(delimiter)) == null ? null : $0.assert$SourceString());
   return new NodeList(beginToken, nodes, endToken, sourceDelimiter);
 }
 NodeListener.prototype.log = function(message) {
@@ -3460,7 +3849,7 @@ PartialFunctionElement.prototype.parseNode = function(canceler, logger) {
   this.node = (($0 = parse(canceler, logger, (function (p) {
     return p.parseFunction$1($this.beginToken);
   })
-  )) && $0.is$FunctionExpression());
+  )) == null ? null : $0.assert$FunctionExpression());
   return this.node;
 }
 // ********** Code for PartialClassElement **************
@@ -3478,7 +3867,7 @@ PartialClassElement.prototype.parseNode = function(canceler, logger) {
   this.node = (($0 = parse(canceler, logger, (function (p) {
     return p.parseClass$1($this.beginToken);
   })
-  )) && $0.is$ClassNode());
+  )) == null ? null : $0.assert$ClassNode());
   return this.node;
 }
 // ********** Code for Parser **************
@@ -3595,7 +3984,7 @@ Parser.prototype.skipBlock = function(token) {
   if (!$notnull_bool(this.optional('{', token))) {
     return this.listener.expectedBlock(token);
   }
-  var beginGroupToken = (token && token.is$BeginGroupToken());
+  var beginGroupToken = (token == null ? null : token.assert$BeginGroupToken());
   $assert(beginGroupToken.endGroup == null || beginGroupToken.endGroup.kind === 125/*null.$RBRACE*/, "beginGroupToken.endGroup === null ||\n           beginGroupToken.endGroup.kind === $RBRACE", "parser.dart", 127, 12);
   return beginGroupToken.endGroup;
 }
@@ -3692,22 +4081,22 @@ Parser.prototype.parseType = function(token) {
 Parser.prototype.parseTypeArgumentsOpt = function(token) {
   var $this = this; // closure support
   return this.parseStuff(token, (function (t) {
-    return $this.listener.beginTypeArguments((t && t.is$Token()));
+    return $this.listener.beginTypeArguments((t == null ? null : t.assert$Token()));
   })
   , (function (t) {
-    return $this.parseType((t && t.is$Token()));
+    return $this.parseType((t == null ? null : t.assert$Token()));
   })
   , (function (c, bt, et) {
-    return $this.listener.endTypeArguments($assert_num(c), (bt && bt.is$Token()), (et && et.is$Token()));
+    return $this.listener.endTypeArguments($assert_num(c), (bt == null ? null : bt.assert$Token()), (et == null ? null : et.assert$Token()));
   })
   , (function (t) {
-    return $this.listener.handleNoTypeArguments((t && t.is$Token()));
+    return $this.listener.handleNoTypeArguments((t == null ? null : t.assert$Token()));
   })
   );
 }
 Parser.prototype.parseTypeVariablesOpt = function(token) {
   if ($notnull_bool(this.optional('<', token))) {
-    var beginGroupToken = (token && token.is$BeginGroupToken());
+    var beginGroupToken = (token == null ? null : token.assert$BeginGroupToken());
     token = beginGroupToken.endGroup.next;
   }
   this.listener.handleNoTypeVariables(token);
@@ -3720,7 +4109,7 @@ Parser.prototype.parseStuff = function(token, beginStuff, stuffParser, endStuff,
     beginStuff.call$1(begin);
     var count = 0;
     do {
-      token = (($0 = stuffParser.call$1(token.next)) && $0.is$Token());
+      token = (($0 = stuffParser.call$1(token.next)) == null ? null : $0.assert$Token());
       ++count;
     }
     while ($notnull_bool(this.optional(',', token)))
@@ -3762,7 +4151,7 @@ Parser.prototype.parseTopLevelMember = function(token) {
     this.listener.endTopLevelField(start, token);
   }
   else {
-    token = this.skipFormals((token && token.is$BeginGroupToken())).next;
+    token = this.skipFormals((token == null ? null : token.assert$BeginGroupToken())).next;
     token = this.parseFunctionBody(token);
     this.listener.endTopLevelMethod(start, token);
   }
@@ -3829,7 +4218,7 @@ Parser.prototype.peekAfterType = function(token) {
     }
   }
   if (peek.kind === 60/*null.LT_TOKEN*/) {
-    var beginGroupToken = (peek && peek.is$BeginGroupToken());
+    var beginGroupToken = (peek == null ? null : peek.assert$BeginGroupToken());
     var gtToken = beginGroupToken.endGroup;
     if (gtToken != null) {
       return gtToken.next;
@@ -3887,7 +4276,7 @@ Parser.prototype.parseMember = function(token) {
     this.listener.endField(start, token);
   }
   else {
-    token = this.skipFormals((token && token.is$BeginGroupToken())).next;
+    token = this.skipFormals((token == null ? null : token.assert$BeginGroupToken())).next;
     token = this.parseInitializersOpt(token);
     if (!$notnull_bool(this.optional(';', token))) {
       token = this.parseFunctionBody(token);
@@ -3995,7 +4384,7 @@ Parser.prototype.parseExpressionStatementOrDeclaration = function(token) {
       return this.parseVariablesDeclaration(token);
     }
     else if (afterIdKind === 40/*null.LPAREN_TOKEN*/) {
-      var beginParen = (afterId && afterId.is$BeginGroupToken());
+      var beginParen = (afterId == null ? null : afterId.assert$BeginGroupToken());
       var endParen = beginParen.endGroup;
       var afterParens = endParen.next;
       if ($notnull_bool(this.optional('{', afterParens)) || $notnull_bool(this.optional('=>', afterParens))) {
@@ -4164,7 +4553,7 @@ Parser.prototype.parsePrimary = function(token) {
   }
 }
 Parser.prototype.parseParenthesizedExpression = function(token) {
-  var begin = (token && token.is$BeginGroupToken());
+  var begin = (token == null ? null : token.assert$BeginGroupToken());
   token = this.expect('(', token);
   token = this.parseExpression(token);
   $assert(begin.endGroup === token, "begin.endGroup === token", "parser.dart", 731, 12);
@@ -4349,10 +4738,10 @@ Parser.prototype.parseThrowStatement = function(token) {
   }
 }
 Parser.prototype.parseClass$1 = function($0) {
-  return this.parseClass(($0 && $0.is$Token()));
+  return this.parseClass(($0 == null ? null : $0.assert$Token()));
 };
 Parser.prototype.parseFunction$1 = function($0) {
-  return this.parseFunction(($0 && $0.is$Token()));
+  return this.parseFunction(($0 == null ? null : $0.assert$Token()));
 };
 // ********** Code for ParserTask **************
 function ParserTask(compiler) {
@@ -4369,7 +4758,7 @@ ParserTask.prototype.parse = function(element) {
   return (($0 = this.measure((function () {
     return element.parseNode($this.compiler, $this.compiler);
   })
-  )) && $0.is$Node());
+  )) == null ? null : $0.assert$Node());
 }
 // ********** Code for PartialParser **************
 function PartialParser(listener) {
@@ -4388,7 +4777,7 @@ PartialParser.prototype.skipExpression = function(token) {
     var kind = token.kind;
     if ((token.kind === 0/*null.EOF_TOKEN*/) || (token.kind === 59/*null.SEMICOLON_TOKEN*/)) return token;
     if ((token instanceof BeginGroupToken)) {
-      var begin = (token && token.is$BeginGroupToken());
+      var begin = (token == null ? null : token.assert$BeginGroupToken());
       token = (begin.endGroup != null) ? begin.endGroup : token;
     }
     token = token.next;
@@ -5604,8 +5993,8 @@ ScannerTask.prototype.scan = function(script) {
     var $0;
     var elements = $this.scanElements(script.get$text());
     for (var link = elements;
-     !$notnull_bool(link.isEmpty()); link = (($0 = link.get$tail()) && $0.is$Link_Element())) {
-      $this.compiler.universe.define((($0 = link.get$head()) && $0.is$Element()));
+     !$notnull_bool(link.isEmpty()); link = (($0 = link.get$tail()) == null ? null : $0.assert$Link_Element())) {
+      $this.compiler.universe.define((($0 = link.get$head()) == null ? null : $0.assert$Element()));
     }
   })
   );
@@ -5644,7 +6033,7 @@ StringScanner.prototype.appendByteStringToken = function(kind, value) {
   this.tail = this.tail.next;
 }
 StringScanner.prototype.appendByteStringToken$2 = function($0, $1) {
-  return this.appendByteStringToken($assert_num($0), ($1 && $1.is$SourceString()));
+  return this.appendByteStringToken($assert_num($0), ($1 == null ? null : $1.assert$SourceString()));
 };
 // ********** Code for SubstringWrapper **************
 function SubstringWrapper(internalString, begin, end) {
@@ -5653,13 +6042,14 @@ function SubstringWrapper(internalString, begin, end) {
   this.end = end;
   // Initializers done
 }
-SubstringWrapper.prototype.is$SourceString = function(){return this;};
+SubstringWrapper.prototype.is$SourceString = function(){return true};
+SubstringWrapper.prototype.assert$SourceString = function(){return this};
 SubstringWrapper.prototype.get$end = function() { return this.end; };
 SubstringWrapper.prototype.hashCode = function() {
   return this.toString().hashCode();
 }
 SubstringWrapper.prototype.$eq = function(other) {
-  return !!(other && other.is$SourceString) && this.toString() == other.toString$0();
+  return !!(other && other.is$SourceString()) && this.toString() == other.toString$0();
 }
 SubstringWrapper.prototype.printOn = function(sb) {
   sb.add(this);
@@ -5672,7 +6062,7 @@ SubstringWrapper.prototype.get$stringValue = function() {
 }
 SubstringWrapper.prototype.hashCode$0 = SubstringWrapper.prototype.hashCode;
 SubstringWrapper.prototype.printOn$1 = function($0) {
-  return this.printOn(($0 && $0.is$StringBuffer()));
+  return this.printOn(($0 == null ? null : $0.assert$StringBuffer()));
 };
 SubstringWrapper.prototype.toString$0 = SubstringWrapper.prototype.toString;
 // ********** Code for Token **************
@@ -5681,7 +6071,7 @@ function Token(kind, charOffset) {
   this.charOffset = charOffset;
   // Initializers done
 }
-Token.prototype.is$Token = function(){return this;};
+Token.prototype.assert$Token = function(){return this};
 Token.prototype.get$kind = function() { return this.kind; };
 Token.prototype.get$charOffset = function() { return this.charOffset; };
 Token.prototype.get$value = function() {
@@ -5737,13 +6127,14 @@ function StringWrapper(stringValue) {
   this.stringValue = stringValue;
   // Initializers done
 }
-StringWrapper.prototype.is$SourceString = function(){return this;};
+StringWrapper.prototype.is$SourceString = function(){return true};
+StringWrapper.prototype.assert$SourceString = function(){return this};
 StringWrapper.prototype.get$stringValue = function() { return this.stringValue; };
 StringWrapper.prototype.hashCode = function() {
   return this.stringValue.hashCode();
 }
 StringWrapper.prototype.$eq = function(other) {
-  return !!(other && other.is$SourceString) && this.toString() == other.toString$0();
+  return !!(other && other.is$SourceString()) && this.toString() == other.toString$0();
 }
 StringWrapper.prototype.printOn = function(sb) {
   sb.add(this.stringValue);
@@ -5753,7 +6144,7 @@ StringWrapper.prototype.toString = function() {
 }
 StringWrapper.prototype.hashCode$0 = StringWrapper.prototype.hashCode;
 StringWrapper.prototype.printOn$1 = function($0) {
-  return this.printOn(($0 && $0.is$StringBuffer()));
+  return this.printOn(($0 == null ? null : $0.assert$StringBuffer()));
 };
 StringWrapper.prototype.toString$0 = StringWrapper.prototype.toString;
 // ********** Code for BeginGroupToken **************
@@ -5762,7 +6153,7 @@ function BeginGroupToken(kind, value, charOffset) {
   StringToken.call(this, kind, value, charOffset);
 }
 $inherits(BeginGroupToken, StringToken);
-BeginGroupToken.prototype.is$BeginGroupToken = function(){return this;};
+BeginGroupToken.prototype.assert$BeginGroupToken = function(){return this};
 BeginGroupToken.prototype.get$endGroup = function() { return this.endGroup; };
 BeginGroupToken.prototype.set$endGroup = function(value) { return this.endGroup = value; };
 // ********** Code for top level **************
@@ -5779,7 +6170,7 @@ function Node() {
   this._hashCode = ++$globals.Node__HASH_COUNTER;
   // Initializers done
 }
-Node.prototype.is$Node = function(){return this;};
+Node.prototype.assert$Node = function(){return this};
 Node.prototype.hashCode = function() {
   return this._hashCode;
 }
@@ -5808,7 +6199,7 @@ Node.prototype.asSendSet = function() {
   return null;
 }
 Node.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$Visitor()));
+  return this.accept(($0 == null ? null : $0.assert$Visitor()));
 };
 Node.prototype.getBeginToken$0 = Node.prototype.getBeginToken;
 Node.prototype.getEndToken$0 = Node.prototype.getEndToken;
@@ -5826,7 +6217,7 @@ function ClassNode(name, superclass, interfaces, beginToken, extendsKeyword, end
   Node.call(this);
 }
 $inherits(ClassNode, Node);
-ClassNode.prototype.is$ClassNode = function(){return this;};
+ClassNode.prototype.assert$ClassNode = function(){return this};
 ClassNode.prototype.get$name = function() { return this.name; };
 ClassNode.prototype.get$interfaces = function() { return this.interfaces; };
 ClassNode.prototype.accept = function(visitor) {
@@ -5845,7 +6236,7 @@ ClassNode.prototype.getEndToken = function() {
   return this.endToken;
 }
 ClassNode.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$Visitor()));
+  return this.accept(($0 == null ? null : $0.assert$Visitor()));
 };
 ClassNode.prototype.getBeginToken$0 = ClassNode.prototype.getBeginToken;
 ClassNode.prototype.getEndToken$0 = ClassNode.prototype.getEndToken;
@@ -5855,14 +6246,14 @@ function Expression() {
   Node.call(this);
 }
 $inherits(Expression, Node);
-Expression.prototype.is$Expression = function(){return this;};
+Expression.prototype.assert$Expression = function(){return this};
 // ********** Code for Statement **************
 function Statement() {
   // Initializers done
   Node.call(this);
 }
 $inherits(Statement, Node);
-Statement.prototype.is$Statement = function(){return this;};
+Statement.prototype.assert$Statement = function(){return this};
 // ********** Code for Send **************
 function Send(receiver, selector, argumentsNode) {
   this.receiver = receiver;
@@ -5921,15 +6312,15 @@ Send.prototype.getEndToken = function() {
   if (this.argumentsNode != null) token = this.argumentsNode.getEndToken();
   if (token != null) return token;
   if (this.selector != null) {
-    return (($0 = this.selector.getEndToken()) && $0.is$Token());
+    return (($0 = this.selector.getEndToken()) == null ? null : $0.assert$Token());
   }
-  return (($0 = this.receiver.getBeginToken()) && $0.is$Token());
+  return (($0 = this.receiver.getBeginToken()) == null ? null : $0.assert$Token());
 }
 Send.prototype.copyWithReceiver = function(receiver) {
   return new Send(receiver, this.selector, this.argumentsNode);
 }
 Send.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$Visitor()));
+  return this.accept(($0 == null ? null : $0.assert$Visitor()));
 };
 Send.prototype.getBeginToken$0 = Send.prototype.getBeginToken;
 Send.prototype.getEndToken$0 = Send.prototype.getEndToken;
@@ -5964,7 +6355,7 @@ SendSet.prefix$ctor = function(receiver, selector, assignmentOperator) {
 }
 SendSet.prefix$ctor.prototype = SendSet.prototype;
 $inherits(SendSet, Send);
-SendSet.prototype.is$SendSet = function(){return this;};
+SendSet.prototype.assert$SendSet = function(){return this};
 SendSet.prototype.asSendSet = function() {
   return this;
 }
@@ -5975,7 +6366,7 @@ SendSet.prototype.copyWithReceiver = function(receiver) {
   $throw('not implemented');
 }
 SendSet.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$Visitor()));
+  return this.accept(($0 == null ? null : $0.assert$Visitor()));
 };
 // ********** Code for NodeList **************
 function NodeList(beginToken, nodes, endToken, delimiter) {
@@ -5992,10 +6383,10 @@ NodeList.singleton$ctor = function(node) {
 }
 NodeList.singleton$ctor.prototype = NodeList.prototype;
 $inherits(NodeList, Node);
-NodeList.prototype.is$NodeList = function(){return this;};
+NodeList.prototype.assert$NodeList = function(){return this};
 NodeList.prototype.get$nodes = function() {
   var $0;
-  return (($0 = this._nodes != null ? this._nodes : const$209/*const EmptyLink<Node>()*/) && $0.is$Link_Node());
+  return (($0 = this._nodes != null ? this._nodes : const$209/*const EmptyLink<Node>()*/) == null ? null : $0.assert$Link_Node());
 }
 NodeList.prototype.accept = function(visitor) {
   return visitor.visitNodeList(this);
@@ -6005,12 +6396,12 @@ NodeList.prototype.getBeginToken = function() {
   if (this.beginToken != null) return this.beginToken;
   if (this.get$nodes() != null) {
     for (var link = this.get$nodes();
-     !$notnull_bool(link.isEmpty()); link = (($0 = link.get$tail()) && $0.is$Link_Node())) {
+     !$notnull_bool(link.isEmpty()); link = (($0 = link.get$tail()) == null ? null : $0.assert$Link_Node())) {
       if (link.get$head().getBeginToken$0() != null) {
-        return (($0 = link.get$head().getBeginToken$0()) && $0.is$Token());
+        return (($0 = link.get$head().getBeginToken$0()) == null ? null : $0.assert$Token());
       }
       if (link.get$head().getEndToken$0() != null) {
-        return (($0 = link.get$head().getEndToken$0()) && $0.is$Token());
+        return (($0 = link.get$head().getEndToken$0()) == null ? null : $0.assert$Token());
       }
     }
   }
@@ -6022,14 +6413,14 @@ NodeList.prototype.getEndToken = function() {
   if (this.get$nodes() != null) {
     var link = this.get$nodes();
     if ($notnull_bool(link.isEmpty())) return this.beginToken;
-    while (!$notnull_bool(link.get$tail().isEmpty$0())) link = (($0 = link.get$tail()) && $0.is$Link_Node());
-    if (link.get$head().getEndToken$0() != null) return (($0 = link.get$head().getEndToken$0()) && $0.is$Token());
-    if (link.get$head().getBeginToken$0() != null) return (($0 = link.get$head().getBeginToken$0()) && $0.is$Token());
+    while (!$notnull_bool(link.get$tail().isEmpty$0())) link = (($0 = link.get$tail()) == null ? null : $0.assert$Link_Node());
+    if (link.get$head().getEndToken$0() != null) return (($0 = link.get$head().getEndToken$0()) == null ? null : $0.assert$Token());
+    if (link.get$head().getBeginToken$0() != null) return (($0 = link.get$head().getBeginToken$0()) == null ? null : $0.assert$Token());
   }
   return this.beginToken;
 }
 NodeList.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$Visitor()));
+  return this.accept(($0 == null ? null : $0.assert$Visitor()));
 };
 NodeList.prototype.getBeginToken$0 = NodeList.prototype.getBeginToken;
 NodeList.prototype.getEndToken$0 = NodeList.prototype.getEndToken;
@@ -6051,7 +6442,7 @@ Block.prototype.getEndToken = function() {
   return this.statements.getEndToken();
 }
 Block.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$Visitor()));
+  return this.accept(($0 == null ? null : $0.assert$Visitor()));
 };
 Block.prototype.getBeginToken$0 = Block.prototype.getBeginToken;
 Block.prototype.getEndToken$0 = Block.prototype.getEndToken;
@@ -6080,7 +6471,7 @@ If.prototype.getEndToken = function() {
   return this.elsePart.getEndToken();
 }
 If.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$Visitor()));
+  return this.accept(($0 == null ? null : $0.assert$Visitor()));
 };
 If.prototype.getBeginToken$0 = If.prototype.getBeginToken;
 If.prototype.getEndToken$0 = If.prototype.getEndToken;
@@ -6107,7 +6498,7 @@ For.prototype.getEndToken = function() {
   return this.body.getEndToken();
 }
 For.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$Visitor()));
+  return this.accept(($0 == null ? null : $0.assert$Visitor()));
 };
 For.prototype.getBeginToken$0 = For.prototype.getBeginToken;
 For.prototype.getEndToken$0 = For.prototype.getEndToken;
@@ -6121,7 +6512,7 @@ function FunctionExpression(name, parameters, body, returnType) {
   Expression.call(this);
 }
 $inherits(FunctionExpression, Expression);
-FunctionExpression.prototype.is$FunctionExpression = function(){return this;};
+FunctionExpression.prototype.assert$FunctionExpression = function(){return this};
 FunctionExpression.prototype.get$name = function() { return this.name; };
 FunctionExpression.prototype.get$parameters = function() { return this.parameters; };
 FunctionExpression.prototype.get$body = function() { return this.body; };
@@ -6136,7 +6527,7 @@ FunctionExpression.prototype.getEndToken = function() {
   return this.body.getEndToken();
 }
 FunctionExpression.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$Visitor()));
+  return this.accept(($0 == null ? null : $0.assert$Visitor()));
 };
 FunctionExpression.prototype.getBeginToken$0 = FunctionExpression.prototype.getBeginToken;
 FunctionExpression.prototype.getEndToken$0 = FunctionExpression.prototype.getEndToken;
@@ -6207,7 +6598,7 @@ LiteralInt.prototype.accept = function(visitor) {
   return visitor.visitLiteralInt(this);
 }
 LiteralInt.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$Visitor()));
+  return this.accept(($0 == null ? null : $0.assert$Visitor()));
 };
 // ********** Code for LiteralDouble **************
 function LiteralDouble(token, handler) {
@@ -6228,7 +6619,7 @@ LiteralDouble.prototype.accept = function(visitor) {
   return visitor.visitLiteralDouble(this);
 }
 LiteralDouble.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$Visitor()));
+  return this.accept(($0 == null ? null : $0.assert$Visitor()));
 };
 // ********** Code for LiteralBool **************
 function LiteralBool(token, handler) {
@@ -6256,7 +6647,7 @@ LiteralBool.prototype.accept = function(visitor) {
   return visitor.visitLiteralBool(this);
 }
 LiteralBool.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$Visitor()));
+  return this.accept(($0 == null ? null : $0.assert$Visitor()));
 };
 // ********** Code for LiteralString **************
 function LiteralString(token) {
@@ -6264,16 +6655,16 @@ function LiteralString(token) {
   Literal_SourceString.call(this, token, to$call$2(null));
 }
 $inherits(LiteralString, Literal_SourceString);
-LiteralString.prototype.is$LiteralString = function(){return this;};
+LiteralString.prototype.assert$LiteralString = function(){return this};
 LiteralString.prototype.get$value = function() {
   var $0;
-  return (($0 = this.token.get$value()) && $0.is$SourceString());
+  return (($0 = this.token.get$value()) == null ? null : $0.assert$SourceString());
 }
 LiteralString.prototype.accept = function(visitor) {
   return visitor.visitLiteralString(this);
 }
 LiteralString.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$Visitor()));
+  return this.accept(($0 == null ? null : $0.assert$Visitor()));
 };
 // ********** Code for LiteralNull **************
 function LiteralNull(token) {
@@ -6288,7 +6679,7 @@ LiteralNull.prototype.accept = function(visitor) {
   return visitor.visitLiteralNull(this);
 }
 LiteralNull.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$Visitor()));
+  return this.accept(($0 == null ? null : $0.assert$Visitor()));
 };
 // ********** Code for Identifier **************
 function Identifier(token) {
@@ -6297,10 +6688,10 @@ function Identifier(token) {
   Expression.call(this);
 }
 $inherits(Identifier, Expression);
-Identifier.prototype.is$Identifier = function(){return this;};
+Identifier.prototype.assert$Identifier = function(){return this};
 Identifier.prototype.get$source = function() {
   var $0;
-  return (($0 = this.token.get$value()) && $0.is$SourceString());
+  return (($0 = this.token.get$value()) == null ? null : $0.assert$SourceString());
 }
 Identifier.prototype.accept = function(visitor) {
   return visitor.visitIdentifier(this);
@@ -6312,7 +6703,7 @@ Identifier.prototype.getEndToken = function() {
   return this.token;
 }
 Identifier.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$Visitor()));
+  return this.accept(($0 == null ? null : $0.assert$Visitor()));
 };
 Identifier.prototype.getBeginToken$0 = Identifier.prototype.getBeginToken;
 Identifier.prototype.getEndToken$0 = Identifier.prototype.getEndToken;
@@ -6322,7 +6713,7 @@ function Operator(token) {
   Identifier.call(this, token);
 }
 $inherits(Operator, Identifier);
-Operator.prototype.is$Operator = function(){return this;};
+Operator.prototype.assert$Operator = function(){return this};
 Operator.prototype.asOperator = function() {
   return this;
 }
@@ -6330,7 +6721,7 @@ Operator.prototype.accept = function(visitor) {
   return visitor.visitOperator(this);
 }
 Operator.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$Visitor()));
+  return this.accept(($0 == null ? null : $0.assert$Visitor()));
 };
 // ********** Code for Return **************
 function Return(beginToken, endToken, expression) {
@@ -6354,7 +6745,7 @@ Return.prototype.getEndToken = function() {
   return this.endToken;
 }
 Return.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$Visitor()));
+  return this.accept(($0 == null ? null : $0.assert$Visitor()));
 };
 Return.prototype.getBeginToken$0 = Return.prototype.getBeginToken;
 Return.prototype.getEndToken$0 = Return.prototype.getEndToken;
@@ -6366,19 +6757,19 @@ function ExpressionStatement(expression, endToken) {
   Statement.call(this);
 }
 $inherits(ExpressionStatement, Statement);
-ExpressionStatement.prototype.is$ExpressionStatement = function(){return this;};
+ExpressionStatement.prototype.assert$ExpressionStatement = function(){return this};
 ExpressionStatement.prototype.accept = function(visitor) {
   return visitor.visitExpressionStatement(this);
 }
 ExpressionStatement.prototype.getBeginToken = function() {
   var $0;
-  return (($0 = this.expression.getBeginToken()) && $0.is$Token());
+  return (($0 = this.expression.getBeginToken()) == null ? null : $0.assert$Token());
 }
 ExpressionStatement.prototype.getEndToken = function() {
   return this.endToken;
 }
 ExpressionStatement.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$Visitor()));
+  return this.accept(($0 == null ? null : $0.assert$Visitor()));
 };
 ExpressionStatement.prototype.getBeginToken$0 = ExpressionStatement.prototype.getBeginToken;
 ExpressionStatement.prototype.getEndToken$0 = ExpressionStatement.prototype.getEndToken;
@@ -6401,7 +6792,7 @@ Throw.prototype.getEndToken = function() {
   return this.endToken;
 }
 Throw.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$Visitor()));
+  return this.accept(($0 == null ? null : $0.assert$Visitor()));
 };
 Throw.prototype.getBeginToken$0 = Throw.prototype.getBeginToken;
 Throw.prototype.getEndToken$0 = Throw.prototype.getEndToken;
@@ -6412,21 +6803,20 @@ function TypeAnnotation(typeName) {
   Node.call(this);
 }
 $inherits(TypeAnnotation, Node);
-TypeAnnotation.prototype.is$TypeAnnotation = function(){return this;};
-TypeAnnotation.prototype.get$typeName = function() { return this.typeName; };
+TypeAnnotation.prototype.assert$TypeAnnotation = function(){return this};
 TypeAnnotation.prototype.accept = function(visitor) {
   return visitor.visitTypeAnnotation(this);
 }
 TypeAnnotation.prototype.getBeginToken = function() {
   var $0;
-  return (($0 = this.typeName.getBeginToken()) && $0.is$Token());
+  return (($0 = this.typeName.getBeginToken()) == null ? null : $0.assert$Token());
 }
 TypeAnnotation.prototype.getEndToken = function() {
   var $0;
-  return (($0 = this.typeName.getEndToken()) && $0.is$Token());
+  return (($0 = this.typeName.getEndToken()) == null ? null : $0.assert$Token());
 }
 TypeAnnotation.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$Visitor()));
+  return this.accept(($0 == null ? null : $0.assert$Visitor()));
 };
 TypeAnnotation.prototype.getBeginToken$0 = TypeAnnotation.prototype.getBeginToken;
 TypeAnnotation.prototype.getEndToken$0 = TypeAnnotation.prototype.getEndToken;
@@ -6440,7 +6830,7 @@ function VariableDefinitions(type, modifiers, definitions, endToken) {
   Statement.call(this);
 }
 $inherits(VariableDefinitions, Statement);
-VariableDefinitions.prototype.is$VariableDefinitions = function(){return this;};
+VariableDefinitions.prototype.assert$VariableDefinitions = function(){return this};
 VariableDefinitions.prototype.get$type = function() { return this.type; };
 VariableDefinitions.prototype.get$definitions = function() { return this.definitions; };
 VariableDefinitions.prototype.accept = function(visitor) {
@@ -6453,7 +6843,7 @@ VariableDefinitions.prototype.getEndToken = function() {
   return this.endToken;
 }
 VariableDefinitions.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$Visitor()));
+  return this.accept(($0 == null ? null : $0.assert$Visitor()));
 };
 VariableDefinitions.prototype.getBeginToken$0 = VariableDefinitions.prototype.getBeginToken;
 VariableDefinitions.prototype.getEndToken$0 = VariableDefinitions.prototype.getEndToken;
@@ -6485,7 +6875,7 @@ DoWhile.prototype.getEndToken = function() {
   return this.endToken;
 }
 DoWhile.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$Visitor()));
+  return this.accept(($0 == null ? null : $0.assert$Visitor()));
 };
 DoWhile.prototype.getBeginToken$0 = DoWhile.prototype.getBeginToken;
 DoWhile.prototype.getEndToken$0 = DoWhile.prototype.getEndToken;
@@ -6507,7 +6897,7 @@ While.prototype.getEndToken = function() {
   return this.body.getEndToken();
 }
 While.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$Visitor()));
+  return this.accept(($0 == null ? null : $0.assert$Visitor()));
 };
 While.prototype.getBeginToken$0 = While.prototype.getBeginToken;
 While.prototype.getEndToken$0 = While.prototype.getEndToken;
@@ -6519,7 +6909,7 @@ function ParenthesizedExpression(expression, beginToken) {
   Expression.call(this);
 }
 $inherits(ParenthesizedExpression, Expression);
-ParenthesizedExpression.prototype.is$ParenthesizedExpression = function(){return this;};
+ParenthesizedExpression.prototype.assert$ParenthesizedExpression = function(){return this};
 ParenthesizedExpression.prototype.accept = function(visitor) {
   return visitor.visitParenthesizedExpression(this);
 }
@@ -6530,7 +6920,7 @@ ParenthesizedExpression.prototype.getEndToken = function() {
   return this.beginToken.endGroup;
 }
 ParenthesizedExpression.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$Visitor()));
+  return this.accept(($0 == null ? null : $0.assert$Visitor()));
 };
 ParenthesizedExpression.prototype.getBeginToken$0 = ParenthesizedExpression.prototype.getBeginToken;
 ParenthesizedExpression.prototype.getEndToken$0 = ParenthesizedExpression.prototype.getEndToken;
@@ -6539,7 +6929,7 @@ function Unparser(printDebugInfo) {
   this.printDebugInfo = printDebugInfo;
   // Initializers done
 }
-Unparser.prototype.is$Visitor = function(){return this;};
+Unparser.prototype.assert$Visitor = function(){return this};
 Unparser.prototype.unparse = function(node) {
   this.sb = new StringBufferImpl("");
   this.visit(node);
@@ -6579,7 +6969,7 @@ Unparser.prototype.visitClassNode = function(node) {
 Unparser.prototype.visitExpressionStatement = function(node) {
   var $0;
   this.visit(node.expression);
-  this.add((($0 = node.endToken.get$value()) && $0.is$SourceString()));
+  this.add((($0 = node.endToken.get$value()) == null ? null : $0.assert$SourceString()));
 }
 Unparser.prototype.visitFor = function(node) {
   node.forToken.get$value().printOn$1(this.sb);
@@ -6601,57 +6991,57 @@ Unparser.prototype.visitFunctionExpression = function(node) {
 }
 Unparser.prototype.visitIdentifier = function(node) {
   var $0;
-  this.add((($0 = node.token.get$value()) && $0.is$SourceString()));
+  this.add((($0 = node.token.get$value()) == null ? null : $0.assert$SourceString()));
 }
 Unparser.prototype.visitIf = function(node) {
   var $0;
-  this.add((($0 = node.ifToken.get$value()) && $0.is$SourceString()));
+  this.add((($0 = node.ifToken.get$value()) == null ? null : $0.assert$SourceString()));
   this.visit(node.condition);
   this.visit(node.thenPart);
   if ($notnull_bool(node.get$hasElsePart())) {
-    this.add((($0 = node.elseToken.get$value()) && $0.is$SourceString()));
+    this.add((($0 = node.elseToken.get$value()) == null ? null : $0.assert$SourceString()));
     this.visit(node.elsePart);
   }
 }
 Unparser.prototype.visitLiteralBool = function(node) {
   var $0;
-  this.add((($0 = node.token.get$value()) && $0.is$SourceString()));
+  this.add((($0 = node.token.get$value()) == null ? null : $0.assert$SourceString()));
 }
 Unparser.prototype.visitLiteralDouble = function(node) {
   var $0;
-  this.add((($0 = node.token.get$value()) && $0.is$SourceString()));
+  this.add((($0 = node.token.get$value()) == null ? null : $0.assert$SourceString()));
 }
 Unparser.prototype.visitLiteralInt = function(node) {
   var $0;
-  this.add((($0 = node.token.get$value()) && $0.is$SourceString()));
+  this.add((($0 = node.token.get$value()) == null ? null : $0.assert$SourceString()));
 }
 Unparser.prototype.visitLiteralString = function(node) {
   var $0;
-  this.add((($0 = node.token.get$value()) && $0.is$SourceString()));
+  this.add((($0 = node.token.get$value()) == null ? null : $0.assert$SourceString()));
 }
 Unparser.prototype.visitLiteralNull = function(node) {
   var $0;
-  this.add((($0 = node.token.get$value()) && $0.is$SourceString()));
+  this.add((($0 = node.token.get$value()) == null ? null : $0.assert$SourceString()));
 }
 Unparser.prototype.visitNodeList = function(node) {
   var $0;
-  if (node.beginToken != null) this.add((($0 = node.beginToken.get$value()) && $0.is$SourceString()));
+  if (node.beginToken != null) this.add((($0 = node.beginToken.get$value()) == null ? null : $0.assert$SourceString()));
   if (node.get$nodes() != null) {
     node.get$nodes().printOn(this.sb, node.delimiter);
   }
-  if (node.endToken != null) this.add((($0 = node.endToken.get$value()) && $0.is$SourceString()));
+  if (node.endToken != null) this.add((($0 = node.endToken.get$value()) == null ? null : $0.assert$SourceString()));
 }
 Unparser.prototype.visitOperator = function(node) {
   this.visitIdentifier(node);
 }
 Unparser.prototype.visitReturn = function(node) {
   var $0;
-  this.add((($0 = node.beginToken.get$value()) && $0.is$SourceString()));
+  this.add((($0 = node.beginToken.get$value()) == null ? null : $0.assert$SourceString()));
   if ($notnull_bool(node.get$hasExpression())) {
     this.sb.add(' ');
     this.visit(node.expression);
   }
-  this.add((($0 = node.endToken.get$value()) && $0.is$SourceString()));
+  this.add((($0 = node.endToken.get$value()) == null ? null : $0.assert$SourceString()));
 }
 Unparser.prototype.visitSend = function(node) {
   if ($notnull_bool(node.get$isPrefix())) {
@@ -6673,7 +7063,7 @@ Unparser.prototype.visitSendSet = function(node) {
     this.sb.add('.');
   }
   this.visit(node.selector);
-  this.add((($0 = node.assignmentOperator.token.get$value()) && $0.is$SourceString()));
+  this.add((($0 = node.assignmentOperator.token.get$value()) == null ? null : $0.assert$SourceString()));
   this.visit(node.argumentsNode);
 }
 Unparser.prototype.visitThrow = function(node) {
@@ -6697,23 +7087,23 @@ Unparser.prototype.visitVariableDefinitions = function(node) {
   this.sb.add(' ');
   this.visit(node.definitions);
   if ($notnull_bool($eq(node.endToken.get$value(), const$223/*const SourceString(';')*/))) {
-    this.add((($0 = node.endToken.get$value()) && $0.is$SourceString()));
+    this.add((($0 = node.endToken.get$value()) == null ? null : $0.assert$SourceString()));
   }
 }
 Unparser.prototype.visitDoWhile = function(node) {
   var $0;
-  this.add((($0 = node.doKeyword.get$value()) && $0.is$SourceString()));
+  this.add((($0 = node.doKeyword.get$value()) == null ? null : $0.assert$SourceString()));
   this.sb.add(' ');
   this.visit(node.body);
   this.sb.add(' ');
-  this.add((($0 = node.whileKeyword.get$value()) && $0.is$SourceString()));
+  this.add((($0 = node.whileKeyword.get$value()) == null ? null : $0.assert$SourceString()));
   this.sb.add(' ');
   this.visit(node.condition);
   this.sb.add(node.endToken.get$value());
 }
 Unparser.prototype.visitWhile = function(node) {
   var $0;
-  this.add((($0 = node.whileKeyword.get$value()) && $0.is$SourceString()));
+  this.add((($0 = node.whileKeyword.get$value()) == null ? null : $0.assert$SourceString()));
   this.sb.add(' ');
   this.visit(node.condition);
   this.sb.add(' ');
@@ -6721,21 +7111,21 @@ Unparser.prototype.visitWhile = function(node) {
 }
 Unparser.prototype.visitParenthesizedExpression = function(node) {
   var $0;
-  this.add((($0 = node.getBeginToken().get$value()) && $0.is$SourceString()));
+  this.add((($0 = node.getBeginToken().get$value()) == null ? null : $0.assert$SourceString()));
   this.visit(node.expression);
-  this.add((($0 = node.getEndToken().get$value()) && $0.is$SourceString()));
+  this.add((($0 = node.getEndToken().get$value()) == null ? null : $0.assert$SourceString()));
 }
 Unparser.prototype.add$1 = function($0) {
-  return this.add(($0 && $0.is$SourceString()));
+  return this.add(($0 == null ? null : $0.assert$SourceString()));
 };
 Unparser.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$Node()));
+  return this.visit(($0 == null ? null : $0.assert$Node()));
 };
 // ********** Code for AbstractVisitor **************
 function AbstractVisitor() {
   // Initializers done
 }
-AbstractVisitor.prototype.is$Visitor = function(){return this;};
+AbstractVisitor.prototype.assert$Visitor = function(){return this};
 AbstractVisitor.prototype.visitExpression = function(node) {
   return this.visitNode(node);
 }
@@ -6759,27 +7149,27 @@ function AbstractVisitor_Element() {
   // Initializers done
 }
 $inherits(AbstractVisitor_Element, AbstractVisitor);
-AbstractVisitor_Element.prototype.is$Visitor = function(){return this;};
+AbstractVisitor_Element.prototype.assert$Visitor = function(){return this};
 AbstractVisitor_Element.prototype.visitClassNode = function(node) {
   var $0;
-  return (($0 = this.visitNode(node)) && $0.is$Element());
+  return (($0 = this.visitNode(node)) == null ? null : $0.assert$Element());
 }
 AbstractVisitor_Element.prototype.visitTypeAnnotation = function(node) {
   var $0;
-  return (($0 = this.visitNode(node)) && $0.is$Element());
+  return (($0 = this.visitNode(node)) == null ? null : $0.assert$Element());
 }
 // ********** Code for AbstractVisitor_SourceString **************
 function AbstractVisitor_SourceString() {
   // Initializers done
 }
 $inherits(AbstractVisitor_SourceString, AbstractVisitor);
-AbstractVisitor_SourceString.prototype.is$Visitor = function(){return this;};
+AbstractVisitor_SourceString.prototype.assert$Visitor = function(){return this};
 // ********** Code for AbstractVisitor_Type **************
 function AbstractVisitor_Type() {
   // Initializers done
 }
 $inherits(AbstractVisitor_Type, AbstractVisitor);
-AbstractVisitor_Type.prototype.is$Visitor = function(){return this;};
+AbstractVisitor_Type.prototype.assert$Visitor = function(){return this};
 AbstractVisitor_Type.prototype.visitBlock = function(node) {
   return this.visitStatement(node);
 }
@@ -6788,7 +7178,7 @@ AbstractVisitor_Type.prototype.visitDoWhile = function(node) {
 }
 AbstractVisitor_Type.prototype.visitExpression = function(node) {
   var $0;
-  return (($0 = this.visitNode(node)) && $0.is$Type());
+  return (($0 = this.visitNode(node)) == null ? null : $0.assert$Type());
 }
 AbstractVisitor_Type.prototype.visitExpressionStatement = function(node) {
   return this.visitStatement(node);
@@ -6828,11 +7218,11 @@ AbstractVisitor_Type.prototype.visitLoop = function(node) {
 }
 AbstractVisitor_Type.prototype.visitNodeList = function(node) {
   var $0;
-  return (($0 = this.visitNode(node)) && $0.is$Type());
+  return (($0 = this.visitNode(node)) == null ? null : $0.assert$Type());
 }
 AbstractVisitor_Type.prototype.visitOperator = function(node) {
   var $0;
-  return (($0 = this.visitIdentifier(node)) && $0.is$Type());
+  return (($0 = this.visitIdentifier(node)) == null ? null : $0.assert$Type());
 }
 AbstractVisitor_Type.prototype.visitParenthesizedExpression = function(node) {
   return this.visitExpression(node);
@@ -6848,7 +7238,7 @@ AbstractVisitor_Type.prototype.visitSendSet = function(node) {
 }
 AbstractVisitor_Type.prototype.visitStatement = function(node) {
   var $0;
-  return (($0 = this.visitNode(node)) && $0.is$Type());
+  return (($0 = this.visitNode(node)) == null ? null : $0.assert$Type());
 }
 AbstractVisitor_Type.prototype.visitThrow = function(node) {
   return this.visitStatement(node);
@@ -6862,7 +7252,7 @@ AbstractVisitor_Type.prototype.visitWhile = function(node) {
 // ********** Code for top level **************
 function firstBeginToken(first, second) {
   var $0;
-  return (($0 = (first != null) ? first.getBeginToken() : second.getBeginToken()) && $0.is$Token());
+  return (($0 = (first != null) ? first.getBeginToken() : second.getBeginToken()) == null ? null : $0.assert$Token());
 }
 //  ********** Library elements **************
 // ********** Code for ElementKind **************
@@ -6882,7 +7272,7 @@ function Element(name, kind, enclosingElement) {
   this.enclosingElement = enclosingElement;
   // Initializers done
 }
-Element.prototype.is$Element = function(){return this;};
+Element.prototype.assert$Element = function(){return this};
 Element.prototype.get$name = function() { return this.name; };
 Element.prototype.get$kind = function() { return this.kind; };
 Element.prototype.get$enclosingElement = function() { return this.enclosingElement; };
@@ -6890,7 +7280,7 @@ Element.prototype.hashCode = function() {
   return this.name.hashCode();
 }
 Element.prototype.computeType$2 = function($0, $1) {
-  return this.computeType(($0 && $0.is$Compiler()), ($1 && $1.is$Types()));
+  return this.computeType(($0 == null ? null : $0.assert$Compiler()), ($1 == null ? null : $1.assert$Types()));
 };
 Element.prototype.hashCode$0 = Element.prototype.hashCode;
 // ********** Code for VariableElement **************
@@ -6901,7 +7291,7 @@ function VariableElement(node, typeAnnotation, kind, name, enclosingElement) {
   Element.call(this, name, kind, enclosingElement);
 }
 $inherits(VariableElement, Element);
-VariableElement.prototype.is$VariableElement = function(){return this;};
+VariableElement.prototype.assert$VariableElement = function(){return this};
 VariableElement.prototype.get$type = function() { return this.type; };
 VariableElement.prototype.set$type = function(value) { return this.type = value; };
 VariableElement.prototype.parseNode = function(canceler, logger) {
@@ -6913,7 +7303,7 @@ VariableElement.prototype.computeType = function(compiler, types) {
   return this.type;
 }
 VariableElement.prototype.computeType$2 = function($0, $1) {
-  return this.computeType(($0 && $0.is$Compiler()), ($1 && $1.is$Types()));
+  return this.computeType(($0 == null ? null : $0.assert$Compiler()), ($1 == null ? null : $1.assert$Types()));
 };
 // ********** Code for ForeignElement **************
 function ForeignElement(name) {
@@ -6925,7 +7315,7 @@ ForeignElement.prototype.computeType = function(compiler, types) {
   return types.dynamicType;
 }
 ForeignElement.prototype.computeType$2 = function($0, $1) {
-  return this.computeType(($0 && $0.is$Compiler()), ($1 && $1.is$Types()));
+  return this.computeType(($0 == null ? null : $0.assert$Compiler()), ($1 == null ? null : $1.assert$Types()));
 };
 // ********** Code for FunctionElement **************
 function FunctionElement(name) {
@@ -6939,31 +7329,31 @@ FunctionElement.node$ctor = function(node, enclosing) {
 }
 FunctionElement.node$ctor.prototype = FunctionElement.prototype;
 $inherits(FunctionElement, Element);
-FunctionElement.prototype.is$FunctionElement = function(){return this;};
+FunctionElement.prototype.assert$FunctionElement = function(){return this};
 FunctionElement.prototype.get$parameters = function() { return this.parameters; };
 FunctionElement.prototype.set$parameters = function(value) { return this.parameters = value; };
 FunctionElement.prototype.get$type = function() { return this.type; };
 FunctionElement.prototype.set$type = function(value) { return this.type = value; };
 FunctionElement.prototype.computeType = function(compiler, types) {
   var $0;
-  if (this.type != null) return (($0 = this.type) && $0.is$FunctionType());
+  if (this.type != null) return (($0 = this.type) == null ? null : $0.assert$FunctionType());
   if (this.parameters == null) compiler.resolveSignature(this);
-  var node = (($0 = this.parseNode(compiler, compiler)) && $0.is$FunctionExpression());
+  var node = (($0 = this.parseNode(compiler, compiler)) == null ? null : $0.assert$FunctionExpression());
   var returnType = getType(node.returnType, types);
   if (returnType == null) compiler.cancel(('unknown type ' + node.returnType));
   var parameterTypes = new LinkBuilderImplementation();
   for (var link = this.parameters;
-   !$notnull_bool(link.isEmpty()); link = (($0 = link.get$tail()) && $0.is$Link_Element())) {
+   !$notnull_bool(link.isEmpty()); link = (($0 = link.get$tail()) == null ? null : $0.assert$Link_Element())) {
     parameterTypes.addLast(link.get$head().computeType$2(compiler, types));
   }
-  this.type = new FunctionType(returnType, (($0 = parameterTypes.toLink()) && $0.is$Link_Type()));
-  return (($0 = this.type) && $0.is$FunctionType());
+  this.type = new FunctionType(returnType, (($0 = parameterTypes.toLink()) == null ? null : $0.assert$Link_Type()));
+  return (($0 = this.type) == null ? null : $0.assert$FunctionType());
 }
 FunctionElement.prototype.parseNode = function(canceler, logger) {
   return this.node;
 }
 FunctionElement.prototype.computeType$2 = function($0, $1) {
-  return this.computeType(($0 && $0.is$Compiler()), $1);
+  return this.computeType(($0 == null ? null : $0.assert$Compiler()), $1);
 };
 // ********** Code for ClassElement **************
 function ClassElement(name) {
@@ -6973,7 +7363,7 @@ function ClassElement(name) {
   Element.call(this, name, const$214, null);
 }
 $inherits(ClassElement, Element);
-ClassElement.prototype.is$ClassElement = function(){return this;};
+ClassElement.prototype.assert$ClassElement = function(){return this};
 ClassElement.prototype.get$type = function() { return this.type; };
 ClassElement.prototype.set$type = function(value) { return this.type = value; };
 ClassElement.prototype.get$interfaces = function() { return this.interfaces; };
@@ -6991,15 +7381,15 @@ ClassElement.prototype.resolve = function(compiler) {
 }
 ClassElement.prototype.computeType$2 = ClassElement.prototype.computeType;
 ClassElement.prototype.resolve$1 = function($0) {
-  return this.resolve(($0 && $0.is$Compiler()));
+  return this.resolve(($0 == null ? null : $0.assert$Compiler()));
 };
 // ********** Code for top level **************
 function getType(annotation, types) {
   var $0;
   if (annotation == null || annotation.typeName == null) {
-    return (($0 = types.get$dynamicType()) && $0.is$Type());
+    return (($0 = types.get$dynamicType()) == null ? null : $0.assert$Type());
   }
-  return (($0 = types.lookup$1(annotation.typeName.get$source())) && $0.is$Type());
+  return (($0 = types.lookup$1(annotation.typeName.get$source())) == null ? null : $0.assert$Type());
 }
 //  ********** Library ssa **************
 // ********** Code for SsaBuilderTask **************
@@ -7016,18 +7406,18 @@ SsaBuilderTask.prototype.build = function(tree, elements) {
   var $0;
   return (($0 = this.measure((function () {
     var $0;
-    var function_ = (tree && tree.is$FunctionExpression());
+    var function_ = (tree == null ? null : tree.assert$FunctionExpression());
     $globals.HInstruction_idCounter = 0;
     var graph = $this.compileMethod(function_.parameters, function_.body, elements);
     $assert(graph.isValid(), "graph.isValid()", "builder.dart", 15, 14);
     if (false/*null.GENERATE_SSA_TRACE*/) {
-      var name = (($0 = function_.name) && $0.is$Identifier());
+      var name = (($0 = function_.name) == null ? null : $0.assert$Identifier());
       HTracer.HTracer$singleton$factory().traceCompilation(name.get$source().toString());
       HTracer.HTracer$singleton$factory().traceGraph('builder', graph);
     }
     return graph;
   })
-  )) && $0.is$HGraph());
+  )) == null ? null : $0.assert$HGraph());
 }
 SsaBuilderTask.prototype.compileMethod = function(parameters, body, elements) {
   var builder = new SsaBuilder(this.compiler, elements);
@@ -7040,7 +7430,7 @@ function SsaBuilder(compiler, elements) {
   this.elements = elements;
   // Initializers done
 }
-SsaBuilder.prototype.is$Visitor = function(){return this;};
+SsaBuilder.prototype.assert$Visitor = function(){return this};
 SsaBuilder.prototype.get$definitions = function() { return this.definitions; };
 SsaBuilder.prototype.set$definitions = function(value) { return this.definitions = value; };
 SsaBuilder.prototype.build = function(parameters, body) {
@@ -7083,7 +7473,7 @@ SsaBuilder.prototype.push = function(instruction) {
 }
 SsaBuilder.prototype.pop = function() {
   var $0;
-  return (($0 = this.stack.removeLast()) && $0.is$HInstruction());
+  return (($0 = this.stack.removeLast()) == null ? null : $0.assert$HInstruction());
 }
 SsaBuilder.prototype.popBoolified = function() {
   var boolified = new HBoolify(this.pop());
@@ -7110,15 +7500,15 @@ SsaBuilder.prototype.visitParameterValues = function(parameters) {
   var $0;
   var parameterIndex = 0;
   for (var link = parameters.get$nodes();
-   !$notnull_bool(link.isEmpty()); link = (($0 = link.get$tail()) && $0.is$Link_Node())) {
-    var container = (($0 = link.get$head()) && $0.is$VariableDefinitions());
+   !$notnull_bool(link.isEmpty()); link = (($0 = link.get$tail()) == null ? null : $0.assert$Link_Node())) {
+    var container = (($0 = link.get$head()) == null ? null : $0.assert$VariableDefinitions());
     var identifierLink = container.definitions.get$nodes();
     $assert(!$notnull_bool(identifierLink.isEmpty()) && $notnull_bool(identifierLink.get$tail().isEmpty$0()), "!identifierLink.isEmpty() && identifierLink.tail.isEmpty()", "builder.dart", 135, 14);
     if (!(identifierLink.get$head() instanceof Identifier)) {
       this.compiler.unimplemented("SsaBuilder.visitParameterValues non-identifier");
     }
-    var parameterId = (($0 = identifierLink.get$head()) && $0.is$Identifier());
-    var element = (($0 = this.elements.$index(parameterId)) && $0.is$VariableElement());
+    var parameterId = (($0 = identifierLink.get$head()) == null ? null : $0.assert$Identifier());
+    var element = (($0 = this.elements.$index(parameterId)) == null ? null : $0.assert$VariableElement());
     var parameter = new HParameterValue(element);
     this.add(parameter);
     this.definitions.$setindex(element, this.guard(element.type, parameter));
@@ -7127,8 +7517,8 @@ SsaBuilder.prototype.visitParameterValues = function(parameters) {
 SsaBuilder.prototype.visitBlock = function(node) {
   var $0;
   for (var link = node.statements.get$nodes();
-   !$notnull_bool(link.isEmpty()); link = (($0 = link.get$tail()) && $0.is$Link_Node())) {
-    this.visit((($0 = link.get$head()) && $0.is$Node()));
+   !$notnull_bool(link.isEmpty()); link = (($0 = link.get$tail()) == null ? null : $0.assert$Link_Node())) {
+    this.visit((($0 = link.get$head()) == null ? null : $0.assert$Node()));
     if ($notnull_bool(this.isAborted())) {
       if (!this.stack.isEmpty()) this.compiler.cancel('non-empty instruction stack');
       return;
@@ -7165,7 +7555,7 @@ SsaBuilder.prototype.endLoop = function(loopEntry, branchBlock, doUpdateDefiniti
   loopEntry.forEachPhi((function (phi) {
     var $0;
     var element = phi.element;
-    var postLoopDefinition = (($0 = $this.definitions.$index(element)) && $0.is$HInstruction());
+    var postLoopDefinition = (($0 = $this.definitions.$index(element)) == null ? null : $0.assert$HInstruction());
     phi.addInput(postLoopDefinition);
     if ($notnull_bool(doUpdateDefinitions) && phi.inputs.$index(0) !== postLoopDefinition && exitDefinitions.containsKey(element)) {
       exitDefinitions.$setindex(element, postLoopDefinition);
@@ -7211,7 +7601,7 @@ SsaBuilder.prototype.visitLoop = function(initializer, condition, update, body)
 SsaBuilder.prototype.visitFor = function(node) {
   var $0;
   $assert(node.initializer != null && node.get$condition() != null && node.update != null && node.body != null, "node.initializer !== null && node.condition !== null &&\n           node.update !== null && node.body !== null", "builder.dart", 275, 12);
-  this.visitLoop(node.initializer, node.get$condition(), (($0 = node.update) && $0.is$Expression()), node.body);
+  this.visitLoop(node.initializer, node.get$condition(), (($0 = node.update) == null ? null : $0.assert$Expression()), node.body);
 }
 SsaBuilder.prototype.visitWhile = function(node) {
   this.visitLoop(null, node.condition, null, node.body);
@@ -7239,9 +7629,9 @@ SsaBuilder.prototype.visitFunctionExpression = function(node) {
 }
 SsaBuilder.prototype.visitIdentifier = function(node) {
   var $0;
-  var element = (($0 = this.elements.$index(node)) && $0.is$Element());
+  var element = (($0 = this.elements.$index(node)) == null ? null : $0.assert$Element());
   this.compiler.ensure(element != null);
-  var def = (($0 = this.definitions.$index(element)) && $0.is$HInstruction());
+  var def = (($0 = this.definitions.$index(element)) == null ? null : $0.assert$HInstruction());
   $assert(def != null, "def !== null", "builder.dart", 317, 12);
   this.stack.add(def);
 }
@@ -7249,14 +7639,14 @@ SsaBuilder.prototype.joinDefinitions = function(joinBlock, incoming1, incoming2)
   var joinedDefinitions = new HashMapImplementation();
   incoming1.forEach((function (element, instruction) {
     var $0;
-    var other = (($0 = incoming2.$index(element)) && $0.is$HInstruction());
+    var other = (($0 = incoming2.$index(element)) == null ? null : $0.assert$HInstruction());
     if (other == null) return;
     if (instruction === other) {
       joinedDefinitions.$setindex(element, instruction);
     }
     else {
       var phi = new HPhi.manyInputs$ctor(element, [instruction, other]);
-      joinBlock.addPhi((phi && phi.is$HPhi()));
+      joinBlock.addPhi((phi == null ? null : phi.assert$HPhi()));
       joinedDefinitions.$setindex(element, phi);
     }
   })
@@ -7464,9 +7854,9 @@ SsaBuilder.prototype.visitBinary = function(left, op, right, element) {
 }
 SsaBuilder.prototype.visitSend = function(node) {
   var $0;
-  var element = (($0 = this.elements.$index(node)) && $0.is$Element());
+  var element = (($0 = this.elements.$index(node)) == null ? null : $0.assert$Element());
   if ((node.selector instanceof Operator)) {
-    var op = (($0 = node.selector) && $0.is$Operator());
+    var op = (($0 = node.selector) == null ? null : $0.assert$Operator());
     if ($notnull_bool($eq(const$278/*const SourceString("&&")*/, op.get$source())) || $notnull_bool($eq(const$279/*const SourceString("||")*/, op.get$source()))) {
       this.visitLogicalAndOr(node, op);
     }
@@ -7481,29 +7871,29 @@ SsaBuilder.prototype.visitSend = function(node) {
       this.visit(node.argumentsNode);
       var right = this.pop();
       var left = this.pop();
-      this.visitBinary((left && left.is$HInstruction()), op, (right && right.is$HInstruction()), element);
+      this.visitBinary((left == null ? null : left.assert$HInstruction()), op, (right == null ? null : right.assert$HInstruction()), element);
     }
   }
   else if ($notnull_bool(node.get$isPropertyAccess())) {
     if (node.receiver != null) {
       this.compiler.unimplemented("SsaBuilder.visitSend with receiver");
     }
-    var instruction = (($0 = this.definitions.$index(element)) && $0.is$HInstruction());
+    var instruction = (($0 = this.definitions.$index(element)) == null ? null : $0.assert$HInstruction());
     $assert(instruction != null, "instruction !== null", "builder.dart", 528, 14);
     this.stack.add(instruction);
   }
   else {
     var link = node.get$arguments();
     if (element.kind === const$219/*ElementKind.FOREIGN*/) {
-      link = (($0 = link.get$tail()) && $0.is$Link_Node());
+      link = (($0 = link.get$tail()) == null ? null : $0.assert$Link_Node());
     }
     var arguments = [];
-    for (; !$notnull_bool(link.isEmpty()); link = (($0 = link.get$tail()) && $0.is$Link_Node())) {
-      this.visit((($0 = link.get$head()) && $0.is$Node()));
+    for (; !$notnull_bool(link.isEmpty()); link = (($0 = link.get$tail()) == null ? null : $0.assert$Link_Node())) {
+      this.visit((($0 = link.get$head()) == null ? null : $0.assert$Node()));
       arguments.add$1(this.pop());
     }
     if (element.kind === const$219/*ElementKind.FOREIGN*/) {
-      var literal = (($0 = node.get$arguments().get$head()) && $0.is$LiteralString());
+      var literal = (($0 = node.get$arguments().get$head()) == null ? null : $0.assert$LiteralString());
       this.compiler.ensure((literal instanceof LiteralString));
       this.push(new HForeign(arguments, this.unquote(literal)));
     }
@@ -7514,7 +7904,7 @@ SsaBuilder.prototype.visitSend = function(node) {
 }
 SsaBuilder.prototype.updateDefinition = function(node, value) {
   var $0;
-  var element = (($0 = this.elements.$index(node)) && $0.is$VariableElement());
+  var element = (($0 = this.elements.$index(node)) == null ? null : $0.assert$VariableElement());
   value = this.guard(element.type, value);
   this.definitions.$setindex(element, value);
   return value;
@@ -7528,15 +7918,15 @@ SsaBuilder.prototype.visitSendSet = function(node) {
   if ($notnull_bool($eq(const$281/*const SourceString("=")*/, op.get$source()))) {
     var link = node.get$arguments();
     $assert(!$notnull_bool(link.isEmpty()) && $notnull_bool(link.get$tail().isEmpty$0()), "!link.isEmpty() && link.tail.isEmpty()", "builder.dart", 567, 14);
-    this.visit((($0 = link.get$head()) && $0.is$Node()));
+    this.visit((($0 = link.get$head()) == null ? null : $0.assert$Node()));
     this.stack.add(this.updateDefinition(node, this.pop()));
   }
   else {
     $assert($notnull_bool($eq(const$284/*const SourceString("++")*/, op.get$source())) || $notnull_bool($eq(const$285/*const SourceString("--")*/, op.get$source())) || node.assignmentOperator.get$source().get$stringValue().endsWith("="), "const SourceString(\"++\") == op.source ||\n             const SourceString(\"--\") == op.source ||\n             node.assignmentOperator.source.stringValue.endsWith(\"=\")", "builder.dart", 571, 14);
     var isCompoundAssignment = !$notnull_bool(node.get$arguments().isEmpty());
     var isPrefix = !$notnull_bool(node.get$isPostfix());
-    var getter = (($0 = this.elements.$index(node.selector)) && $0.is$Element());
-    var left = (($0 = this.definitions.$index(getter)) && $0.is$HInstruction());
+    var getter = (($0 = this.elements.$index(node.selector)) == null ? null : $0.assert$Element());
+    var left = (($0 = this.definitions.$index(getter)) == null ? null : $0.assert$HInstruction());
     var right;
     if ($notnull_bool(isCompoundAssignment)) {
       this.visit(node.argumentsNode);
@@ -7546,7 +7936,7 @@ SsaBuilder.prototype.visitSendSet = function(node) {
       right = new HLiteral(1);
       this.add(right);
     }
-    var opElement = (($0 = this.elements.$index(op)) && $0.is$Element());
+    var opElement = (($0 = this.elements.$index(op)) == null ? null : $0.assert$Element());
     this.visitBinary(left, op, right, opElement);
     var operation = this.pop();
     $assert(operation != null, "operation !== null", "builder.dart", 589, 14);
@@ -7577,8 +7967,8 @@ SsaBuilder.prototype.visitLiteralNull = function(node) {
 SsaBuilder.prototype.visitNodeList = function(node) {
   var $0;
   for (var link = node.get$nodes();
-   !$notnull_bool(link.isEmpty()); link = (($0 = link.get$tail()) && $0.is$Link_Node())) {
-    this.visit((($0 = link.get$head()) && $0.is$Node()));
+   !$notnull_bool(link.isEmpty()); link = (($0 = link.get$tail()) == null ? null : $0.assert$Link_Node())) {
+    this.visit((($0 = link.get$head()) == null ? null : $0.assert$Node()));
   }
 }
 SsaBuilder.prototype.visitParenthesizedExpression = function(node) {
@@ -7612,8 +8002,8 @@ SsaBuilder.prototype.visitTypeAnnotation = function(node) {
 SsaBuilder.prototype.visitVariableDefinitions = function(node) {
   var $0;
   for (var link = node.definitions.get$nodes();
-   !$notnull_bool(link.isEmpty()); link = (($0 = link.get$tail()) && $0.is$Link_Node())) {
-    var definition = (($0 = link.get$head()) && $0.is$Node());
+   !$notnull_bool(link.isEmpty()); link = (($0 = link.get$tail()) == null ? null : $0.assert$Link_Node())) {
+    var definition = (($0 = link.get$head()) == null ? null : $0.assert$Node());
     if ((definition instanceof Identifier)) {
       var initialValue = new HLiteral(null);
       this.add(initialValue);
@@ -7621,16 +8011,16 @@ SsaBuilder.prototype.visitVariableDefinitions = function(node) {
     }
     else {
       $assert((definition instanceof SendSet), "definition is SendSet", "builder.dart", 669, 16);
-      this.visitSendSet((definition && definition.is$SendSet()));
+      this.visitSendSet((definition == null ? null : definition.assert$SendSet()));
       this.pop();
     }
   }
 }
 SsaBuilder.prototype.add$1 = function($0) {
-  return this.add(($0 && $0.is$HInstruction()));
+  return this.add(($0 == null ? null : $0.assert$HInstruction()));
 };
 SsaBuilder.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$Node()));
+  return this.visit(($0 == null ? null : $0.assert$Node()));
 };
 // ********** Code for SsaCodeGeneratorTask **************
 function SsaCodeGeneratorTask(compiler) {
@@ -7647,8 +8037,8 @@ SsaCodeGeneratorTask.prototype.generate = function(function_, graph) {
     var $0;
     var parameterNames = new LinkedHashMapImplementation();
     for (var link = function_.parameters;
-     !$notnull_bool(link.isEmpty()); link = (($0 = link.get$tail()) && $0.is$Link_Element())) {
-      var element = (($0 = link.get$head()) && $0.is$Element());
+     !$notnull_bool(link.isEmpty()); link = (($0 = link.get$tail()) == null ? null : $0.assert$Link_Element())) {
+      var element = (($0 = link.get$head()) == null ? null : $0.assert$Element());
       parameterNames.$setindex(element, JsNames.getValid(('' + element.name)));
     }
     var code = $this.generateMethod(function_.name, parameterNames, graph);
@@ -7673,7 +8063,7 @@ SsaCodeGeneratorTask.prototype.generateMethod = function(methodName, parameterNa
   var codegen = new SsaCodeGenerator(this.compiler, buffer, parameterNames);
   codegen.visitGraph(graph);
   var parameters = new StringBufferImpl("");
-  var names = (($0 = parameterNames.getValues()) && $0.is$List_String());
+  var names = (($0 = parameterNames.getValues()) == null ? null : $0.assert$List_String());
   for (var i = 0;
    i < $assert_num(names.length); i++) {
     if (i != 0) parameters.add(', ');
@@ -7696,7 +8086,7 @@ function SsaCodeGenerator(compiler, buffer, parameterNames) {
     this.prefixes.$setindex(name, 0);
   }
 }
-SsaCodeGenerator.prototype.is$HVisitor = function(){return this;};
+SsaCodeGenerator.prototype.assert$HVisitor = function(){return this};
 SsaCodeGenerator.prototype.get$names = function() { return this.names; };
 SsaCodeGenerator.prototype.visitGraph = function(graph) {
   this.currentGraph = graph;
@@ -7753,7 +8143,7 @@ SsaCodeGenerator.prototype.invoke = function(element, arguments) {
   for (var i = 0;
    i < arguments.length; i++) {
     if (i != 0) this.buffer.add(', ');
-    this.use((($0 = arguments.$index(i)) && $0.is$HInstruction()));
+    this.use((($0 = arguments.$index(i)) == null ? null : $0.assert$HInstruction()));
   }
   this.buffer.add(")");
 }
@@ -7803,9 +8193,9 @@ SsaCodeGenerator.prototype.visitInvokeBinary = function(node, useOperator, op) {
   var $0;
   if ($notnull_bool(useOperator)) {
     this.buffer.add('(');
-    this.use((($0 = node.inputs.$index(0)) && $0.is$HInstruction()));
+    this.use((($0 = node.inputs.$index(0)) == null ? null : $0.assert$HInstruction()));
     this.buffer.add((' ' + op + ' '));
-    this.use((($0 = node.inputs.$index(1)) && $0.is$HInstruction()));
+    this.use((($0 = node.inputs.$index(1)) == null ? null : $0.assert$HInstruction()));
     this.buffer.add(')');
   }
   else {
@@ -7816,7 +8206,7 @@ SsaCodeGenerator.prototype.visitInvokeUnary = function(node, useOperator, op) {
   var $0;
   if ($notnull_bool(useOperator)) {
     this.buffer.add(('(' + op));
-    this.use((($0 = node.inputs.$index(0)) && $0.is$HInstruction()));
+    this.use((($0 = node.inputs.$index(0)) == null ? null : $0.assert$HInstruction()));
     this.buffer.add(')');
   }
   else {
@@ -7881,7 +8271,7 @@ SsaCodeGenerator.prototype.visitBoolify = function(node) {
   var $0;
   $assert(node.inputs.length == 1, "node.inputs.length == 1", "codegen.dart", 248, 12);
   this.buffer.add('(');
-  this.use((($0 = node.inputs.$index(0)) && $0.is$HInstruction()));
+  this.use((($0 = node.inputs.$index(0)) == null ? null : $0.assert$HInstruction()));
   this.buffer.add(' === true)');
 }
 SsaCodeGenerator.prototype.visitExit = function(node) {
@@ -7897,18 +8287,18 @@ SsaCodeGenerator.prototype.visitGoto = function(node) {
     unreachable();
   }
   $assert($eq(dominated.$index(0), this.currentBlock.successors.$index(0)), "dominated[0] == currentBlock.successors[0]", "codegen.dart", 271, 12);
-  this.visitBasicBlock((($0 = dominated.$index(0)) && $0.is$HBasicBlock()));
+  this.visitBasicBlock((($0 = dominated.$index(0)) == null ? null : $0.assert$HBasicBlock()));
 }
 SsaCodeGenerator.prototype.visitIf = function(node) {
   var $0;
   var ifBlock = this.currentBlock;
   this.buffer.add('if (');
-  this.use((($0 = node.inputs.$index(0)) && $0.is$HInstruction()));
+  this.use((($0 = node.inputs.$index(0)) == null ? null : $0.assert$HInstruction()));
   this.buffer.add(') {\n');
   this.indent++;
   var dominated = this.currentBlock.dominatedBlocks;
   $assert(dominated.$index(0) === ifBlock.successors.$index(0), "dominated[0] === ifBlock.successors[0]", "codegen.dart", 284, 12);
-  this.visitBasicBlock((($0 = ifBlock.successors.$index(0)) && $0.is$HBasicBlock()));
+  this.visitBasicBlock((($0 = ifBlock.successors.$index(0)) == null ? null : $0.assert$HBasicBlock()));
   this.indent--;
   this.addIndentation();
   var nextDominatedIndex;
@@ -7916,7 +8306,7 @@ SsaCodeGenerator.prototype.visitIf = function(node) {
     $assert(dominated.$index(1) === ifBlock.successors.$index(1), "dominated[1] === ifBlock.successors[1]", "codegen.dart", 290, 14);
     this.buffer.add('} else {\n');
     this.indent++;
-    this.visitBasicBlock((($0 = ifBlock.successors.$index(1)) && $0.is$HBasicBlock()));
+    this.visitBasicBlock((($0 = ifBlock.successors.$index(1)) == null ? null : $0.assert$HBasicBlock()));
     this.indent--;
     this.addIndentation();
     this.buffer.add("}\n");
@@ -7925,7 +8315,7 @@ SsaCodeGenerator.prototype.visitIf = function(node) {
     this.buffer.add("}\n");
   }
   if ($notnull_bool(node.hasElse) && dominated.length == 3) {
-    this.visitBasicBlock((($0 = dominated.$index(2)) && $0.is$HBasicBlock()));
+    this.visitBasicBlock((($0 = dominated.$index(2)) == null ? null : $0.assert$HBasicBlock()));
   }
   else if ($notnull_bool(node.hasElse)) {
     $assert(dominated.length == 2, "dominated.length == 2", "codegen.dart", 318, 14);
@@ -7933,14 +8323,14 @@ SsaCodeGenerator.prototype.visitIf = function(node) {
   }
   else if (!$notnull_bool(node.hasElse) && dominated.length == 2) {
     $assert(!$notnull_bool(dominated.$index(1).isExitBlock$0()), "!dominated[1].isExitBlock()", "codegen.dart", 323, 14);
-    this.visitBasicBlock((($0 = dominated.$index(1)) && $0.is$HBasicBlock()));
+    this.visitBasicBlock((($0 = dominated.$index(1)) == null ? null : $0.assert$HBasicBlock()));
   }
   else {
     $assert(!$notnull_bool(node.hasElse), "!node.hasElse", "codegen.dart", 328, 14);
     $assert(dominated.length == 3, "dominated.length == 3", "codegen.dart", 329, 14);
     $assert(dominated.$index(2).isExitBlock$0(), "dominated[2].isExitBlock()", "codegen.dart", 330, 14);
-    this.visitBasicBlock((($0 = dominated.$index(1)) && $0.is$HBasicBlock()));
-    this.visitBasicBlock((($0 = dominated.$index(2)) && $0.is$HBasicBlock()));
+    this.visitBasicBlock((($0 = dominated.$index(1)) == null ? null : $0.assert$HBasicBlock()));
+    this.visitBasicBlock((($0 = dominated.$index(2)) == null ? null : $0.assert$HBasicBlock()));
   }
 }
 SsaCodeGenerator.prototype.visitInvoke = function(node) {
@@ -7953,10 +8343,10 @@ SsaCodeGenerator.prototype.visitForeign = function(node) {
   var inputs = node.inputs;
   for (var i = 0;
    i < inputs.length; i++) {
-    var input = (($0 = inputs.$index(i)) && $0.is$HInstruction());
+    var input = (($0 = inputs.$index(i)) == null ? null : $0.assert$HInstruction());
     var name = null;
     if ((input instanceof HParameterValue)) {
-      name = this.parameter((input && input.is$HParameterValue()));
+      name = this.parameter((input == null ? null : input.assert$HParameterValue()));
     }
     else {
       $assert(!$notnull_bool(input.generateAtUseSite()), "!input.generateAtUseSite()", "codegen.dart", 350, 16);
@@ -7981,7 +8371,7 @@ SsaCodeGenerator.prototype.visitLoopBranch = function(node) {
   var $0;
   var branchBlock = this.currentBlock;
   this.buffer.add('if (!(');
-  this.use((($0 = node.inputs.$index(0)) && $0.is$HInstruction()));
+  this.use((($0 = node.inputs.$index(0)) == null ? null : $0.assert$HInstruction()));
   this.buffer.add(')) break;\n');
   var dominated = this.currentBlock.dominatedBlocks;
   var loopSuccessor;
@@ -8004,7 +8394,7 @@ SsaCodeGenerator.prototype.visitNot = function(node) {
   var $0;
   $assert(node.inputs.length == 1, "node.inputs.length == 1", "codegen.dart", 395, 12);
   this.buffer.add('(!');
-  this.use((($0 = node.inputs.$index(0)) && $0.is$HInstruction()));
+  this.use((($0 = node.inputs.$index(0)) == null ? null : $0.assert$HInstruction()));
   this.buffer.add(')');
 }
 SsaCodeGenerator.prototype.visitParameterValue = function(node) {
@@ -8016,20 +8406,20 @@ SsaCodeGenerator.prototype.visitPhi = function(node) {
 SsaCodeGenerator.prototype.visitReturn = function(node) {
   var $0;
   $assert(node.inputs.length == 1, "node.inputs.length == 1", "codegen.dart", 411, 12);
-  var input = (($0 = node.inputs.$index(0)) && $0.is$HInstruction());
+  var input = (($0 = node.inputs.$index(0)) == null ? null : $0.assert$HInstruction());
   if ($notnull_bool(input.isLiteralNull())) {
     this.buffer.add('return;\n');
   }
   else {
     this.buffer.add('return ');
-    this.use((($0 = node.inputs.$index(0)) && $0.is$HInstruction()));
+    this.use((($0 = node.inputs.$index(0)) == null ? null : $0.assert$HInstruction()));
     this.buffer.add(';\n');
   }
 }
 SsaCodeGenerator.prototype.visitThrow = function(node) {
   var $0;
   this.buffer.add('throw ');
-  this.use((($0 = node.inputs.$index(0)) && $0.is$HInstruction()));
+  this.use((($0 = node.inputs.$index(0)) == null ? null : $0.assert$HInstruction()));
   this.buffer.add(';\n');
 }
 SsaCodeGenerator.prototype.visitTypeGuard = function(node) {
@@ -8047,7 +8437,7 @@ SsaCodeGenerator.prototype.visitTypeGuard = function(node) {
   var element = this.compiler.universe.find(name);
   this.compiler.worklist.add(element);
   this.buffer.add(('' + name + '('));
-  this.use((($0 = node.inputs.$index(0)) && $0.is$HInstruction()));
+  this.use((($0 = node.inputs.$index(0)) == null ? null : $0.assert$HInstruction()));
   this.buffer.add(')');
 }
 SsaCodeGenerator.prototype.addIndentation = function() {
@@ -8103,7 +8493,7 @@ HGraphVisitor.prototype.visitDominatorTree = function(graph) {
     var dominated = block.dominatedBlocks;
     for (var i = 0;
      i < dominated.length; i++) {
-      visitBasicBlockAndSuccessors((($0 = dominated.$index(i)) && $0.is$HBasicBlock()));
+      visitBasicBlockAndSuccessors((($0 = dominated.$index(i)) == null ? null : $0.assert$HBasicBlock()));
     }
   }
   visitBasicBlockAndSuccessors(graph.entry);
@@ -8115,7 +8505,7 @@ HGraphVisitor.prototype.visitPostDominatorTree = function(graph) {
     var dominated = block.dominatedBlocks;
     for (var i = dominated.length - 1;
      i >= 0; i--) {
-      visitBasicBlockAndSuccessors((($0 = dominated.$index(i)) && $0.is$HBasicBlock()));
+      visitBasicBlockAndSuccessors((($0 = dominated.$index(i)) == null ? null : $0.assert$HBasicBlock()));
     }
     $this.visitBasicBlock(block);
   }
@@ -8147,7 +8537,7 @@ function HGraph() {
   this.entry = this.addNewBlock();
   this.exit = new HBasicBlock();
 }
-HGraph.prototype.is$HGraph = function(){return this;};
+HGraph.prototype.assert$HGraph = function(){return this};
 HGraph.prototype.addBlock = function(block) {
   var id = this.blocks.length;
   block.id = id;
@@ -8174,16 +8564,16 @@ HGraph.prototype.assignDominators = function() {
   var $0;
   for (var i = 0, length = this.blocks.length;
    i < length; i++) {
-    var block = (($0 = this.blocks.$index(i)) && $0.is$HBasicBlock());
+    var block = (($0 = this.blocks.$index(i)) == null ? null : $0.assert$HBasicBlock());
     var predecessors = block.predecessors;
     if ($notnull_bool(block.isLoopHeader())) {
       $assert(predecessors.length >= 2, "predecessors.length >= 2", "nodes.dart", 139, 16);
-      block.assignCommonDominator((($0 = predecessors.$index(0)) && $0.is$HBasicBlock()));
+      block.assignCommonDominator((($0 = predecessors.$index(0)) == null ? null : $0.assert$HBasicBlock()));
     }
     else {
       for (var j = predecessors.length - 1;
        j >= 0; j--) {
-        block.assignCommonDominator((($0 = predecessors.$index(j)) && $0.is$HBasicBlock()));
+        block.assignCommonDominator((($0 = predecessors.$index(j)) == null ? null : $0.assert$HBasicBlock()));
       }
     }
   }
@@ -8199,7 +8589,7 @@ function HBaseVisitor() {
   HGraphVisitor.call(this);
 }
 $inherits(HBaseVisitor, HGraphVisitor);
-HBaseVisitor.prototype.is$HVisitor = function(){return this;};
+HBaseVisitor.prototype.assert$HVisitor = function(){return this};
 HBaseVisitor.prototype.visitBasicBlock = function(node) {
   this.currentBlock = node;
   var instruction = node.first;
@@ -8413,7 +8803,7 @@ HInstructionList.prototype.contains = function(instruction) {
   return false;
 }
 HInstructionList.prototype.contains$1 = function($0) {
-  return this.contains(($0 && $0.is$HInstruction()));
+  return this.contains(($0 == null ? null : $0.assert$HInstruction()));
 };
 HInstructionList.prototype.isEmpty$0 = HInstructionList.prototype.isEmpty;
 HInstructionList.prototype.last$0 = function() {
@@ -8443,7 +8833,7 @@ HBasicBlock.withId$ctor = function(id) {
 }
 HBasicBlock.withId$ctor.prototype = HBasicBlock.prototype;
 $inherits(HBasicBlock, HInstructionList);
-HBasicBlock.prototype.is$HBasicBlock = function(){return this;};
+HBasicBlock.prototype.assert$HBasicBlock = function(){return this};
 HBasicBlock.prototype.get$id = function() { return this.id; };
 HBasicBlock.prototype.set$id = function(value) { return this.id = value; };
 HBasicBlock.prototype.get$phis = function() { return this.phis; };
@@ -8546,7 +8936,7 @@ HBasicBlock.prototype.postProcessLoopHeader = function() {
   $assert(this.isLoopHeader(), "isLoopHeader()", "nodes.dart", 425, 12);
   for (var i = 1, length = this.predecessors.length;
    i < length; i++) {
-    this.loopInformation.addBackEdge((($0 = this.predecessors.$index(i)) && $0.is$HBasicBlock()));
+    this.loopInformation.addBackEdge((($0 = this.predecessors.$index(i)) == null ? null : $0.assert$HBasicBlock()));
   }
 }
 HBasicBlock.prototype.rewrite = function(from, to) {
@@ -8624,10 +9014,10 @@ HBasicBlock.prototype.assignCommonDominator = function(predecessor) {
 }
 HBasicBlock.prototype.forEachPhi = function(f) {
   var $0;
-  var current = (($0 = this.phis.first) && $0.is$HPhi());
+  var current = (($0 = this.phis.first) == null ? null : $0.assert$HPhi());
   while (current != null) {
     f(current);
-    current = (($0 = current.next) && $0.is$HPhi());
+    current = (($0 = current.next) == null ? null : $0.assert$HPhi());
   }
 }
 HBasicBlock.prototype.isValid = function() {
@@ -8637,17 +9027,17 @@ HBasicBlock.prototype.isValid = function() {
   return validator.isValid;
 }
 HBasicBlock.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$HVisitor()));
+  return this.accept(($0 == null ? null : $0.assert$HVisitor()));
 };
 HBasicBlock.prototype.add$1 = function($0) {
-  return this.add(($0 && $0.is$HInstruction()));
+  return this.add(($0 == null ? null : $0.assert$HInstruction()));
 };
 HBasicBlock.prototype.forEachPhi$1 = function($0) {
   return this.forEachPhi(to$call$1($0));
 };
 HBasicBlock.prototype.isExitBlock$0 = HBasicBlock.prototype.isExitBlock;
 HBasicBlock.prototype.removePhi$1 = function($0) {
-  return this.removePhi(($0 && $0.is$HPhi()));
+  return this.removePhi(($0 == null ? null : $0.assert$HPhi()));
 };
 // ********** Code for HLoopInformation **************
 function HLoopInformation(header) {
@@ -8674,7 +9064,7 @@ HLoopInformation.prototype.addBlock = function(block) {
     this.blocks.add(block);
     for (var i = 0, length = block.predecessors.length;
      i < length; i++) {
-      this.addBlock((($0 = block.predecessors.$index(i)) && $0.is$HBasicBlock()));
+      this.addBlock((($0 = block.predecessors.$index(i)) == null ? null : $0.assert$HBasicBlock()));
     }
   }
 }
@@ -8684,7 +9074,7 @@ HLoopInformation.prototype.getLastBackEdge = function() {
   var result = null;
   for (var i = 0, length = this.backEdges.length;
    i < length; i++) {
-    var current = (($0 = this.backEdges.$index(i)) && $0.is$HBasicBlock());
+    var current = (($0 = this.backEdges.$index(i)) == null ? null : $0.assert$HBasicBlock());
     if (current.id > maxId) {
       maxId = current.id;
       result = current;
@@ -8703,7 +9093,7 @@ function HInstruction(inputs) {
   this.usedBy = [];
   // Initializers done
 }
-HInstruction.prototype.is$HInstruction = function(){return this;};
+HInstruction.prototype.assert$HInstruction = function(){return this};
 HInstruction.prototype.get$id = function() { return this.id; };
 HInstruction.prototype.get$inputs = function() { return this.inputs; };
 HInstruction.prototype.get$usedBy = function() { return this.usedBy; };
@@ -8866,7 +9256,7 @@ HInstruction.prototype.notifyRemovedFromBlock = function(block) {
   $assert(this.block === block, "this.block === block", "nodes.dart", 761, 12);
   for (var i = 0;
    i < this.inputs.length; i++) {
-    var inputUsedBy = (($0 = this.inputs.$index(i).get$usedBy()) && $0.is$List());
+    var inputUsedBy = (($0 = this.inputs.$index(i).get$usedBy()) == null ? null : $0.assert$List());
     for (var j = 0;
      j < inputUsedBy.length; j++) {
       if (inputUsedBy.$index(j) === this) {
@@ -8895,17 +9285,17 @@ HInstruction.prototype.isValid = function() {
   return validator.isValid;
 }
 HInstruction.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$HVisitor()));
+  return this.accept(($0 == null ? null : $0.assert$HVisitor()));
 };
 HInstruction.prototype.block$0 = function() {
   return this.block();
 };
 HInstruction.prototype.clearGenerateAtUseSite$0 = HInstruction.prototype.clearGenerateAtUseSite;
 HInstruction.prototype.computeDesiredInputType$1 = function($0) {
-  return this.computeDesiredInputType(($0 && $0.is$HInstruction()));
+  return this.computeDesiredInputType(($0 == null ? null : $0.assert$HInstruction()));
 };
 HInstruction.prototype.dataEquals$1 = function($0) {
-  return this.dataEquals(($0 && $0.is$HInstruction()));
+  return this.dataEquals(($0 == null ? null : $0.assert$HInstruction()));
 };
 HInstruction.prototype.hashCode$0 = HInstruction.prototype.hashCode;
 HInstruction.prototype.isInBasicBlock$0 = HInstruction.prototype.isInBasicBlock;
@@ -8944,10 +9334,10 @@ HBoolify.prototype.dataEquals = function(other) {
   return true;
 }
 HBoolify.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$HVisitor()));
+  return this.accept(($0 == null ? null : $0.assert$HVisitor()));
 };
 HBoolify.prototype.dataEquals$1 = function($0) {
-  return this.dataEquals(($0 && $0.is$HInstruction()));
+  return this.dataEquals(($0 == null ? null : $0.assert$HInstruction()));
 };
 // ********** Code for HTypeGuard **************
 function HTypeGuard(type, value) {
@@ -8956,7 +9346,7 @@ function HTypeGuard(type, value) {
   this.type = $assert_num(type);
 }
 $inherits(HTypeGuard, HInstruction);
-HTypeGuard.prototype.is$HTypeGuard = function(){return this;};
+HTypeGuard.prototype.assert$HTypeGuard = function(){return this};
 HTypeGuard.prototype.prepareGvn = function() {
   $assert(!$notnull_bool(this.hasSideEffects()), "!hasSideEffects()", "nodes.dart", 811, 12);
   this.setUseGvn();
@@ -8977,10 +9367,10 @@ HTypeGuard.prototype.dataEquals = function(other) {
   return this.type == other.type;
 }
 HTypeGuard.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$HVisitor()));
+  return this.accept(($0 == null ? null : $0.assert$HVisitor()));
 };
 HTypeGuard.prototype.dataEquals$1 = function($0) {
-  return this.dataEquals(($0 && $0.is$HTypeGuard()));
+  return this.dataEquals(($0 == null ? null : $0.assert$HTypeGuard()));
 };
 // ********** Code for HConditionalBranch **************
 function HConditionalBranch(inputs) {
@@ -9011,7 +9401,7 @@ HInvoke.prototype.accept = function(visitor) {
   return visitor.visitInvoke(this);
 }
 HInvoke.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$HVisitor()));
+  return this.accept(($0 == null ? null : $0.assert$HVisitor()));
 };
 HInvoke.prototype.toString$0 = HInvoke.prototype.toString;
 // ********** Code for HForeign **************
@@ -9026,7 +9416,7 @@ HForeign.prototype.accept = function(visitor) {
   return visitor.visitForeign(this);
 }
 HForeign.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$HVisitor()));
+  return this.accept(($0 == null ? null : $0.assert$HVisitor()));
 };
 // ********** Code for HArithmetic **************
 function HArithmetic(element, inputs) {
@@ -9058,7 +9448,7 @@ HArithmetic.prototype.hasExpectedType = function() {
   return this.type == 2/*HInstruction.TYPE_NUMBER*/;
 }
 HArithmetic.prototype.computeDesiredInputType$1 = function($0) {
-  return this.computeDesiredInputType(($0 && $0.is$HInstruction()));
+  return this.computeDesiredInputType(($0 == null ? null : $0.assert$HInstruction()));
 };
 // ********** Code for HBinaryArithmetic **************
 function HBinaryArithmetic(element, left, right) {
@@ -9069,8 +9459,8 @@ $inherits(HBinaryArithmetic, HArithmetic);
 HBinaryArithmetic.prototype.fold = function() {
   var $0;
   if ($notnull_bool(this.inputs.$index(0).isLiteralNumber$0()) && $notnull_bool(this.inputs.$index(1).isLiteralNumber$0())) {
-    var op1 = (($0 = this.inputs.$index(0)) && $0.is$HLiteral());
-    var op2 = (($0 = this.inputs.$index(1)) && $0.is$HLiteral());
+    var op1 = (($0 = this.inputs.$index(0)) == null ? null : $0.assert$HLiteral());
+    var op2 = (($0 = this.inputs.$index(1)) == null ? null : $0.assert$HLiteral());
     return new HLiteral(this.evaluate($assert_num(op1.value), $assert_num(op2.value)));
   }
   return this;
@@ -9111,13 +9501,13 @@ HAdd.prototype.hasExpectedType = function() {
   return this.type == 0/*HInstruction.TYPE_UNKNOWN*/;
 }
 HAdd.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$HVisitor()));
+  return this.accept(($0 == null ? null : $0.assert$HVisitor()));
 };
 HAdd.prototype.computeDesiredInputType$1 = function($0) {
-  return this.computeDesiredInputType(($0 && $0.is$HInstruction()));
+  return this.computeDesiredInputType(($0 == null ? null : $0.assert$HInstruction()));
 };
 HAdd.prototype.dataEquals$1 = function($0) {
-  return this.dataEquals(($0 && $0.is$HInstruction()));
+  return this.dataEquals(($0 == null ? null : $0.assert$HInstruction()));
 };
 // ********** Code for HDivide **************
 function HDivide(element, left, right) {
@@ -9138,10 +9528,10 @@ HDivide.prototype.dataEquals = function(other) {
   return true;
 }
 HDivide.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$HVisitor()));
+  return this.accept(($0 == null ? null : $0.assert$HVisitor()));
 };
 HDivide.prototype.dataEquals$1 = function($0) {
-  return this.dataEquals(($0 && $0.is$HInstruction()));
+  return this.dataEquals(($0 == null ? null : $0.assert$HInstruction()));
 };
 // ********** Code for HModulo **************
 function HModulo(element, left, right) {
@@ -9162,10 +9552,10 @@ HModulo.prototype.dataEquals = function(other) {
   return true;
 }
 HModulo.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$HVisitor()));
+  return this.accept(($0 == null ? null : $0.assert$HVisitor()));
 };
 HModulo.prototype.dataEquals$1 = function($0) {
-  return this.dataEquals(($0 && $0.is$HInstruction()));
+  return this.dataEquals(($0 == null ? null : $0.assert$HInstruction()));
 };
 // ********** Code for HMultiply **************
 function HMultiply(element, left, right) {
@@ -9186,10 +9576,10 @@ HMultiply.prototype.dataEquals = function(other) {
   return true;
 }
 HMultiply.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$HVisitor()));
+  return this.accept(($0 == null ? null : $0.assert$HVisitor()));
 };
 HMultiply.prototype.dataEquals$1 = function($0) {
-  return this.dataEquals(($0 && $0.is$HInstruction()));
+  return this.dataEquals(($0 == null ? null : $0.assert$HInstruction()));
 };
 // ********** Code for HSubtract **************
 function HSubtract(element, left, right) {
@@ -9210,10 +9600,10 @@ HSubtract.prototype.dataEquals = function(other) {
   return true;
 }
 HSubtract.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$HVisitor()));
+  return this.accept(($0 == null ? null : $0.assert$HVisitor()));
 };
 HSubtract.prototype.dataEquals$1 = function($0) {
-  return this.dataEquals(($0 && $0.is$HInstruction()));
+  return this.dataEquals(($0 == null ? null : $0.assert$HInstruction()));
 };
 // ********** Code for HTruncatingDivide **************
 function HTruncatingDivide(element, left, right) {
@@ -9240,10 +9630,10 @@ HTruncatingDivide.prototype.dataEquals = function(other) {
   return true;
 }
 HTruncatingDivide.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$HVisitor()));
+  return this.accept(($0 == null ? null : $0.assert$HVisitor()));
 };
 HTruncatingDivide.prototype.dataEquals$1 = function($0) {
-  return this.dataEquals(($0 && $0.is$HInstruction()));
+  return this.dataEquals(($0 == null ? null : $0.assert$HInstruction()));
 };
 // ********** Code for HBinaryBitOp **************
 function HBinaryBitOp(element, left, right) {
@@ -9254,8 +9644,8 @@ $inherits(HBinaryBitOp, HBinaryArithmetic);
 HBinaryBitOp.prototype.fold = function() {
   var $0;
   if ($notnull_bool(this.inputs.$index(0).isLiteralNumber$0()) && $notnull_bool(this.inputs.$index(1).isLiteralNumber$0())) {
-    var op1 = (($0 = this.inputs.$index(0)) && $0.is$HLiteral());
-    var op2 = (($0 = this.inputs.$index(1)) && $0.is$HLiteral());
+    var op1 = (($0 = this.inputs.$index(0)) == null ? null : $0.assert$HLiteral());
+    var op2 = (($0 = this.inputs.$index(1)) == null ? null : $0.assert$HLiteral());
     if ((typeof(op1.value) == 'number') && (typeof(op2.value) == 'number')) {
       return new HLiteral(this.evaluate($assert_num(op1.value), $assert_num(op2.value)));
     }
@@ -9275,7 +9665,7 @@ HShiftLeft.prototype.fold = function() {
   var $0;
   if ($notnull_bool(this.inputs.$index(1).isLiteralNumber$0())) {
     var MAX_SHIFT_LEFT_AMOUNT = 50;
-    var op2 = (($0 = this.inputs.$index(1)) && $0.is$HLiteral());
+    var op2 = (($0 = this.inputs.$index(1)) == null ? null : $0.assert$HLiteral());
     if (op2.value < 0 || op2.value > MAX_SHIFT_LEFT_AMOUNT) return this;
   }
   return HBinaryBitOp.prototype.fold.call(this);
@@ -9290,10 +9680,10 @@ HShiftLeft.prototype.dataEquals = function(other) {
   return true;
 }
 HShiftLeft.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$HVisitor()));
+  return this.accept(($0 == null ? null : $0.assert$HVisitor()));
 };
 HShiftLeft.prototype.dataEquals$1 = function($0) {
-  return this.dataEquals(($0 && $0.is$HInstruction()));
+  return this.dataEquals(($0 == null ? null : $0.assert$HInstruction()));
 };
 // ********** Code for HShiftRight **************
 function HShiftRight(element, left, right) {
@@ -9307,7 +9697,7 @@ HShiftRight.prototype.accept = function(visitor) {
 HShiftRight.prototype.fold = function() {
   var $0;
   if ($notnull_bool(this.inputs.$index(1).isLiteralNumber$0())) {
-    var op2 = (($0 = this.inputs.$index(1)) && $0.is$HLiteral());
+    var op2 = (($0 = this.inputs.$index(1)) == null ? null : $0.assert$HLiteral());
     if (op2.value < 0) return this;
   }
   return HBinaryBitOp.prototype.fold.call(this);
@@ -9322,10 +9712,10 @@ HShiftRight.prototype.dataEquals = function(other) {
   return true;
 }
 HShiftRight.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$HVisitor()));
+  return this.accept(($0 == null ? null : $0.assert$HVisitor()));
 };
 HShiftRight.prototype.dataEquals$1 = function($0) {
-  return this.dataEquals(($0 && $0.is$HInstruction()));
+  return this.dataEquals(($0 == null ? null : $0.assert$HInstruction()));
 };
 // ********** Code for HBitOr **************
 function HBitOr(element, left, right) {
@@ -9346,10 +9736,10 @@ HBitOr.prototype.dataEquals = function(other) {
   return true;
 }
 HBitOr.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$HVisitor()));
+  return this.accept(($0 == null ? null : $0.assert$HVisitor()));
 };
 HBitOr.prototype.dataEquals$1 = function($0) {
-  return this.dataEquals(($0 && $0.is$HInstruction()));
+  return this.dataEquals(($0 == null ? null : $0.assert$HInstruction()));
 };
 // ********** Code for HBitAnd **************
 function HBitAnd(element, left, right) {
@@ -9370,10 +9760,10 @@ HBitAnd.prototype.dataEquals = function(other) {
   return true;
 }
 HBitAnd.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$HVisitor()));
+  return this.accept(($0 == null ? null : $0.assert$HVisitor()));
 };
 HBitAnd.prototype.dataEquals$1 = function($0) {
-  return this.dataEquals(($0 && $0.is$HInstruction()));
+  return this.dataEquals(($0 == null ? null : $0.assert$HInstruction()));
 };
 // ********** Code for HBitXor **************
 function HBitXor(element, left, right) {
@@ -9394,10 +9784,10 @@ HBitXor.prototype.dataEquals = function(other) {
   return true;
 }
 HBitXor.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$HVisitor()));
+  return this.accept(($0 == null ? null : $0.assert$HVisitor()));
 };
 HBitXor.prototype.dataEquals$1 = function($0) {
-  return this.dataEquals(($0 && $0.is$HInstruction()));
+  return this.dataEquals(($0 == null ? null : $0.assert$HInstruction()));
 };
 // ********** Code for HUnaryArithmetic **************
 function HUnaryArithmetic(element, input) {
@@ -9417,7 +9807,7 @@ HNegate.prototype.accept = function(visitor) {
 HNegate.prototype.fold = function() {
   var $0;
   if ($notnull_bool(this.inputs.$index(0).isLiteralNumber$0())) {
-    var input = (($0 = this.inputs.$index(0)) && $0.is$HLiteral());
+    var input = (($0 = this.inputs.$index(0)) == null ? null : $0.assert$HLiteral());
     return new HLiteral(this.evaluate($assert_num(input.value)));
   }
   return this;
@@ -9432,10 +9822,10 @@ HNegate.prototype.dataEquals = function(other) {
   return true;
 }
 HNegate.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$HVisitor()));
+  return this.accept(($0 == null ? null : $0.assert$HVisitor()));
 };
 HNegate.prototype.dataEquals$1 = function($0) {
-  return this.dataEquals(($0 && $0.is$HInstruction()));
+  return this.dataEquals(($0 == null ? null : $0.assert$HInstruction()));
 };
 // ********** Code for HBitNot **************
 function HBitNot(element, input) {
@@ -9449,7 +9839,7 @@ HBitNot.prototype.accept = function(visitor) {
 HBitNot.prototype.fold = function() {
   var $0;
   if ($notnull_bool(this.inputs.$index(0).isLiteralNumber$0())) {
-    var input = (($0 = this.inputs.$index(0)) && $0.is$HLiteral());
+    var input = (($0 = this.inputs.$index(0)) == null ? null : $0.assert$HLiteral());
     if ((typeof(input.value) == 'number')) return new HLiteral(this.evaluate($assert_num(input.value)));
   }
   return this;
@@ -9464,10 +9854,10 @@ HBitNot.prototype.dataEquals = function(other) {
   return true;
 }
 HBitNot.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$HVisitor()));
+  return this.accept(($0 == null ? null : $0.assert$HVisitor()));
 };
 HBitNot.prototype.dataEquals$1 = function($0) {
-  return this.dataEquals(($0 && $0.is$HInstruction()));
+  return this.dataEquals(($0 == null ? null : $0.assert$HInstruction()));
 };
 // ********** Code for HExit **************
 function HExit() {
@@ -9482,7 +9872,7 @@ HExit.prototype.accept = function(visitor) {
   return visitor.visitExit(this);
 }
 HExit.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$HVisitor()));
+  return this.accept(($0 == null ? null : $0.assert$HVisitor()));
 };
 HExit.prototype.toString$0 = HExit.prototype.toString;
 // ********** Code for HGoto **************
@@ -9498,7 +9888,7 @@ HGoto.prototype.accept = function(visitor) {
   return visitor.visitGoto(this);
 }
 HGoto.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$HVisitor()));
+  return this.accept(($0 == null ? null : $0.assert$HVisitor()));
 };
 HGoto.prototype.toString$0 = HGoto.prototype.toString;
 // ********** Code for HIf **************
@@ -9515,7 +9905,7 @@ HIf.prototype.accept = function(visitor) {
   return visitor.visitIf(this);
 }
 HIf.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$HVisitor()));
+  return this.accept(($0 == null ? null : $0.assert$HVisitor()));
 };
 HIf.prototype.toString$0 = HIf.prototype.toString;
 // ********** Code for HLoopBranch **************
@@ -9531,7 +9921,7 @@ HLoopBranch.prototype.accept = function(visitor) {
   return visitor.visitLoopBranch(this);
 }
 HLoopBranch.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$HVisitor()));
+  return this.accept(($0 == null ? null : $0.assert$HVisitor()));
 };
 HLoopBranch.prototype.toString$0 = HLoopBranch.prototype.toString;
 // ********** Code for HLiteral **************
@@ -9541,7 +9931,7 @@ function HLiteral(value) {
   HInstruction.call(this, []);
 }
 $inherits(HLiteral, HInstruction);
-HLiteral.prototype.is$HLiteral = function(){return this;};
+HLiteral.prototype.assert$HLiteral = function(){return this};
 HLiteral.prototype.get$value = function() { return this.value; };
 HLiteral.prototype.prepareGvn = function() {
   $assert(!$notnull_bool(this.hasSideEffects()), "!hasSideEffects()", "nodes.dart", 1139, 12);
@@ -9582,7 +9972,7 @@ HLiteral.prototype.isLiteralNumber = function() {
 }
 HLiteral.prototype.isLiteralString = function() {
   var $0;
-  return !!(($0 = this.value) && $0.is$SourceString);
+  return !!(($0 = this.value) && $0.is$SourceString());
 }
 HLiteral.prototype.typeEquals = function(other) {
   return (other instanceof HLiteral);
@@ -9591,10 +9981,10 @@ HLiteral.prototype.dataEquals = function(other) {
   return $assert_bool($eq(this.value, other.value));
 }
 HLiteral.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$HVisitor()));
+  return this.accept(($0 == null ? null : $0.assert$HVisitor()));
 };
 HLiteral.prototype.dataEquals$1 = function($0) {
-  return this.dataEquals(($0 && $0.is$HLiteral()));
+  return this.dataEquals(($0 == null ? null : $0.assert$HLiteral()));
 };
 HLiteral.prototype.isLiteralNumber$0 = HLiteral.prototype.isLiteralNumber;
 HLiteral.prototype.isLiteralString$0 = HLiteral.prototype.isLiteralString;
@@ -9625,10 +10015,10 @@ HNot.prototype.dataEquals = function(other) {
   return true;
 }
 HNot.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$HVisitor()));
+  return this.accept(($0 == null ? null : $0.assert$HVisitor()));
 };
 HNot.prototype.dataEquals$1 = function($0) {
-  return this.dataEquals(($0 && $0.is$HInstruction()));
+  return this.dataEquals(($0 == null ? null : $0.assert$HInstruction()));
 };
 // ********** Code for HParameterValue **************
 function HParameterValue(element) {
@@ -9638,7 +10028,7 @@ function HParameterValue(element) {
   this.setGenerateAtUseSite();
 }
 $inherits(HParameterValue, HInstruction);
-HParameterValue.prototype.is$HParameterValue = function(){return this;};
+HParameterValue.prototype.assert$HParameterValue = function(){return this};
 HParameterValue.prototype.get$element = function() { return this.element; };
 HParameterValue.prototype.prepareGvn = function() {
   $assert(!$notnull_bool(this.hasSideEffects()), "!hasSideEffects()", "nodes.dart", 1191, 12);
@@ -9650,7 +10040,7 @@ HParameterValue.prototype.accept = function(visitor) {
   return visitor.visitParameterValue(this);
 }
 HParameterValue.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$HVisitor()));
+  return this.accept(($0 == null ? null : $0.assert$HVisitor()));
 };
 HParameterValue.prototype.toString$0 = HParameterValue.prototype.toString;
 // ********** Code for HPhi **************
@@ -9668,7 +10058,7 @@ HPhi.manyInputs$ctor = function(element, inputs) {
 }
 HPhi.manyInputs$ctor.prototype = HPhi.prototype;
 $inherits(HPhi, HInstruction);
-HPhi.prototype.is$HPhi = function(){return this;};
+HPhi.prototype.assert$HPhi = function(){return this};
 HPhi.prototype.get$element = function() { return this.element; };
 HPhi.prototype.addInput = function(input) {
   $assert(this.isInBasicBlock(), "isInBasicBlock()", "nodes.dart", 1208, 12);
@@ -9703,10 +10093,10 @@ HPhi.prototype.accept = function(visitor) {
   return visitor.visitPhi(this);
 }
 HPhi.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$HVisitor()));
+  return this.accept(($0 == null ? null : $0.assert$HVisitor()));
 };
 HPhi.prototype.computeDesiredInputType$1 = function($0) {
-  return this.computeDesiredInputType(($0 && $0.is$HInstruction()));
+  return this.computeDesiredInputType(($0 == null ? null : $0.assert$HInstruction()));
 };
 HPhi.prototype.toString$0 = HPhi.prototype.toString;
 // ********** Code for HRelational **************
@@ -9738,7 +10128,7 @@ HRelational.prototype.hasExpectedType = function() {
   return this.type == 1/*HInstruction.TYPE_BOOLEAN*/;
 }
 HRelational.prototype.computeDesiredInputType$1 = function($0) {
-  return this.computeDesiredInputType(($0 && $0.is$HInstruction()));
+  return this.computeDesiredInputType(($0 == null ? null : $0.assert$HInstruction()));
 };
 // ********** Code for HEquals **************
 function HEquals(element, left, right) {
@@ -9759,10 +10149,10 @@ HEquals.prototype.dataEquals = function(other) {
   return true;
 }
 HEquals.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$HVisitor()));
+  return this.accept(($0 == null ? null : $0.assert$HVisitor()));
 };
 HEquals.prototype.dataEquals$1 = function($0) {
-  return this.dataEquals(($0 && $0.is$HInstruction()));
+  return this.dataEquals(($0 == null ? null : $0.assert$HInstruction()));
 };
 // ********** Code for HGreater **************
 function HGreater(element, left, right) {
@@ -9783,10 +10173,10 @@ HGreater.prototype.dataEquals = function(other) {
   return true;
 }
 HGreater.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$HVisitor()));
+  return this.accept(($0 == null ? null : $0.assert$HVisitor()));
 };
 HGreater.prototype.dataEquals$1 = function($0) {
-  return this.dataEquals(($0 && $0.is$HInstruction()));
+  return this.dataEquals(($0 == null ? null : $0.assert$HInstruction()));
 };
 // ********** Code for HGreaterEqual **************
 function HGreaterEqual(element, left, right) {
@@ -9807,10 +10197,10 @@ HGreaterEqual.prototype.dataEquals = function(other) {
   return true;
 }
 HGreaterEqual.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$HVisitor()));
+  return this.accept(($0 == null ? null : $0.assert$HVisitor()));
 };
 HGreaterEqual.prototype.dataEquals$1 = function($0) {
-  return this.dataEquals(($0 && $0.is$HInstruction()));
+  return this.dataEquals(($0 == null ? null : $0.assert$HInstruction()));
 };
 // ********** Code for HLess **************
 function HLess(element, left, right) {
@@ -9831,10 +10221,10 @@ HLess.prototype.dataEquals = function(other) {
   return true;
 }
 HLess.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$HVisitor()));
+  return this.accept(($0 == null ? null : $0.assert$HVisitor()));
 };
 HLess.prototype.dataEquals$1 = function($0) {
-  return this.dataEquals(($0 && $0.is$HInstruction()));
+  return this.dataEquals(($0 == null ? null : $0.assert$HInstruction()));
 };
 // ********** Code for HLessEqual **************
 function HLessEqual(element, left, right) {
@@ -9855,10 +10245,10 @@ HLessEqual.prototype.dataEquals = function(other) {
   return true;
 }
 HLessEqual.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$HVisitor()));
+  return this.accept(($0 == null ? null : $0.assert$HVisitor()));
 };
 HLessEqual.prototype.dataEquals$1 = function($0) {
-  return this.dataEquals(($0 && $0.is$HInstruction()));
+  return this.dataEquals(($0 == null ? null : $0.assert$HInstruction()));
 };
 // ********** Code for HReturn **************
 function HReturn(value) {
@@ -9873,7 +10263,7 @@ HReturn.prototype.accept = function(visitor) {
   return visitor.visitReturn(this);
 }
 HReturn.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$HVisitor()));
+  return this.accept(($0 == null ? null : $0.assert$HVisitor()));
 };
 HReturn.prototype.toString$0 = HReturn.prototype.toString;
 // ********** Code for HThrow **************
@@ -9889,7 +10279,7 @@ HThrow.prototype.accept = function(visitor) {
   return visitor.visitThrow(this);
 }
 HThrow.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$HVisitor()));
+  return this.accept(($0 == null ? null : $0.assert$HVisitor()));
 };
 HThrow.prototype.toString$0 = HThrow.prototype.toString;
 // ********** Code for HNonSsaInstruction **************
@@ -9913,7 +10303,7 @@ function HLoad(local, type) {
 $inherits(HLoad, HNonSsaInstruction);
 HLoad.prototype.get$local = function() {
   var $0;
-  return (($0 = this.inputs.$index(0)) && $0.is$HLocal());
+  return (($0 = this.inputs.$index(0)) == null ? null : $0.assert$HLocal());
 }
 HLoad.prototype.toString = function() {
   return 'load';
@@ -9922,7 +10312,7 @@ HLoad.prototype.accept = function(visitor) {
   return visitor.visitLoad(this);
 }
 HLoad.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$HVisitor()));
+  return this.accept(($0 == null ? null : $0.assert$HVisitor()));
 };
 HLoad.prototype.toString$0 = HLoad.prototype.toString;
 // ********** Code for HStore **************
@@ -9933,11 +10323,11 @@ function HStore(local, value) {
 $inherits(HStore, HNonSsaInstruction);
 HStore.prototype.get$local = function() {
   var $0;
-  return (($0 = this.inputs.$index(0)) && $0.is$HLocal());
+  return (($0 = this.inputs.$index(0)) == null ? null : $0.assert$HLocal());
 }
 HStore.prototype.get$value = function() {
   var $0;
-  return (($0 = this.inputs.$index(1)) && $0.is$HInstruction());
+  return (($0 = this.inputs.$index(1)) == null ? null : $0.assert$HInstruction());
 }
 HStore.prototype.toString = function() {
   return 'store';
@@ -9946,7 +10336,7 @@ HStore.prototype.accept = function(visitor) {
   return visitor.visitStore(this);
 }
 HStore.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$HVisitor()));
+  return this.accept(($0 == null ? null : $0.assert$HVisitor()));
 };
 HStore.prototype.toString$0 = HStore.prototype.toString;
 // ********** Code for HLocal **************
@@ -9957,7 +10347,7 @@ function HLocal(element) {
   this.declaredBy = this;
 }
 $inherits(HLocal, HNonSsaInstruction);
-HLocal.prototype.is$HLocal = function(){return this;};
+HLocal.prototype.assert$HLocal = function(){return this};
 HLocal.prototype.get$element = function() { return this.element; };
 HLocal.prototype.set$element = function(value) { return this.element = value; };
 HLocal.prototype.toString = function() {
@@ -9967,7 +10357,7 @@ HLocal.prototype.accept = function(visitor) {
   return visitor.visitLocal(this);
 }
 HLocal.prototype.accept$1 = function($0) {
-  return this.accept(($0 && $0.is$HVisitor()));
+  return this.accept(($0 == null ? null : $0.assert$HVisitor()));
 };
 HLocal.prototype.toString$0 = HLocal.prototype.toString;
 // ********** Code for SsaOptimizerTask **************
@@ -10006,7 +10396,7 @@ SsaConstantFolder.prototype.visitBasicBlock = function(block) {
   var instruction = block.first;
   while (instruction != null) {
     var next = instruction.next;
-    var replacement = (($0 = instruction.accept(this)) && $0.is$HInstruction());
+    var replacement = (($0 = instruction.accept(this)) == null ? null : $0.assert$HInstruction());
     if (replacement !== instruction) {
       if (!$notnull_bool(replacement.isInBasicBlock())) {
         block.addAfter(instruction, replacement);
@@ -10024,7 +10414,7 @@ SsaConstantFolder.prototype.visitBoolify = function(node) {
   var $0;
   var inputs = node.inputs;
   $assert(inputs.length == 1, "inputs.length == 1", "optimize.dart", 56, 12);
-  var input = (($0 = inputs.$index(0)) && $0.is$HInstruction());
+  var input = (($0 = inputs.$index(0)) == null ? null : $0.assert$HInstruction());
   if ($notnull_bool(input.isBoolean())) return input;
   if (!$notnull_bool(input.isUnknown())) return new HLiteral(false);
   return node;
@@ -10033,9 +10423,9 @@ SsaConstantFolder.prototype.visitNot = function(node) {
   var $0;
   var inputs = node.inputs;
   $assert(inputs.length == 1, "inputs.length == 1", "optimize.dart", 66, 12);
-  var input = (($0 = inputs.$index(0)) && $0.is$HInstruction());
+  var input = (($0 = inputs.$index(0)) == null ? null : $0.assert$HInstruction());
   if ((input instanceof HLiteral)) {
-    var literal = (input && input.is$HLiteral());
+    var literal = (input == null ? null : input.assert$HLiteral());
     return new HLiteral(literal.value !== true);
   }
   return node;
@@ -10046,8 +10436,8 @@ SsaConstantFolder.prototype.visitArithmetic = function(node) {
 SsaConstantFolder.prototype.visitAdd = function(node) {
   var $0;
   if ($notnull_bool(node.inputs.$index(0).isLiteralString$0()) && (node.inputs.$index(1) instanceof HLiteral)) {
-    var op1 = (($0 = node.inputs.$index(0)) && $0.is$HLiteral());
-    var op2 = (($0 = node.inputs.$index(1)) && $0.is$HLiteral());
+    var op1 = (($0 = node.inputs.$index(0)) == null ? null : $0.assert$HLiteral());
+    var op2 = (($0 = node.inputs.$index(1)) == null ? null : $0.assert$HLiteral());
     return new HLiteral(new StringWrapper(("" + op1.value + " + " + op2.value)));
   }
   return this.visitArithmetic(node);
@@ -10057,8 +10447,8 @@ SsaConstantFolder.prototype.visitRelational = function(node) {
   var inputs = node.inputs;
   $assert(inputs.length == 2, "inputs.length == 2", "optimize.dart", 93, 12);
   if ($notnull_bool(inputs.$index(0).isLiteralNumber$0()) && $notnull_bool(inputs.$index(1).isLiteralNumber$0())) {
-    var op1 = (($0 = inputs.$index(0)) && $0.is$HLiteral());
-    var op2 = (($0 = inputs.$index(1)) && $0.is$HLiteral());
+    var op1 = (($0 = inputs.$index(0)) == null ? null : $0.assert$HLiteral());
+    var op2 = (($0 = inputs.$index(1)) == null ? null : $0.assert$HLiteral());
     var folded = node.evaluate($assert_num(op1.value), $assert_num(op2.value));
     return new HLiteral(folded);
   }
@@ -10068,16 +10458,16 @@ SsaConstantFolder.prototype.visitEquals = function(node) {
   var $0;
   var inputs = node.inputs;
   if ((inputs.$index(0) instanceof HLiteral) && (inputs.$index(1) instanceof HLiteral)) {
-    var op1 = (($0 = inputs.$index(0)) && $0.is$HLiteral());
-    var op2 = (($0 = inputs.$index(1)) && $0.is$HLiteral());
+    var op1 = (($0 = inputs.$index(0)) == null ? null : $0.assert$HLiteral());
+    var op2 = (($0 = inputs.$index(1)) == null ? null : $0.assert$HLiteral());
     return new HLiteral($eq(op1.value, op2.value));
   }
   return node;
 }
 SsaConstantFolder.prototype.visitTypeGuard = function(node) {
   var $0;
-  var value = (($0 = node.inputs.$index(0)) && $0.is$HInstruction());
-  return (($0 = (value.type == node.type) ? value : node) && $0.is$HInstruction());
+  var value = (($0 = node.inputs.$index(0)) == null ? null : $0.assert$HInstruction());
+  return (($0 = (value.type == node.type) ? value : node) == null ? null : $0.assert$HInstruction());
 }
 // ********** Code for SsaTypePropagator **************
 function SsaTypePropagator() {
@@ -10116,7 +10506,7 @@ SsaTypePropagator.prototype.processWorklist = function() {
   var $0;
   while (!this.worklist.isEmpty()) {
     var id = $assert_num(this.worklist.removeLast());
-    var instruction = (($0 = this.workmap.$index(id)) && $0.is$HInstruction());
+    var instruction = (($0 = this.workmap.$index(id)) == null ? null : $0.assert$HInstruction());
     $assert(instruction != null, "instruction !== null", "optimize.dart", 156, 14);
     this.workmap.remove(id);
     if ($notnull_bool(instruction.updateType())) this.addUsersAndInputsToWorklist(instruction);
@@ -10126,11 +10516,11 @@ SsaTypePropagator.prototype.addUsersAndInputsToWorklist = function(instruction)
   var $0;
   for (var i = 0, length = instruction.usedBy.length;
    i < length; i++) {
-    this.addToWorklist((($0 = instruction.usedBy.$index(i)) && $0.is$HInstruction()));
+    this.addToWorklist((($0 = instruction.usedBy.$index(i)) == null ? null : $0.assert$HInstruction()));
   }
   for (var i = 0, length = instruction.inputs.length;
    i < length; i++) {
-    this.addToWorklist((($0 = instruction.inputs.$index(i)) && $0.is$HInstruction()));
+    this.addToWorklist((($0 = instruction.inputs.$index(i)) == null ? null : $0.assert$HInstruction()));
   }
 }
 SsaTypePropagator.prototype.addToWorklist = function(instruction) {
@@ -10186,7 +10576,7 @@ SsaDeadCodeEliminator.prototype.visitBasicBlock = function(block) {
   while (instruction != null) {
     var previous = instruction.previous;
     if ($notnull_bool(SsaDeadCodeEliminator.isDeadCode(instruction))) block.remove(instruction);
-    instruction = (previous && previous.is$HInstruction());
+    instruction = (previous == null ? null : previous.assert$HInstruction());
   }
 }
 // ********** Code for SsaDeadPhiEliminator **************
@@ -10214,7 +10604,7 @@ SsaDeadPhiEliminator.prototype.visitGraph = function(graph) {
     );
   }
   while (!worklist.isEmpty()) {
-    var phi = (($0 = worklist.removeLast()) && $0.is$HPhi());
+    var phi = (($0 = worklist.removeLast()) == null ? null : $0.assert$HPhi());
     var $list = phi.inputs;
     for (var $i = 0;$i < $list.length; $i++) {
       var input = $list.$index($i);
@@ -10227,10 +10617,10 @@ SsaDeadPhiEliminator.prototype.visitGraph = function(graph) {
   var $list = graph.blocks;
   for (var $i = 0;$i < $list.length; $i++) {
     var block = $list.$index($i);
-    var current = (($0 = block.get$phis().get$first()) && $0.is$HPhi());
+    var current = (($0 = block.get$phis().get$first()) == null ? null : $0.assert$HPhi());
     var next = null;
     while (current != null) {
-      next = (($0 = current.next) && $0.is$HPhi());
+      next = (($0 = current.next) == null ? null : $0.assert$HPhi());
       if (!livePhis.contains(current)) block.removePhi$1(current);
       current = next;
     }
@@ -10252,13 +10642,13 @@ SsaRedundantPhiEliminator.prototype.visitGraph = function(graph) {
     );
   }
   while (!worklist.isEmpty()) {
-    var phi = (($0 = worklist.removeLast()) && $0.is$HPhi());
+    var phi = (($0 = worklist.removeLast()) == null ? null : $0.assert$HPhi());
     if (!$notnull_bool(phi.isInBasicBlock())) continue;
     $assert(phi.inputs.$index(0) !== phi, "phi.inputs[0] !== phi", "optimize.dart", 295, 14);
-    var candidate = (($0 = phi.inputs.$index(0)) && $0.is$HInstruction());
+    var candidate = (($0 = phi.inputs.$index(0)) == null ? null : $0.assert$HInstruction());
     for (var i = 1;
      i < phi.inputs.length; i++) {
-      var input = (($0 = phi.inputs.$index(i)) && $0.is$HInstruction());
+      var input = (($0 = phi.inputs.$index(i)) == null ? null : $0.assert$HInstruction());
       if (input !== candidate && input !== phi) {
         candidate = null;
         break;
@@ -10289,20 +10679,20 @@ SsaGlobalValueNumberer.prototype.moveLoopInvariantCode = function(graph) {
   var $0;
   for (var i = graph.blocks.length - 1;
    i >= 0; i--) {
-    var block = (($0 = graph.blocks.$index(i)) && $0.is$HBasicBlock());
+    var block = (($0 = graph.blocks.$index(i)) == null ? null : $0.assert$HBasicBlock());
     if ($notnull_bool(block.isLoopHeader())) {
       var changesFlags = $assert_num(this.loopChangesFlags.$index(block.id));
       var last = block.loopInformation.getLastBackEdge();
       for (var j = block.id;
        j <= last.id; j++) {
-        this.moveLoopInvariantCodeFromBlock((($0 = graph.blocks.$index(j)) && $0.is$HBasicBlock()), block, changesFlags);
+        this.moveLoopInvariantCodeFromBlock((($0 = graph.blocks.$index(j)) == null ? null : $0.assert$HBasicBlock()), block, changesFlags);
       }
     }
   }
 }
 SsaGlobalValueNumberer.prototype.moveLoopInvariantCodeFromBlock = function(block, loopHeader, changesFlags) {
   var $0;
-  var preheader = (($0 = loopHeader.predecessors.$index(0)) && $0.is$HBasicBlock());
+  var preheader = (($0 = loopHeader.predecessors.$index(0)) == null ? null : $0.assert$HBasicBlock());
   var dependsFlags = HInstruction.computeDependsOnFlags(changesFlags);
   var instruction = block.first;
   while (instruction != null) {
@@ -10312,7 +10702,7 @@ SsaGlobalValueNumberer.prototype.moveLoopInvariantCodeFromBlock = function(block
       var inputs = instruction.inputs;
       for (var i = 0, length = inputs.length;
        i < length; i++) {
-        if ($notnull_bool(this.isInputDefinedAfterDominator((($0 = inputs.$index(i)) && $0.is$HInstruction()), preheader))) {
+        if ($notnull_bool(this.isInputDefinedAfterDominator((($0 = inputs.$index(i)) == null ? null : $0.assert$HInstruction()), preheader))) {
           loopInvariantInputs = false;
           break;
         }
@@ -10353,7 +10743,7 @@ SsaGlobalValueNumberer.prototype.visitBasicBlock = function(block, values) {
   var dominatedBlocks = block.dominatedBlocks;
   for (var i = 0, length = dominatedBlocks.length;
    i < length; i++) {
-    var dominated = (($0 = dominatedBlocks.$index(i)) && $0.is$HBasicBlock());
+    var dominated = (($0 = dominatedBlocks.$index(i)) == null ? null : $0.assert$HBasicBlock());
     var successorValues = (i == length - 1) ? values : values.copy();
     $assert(block.id < dominated.id, "block.id < dominated.id", "optimize.dart", 414, 14);
     if (!$notnull_bool(successorValues.isEmpty()) && block.id + 1 < dominated.id) {
@@ -10373,7 +10763,7 @@ SsaGlobalValueNumberer.prototype.computeChangesFlags = function(graph) {
    i < length; i++) this.loopChangesFlags.$setindex(i, 0);
   for (var i = length - 1;
    i >= 0; i--) {
-    var block = (($0 = graph.blocks.$index(i)) && $0.is$HBasicBlock());
+    var block = (($0 = graph.blocks.$index(i)) == null ? null : $0.assert$HBasicBlock());
     var id = block.id;
     var changesFlags = 0;
     var instruction = block.first;
@@ -10399,7 +10789,7 @@ SsaGlobalValueNumberer.prototype.getChangesFlagsForDominatedBlock = function(dom
   var predecessors = dominated.predecessors;
   for (var i = 0, length = predecessors.length;
    i < length; i++) {
-    var block = (($0 = predecessors.$index(i)) && $0.is$HBasicBlock());
+    var block = (($0 = predecessors.$index(i)) == null ? null : $0.assert$HBasicBlock());
     var id = block.id;
     if (dominator.id < id && id < dominated.id && !this.visited.contains(id)) {
       this.visited.add(id);
@@ -10433,11 +10823,11 @@ SsaInstructionMerger.prototype.visitInstruction = function(node) {
   var i = inputs.length - 1;
   for (; i >= 0; i--) {
     if (previousUnused == null) break;
-    var input = (($0 = inputs.$index(i)) && $0.is$HInstruction());
+    var input = (($0 = inputs.$index(i)) == null ? null : $0.assert$HInstruction());
     if (input.usedBy.length != 1) break;
     if (input !== previousUnused) break;
     var remarkTypeGuardInput = false;
-    if ((input instanceof HTypeGuard)) remarkTypeGuardInput = this.typeGuardCheck((input && input.is$HTypeGuard()));
+    if ((input instanceof HTypeGuard)) remarkTypeGuardInput = this.typeGuardCheck((input == null ? null : input.assert$HTypeGuard()));
     if (!$notnull_bool(input.generateAtUseSite())) {
       this.markedByMerger.add(input);
       input.setGenerateAtUseSite();
@@ -10446,8 +10836,8 @@ SsaInstructionMerger.prototype.visitInstruction = function(node) {
     previousUnused = previousUnused.previous;
   }
   for (; i >= 0; i--) {
-    var input = (($0 = inputs.$index(i)) && $0.is$HInstruction());
-    if ((input instanceof HTypeGuard)) this.typeGuardCheck((input && input.is$HTypeGuard()));
+    var input = (($0 = inputs.$index(i)) == null ? null : $0.assert$HInstruction());
+    if ((input instanceof HTypeGuard)) this.typeGuardCheck((input == null ? null : input.assert$HTypeGuard()));
   }
 }
 // ********** Code for SsaTypeGuardUnuser **************
@@ -10462,7 +10852,7 @@ SsaTypeGuardUnuser.prototype.visitGraph = function(graph) {
 SsaTypeGuardUnuser.prototype.visitTypeGuard = function(node) {
   var $0;
   if ($notnull_bool(node.generateAtUseSite())) return;
-  this.currentBlock.rewrite(node, (($0 = node.inputs.$index(0)) && $0.is$HInstruction()));
+  this.currentBlock.rewrite(node, (($0 = node.inputs.$index(0)) == null ? null : $0.assert$HInstruction()));
 }
 // ********** Code for SsaPhiEliminator **************
 function SsaPhiEliminator() {
@@ -10510,9 +10900,9 @@ SsaPhiEliminator.prototype.visitBasicBlock = function(block) {
   var $0;
   this.currentBlock = block;
   var loads = [];
-  var phi = (($0 = block.phis.first) && $0.is$HPhi());
+  var phi = (($0 = block.phis.first) == null ? null : $0.assert$HPhi());
   while (phi != null) {
-    var next = (($0 = phi.next) && $0.is$HPhi());
+    var next = (($0 = phi.next) == null ? null : $0.assert$HPhi());
     this.visitPhi(phi, loads);
     phi = next;
   }
@@ -10531,7 +10921,7 @@ SsaPhiEliminator.prototype.visitPhi = function(phi, loads) {
       }
       return local0;
     })
-    )) && $0.is$HLocal());
+    )) == null ? null : $0.assert$HLocal());
   }
   else {
     local = new HLocal(null);
@@ -10541,10 +10931,10 @@ SsaPhiEliminator.prototype.visitPhi = function(phi, loads) {
   var stores = [];
   for (var i = 0, len = predecessors.length;
    i < len; i++) {
-    var value = (($0 = phi.inputs.$index(i)) && $0.is$HInstruction());
+    var value = (($0 = phi.inputs.$index(i)) == null ? null : $0.assert$HInstruction());
     if ((value instanceof HLoad) && value.get$dynamic().get$local() === local) continue;
     if (((value instanceof HPhi)) && (local.element != null) && (value.get$dynamic().get$element() === local.element)) continue;
-    var store = this.addStore((($0 = predecessors.$index(i)) && $0.is$HBasicBlock()), this.currentBlock.dominator, local, value);
+    var store = this.addStore((($0 = predecessors.$index(i)) == null ? null : $0.assert$HBasicBlock()), this.currentBlock.dominator, local, value);
     if (store != null) {
       if (local.declaredBy === local) {
         var storeBlock = store.block;
@@ -10672,9 +11062,9 @@ HTracer.prototype.visitBasicBlock = function(block) {
         $this.printProperty("method", "None");
         block.forEachPhi((function (phi) {
           var $0;
-          var phiId = stringifier.temporaryId((phi && phi.is$HInstruction()));
-          var inputId1 = stringifier.temporaryId((($0 = phi.get$inputs().$index(0)) && $0.is$HInstruction()));
-          var inputId2 = stringifier.temporaryId((($0 = phi.get$inputs().$index(1)) && $0.is$HInstruction()));
+          var phiId = stringifier.temporaryId((phi == null ? null : phi.assert$HInstruction()));
+          var inputId1 = stringifier.temporaryId((($0 = phi.get$inputs().$index(0)) == null ? null : $0.assert$HInstruction()));
+          var inputId2 = stringifier.temporaryId((($0 = phi.get$inputs().$index(1)) == null ? null : $0.assert$HInstruction()));
           $this.print(("" + phi.get$id() + " " + phiId + " [ " + inputId1 + " " + inputId2 + " ]"));
         })
         );
@@ -10734,7 +11124,7 @@ function HInstructionStringifier(currentBlock) {
   this.currentBlock = currentBlock;
   // Initializers done
 }
-HInstructionStringifier.prototype.is$HVisitor = function(){return this;};
+HInstructionStringifier.prototype.assert$HVisitor = function(){return this};
 HInstructionStringifier.prototype.visit = function(node) {
   return node.accept(this);
 }
@@ -10778,7 +11168,7 @@ HInstructionStringifier.prototype.temporaryId = function(instruction) {
 }
 HInstructionStringifier.prototype.visitBoolify = function(node) {
   var $0;
-  return ("Boolify: " + this.temporaryId((($0 = node.inputs.$index(0)) && $0.is$HInstruction())));
+  return ("Boolify: " + this.temporaryId((($0 = node.inputs.$index(0)) == null ? null : $0.assert$HInstruction())));
 }
 HInstructionStringifier.prototype.visitAdd = function(node) {
   return this.visitInvoke(node);
@@ -10806,7 +11196,7 @@ HInstructionStringifier.prototype.visitExit = function(node) {
 }
 HInstructionStringifier.prototype.visitGoto = function(node) {
   var $0;
-  var target = (($0 = this.currentBlock.successors.$index(0)) && $0.is$HBasicBlock());
+  var target = (($0 = this.currentBlock.successors.$index(0)) == null ? null : $0.assert$HBasicBlock());
   return ("Goto: (B" + target.id + ")");
 }
 HInstructionStringifier.prototype.visitGreater = function(node) {
@@ -10817,9 +11207,9 @@ HInstructionStringifier.prototype.visitGreaterEqual = function(node) {
 }
 HInstructionStringifier.prototype.visitIf = function(node) {
   var $0;
-  var thenBlock = (($0 = this.currentBlock.successors.$index(0)) && $0.is$HBasicBlock());
-  var elseBlock = (($0 = this.currentBlock.successors.$index(1)) && $0.is$HBasicBlock());
-  var conditionId = this.temporaryId((($0 = node.inputs.$index(0)) && $0.is$HInstruction()));
+  var thenBlock = (($0 = this.currentBlock.successors.$index(0)) == null ? null : $0.assert$HBasicBlock());
+  var elseBlock = (($0 = this.currentBlock.successors.$index(1)) == null ? null : $0.assert$HBasicBlock());
+  var conditionId = this.temporaryId((($0 = node.inputs.$index(0)) == null ? null : $0.assert$HInstruction()));
   return ("If (" + conditionId + "): (B" + thenBlock.id + ") else (B" + elseBlock.id + ")");
 }
 HInstructionStringifier.prototype.visitGenericInvoke = function(invokeType, functionName, arguments) {
@@ -10828,7 +11218,7 @@ HInstructionStringifier.prototype.visitGenericInvoke = function(invokeType, func
   for (var i = 0;
    i < arguments.length; i++) {
     if (i != 0) argumentsString.add(", ");
-    argumentsString.add(this.temporaryId((($0 = arguments.$index(i)) && $0.is$HInstruction())));
+    argumentsString.add(this.temporaryId((($0 = arguments.$index(i)) == null ? null : $0.assert$HInstruction())));
   }
   return ("" + invokeType + ": " + functionName + "(" + argumentsString + ")");
 }
@@ -10851,7 +11241,7 @@ HInstructionStringifier.prototype.visitLiteral = function(literal) {
 }
 HInstructionStringifier.prototype.visitLoad = function(node) {
   var $0;
-  return ("Load: " + this.temporaryId((($0 = node.inputs.$index(0)) && $0.is$HInstruction())));
+  return ("Load: " + this.temporaryId((($0 = node.inputs.$index(0)) == null ? null : $0.assert$HInstruction())));
 }
 HInstructionStringifier.prototype.visitLocal = function(node) {
   if (node.element != null) {
@@ -10863,9 +11253,9 @@ HInstructionStringifier.prototype.visitLocal = function(node) {
 }
 HInstructionStringifier.prototype.visitLoopBranch = function(branch) {
   var $0;
-  var bodyBlock = (($0 = this.currentBlock.successors.$index(0)) && $0.is$HBasicBlock());
-  var exitBlock = (($0 = this.currentBlock.successors.$index(1)) && $0.is$HBasicBlock());
-  var conditionId = this.temporaryId((($0 = branch.inputs.$index(0)) && $0.is$HInstruction()));
+  var bodyBlock = (($0 = this.currentBlock.successors.$index(0)) == null ? null : $0.assert$HBasicBlock());
+  var exitBlock = (($0 = this.currentBlock.successors.$index(1)) == null ? null : $0.assert$HBasicBlock());
+  var conditionId = this.temporaryId((($0 = branch.inputs.$index(0)) == null ? null : $0.assert$HInstruction()));
   return ("While (" + conditionId + "): (B" + bodyBlock.id + ") then (B" + exitBlock.id + ")");
 }
 HInstructionStringifier.prototype.visitModulo = function(node) {
@@ -10879,18 +11269,18 @@ HInstructionStringifier.prototype.visitNegate = function(node) {
 }
 HInstructionStringifier.prototype.visitNot = function(node) {
   var $0;
-  return ("Not: " + this.temporaryId((($0 = node.inputs.$index(0)) && $0.is$HInstruction())));
+  return ("Not: " + this.temporaryId((($0 = node.inputs.$index(0)) == null ? null : $0.assert$HInstruction())));
 }
 HInstructionStringifier.prototype.visitParameterValue = function(node) {
   return ("p" + node.element.name);
 }
 HInstructionStringifier.prototype.visitPhi = function(phi) {
   var $0;
-  return ("Phi(" + this.temporaryId((($0 = phi.inputs.$index(0)) && $0.is$HInstruction())) + ", " + this.temporaryId((($0 = phi.inputs.$index(1)) && $0.is$HInstruction())) + ")");
+  return ("Phi(" + this.temporaryId((($0 = phi.inputs.$index(0)) == null ? null : $0.assert$HInstruction())) + ", " + this.temporaryId((($0 = phi.inputs.$index(1)) == null ? null : $0.assert$HInstruction())) + ")");
 }
 HInstructionStringifier.prototype.visitReturn = function(node) {
   var $0;
-  return ("Return " + this.temporaryId((($0 = node.inputs.$index(0)) && $0.is$HInstruction())));
+  return ("Return " + this.temporaryId((($0 = node.inputs.$index(0)) == null ? null : $0.assert$HInstruction())));
 }
 HInstructionStringifier.prototype.visitShiftLeft = function(node) {
   return this.visitInvoke(node);
@@ -10900,8 +11290,8 @@ HInstructionStringifier.prototype.visitShiftRight = function(node) {
 }
 HInstructionStringifier.prototype.visitStore = function(node) {
   var $0;
-  var localId = this.temporaryId((($0 = node.inputs.$index(0)) && $0.is$HInstruction()));
-  var valueId = this.temporaryId((($0 = node.inputs.$index(1)) && $0.is$HInstruction()));
+  var localId = this.temporaryId((($0 = node.inputs.$index(0)) == null ? null : $0.assert$HInstruction()));
+  var valueId = this.temporaryId((($0 = node.inputs.$index(1)) == null ? null : $0.assert$HInstruction()));
   return ("Store: " + localId + " := " + valueId);
 }
 HInstructionStringifier.prototype.visitSubtract = function(node) {
@@ -10909,7 +11299,7 @@ HInstructionStringifier.prototype.visitSubtract = function(node) {
 }
 HInstructionStringifier.prototype.visitThrow = function(node) {
   var $0;
-  return ("Throw " + this.temporaryId((($0 = node.inputs.$index(0)) && $0.is$HInstruction())));
+  return ("Throw " + this.temporaryId((($0 = node.inputs.$index(0)) == null ? null : $0.assert$HInstruction())));
 }
 HInstructionStringifier.prototype.visitTruncatingDivide = function(node) {
   return this.visitInvoke(node);
@@ -10933,10 +11323,10 @@ HInstructionStringifier.prototype.visitTypeGuard = function(node) {
       unreachable();
 
   }
-  return ("TypeGuard: " + this.temporaryId((($0 = node.inputs.$index(0)) && $0.is$HInstruction())) + " is " + type);
+  return ("TypeGuard: " + this.temporaryId((($0 = node.inputs.$index(0)) == null ? null : $0.assert$HInstruction())) + " is " + type);
 }
 HInstructionStringifier.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$HInstruction()));
+  return this.visit(($0 == null ? null : $0.assert$HInstruction()));
 };
 // ********** Code for HValidator **************
 function HValidator() {
@@ -11041,13 +11431,13 @@ HValidator.prototype.visitInstruction = function(instruction) {
   function hasCorrectInputs(instruction) {
     var $0;
     var inBasicBlock = $assert_bool(instruction.isInBasicBlock$0());
-    return HValidator.everyInstruction((($0 = instruction.get$inputs()) && $0.is$List_HInstruction()), (function (input, count) {
+    return HValidator.everyInstruction((($0 = instruction.get$inputs()) == null ? null : $0.assert$List_HInstruction()), (function (input, count) {
       var $0;
       if ($notnull_bool(inBasicBlock)) {
-        return HValidator.countInstruction((($0 = input.get$usedBy()) && $0.is$List_HInstruction()), (instruction && instruction.is$HInstruction())) == count;
+        return HValidator.countInstruction((($0 = input.get$usedBy()) == null ? null : $0.assert$List_HInstruction()), (instruction == null ? null : instruction.assert$HInstruction())) == count;
       }
       else {
-        return HValidator.countInstruction((($0 = input.get$usedBy()) && $0.is$List_HInstruction()), (instruction && instruction.is$HInstruction())) == 0;
+        return HValidator.countInstruction((($0 = input.get$usedBy()) == null ? null : $0.assert$List_HInstruction()), (instruction == null ? null : instruction.assert$HInstruction())) == 0;
       }
     })
     );
@@ -11055,9 +11445,9 @@ HValidator.prototype.visitInstruction = function(instruction) {
   function hasCorrectUses(instruction) {
     var $0;
     if (!$notnull_bool(instruction.isInBasicBlock$0())) return true;
-    return HValidator.everyInstruction((($0 = instruction.get$usedBy()) && $0.is$List_HInstruction()), (function (use, count) {
+    return HValidator.everyInstruction((($0 = instruction.get$usedBy()) == null ? null : $0.assert$List_HInstruction()), (function (use, count) {
       var $0;
-      return HValidator.countInstruction((($0 = use.get$inputs()) && $0.is$List_HInstruction()), (instruction && instruction.is$HInstruction())) == count;
+      return HValidator.countInstruction((($0 = use.get$inputs()) == null ? null : $0.assert$List_HInstruction()), (instruction == null ? null : instruction.assert$HInstruction())) == count;
     })
     );
   }
@@ -11092,7 +11482,7 @@ ValueSet.prototype.add = function(instruction) {
 ValueSet.prototype.lookup = function(instruction) {
   var $0;
   var index = this.tableIndexForInstruction(instruction);
-  for (var node = (($0 = this.table.$index(index)) && $0.is$ValueSetNode());
+  for (var node = (($0 = this.table.$index(index)) == null ? null : $0.assert$ValueSetNode());
    node != null; node = node.next) {
     var cached = node.value;
     if ($notnull_bool(cached.equals(instruction))) return cached;
@@ -11105,7 +11495,7 @@ ValueSet.prototype.kill = function(flags) {
   for (var i = 0, length = this.table.length;
    i < length; i++) {
     var previous = null;
-    var current = (($0 = this.table.$index(i)) && $0.is$ValueSetNode());
+    var current = (($0 = this.table.$index(i)) == null ? null : $0.assert$ValueSetNode());
     while (current != null) {
       var next = current.next;
       var cached = current.value;
@@ -11130,7 +11520,7 @@ ValueSet.prototype.copy = function() {
   var result = new ValueSet();
   for (var i = 0, length = this.table.length;
    i < length; i++) {
-    var current = (($0 = this.table.$index(i)) && $0.is$ValueSetNode());
+    var current = (($0 = this.table.$index(i)) == null ? null : $0.assert$ValueSetNode());
     while (current != null) {
       result.add(current.value);
       current = current.next;
@@ -11142,11 +11532,11 @@ ValueSet.prototype.tableIndexForInstruction = function(instruction) {
   return 0;
 }
 ValueSet.prototype.add$1 = function($0) {
-  return this.add(($0 && $0.is$HInstruction()));
+  return this.add(($0 == null ? null : $0.assert$HInstruction()));
 };
 ValueSet.prototype.isEmpty$0 = ValueSet.prototype.isEmpty;
 ValueSet.prototype.lookup$1 = function($0) {
-  return this.lookup(($0 && $0.is$HInstruction()));
+  return this.lookup(($0 == null ? null : $0.assert$HInstruction()));
 };
 // ********** Code for ValueSetNode **************
 function ValueSetNode(value, next) {
@@ -11154,7 +11544,7 @@ function ValueSetNode(value, next) {
   this.next = next;
   // Initializers done
 }
-ValueSetNode.prototype.is$ValueSetNode = function(){return this;};
+ValueSetNode.prototype.assert$ValueSetNode = function(){return this};
 ValueSetNode.prototype.get$value = function() { return this.value; };
 ValueSetNode.prototype.next$0 = function() {
   return this.next();
@@ -11176,7 +11566,7 @@ function Compiler(script) {
   this.generator = new SsaCodeGeneratorTask(this);
   this.tasks = [this.scanner, this.parser, this.resolver, this.checker, this.builder, this.optimizer, this.generator];
 }
-Compiler.prototype.is$Compiler = function(){return this;};
+Compiler.prototype.assert$Compiler = function(){return this};
 Compiler.prototype.get$generator = function() { return this.generator; };
 Compiler.prototype.set$generator = function(value) { return this.generator = value; };
 Compiler.prototype.ensure = function(condition) {
@@ -11223,33 +11613,33 @@ Compiler.prototype.runCompiler = function() {
   if (element == null) this.cancel(('Could not find ' + const$221/*Compiler.MAIN*/));
   this.compileMethod(element);
   while (!this.worklist.isEmpty()) {
-    this.compileMethod((($0 = this.worklist.removeLast()) && $0.is$Element()));
+    this.compileMethod((($0 = this.worklist.removeLast()) == null ? null : $0.assert$Element()));
   }
 }
 Compiler.prototype.compileMethod = function(element) {
   var code = $assert_String(this.universe.generatedCode.$index(element));
   if (code != null) return code;
   var tree = this.parser.parse(element);
-  var elements = this.resolver.resolve((tree && tree.is$FunctionExpression()));
+  var elements = this.resolver.resolve((tree == null ? null : tree.assert$FunctionExpression()));
   this.checker.check(tree, elements);
   var graph = this.builder.build(tree, elements);
   this.optimizer.optimize(graph);
-  code = this.generator.generate((element && element.is$FunctionElement()), graph);
+  code = this.generator.generate((element == null ? null : element.assert$FunctionElement()), graph);
   this.universe.addGeneratedCode(element, code);
   return code;
 }
 Compiler.prototype.resolveType = function(element) {
   var $0;
-  this.resolver.resolveType((($0 = this.parser.parse(element)) && $0.is$ClassNode()));
+  this.resolver.resolveType((($0 = this.parser.parse(element)) == null ? null : $0.assert$ClassNode()));
 }
 Compiler.prototype.resolveSignature = function(element) {
   var $0;
-  this.resolver.resolveSignature((($0 = this.parser.parse(element)) && $0.is$FunctionExpression()));
+  this.resolver.resolveSignature((($0 = this.parser.parse(element)) == null ? null : $0.assert$FunctionExpression()));
 }
 Compiler.prototype.getGeneratedCode = function() {
   var $0;
   var buffer = new StringBufferImpl("");
-  var codeBlocks = (($0 = this.universe.generatedCode.getValues()) && $0.is$List_String());
+  var codeBlocks = (($0 = this.universe.generatedCode.getValues()) == null ? null : $0.assert$List_String());
   for (var i = codeBlocks.length - 1;
    i >= 0; i--) {
     buffer.add(codeBlocks.$index(i));
@@ -11317,7 +11707,7 @@ ResolverTask.prototype.resolve = function(tree) {
     }
     return visitor.mapping;
   })
-  )) && $0.is$Map_Node$Element());
+  )) == null ? null : $0.assert$Map_Node$Element());
 }
 ResolverTask.prototype.resolveType = function(tree) {
   var $this = this; // closure support
@@ -11336,7 +11726,7 @@ ResolverTask.prototype.resolveSignature = function(node) {
   );
 }
 ResolverTask.prototype.resolve$1 = function($0) {
-  return this.resolve(($0 && $0.is$FunctionExpression()));
+  return this.resolve(($0 == null ? null : $0.assert$FunctionExpression()));
 };
 // ********** Code for ResolverVisitor **************
 function ResolverVisitor(compiler) {
@@ -11352,13 +11742,13 @@ ResolverVisitor.from$ctor = function(other) {
   // Initializers done
 }
 ResolverVisitor.from$ctor.prototype = ResolverVisitor.prototype;
-ResolverVisitor.prototype.is$Visitor = function(){return this;};
+ResolverVisitor.prototype.assert$Visitor = function(){return this};
 ResolverVisitor.prototype.error = function(node, kind, arguments) {
-  var error = new ResolutionError(kind, (arguments && arguments.is$List_Type()));
+  var error = new ResolutionError(kind, (arguments == null ? null : arguments.assert$List_Type()));
   this.compiler.cancel(error.toString());
 }
 ResolverVisitor.prototype.warning = function(node, kind, arguments) {
-  var warning = new ResolutionWarning(kind, (arguments && arguments.is$List_Type()));
+  var warning = new ResolutionWarning(kind, (arguments == null ? null : arguments.assert$List_Type()));
   this.compiler.reportWarning(node, warning);
 }
 ResolverVisitor.prototype.cancel = function(node, message) {
@@ -11387,7 +11777,7 @@ ResolverVisitor.prototype.visitTypeAnnotation = function(node) {
     this.warning(node, const$230/*MessageKind.NOT_A_TYPE*/, [name]);
   }
   else {
-    var cls = (element && element.is$ClassElement());
+    var cls = (element == null ? null : element.assert$ClassElement());
     this.compiler.resolver.toResolve.add(element);
   }
   return this.useElement(node, element);
@@ -11407,7 +11797,7 @@ ResolverVisitor.prototype.useElement = function(node, element) {
   return element;
 }
 ResolverVisitor.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$Node()));
+  return this.visit(($0 == null ? null : $0.assert$Node()));
 };
 // ********** Code for SignatureResolverVisitor **************
 function SignatureResolverVisitor(compiler) {
@@ -11417,19 +11807,19 @@ function SignatureResolverVisitor(compiler) {
 $inherits(SignatureResolverVisitor, ResolverVisitor);
 SignatureResolverVisitor.prototype.visitFunctionExpression = function(node) {
   var $0;
-  var enclosingElement = (($0 = this.context.lookup((($0 = node.name.get$dynamic().get$source()) && $0.is$SourceString()))) && $0.is$FunctionElement());
+  var enclosingElement = (($0 = this.context.lookup((($0 = node.name.get$dynamic().get$source()) == null ? null : $0.assert$SourceString()))) == null ? null : $0.assert$FunctionElement());
   this.useElement(node, enclosingElement);
   this.context = new Scope.enclosing$ctor(this.context, enclosingElement);
   if (enclosingElement.parameters == null) {
     var visitor = new ParametersVisitor(this);
     visitor.visit(node.parameters);
-    enclosingElement.parameters = (($0 = visitor.elements.toLink()) && $0.is$Link_Element());
+    enclosingElement.parameters = (($0 = visitor.elements.toLink()) == null ? null : $0.assert$Link_Element());
   }
   else {
     var parameterNodes = node.parameters.get$nodes();
     for (var link = enclosingElement.parameters;
-     !$notnull_bool(link.isEmpty()) && !$notnull_bool(parameterNodes.isEmpty()); link = (($0 = link.get$tail()) && $0.is$Link_Element()), parameterNodes = (($0 = parameterNodes.get$tail()) && $0.is$Link_Node())) {
-      this.defineElement((($0 = parameterNodes.get$head().get$definitions().get$nodes().get$head()) && $0.is$Node()), (($0 = link.get$head()) && $0.is$Element()));
+     !$notnull_bool(link.isEmpty()) && !$notnull_bool(parameterNodes.isEmpty()); link = (($0 = link.get$tail()) == null ? null : $0.assert$Link_Element()), parameterNodes = (($0 = parameterNodes.get$tail()) == null ? null : $0.assert$Link_Node())) {
+      this.defineElement((($0 = parameterNodes.get$head().get$definitions().get$nodes().get$head()) == null ? null : $0.assert$Node()), (($0 = link.get$head()) == null ? null : $0.assert$Element()));
     }
   }
   return enclosingElement;
@@ -11448,7 +11838,7 @@ FullResolverVisitor.prototype.visitClassNode = function(node) {
 FullResolverVisitor.prototype.visitIn = function(node, scope) {
   var $0;
   this.context = scope;
-  var element = (($0 = this.visit(node)) && $0.is$Element());
+  var element = (($0 = this.visit(node)) == null ? null : $0.assert$Element());
   this.context = this.context.parent;
   return element;
 }
@@ -11477,7 +11867,7 @@ FullResolverVisitor.prototype.visitFunctionExpression = function(node) {
   this.context = new Scope.enclosing$ctor(this.context, enclosingElement);
   var visitor = new ParametersVisitor(this);
   visitor.visit(node.parameters);
-  enclosingElement.parameters = (($0 = visitor.elements.toLink()) && $0.is$Link_Element());
+  enclosingElement.parameters = (($0 = visitor.elements.toLink()) == null ? null : $0.assert$Link_Element());
   this.visit(node.body);
   this.context = this.context.parent;
   return enclosingElement;
@@ -11531,7 +11921,7 @@ FullResolverVisitor.prototype.mapAssignmentOperatorToMethodName = function(name)
 FullResolverVisitor.prototype.visitSend = function(node) {
   var $0;
   this.visit(node.receiver);
-  var identifier = (($0 = node.selector) && $0.is$Identifier());
+  var identifier = (($0 = node.selector) == null ? null : $0.assert$Identifier());
   if (node.receiver != null && !(identifier instanceof Operator)) {
     this.cancel(node, 'Cannot handle qualified method calls');
   }
@@ -11545,8 +11935,8 @@ FullResolverVisitor.prototype.visitSend = function(node) {
 }
 FullResolverVisitor.prototype.visitSendSet = function(node) {
   var $0;
-  var receiver = (($0 = this.visit(node.receiver)) && $0.is$Element());
-  var selector = (($0 = node.selector) && $0.is$Identifier());
+  var receiver = (($0 = this.visit(node.receiver)) == null ? null : $0.assert$Element());
+  var selector = (($0 = node.selector) == null ? null : $0.assert$Identifier());
   if (receiver != null) {
     this.compiler.unimplemented('Resolver: property access');
   }
@@ -11583,8 +11973,8 @@ FullResolverVisitor.prototype.visitLiteralNull = function(node) {
 FullResolverVisitor.prototype.visitNodeList = function(node) {
   var $0;
   for (var link = node.get$nodes();
-   !$notnull_bool(link.isEmpty()); link = (($0 = link.get$tail()) && $0.is$Link_Node())) {
-    this.visit((($0 = link.get$head()) && $0.is$Node()));
+   !$notnull_bool(link.isEmpty()); link = (($0 = link.get$tail()) == null ? null : $0.assert$Link_Node())) {
+    this.visit((($0 = link.get$head()) == null ? null : $0.assert$Node()));
   }
 }
 FullResolverVisitor.prototype.visitOperator = function(node) {
@@ -11618,13 +12008,13 @@ function ClassResolverVisitor(compiler) {
 $inherits(ClassResolverVisitor, AbstractVisitor_Type);
 ClassResolverVisitor.prototype.visitClassNode = function(node) {
   var $0;
-  var element = (($0 = this.context.lookup(node.name.get$source())) && $0.is$ClassElement());
+  var element = (($0 = this.context.lookup(node.name.get$source())) == null ? null : $0.assert$ClassElement());
   this.compiler.ensure(element != null);
   this.compiler.ensure(!$notnull_bool(element.isResolved));
   element.supertype = this.visit(node.superclass);
   for (var link = node.interfaces.get$nodes();
-   !$notnull_bool(link.isEmpty()); link = (($0 = link.get$tail()) && $0.is$Link_Node())) {
-    element.interfaces = (($0 = element.interfaces.prepend(this.visit((($0 = link.get$head()) && $0.is$Node())))) && $0.is$Link_Type());
+   !$notnull_bool(link.isEmpty()); link = (($0 = link.get$tail()) == null ? null : $0.assert$Link_Node())) {
+    element.interfaces = (($0 = element.interfaces.prepend(this.visit((($0 = link.get$head()) == null ? null : $0.assert$Node())))) == null ? null : $0.assert$Link_Type());
   }
   return element.computeType(this.compiler, null);
 }
@@ -11640,20 +12030,20 @@ ClassResolverVisitor.prototype.visitTypeAnnotation = function(node) {
   }
   else {
     this.compiler.resolver.toResolve.add(element);
-    return (($0 = element.computeType(this.compiler, null)) && $0.is$Type());
+    return (($0 = element.computeType(this.compiler, null)) == null ? null : $0.assert$Type());
   }
   return null;
 }
 ClassResolverVisitor.prototype.visit = function(node) {
   var $0;
   if (node == null) return null;
-  return (($0 = node.accept(this)) && $0.is$Type());
+  return (($0 = node.accept(this)) == null ? null : $0.assert$Type());
 }
 ClassResolverVisitor.prototype.visitNode = function(node) {
   this.compiler.cancel('internal error');
 }
 ClassResolverVisitor.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$Node()));
+  return this.visit(($0 == null ? null : $0.assert$Node()));
 };
 // ********** Code for VariableDefinitionsVisitor **************
 function VariableDefinitionsVisitor(definitions, resolver, kind) {
@@ -11674,9 +12064,9 @@ VariableDefinitionsVisitor.prototype.visitSendSet = function(node) {
   if (node.receiver != null) {
     this.resolver.cancel(node, "receiver on a variable definition not implemented");
   }
-  var selector = (($0 = node.selector) && $0.is$Identifier());
-  this.resolver.visit((($0 = node.get$arguments().get$head()) && $0.is$Node()));
-  return (($0 = this.visit(node.selector)) && $0.is$SourceString());
+  var selector = (($0 = node.selector) == null ? null : $0.assert$Identifier());
+  this.resolver.visit((($0 = node.get$arguments().get$head()) == null ? null : $0.assert$Node()));
+  return (($0 = this.visit(node.selector)) == null ? null : $0.assert$SourceString());
 }
 VariableDefinitionsVisitor.prototype.visitIdentifier = function(node) {
   return node.get$source();
@@ -11684,17 +12074,17 @@ VariableDefinitionsVisitor.prototype.visitIdentifier = function(node) {
 VariableDefinitionsVisitor.prototype.visitNodeList = function(node) {
   var $0;
   for (var link = node.get$nodes();
-   !$notnull_bool(link.isEmpty()); link = (($0 = link.get$tail()) && $0.is$Link_Node())) {
-    var name = (($0 = this.visit((($0 = link.get$head()) && $0.is$Node()))) && $0.is$SourceString());
-    var element = new VariableElement((($0 = link.get$head()) && $0.is$Node()), this.definitions.type, this.kind, name, this.resolver.context.enclosingElement);
-    this.resolver.defineElement((($0 = link.get$head()) && $0.is$Node()), element);
+   !$notnull_bool(link.isEmpty()); link = (($0 = link.get$tail()) == null ? null : $0.assert$Link_Node())) {
+    var name = (($0 = this.visit((($0 = link.get$head()) == null ? null : $0.assert$Node()))) == null ? null : $0.assert$SourceString());
+    var element = new VariableElement((($0 = link.get$head()) == null ? null : $0.assert$Node()), this.definitions.type, this.kind, name, this.resolver.context.enclosingElement);
+    this.resolver.defineElement((($0 = link.get$head()) == null ? null : $0.assert$Node()), element);
   }
 }
 VariableDefinitionsVisitor.prototype.visit = function(node) {
   return node.accept(this);
 }
 VariableDefinitionsVisitor.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$Node()));
+  return this.visit(($0 == null ? null : $0.assert$Node()));
 };
 // ********** Code for ParametersVisitor **************
 function ParametersVisitor(resolver) {
@@ -11707,8 +12097,8 @@ $inherits(ParametersVisitor, AbstractVisitor_Element);
 ParametersVisitor.prototype.visitNodeList = function(node) {
   var $0;
   for (var link = node.get$nodes();
-   !$notnull_bool(link.isEmpty()); link = (($0 = link.get$tail()) && $0.is$Link_Node())) {
-    this.elements.addLast(this.visit((($0 = link.get$head()) && $0.is$Node())));
+   !$notnull_bool(link.isEmpty()); link = (($0 = link.get$tail()) == null ? null : $0.assert$Link_Node())) {
+    this.elements.addLast(this.visit((($0 = link.get$head()) == null ? null : $0.assert$Node())));
   }
 }
 ParametersVisitor.prototype.visitVariableDefinitions = function(node) {
@@ -11721,7 +12111,7 @@ ParametersVisitor.prototype.visit = function(node) {
   return node.accept(this);
 }
 ParametersVisitor.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$Node()));
+  return this.visit(($0 == null ? null : $0.assert$Node()));
 };
 // ********** Code for Scope **************
 function Scope(parent) {
@@ -11746,21 +12136,21 @@ Scope.prototype.get$parent = function() { return this.parent; };
 Scope.prototype.get$enclosingElement = function() { return this.enclosingElement; };
 Scope.prototype.lookup = function(name) {
   var $0;
-  var element = (($0 = this.elements.$index(name)) && $0.is$Element());
+  var element = (($0 = this.elements.$index(name)) == null ? null : $0.assert$Element());
   if (element != null) return element;
   return this.parent.lookup(name);
 }
 Scope.prototype.add = function(element) {
   var $0;
-  if (this.elements.containsKey(element.name)) return (($0 = this.elements.$index(element.name)) && $0.is$Element());
+  if (this.elements.containsKey(element.name)) return (($0 = this.elements.$index(element.name)) == null ? null : $0.assert$Element());
   this.elements.$setindex(element.name, element);
   return element;
 }
 Scope.prototype.add$1 = function($0) {
-  return this.add(($0 && $0.is$Element()));
+  return this.add(($0 == null ? null : $0.assert$Element()));
 };
 Scope.prototype.lookup$1 = function($0) {
-  return this.lookup(($0 && $0.is$SourceString()));
+  return this.lookup(($0 == null ? null : $0.assert$SourceString()));
 };
 // ********** Code for TopScope **************
 function TopScope(universe) {
@@ -11776,10 +12166,10 @@ TopScope.prototype.add = function(element) {
   $throw("Cannot add an element in the top scope");
 }
 TopScope.prototype.add$1 = function($0) {
-  return this.add(($0 && $0.is$Element()));
+  return this.add(($0 == null ? null : $0.assert$Element()));
 };
 TopScope.prototype.lookup$1 = function($0) {
-  return this.lookup(($0 && $0.is$SourceString()));
+  return this.lookup(($0 == null ? null : $0.assert$SourceString()));
 };
 // ********** Code for leg_Script **************
 function leg_Script(file) {
@@ -11828,7 +12218,7 @@ SimpleType.named$ctor = function(name) {
   // Initializers done
 }
 SimpleType.named$ctor.prototype = SimpleType.prototype;
-SimpleType.prototype.is$Type = function(){return this;};
+SimpleType.prototype.assert$Type = function(){return this};
 SimpleType.prototype.get$name = function() { return this.name; };
 SimpleType.prototype.get$element = function() { return this.element; };
 SimpleType.prototype.toString = function() {
@@ -11841,8 +12231,8 @@ function FunctionType(returnType, parameterTypes) {
   this.parameterTypes = parameterTypes;
   // Initializers done
 }
-FunctionType.prototype.is$FunctionType = function(){return this;};
-FunctionType.prototype.is$Type = function(){return this;};
+FunctionType.prototype.assert$FunctionType = function(){return this};
+FunctionType.prototype.assert$Type = function(){return this};
 FunctionType.prototype.get$returnType = function() { return this.returnType; };
 FunctionType.prototype.toString = function() {
   var sb = new StringBufferImpl("");
@@ -11864,7 +12254,7 @@ function Types() {
   this.objectType = new SimpleType.named$ctor(const$18/*Types.OBJECT*/);
   // Initializers done
 }
-Types.prototype.is$Types = function(){return this;};
+Types.prototype.assert$Types = function(){return this};
 Types.prototype.get$dynamicType = function() { return this.dynamicType; };
 Types.prototype.lookup = function(s) {
   if ($notnull_bool($eq(const$6/*Types.VOID*/, s))) {
@@ -11897,7 +12287,7 @@ Types.prototype.isAssignable = function(r, s) {
   return $notnull_bool(this.isSubtype(r, s)) || $notnull_bool(this.isSubtype(s, r));
 }
 Types.prototype.lookup$1 = function($0) {
-  return this.lookup(($0 && $0.is$SourceString()));
+  return this.lookup(($0 == null ? null : $0.assert$SourceString()));
 };
 // ********** Code for CancelTypeCheckException **************
 function CancelTypeCheckException(node, reason) {
@@ -11912,7 +12302,7 @@ function TypeCheckerVisitor(compiler, elements, types) {
   this.types = types;
   // Initializers done
 }
-TypeCheckerVisitor.prototype.is$Visitor = function(){return this;};
+TypeCheckerVisitor.prototype.assert$Visitor = function(){return this};
 TypeCheckerVisitor.prototype.get$types = function() { return this.types; };
 TypeCheckerVisitor.prototype.set$types = function(value) { return this.types = value; };
 TypeCheckerVisitor.prototype.fail = function(node, reason) {
@@ -11938,7 +12328,7 @@ TypeCheckerVisitor.prototype.typeWithDefault = function(node, defaultValue) {
 TypeCheckerVisitor.prototype.type = function(node) {
   var $0;
   if (node == null) this.fail(null, 'unexpected node: null');
-  var result = (($0 = node.accept(this)) && $0.is$Type());
+  var result = (($0 = node.accept(this)) == null ? null : $0.assert$Type());
   return result;
 }
 TypeCheckerVisitor.prototype.get$type = function() {
@@ -11978,7 +12368,7 @@ TypeCheckerVisitor.prototype.visitFor = function(node) {
 TypeCheckerVisitor.prototype.visitFunctionExpression = function(node) {
   var $0;
   var element = this.elements.$index(node);
-  var functionType = (($0 = element.computeType$2(this.compiler, this.types)) && $0.is$FunctionType());
+  var functionType = (($0 = element.computeType$2(this.compiler, this.types)) == null ? null : $0.assert$FunctionType());
   var returnType = functionType.returnType;
   var previous = this.expectedReturnType;
   this.expectedReturnType = returnType;
@@ -11998,12 +12388,12 @@ TypeCheckerVisitor.prototype.visitIf = function(node) {
 TypeCheckerVisitor.prototype.visitSend = function(node) {
   var $0;
   var target = this.elements.$index(node);
-  var selector = (($0 = node.selector) && $0.is$Identifier());
+  var selector = (($0 = node.selector) == null ? null : $0.assert$Identifier());
   var name = selector.get$source().get$stringValue();
   if (target != null) {
     if (selector.asOperator() != null) {
       this.type(node.receiver);
-      if (node.get$arguments().get$head() != null) this.type((($0 = node.get$arguments().get$head()) && $0.is$Node()));
+      if (node.get$arguments().get$head() != null) this.type((($0 = node.get$arguments().get$head()) == null ? null : $0.assert$Node()));
       if (name === '+' || name === '=' || name === '-' || name === '*' || name === '/' || name === '%' || name === '~/' || name === '|' || name === '&' || name === '^' || name === '~' || name === '<<' || name === '>>') {
         return this.types.dynamicType;
       }
@@ -12016,7 +12406,7 @@ TypeCheckerVisitor.prototype.visitSend = function(node) {
     }
     var targetType = target.computeType$2(this.compiler, this.types);
     if ($notnull_bool(node.get$isPropertyAccess())) {
-      return (targetType && targetType.is$Type());
+      return (targetType == null ? null : targetType.assert$Type());
     }
     else if ($notnull_bool(node.get$isFunctionObjectInvocation())) {
       this.fail(node);
@@ -12028,15 +12418,15 @@ TypeCheckerVisitor.prototype.visitSend = function(node) {
         }
         this.fail(node, 'can only handle function types');
       }
-      var funType = (targetType && targetType.is$FunctionType());
+      var funType = (targetType == null ? null : targetType.assert$FunctionType());
       var formals = funType.parameterTypes;
       var arguments = node.get$arguments();
       while ((!$notnull_bool(formals.isEmpty())) && (!$notnull_bool(arguments.isEmpty()))) {
-        var argument = (($0 = arguments.get$head()) && $0.is$Node());
+        var argument = (($0 = arguments.get$head()) == null ? null : $0.assert$Node());
         var argumentType = this.type(argument);
-        this.checkAssignable(argument, (($0 = formals.get$head()) && $0.is$Type()), argumentType);
-        formals = (($0 = formals.get$tail()) && $0.is$Link_Type());
-        arguments = (($0 = arguments.get$tail()) && $0.is$Link_Node());
+        this.checkAssignable(argument, (($0 = formals.get$head()) == null ? null : $0.assert$Type()), argumentType);
+        formals = (($0 = formals.get$tail()) == null ? null : $0.assert$Link_Type());
+        arguments = (($0 = arguments.get$tail()) == null ? null : $0.assert$Link_Node());
       }
       if (!$notnull_bool(formals.isEmpty())) {
         this.reportTypeWarning(node, const$264/*MessageKind.MISSING_ARGUMENT*/, const$21/*const []*/);
@@ -12053,7 +12443,7 @@ TypeCheckerVisitor.prototype.visitSend = function(node) {
       var firstArgument = node.receiver;
       this.checkAssignable(firstArgument, this.types.boolType, this.type(firstArgument));
       if (!$notnull_bool(arguments.isEmpty())) {
-        var secondArgument = (($0 = arguments.get$head()) && $0.is$Node());
+        var secondArgument = (($0 = arguments.get$head()) == null ? null : $0.assert$Node());
         this.checkAssignable(secondArgument, this.types.boolType, this.type(secondArgument));
       }
       return this.types.boolType;
@@ -12064,18 +12454,18 @@ TypeCheckerVisitor.prototype.visitSend = function(node) {
 TypeCheckerVisitor.prototype.visitSendSet = function(node) {
   var $0;
   this.compiler.ensure(node.get$arguments() != null);
-  var selector = (($0 = node.selector) && $0.is$Identifier());
+  var selector = (($0 = node.selector) == null ? null : $0.assert$Identifier());
   var name = node.assignmentOperator.get$source().get$stringValue();
   if (name === '++' || name === '--') {
     this.compiler.ensure((node.selector instanceof Identifier));
-    var element = (($0 = this.elements.$index(node.selector)) && $0.is$Element());
-    var receiverType = (($0 = element.computeType(this.compiler, this.types)) && $0.is$Type());
+    var element = (($0 = this.elements.$index(node.selector)) == null ? null : $0.assert$Element());
+    var receiverType = (($0 = element.computeType(this.compiler, this.types)) == null ? null : $0.assert$Type());
     return $notnull_bool(node.get$isPrefix()) ? this.types.intType : receiverType;
   }
   else {
     this.compiler.ensure(!$notnull_bool(node.get$arguments().isEmpty()));
-    var targetType = (($0 = this.elements.$index(node).computeType$2(this.compiler, this.types)) && $0.is$Type());
-    var value = (($0 = node.get$arguments().get$head()) && $0.is$Node());
+    var targetType = (($0 = this.elements.$index(node).computeType$2(this.compiler, this.types)) == null ? null : $0.assert$Type());
+    var value = (($0 = node.get$arguments().get$head()) == null ? null : $0.assert$Node());
     this.checkAssignable(value, targetType, this.type(value));
     return targetType;
   }
@@ -12098,8 +12488,8 @@ TypeCheckerVisitor.prototype.visitLiteralNull = function(node) {
 TypeCheckerVisitor.prototype.visitNodeList = function(node) {
   var $0;
   for (var link = node.get$nodes();
-   !$notnull_bool(link.isEmpty()); link = (($0 = link.get$tail()) && $0.is$Link_Node())) {
-    this.type((($0 = link.get$head()) && $0.is$Node()));
+   !$notnull_bool(link.isEmpty()); link = (($0 = link.get$tail()) == null ? null : $0.assert$Link_Node())) {
+    this.type((($0 = link.get$head()) == null ? null : $0.assert$Node()));
   }
   return null;
 }
@@ -12131,7 +12521,7 @@ TypeCheckerVisitor.prototype.visitTypeAnnotation = function(node) {
   var $0;
   if (node.typeName == null) return this.types.dynamicType;
   var name = node.typeName.get$source();
-  var type = (($0 = this.elements.$index(node)) && $0.is$Type());
+  var type = (($0 = this.elements.$index(node)) == null ? null : $0.assert$Type());
   if (type == null) type = this.types.lookup(name);
   if (type == null) {
     return this.types.dynamicType;
@@ -12146,11 +12536,11 @@ TypeCheckerVisitor.prototype.visitVariableDefinitions = function(node) {
     type = this.types.dynamicType;
   }
   for (var link = node.definitions.get$nodes();
-   !$notnull_bool(link.isEmpty()); link = (($0 = link.get$tail()) && $0.is$Link_Node())) {
-    var initialization = (($0 = link.get$head()) && $0.is$Node());
+   !$notnull_bool(link.isEmpty()); link = (($0 = link.get$tail()) == null ? null : $0.assert$Link_Node())) {
+    var initialization = (($0 = link.get$head()) == null ? null : $0.assert$Node());
     this.compiler.ensure((initialization instanceof Identifier) || (initialization instanceof Send));
     if ((initialization instanceof Send)) {
-      var initializer = this.nonVoidType((($0 = link.get$head()) && $0.is$Node()));
+      var initializer = this.nonVoidType((($0 = link.get$head()) == null ? null : $0.assert$Node()));
       this.checkAssignable(node, type, initializer);
     }
   }
@@ -12172,7 +12562,7 @@ function Universe() {
 }
 Universe.prototype.find = function(name) {
   var $0;
-  return (($0 = this.elements.$index(name)) && $0.is$Element());
+  return (($0 = this.elements.$index(name)) == null ? null : $0.assert$Element());
 }
 Universe.prototype.define = function(element) {
   $assert(this.elements.$index(element.name) == null, "elements[element.name] == null", "universe.dart", 20, 12);
@@ -12282,7 +12672,7 @@ WorldCompiler.prototype.spanFromNode = function(node) {
 }
 WorldCompiler.prototype.reportWarning = function(node, message) {
   var $0;
-  this.world.warning(('' + message + '.'), (($0 = this.spanFromNode(node)) && $0.is$SourceSpan()));
+  this.world.warning(('' + message + '.'), (($0 = this.spanFromNode(node)) == null ? null : $0.assert$SourceSpan()));
 }
 WorldCompiler.prototype.readScript = function(filename) {
   var text = $globals.world.files.readAll(filename);
@@ -12302,7 +12692,7 @@ WorldCompiler.prototype.cancel = function(reason, node, token, instruction) {
     var end = begin + tokenString.length;
     print(this.script.file.getLocationMessage$4(("cancel leg: " + reason), begin, end, true));
   }
-  Compiler.prototype.cancel.call(this, reason, node, (token && token.is$Token()), (instruction && instruction.is$HInstruction()));
+  Compiler.prototype.cancel.call(this, reason, node, (token == null ? null : token.assert$Token()), (instruction == null ? null : instruction.assert$HInstruction()));
 }
 // ********** Code for top level **************
 function compile(world) {
@@ -12320,7 +12710,7 @@ function CodeWriter() {
   this._buf = new StringBufferImpl("");
   // Initializers done
 }
-CodeWriter.prototype.is$CodeWriter = function(){return this;};
+CodeWriter.prototype.assert$CodeWriter = function(){return this};
 CodeWriter.prototype.get$text = function() {
   return this._buf.toString();
 }
@@ -12373,10 +12763,8 @@ CodeWriter.prototype.nextBlock = function(text) {
 }
 // ********** Code for CoreJs **************
 function CoreJs() {
-  this.useTypeNameOf = false
   this.useStackTraceOf = false
   this.useThrow = false
-  this.useVarMethod = false
   this.useGenStub = false
   this.useMap = false
   this.useAssert = false
@@ -12387,7 +12775,11 @@ function CoreJs() {
   this.useWrap1 = false
   this.useIsolates = false
   this.useToString = false
+  this._generatedTypeNameOf = false
+  this._generatedDynamicProto = false
+  this._generatedInherits = false
   this._usedOperators = $map([]);
+  this.writer = new CodeWriter();
   // Initializers done
 }
 CoreJs.prototype.useOperator = function(name) {
@@ -12439,21 +12831,35 @@ CoreJs.prototype.useOperator = function(name) {
   }
   this._usedOperators.$setindex(name, code);
 }
+CoreJs.prototype.ensureDynamicProto = function() {
+  if ($notnull_bool(this._generatedDynamicProto)) return;
+  this._generatedDynamicProto = true;
+  this.ensureTypeNameOf();
+  this.writer.writeln("function $dynamic(name) {\n  var f = Object.prototype[name];\n  if (f && f.methods) return f.methods;\n\n  var methods = {};\n  if (f) methods.Object = f;\n  function $dynamicBind() {\n    // Find the target method\n    var method;\n    var proto = Object.getPrototypeOf(this);\n    var obj = proto;\n    do {\n      method = methods[obj.$typeNameOf()];\n      if (method) break;\n      obj = Object.getPrototypeOf(obj);\n    } while (obj);\n\n    // Patch the prototype, but don't overwrite an existing stub, like\n    // the one on Object.prototype.\n    if (!proto.hasOwnProperty(name)) proto[name] = method || methods.Object;\n\n    return method.apply(this, Array.prototype.slice.call(arguments));\n  };\n  $dynamicBind.methods = methods;\n  Object.prototype[name] = $dynamicBind;\n  return methods;\n}");
+}
+CoreJs.prototype.ensureTypeNameOf = function() {
+  if ($notnull_bool(this._generatedTypeNameOf)) return;
+  this._generatedTypeNameOf = true;
+  this.writer.writeln("Object.prototype.$typeNameOf = function() {\n  if ((typeof(window) != 'undefined' && window.constructor.name == 'DOMWindow')\n      || typeof(process) != 'undefined') { // fast-path for Chrome and Node\n    return this.constructor.name;\n  }\n  var str = Object.prototype.toString.call(this);\n  str = str.substring(8, str.length - 1);\n  if (str == 'Window') str = 'DOMWindow';\n  return str;\n}");
+}
+CoreJs.prototype.ensureInheritsHelper = function() {
+  if ($notnull_bool(this._generatedInherits)) return;
+  this._generatedInherits = true;
+  this.writer.writeln("/** Implements extends for Dart classes on JavaScript prototypes. */\nfunction $inherits(child, parent) {\n  if (child.prototype.__proto__) {\n    child.prototype.__proto__ = parent.prototype;\n  } else {\n    function tmp() {};\n    tmp.prototype = parent.prototype;\n    child.prototype = new tmp();\n    child.prototype.constructor = child;\n  }\n}");
+}
 CoreJs.prototype.generate = function(w) {
-  if ($notnull_bool(this.useVarMethod)) {
-    this.useTypeNameOf = true;
-    w.writeln("function $varMethod(name, methods) {\n  Object.prototype[name] = function() {\n    $patchMethod(this, name, methods);\n    return this[name].apply(this, Array.prototype.slice.call(arguments));\n  };\n}\nfunction $patchMethod(obj, name, methods) {\n  // Get the prototype to patch.\n  // Don't overwrite an existing stub, like the one on Object.prototype\n  var proto = Object.getPrototypeOf(obj);\n  if (!proto || proto.hasOwnProperty(name)) proto = obj;\n  var method;\n  while (obj && !(method = methods[obj.$typeNameOf()])) {\n    obj = Object.getPrototypeOf(obj);\n  }\n  obj[name] = method || methods['Object'];\n}");
-  }
+  w.write(this.writer.get$text());
+  this.writer = w;
   if ($notnull_bool(this.useGenStub)) {
     this.useThrow = true;
-    w.writeln("/**\n * Generates a dynamic call stub for a function.\n * Our goal is to create a stub method like this on-the-fly:\n *   function($0, $1, capture) { this($0, $1, true, capture); }\n *\n * This stub then replaces the dynamic one on Function, with one that is\n * specialized for that particular function, taking into account its default\n * arguments.\n */\nFunction.prototype.$genStub = function(argsLength, names) {\n  // TODO(jmesserly): only emit $genStub if actually needed\n\n  // Fast path: if no named arguments and arg count matches\n  if (this.length == argsLength && !names) {\n    return this;\n  }\n\n  function $throwArgMismatch() {\n    // TODO(jmesserly): better error message\n    $throw(new ClosureArgumentMismatchException());\n  }\n\n  var paramsNamed = this.$optional ? (this.$optional.length / 2) : 0;\n  var paramsBare = this.length - paramsNamed;\n  var argsNamed = names ? names.length : 0;\n  var argsBare = argsLength - argsNamed;\n\n  // Check we got the right number of arguments\n  if (argsBare < paramsBare || argsLength > this.length ||\n      argsNamed > paramsNamed) {\n    return $throwArgMismatch;\n  }\n\n  // First, fill in all of the default values\n  var p = new Array(paramsBare);\n  if (paramsNamed) {\n    p = p.concat(this.$optional.slice(paramsNamed));\n  }\n  // Fill in positional args\n  var a = new Array(argsLength);\n  for (var i = 0; i < argsBare; i++) {\n    p[i] = a[i] = '$' + i;\n  }\n  // Then overwrite with supplied values for optional args\n  var lastParameterIndex;\n  var namesInOrder = true;\n  for (var i = 0; i < argsNamed; i++) {\n    var name = names[i];\n    a[i + argsBare] = name;\n    var j = this.$optional.indexOf(name, 0);\n    if (j < 0 || j >= paramsNamed) {\n      return $throwArgMismatch;\n    } else if (lastParameterIndex && lastParameterIndex > j) {\n      namesInOrder = false;\n    }\n    p[j + paramsBare] = name;\n    lastParameterIndex = j;\n  }\n\n  if (this.length == argsLength && namesInOrder) {\n    // Fast path #2: named arguments, but they're in order.\n    return this;\n  }\n\n  // Note: using Function instead of 'eval' to get a clean scope.\n  // TODO(jmesserly): evaluate the performance of these stubs.\n  var f = 'function(' + a.join(',') + '){return $f(' + p.join(',') + ');}';\n  return new Function('$f', 'return ' + f + '').call(null, this);\n}");
+    w.writeln("/**\n * Generates a dynamic call stub for a function.\n * Our goal is to create a stub method like this on-the-fly:\n *   function($0, $1, capture) { return this($0, $1, true, capture); }\n *\n * This stub then replaces the dynamic one on Function, with one that is\n * specialized for that particular function, taking into account its default\n * arguments.\n */\nFunction.prototype.$genStub = function(argsLength, names) {\n  // Fast path: if no named arguments and arg count matches\n  if (this.length == argsLength && !names) {\n    return this;\n  }\n\n  function $throwArgMismatch() {\n    // TODO(jmesserly): better error message\n    $throw(new ClosureArgumentMismatchException());\n  }\n\n  var paramsNamed = this.$optional ? (this.$optional.length / 2) : 0;\n  var paramsBare = this.length - paramsNamed;\n  var argsNamed = names ? names.length : 0;\n  var argsBare = argsLength - argsNamed;\n\n  // Check we got the right number of arguments\n  if (argsBare < paramsBare || argsLength > this.length ||\n      argsNamed > paramsNamed) {\n    return $throwArgMismatch;\n  }\n\n  // First, fill in all of the default values\n  var p = new Array(paramsBare);\n  if (paramsNamed) {\n    p = p.concat(this.$optional.slice(paramsNamed));\n  }\n  // Fill in positional args\n  var a = new Array(argsLength);\n  for (var i = 0; i < argsBare; i++) {\n    p[i] = a[i] = '$' + i;\n  }\n  // Then overwrite with supplied values for optional args\n  var lastParameterIndex;\n  var namesInOrder = true;\n  for (var i = 0; i < argsNamed; i++) {\n    var name = names[i];\n    a[i + argsBare] = name;\n    var j = this.$optional.indexOf(name, 0);\n    if (j < 0 || j >= paramsNamed) {\n      return $throwArgMismatch;\n    } else if (lastParameterIndex && lastParameterIndex > j) {\n      namesInOrder = false;\n    }\n    p[j + paramsBare] = name;\n    lastParameterIndex = j;\n  }\n\n  if (this.length == argsLength && namesInOrder) {\n    // Fast path #2: named arguments, but they're in order.\n    return this;\n  }\n\n  // Note: using Function instead of 'eval' to get a clean scope.\n  // TODO(jmesserly): evaluate the performance of these stubs.\n  var f = 'function(' + a.join(',') + '){return $f(' + p.join(',') + ');}';\n  return new Function('$f', 'return ' + f + '').call(null, this);\n}");
   }
   if ($notnull_bool(this.useStackTraceOf)) {
     w.writeln("function $stackTraceOf(e) {\n  // TODO(jmesserly): we shouldn't be relying on the e.stack property.\n  // Need to mangle it.\n  return  (e && e.stack) ? e.stack : null;\n}");
   }
   if ($notnull_bool(this.useNotNullBool)) {
     this.useThrow = true;
-    w.writeln("function $notnull_bool(test) {\n  return (test === true || test === false) ? test : test.is$bool(); // TypeError\n}");
+    w.writeln("function $notnull_bool(test) {\n  if (test === true || test === false) return test;\n  $throw(new TypeError(test, 'bool'));\n}");
   }
   if ($notnull_bool(this.useAssert)) {
     this.useThrow = true;
@@ -12468,9 +12874,6 @@ CoreJs.prototype.generate = function(w) {
   if ($notnull_bool(this.useToString)) {
     w.writeln("function $toString(o) {\n  if (o == null) return 'null';\n  var t = typeof(o);\n  if (t == 'object') { return o.toString(); }\n  else if (t == 'string') { return o; }\n  else if (t == 'bool') { return ''+o; }\n  else if (t == 'number') { return ''+o; }\n  else return o.toString();\n}");
   }
-  if ($notnull_bool(this.useTypeNameOf)) {
-    w.writeln("Object.prototype.$typeNameOf = function() {\n  if ((typeof(window) != 'undefined' && window.constructor.name == 'DOMWindow')\n      || typeof(process) != 'undefined') { // fast-path for Chrome and Node\n    return this.constructor.name;\n  }\n  var str = Object.prototype.toString.call(this);\n  str = str.substring(8, str.length - 1);\n  if (str == 'Window') \n    str = 'DOMWindow';\n  return str;\n}");
-  }
   if ($notnull_bool(this.useIndex)) {
     w.writeln("Object.prototype.$index = function(i) { return this[i]; }\nArray.prototype.$index = function(i) { return this[i]; }\nString.prototype.$index = function(i) { return this[i]; }");
   }
@@ -12501,7 +12904,7 @@ CoreJs.prototype.generate = function(w) {
   }
 }
 CoreJs.prototype.generate$1 = function($0) {
-  return this.generate(($0 && $0.is$CodeWriter()));
+  return this.generate(($0 == null ? null : $0.assert$CodeWriter()));
 };
 // ********** Code for lang_Element **************
 function lang_Element(name, _enclosingElement) {
@@ -12510,7 +12913,7 @@ function lang_Element(name, _enclosingElement) {
   // Initializers done
   this._jsname = this.name;
 }
-lang_Element.prototype.is$lang_Element = function(){return this;};
+lang_Element.prototype.assert$lang_Element = function(){return this};
 lang_Element.prototype.get$name = function() { return this.name; };
 lang_Element.prototype.set$name = function(value) { return this.name = value; };
 lang_Element.prototype.get$library = function() {
@@ -12536,7 +12939,7 @@ lang_Element.prototype.get$typeParameters = function() {
 }
 lang_Element.prototype.get$enclosingElement = function() {
   var $0;
-  return (($0 = this._enclosingElement == null ? this.get$library() : this._enclosingElement) && $0.is$lang_Element());
+  return (($0 = this._enclosingElement == null ? this.get$library() : this._enclosingElement) == null ? null : $0.assert$lang_Element());
 }
 lang_Element.prototype.set$enclosingElement = function(e) {
   return this._enclosingElement = e;
@@ -12546,7 +12949,7 @@ lang_Element.prototype.resolveType = function(node, typeErrors) {
   if (node == null) return $globals.world.varType;
   if (node.type != null) return node.type;
   if ((node instanceof NameTypeReference)) {
-    var typeRef = (node && node.is$NameTypeReference());
+    var typeRef = (node == null ? null : node.assert$NameTypeReference());
     var name;
     if (typeRef.names != null) {
       name = $assert_String(typeRef.names.last().get$name());
@@ -12559,7 +12962,7 @@ lang_Element.prototype.resolveType = function(node, typeErrors) {
       for (var $i = 0;$i < $list.length; $i++) {
         var tp = $list.$index($i);
         if ($notnull_bool($eq(tp.get$name(), name))) {
-          typeRef.type = (tp && tp.is$lang_Type());
+          typeRef.type = (tp == null ? null : tp.assert$lang_Type());
         }
       }
     }
@@ -12569,7 +12972,7 @@ lang_Element.prototype.resolveType = function(node, typeErrors) {
     return this.get$enclosingElement().resolveType(node, typeErrors);
   }
   else if ((node instanceof GenericTypeReference)) {
-    var typeRef = (node && node.is$GenericTypeReference());
+    var typeRef = (node == null ? null : node.assert$GenericTypeReference());
     var baseType = this.resolveType(typeRef.baseType, typeErrors);
     if (!$notnull_bool(baseType.get$isGeneric())) {
       $globals.world.error(('' + baseType.get$name() + ' is not generic'), typeRef.span);
@@ -12583,16 +12986,16 @@ lang_Element.prototype.resolveType = function(node, typeErrors) {
     for (var i = 0;
      i < typeRef.typeArguments.length; i++) {
       var extendsType = baseType.get$typeParameters().$index(i).get$extendsType();
-      var typeArg = this.resolveType((($0 = typeRef.typeArguments.$index(i)) && $0.is$TypeReference()), typeErrors);
+      var typeArg = this.resolveType((($0 = typeRef.typeArguments.$index(i)) == null ? null : $0.assert$TypeReference()), typeErrors);
       typeArgs.add$1(typeArg);
       if ($notnull_bool($ne(extendsType, null)) && !(typeArg instanceof ParameterType)) {
         typeArg.ensureSubtypeOf$3(extendsType, typeRef.typeArguments.$index(i).get$span(), typeErrors);
       }
     }
-    typeRef.type = (($0 = baseType.getOrMakeConcreteType$1(typeArgs)) && $0.is$lang_Type());
+    typeRef.type = (($0 = baseType.getOrMakeConcreteType$1(typeArgs)) == null ? null : $0.assert$lang_Type());
   }
   else if ((node instanceof FunctionTypeReference)) {
-    var typeRef = (node && node.is$FunctionTypeReference());
+    var typeRef = (node == null ? null : node.assert$FunctionTypeReference());
     var name = '';
     if (typeRef.func.name != null) {
       name = typeRef.func.name.name;
@@ -12609,7 +13012,6 @@ lang_Element.prototype.resolve$0 = lang_Element.prototype.resolve;
 // ********** Code for WorldGenerator **************
 function WorldGenerator(main, writer) {
   this.hasStatics = false
-  this._inheritsGenerated = false
   this.main = main;
   this.writer = writer;
   this.globals = $map([]);
@@ -12620,7 +13022,7 @@ WorldGenerator.prototype.run = function() {
   var $0;
   var metaGen = new MethodGenerator(this.main, null);
   var mainTarget = new Value.type$ctor(this.main.declaringType, this.main.get$span());
-  var mainCall = this.main.invoke((metaGen && metaGen.is$MethodGenerator()), null, (mainTarget && mainTarget.is$Value()), Arguments.get$EMPTY(), false);
+  var mainCall = this.main.invoke((metaGen == null ? null : metaGen.assert$MethodGenerator()), null, (mainTarget == null ? null : mainTarget.assert$Value()), Arguments.get$EMPTY(), false);
   this.main.declaringType.markUsed();
   if ($notnull_bool($globals.options.compileAll)) {
     this.markLibraryUsed($globals.world.corelib);
@@ -12630,17 +13032,17 @@ WorldGenerator.prototype.run = function() {
     $globals.world.corelib.types.$index('BadNumberFormatException').markUsed$0();
     $globals.world.get$coreimpl().types.$index('NumImplementation').markUsed$0();
     $globals.world.get$coreimpl().types.$index('StringImplementation').markUsed$0();
-    this.genMethod((($0 = $globals.world.get$coreimpl().types.$index('StringImplementation').getMember$1('contains')) && $0.is$Member()));
+    this.genMethod((($0 = $globals.world.get$coreimpl().types.$index('StringImplementation').getMember$1('contains')) == null ? null : $0.assert$Member()));
   }
   if ($notnull_bool($globals.world.corelib.types.$index('Isolate').get$isUsed()) || $notnull_bool($globals.world.get$coreimpl().types.$index('ReceivePortImpl').get$isUsed())) {
     if ($notnull_bool(this.corejs.useWrap0) || $notnull_bool(this.corejs.useWrap1)) {
-      this.genMethod((($0 = $globals.world.get$coreimpl().types.$index('IsolateContext').getMember$1('eval')) && $0.is$Member()));
-      this.genMethod((($0 = $globals.world.get$coreimpl().types.$index('EventLoop').getMember$1('run')) && $0.is$Member()));
+      this.genMethod((($0 = $globals.world.get$coreimpl().types.$index('IsolateContext').getMember$1('eval')) == null ? null : $0.assert$Member()));
+      this.genMethod((($0 = $globals.world.get$coreimpl().types.$index('EventLoop').getMember$1('run')) == null ? null : $0.assert$Member()));
     }
     this.corejs.useIsolates = true;
-    var isolateMain = (($0 = $globals.world.get$coreimpl().topType.resolveMember('startRootIsolate').members.$index(0)) && $0.is$MethodMember());
+    var isolateMain = (($0 = $globals.world.get$coreimpl().topType.resolveMember('startRootIsolate').members.$index(0)) == null ? null : $0.assert$MethodMember());
     var isolateMainTarget = new Value.type$ctor($globals.world.get$coreimpl().topType, this.main.get$span());
-    mainCall = isolateMain.invoke((metaGen && metaGen.is$MethodGenerator()), null, (isolateMainTarget && isolateMainTarget.is$Value()), new Arguments(null, [this.main._get((metaGen && metaGen.is$MethodGenerator()), this.main.definition, null, false)]), false);
+    mainCall = isolateMain.invoke((metaGen == null ? null : metaGen.assert$MethodGenerator()), null, (isolateMainTarget == null ? null : isolateMainTarget.assert$Value()), new Arguments(null, [this.main._get((metaGen == null ? null : metaGen.assert$MethodGenerator()), this.main.definition, null, false)]), false);
   }
   this.writeTypes($globals.world.get$coreimpl());
   this.writeTypes($globals.world.corelib);
@@ -12656,7 +13058,7 @@ WorldGenerator.prototype.markLibraryUsed = function(l) {
   l.isMarked = true;
   l.imports.forEach((function (i) {
     var $0;
-    return $this.markLibraryUsed((($0 = i.get$library()) && $0.is$Library()));
+    return $this.markLibraryUsed((($0 = i.get$library()) == null ? null : $0.assert$Library()));
   })
   );
   var $list = l.types.getValues();
@@ -12672,10 +13074,10 @@ WorldGenerator.prototype.markLibraryUsed = function(l) {
     for (var $i0 = type.get$members().getValues$0().iterator$0(); $i0.hasNext$0(); ) {
       var member = $i0.next$0();
       if ((member instanceof PropertyMember)) {
-        if ($notnull_bool($ne(member.get$getter(), null))) this.genMethod((($0 = member.get$getter()) && $0.is$Member()));
-        if ($notnull_bool($ne(member.get$setter(), null))) this.genMethod((($0 = member.get$setter()) && $0.is$Member()));
+        if ($notnull_bool($ne(member.get$getter(), null))) this.genMethod((($0 = member.get$getter()) == null ? null : $0.assert$Member()));
+        if ($notnull_bool($ne(member.get$setter(), null))) this.genMethod((($0 = member.get$setter()) == null ? null : $0.assert$Member()));
       }
-      if ($notnull_bool(member.get$isMethod())) this.genMethod((member && member.is$Member()));
+      if ($notnull_bool(member.get$isMethod())) this.genMethod((member == null ? null : member.assert$Member()));
     }
   }
 }
@@ -12686,7 +13088,7 @@ WorldGenerator.prototype.globalForStaticField = function(field, fieldValue, depe
   if (!this.globals.containsKey(fullname)) {
     this.globals.$setindex(fullname, GlobalValue.GlobalValue$fromStatic$factory(field, fieldValue, dependencies));
   }
-  return (($0 = this.globals.$index(fullname)) && $0.is$GlobalValue());
+  return (($0 = this.globals.$index(fullname)) == null ? null : $0.assert$GlobalValue());
 }
 WorldGenerator.prototype.globalForConst = function(exp, dependencies) {
   var $0;
@@ -12694,8 +13096,8 @@ WorldGenerator.prototype.globalForConst = function(exp, dependencies) {
   if (!this.globals.containsKey(key)) {
     this.globals.$setindex(key, GlobalValue.GlobalValue$fromConst$factory(this.globals.get$length(), exp, dependencies));
   }
-  $assert($eq(this.globals.$index(key).get$type(), exp.type), "globals[key].type == exp.type", "gen.dart", 128, 12);
-  return (($0 = this.globals.$index(key)) && $0.is$GlobalValue());
+  $assert($eq(this.globals.$index(key).get$type(), exp.type), "globals[key].type == exp.type", "gen.dart", 130, 12);
+  return (($0 = this.globals.$index(key)) == null ? null : $0.assert$GlobalValue());
 }
 WorldGenerator.prototype.writeTypes = function(lib) {
   var $0;
@@ -12704,7 +13106,7 @@ WorldGenerator.prototype.writeTypes = function(lib) {
   var $list = lib.imports;
   for (var $i = 0;$i < $list.length; $i++) {
     var import_ = $list.$index($i);
-    this.writeTypes((($0 = import_.get$library()) && $0.is$Library()));
+    this.writeTypes((($0 = import_.get$library()) == null ? null : $0.assert$Library()));
   }
   for (var i = 0;
    i < lib.sources.length; i++) {
@@ -12726,19 +13128,19 @@ WorldGenerator.prototype.writeTypes = function(lib) {
   var $list = this._orderValues(lib.types);
   for (var $i = 0;$i < $list.length; $i++) {
     var type = $list.$index($i);
-    if ($notnull_bool(type.get$isUsed()) && $notnull_bool(type.get$isClass())) {
-      this.writeType((type && type.is$lang_Type()));
+    if (($notnull_bool(type.get$isUsed()) || $notnull_bool(type.get$isHiddenNativeType())) && $notnull_bool(type.get$isClass())) {
+      this.writeType((type == null ? null : type.assert$lang_Type()));
       if ($notnull_bool(type.get$isGeneric())) {
         var $list0 = this._orderValues(type._concreteTypes);
         for (var $i0 = 0;$i0 < $list0.length; $i0++) {
           var ct = $list0.$index($i0);
-          this.writeType((ct && ct.is$lang_Type()));
+          this.writeType((ct == null ? null : ct.assert$lang_Type()));
         }
       }
     }
-    if ($notnull_bool(type.get$isFunction()) && $notnull_bool($ne(type.get$varStubs(), null))) {
+    else if ($notnull_bool(type.get$isFunction()) && type.get$varStubs().length > 0) {
       this.writer.comment(('// ********** Code for ' + type.get$jsname() + ' **************'));
-      this._writeDynamicStubs((type && type.is$lang_Type()));
+      this._writeDynamicStubs((type == null ? null : type.assert$lang_Type()));
     }
     if ($notnull_bool($ne(type.get$typeCheckCode(), null))) {
       this.writer.writeln($assert_String(type.get$typeCheckCode()));
@@ -12750,13 +13152,28 @@ WorldGenerator.prototype.genMethod = function(meth, enclosingMethod) {
     new MethodGenerator(meth, enclosingMethod).run();
   }
 }
+WorldGenerator.prototype._prototypeOf = function(type, name) {
+  if ($notnull_bool(type.get$isHiddenNativeType())) {
+    this.corejs.ensureDynamicProto();
+    return ('\$dynamic("' + name + '").' + type.get$jsname());
+  }
+  else {
+    return ('' + type.get$jsname() + '.prototype.' + name);
+  }
+}
 WorldGenerator.prototype._maybeIsTest = function(onType, checkType) {
-  if (!$notnull_bool(checkType.isTested)) return;
-  var value = 'false';
-  if ($notnull_bool(onType.isSubtypeOf(checkType))) {
-    value = 'function(){return this;}';
+  var isSubtype = onType.isSubtypeOf(checkType);
+  if ($notnull_bool(checkType.isTested)) {
+    this.writer.writeln(this._prototypeOf(onType, ('is\$' + checkType.get$jsname())) + (' = function(){return ' + isSubtype + '};'));
+  }
+  if ($notnull_bool(checkType.isChecked)) {
+    var body = 'return this';
+    var checkName = ('assert\$' + checkType.get$jsname());
+    if (!$notnull_bool(isSubtype)) {
+      body = $assert_String($globals.world.objectType.varStubs.$index(checkName).get$body());
+    }
+    this.writer.writeln(this._prototypeOf(onType, checkName) + (' = function(){' + body + '};'));
   }
-  this.writer.writeln(('' + onType.get$jsname() + '.prototype.is\$' + checkType.get$jsname() + ' = ') + ('' + value + ';'));
 }
 WorldGenerator.prototype.writeType = function(type) {
   var $0;
@@ -12783,7 +13200,7 @@ WorldGenerator.prototype.writeType = function(type) {
     }
   }
   else {
-    var standardConstructor = (($0 = type.get$constructors().$index('')) && $0.is$Member());
+    var standardConstructor = (($0 = type.get$constructors().$index('')) == null ? null : $0.assert$Member());
     if (standardConstructor == null || standardConstructor.generator == null) {
       if (!$notnull_bool(type.get$isNative())) {
         this.writer.writeln(('function ' + type.get$jsname() + '() {}'));
@@ -12802,8 +13219,8 @@ WorldGenerator.prototype.writeType = function(type) {
   }
   if (!$notnull_bool(type.get$isTop())) {
     if ((type instanceof ConcreteType)) {
-      var c = (type && type.is$ConcreteType());
-      this._ensureInheritsHelper();
+      var c = (type == null ? null : type.assert$ConcreteType());
+      this.corejs.ensureInheritsHelper();
       this.writer.writeln(('\$inherits(' + c.get$jsname() + ', ' + c.genericType.get$jsname() + ');'));
       for (var p = c._parent;
        (p instanceof ConcreteType); p = p._parent) {
@@ -12813,7 +13230,7 @@ WorldGenerator.prototype.writeType = function(type) {
     }
     else if (!$notnull_bool(type.get$isNative())) {
       if (type.get$parent() != null && !$notnull_bool(type.get$parent().get$isObject())) {
-        this._ensureInheritsHelper();
+        this.corejs.ensureInheritsHelper();
         this.writer.writeln(('\$inherits(' + type.get$jsname() + ', ' + type.get$parent().get$jsname() + ');'));
       }
     }
@@ -12825,7 +13242,7 @@ WorldGenerator.prototype.writeType = function(type) {
     var $list = this._orderValues(type.get$genericType()._concreteTypes);
     for (var $i = 0;$i < $list.length; $i++) {
       var ct = $list.$index($i);
-      this._maybeIsTest(type, (ct && ct.is$lang_Type()));
+      this._maybeIsTest(type, (ct == null ? null : ct.assert$lang_Type()));
     }
   }
   if (type.get$interfaces() != null) {
@@ -12835,12 +13252,12 @@ WorldGenerator.prototype.writeType = function(type) {
     seen.addAll(type.get$interfaces());
     while (!worklist.isEmpty()) {
       var interface_ = worklist.removeLast();
-      this._maybeIsTest(type, (($0 = interface_.get$genericType()) && $0.is$lang_Type()));
+      this._maybeIsTest(type, (($0 = interface_.get$genericType()) == null ? null : $0.assert$lang_Type()));
       if (interface_.get$genericType()._concreteTypes != null) {
         var $list = this._orderValues(interface_.get$genericType()._concreteTypes);
         for (var $i = 0;$i < $list.length; $i++) {
           var ct = $list.$index($i);
-          this._maybeIsTest(type, (ct && ct.is$lang_Type()));
+          this._maybeIsTest(type, (ct == null ? null : ct.assert$lang_Type()));
         }
       }
       var $list = interface_.get$interfaces();
@@ -12858,22 +13275,17 @@ WorldGenerator.prototype.writeType = function(type) {
   for (var $i = 0;$i < $list.length; $i++) {
     var member = $list.$index($i);
     if ((member instanceof FieldMember)) {
-      this._writeField((member && member.is$FieldMember()));
+      this._writeField((member == null ? null : member.assert$FieldMember()));
     }
     if ((member instanceof PropertyMember)) {
-      this._writeProperty((member && member.is$PropertyMember()));
+      this._writeProperty((member == null ? null : member.assert$PropertyMember()));
     }
     if ($notnull_bool(member.get$isMethod())) {
-      this._writeMethod((member && member.is$Member()));
+      this._writeMethod((member == null ? null : member.assert$Member()));
     }
   }
   this._writeDynamicStubs(type);
 }
-WorldGenerator.prototype._ensureInheritsHelper = function() {
-  if ($notnull_bool(this._inheritsGenerated)) return;
-  this._inheritsGenerated = true;
-  this.writer.writeln("/** Implements extends for Dart classes on JavaScript prototypes. */\nfunction $inherits(child, parent) {\n  if (child.prototype.__proto__) {\n    child.prototype.__proto__ = parent.prototype;\n  } else {\n    function tmp() {};\n    tmp.prototype = parent.prototype;\n    child.prototype = new tmp();\n    child.prototype.constructor = child;\n  }\n}");
-}
 WorldGenerator.prototype._ensureInheritMembersHelper = function() {
   if (this._mixins != null) return;
   this._mixins = new CodeWriter();
@@ -12881,12 +13293,10 @@ WorldGenerator.prototype._ensureInheritMembersHelper = function() {
   this._mixins.writeln("/** Implements extends for generic types. */\nfunction $inheritsMembers(child, parent) {\n  child = child.prototype;\n  parent = parent.prototype;\n  Object.getOwnPropertyNames(parent).forEach(function(name) {\n    if (typeof(child[name]) == 'undefined') child[name] = parent[name];\n  });\n}");
 }
 WorldGenerator.prototype._writeDynamicStubs = function(type) {
-  if (type.varStubs != null) {
-    var $list = orderValuesByKeys(type.varStubs);
-    for (var $i = 0;$i < $list.length; $i++) {
-      var stub = $list.$index($i);
-      stub.generate$1(this.writer);
-    }
+  var $list = orderValuesByKeys(type.varStubs);
+  for (var $i = 0;$i < $list.length; $i++) {
+    var stub = $list.$index($i);
+    stub.generate$1(this.writer);
   }
 }
 WorldGenerator.prototype._writeStaticField = function(field) {
@@ -12907,9 +13317,9 @@ WorldGenerator.prototype._writeField = function(field) {
     this.writer.writeln(('var ' + field.get$jsname() + ';'));
   }
   if ($notnull_bool(field._providePropertySyntax)) {
-    this.writer.writeln(('' + field.declaringType.get$jsname() + '.prototype.get\$' + field.get$jsname() + ' = ') + ('function() { return this.' + field.get$jsname() + '; };'));
+    this.writer.writeln(this._prototypeOf(field.declaringType, ('get\$' + field.get$jsname())) + (' = function() { return this.' + field.get$jsname() + '; };'));
     if (!$notnull_bool(field.isFinal)) {
-      this.writer.writeln(('' + field.declaringType.get$jsname() + '.prototype.set\$' + field.get$jsname() + ' = ') + ('function(value) { return this.' + field.get$jsname() + ' = value; };'));
+      this.writer.writeln(this._prototypeOf(field.declaringType, ('set\$' + field.get$jsname())) + (' = function(value) { return this.' + field.get$jsname() + ' = value; };'));
     }
   }
 }
@@ -12949,7 +13359,7 @@ WorldGenerator.prototype.writeGlobals = function() {
     for (var $i = list.iterator$0(); $i.hasNext$0(); ) {
       var global = $i.next$0();
       if ($notnull_bool($ne(global.get$field(), null))) {
-        this._writeStaticField((($0 = global.get$field()) && $0.is$FieldMember()));
+        this._writeStaticField((($0 = global.get$field()) == null ? null : $0.assert$FieldMember()));
       }
     }
     this.writer.exitBlock('}');
@@ -12971,7 +13381,7 @@ WorldGenerator.prototype.writeGlobals = function() {
 }
 WorldGenerator.prototype._orderValues = function(map) {
   var $0;
-  var values = (($0 = map.getValues()) && $0.is$List());
+  var values = (($0 = map.getValues()) == null ? null : $0.assert$List());
   values.sort(this.get$_compareMembers());
   return values;
 }
@@ -12992,10 +13402,10 @@ WorldGenerator.prototype.useMapFactory = function() {
   this.corejs.useMap = true;
   var factType = $globals.world.get$coreimpl().types.$index('HashMapImplementation');
   var m = factType.resolveMember$1('\$setindex');
-  this.genMethod((($0 = m.get$members().$index(0)) && $0.is$Member()));
+  this.genMethod((($0 = m.get$members().$index(0)) == null ? null : $0.assert$Member()));
   var c = factType.getConstructor$1('');
-  this.genMethod((c && c.is$Member()));
-  return (factType && factType.is$lang_Type());
+  this.genMethod((c == null ? null : c.assert$Member()));
+  return (factType == null ? null : factType.assert$lang_Type());
 }
 // ********** Code for BlockScope **************
 function BlockScope(enclosingMethod, parent, reentrant) {
@@ -13012,7 +13422,7 @@ function BlockScope(enclosingMethod, parent, reentrant) {
     this.reentrant = $notnull_bool(reentrant) || $notnull_bool(this.parent.reentrant);
   }
 }
-BlockScope.prototype.is$BlockScope = function(){return this;};
+BlockScope.prototype.assert$BlockScope = function(){return this};
 BlockScope.prototype.get$enclosingMethod = function() { return this.enclosingMethod; };
 BlockScope.prototype.set$enclosingMethod = function(value) { return this.enclosingMethod = value; };
 BlockScope.prototype.get$parent = function() { return this.parent; };
@@ -13027,7 +13437,7 @@ BlockScope.prototype.get$isMethodScope = function() {
 BlockScope.prototype.get$methodScope = function() {
   var s = this;
   while (!$notnull_bool(s.get$isMethodScope())) s = s.get$parent();
-  return (s && s.is$BlockScope());
+  return (s == null ? null : s.assert$BlockScope());
 }
 BlockScope.prototype.lookup = function(name) {
   var ret = this._vars.$index(name);
@@ -13073,14 +13483,14 @@ BlockScope.prototype.create = function(name, type, span, isFinal, isParameter) {
   ret.set$isFinal(isFinal);
   this._vars.$setindex(name, ret);
   if (name != jsName) this._jsNames.add(jsName);
-  return (ret && ret.is$Value());
+  return (ret == null ? null : ret.assert$Value());
 }
 BlockScope.prototype.declareParameter = function(p) {
   return this.create(p.name, p.type, p.definition.span, false, true);
 }
 BlockScope.prototype.declare = function(id) {
   var type = this.enclosingMethod.method.resolveType(id.type, false);
-  return this.create(id.name.name, (type && type.is$lang_Type()), id.span, false, false);
+  return this.create(id.name.name, (type == null ? null : type.assert$lang_Type()), id.span, false, false);
 }
 BlockScope.prototype.getRethrow = function() {
   var $0;
@@ -13088,7 +13498,7 @@ BlockScope.prototype.getRethrow = function() {
   while ($notnull_bool(scope.get$rethrow() == null) && $notnull_bool($ne(scope.get$parent(), null))) {
     scope = scope.get$parent();
   }
-  return (($0 = scope.get$rethrow()) && $0.is$Value());
+  return (($0 = scope.get$rethrow()) == null ? null : $0.assert$Value());
 }
 BlockScope.prototype.lookup$1 = function($0) {
   return this.lookup($assert_String($0));
@@ -13109,14 +13519,14 @@ function MethodGenerator(method, enclosingMethod) {
     this._scope = new BlockScope(this, null, false);
   }
   if (this.enclosingMethod != null && this.method.name != '') {
-    var m = (($0 = this.method) && $0.is$MethodMember());
+    var m = (($0 = this.method) == null ? null : $0.assert$MethodMember());
     this._scope.create(m.name, m.get$functionType(), m.definition.span, true, false);
   }
   this._usedTemps = new HashSetImplementation();
   this._freeTemps = [];
 }
-MethodGenerator.prototype.is$MethodGenerator = function(){return this;};
-MethodGenerator.prototype.is$TreeVisitor = function(){return this;};
+MethodGenerator.prototype.assert$MethodGenerator = function(){return this};
+MethodGenerator.prototype.assert$TreeVisitor = function(){return this};
 MethodGenerator.prototype.get$enclosingMethod = function() { return this.enclosingMethod; };
 MethodGenerator.prototype.set$enclosingMethod = function(value) { return this.enclosingMethod = value; };
 MethodGenerator.prototype.get$needsThis = function() { return this.needsThis; };
@@ -13192,11 +13602,11 @@ MethodGenerator.prototype.writeDefinition = function(defWriter, lambda) {
       return x.compareTo$1(y);
     })
     );
-    paramCode = ListFactory.ListFactory$from$factory((names && names.is$Iterable()));
+    paramCode = ListFactory.ListFactory$from$factory((names == null ? null : names.assert$Iterable()));
     paramCode.addAll$1(this._paramCode);
   }
   var _params = ('(' + Strings.join(this._paramCode, ", ") + ')');
-  var params = ('(' + Strings.join((paramCode && paramCode.is$List_String()), ", ") + ')');
+  var params = ('(' + Strings.join((paramCode == null ? null : paramCode.assert$List_String()), ", ") + ')');
   if ($notnull_bool(this.method.declaringType.get$isTop()) && !$notnull_bool(this.get$isClosure())) {
     defWriter.enterBlock(('function ' + this.method.get$jsname() + params + ' {'));
   }
@@ -13237,7 +13647,7 @@ MethodGenerator.prototype.writeDefinition = function(defWriter, lambda) {
     defWriter.writeln('var \$this = this; // closure support');
   }
   if (this._usedTemps.get$length() > 0 || this._freeTemps.length > 0) {
-    $assert(this._usedTemps.get$length() == 0, "_usedTemps.length == 0", "gen.dart", 817, 14);
+    $assert(this._usedTemps.get$length() == 0, "_usedTemps.length == 0", "gen.dart", 812, 14);
     this._freeTemps.addAll(this._usedTemps);
     this._freeTemps.sort((function (x, y) {
       return x.compareTo$1(y);
@@ -13247,7 +13657,7 @@ MethodGenerator.prototype.writeDefinition = function(defWriter, lambda) {
   }
   defWriter.writeln(this.writer.get$text());
   if ($notnull_bool($ne(names, null))) {
-    defWriter.exitBlock(('}).bind(null, ' + Strings.join((names && names.is$List_String()), ", ") + ')'));
+    defWriter.exitBlock(('}).bind(null, ' + Strings.join((names == null ? null : names.assert$List_String()), ", ") + ')'));
   }
   else if ($notnull_bool(this.get$isClosure()) && this.method.name == '') {
     defWriter.exitBlock('})');
@@ -13260,7 +13670,7 @@ MethodGenerator.prototype.writeDefinition = function(defWriter, lambda) {
   }
   this._provideOptionalParamInfo(defWriter);
   if ((this.method instanceof MethodMember)) {
-    var m = (($0 = this.method) && $0.is$MethodMember());
+    var m = (($0 = this.method) == null ? null : $0.assert$MethodMember());
     if ($notnull_bool(m._providePropertySyntax)) {
       defWriter.enterBlock(('' + m.declaringType.get$jsname() + '.prototype') + ('.get\$' + m.get$jsname() + ' = function() {'));
       defWriter.writeln(('return ' + m.declaringType.get$jsname() + '.prototype.') + ('' + m.get$jsname() + '.bind(this);'));
@@ -13274,7 +13684,7 @@ MethodGenerator.prototype.writeDefinition = function(defWriter, lambda) {
 MethodGenerator.prototype._provideOptionalParamInfo = function(defWriter) {
   var $0;
   if ((this.method instanceof MethodMember)) {
-    var meth = (($0 = this.method) && $0.is$MethodMember());
+    var meth = (($0 = this.method) == null ? null : $0.assert$MethodMember());
     if ($notnull_bool(meth._provideOptionalParamInfo)) {
       var optNames = [];
       var optValues = [];
@@ -13298,7 +13708,7 @@ MethodGenerator.prototype._provideOptionalParamInfo = function(defWriter) {
           start = meth.declaringType.get$jsname() + '.prototype.';
         }
         optNames.addAll$1(optValues);
-        var optional = "['" + Strings.join((optNames && optNames.is$List_String()), "', '") + "']";
+        var optional = "['" + Strings.join((optNames == null ? null : optNames.assert$List_String()), "', '") + "']";
         defWriter.writeln(('' + start + meth.get$jsname() + '.\$optional = ' + optional));
       }
     }
@@ -13331,10 +13741,10 @@ MethodGenerator.prototype.writeBody = function() {
     if ($notnull_bool($ne(initializers, null)) && $notnull_bool(p.get$isInitializer())) {
       var field = this.method.declaringType.getMember($assert_String(p.get$name()));
       if ($notnull_bool(field == null)) {
-        $globals.world.error('bad this parameter - no matching field', (($0 = p.get$definition().get$span()) && $0.is$SourceSpan()));
+        $globals.world.error('bad this parameter - no matching field', (($0 = p.get$definition().get$span()) == null ? null : $0.assert$SourceSpan()));
       }
       if (!$notnull_bool(field.get$isField())) {
-        $globals.world.error(('"this.' + p.get$name() + '" does not refer to a field'), (($0 = p.get$definition().get$span()) && $0.is$SourceSpan()));
+        $globals.world.error(('"this.' + p.get$name() + '" does not refer to a field'), (($0 = p.get$definition().get$span()) == null ? null : $0.assert$SourceSpan()));
       }
       var paramValue = new Value(field.get$returnType(), p.get$name(), p.get$definition().get$span(), false);
       this._paramCode.add(paramValue.get$code());
@@ -13342,13 +13752,13 @@ MethodGenerator.prototype.writeBody = function() {
       initializedFields.add$1(p.get$name());
     }
     else {
-      var paramValue = this._scope.declareParameter((p && p.is$Parameter()));
+      var paramValue = this._scope.declareParameter((p == null ? null : p.assert$Parameter()));
       this._paramCode.add(paramValue.get$code());
     }
   }
   var body = this.method.get$definition().get$body();
   if ($notnull_bool(body == null) && !$notnull_bool(this.method.get$isConstructor()) && !$notnull_bool(this.method.get$isNative())) {
-    $globals.world.error(('unexpected empty body for ' + this.method.name), (($0 = this.method.get$definition().get$span()) && $0.is$SourceSpan()));
+    $globals.world.error(('unexpected empty body for ' + this.method.name), (($0 = this.method.get$definition().get$span()) == null ? null : $0.assert$SourceSpan()));
   }
   var initializerCall = null;
   var declaredInitializers = this.method.get$definition().get$initializers();
@@ -13362,57 +13772,57 @@ MethodGenerator.prototype.writeBody = function() {
         var init = $i.next$0();
         if ((init instanceof CallExpression)) {
           if ($notnull_bool($ne(initializerCall, null))) {
-            $globals.world.error('only one initializer redirecting call is allowed', (($0 = init.get$span()) && $0.is$SourceSpan()));
+            $globals.world.error('only one initializer redirecting call is allowed', (($0 = init.get$span()) == null ? null : $0.assert$SourceSpan()));
           }
           initializerCall = init;
         }
         else if ((init instanceof BinaryExpression) && TokenKind.kindFromAssign($assert_num(init.get$op().get$kind())) == 0) {
           var left = init.get$x();
           if (!((left instanceof DotExpression) && (left.get$self() instanceof ThisExpression) || (left instanceof VarExpression))) {
-            $globals.world.error('invalid left side of initializer', (($0 = left.get$span()) && $0.is$SourceSpan()));
+            $globals.world.error('invalid left side of initializer', (($0 = left.get$span()) == null ? null : $0.assert$SourceSpan()));
             continue;
           }
           var f = this.method.declaringType.getMember($assert_String(left.get$name().get$name()));
           if ($notnull_bool(f == null)) {
-            $globals.world.error('bad initializer - no matching field', (($0 = left.get$span()) && $0.is$SourceSpan()));
+            $globals.world.error('bad initializer - no matching field', (($0 = left.get$span()) == null ? null : $0.assert$SourceSpan()));
             continue;
           }
           else if (!$notnull_bool(f.get$isField())) {
-            $globals.world.error(('"' + left.get$name().get$name() + '" does not refer to a field'), (($0 = left.get$span()) && $0.is$SourceSpan()));
+            $globals.world.error(('"' + left.get$name().get$name() + '" does not refer to a field'), (($0 = left.get$span()) == null ? null : $0.assert$SourceSpan()));
             continue;
           }
           initializedFields.add$1(f.get$name());
-          this.writer.writeln(('this.' + f.get$jsname() + ' = ' + this.visitValue((($0 = init.get$y()) && $0.is$lang_Expression())).get$code() + ';'));
+          this.writer.writeln(('this.' + f.get$jsname() + ' = ' + this.visitValue((($0 = init.get$y()) == null ? null : $0.assert$lang_Expression())).get$code() + ';'));
         }
         else {
-          $globals.world.error('invalid initializer', (($0 = init.get$span()) && $0.is$SourceSpan()));
+          $globals.world.error('invalid initializer', (($0 = init.get$span()) == null ? null : $0.assert$SourceSpan()));
         }
       }
     }
     this.writer.comment('// Initializers done');
   }
-  if ($notnull_bool(this.method.get$isConstructor()) && $notnull_bool(initializerCall == null)) {
+  if ($notnull_bool(this.method.get$isConstructor()) && $notnull_bool(initializerCall == null) && !$notnull_bool(this.method.get$isNative())) {
     var parentType = this.method.declaringType.get$parent();
     if ($notnull_bool($ne(parentType, null)) && !$notnull_bool(parentType.get$isObject())) {
       initializerCall = new CallExpression(new SuperExpression(this.method.get$span()), [], this.method.get$span());
     }
   }
   if ($notnull_bool($ne(initializerCall, null))) {
-    var target = this._writeInitializerCall((initializerCall && initializerCall.is$CallExpression()));
+    var target = this._writeInitializerCall((initializerCall == null ? null : initializerCall.assert$CallExpression()));
     if (!$notnull_bool(target.get$isSuper())) {
       if (initializers.length > 0) {
         var $list = this.method.get$parameters();
         for (var $i = 0;$i < $list.length; $i++) {
           var p = $list.$index($i);
           if ($notnull_bool(p.get$isInitializer())) {
-            $globals.world.error('no initialization allowed on redirecting constructors', (($0 = p.get$definition().get$span()) && $0.is$SourceSpan()));
+            $globals.world.error('no initialization allowed on redirecting constructors', (($0 = p.get$definition().get$span()) == null ? null : $0.assert$SourceSpan()));
             break;
           }
         }
       }
       if ($notnull_bool($ne(declaredInitializers, null)) && declaredInitializers.length > 1) {
         var init = $notnull_bool($eq(declaredInitializers.$index(0), initializerCall)) ? declaredInitializers.$index(1) : declaredInitializers.$index(0);
-        $globals.world.error('no initialization allowed on redirecting constructors', (($0 = init.get$span()) && $0.is$SourceSpan()));
+        $globals.world.error('no initialization allowed on redirecting constructors', (($0 = init.get$span()) == null ? null : $0.assert$SourceSpan()));
       }
       initializedFields = null;
     }
@@ -13421,26 +13831,26 @@ MethodGenerator.prototype.writeBody = function() {
     for (var $i = allMembers.iterator$0(); $i.hasNext$0(); ) {
       var member = $i.next$0();
       if ($notnull_bool(member.get$isField()) && $notnull_bool(member.get$isFinal()) && !$notnull_bool(member.get$isStatic()) && !$notnull_bool(this.method.get$isNative()) && !$notnull_bool(initializedFields.contains$1(member.get$name()))) {
-        $globals.world.error(('Field "' + member.get$name() + '" is final and was not initialized'), (($0 = this.method.get$definition().get$span()) && $0.is$SourceSpan()));
+        $globals.world.error(('Field "' + member.get$name() + '" is final and was not initialized'), (($0 = this.method.get$definition().get$span()) == null ? null : $0.assert$SourceSpan()));
       }
     }
   }
-  this.visitStatementsInBlock((body && body.is$lang_Statement()));
+  this.visitStatementsInBlock((body == null ? null : body.assert$lang_Statement()));
 }
 MethodGenerator.prototype._writeInitializerCall = function(node) {
   var contructorName = '';
   var targetExp = node.target;
   if ((targetExp instanceof DotExpression)) {
-    var dot = (targetExp && targetExp.is$DotExpression());
+    var dot = (targetExp == null ? null : targetExp.assert$DotExpression());
     targetExp = dot.self;
     contructorName = dot.name.name;
   }
   var target = null;
   if ((targetExp instanceof SuperExpression)) {
-    target = this._makeSuperValue((targetExp && targetExp.is$lang_Node()));
+    target = this._makeSuperValue((targetExp == null ? null : targetExp.assert$lang_Node()));
   }
   else if ((targetExp instanceof ThisExpression)) {
-    target = this._makeThisValue((targetExp && targetExp.is$lang_Node()));
+    target = this._makeThisValue((targetExp == null ? null : targetExp.assert$lang_Node()));
   }
   else {
     $globals.world.error('bad call in initializers', node.span);
@@ -13455,12 +13865,12 @@ MethodGenerator.prototype._writeInitializerCall = function(node) {
     }
     other = other.get$initDelegate();
   }
-  $globals.world.gen.genMethod((m && m.is$Member()));
+  $globals.world.gen.genMethod((m == null ? null : m.assert$Member()));
   var value = m.invoke$4(this, node, target, this._makeArgs(node.arguments));
   if ($notnull_bool($ne(target.get$type(), $globals.world.objectType))) {
     this.writer.writeln(('' + value.get$code() + ';'));
   }
-  return (target && target.is$Value());
+  return (target == null ? null : target.assert$Value());
 }
 MethodGenerator.prototype._makeArgs = function(arguments) {
   var $0;
@@ -13472,9 +13882,9 @@ MethodGenerator.prototype._makeArgs = function(arguments) {
       seenLabel = true;
     }
     else if ($notnull_bool(seenLabel)) {
-      $globals.world.error('bare argument can not follow named arguments', (($0 = arg.get$span()) && $0.is$SourceSpan()));
+      $globals.world.error('bare argument can not follow named arguments', (($0 = arg.get$span()) == null ? null : $0.assert$SourceSpan()));
     }
-    args.add$1(this.visitValue((($0 = arg.get$value()) && $0.is$lang_Expression())));
+    args.add$1(this.visitValue((($0 = arg.get$value()) == null ? null : $0.assert$lang_Expression())));
   }
   return new Arguments(arguments, args);
 }
@@ -13485,14 +13895,14 @@ MethodGenerator.prototype._invokeNative = function(name, arguments) {
     args = new Arguments(null, arguments);
   }
   var method = $globals.world.corelib.topType.members.$index(name);
-  return (($0 = method.invoke$4(this, method.get$definition(), new Value($globals.world.corelib.topType, null, null, true), args)) && $0.is$Value());
+  return (($0 = method.invoke$4(this, method.get$definition(), new Value($globals.world.corelib.topType, null, null, true), args)) == null ? null : $0.assert$Value());
 }
 MethodGenerator._escapeString = function(text) {
   return text.replaceAll('\\', '\\\\').replaceAll('"', '\\"').replaceAll('\n', '\\n').replaceAll('\r', '\\r');
 }
 MethodGenerator.prototype.visitStatementsInBlock = function(body) {
   if ((body instanceof BlockStatement)) {
-    var block = (body && body.is$BlockStatement());
+    var block = (body == null ? null : body.assert$BlockStatement());
     var $list = block.body;
     for (var $i = 0;$i < $list.length; $i++) {
       var stmt = $list.$index($i);
@@ -13515,8 +13925,8 @@ MethodGenerator.prototype._makeLambdaMethod = function(name, func) {
   meth.set$isLambda(true);
   meth.set$enclosingElement(this.method);
   meth.resolve$0();
-  $globals.world.gen.genMethod((meth && meth.is$Member()), this);
-  return (meth && meth.is$MethodMember());
+  $globals.world.gen.genMethod((meth == null ? null : meth.assert$Member()), this);
+  return (meth == null ? null : meth.assert$MethodMember());
 }
 MethodGenerator.prototype.visitBool = function(node) {
   return this.visitValue(node).convertTo$3(this, $globals.world.nonNullBool, node);
@@ -13532,7 +13942,7 @@ MethodGenerator.prototype.visitTypedValue = function(node, expectedType) {
 }
 MethodGenerator.prototype.visitVoid = function(node) {
   if ((node instanceof PostfixExpression)) {
-    var value = this.visitPostfixExpression((node && node.is$PostfixExpression()), true);
+    var value = this.visitPostfixExpression((node == null ? null : node.assert$PostfixExpression()), true);
     value.checkFirstClass$1(node.span);
     return value;
   }
@@ -13541,7 +13951,7 @@ MethodGenerator.prototype.visitVoid = function(node) {
 MethodGenerator.prototype.visitDietStatement = function(node) {
   var $0;
   var parser = new lang_Parser(node.span.file, false, false, false, node.span.start);
-  this.visitStatementsInBlock((($0 = parser.block$0()) && $0.is$lang_Statement()));
+  this.visitStatementsInBlock((($0 = parser.block$0()) == null ? null : $0.assert$lang_Statement()));
   return false;
 }
 MethodGenerator.prototype.visitVariableDefinition = function(node) {
@@ -13559,7 +13969,7 @@ MethodGenerator.prototype.visitVariableDefinition = function(node) {
       this.writer.write(', ');
     }
     var name = node.names.$index(i).get$name();
-    var value = this.visitValue((($0 = node.values.$index(i)) && $0.is$lang_Expression()));
+    var value = this.visitValue((($0 = node.values.$index(i)) == null ? null : $0.assert$lang_Expression()));
     if ($notnull_bool(isFinal)) {
       if ($notnull_bool(value == null)) {
         $globals.world.error('no value specified for final variable', node.span);
@@ -13568,7 +13978,7 @@ MethodGenerator.prototype.visitVariableDefinition = function(node) {
         if ($notnull_bool(thisType.get$isVar())) thisType = value.get$type();
       }
     }
-    var val = this._scope.create($assert_String(name), (thisType && thisType.is$lang_Type()), (($0 = node.names.$index(i).get$span()) && $0.is$SourceSpan()), $assert_bool(isFinal), false);
+    var val = this._scope.create($assert_String(name), (thisType == null ? null : thisType.assert$lang_Type()), (($0 = node.names.$index(i).get$span()) == null ? null : $0.assert$SourceSpan()), $assert_bool(isFinal), false);
     if ($notnull_bool(value == null)) {
       if ($notnull_bool(this._scope.reentrant)) {
         this.writer.write(('' + val.get$code() + ' = null'));
@@ -13589,7 +13999,7 @@ MethodGenerator.prototype.visitFunctionDefinition = function(node) {
   var $0;
   var name = $globals.world.toJsIdentifier(node.name.name);
   var meth = this._makeLambdaMethod($assert_String(name), node);
-  var funcValue = this._scope.create($assert_String(name), (($0 = meth.get$functionType()) && $0.is$lang_Type()), (($0 = this.method.get$definition().get$span()) && $0.is$SourceSpan()), true, false);
+  var funcValue = this._scope.create($assert_String(name), (($0 = meth.get$functionType()) == null ? null : $0.assert$lang_Type()), (($0 = this.method.get$definition().get$span()) == null ? null : $0.assert$SourceSpan()), true, false);
   meth.get$generator().writeDefinition$2(this.writer);
   return false;
 }
@@ -13629,8 +14039,8 @@ MethodGenerator.prototype.visitAssertStatement = function(node) {
   var test = this.visitValue(node.test);
   if ($notnull_bool($globals.options.enableAsserts)) {
     var err = $globals.world.corelib.types.$index('AssertError');
-    $globals.world.gen.genMethod((($0 = err.getConstructor$1('')) && $0.is$Member()));
-    $globals.world.gen.genMethod((($0 = err.get$members().$index('toString')) && $0.is$Member()));
+    $globals.world.gen.genMethod((($0 = err.getConstructor$1('_internal')) == null ? null : $0.assert$Member()));
+    $globals.world.gen.genMethod((($0 = err.get$members().$index('toString')) == null ? null : $0.assert$Member()));
     var span = node.test.span;
     var line = span.get$file().getLine$1(span.get$start());
     var column = span.get$file().getColumn$2(line, span.get$start());
@@ -13703,7 +14113,7 @@ MethodGenerator.prototype.visitForStatement = function(node) {
   for (var $i = 0;$i < $list.length; $i++) {
     var s = $list.$index($i);
     if ($notnull_bool(needsComma)) this.writer.write(', ');
-    var sv = this.visitVoid((s && s.is$lang_Expression()));
+    var sv = this.visitVoid((s == null ? null : s.assert$lang_Expression()));
     this.writer.write($assert_String(sv.get$code()));
     needsComma = true;
   }
@@ -13727,10 +14137,10 @@ MethodGenerator.prototype.visitForInStatement = function(node) {
   var list = node.list.visit(this);
   this._pushBlock(true);
   var isFinal = this._isFinal(node.item.type);
-  var item = this._scope.create($assert_String(itemName), (itemType && itemType.is$lang_Type()), node.item.name.span, isFinal, false);
-  var listVar = (list && list.is$Value());
+  var item = this._scope.create($assert_String(itemName), (itemType == null ? null : itemType.assert$lang_Type()), node.item.name.span, isFinal, false);
+  var listVar = (list == null ? null : list.assert$Value());
   if ($notnull_bool(list.get$needsTemp())) {
-    listVar = this._scope.create('\$list', (($0 = list.get$type()) && $0.is$lang_Type()), null, false, false);
+    listVar = this._scope.create('\$list', (($0 = list.get$type()) == null ? null : $0.assert$lang_Type()), null, false, false);
     this.writer.writeln(('var ' + listVar.code + ' = ' + list.get$code() + ';'));
   }
   if ($notnull_bool(list.get$type().get$isList())) {
@@ -13742,7 +14152,7 @@ MethodGenerator.prototype.visitForInStatement = function(node) {
   else {
     this._pushBlock(false);
     var iterator = list.invoke$4(this, 'iterator', node.list, Arguments.get$EMPTY());
-    var tmpi = this._scope.create('\$i', (($0 = iterator.get$type()) && $0.is$lang_Type()), null, false, false);
+    var tmpi = this._scope.create('\$i', (($0 = iterator.get$type()) == null ? null : $0.assert$lang_Type()), null, false, false);
     var hasNext = tmpi.invoke$4(this, 'hasNext', node.list, Arguments.get$EMPTY());
     var next = tmpi.invoke$4(this, 'next', node.list, Arguments.get$EMPTY());
     this.writer.enterBlock(('for (var ' + tmpi.get$code() + ' = ' + iterator.get$code() + '; ' + hasNext.get$code() + '; ) {'));
@@ -13766,26 +14176,26 @@ MethodGenerator.prototype.visitTryStatement = function(node) {
   if (node.catches.length == 1) {
     var catch_ = node.catches.$index(0);
     this._pushBlock(false);
-    var ex = this._scope.declare((($0 = catch_.get$exception()) && $0.is$DeclaredIdentifier()));
-    this._scope.rethrow = (ex && ex.is$Value());
+    var ex = this._scope.declare((($0 = catch_.get$exception()) == null ? null : $0.assert$DeclaredIdentifier()));
+    this._scope.rethrow = (ex == null ? null : ex.assert$Value());
     this.writer.nextBlock(('} catch (' + ex.get$code() + ') {'));
     if ($notnull_bool($ne(catch_.get$trace(), null))) {
-      var trace = this._scope.declare((($0 = catch_.get$trace()) && $0.is$DeclaredIdentifier()));
+      var trace = this._scope.declare((($0 = catch_.get$trace()) == null ? null : $0.assert$DeclaredIdentifier()));
       this.writer.writeln(('var ' + trace.get$code() + ' = \$stackTraceOf(' + ex.get$code() + ');'));
       $globals.world.gen.corejs.useStackTraceOf = true;
     }
-    this._genToDartException((ex && ex.is$Value()), node);
+    this._genToDartException((ex == null ? null : ex.assert$Value()), node);
     if (!$notnull_bool(ex.get$type().get$isVarOrObject())) {
       var test = ex.instanceOf$3$isTrue$forceCheck(this, ex.get$type(), catch_.get$exception().get$span(), false, true);
       this.writer.writeln(('if (' + test.get$code() + ') throw ' + ex.get$code() + ';'));
     }
-    this.visitStatementsInBlock((($0 = node.catches.$index(0).get$body()) && $0.is$lang_Statement()));
+    this.visitStatementsInBlock((($0 = node.catches.$index(0).get$body()) == null ? null : $0.assert$lang_Statement()));
     this._popBlock();
   }
   else if (node.catches.length > 0) {
     this._pushBlock(false);
     var ex = this._scope.create('\$ex', $globals.world.varType, null, false, false);
-    this._scope.rethrow = (ex && ex.is$Value());
+    this._scope.rethrow = (ex == null ? null : ex.assert$Value());
     this.writer.nextBlock(('} catch (' + ex.get$code() + ') {'));
     var trace = null;
     if (node.catches.some((function (c) {
@@ -13796,13 +14206,13 @@ MethodGenerator.prototype.visitTryStatement = function(node) {
       this.writer.writeln(('var ' + trace.get$code() + ' = \$stackTraceOf(' + ex.get$code() + ');'));
       $globals.world.gen.corejs.useStackTraceOf = true;
     }
-    this._genToDartException((ex && ex.is$Value()), node);
+    this._genToDartException((ex == null ? null : ex.assert$Value()), node);
     var needsRethrow = true;
     for (var i = 0;
      i < node.catches.length; i++) {
       var catch_ = node.catches.$index(i);
       this._pushBlock(false);
-      var tmp = this._scope.declare((($0 = catch_.get$exception()) && $0.is$DeclaredIdentifier()));
+      var tmp = this._scope.declare((($0 = catch_.get$exception()) == null ? null : $0.assert$DeclaredIdentifier()));
       if (!$notnull_bool(tmp.get$type().get$isVarOrObject())) {
         var test = ex.instanceOf$3$isTrue$forceCheck(this, tmp.get$type(), catch_.get$exception().get$span(), true, true);
         if (i == 0) {
@@ -13817,14 +14227,14 @@ MethodGenerator.prototype.visitTryStatement = function(node) {
       }
       this.writer.writeln(('var ' + tmp.get$code() + ' = ' + ex.get$code() + ';'));
       if ($notnull_bool($ne(catch_.get$trace(), null))) {
-        var tmptrace = this._scope.declare((($0 = catch_.get$trace()) && $0.is$DeclaredIdentifier()));
+        var tmptrace = this._scope.declare((($0 = catch_.get$trace()) == null ? null : $0.assert$DeclaredIdentifier()));
         this.writer.writeln(('var ' + tmptrace.get$code() + ' = ' + trace.get$code() + ';'));
       }
-      this.visitStatementsInBlock((($0 = catch_.get$body()) && $0.is$lang_Statement()));
+      this.visitStatementsInBlock((($0 = catch_.get$body()) == null ? null : $0.assert$lang_Statement()));
       this._popBlock();
       if ($notnull_bool(tmp.get$type().get$isVarOrObject())) {
         if (i + 1 < node.catches.length) {
-          $globals.world.warning('Unreachable catch clause', (($0 = node.catches.$index(i + 1)) && $0.is$SourceSpan()));
+          $globals.world.warning('Unreachable catch clause', (($0 = node.catches.$index(i + 1)) == null ? null : $0.assert$SourceSpan()));
         }
         if (i > 0) {
           this.writer.exitBlock('}');
@@ -13857,7 +14267,7 @@ MethodGenerator.prototype.visitSwitchStatement = function(node) {
   for (var $i = 0;$i < $list.length; $i++) {
     var case_ = $list.$index($i);
     if ($notnull_bool($ne(case_.get$label(), null))) {
-      $globals.world.error('unimplemented: labeled case statement', (($0 = case_.get$span()) && $0.is$SourceSpan()));
+      $globals.world.error('unimplemented: labeled case statement', (($0 = case_.get$span()) == null ? null : $0.assert$SourceSpan()));
     }
     this._pushBlock(false);
     for (var i = 0;
@@ -13865,12 +14275,12 @@ MethodGenerator.prototype.visitSwitchStatement = function(node) {
       var expr = case_.get$cases().$index(i);
       if ($notnull_bool(expr == null)) {
         if (i < case_.get$cases().length - 1) {
-          $globals.world.error('default clause must be the last case', (($0 = case_.get$span()) && $0.is$SourceSpan()));
+          $globals.world.error('default clause must be the last case', (($0 = case_.get$span()) == null ? null : $0.assert$SourceSpan()));
         }
         this.writer.writeln('default:');
       }
       else {
-        var value = this.visitValue((expr && expr.is$lang_Expression()));
+        var value = this.visitValue((expr == null ? null : expr.assert$lang_Expression()));
         this.writer.writeln(('case ' + value.get$code() + ':'));
       }
     }
@@ -13894,7 +14304,7 @@ MethodGenerator.prototype._visitAllStatements = function(statementList, exits) {
     var stmt = statementList.$index(i);
     exits = stmt.visit$1(this);
     if ($notnull_bool($ne(stmt, statementList.$index(statementList.length - 1))) && $notnull_bool(exits)) {
-      $globals.world.warning('unreachable code', (($0 = statementList.$index(i + 1).get$span()) && $0.is$SourceSpan()));
+      $globals.world.warning('unreachable code', (($0 = statementList.$index(i + 1).get$span()) == null ? null : $0.assert$SourceSpan()));
     }
   }
   return $assert_bool(exits);
@@ -13983,13 +14393,13 @@ MethodGenerator.prototype.visitCallExpression = function(node) {
   var position = node.target;
   var name = '\$call';
   if ((node.target instanceof DotExpression)) {
-    var dot = (($0 = node.target) && $0.is$DotExpression());
+    var dot = (($0 = node.target) == null ? null : $0.assert$DotExpression());
     target = dot.self.visit(this);
     name = dot.name.name;
     position = dot.name;
   }
   else if ((node.target instanceof VarExpression)) {
-    var varExpr = (($0 = node.target) && $0.is$VarExpression());
+    var varExpr = (($0 = node.target) == null ? null : $0.assert$VarExpression());
     name = varExpr.name.name;
     target = this._scope.lookup($assert_String(name));
     if ($notnull_bool($ne(target, null))) {
@@ -14073,13 +14483,13 @@ MethodGenerator.prototype._visitAssign = function(kind, xn, yn, position, captur
     ;
   }
   if ((xn instanceof VarExpression)) {
-    return this._visitVarAssign(kind, (xn && xn.is$VarExpression()), yn, position, captureOriginal);
+    return this._visitVarAssign(kind, (xn == null ? null : xn.assert$VarExpression()), yn, position, captureOriginal);
   }
   else if ((xn instanceof IndexExpression)) {
-    return this._visitIndexAssign(kind, (xn && xn.is$IndexExpression()), yn, position, captureOriginal);
+    return this._visitIndexAssign(kind, (xn == null ? null : xn.assert$IndexExpression()), yn, position, captureOriginal);
   }
   else if ((xn instanceof DotExpression)) {
-    return this._visitDotAssign(kind, (xn && xn.is$DotExpression()), yn, position, captureOriginal);
+    return this._visitDotAssign(kind, (xn == null ? null : xn.assert$DotExpression()), yn, position, captureOriginal);
   }
   else {
     $globals.world.error('illegal lhs', position.span);
@@ -14098,7 +14508,7 @@ MethodGenerator.prototype._visitVarAssign = function(kind, xn, yn, position, cap
       }
       else if (!$notnull_bool(members.get$treatAsField()) || $notnull_bool(members.get$containsMethods())) {
         var right = x.get_$3(this, name, position);
-        right = captureOriginal((right && right.is$Value()));
+        right = captureOriginal((right == null ? null : right.assert$Value()));
         y = right.invoke$4(this, TokenKind.binaryMethodName(kind), position, new Arguments(null, [y]));
         return x.set_$4(this, name, position, y);
       }
@@ -14116,7 +14526,7 @@ MethodGenerator.prototype._visitVarAssign = function(kind, xn, yn, position, cap
       if (!$notnull_bool(members.get$treatAsField()) || $notnull_bool(members.get$containsMethods())) {
         if (kind != 0) {
           var right = members._get$3(this, position, x);
-          right = captureOriginal((right && right.is$Value()));
+          right = captureOriginal((right == null ? null : right.assert$Value()));
           y = right.invoke$4(this, TokenKind.binaryMethodName(kind), position, new Arguments(null, [y]));
         }
         return members._set$4(this, position, x, y);
@@ -14131,17 +14541,17 @@ MethodGenerator.prototype._visitVarAssign = function(kind, xn, yn, position, cap
   }
   y = y.convertTo$3(this, x.get$type(), yn);
   if (kind == 0) {
-    x = captureOriginal((x && x.is$Value()));
+    x = captureOriginal((x == null ? null : x.assert$Value()));
     return new Value(y.get$type(), ('' + x.get$code() + ' = ' + y.get$code()), position.span, true);
   }
   else if ($notnull_bool(x.get$type().get$isNum()) && $notnull_bool(y.get$type().get$isNum()) && (kind != 46/*TokenKind.TRUNCDIV*/)) {
-    x = captureOriginal((x && x.is$Value()));
+    x = captureOriginal((x == null ? null : x.assert$Value()));
     var op = TokenKind.kindToString(kind);
     return new Value(y.get$type(), ('' + x.get$code() + ' ' + op + '= ' + y.get$code()), position.span, true);
   }
   else {
     var right = x;
-    right = captureOriginal((right && right.is$Value()));
+    right = captureOriginal((right == null ? null : right.assert$Value()));
     y = right.invoke$4(this, TokenKind.binaryMethodName(kind), position, new Arguments(null, [y]));
     return new Value(y.get$type(), ('' + x.get$code() + ' = ' + y.get$code()), position.span, true);
   }
@@ -14153,16 +14563,16 @@ MethodGenerator.prototype._visitIndexAssign = function(kind, xn, yn, position, c
   var tmptarget = target;
   var tmpindex = index;
   if (kind != 0) {
-    tmptarget = this.getTemp((target && target.is$Value()));
-    tmpindex = this.getTemp((index && index.is$Value()));
-    index = this.assignTemp((tmpindex && tmpindex.is$Value()), (index && index.is$Value()));
+    tmptarget = this.getTemp((target == null ? null : target.assert$Value()));
+    tmpindex = this.getTemp((index == null ? null : index.assert$Value()));
+    index = this.assignTemp((tmpindex == null ? null : tmpindex.assert$Value()), (index == null ? null : index.assert$Value()));
     var right = tmptarget.invoke$4(this, '\$index', position, new Arguments(null, [tmpindex]));
-    right = captureOriginal((right && right.is$Value()));
+    right = captureOriginal((right == null ? null : right.assert$Value()));
     y = right.invoke$4(this, TokenKind.binaryMethodName(kind), position, new Arguments(null, [y]));
   }
-  var ret = this.assignTemp((tmptarget && tmptarget.is$Value()), (target && target.is$Value())).invoke(this, '\$setindex', position, new Arguments(null, [index, y]), false);
-  if ($notnull_bool($ne(tmptarget, target))) this.freeTemp((tmptarget && tmptarget.is$Value()));
-  if ($notnull_bool($ne(tmpindex, index))) this.freeTemp((tmpindex && tmpindex.is$Value()));
+  var ret = this.assignTemp((tmptarget == null ? null : tmptarget.assert$Value()), (target == null ? null : target.assert$Value())).invoke(this, '\$setindex', position, new Arguments(null, [index, y]), false);
+  if ($notnull_bool($ne(tmptarget, target))) this.freeTemp((tmptarget == null ? null : tmptarget.assert$Value()));
+  if ($notnull_bool($ne(tmpindex, index))) this.freeTemp((tmpindex == null ? null : tmpindex.assert$Value()));
   return ret;
 }
 MethodGenerator.prototype._visitDotAssign = function(kind, xn, yn, position, captureOriginal) {
@@ -14170,13 +14580,13 @@ MethodGenerator.prototype._visitDotAssign = function(kind, xn, yn, position, cap
   var y = this.visitValue(yn);
   var tmptarget = target;
   if (kind != 0) {
-    tmptarget = this.getTemp((target && target.is$Value()));
+    tmptarget = this.getTemp((target == null ? null : target.assert$Value()));
     var right = tmptarget.get_$3(this, xn.name.name, xn.name);
-    right = captureOriginal((right && right.is$Value()));
+    right = captureOriginal((right == null ? null : right.assert$Value()));
     y = right.invoke$4(this, TokenKind.binaryMethodName(kind), position, new Arguments(null, [y]));
   }
-  var ret = this.assignTemp((tmptarget && tmptarget.is$Value()), (target && target.is$Value())).set_(this, xn.name.name, xn.name, (y && y.is$Value()), false);
-  if ($notnull_bool($ne(tmptarget, target))) this.freeTemp((tmptarget && tmptarget.is$Value()));
+  var ret = this.assignTemp((tmptarget == null ? null : tmptarget.assert$Value()), (target == null ? null : target.assert$Value())).set_(this, xn.name.name, xn.name, (y == null ? null : y.assert$Value()), false);
+  if ($notnull_bool($ne(tmptarget, target))) this.freeTemp((tmptarget == null ? null : tmptarget.assert$Value()));
   return ret;
 }
 MethodGenerator.prototype.visitUnaryExpression = function(node) {
@@ -14192,14 +14602,14 @@ MethodGenerator.prototype.visitUnaryExpression = function(node) {
       else {
         var kind = (16/*TokenKind.INCR*/ == node.op.kind ? 42/*TokenKind.ADD*/ : 43/*TokenKind.SUB*/);
         var operand = new LiteralExpression(1, new TypeReference(node.span, $globals.world.numType), '1', node.span);
-        return this._visitAssign($assert_num(kind), node.self, (operand && operand.is$lang_Expression()), node, to$call$1(null));
+        return this._visitAssign($assert_num(kind), node.self, (operand == null ? null : operand.assert$lang_Expression()), node, to$call$1(null));
       }
 
     case 19/*TokenKind.NOT*/:
 
       if ($notnull_bool(value.get$type().get$isBool()) && $notnull_bool(value.get$isConst())) {
         var newVal = !$notnull_bool(value.get$actualValue());
-        return EvaluatedValue.EvaluatedValue$factory((($0 = value.get$type()) && $0.is$lang_Type()), newVal, ('' + newVal), node.span);
+        return EvaluatedValue.EvaluatedValue$factory((($0 = value.get$type()) == null ? null : $0.assert$lang_Type()), newVal, ('' + newVal), node.span);
       }
       else {
         var newVal = value.convertTo$3(this, $globals.world.nonNullBool, node);
@@ -14239,14 +14649,14 @@ MethodGenerator.prototype.visitPostfixExpression = function(node, isVoid) {
   var kind = (16/*TokenKind.INCR*/ == node.op.kind) ? 42/*TokenKind.ADD*/ : 43/*TokenKind.SUB*/;
   var operand = new LiteralExpression(1, new TypeReference(node.span, $globals.world.numType), '1', node.span);
   var tmpleft = null, left = null;
-  var ret = this._visitAssign($assert_num(kind), node.body, (operand && operand.is$lang_Expression()), node, (function (l) {
+  var ret = this._visitAssign($assert_num(kind), node.body, (operand == null ? null : operand.assert$lang_Expression()), node, (function (l) {
     if ($notnull_bool(isVoid)) {
       return l;
     }
     else {
       left = l;
-      tmpleft = $this.forceTemp((l && l.is$Value()));
-      return $this.assignTemp((tmpleft && tmpleft.is$Value()), (left && left.is$Value()));
+      tmpleft = $this.forceTemp((l == null ? null : l.assert$Value()));
+      return $this.assignTemp((tmpleft == null ? null : tmpleft.assert$Value()), (left == null ? null : left.assert$Value()));
     }
   })
   );
@@ -14254,7 +14664,7 @@ MethodGenerator.prototype.visitPostfixExpression = function(node, isVoid) {
     ret = new Value(ret.get$type(), ("(" + ret.get$code() + ", " + tmpleft.get$code() + ")"), node.span, true);
   }
   if ($notnull_bool($ne(tmpleft, left))) {
-    this.freeTemp((tmpleft && tmpleft.is$Value()));
+    this.freeTemp((tmpleft == null ? null : tmpleft.assert$Value()));
   }
   return ret;
 }
@@ -14266,12 +14676,12 @@ MethodGenerator.prototype.visitNewExpression = function(node) {
     constructorName = node.name.name;
   }
   if ($notnull_bool($eq(constructorName, '')) && !(typeRef instanceof GenericTypeReference) && $notnull_bool($ne(typeRef.get$names(), null))) {
-    var names = ListFactory.ListFactory$from$factory((($0 = typeRef.get$names()) && $0.is$Iterable()));
+    var names = ListFactory.ListFactory$from$factory((($0 = typeRef.get$names()) == null ? null : $0.assert$Iterable()));
     constructorName = names.removeLast$0().get$name();
     if ($notnull_bool($eq(names.length, 0))) names = null;
-    typeRef = new NameTypeReference(typeRef.get$isFinal(), typeRef.get$name(), names, (($0 = typeRef.get$span()) && $0.is$SourceSpan()));
+    typeRef = new NameTypeReference(typeRef.get$isFinal(), typeRef.get$name(), names, (($0 = typeRef.get$span()) == null ? null : $0.assert$SourceSpan()));
   }
-  var type = this.method.resolveType((typeRef && typeRef.is$TypeReference()), true);
+  var type = this.method.resolveType((typeRef == null ? null : typeRef.assert$TypeReference()), true);
   if ($notnull_bool(type.get$isTop())) {
     type = type.get$library().findTypeByName$1(constructorName);
     constructorName = '';
@@ -14292,8 +14702,8 @@ MethodGenerator.prototype.visitNewExpression = function(node) {
     var $list = node.arguments;
     for (var $i = 0;$i < $list.length; $i++) {
       var arg = $list.$index($i);
-      if (!$notnull_bool(this.visitValue((($0 = arg.get$value()) && $0.is$lang_Expression())).get$isConst())) {
-        $globals.world.error('const constructor expects const arguments', (($0 = arg.get$span()) && $0.is$SourceSpan()));
+      if (!$notnull_bool(this.visitValue((($0 = arg.get$value()) == null ? null : $0.assert$lang_Expression())).get$isConst())) {
+        $globals.world.error('const constructor expects const arguments', (($0 = arg.get$span()) == null ? null : $0.assert$SourceSpan()));
       }
     }
   }
@@ -14307,11 +14717,11 @@ MethodGenerator.prototype.visitListExpression = function(node) {
   var $list = node.values;
   for (var $i = 0;$i < $list.length; $i++) {
     var item = $list.$index($i);
-    var arg = this.visitValue((item && item.is$lang_Expression()));
+    var arg = this.visitValue((item == null ? null : item.assert$lang_Expression()));
     argValues.add$1(arg);
     if ($notnull_bool(node.isConst)) {
       if (!$notnull_bool(arg.get$isConst())) {
-        $globals.world.error('const list can only contain const values', (($0 = item.get$span()) && $0.is$SourceSpan()));
+        $globals.world.error('const list can only contain const values', (($0 = item.get$span()) == null ? null : $0.assert$SourceSpan()));
         argsCode.add$1(arg.get$code());
       }
       else {
@@ -14323,13 +14733,13 @@ MethodGenerator.prototype.visitListExpression = function(node) {
     }
   }
   $globals.world.get$coreimpl().types.$index('ListFactory').markUsed$0();
-  var code = ('[' + Strings.join((argsCode && argsCode.is$List_String()), ", ") + ']');
+  var code = ('[' + Strings.join((argsCode == null ? null : argsCode.assert$List_String()), ", ") + ']');
   var value = new Value($globals.world.listType, code, node.span, true);
   if ($notnull_bool(node.isConst)) {
     var immutableList = $globals.world.get$coreimpl().types.$index('ImmutableList');
     var immutableListCtor = immutableList.getConstructor$1('from');
     var result = immutableListCtor.invoke$4(this, node, new Value.type$ctor(value.get$type(), node.span), new Arguments(null, [value]));
-    value = $globals.world.gen.globalForConst(ConstListValue.ConstListValue$factory((immutableList && immutableList.is$lang_Type()), (argValues && argValues.is$List_EvaluatedValue()), ('const ' + code), $assert_String(result.get$code()), node.span), (argValues && argValues.is$List_Value()));
+    value = $globals.world.gen.globalForConst(ConstListValue.ConstListValue$factory((immutableList == null ? null : immutableList.assert$lang_Type()), (argValues == null ? null : argValues.assert$List_EvaluatedValue()), ('const ' + code), $assert_String(result.get$code()), node.span), (argValues == null ? null : argValues.assert$List_Value()));
   }
   return value;
 }
@@ -14340,14 +14750,14 @@ MethodGenerator.prototype.visitMapExpression = function(node) {
   var argsCode = [];
   for (var i = 0;
    i < node.items.length; i += 2) {
-    var key = this.visitTypedValue((($0 = node.items.$index(i)) && $0.is$lang_Expression()), $globals.world.stringType);
+    var key = this.visitTypedValue((($0 = node.items.$index(i)) == null ? null : $0.assert$lang_Expression()), $globals.world.stringType);
     var valueItem = node.items.$index(i + 1);
-    var value = this.visitValue((valueItem && valueItem.is$lang_Expression()));
+    var value = this.visitValue((valueItem == null ? null : valueItem.assert$lang_Expression()));
     argValues.add$1(key);
     argValues.add$1(value);
     if ($notnull_bool(node.isConst)) {
       if (!$notnull_bool(key.get$isConst()) || !$notnull_bool(value.get$isConst())) {
-        $globals.world.error('const map can only contain const values', (($0 = valueItem.get$span()) && $0.is$SourceSpan()));
+        $globals.world.error('const map can only contain const values', (($0 = valueItem.get$span()) == null ? null : $0.assert$SourceSpan()));
         argsCode.add$1(key.get$code());
         argsCode.add$1(value.get$code());
       }
@@ -14361,15 +14771,15 @@ MethodGenerator.prototype.visitMapExpression = function(node) {
       argsCode.add$1(value.get$code());
     }
   }
-  var argList = ('[' + Strings.join((argsCode && argsCode.is$List_String()), ", ") + ']');
+  var argList = ('[' + Strings.join((argsCode == null ? null : argsCode.assert$List_String()), ", ") + ']');
   var code = ('\$map(' + argList + ')');
   if ($notnull_bool(node.isConst)) {
     var immutableMap = $globals.world.get$coreimpl().types.$index('ImmutableMap');
     var immutableMapCtor = immutableMap.getConstructor$1('');
     var argsValue = new Value($globals.world.listType, argList, node.span, true);
     var result = immutableMapCtor.invoke$4(this, node, new Value.type$ctor(immutableMap, node.span), new Arguments(null, [argsValue]));
-    var value = ConstMapValue.ConstMapValue$factory((immutableMap && immutableMap.is$lang_Type()), (argValues && argValues.is$List_EvaluatedValue()), code, $assert_String(result.get$code()), node.span);
-    return $globals.world.gen.globalForConst(value, (argValues && argValues.is$List_Value()));
+    var value = ConstMapValue.ConstMapValue$factory((immutableMap == null ? null : immutableMap.assert$lang_Type()), (argValues == null ? null : argValues.assert$List_EvaluatedValue()), code, $assert_String(result.get$code()), node.span);
+    return $globals.world.gen.globalForConst(value, (argValues == null ? null : argValues.assert$List_Value()));
   }
   return new Value(mapImplType, code, node.span, true);
 }
@@ -14379,7 +14789,7 @@ MethodGenerator.prototype.visitConditionalExpression = function(node) {
   var trueBranch = this.visitValue(node.trueBranch);
   var falseBranch = this.visitValue(node.falseBranch);
   var code = ('' + test.get$code() + ' ? ' + trueBranch.get$code() + ' : ' + falseBranch.get$code());
-  return new Value(lang_Type.union((($0 = trueBranch.get$type()) && $0.is$lang_Type()), (($0 = falseBranch.get$type()) && $0.is$lang_Type())), code, node.span, true);
+  return new Value(lang_Type.union((($0 = trueBranch.get$type()) == null ? null : $0.assert$lang_Type()), (($0 = falseBranch.get$type()) == null ? null : $0.assert$lang_Type())), code, node.span, true);
 }
 MethodGenerator.prototype.visitIsExpression = function(node) {
   var value = this.visitValue(node.x);
@@ -14390,7 +14800,7 @@ MethodGenerator.prototype.visitParenExpression = function(node) {
   var $0;
   var body = this.visitValue(node.body);
   if ($notnull_bool(body.get$isConst())) {
-    return EvaluatedValue.EvaluatedValue$factory((($0 = body.get$type()) && $0.is$lang_Type()), body.get$actualValue(), ('(' + body.get$canonicalCode() + ')'), node.span);
+    return EvaluatedValue.EvaluatedValue$factory((($0 = body.get$type()) == null ? null : $0.assert$lang_Type()), body.get$actualValue(), ('(' + body.get$canonicalCode() + ')'), node.span);
   }
   return new Value(body.get$type(), ('(' + body.get$code() + ')'), node.span, true);
 }
@@ -14409,7 +14819,7 @@ MethodGenerator.prototype._makeMissingValue = function(name) {
 }
 MethodGenerator.prototype._makeThisOrType = function(span) {
   var $0;
-  return new BareValue(this, (($0 = this._getOutermostMethod()) && $0.is$MethodGenerator()), span);
+  return new BareValue(this, (($0 = this._getOutermostMethod()) == null ? null : $0.assert$MethodGenerator()), span);
 }
 MethodGenerator.prototype.visitThisExpression = function(node) {
   return this._makeThisValue(node);
@@ -14422,7 +14832,7 @@ MethodGenerator.prototype.visitNullExpression = function(node) {
 }
 MethodGenerator.prototype._isUnaryIncrement = function(item) {
   if ((item instanceof UnaryExpression)) {
-    var u = (item && item.is$UnaryExpression());
+    var u = (item == null ? null : item.assert$UnaryExpression());
     return u.op.kind == 16/*TokenKind.INCR*/ || u.op.kind == 17/*TokenKind.DECR*/;
   }
   else {
@@ -14432,23 +14842,23 @@ MethodGenerator.prototype._isUnaryIncrement = function(item) {
 MethodGenerator.prototype.visitLiteralExpression = function(node) {
   var $0;
   var type = node.type.type;
-  $assert($ne(type, null), "type != null", "gen.dart", 2269, 12);
-  if (!!(($0 = node.value) && $0.is$List)) {
+  $assert($ne(type, null), "type != null", "gen.dart", 2264, 12);
+  if (!!(($0 = node.value) && $0.is$List())) {
     var items = [];
     var $list = node.value;
     for (var $i = node.value.iterator$0(); $i.hasNext$0(); ) {
       var item = $i.next$0();
-      var val = this.visitValue((item && item.is$lang_Expression()));
+      var val = this.visitValue((item == null ? null : item.assert$lang_Expression()));
       val.invoke$4(this, 'toString', item, Arguments.get$EMPTY());
       var code = val.get$code();
-      if ((item instanceof BinaryExpression) || (item instanceof ConditionalExpression) || (item instanceof PostfixExpression) || $notnull_bool(this._isUnaryIncrement((item && item.is$lang_Expression())))) {
+      if ((item instanceof BinaryExpression) || (item instanceof ConditionalExpression) || (item instanceof PostfixExpression) || $notnull_bool(this._isUnaryIncrement((item == null ? null : item.assert$lang_Expression())))) {
         code = ('(' + code + ')');
       }
       if ($notnull_bool($eq(items.length, 0)) || ($notnull_bool($ne(code, "''")) && $notnull_bool($ne(code, '""')))) {
         items.add$1(code);
       }
     }
-    return new Value(type, ('(' + Strings.join((items && items.is$List_String()), " + ") + ')'), node.span, true);
+    return new Value(type, ('(' + Strings.join((items == null ? null : items.assert$List_String()), " + ") + ')'), node.span, true);
   }
   var text = node.text;
   if ($notnull_bool(type.get$isString())) {
@@ -14467,13 +14877,13 @@ MethodGenerator.prototype.visitLiteralExpression = function(node) {
       node.text = $assert_String(text);
     }
   }
-  return EvaluatedValue.EvaluatedValue$factory((type && type.is$lang_Type()), node.value, node.text, null);
+  return EvaluatedValue.EvaluatedValue$factory((type == null ? null : type.assert$lang_Type()), node.value, node.text, null);
 }
 MethodGenerator.prototype.visitPostfixExpression$1 = function($0) {
-  return this.visitPostfixExpression(($0 && $0.is$PostfixExpression()), false);
+  return this.visitPostfixExpression(($0 == null ? null : $0.assert$PostfixExpression()), false);
 };
 MethodGenerator.prototype.writeDefinition$2 = function($0, $1) {
-  return this.writeDefinition(($0 && $0.is$CodeWriter()), ($1 && $1.is$LambdaExpression()));
+  return this.writeDefinition(($0 == null ? null : $0.assert$CodeWriter()), ($1 == null ? null : $1.assert$LambdaExpression()));
 };
 // ********** Code for Arguments **************
 function Arguments(nodes, values) {
@@ -14481,7 +14891,7 @@ function Arguments(nodes, values) {
   this.values = values;
   // Initializers done
 }
-Arguments.prototype.is$Arguments = function(){return this;};
+Arguments.prototype.assert$Arguments = function(){return this};
 Arguments.Arguments$bare$factory = function(arity) {
   var values = [];
   for (var i = 0;
@@ -14527,7 +14937,7 @@ Arguments.prototype.getIndexOfName = function(name) {
 Arguments.prototype.getValue = function(name) {
   var $0;
   var i = this.getIndexOfName(name);
-  return (($0 = i >= 0 ? this.values.$index(i) : null) && $0.is$Value());
+  return (($0 = i >= 0 ? this.values.$index(i) : null) == null ? null : $0.assert$Value());
 }
 Arguments.prototype.get$bareCount = function() {
   if (this._bareCount == null) {
@@ -14550,8 +14960,8 @@ Arguments.prototype.getCode = function() {
    i < this.get$length(); i++) {
     argsCode.add$1(this.values.$index(i).get$code());
   }
-  Arguments.removeTrailingNulls((argsCode && argsCode.is$List_Value()));
-  return Strings.join((argsCode && argsCode.is$List_String()), ", ");
+  Arguments.removeTrailingNulls((argsCode == null ? null : argsCode.assert$List_Value()));
+  return Strings.join((argsCode == null ? null : argsCode.assert$List_String()), ", ");
 }
 Arguments.removeTrailingNulls = function(argsCode) {
   while (argsCode.length > 0 && $notnull_bool($eq(argsCode.last(), 'null'))) {
@@ -14564,7 +14974,7 @@ Arguments.prototype.getNames = function() {
    i < this.get$length(); i++) {
     names.add$1(this.getName(i));
   }
-  return (names && names.is$List_String());
+  return (names == null ? null : names.assert$List_String());
 }
 Arguments.prototype.toCallStubArgs = function() {
   var result = [];
@@ -14606,7 +15016,7 @@ function Library(baseSource) {
   this._privateMembers = $map([]);
 }
 $inherits(Library, lang_Element);
-Library.prototype.is$Library = function(){return this;};
+Library.prototype.assert$Library = function(){return this};
 Library.prototype.get$baseSource = function() { return this.baseSource; };
 Library.prototype.get$types = function() { return this.types; };
 Library.prototype.set$types = function(value) { return this.types = value; };
@@ -14648,10 +15058,10 @@ Library.prototype.addNative = function(fullname) {
 Library.prototype._findMembers = function(name) {
   var $0;
   if (name.startsWith('_')) {
-    return (($0 = this._privateMembers.$index(name)) && $0.is$MemberSet());
+    return (($0 = this._privateMembers.$index(name)) == null ? null : $0.assert$MemberSet());
   }
   else {
-    return (($0 = $globals.world._members.$index(name)) && $0.is$MemberSet());
+    return (($0 = $globals.world._members.$index(name)) == null ? null : $0.assert$MemberSet());
   }
 }
 Library.prototype._addMember = function(member) {
@@ -14701,13 +15111,13 @@ Library.prototype.addType = function(name, definition, isClass) {
       existingType.setDefinition$1(definition);
     }
     else {
-      $globals.world.warning(('duplicate definition of ' + name), definition.span, (($0 = existingType.get$span()) && $0.is$SourceSpan()));
+      $globals.world.warning(('duplicate definition of ' + name), definition.span, (($0 = existingType.get$span()) == null ? null : $0.assert$SourceSpan()));
     }
   }
   else {
-    this.types.$setindex(name, new DefinedType(name, this, (definition && definition.is$Definition()), isClass));
+    this.types.$setindex(name, new DefinedType(name, this, (definition == null ? null : definition.assert$Definition()), isClass));
   }
-  return (($0 = this.types.$index(name)) && $0.is$DefinedType());
+  return (($0 = this.types.$index(name)) == null ? null : $0.assert$DefinedType());
 }
 Library.prototype.findType = function(type) {
   var result = this.findTypeByName(type.name.name);
@@ -14738,21 +15148,21 @@ Library.prototype.findTypeByName = function(name) {
     }
     if ($notnull_bool($ne(newRet, null))) {
       if ($notnull_bool($ne(ret, null)) && $notnull_bool($ne(ret, newRet))) {
-        $globals.world.error(('conflicting types for "' + name + '"'), (($0 = ret.get$span()) && $0.is$SourceSpan()), (($0 = newRet.get$span()) && $0.is$SourceSpan()));
+        $globals.world.error(('conflicting types for "' + name + '"'), (($0 = ret.get$span()) == null ? null : $0.assert$SourceSpan()), (($0 = newRet.get$span()) == null ? null : $0.assert$SourceSpan()));
       }
       else {
         ret = newRet;
       }
     }
   }
-  return (ret && ret.is$lang_Type());
+  return (ret == null ? null : ret.assert$lang_Type());
 }
 Library.prototype.resolveType = function(node, typeErrors) {
   if (node == null) return $globals.world.varType;
   if (node.type != null) return node.type;
-  node.type = this.findType((node && node.is$NameTypeReference()));
+  node.type = this.findType((node == null ? null : node.assert$NameTypeReference()));
   if (node.type == null) {
-    var message = ('cannot find type ' + Library._getDottedName((node && node.is$NameTypeReference())));
+    var message = ('cannot find type ' + Library._getDottedName((node == null ? null : node.assert$NameTypeReference())));
     if ($notnull_bool(typeErrors)) {
       $globals.world.error($assert_String(message), node.span);
       node.type = $globals.world.objectType;
@@ -14770,7 +15180,7 @@ Library._getDottedName = function(type) {
       return n.get$name();
     })
     );
-    return type.name.name + '.' + Strings.join((names && names.is$List_String()), '.');
+    return type.name.name + '.' + Strings.join((names == null ? null : names.assert$List_String()), '.');
   }
   else {
     return type.name.name;
@@ -14786,7 +15196,7 @@ Library.prototype.lookup = function(name, span) {
   var newRet = this.topType.getMember(name);
   if ($notnull_bool($ne(newRet, null))) {
     if ($notnull_bool($ne(ret, null)) && $notnull_bool($ne(ret, newRet))) {
-      $globals.world.error(('conflicting members for "' + name + '"'), span, (($0 = ret.get$span()) && $0.is$SourceSpan()), (($0 = newRet.get$span()) && $0.is$SourceSpan()));
+      $globals.world.error(('conflicting members for "' + name + '"'), span, (($0 = ret.get$span()) == null ? null : $0.assert$SourceSpan()), (($0 = newRet.get$span()) == null ? null : $0.assert$SourceSpan()));
     }
     else {
       ret = newRet;
@@ -14799,7 +15209,7 @@ Library.prototype.lookup = function(name, span) {
       newRet = imported.get$library().get$topType().getMember$1(name);
       if ($notnull_bool($ne(newRet, null))) {
         if ($notnull_bool($ne(ret, null)) && $notnull_bool($ne(ret, newRet))) {
-          $globals.world.error(('conflicting members for "' + name + '"'), span, (($0 = ret.get$span()) && $0.is$SourceSpan()), (($0 = newRet.get$span()) && $0.is$SourceSpan()));
+          $globals.world.error(('conflicting members for "' + name + '"'), span, (($0 = ret.get$span()) == null ? null : $0.assert$SourceSpan()), (($0 = newRet.get$span()) == null ? null : $0.assert$SourceSpan()));
         }
         else {
           ret = newRet;
@@ -14807,7 +15217,7 @@ Library.prototype.lookup = function(name, span) {
       }
     }
   }
-  return (ret && ret.is$Member());
+  return (ret == null ? null : ret.assert$Member());
 }
 Library.prototype.resolve = function() {
   if (this.name == null) {
@@ -14852,7 +15262,7 @@ function _LibraryVisitor(library) {
   this.currentType = this.library.topType;
   this.sources = [];
 }
-_LibraryVisitor.prototype.is$TreeVisitor = function(){return this;};
+_LibraryVisitor.prototype.assert$TreeVisitor = function(){return this};
 _LibraryVisitor.prototype.get$library = function() { return this.library; };
 _LibraryVisitor.prototype.get$isTop = function() { return this.isTop; };
 _LibraryVisitor.prototype.set$isTop = function(value) { return this.isTop = value; };
@@ -14894,7 +15304,7 @@ _LibraryVisitor.prototype.addSource = function(source) {
   this.sources = [];
   for (var $i = newSources.iterator$0(); $i.hasNext$0(); ) {
     var source0 = $i.next$0();
-    this.addSource((source0 && source0.is$SourceFile()));
+    this.addSource((source0 == null ? null : source0.assert$SourceFile()));
   }
 }
 _LibraryVisitor.prototype.visitDirectiveDefinition = function(node) {
@@ -14989,7 +15399,7 @@ _LibraryVisitor.prototype.getFirstStringArg = function(node) {
   if ($notnull_bool($ne(arg.get$label(), null))) {
     $globals.world.error('label not allowed for directive', node.span);
   }
-  return this._parseStringArgument((arg && arg.is$ArgumentNode()));
+  return this._parseStringArgument((arg == null ? null : arg.assert$ArgumentNode()));
 }
 _LibraryVisitor.prototype.tryGetNamedStringArg = function(node, argName) {
   var args = node.arguments.filter((function (a) {
@@ -15004,14 +15414,14 @@ _LibraryVisitor.prototype.tryGetNamedStringArg = function(node, argName) {
   }
   for (var $i = args.iterator$0(); $i.hasNext$0(); ) {
     var arg = $i.next$0();
-    return this._parseStringArgument((arg && arg.is$ArgumentNode()));
+    return this._parseStringArgument((arg == null ? null : arg.assert$ArgumentNode()));
   }
 }
 _LibraryVisitor.prototype._parseStringArgument = function(arg) {
   var $0;
   var expr = arg.value;
   if (!(expr instanceof LiteralExpression) || !$notnull_bool(expr.get$type().get$type().get$isString())) {
-    $globals.world.error('expected string', (($0 = expr.get$span()) && $0.is$SourceSpan()));
+    $globals.world.error('expected string', (($0 = expr.get$span()) == null ? null : $0.assert$SourceSpan()));
   }
   return parseStringLiteral($assert_String(expr.get$value()));
 }
@@ -15023,7 +15433,7 @@ _LibraryVisitor.prototype.visitTypeDefinition = function(node) {
     var member = $list.$index($i);
     member.visit$1(this);
   }
-  this.currentType = (oldType && oldType.is$DefinedType());
+  this.currentType = (oldType == null ? null : oldType.assert$DefinedType());
 }
 _LibraryVisitor.prototype.visitVariableDefinition = function(node) {
   this.currentType.addField(node);
@@ -15036,7 +15446,7 @@ _LibraryVisitor.prototype.visitFunctionTypeDefinition = function(node) {
   type.addMethod$2('\$call', node.func);
 }
 _LibraryVisitor.prototype.addSource$1 = function($0) {
-  return this.addSource(($0 && $0.is$SourceFile()));
+  return this.addSource(($0 == null ? null : $0.assert$SourceFile()));
 };
 // ********** Code for Parameter **************
 function Parameter(definition, method) {
@@ -15045,7 +15455,7 @@ function Parameter(definition, method) {
   this.method = method;
   // Initializers done
 }
-Parameter.prototype.is$Parameter = function(){return this;};
+Parameter.prototype.assert$Parameter = function(){return this};
 Parameter.prototype.get$definition = function() { return this.definition; };
 Parameter.prototype.set$definition = function(value) { return this.definition = value; };
 Parameter.prototype.get$name = function() { return this.name; };
@@ -15089,7 +15499,7 @@ Parameter.prototype.genValue = function(method, context) {
   if (context == null) {
     context = new MethodGenerator(method, null);
   }
-  this.value = (($0 = this.definition.value.visit(context)) && $0.is$Value());
+  this.value = (($0 = this.definition.value.visit(context)) == null ? null : $0.assert$Value());
   this.value = this.value.convertTo(context, this.type, this.definition.value, false);
 }
 Parameter.prototype.copyWithNewType = function(newMethod, newType) {
@@ -15098,16 +15508,16 @@ Parameter.prototype.copyWithNewType = function(newMethod, newType) {
   ret.set$type(newType);
   ret.set$name(this.name);
   ret.set$isInitializer(this.isInitializer);
-  return (ret && ret.is$Parameter());
+  return (ret == null ? null : ret.assert$Parameter());
 }
 Parameter.prototype.get$isOptional = function() {
   return this.definition != null && this.definition.value != null;
 }
 Parameter.prototype.copyWithNewType$2 = function($0, $1) {
-  return this.copyWithNewType(($0 && $0.is$Member()), ($1 && $1.is$lang_Type()));
+  return this.copyWithNewType(($0 == null ? null : $0.assert$Member()), ($1 == null ? null : $1.assert$lang_Type()));
 };
 Parameter.prototype.genValue$2 = function($0, $1) {
-  return this.genValue(($0 && $0.is$MethodMember()), ($1 && $1.is$MethodGenerator()));
+  return this.genValue(($0 == null ? null : $0.assert$MethodMember()), ($1 == null ? null : $1.assert$MethodGenerator()));
 };
 Parameter.prototype.resolve$0 = Parameter.prototype.resolve;
 // ********** Code for Member **************
@@ -15118,7 +15528,7 @@ function Member(name, declaringType) {
   lang_Element.call(this, name, declaringType);
 }
 $inherits(Member, lang_Element);
-Member.prototype.is$Member = function(){return this;};
+Member.prototype.assert$Member = function(){return this};
 Member.prototype.get$declaringType = function() { return this.declaringType; };
 Member.prototype.get$generator = function() { return this.generator; };
 Member.prototype.set$generator = function(value) { return this.generator = value; };
@@ -15190,7 +15600,7 @@ Member.prototype.get$inferredResult = function() {
   if ($notnull_bool(t.get$isBool()) && ($notnull_bool(this.get$library().get$isCore()) || $notnull_bool(this.get$library().get$isCoreImpl()))) {
     return $globals.world.nonNullBool;
   }
-  return (t && t.is$lang_Type());
+  return (t == null ? null : t.assert$lang_Type());
 }
 Member.prototype.get$definition = function() {
   return null;
@@ -15204,7 +15614,7 @@ Member.prototype.canInvoke = function(context, args) {
 Member.prototype.invoke = function(context, node, target, args, isDynamic) {
   var $0;
   var newTarget = this._get(context, node, target, isDynamic);
-  return (($0 = newTarget.invoke$5(context, '\$call', node, args, isDynamic)) && $0.is$Value());
+  return (($0 = newTarget.invoke$5(context, '\$call', node, args, isDynamic)) == null ? null : $0.assert$Value());
 }
 Member.prototype.override = function(other) {
   if ($notnull_bool(this.get$isStatic())) {
@@ -15231,24 +15641,24 @@ Member.prototype.hashCode = function() {
   return (this.declaringType.hashCode() << 4) ^ this.name.hashCode();
 }
 Member.prototype._get$3 = function($0, $1, $2) {
-  return this._get(($0 && $0.is$MethodGenerator()), ($1 && $1.is$lang_Node()), ($2 && $2.is$Value()));
+  return this._get(($0 == null ? null : $0.assert$MethodGenerator()), ($1 == null ? null : $1.assert$lang_Node()), ($2 == null ? null : $2.assert$Value()));
 };
 Member.prototype._set$4 = function($0, $1, $2, $3) {
-  return this._set(($0 && $0.is$MethodGenerator()), ($1 && $1.is$lang_Node()), ($2 && $2.is$Value()), ($3 && $3.is$Value()));
+  return this._set(($0 == null ? null : $0.assert$MethodGenerator()), ($1 == null ? null : $1.assert$lang_Node()), ($2 == null ? null : $2.assert$Value()), ($3 == null ? null : $3.assert$Value()));
 };
 Member.prototype.canInvoke$2 = function($0, $1) {
-  return this.canInvoke(($0 && $0.is$MethodGenerator()), ($1 && $1.is$Arguments()));
+  return this.canInvoke(($0 == null ? null : $0.assert$MethodGenerator()), ($1 == null ? null : $1.assert$Arguments()));
 };
 Member.prototype.computeValue$0 = Member.prototype.computeValue;
 Member.prototype.hashCode$0 = Member.prototype.hashCode;
 Member.prototype.invoke$4 = function($0, $1, $2, $3) {
-  return this.invoke(($0 && $0.is$MethodGenerator()), ($1 && $1.is$lang_Node()), ($2 && $2.is$Value()), ($3 && $3.is$Arguments()), false);
+  return this.invoke(($0 == null ? null : $0.assert$MethodGenerator()), ($1 == null ? null : $1.assert$lang_Node()), ($2 == null ? null : $2.assert$Value()), ($3 == null ? null : $3.assert$Arguments()), false);
 };
 Member.prototype.invoke$4$isDynamic = function($0, $1, $2, $3, isDynamic) {
-  return this.invoke(($0 && $0.is$MethodGenerator()), ($1 && $1.is$lang_Node()), ($2 && $2.is$Value()), ($3 && $3.is$Arguments()), $assert_bool(isDynamic));
+  return this.invoke(($0 == null ? null : $0.assert$MethodGenerator()), ($1 == null ? null : $1.assert$lang_Node()), ($2 == null ? null : $2.assert$Value()), ($3 == null ? null : $3.assert$Arguments()), $assert_bool(isDynamic));
 };
 Member.prototype.invoke$5 = function($0, $1, $2, $3, $4) {
-  return this.invoke(($0 && $0.is$MethodGenerator()), ($1 && $1.is$lang_Node()), ($2 && $2.is$Value()), ($3 && $3.is$Arguments()), $assert_bool($4));
+  return this.invoke(($0 == null ? null : $0.assert$MethodGenerator()), ($1 == null ? null : $1.assert$lang_Node()), ($2 == null ? null : $2.assert$Value()), ($3 == null ? null : $3.assert$Arguments()), $assert_bool($4));
 };
 Member.prototype.provideFieldSyntax$0 = Member.prototype.provideFieldSyntax;
 Member.prototype.providePropertySyntax$0 = Member.prototype.providePropertySyntax;
@@ -15259,7 +15669,7 @@ function TypeMember(type) {
   Member.call(this, type.name, type.library.topType);
 }
 $inherits(TypeMember, Member);
-TypeMember.prototype.is$TypeMember = function(){return this;};
+TypeMember.prototype.assert$TypeMember = function(){return this};
 TypeMember.prototype.get$type = function() { return this.type; };
 TypeMember.prototype.get$span = function() {
   return this.type.definition.span;
@@ -15289,22 +15699,22 @@ TypeMember.prototype.invoke = function(context, node, target, args, isDynamic) {
   $globals.world.error('cannot invoke type', node.span);
 }
 TypeMember.prototype._get$3 = function($0, $1, $2) {
-  return this._get(($0 && $0.is$MethodGenerator()), ($1 && $1.is$lang_Node()), ($2 && $2.is$Value()), false);
+  return this._get(($0 == null ? null : $0.assert$MethodGenerator()), ($1 == null ? null : $1.assert$lang_Node()), ($2 == null ? null : $2.assert$Value()), false);
 };
 TypeMember.prototype._set$4 = function($0, $1, $2, $3) {
-  return this._set(($0 && $0.is$MethodGenerator()), ($1 && $1.is$lang_Node()), ($2 && $2.is$Value()), ($3 && $3.is$Value()), false);
+  return this._set(($0 == null ? null : $0.assert$MethodGenerator()), ($1 == null ? null : $1.assert$lang_Node()), ($2 == null ? null : $2.assert$Value()), ($3 == null ? null : $3.assert$Value()), false);
 };
 TypeMember.prototype.canInvoke$2 = function($0, $1) {
-  return this.canInvoke(($0 && $0.is$MethodGenerator()), ($1 && $1.is$Arguments()));
+  return this.canInvoke(($0 == null ? null : $0.assert$MethodGenerator()), ($1 == null ? null : $1.assert$Arguments()));
 };
 TypeMember.prototype.invoke$4 = function($0, $1, $2, $3) {
-  return this.invoke(($0 && $0.is$MethodGenerator()), ($1 && $1.is$lang_Node()), ($2 && $2.is$Value()), ($3 && $3.is$Arguments()), false);
+  return this.invoke(($0 == null ? null : $0.assert$MethodGenerator()), ($1 == null ? null : $1.assert$lang_Node()), ($2 == null ? null : $2.assert$Value()), ($3 == null ? null : $3.assert$Arguments()), false);
 };
 TypeMember.prototype.invoke$4$isDynamic = function($0, $1, $2, $3, isDynamic) {
-  return this.invoke(($0 && $0.is$MethodGenerator()), ($1 && $1.is$lang_Node()), ($2 && $2.is$Value()), ($3 && $3.is$Arguments()), $assert_bool(isDynamic));
+  return this.invoke(($0 == null ? null : $0.assert$MethodGenerator()), ($1 == null ? null : $1.assert$lang_Node()), ($2 == null ? null : $2.assert$Value()), ($3 == null ? null : $3.assert$Arguments()), $assert_bool(isDynamic));
 };
 TypeMember.prototype.invoke$5 = function($0, $1, $2, $3, $4) {
-  return this.invoke(($0 && $0.is$MethodGenerator()), ($1 && $1.is$lang_Node()), ($2 && $2.is$Value()), ($3 && $3.is$Arguments()), $assert_bool($4));
+  return this.invoke(($0 == null ? null : $0.assert$MethodGenerator()), ($1 == null ? null : $1.assert$lang_Node()), ($2 == null ? null : $2.assert$Value()), ($3 == null ? null : $3.assert$Arguments()), $assert_bool($4));
 };
 // ********** Code for FieldMember **************
 function FieldMember(name, declaringType, definition, value) {
@@ -15317,7 +15727,7 @@ function FieldMember(name, declaringType, definition, value) {
   Member.call(this, name, declaringType);
 }
 $inherits(FieldMember, Member);
-FieldMember.prototype.is$FieldMember = function(){return this;};
+FieldMember.prototype.assert$FieldMember = function(){return this};
 FieldMember.prototype.get$definition = function() { return this.definition; };
 FieldMember.prototype.get$value = function() { return this.value; };
 FieldMember.prototype.get$type = function() { return this.type; };
@@ -15352,7 +15762,7 @@ FieldMember.prototype.providePropertySyntax = function() {
 }
 FieldMember.prototype.get$span = function() {
   var $0;
-  return (($0 = this.definition == null ? null : this.definition.span) && $0.is$SourceSpan());
+  return (($0 = this.definition == null ? null : this.definition.span) == null ? null : $0.assert$SourceSpan());
 }
 FieldMember.prototype.get$returnType = function() {
   return this.type;
@@ -15376,18 +15786,18 @@ FieldMember.prototype.resolve = function() {
       var mod = $list.$index($i);
       if ($notnull_bool($eq(mod.get$kind(), 86/*TokenKind.STATIC*/))) {
         if ($notnull_bool(this.isStatic)) {
-          $globals.world.error('duplicate static modifier', (($0 = mod.get$span()) && $0.is$SourceSpan()));
+          $globals.world.error('duplicate static modifier', (($0 = mod.get$span()) == null ? null : $0.assert$SourceSpan()));
         }
         this.isStatic = true;
       }
       else if ($notnull_bool($eq(mod.get$kind(), 97/*TokenKind.FINAL*/))) {
         if ($notnull_bool(this.isFinal)) {
-          $globals.world.error('duplicate final modifier', (($0 = mod.get$span()) && $0.is$SourceSpan()));
+          $globals.world.error('duplicate final modifier', (($0 = mod.get$span()) == null ? null : $0.assert$SourceSpan()));
         }
         this.isFinal = true;
       }
       else {
-        $globals.world.error(('' + mod + ' modifier not allowed on field'), (($0 = mod.get$span()) && $0.is$SourceSpan()));
+        $globals.world.error(('' + mod + ' modifier not allowed on field'), (($0 = mod.get$span()) == null ? null : $0.assert$SourceSpan()));
       }
     }
   }
@@ -15412,7 +15822,7 @@ FieldMember.prototype.computeValue = function() {
     var finalMethod = new MethodMember('final_context', this.declaringType, null);
     finalMethod.set$isStatic(true);
     var finalGen = new MethodGenerator(finalMethod, null);
-    this._computedValue = (($0 = this.value.visit((finalGen && finalGen.is$TreeVisitor()))) && $0.is$Value());
+    this._computedValue = (($0 = this.value.visit((finalGen == null ? null : finalGen.assert$TreeVisitor()))) == null ? null : $0.assert$Value());
     if (!$notnull_bool(this._computedValue.get$isConst())) {
       if ($notnull_bool(this.isStatic)) {
         $globals.world.error('non constant static field must be initialized in functions', this.value.span);
@@ -15436,7 +15846,7 @@ FieldMember.prototype._get = function(context, node, target, isDynamic) {
   if ($notnull_bool(this.isStatic)) {
     var cv = this.computeValue();
     if ($notnull_bool(this.isFinal)) {
-      return (cv && cv.is$Value());
+      return (cv == null ? null : cv.assert$Value());
     }
     $globals.world.gen.hasStatics = true;
     if ($notnull_bool(this.declaringType.get$isTop())) {
@@ -15460,7 +15870,7 @@ FieldMember.prototype._get = function(context, node, target, isDynamic) {
   else if ($notnull_bool(target.get$isConst()) && $notnull_bool(this.isFinal)) {
     var constTarget = (target instanceof GlobalValue) ? target.get$dynamic().get$exp() : target;
     if ((constTarget instanceof ConstObjectValue)) {
-      return (($0 = constTarget.get$fields().$index(this.name)) && $0.is$Value());
+      return (($0 = constTarget.get$fields().$index(this.name)) == null ? null : $0.assert$Value());
     }
     else if ($notnull_bool($eq(constTarget.get$type(), $globals.world.stringType)) && this.name == 'length') {
       return new Value(this.type, ('' + constTarget.get$actualValue().length), node.span, true);
@@ -15474,10 +15884,10 @@ FieldMember.prototype._set = function(context, node, target, value, isDynamic) {
   return new Value(this.type, ('' + lhs.get$code() + ' = ' + value.code), node.span, true);
 }
 FieldMember.prototype._get$3 = function($0, $1, $2) {
-  return this._get(($0 && $0.is$MethodGenerator()), ($1 && $1.is$lang_Node()), ($2 && $2.is$Value()), false);
+  return this._get(($0 == null ? null : $0.assert$MethodGenerator()), ($1 == null ? null : $1.assert$lang_Node()), ($2 == null ? null : $2.assert$Value()), false);
 };
 FieldMember.prototype._set$4 = function($0, $1, $2, $3) {
-  return this._set(($0 && $0.is$MethodGenerator()), ($1 && $1.is$lang_Node()), ($2 && $2.is$Value()), ($3 && $3.is$Value()), false);
+  return this._set(($0 == null ? null : $0.assert$MethodGenerator()), ($1 == null ? null : $1.assert$lang_Node()), ($2 == null ? null : $2.assert$Value()), ($3 == null ? null : $3.assert$Value()), false);
 };
 FieldMember.prototype.computeValue$0 = FieldMember.prototype.computeValue;
 FieldMember.prototype.provideFieldSyntax$0 = FieldMember.prototype.provideFieldSyntax;
@@ -15490,14 +15900,14 @@ function PropertyMember(name, declaringType) {
   Member.call(this, name, declaringType);
 }
 $inherits(PropertyMember, Member);
-PropertyMember.prototype.is$PropertyMember = function(){return this;};
+PropertyMember.prototype.assert$PropertyMember = function(){return this};
 PropertyMember.prototype.get$getter = function() { return this.getter; };
 PropertyMember.prototype.set$getter = function(value) { return this.getter = value; };
 PropertyMember.prototype.get$setter = function() { return this.setter; };
 PropertyMember.prototype.set$setter = function(value) { return this.setter = value; };
 PropertyMember.prototype.get$span = function() {
   var $0;
-  return (($0 = this.getter != null ? this.getter.get$span() : null) && $0.is$SourceSpan());
+  return (($0 = this.getter != null ? this.getter.get$span() : null) == null ? null : $0.assert$SourceSpan());
 }
 PropertyMember.prototype.get$canGet = function() {
   return this.getter != null;
@@ -15560,11 +15970,11 @@ PropertyMember.prototype.addFromParent = function(parentMember) {
   var $0;
   var parent;
   if ((parentMember instanceof ConcreteMember)) {
-    var c = (parentMember && parentMember.is$ConcreteMember());
-    parent = (($0 = c.baseMember) && $0.is$PropertyMember());
+    var c = (parentMember == null ? null : parentMember.assert$ConcreteMember());
+    parent = (($0 = c.baseMember) == null ? null : $0.assert$PropertyMember());
   }
   else {
-    parent = (parentMember && parentMember.is$PropertyMember());
+    parent = (parentMember == null ? null : parentMember.assert$PropertyMember());
   }
   if (this.getter == null) this.getter = parent.getter;
   if (this.setter == null) this.setter = parent.setter;
@@ -15575,10 +15985,10 @@ PropertyMember.prototype.resolve = function() {
   this.get$library()._addMember(this);
 }
 PropertyMember.prototype._get$3 = function($0, $1, $2) {
-  return this._get(($0 && $0.is$MethodGenerator()), ($1 && $1.is$lang_Node()), ($2 && $2.is$Value()), false);
+  return this._get(($0 == null ? null : $0.assert$MethodGenerator()), ($1 == null ? null : $1.assert$lang_Node()), ($2 == null ? null : $2.assert$Value()), false);
 };
 PropertyMember.prototype._set$4 = function($0, $1, $2, $3) {
-  return this._set(($0 && $0.is$MethodGenerator()), ($1 && $1.is$lang_Node()), ($2 && $2.is$Value()), ($3 && $3.is$Value()), false);
+  return this._set(($0 == null ? null : $0.assert$MethodGenerator()), ($1 == null ? null : $1.assert$lang_Node()), ($2 == null ? null : $2.assert$Value()), ($3 == null ? null : $3.assert$Value()), false);
 };
 PropertyMember.prototype.provideFieldSyntax$0 = PropertyMember.prototype.provideFieldSyntax;
 PropertyMember.prototype.providePropertySyntax$0 = PropertyMember.prototype.providePropertySyntax;
@@ -15603,7 +16013,7 @@ function ConcreteMember(name, declaringType, baseMember) {
   }
 }
 $inherits(ConcreteMember, Member);
-ConcreteMember.prototype.is$ConcreteMember = function(){return this;};
+ConcreteMember.prototype.assert$ConcreteMember = function(){return this};
 ConcreteMember.prototype.get$returnType = function() { return this.returnType; };
 ConcreteMember.prototype.set$returnType = function(value) { return this.returnType = value; };
 ConcreteMember.prototype.get$parameters = function() { return this.parameters; };
@@ -15670,7 +16080,7 @@ ConcreteMember.prototype.get$constructorName = function() {
 }
 ConcreteMember.prototype.get$definition = function() {
   var $0;
-  return (($0 = this.baseMember.get$definition()) && $0.is$Definition());
+  return (($0 = this.baseMember.get$definition()) == null ? null : $0.assert$Definition());
 }
 ConcreteMember.prototype.get$initDelegate = function() {
   return this.baseMember.get$initDelegate();
@@ -15681,7 +16091,7 @@ ConcreteMember.prototype.set$initDelegate = function(ctor) {
 ConcreteMember.prototype.resolveType = function(node, isRequired) {
   var $0;
   var type = this.baseMember.resolveType(node, isRequired);
-  return (($0 = type.resolveTypeParams$1(this.declaringType)) && $0.is$lang_Type());
+  return (($0 = type.resolveTypeParams$1(this.declaringType)) == null ? null : $0.assert$lang_Type());
 }
 ConcreteMember.prototype.computeValue = function() {
   return this.baseMember.computeValue();
@@ -15709,23 +16119,23 @@ ConcreteMember.prototype.invoke = function(context, node, target, args, isDynami
   return new Value(this.get$inferredResult(), code, node.span, true);
 }
 ConcreteMember.prototype._get$3 = function($0, $1, $2) {
-  return this._get(($0 && $0.is$MethodGenerator()), ($1 && $1.is$lang_Node()), ($2 && $2.is$Value()), false);
+  return this._get(($0 == null ? null : $0.assert$MethodGenerator()), ($1 == null ? null : $1.assert$lang_Node()), ($2 == null ? null : $2.assert$Value()), false);
 };
 ConcreteMember.prototype._set$4 = function($0, $1, $2, $3) {
-  return this._set(($0 && $0.is$MethodGenerator()), ($1 && $1.is$lang_Node()), ($2 && $2.is$Value()), ($3 && $3.is$Value()), false);
+  return this._set(($0 == null ? null : $0.assert$MethodGenerator()), ($1 == null ? null : $1.assert$lang_Node()), ($2 == null ? null : $2.assert$Value()), ($3 == null ? null : $3.assert$Value()), false);
 };
 ConcreteMember.prototype.canInvoke$2 = function($0, $1) {
-  return this.canInvoke(($0 && $0.is$MethodGenerator()), ($1 && $1.is$Arguments()));
+  return this.canInvoke(($0 == null ? null : $0.assert$MethodGenerator()), ($1 == null ? null : $1.assert$Arguments()));
 };
 ConcreteMember.prototype.computeValue$0 = ConcreteMember.prototype.computeValue;
 ConcreteMember.prototype.invoke$4 = function($0, $1, $2, $3) {
-  return this.invoke(($0 && $0.is$MethodGenerator()), ($1 && $1.is$lang_Node()), ($2 && $2.is$Value()), ($3 && $3.is$Arguments()), false);
+  return this.invoke(($0 == null ? null : $0.assert$MethodGenerator()), ($1 == null ? null : $1.assert$lang_Node()), ($2 == null ? null : $2.assert$Value()), ($3 == null ? null : $3.assert$Arguments()), false);
 };
 ConcreteMember.prototype.invoke$4$isDynamic = function($0, $1, $2, $3, isDynamic) {
-  return this.invoke(($0 && $0.is$MethodGenerator()), ($1 && $1.is$lang_Node()), ($2 && $2.is$Value()), ($3 && $3.is$Arguments()), $assert_bool(isDynamic));
+  return this.invoke(($0 == null ? null : $0.assert$MethodGenerator()), ($1 == null ? null : $1.assert$lang_Node()), ($2 == null ? null : $2.assert$Value()), ($3 == null ? null : $3.assert$Arguments()), $assert_bool(isDynamic));
 };
 ConcreteMember.prototype.invoke$5 = function($0, $1, $2, $3, $4) {
-  return this.invoke(($0 && $0.is$MethodGenerator()), ($1 && $1.is$lang_Node()), ($2 && $2.is$Value()), ($3 && $3.is$Arguments()), $assert_bool($4));
+  return this.invoke(($0 == null ? null : $0.assert$MethodGenerator()), ($1 == null ? null : $1.assert$lang_Node()), ($2 == null ? null : $2.assert$Value()), ($3 == null ? null : $3.assert$Arguments()), $assert_bool($4));
 };
 ConcreteMember.prototype.provideFieldSyntax$0 = ConcreteMember.prototype.provideFieldSyntax;
 ConcreteMember.prototype.providePropertySyntax$0 = ConcreteMember.prototype.providePropertySyntax;
@@ -15744,7 +16154,7 @@ function MethodMember(name, declaringType, definition) {
   Member.call(this, name, declaringType);
 }
 $inherits(MethodMember, Member);
-MethodMember.prototype.is$MethodMember = function(){return this;};
+MethodMember.prototype.assert$MethodMember = function(){return this};
 MethodMember.prototype.get$definition = function() { return this.definition; };
 MethodMember.prototype.set$definition = function(value) { return this.definition = value; };
 MethodMember.prototype.get$returnType = function() { return this.returnType; };
@@ -15782,7 +16192,7 @@ MethodMember.prototype.get$canSet = function() {
 }
 MethodMember.prototype.get$span = function() {
   var $0;
-  return (($0 = this.definition == null ? null : this.definition.span) && $0.is$SourceSpan());
+  return (($0 = this.definition == null ? null : this.definition.span) == null ? null : $0.assert$SourceSpan());
 }
 MethodMember.prototype.get$constructorName = function() {
   var returnType = this.definition.returnType;
@@ -15999,9 +16409,9 @@ MethodMember.prototype.invoke = function(context, node, target, args, isDynamic)
       }
       $globals.world.internalError(('wrong named arguments calling ' + this.name), node.span);
     }
-    Arguments.removeTrailingNulls((argsCode && argsCode.is$List_Value()));
+    Arguments.removeTrailingNulls((argsCode == null ? null : argsCode.assert$List_Value()));
   }
-  var argsString = Strings.join((argsCode && argsCode.is$List_String()), ', ');
+  var argsString = Strings.join((argsCode == null ? null : argsCode.assert$List_String()), ', ');
   if ($notnull_bool(this.get$isConstructor())) {
     return this._invokeConstructor(context, node, target, args, argsString);
   }
@@ -16024,7 +16434,7 @@ MethodMember.prototype.invoke = function(context, node, target, args, isDynamic)
   var code = ('' + target.code + '.' + this.get$jsname() + '(' + argsString + ')');
   if ($notnull_bool(target.get$isConst())) {
     if ((target instanceof GlobalValue)) {
-      target = (($0 = target.get$dynamic().get$exp()) && $0.is$Value());
+      target = (($0 = target.get$dynamic().get$exp()) == null ? null : $0.assert$Value());
     }
     if (this.name == 'get\$length') {
       if ((target instanceof ConstListValue) || (target instanceof ConstMapValue)) {
@@ -16038,7 +16448,7 @@ MethodMember.prototype.invoke = function(context, node, target, args, isDynamic)
     }
   }
   if (this.name == 'get\$typeName' && $eq(this.declaringType.get$library(), $globals.world.get$dom())) {
-    $globals.world.gen.corejs.useTypeNameOf = true;
+    $globals.world.gen.corejs.ensureTypeNameOf();
   }
   return new Value(this.get$inferredResult(), code, node.span, true);
 }
@@ -16099,10 +16509,10 @@ MethodMember.prototype._invokeConstConstructor = function(node, code, target, ar
     for (var $i = 0;$i < $list.length; $i++) {
       var init = $list.$index($i);
       if ((init instanceof CallExpression)) {
-        var delegateArgs = this.generator._makeArgs((($0 = init.get$arguments()) && $0.is$List_ArgumentNode()));
-        var value = this.initDelegate.invoke(this.generator, node, target, (delegateArgs && delegateArgs.is$Arguments()), false);
+        var delegateArgs = this.generator._makeArgs((($0 = init.get$arguments()) == null ? null : $0.assert$List_ArgumentNode()));
+        var value = this.initDelegate.invoke(this.generator, node, target, (delegateArgs == null ? null : delegateArgs.assert$Arguments()), false);
         if ((init.get$target() instanceof ThisExpression)) {
-          return (value && value.is$Value());
+          return (value == null ? null : value.assert$Value());
         }
         else {
           if ((value instanceof GlobalValue)) {
@@ -16116,7 +16526,7 @@ MethodMember.prototype._invokeConstConstructor = function(node, code, target, ar
         }
       }
       else {
-        var assign = (init && init.is$BinaryExpression());
+        var assign = (init == null ? null : init.assert$BinaryExpression());
         var x = assign.x;
         var fname = x.get$name().get$name();
         var val = this.generator.visitValue(assign.y);
@@ -16279,7 +16689,7 @@ MethodMember.prototype._invokeBuiltin = function(context, node, target, args, ar
     }
     else if (this.name == '\$add') {
       if ($notnull_bool(allConst)) {
-        var value = this._normConcat(target, (($0 = args.values.$index(0)) && $0.is$Value()));
+        var value = this._normConcat(target, (($0 = args.values.$index(0)) == null ? null : $0.assert$Value()));
         return EvaluatedValue.EvaluatedValue$factory($globals.world.stringType, value, value, node.span);
       }
       return new Value(this.declaringType, ('' + target.code + ' + ' + argsCode.$index(0)), node.span, true);
@@ -16315,7 +16725,7 @@ MethodMember.prototype._invokeBuiltin = function(context, node, target, args, ar
   }
   if ($notnull_bool(this.get$isCallMethod())) {
     this.declaringType.markUsed();
-    return new Value(this.get$inferredResult(), ('' + target.code + '(' + Strings.join((argsCode && argsCode.is$List_String()), ", ") + ')'), node.span, true);
+    return new Value(this.get$inferredResult(), ('' + target.code + '(' + Strings.join((argsCode == null ? null : argsCode.assert$List_String()), ", ") + ')'), node.span, true);
   }
   if (this.name == '\$index') {
     $globals.world.gen.corejs.useIndex = true;
@@ -16323,7 +16733,7 @@ MethodMember.prototype._invokeBuiltin = function(context, node, target, args, ar
   else if (this.name == '\$setindex') {
     $globals.world.gen.corejs.useSetIndex = true;
   }
-  var argsString = Strings.join((argsCode && argsCode.is$List_String()), ', ');
+  var argsString = Strings.join((argsCode == null ? null : argsCode.assert$List_String()), ', ');
   return new Value(this.get$inferredResult(), ('' + target.code + '.' + this.get$jsname() + '(' + argsString + ')'), node.span, true);
 }
 MethodMember.prototype._normConcat = function(a, b) {
@@ -16363,35 +16773,35 @@ MethodMember.prototype.resolve = function() {
       var mod = $list.$index($i);
       if ($notnull_bool($eq(mod.get$kind(), 86/*TokenKind.STATIC*/))) {
         if ($notnull_bool(this.isStatic)) {
-          $globals.world.error('duplicate static modifier', (($0 = mod.get$span()) && $0.is$SourceSpan()));
+          $globals.world.error('duplicate static modifier', (($0 = mod.get$span()) == null ? null : $0.assert$SourceSpan()));
         }
         this.isStatic = true;
       }
       else if ($notnull_bool(this.get$isConstructor()) && $notnull_bool($eq(mod.get$kind(), 91/*TokenKind.CONST*/))) {
         if ($notnull_bool(this.isConst)) {
-          $globals.world.error('duplicate const modifier', (($0 = mod.get$span()) && $0.is$SourceSpan()));
+          $globals.world.error('duplicate const modifier', (($0 = mod.get$span()) == null ? null : $0.assert$SourceSpan()));
         }
         this.isConst = true;
       }
       else if ($notnull_bool($eq(mod.get$kind(), 75/*TokenKind.FACTORY*/))) {
         if ($notnull_bool(this.isFactory)) {
-          $globals.world.error('duplicate factory modifier', (($0 = mod.get$span()) && $0.is$SourceSpan()));
+          $globals.world.error('duplicate factory modifier', (($0 = mod.get$span()) == null ? null : $0.assert$SourceSpan()));
         }
         this.isFactory = true;
       }
       else if ($notnull_bool($eq(mod.get$kind(), 71/*TokenKind.ABSTRACT*/))) {
         if ($notnull_bool(this.isAbstract)) {
           if ($notnull_bool(this.declaringType.get$isClass())) {
-            $globals.world.error('duplicate abstract modifier', (($0 = mod.get$span()) && $0.is$SourceSpan()));
+            $globals.world.error('duplicate abstract modifier', (($0 = mod.get$span()) == null ? null : $0.assert$SourceSpan()));
           }
           else {
-            $globals.world.error('abstract modifier not allowed on interface members', (($0 = mod.get$span()) && $0.is$SourceSpan()));
+            $globals.world.error('abstract modifier not allowed on interface members', (($0 = mod.get$span()) == null ? null : $0.assert$SourceSpan()));
           }
         }
         this.isAbstract = true;
       }
       else {
-        $globals.world.error(('' + mod + ' modifier not allowed on method'), (($0 = mod.get$span()) && $0.is$SourceSpan()));
+        $globals.world.error(('' + mod + ' modifier not allowed on method'), (($0 = mod.get$span()) == null ? null : $0.assert$SourceSpan()));
       }
     }
   }
@@ -16400,7 +16810,7 @@ MethodMember.prototype.resolve = function() {
   }
   if (this.definition.typeParameters != null) {
     if (!$notnull_bool(this.isFactory)) {
-      $globals.world.error('Only factories are allowed to have explicit type parameters', (($0 = this.definition.typeParameters.$index(0).get$span()) && $0.is$SourceSpan()));
+      $globals.world.error('Only factories are allowed to have explicit type parameters', (($0 = this.definition.typeParameters.$index(0).get$span()) == null ? null : $0.assert$SourceSpan()));
     }
     else {
       this.typeParameters = this.definition.typeParameters;
@@ -16447,25 +16857,25 @@ MethodMember.prototype.resolve = function() {
   }
 }
 MethodMember.prototype._get$3 = function($0, $1, $2) {
-  return this._get(($0 && $0.is$MethodGenerator()), ($1 && $1.is$lang_Node()), ($2 && $2.is$Value()), false);
+  return this._get(($0 == null ? null : $0.assert$MethodGenerator()), ($1 == null ? null : $1.assert$lang_Node()), ($2 == null ? null : $2.assert$Value()), false);
 };
 MethodMember.prototype._set$4 = function($0, $1, $2, $3) {
-  return this._set(($0 && $0.is$MethodGenerator()), ($1 && $1.is$lang_Node()), ($2 && $2.is$Value()), ($3 && $3.is$Value()), false);
+  return this._set(($0 == null ? null : $0.assert$MethodGenerator()), ($1 == null ? null : $1.assert$lang_Node()), ($2 == null ? null : $2.assert$Value()), ($3 == null ? null : $3.assert$Value()), false);
 };
 MethodMember.prototype.canInvoke$2 = function($0, $1) {
-  return this.canInvoke(($0 && $0.is$MethodGenerator()), ($1 && $1.is$Arguments()));
+  return this.canInvoke(($0 == null ? null : $0.assert$MethodGenerator()), ($1 == null ? null : $1.assert$Arguments()));
 };
 MethodMember.prototype.invoke$4 = function($0, $1, $2, $3) {
-  return this.invoke(($0 && $0.is$MethodGenerator()), ($1 && $1.is$lang_Node()), ($2 && $2.is$Value()), ($3 && $3.is$Arguments()), false);
+  return this.invoke(($0 == null ? null : $0.assert$MethodGenerator()), ($1 == null ? null : $1.assert$lang_Node()), ($2 == null ? null : $2.assert$Value()), ($3 == null ? null : $3.assert$Arguments()), false);
 };
 MethodMember.prototype.invoke$4$isDynamic = function($0, $1, $2, $3, isDynamic) {
-  return this.invoke(($0 && $0.is$MethodGenerator()), ($1 && $1.is$lang_Node()), ($2 && $2.is$Value()), ($3 && $3.is$Arguments()), $assert_bool(isDynamic));
+  return this.invoke(($0 == null ? null : $0.assert$MethodGenerator()), ($1 == null ? null : $1.assert$lang_Node()), ($2 == null ? null : $2.assert$Value()), ($3 == null ? null : $3.assert$Arguments()), $assert_bool(isDynamic));
 };
 MethodMember.prototype.invoke$5 = function($0, $1, $2, $3, $4) {
-  return this.invoke(($0 && $0.is$MethodGenerator()), ($1 && $1.is$lang_Node()), ($2 && $2.is$Value()), ($3 && $3.is$Arguments()), $assert_bool($4));
+  return this.invoke(($0 == null ? null : $0.assert$MethodGenerator()), ($1 == null ? null : $1.assert$lang_Node()), ($2 == null ? null : $2.assert$Value()), ($3 == null ? null : $3.assert$Arguments()), $assert_bool($4));
 };
 MethodMember.prototype.namesInOrder$1 = function($0) {
-  return this.namesInOrder(($0 && $0.is$Arguments()));
+  return this.namesInOrder(($0 == null ? null : $0.assert$Arguments()));
 };
 MethodMember.prototype.provideFieldSyntax$0 = MethodMember.prototype.provideFieldSyntax;
 MethodMember.prototype.providePropertySyntax$0 = MethodMember.prototype.providePropertySyntax;
@@ -16478,7 +16888,7 @@ function MemberSet(member, isVar) {
   this.isVar = isVar;
   // Initializers done
 }
-MemberSet.prototype.is$MemberSet = function(){return this;};
+MemberSet.prototype.assert$MemberSet = function(){return this};
 MemberSet.prototype.get$name = function() { return this.name; };
 MemberSet.prototype.get$members = function() { return this.members; };
 MemberSet.prototype.get$jsname = function() { return this.jsname; };
@@ -16551,7 +16961,7 @@ MemberSet.prototype._get = function(context, node, target, isDynamic) {
       return m._get(context, node, target, true);
     })
     );
-    returnValue = new Value(this._foldTypes((targets && targets.is$List_Member())), null, node.span, true);
+    returnValue = new Value(this._foldTypes((targets == null ? null : targets.assert$List_Member())), null, node.span, true);
   }
   else {
     if (this.members.length == 1) {
@@ -16590,7 +17000,7 @@ MemberSet.prototype._set = function(context, node, target, value, isDynamic) {
       return m._set(context, node, target, value, true);
     })
     );
-    returnValue = new Value(this._foldTypes((targets && targets.is$List_Member())), null, node.span, true);
+    returnValue = new Value(this._foldTypes((targets == null ? null : targets.assert$List_Member())), null, node.span, true);
   }
   else {
     if (this.members.length == 1) {
@@ -16624,20 +17034,20 @@ MemberSet.prototype.invoke = function(context, node, target, args, isDynamic) {
     return this.invokeOnVar(context, node, target, args);
   }
   if (this.members.length == 1) {
-    return (($0 = this.members.$index(0).invoke$5(context, node, target, args, isDynamic)) && $0.is$Value());
+    return (($0 = this.members.$index(0).invoke$5(context, node, target, args, isDynamic)) == null ? null : $0.assert$Value());
   }
   var targets = this.members.filter((function (m) {
     return m.canInvoke$2(context, args);
   })
   );
   if ($notnull_bool($eq(targets.length, 1))) {
-    return (($0 = targets.$index(0).invoke$5(context, node, target, args, isDynamic)) && $0.is$Value());
+    return (($0 = targets.$index(0).invoke$5(context, node, target, args, isDynamic)) == null ? null : $0.assert$Value());
   }
   var returnValue = null;
   for (var $i = targets.iterator$0(); $i.hasNext$0(); ) {
     var member = $i.next$0();
     var res = member.invoke$4$isDynamic(context, node, target, args, true);
-    returnValue = this._tryUnion(returnValue, (res && res.is$Value()), node);
+    returnValue = this._tryUnion(returnValue, (res == null ? null : res.assert$Value()), node);
   }
   if (returnValue == null) {
     return this._makeError(node, target, 'method');
@@ -16658,7 +17068,7 @@ MemberSet.prototype.invoke = function(context, node, target, args, isDynamic) {
 MemberSet.prototype.invokeOnVar = function(context, node, target, args) {
   var $0;
   var member = this.getVarMember(context, node, args);
-  return (($0 = member.invoke$4(context, node, target, args)) && $0.is$Value());
+  return (($0 = member.invoke$4(context, node, target, args)) == null ? null : $0.assert$Value());
 }
 MemberSet.prototype._tryUnion = function(x, y, node) {
   if (x == null) return y;
@@ -16675,7 +17085,7 @@ MemberSet.prototype._tryUnion = function(x, y, node) {
       ret.set$isSuper($notnull_bool(x.isSuper) && $notnull_bool(y.isSuper));
       ret.set$needsTemp($notnull_bool(x.needsTemp) || $notnull_bool(y.needsTemp));
       ret.set$isType($notnull_bool(x.isType) && $notnull_bool(y.isType));
-      return (ret && ret.is$Value());
+      return (ret == null ? null : ret.assert$Value());
     }
   }
   else {
@@ -16694,38 +17104,38 @@ MemberSet.prototype.getVarMember = function(context, node, args) {
       return m.canInvoke$2(context, args);
     })
     );
-    stub = new VarMethodSet($assert_String(stubName), targets, args, this._foldTypes((targets && targets.is$List_Member())));
+    stub = new VarMethodSet($assert_String(stubName), targets, args, this._foldTypes((targets == null ? null : targets.assert$List_Member())));
     $globals.world.objectType.varStubs.$setindex(stubName, stub);
   }
-  return (stub && stub.is$VarMember());
+  return (stub == null ? null : stub.assert$VarMember());
 }
 MemberSet.prototype._foldTypes = function(targets) {
   var $0;
   return (($0 = reduce(map(targets, (function (t) {
     return t.get$returnType();
   })
-  ), lang_Type.union, $globals.world.varType)) && $0.is$lang_Type());
+  ), lang_Type.union, $globals.world.varType)) == null ? null : $0.assert$lang_Type());
 }
 MemberSet.prototype._get$3 = function($0, $1, $2) {
-  return this._get(($0 && $0.is$MethodGenerator()), ($1 && $1.is$lang_Node()), ($2 && $2.is$Value()), false);
+  return this._get(($0 == null ? null : $0.assert$MethodGenerator()), ($1 == null ? null : $1.assert$lang_Node()), ($2 == null ? null : $2.assert$Value()), false);
 };
 MemberSet.prototype._set$4 = function($0, $1, $2, $3) {
-  return this._set(($0 && $0.is$MethodGenerator()), ($1 && $1.is$lang_Node()), ($2 && $2.is$Value()), ($3 && $3.is$Value()), false);
+  return this._set(($0 == null ? null : $0.assert$MethodGenerator()), ($1 == null ? null : $1.assert$lang_Node()), ($2 == null ? null : $2.assert$Value()), ($3 == null ? null : $3.assert$Value()), false);
 };
 MemberSet.prototype.add$1 = function($0) {
-  return this.add(($0 && $0.is$Member()));
+  return this.add(($0 == null ? null : $0.assert$Member()));
 };
 MemberSet.prototype.canInvoke$2 = function($0, $1) {
-  return this.canInvoke(($0 && $0.is$MethodGenerator()), ($1 && $1.is$Arguments()));
+  return this.canInvoke(($0 == null ? null : $0.assert$MethodGenerator()), ($1 == null ? null : $1.assert$Arguments()));
 };
 MemberSet.prototype.invoke$4 = function($0, $1, $2, $3) {
-  return this.invoke(($0 && $0.is$MethodGenerator()), ($1 && $1.is$lang_Node()), ($2 && $2.is$Value()), ($3 && $3.is$Arguments()), false);
+  return this.invoke(($0 == null ? null : $0.assert$MethodGenerator()), ($1 == null ? null : $1.assert$lang_Node()), ($2 == null ? null : $2.assert$Value()), ($3 == null ? null : $3.assert$Arguments()), false);
 };
 MemberSet.prototype.invoke$4$isDynamic = function($0, $1, $2, $3, isDynamic) {
-  return this.invoke(($0 && $0.is$MethodGenerator()), ($1 && $1.is$lang_Node()), ($2 && $2.is$Value()), ($3 && $3.is$Arguments()), $assert_bool(isDynamic));
+  return this.invoke(($0 == null ? null : $0.assert$MethodGenerator()), ($1 == null ? null : $1.assert$lang_Node()), ($2 == null ? null : $2.assert$Value()), ($3 == null ? null : $3.assert$Arguments()), $assert_bool(isDynamic));
 };
 MemberSet.prototype.invoke$5 = function($0, $1, $2, $3, $4) {
-  return this.invoke(($0 && $0.is$MethodGenerator()), ($1 && $1.is$lang_Node()), ($2 && $2.is$Value()), ($3 && $3.is$Arguments()), $assert_bool($4));
+  return this.invoke(($0 == null ? null : $0.assert$MethodGenerator()), ($1 == null ? null : $1.assert$lang_Node()), ($2 == null ? null : $2.assert$Value()), ($3 == null ? null : $3.assert$Arguments()), $assert_bool($4));
 };
 MemberSet.prototype.toString$0 = MemberSet.prototype.toString;
 // ********** Code for FactoryMap **************
@@ -16739,14 +17149,14 @@ FactoryMap.prototype.getFactoriesFor = function(typeName) {
     ret = $map([]);
     this.factories.$setindex(typeName, ret);
   }
-  return (ret && ret.is$Map_String$Member());
+  return (ret == null ? null : ret.assert$Map_String$Member());
 }
 FactoryMap.prototype.addFactory = function(typeName, name, member) {
   this.getFactoriesFor(typeName).$setindex(name, member);
 }
 FactoryMap.prototype.getFactory = function(typeName, name) {
   var $0;
-  return (($0 = this.getFactoriesFor(typeName).$index(name)) && $0.is$Member());
+  return (($0 = this.getFactoriesFor(typeName).$index(name)) == null ? null : $0.assert$Member());
 }
 FactoryMap.prototype.forEach = function(f) {
   this.factories.forEach((function (_, constructors) {
@@ -16771,7 +17181,7 @@ function lang_Token(kind, source, start, end) {
   this.end = end;
   // Initializers done
 }
-lang_Token.prototype.is$lang_Token = function(){return this;};
+lang_Token.prototype.assert$lang_Token = function(){return this};
 lang_Token.prototype.get$kind = function() { return this.kind; };
 lang_Token.prototype.get$source = function() { return this.source; };
 lang_Token.prototype.get$end = function() { return this.end; };
@@ -16802,8 +17212,8 @@ function SourceFile(filename, _text) {
   this._text = _text;
   // Initializers done
 }
-SourceFile.prototype.is$SourceFile = function(){return this;};
-SourceFile.prototype.is$Comparable = function(){return this;};
+SourceFile.prototype.assert$SourceFile = function(){return this};
+SourceFile.prototype.assert$Comparable = function(){return this};
 SourceFile.prototype.get$filename = function() { return this.filename; };
 SourceFile.prototype.get$orderInLibrary = function() { return this.orderInLibrary; };
 SourceFile.prototype.set$orderInLibrary = function(value) { return this.orderInLibrary = value; };
@@ -16820,7 +17230,7 @@ SourceFile.prototype.get$lineStarts = function() {
       starts.add$1(index);
     }
     starts.add$1(this.get$text().length + 1);
-    this._lineStarts = (starts && starts.is$List_int());
+    this._lineStarts = (starts == null ? null : starts.assert$List_int());
   }
   return this._lineStarts;
 }
@@ -16869,7 +17279,7 @@ SourceFile.prototype.compareTo = function(other) {
   }
 }
 SourceFile.prototype.compareTo$1 = function($0) {
-  return this.compareTo(($0 && $0.is$SourceFile()));
+  return this.compareTo(($0 == null ? null : $0.assert$SourceFile()));
 };
 SourceFile.prototype.getColumn$2 = function($0, $1) {
   return this.getColumn($assert_num($0), $assert_num($1));
@@ -16887,8 +17297,8 @@ function SourceSpan(file, start, end) {
   this.end = end;
   // Initializers done
 }
-SourceSpan.prototype.is$SourceSpan = function(){return this;};
-SourceSpan.prototype.is$Comparable = function(){return this;};
+SourceSpan.prototype.assert$SourceSpan = function(){return this};
+SourceSpan.prototype.assert$Comparable = function(){return this};
 SourceSpan.prototype.get$file = function() { return this.file; };
 SourceSpan.prototype.get$start = function() { return this.start; };
 SourceSpan.prototype.get$end = function() { return this.end; };
@@ -16911,7 +17321,7 @@ SourceSpan.prototype.compareTo = function(other) {
   return this.file.compareTo(other.file);
 }
 SourceSpan.prototype.compareTo$1 = function($0) {
-  return this.compareTo(($0 && $0.is$SourceSpan()));
+  return this.compareTo(($0 == null ? null : $0.assert$SourceSpan()));
 };
 SourceSpan.prototype.toMessageString$1 = function($0) {
   return this.toMessageString($assert_String($0));
@@ -16924,7 +17334,7 @@ function InterpStack(previous, quote, isMultiline) {
   this.depth = -1;
   // Initializers done
 }
-InterpStack.prototype.is$InterpStack = function(){return this;};
+InterpStack.prototype.assert$InterpStack = function(){return this};
 InterpStack.prototype.get$previous = function() { return this.previous; };
 InterpStack.prototype.set$previous = function(value) { return this.previous = value; };
 InterpStack.prototype.get$quote = function() { return this.quote; };
@@ -16937,7 +17347,7 @@ InterpStack.prototype.pop = function() {
 InterpStack.push = function(stack, quote, isMultiline) {
   var newStack = new InterpStack(stack, quote, isMultiline);
   if (stack != null) newStack.set$previous(stack);
-  return (newStack && newStack.is$InterpStack());
+  return (newStack == null ? null : newStack.assert$InterpStack());
 }
 InterpStack.prototype.next$0 = function() {
   return this.next();
@@ -18656,7 +19066,7 @@ function lang_Parser(source, diet, throwOnIncomplete, optionalSemicolons, startO
   this.optionalSemicolons = optionalSemicolons;
   // Initializers done
   this.tokenizer = new Tokenizer(this.source, true, startOffset);
-  this._peekToken = (($0 = this.tokenizer.next()) && $0.is$lang_Token());
+  this._peekToken = (($0 = this.tokenizer.next()) == null ? null : $0.assert$lang_Token());
   this._previousToken = null;
   this._inInitializers = false;
   this._afterParens = [];
@@ -18680,7 +19090,7 @@ lang_Parser.prototype._peek = function() {
 lang_Parser.prototype._lang_next = function() {
   var $0;
   this._previousToken = this._peekToken;
-  this._peekToken = (($0 = this.tokenizer.next()) && $0.is$lang_Token());
+  this._peekToken = (($0 = this.tokenizer.next()) == null ? null : $0.assert$lang_Token());
   return this._previousToken;
 }
 lang_Parser.prototype._peekKind = function(kind) {
@@ -18693,7 +19103,7 @@ lang_Parser.prototype._maybeEat = function(kind) {
   var $0;
   if (this._peekToken.kind == kind) {
     this._previousToken = this._peekToken;
-    this._peekToken = (($0 = this.tokenizer.next()) && $0.is$lang_Token());
+    this._peekToken = (($0 = this.tokenizer.next()) == null ? null : $0.assert$lang_Token());
     return true;
   }
   else {
@@ -18714,7 +19124,7 @@ lang_Parser.prototype._errorExpected = function(expected) {
   if ($notnull_bool(this.throwOnIncomplete)) this.isPrematureEndOfFile();
   var tok = this._lang_next();
   var message = ('expected ' + expected + ', but found ' + tok);
-  this._lang_error($assert_String(message), (($0 = tok.get$span()) && $0.is$SourceSpan()));
+  this._lang_error($assert_String(message), (($0 = tok.get$span()) == null ? null : $0.assert$SourceSpan()));
 }
 lang_Parser.prototype._lang_error = function(message, location) {
   if (location == null) {
@@ -18736,7 +19146,7 @@ lang_Parser.prototype._skipBlock = function() {
       if (depth == 0) return;
     }
     else if ($notnull_bool($eq(tok.get$kind(), 1/*TokenKind.END_OF_FILE*/))) {
-      this._lang_error('unexpected end of file during diet parse', (($0 = tok.get$span()) && $0.is$SourceSpan()));
+      this._lang_error('unexpected end of file during diet parse', (($0 = tok.get$span()) == null ? null : $0.assert$SourceSpan()));
       return;
     }
   }
@@ -18753,7 +19163,7 @@ lang_Parser.prototype.compilationUnit = function() {
   while (!$notnull_bool(this._maybeEat(1/*TokenKind.END_OF_FILE*/))) {
     ret.add$1(this.topLevelDefinition());
   }
-  return (ret && ret.is$List_Definition());
+  return (ret == null ? null : ret.assert$List_Definition());
 }
 lang_Parser.prototype.directive = function() {
   var start = this._peekToken.start;
@@ -18933,7 +19343,7 @@ lang_Parser.prototype.declaration = function(includeOperators) {
     return this.factoryConstructorDeclaration();
   }
   var modifiers = this._readModifiers();
-  return this.finishDefinition(start, (modifiers && modifiers.is$List_Token()), this.declaredIdentifier(includeOperators), null);
+  return this.finishDefinition(start, (modifiers == null ? null : modifiers.assert$List_Token()), this.declaredIdentifier(includeOperators), null);
 }
 lang_Parser.prototype.factoryConstructorDeclaration = function() {
   var $0;
@@ -18957,41 +19367,41 @@ lang_Parser.prototype.factoryConstructorDeclaration = function() {
       name = names.removeLast$0();
     }
     else {
-      name = new lang_Identifier('', (($0 = names.$index(0).get$span()) && $0.is$SourceSpan()));
+      name = new lang_Identifier('', (($0 = names.$index(0).get$span()) == null ? null : $0.assert$SourceSpan()));
     }
   }
   else {
-    name = new lang_Identifier('', (($0 = names.$index(0).get$span()) && $0.is$SourceSpan()));
+    name = new lang_Identifier('', (($0 = names.$index(0).get$span()) == null ? null : $0.assert$SourceSpan()));
   }
   if (names.length > 1) {
-    this._lang_error('unsupported qualified name for factory', (($0 = names.$index(0).get$span()) && $0.is$SourceSpan()));
+    this._lang_error('unsupported qualified name for factory', (($0 = names.$index(0).get$span()) == null ? null : $0.assert$SourceSpan()));
   }
-  type = new NameTypeReference(false, names.$index(0), null, (($0 = names.$index(0).get$span()) && $0.is$SourceSpan()));
+  type = new NameTypeReference(false, names.$index(0), null, (($0 = names.$index(0).get$span()) == null ? null : $0.assert$SourceSpan()));
   var di = new DeclaredIdentifier(type, name, this._makeSpan(start));
-  return this.finishDefinition(start, [factoryToken], di, (typeParams && typeParams.is$List_ParameterType()));
+  return this.finishDefinition(start, [factoryToken], di, (typeParams == null ? null : typeParams.assert$List_ParameterType()));
 }
 lang_Parser.prototype.statement = function() {
   var $0;
   switch (this._peek()) {
     case 88/*TokenKind.BREAK*/:
 
-      return (($0 = this.breakStatement()) && $0.is$lang_Statement());
+      return (($0 = this.breakStatement()) == null ? null : $0.assert$lang_Statement());
 
     case 92/*TokenKind.CONTINUE*/:
 
-      return (($0 = this.continueStatement()) && $0.is$lang_Statement());
+      return (($0 = this.continueStatement()) == null ? null : $0.assert$lang_Statement());
 
     case 105/*TokenKind.RETURN*/:
 
-      return (($0 = this.returnStatement()) && $0.is$lang_Statement());
+      return (($0 = this.returnStatement()) == null ? null : $0.assert$lang_Statement());
 
     case 109/*TokenKind.THROW*/:
 
-      return (($0 = this.throwStatement()) && $0.is$lang_Statement());
+      return (($0 = this.throwStatement()) == null ? null : $0.assert$lang_Statement());
 
     case 72/*TokenKind.ASSERT*/:
 
-      return (($0 = this.assertStatement()) && $0.is$lang_Statement());
+      return (($0 = this.assertStatement()) == null ? null : $0.assert$lang_Statement());
 
     case 114/*TokenKind.WHILE*/:
 
@@ -19003,7 +19413,7 @@ lang_Parser.prototype.statement = function() {
 
     case 99/*TokenKind.FOR*/:
 
-      return (($0 = this.forStatement()) && $0.is$lang_Statement());
+      return (($0 = this.forStatement()) == null ? null : $0.assert$lang_Statement());
 
     case 100/*TokenKind.IF*/:
 
@@ -19011,11 +19421,11 @@ lang_Parser.prototype.statement = function() {
 
     case 107/*TokenKind.SWITCH*/:
 
-      return (($0 = this.switchStatement()) && $0.is$lang_Statement());
+      return (($0 = this.switchStatement()) == null ? null : $0.assert$lang_Statement());
 
     case 111/*TokenKind.TRY*/:
 
-      return (($0 = this.tryStatement()) && $0.is$lang_Statement());
+      return (($0 = this.tryStatement()) == null ? null : $0.assert$lang_Statement());
 
     case 6/*TokenKind.LBRACE*/:
 
@@ -19027,15 +19437,15 @@ lang_Parser.prototype.statement = function() {
 
     case 97/*TokenKind.FINAL*/:
 
-      return (($0 = this.declaration(false)) && $0.is$lang_Statement());
+      return (($0 = this.declaration(false)) == null ? null : $0.assert$lang_Statement());
 
     case 112/*TokenKind.VAR*/:
 
-      return (($0 = this.declaration(false)) && $0.is$lang_Statement());
+      return (($0 = this.declaration(false)) == null ? null : $0.assert$lang_Statement());
 
     default:
 
-      return (($0 = this.finishExpressionAsStatement(this.expression())) && $0.is$lang_Statement());
+      return (($0 = this.finishExpressionAsStatement(this.expression())) == null ? null : $0.assert$lang_Statement());
 
   }
 }
@@ -19061,13 +19471,13 @@ lang_Parser.prototype.finishExpressionAsStatement = function(expr) {
     return this.finishField(start, null, null, expr.get$type(), expr.get$name(), value);
   }
   else if ($notnull_bool(this._isBin(expr, 20/*TokenKind.ASSIGN*/)) && ((expr.get$x() instanceof DeclaredIdentifier))) {
-    var di = (($0 = expr.get$x()) && $0.is$DeclaredIdentifier());
+    var di = (($0 = expr.get$x()) == null ? null : $0.assert$DeclaredIdentifier());
     return this.finishField(start, null, null, di.type, di.name, expr.get$y());
   }
   else if ($notnull_bool(this._isBin(expr, 52/*TokenKind.LT*/)) && $notnull_bool(this._maybeEat(11/*TokenKind.COMMA*/))) {
     var baseType = this._makeType(expr.get$x());
     var typeArgs = [this._makeType(expr.get$y())];
-    var gt = this._finishTypeArguments((baseType && baseType.is$TypeReference()), 0, typeArgs);
+    var gt = this._finishTypeArguments((baseType == null ? null : baseType.assert$TypeReference()), 0, typeArgs);
     var name = this.identifier();
     var value = null;
     if ($notnull_bool(this._maybeEat(20/*TokenKind.ASSIGN*/))) {
@@ -19084,7 +19494,7 @@ lang_Parser.prototype.testCondition = function() {
   this._eatLeftParen();
   var ret = this.expression();
   this._eat(3/*TokenKind.RPAREN*/);
-  return (ret && ret.is$lang_Expression());
+  return (ret == null ? null : ret.assert$lang_Expression());
 }
 lang_Parser.prototype.block = function() {
   var start = this._peekToken.start;
@@ -19163,12 +19573,12 @@ lang_Parser.prototype.forInitializerStatement = function(start) {
       this._eat(11/*TokenKind.COMMA*/);
       var baseType = this._makeType(init.get$x());
       var typeArgs = [this._makeType(init.get$y())];
-      var gt = this._finishTypeArguments((baseType && baseType.is$TypeReference()), 0, typeArgs);
+      var gt = this._finishTypeArguments((baseType == null ? null : baseType.assert$TypeReference()), 0, typeArgs);
       var name = this.identifier();
       init = new DeclaredIdentifier(gt, name, this._makeSpan($assert_num(init.get$span().get$start())));
     }
     if ($notnull_bool(this._maybeEat(101/*TokenKind.IN*/))) {
-      return this._finishForIn(start, (($0 = this._makeDeclaredIdentifier(init)) && $0.is$DeclaredIdentifier()));
+      return this._finishForIn(start, (($0 = this._makeDeclaredIdentifier(init)) == null ? null : $0.assert$DeclaredIdentifier()));
     }
     else {
       return this.finishExpressionAsStatement(init);
@@ -19315,7 +19725,7 @@ lang_Parser.prototype.expression = function() {
 lang_Parser.prototype._makeType = function(expr) {
   var $0;
   if ((expr instanceof VarExpression)) {
-    return new NameTypeReference(false, expr.get$name(), null, (($0 = expr.get$span()) && $0.is$SourceSpan()));
+    return new NameTypeReference(false, expr.get$name(), null, (($0 = expr.get$span()) == null ? null : $0.assert$SourceSpan()));
   }
   else if ((expr instanceof DotExpression)) {
     var type = this._makeType(expr.get$self());
@@ -19335,7 +19745,7 @@ lang_Parser.prototype._makeType = function(expr) {
 }
 lang_Parser.prototype.infixExpression = function(precedence) {
   var $0;
-  return this.finishInfixExpression((($0 = this.unaryExpression()) && $0.is$lang_Expression()), precedence);
+  return this.finishInfixExpression((($0 = this.unaryExpression()) == null ? null : $0.assert$lang_Expression()), precedence);
 }
 lang_Parser.prototype._finishDeclaredId = function(type) {
   var name = this.identifier();
@@ -19353,13 +19763,13 @@ lang_Parser.prototype._fixAsType = function(x) {
     $assert(this._peekKind(52/*TokenKind.LT*/), "_peekKind(TokenKind.LT)", "parser.dart", 810, 14);
     var base = this._makeType(x.x);
     var paramBase = this._makeType(x.y);
-    var firstParam = this.addTypeArguments((paramBase && paramBase.is$TypeReference()), 1);
+    var firstParam = this.addTypeArguments((paramBase == null ? null : paramBase.assert$TypeReference()), 1);
     var type;
     if (firstParam.get$depth() <= 0) {
       type = new GenericTypeReference(base, [firstParam], 0, this._makeSpan(x.span.start));
     }
     else if ($notnull_bool(this._maybeEat(11/*TokenKind.COMMA*/))) {
-      type = this._finishTypeArguments((base && base.is$TypeReference()), 0, [firstParam]);
+      type = this._finishTypeArguments((base == null ? null : base.assert$TypeReference()), 0, [firstParam]);
     }
     else {
       this._eat(53/*TokenKind.GT*/);
@@ -19375,7 +19785,7 @@ lang_Parser.prototype.finishInfixExpression = function(x, precedence) {
     if (prec >= precedence) {
       if (kind == 52/*TokenKind.LT*/ || kind == 53/*TokenKind.GT*/) {
         if ($notnull_bool(this._isBin(x, 52/*TokenKind.LT*/))) {
-          return this._fixAsType((x && x.is$BinaryExpression()));
+          return this._fixAsType((x == null ? null : x.assert$BinaryExpression()));
         }
       }
       var op = this._lang_next();
@@ -19507,7 +19917,7 @@ lang_Parser.prototype.finishCallOrLambdaExpression = function(expr) {
   }
   else {
     if ((expr instanceof DeclaredIdentifier)) {
-      this._lang_error('illegal target for call, did you mean to declare a function?', (($0 = expr.get$span()) && $0.is$SourceSpan()));
+      this._lang_error('illegal target for call, did you mean to declare a function?', (($0 = expr.get$span()) == null ? null : $0.assert$SourceSpan()));
     }
     var args = this.arguments();
     return this.finishPostfixExpression(new CallExpression(expr, args, this._makeSpan($assert_num(expr.get$span().get$start()))));
@@ -19653,7 +20063,7 @@ lang_Parser.prototype.stringInterpolation = function() {
     else {
       text = $add($add(startQuote, text.substring$2(0, text.length - 1)), endQuote);
     }
-    lits.add$1(this.makeStringLiteral($assert_String(text), (($0 = token.get$span()) && $0.is$SourceSpan())));
+    lits.add$1(this.makeStringLiteral($assert_String(text), (($0 = token.get$span()) == null ? null : $0.assert$SourceSpan())));
     if ($notnull_bool(this._maybeEat(6/*TokenKind.LBRACE*/))) {
       lits.add$1(this.expression());
       this._eat(7/*TokenKind.RBRACE*/);
@@ -19663,7 +20073,7 @@ lang_Parser.prototype.stringInterpolation = function() {
     }
     else {
       var id = this.identifier();
-      lits.add$1(new VarExpression(id, (($0 = id.get$span()) && $0.is$SourceSpan())));
+      lits.add$1(new VarExpression(id, (($0 = id.get$span()) == null ? null : $0.assert$SourceSpan())));
     }
   }
   var tok = this._lang_next();
@@ -19671,9 +20081,9 @@ lang_Parser.prototype.stringInterpolation = function() {
     this._errorExpected('interpolated string');
   }
   var text = $add(startQuote, tok.get$text());
-  lits.add$1(this.makeStringLiteral($assert_String(text), (($0 = tok.get$span()) && $0.is$SourceSpan())));
+  lits.add$1(this.makeStringLiteral($assert_String(text), (($0 = tok.get$span()) == null ? null : $0.assert$SourceSpan())));
   var span = this._makeSpan(start);
-  return new LiteralExpression(lits, this._stringTypeRef((span && span.is$SourceSpan())), '\$\$\$', (span && span.is$SourceSpan()));
+  return new LiteralExpression(lits, this._stringTypeRef((span == null ? null : span.assert$SourceSpan())), '\$\$\$', (span == null ? null : span.assert$SourceSpan()));
 }
 lang_Parser.prototype.makeStringLiteral = function(text, span) {
   return new LiteralExpression(text, this._stringTypeRef(span), text, span);
@@ -19681,7 +20091,7 @@ lang_Parser.prototype.makeStringLiteral = function(text, span) {
 lang_Parser.prototype.stringLiteralExpr = function() {
   var $0;
   var token = this._lang_next();
-  return this.makeStringLiteral($assert_String(token.get$text()), (($0 = token.get$span()) && $0.is$SourceSpan()));
+  return this.makeStringLiteral($assert_String(token.get$text()), (($0 = token.get$span()) == null ? null : $0.assert$SourceSpan()));
 }
 lang_Parser.prototype.maybeStringLiteral = function() {
   var kind = this._peek();
@@ -19705,7 +20115,7 @@ lang_Parser.prototype._parenOrLambda = function() {
     var formals = this.formalParameterList();
     var body = this.functionBody(true);
     var func = new FunctionDefinition(null, null, null, formals, null, null, null, body, this._makeSpan(start));
-    return new LambdaExpression(func, (($0 = func.get$span()) && $0.is$SourceSpan()));
+    return new LambdaExpression(func, (($0 = func.get$span()) == null ? null : $0.assert$SourceSpan()));
   }
   else {
     var saved = this._inInitializers;
@@ -19733,17 +20143,17 @@ lang_Parser.prototype._eatLeftParen = function() {
 lang_Parser.prototype._peekAfterCloseParen = function() {
   var $0;
   if (this._afterParensIndex < this._afterParens.length) {
-    return (($0 = this._afterParens.$index(this._afterParensIndex)) && $0.is$lang_Token());
+    return (($0 = this._afterParens.$index(this._afterParensIndex)) == null ? null : $0.assert$lang_Token());
   }
   this._afterParensIndex = 0;
   this._afterParens.clear();
   var tokens = [this._lang_next()];
-  this._lookaheadAfterParens((tokens && tokens.is$List_Token()));
+  this._lookaheadAfterParens((tokens == null ? null : tokens.assert$List_Token()));
   var after = this._peekToken;
   tokens.add$1(after);
   this.tokenizer = new DivertedTokenSource(tokens, this, this.tokenizer);
   this._lang_next();
-  return (after && after.is$lang_Token());
+  return (after == null ? null : after.assert$lang_Token());
 }
 lang_Parser.prototype._lookaheadAfterParens = function(tokens) {
   var saved = this._afterParens.length;
@@ -19920,13 +20330,13 @@ lang_Parser.prototype.finishMapLiteral = function(start, isConst, type) {
 }
 lang_Parser.prototype.finishTypedLiteral = function(start, isConst) {
   var span = this._makeSpan(start);
-  var typeToBeNamedLater = new NameTypeReference(false, null, null, (span && span.is$SourceSpan()));
-  var genericType = this.addTypeArguments((typeToBeNamedLater && typeToBeNamedLater.is$TypeReference()), 0);
+  var typeToBeNamedLater = new NameTypeReference(false, null, null, (span == null ? null : span.assert$SourceSpan()));
+  var genericType = this.addTypeArguments((typeToBeNamedLater == null ? null : typeToBeNamedLater.assert$TypeReference()), 0);
   if ($notnull_bool(this._peekKind(4/*TokenKind.LBRACK*/)) || $notnull_bool(this._peekKind(56/*TokenKind.INDEX*/))) {
-    return this.finishListLiteral(start, isConst, (genericType && genericType.is$TypeReference()));
+    return this.finishListLiteral(start, isConst, (genericType == null ? null : genericType.assert$TypeReference()));
   }
   else if ($notnull_bool(this._peekKind(6/*TokenKind.LBRACE*/))) {
-    return this.finishMapLiteral(start, isConst, (genericType && genericType.is$TypeReference()));
+    return this.finishMapLiteral(start, isConst, (genericType == null ? null : genericType.assert$TypeReference()));
   }
   else {
     this._errorExpected('array or map literal');
@@ -19983,7 +20393,7 @@ lang_Parser.prototype.typeParameters = function() {
   if (!$notnull_bool(closed)) {
     this._eat(53/*TokenKind.GT*/);
   }
-  return (ret && ret.is$List_ParameterType());
+  return (ret == null ? null : ret.assert$List_ParameterType());
 }
 lang_Parser.prototype.get$typeParameters = function() {
   return lang_Parser.prototype.typeParameters.bind(this);
@@ -20025,7 +20435,7 @@ lang_Parser.prototype._finishTypeArguments = function(baseType, depth, types) {
     depth = this._eatClosingAngle(depth);
   }
   var span = this._makeSpan(baseType.span.start);
-  return new GenericTypeReference(baseType, types, depth, (span && span.is$SourceSpan()));
+  return new GenericTypeReference(baseType, types, depth, (span == null ? null : span.assert$SourceSpan()));
 }
 lang_Parser.prototype.typeList = function() {
   var types = [];
@@ -20069,7 +20479,7 @@ lang_Parser.prototype.type = function(depth) {
   }
   var typeRef = new NameTypeReference(isFinal, name, names, this._makeSpan(start));
   if ($notnull_bool(this._peekKind(52/*TokenKind.LT*/))) {
-    return this.addTypeArguments((typeRef && typeRef.is$TypeReference()), depth);
+    return this.addTypeArguments((typeRef == null ? null : typeRef.assert$TypeReference()), depth);
   }
   else {
     return typeRef;
@@ -20096,7 +20506,7 @@ lang_Parser.prototype.formalParameter = function(inOptionalBlock) {
   else if ($notnull_bool(this._peekKind(2/*TokenKind.LPAREN*/))) {
     var formals = this.formalParameterList();
     var func = new FunctionDefinition(null, type, name, formals, null, null, null, null, this._makeSpan(start));
-    type = new FunctionTypeReference(false, func, (($0 = func.get$span()) && $0.is$SourceSpan()));
+    type = new FunctionTypeReference(false, func, (($0 = func.get$span()) == null ? null : $0.assert$SourceSpan()));
   }
   if ($notnull_bool(inOptionalBlock) && $notnull_bool(value == null)) {
     value = new NullExpression(this._makeSpan(start));
@@ -20132,7 +20542,7 @@ lang_Parser.prototype.identifier = function() {
   var $0;
   var tok = this._lang_next();
   if (!$notnull_bool(TokenKind.isIdentifier($assert_num(tok.get$kind())))) {
-    this._lang_error(('expected identifier, but found ' + tok), (($0 = tok.get$span()) && $0.is$SourceSpan()));
+    this._lang_error(('expected identifier, but found ' + tok), (($0 = tok.get$span()) == null ? null : $0.assert$SourceSpan()));
   }
   return new lang_Identifier(tok.get$text(), this._makeSpan($assert_num(tok.get$start())));
 }
@@ -20148,23 +20558,23 @@ lang_Parser.prototype._makeFunction = function(expr, formals, body) {
     type = expr.get$type();
   }
   else {
-    this._lang_error('bad function body', (($0 = expr.get$span()) && $0.is$SourceSpan()));
+    this._lang_error('bad function body', (($0 = expr.get$span()) == null ? null : $0.assert$SourceSpan()));
   }
   var span = new SourceSpan(expr.get$span().get$file(), expr.get$span().get$start(), body.get$span().get$end());
-  var func = new FunctionDefinition(null, type, name, formals, null, null, null, body, (span && span.is$SourceSpan()));
-  return new LambdaExpression(func, (($0 = func.get$span()) && $0.is$SourceSpan()));
+  var func = new FunctionDefinition(null, type, name, formals, null, null, null, body, (span == null ? null : span.assert$SourceSpan()));
+  return new LambdaExpression(func, (($0 = func.get$span()) == null ? null : $0.assert$SourceSpan()));
 }
 lang_Parser.prototype._makeDeclaredIdentifier = function(e) {
   var $0;
   if ((e instanceof VarExpression)) {
-    return new DeclaredIdentifier(null, e.get$name(), (($0 = e.get$span()) && $0.is$SourceSpan()));
+    return new DeclaredIdentifier(null, e.get$name(), (($0 = e.get$span()) == null ? null : $0.assert$SourceSpan()));
   }
   else if ((e instanceof DeclaredIdentifier)) {
     return e;
   }
   else {
     this._lang_error('expected declared identifier');
-    return new DeclaredIdentifier(null, null, (($0 = e.get$span()) && $0.is$SourceSpan()));
+    return new DeclaredIdentifier(null, null, (($0 = e.get$span()) == null ? null : $0.assert$SourceSpan()));
   }
 }
 lang_Parser.prototype._makeLabel = function(expr) {
@@ -20209,11 +20619,11 @@ function lang_Node(span) {
   this.span = span;
   // Initializers done
 }
-lang_Node.prototype.is$lang_Node = function(){return this;};
+lang_Node.prototype.assert$lang_Node = function(){return this};
 lang_Node.prototype.get$span = function() { return this.span; };
 lang_Node.prototype.set$span = function(value) { return this.span = value; };
 lang_Node.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$TreeVisitor()));
+  return this.visit(($0 == null ? null : $0.assert$TreeVisitor()));
 };
 // ********** Code for Definition **************
 function Definition(span) {
@@ -20221,7 +20631,7 @@ function Definition(span) {
   lang_Statement.call(this, span);
 }
 $inherits(Definition, lang_Statement);
-Definition.prototype.is$Definition = function(){return this;};
+Definition.prototype.assert$Definition = function(){return this};
 Definition.prototype.get$typeParameters = function() {
   return null;
 }
@@ -20234,14 +20644,14 @@ function lang_Statement(span) {
   lang_Node.call(this, span);
 }
 $inherits(lang_Statement, lang_Node);
-lang_Statement.prototype.is$lang_Statement = function(){return this;};
+lang_Statement.prototype.assert$lang_Statement = function(){return this};
 // ********** Code for lang_Expression **************
 function lang_Expression(span) {
   // Initializers done
   lang_Node.call(this, span);
 }
 $inherits(lang_Expression, lang_Node);
-lang_Expression.prototype.is$lang_Expression = function(){return this;};
+lang_Expression.prototype.assert$lang_Expression = function(){return this};
 // ********** Code for TypeReference **************
 function TypeReference(span, type) {
   this.type = type;
@@ -20249,7 +20659,7 @@ function TypeReference(span, type) {
   lang_Node.call(this, span);
 }
 $inherits(TypeReference, lang_Node);
-TypeReference.prototype.is$TypeReference = function(){return this;};
+TypeReference.prototype.assert$TypeReference = function(){return this};
 TypeReference.prototype.get$type = function() { return this.type; };
 TypeReference.prototype.set$type = function(value) { return this.type = value; };
 TypeReference.prototype.visit = function(visitor) {
@@ -20259,7 +20669,7 @@ TypeReference.prototype.get$isFinal = function() {
   return false;
 }
 TypeReference.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$TreeVisitor()));
+  return this.visit(($0 == null ? null : $0.assert$TreeVisitor()));
 };
 // ********** Code for DirectiveDefinition **************
 function DirectiveDefinition(name, arguments, span) {
@@ -20277,7 +20687,7 @@ DirectiveDefinition.prototype.visit = function(visitor) {
   return visitor.visitDirectiveDefinition(this);
 }
 DirectiveDefinition.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$TreeVisitor()));
+  return this.visit(($0 == null ? null : $0.assert$TreeVisitor()));
 };
 // ********** Code for TypeDefinition **************
 function TypeDefinition(isClass, name, typeParameters, extendsTypes, implementsTypes, nativeType, factoryType, body, span) {
@@ -20293,7 +20703,7 @@ function TypeDefinition(isClass, name, typeParameters, extendsTypes, implementsT
   Definition.call(this, span);
 }
 $inherits(TypeDefinition, Definition);
-TypeDefinition.prototype.is$TypeDefinition = function(){return this;};
+TypeDefinition.prototype.assert$TypeDefinition = function(){return this};
 TypeDefinition.prototype.get$isClass = function() { return this.isClass; };
 TypeDefinition.prototype.set$isClass = function(value) { return this.isClass = value; };
 TypeDefinition.prototype.get$name = function() { return this.name; };
@@ -20308,7 +20718,7 @@ TypeDefinition.prototype.visit = function(visitor) {
   return visitor.visitTypeDefinition(this);
 }
 TypeDefinition.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$TreeVisitor()));
+  return this.visit(($0 == null ? null : $0.assert$TreeVisitor()));
 };
 // ********** Code for FunctionTypeDefinition **************
 function FunctionTypeDefinition(func, typeParameters, span) {
@@ -20326,7 +20736,7 @@ FunctionTypeDefinition.prototype.visit = function(visitor) {
   return visitor.visitFunctionTypeDefinition(this);
 }
 FunctionTypeDefinition.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$TreeVisitor()));
+  return this.visit(($0 == null ? null : $0.assert$TreeVisitor()));
 };
 // ********** Code for VariableDefinition **************
 function VariableDefinition(modifiers, type, names, values, span) {
@@ -20348,7 +20758,7 @@ VariableDefinition.prototype.visit = function(visitor) {
   return visitor.visitVariableDefinition(this);
 }
 VariableDefinition.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$TreeVisitor()));
+  return this.visit(($0 == null ? null : $0.assert$TreeVisitor()));
 };
 // ********** Code for FunctionDefinition **************
 function FunctionDefinition(modifiers, returnType, name, formals, typeParameters, initializers, nativeBody, body, span) {
@@ -20364,7 +20774,7 @@ function FunctionDefinition(modifiers, returnType, name, formals, typeParameters
   Definition.call(this, span);
 }
 $inherits(FunctionDefinition, Definition);
-FunctionDefinition.prototype.is$FunctionDefinition = function(){return this;};
+FunctionDefinition.prototype.assert$FunctionDefinition = function(){return this};
 FunctionDefinition.prototype.get$returnType = function() { return this.returnType; };
 FunctionDefinition.prototype.set$returnType = function(value) { return this.returnType = value; };
 FunctionDefinition.prototype.get$name = function() { return this.name; };
@@ -20381,7 +20791,7 @@ FunctionDefinition.prototype.visit = function(visitor) {
   return visitor.visitFunctionDefinition(this);
 }
 FunctionDefinition.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$TreeVisitor()));
+  return this.visit(($0 == null ? null : $0.assert$TreeVisitor()));
 };
 // ********** Code for ReturnStatement **************
 function ReturnStatement(value, span) {
@@ -20396,7 +20806,7 @@ ReturnStatement.prototype.visit = function(visitor) {
   return visitor.visitReturnStatement(this);
 }
 ReturnStatement.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$TreeVisitor()));
+  return this.visit(($0 == null ? null : $0.assert$TreeVisitor()));
 };
 // ********** Code for ThrowStatement **************
 function ThrowStatement(value, span) {
@@ -20411,7 +20821,7 @@ ThrowStatement.prototype.visit = function(visitor) {
   return visitor.visitThrowStatement(this);
 }
 ThrowStatement.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$TreeVisitor()));
+  return this.visit(($0 == null ? null : $0.assert$TreeVisitor()));
 };
 // ********** Code for AssertStatement **************
 function AssertStatement(test, span) {
@@ -20424,7 +20834,7 @@ AssertStatement.prototype.visit = function(visitor) {
   return visitor.visitAssertStatement(this);
 }
 AssertStatement.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$TreeVisitor()));
+  return this.visit(($0 == null ? null : $0.assert$TreeVisitor()));
 };
 // ********** Code for BreakStatement **************
 function BreakStatement(label, span) {
@@ -20439,7 +20849,7 @@ BreakStatement.prototype.visit = function(visitor) {
   return visitor.visitBreakStatement(this);
 }
 BreakStatement.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$TreeVisitor()));
+  return this.visit(($0 == null ? null : $0.assert$TreeVisitor()));
 };
 // ********** Code for ContinueStatement **************
 function ContinueStatement(label, span) {
@@ -20454,7 +20864,7 @@ ContinueStatement.prototype.visit = function(visitor) {
   return visitor.visitContinueStatement(this);
 }
 ContinueStatement.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$TreeVisitor()));
+  return this.visit(($0 == null ? null : $0.assert$TreeVisitor()));
 };
 // ********** Code for IfStatement **************
 function IfStatement(test, trueBranch, falseBranch, span) {
@@ -20469,7 +20879,7 @@ IfStatement.prototype.visit = function(visitor) {
   return visitor.visitIfStatement(this);
 }
 IfStatement.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$TreeVisitor()));
+  return this.visit(($0 == null ? null : $0.assert$TreeVisitor()));
 };
 // ********** Code for WhileStatement **************
 function WhileStatement(test, body, span) {
@@ -20485,7 +20895,7 @@ WhileStatement.prototype.visit = function(visitor) {
   return visitor.visitWhileStatement(this);
 }
 WhileStatement.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$TreeVisitor()));
+  return this.visit(($0 == null ? null : $0.assert$TreeVisitor()));
 };
 // ********** Code for DoStatement **************
 function DoStatement(body, test, span) {
@@ -20501,7 +20911,7 @@ DoStatement.prototype.visit = function(visitor) {
   return visitor.visitDoStatement(this);
 }
 DoStatement.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$TreeVisitor()));
+  return this.visit(($0 == null ? null : $0.assert$TreeVisitor()));
 };
 // ********** Code for ForStatement **************
 function ForStatement(init, test, step, body, span) {
@@ -20519,7 +20929,7 @@ ForStatement.prototype.visit = function(visitor) {
   return visitor.visitForStatement(this);
 }
 ForStatement.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$TreeVisitor()));
+  return this.visit(($0 == null ? null : $0.assert$TreeVisitor()));
 };
 // ********** Code for ForInStatement **************
 function ForInStatement(item, list, body, span) {
@@ -20536,7 +20946,7 @@ ForInStatement.prototype.visit = function(visitor) {
   return visitor.visitForInStatement(this);
 }
 ForInStatement.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$TreeVisitor()));
+  return this.visit(($0 == null ? null : $0.assert$TreeVisitor()));
 };
 // ********** Code for TryStatement **************
 function TryStatement(body, catches, finallyBlock, span) {
@@ -20553,7 +20963,7 @@ TryStatement.prototype.visit = function(visitor) {
   return visitor.visitTryStatement(this);
 }
 TryStatement.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$TreeVisitor()));
+  return this.visit(($0 == null ? null : $0.assert$TreeVisitor()));
 };
 // ********** Code for SwitchStatement **************
 function SwitchStatement(test, cases, span) {
@@ -20569,7 +20979,7 @@ SwitchStatement.prototype.visit = function(visitor) {
   return visitor.visitSwitchStatement(this);
 }
 SwitchStatement.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$TreeVisitor()));
+  return this.visit(($0 == null ? null : $0.assert$TreeVisitor()));
 };
 // ********** Code for BlockStatement **************
 function BlockStatement(body, span) {
@@ -20578,14 +20988,14 @@ function BlockStatement(body, span) {
   lang_Statement.call(this, span);
 }
 $inherits(BlockStatement, lang_Statement);
-BlockStatement.prototype.is$BlockStatement = function(){return this;};
+BlockStatement.prototype.assert$BlockStatement = function(){return this};
 BlockStatement.prototype.get$body = function() { return this.body; };
 BlockStatement.prototype.set$body = function(value) { return this.body = value; };
 BlockStatement.prototype.visit = function(visitor) {
   return visitor.visitBlockStatement(this);
 }
 BlockStatement.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$TreeVisitor()));
+  return this.visit(($0 == null ? null : $0.assert$TreeVisitor()));
 };
 // ********** Code for LabeledStatement **************
 function LabeledStatement(name, body, span) {
@@ -20603,7 +21013,7 @@ LabeledStatement.prototype.visit = function(visitor) {
   return visitor.visitLabeledStatement(this);
 }
 LabeledStatement.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$TreeVisitor()));
+  return this.visit(($0 == null ? null : $0.assert$TreeVisitor()));
 };
 // ********** Code for lang_ExpressionStatement **************
 function lang_ExpressionStatement(body, span) {
@@ -20618,7 +21028,7 @@ lang_ExpressionStatement.prototype.visit = function(visitor) {
   return visitor.visitExpressionStatement(this);
 }
 lang_ExpressionStatement.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$TreeVisitor()));
+  return this.visit(($0 == null ? null : $0.assert$TreeVisitor()));
 };
 // ********** Code for EmptyStatement **************
 function EmptyStatement(span) {
@@ -20630,7 +21040,7 @@ EmptyStatement.prototype.visit = function(visitor) {
   return visitor.visitEmptyStatement(this);
 }
 EmptyStatement.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$TreeVisitor()));
+  return this.visit(($0 == null ? null : $0.assert$TreeVisitor()));
 };
 // ********** Code for DietStatement **************
 function DietStatement(span) {
@@ -20642,7 +21052,7 @@ DietStatement.prototype.visit = function(visitor) {
   return visitor.visitDietStatement(this);
 }
 DietStatement.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$TreeVisitor()));
+  return this.visit(($0 == null ? null : $0.assert$TreeVisitor()));
 };
 // ********** Code for LambdaExpression **************
 function LambdaExpression(func, span) {
@@ -20651,14 +21061,14 @@ function LambdaExpression(func, span) {
   lang_Expression.call(this, span);
 }
 $inherits(LambdaExpression, lang_Expression);
-LambdaExpression.prototype.is$LambdaExpression = function(){return this;};
+LambdaExpression.prototype.assert$LambdaExpression = function(){return this};
 LambdaExpression.prototype.get$func = function() { return this.func; };
 LambdaExpression.prototype.set$func = function(value) { return this.func = value; };
 LambdaExpression.prototype.visit = function(visitor) {
   return visitor.visitLambdaExpression(this);
 }
 LambdaExpression.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$TreeVisitor()));
+  return this.visit(($0 == null ? null : $0.assert$TreeVisitor()));
 };
 // ********** Code for CallExpression **************
 function CallExpression(target, arguments, span) {
@@ -20668,7 +21078,7 @@ function CallExpression(target, arguments, span) {
   lang_Expression.call(this, span);
 }
 $inherits(CallExpression, lang_Expression);
-CallExpression.prototype.is$CallExpression = function(){return this;};
+CallExpression.prototype.assert$CallExpression = function(){return this};
 CallExpression.prototype.get$target = function() { return this.target; };
 CallExpression.prototype.set$target = function(value) { return this.target = value; };
 CallExpression.prototype.get$arguments = function() { return this.arguments; };
@@ -20677,7 +21087,7 @@ CallExpression.prototype.visit = function(visitor) {
   return visitor.visitCallExpression(this);
 }
 CallExpression.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$TreeVisitor()));
+  return this.visit(($0 == null ? null : $0.assert$TreeVisitor()));
 };
 // ********** Code for IndexExpression **************
 function IndexExpression(target, index, span) {
@@ -20687,14 +21097,14 @@ function IndexExpression(target, index, span) {
   lang_Expression.call(this, span);
 }
 $inherits(IndexExpression, lang_Expression);
-IndexExpression.prototype.is$IndexExpression = function(){return this;};
+IndexExpression.prototype.assert$IndexExpression = function(){return this};
 IndexExpression.prototype.get$target = function() { return this.target; };
 IndexExpression.prototype.set$target = function(value) { return this.target = value; };
 IndexExpression.prototype.visit = function(visitor) {
   return visitor.visitIndexExpression(this);
 }
 IndexExpression.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$TreeVisitor()));
+  return this.visit(($0 == null ? null : $0.assert$TreeVisitor()));
 };
 // ********** Code for BinaryExpression **************
 function BinaryExpression(op, x, y, span) {
@@ -20705,7 +21115,7 @@ function BinaryExpression(op, x, y, span) {
   lang_Expression.call(this, span);
 }
 $inherits(BinaryExpression, lang_Expression);
-BinaryExpression.prototype.is$BinaryExpression = function(){return this;};
+BinaryExpression.prototype.assert$BinaryExpression = function(){return this};
 BinaryExpression.prototype.get$op = function() { return this.op; };
 BinaryExpression.prototype.set$op = function(value) { return this.op = value; };
 BinaryExpression.prototype.get$x = function() { return this.x; };
@@ -20716,7 +21126,7 @@ BinaryExpression.prototype.visit = function(visitor) {
   return visitor.visitBinaryExpression(this);
 }
 BinaryExpression.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$TreeVisitor()));
+  return this.visit(($0 == null ? null : $0.assert$TreeVisitor()));
 };
 // ********** Code for UnaryExpression **************
 function UnaryExpression(op, self, span) {
@@ -20726,7 +21136,7 @@ function UnaryExpression(op, self, span) {
   lang_Expression.call(this, span);
 }
 $inherits(UnaryExpression, lang_Expression);
-UnaryExpression.prototype.is$UnaryExpression = function(){return this;};
+UnaryExpression.prototype.assert$UnaryExpression = function(){return this};
 UnaryExpression.prototype.get$op = function() { return this.op; };
 UnaryExpression.prototype.set$op = function(value) { return this.op = value; };
 UnaryExpression.prototype.get$self = function() { return this.self; };
@@ -20735,7 +21145,7 @@ UnaryExpression.prototype.visit = function(visitor) {
   return visitor.visitUnaryExpression(this);
 }
 UnaryExpression.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$TreeVisitor()));
+  return this.visit(($0 == null ? null : $0.assert$TreeVisitor()));
 };
 // ********** Code for PostfixExpression **************
 function PostfixExpression(body, op, span) {
@@ -20745,7 +21155,7 @@ function PostfixExpression(body, op, span) {
   lang_Expression.call(this, span);
 }
 $inherits(PostfixExpression, lang_Expression);
-PostfixExpression.prototype.is$PostfixExpression = function(){return this;};
+PostfixExpression.prototype.assert$PostfixExpression = function(){return this};
 PostfixExpression.prototype.get$body = function() { return this.body; };
 PostfixExpression.prototype.set$body = function(value) { return this.body = value; };
 PostfixExpression.prototype.get$op = function() { return this.op; };
@@ -20754,7 +21164,7 @@ PostfixExpression.prototype.visit = function(visitor) {
   return visitor.visitPostfixExpression$1(this);
 }
 PostfixExpression.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$TreeVisitor()));
+  return this.visit(($0 == null ? null : $0.assert$TreeVisitor()));
 };
 // ********** Code for lang_NewExpression **************
 function lang_NewExpression(isConst, type, name, arguments, span) {
@@ -20778,7 +21188,7 @@ lang_NewExpression.prototype.visit = function(visitor) {
   return visitor.visitNewExpression(this);
 }
 lang_NewExpression.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$TreeVisitor()));
+  return this.visit(($0 == null ? null : $0.assert$TreeVisitor()));
 };
 // ********** Code for ListExpression **************
 function ListExpression(isConst, type, values, span) {
@@ -20799,7 +21209,7 @@ ListExpression.prototype.visit = function(visitor) {
   return visitor.visitListExpression(this);
 }
 ListExpression.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$TreeVisitor()));
+  return this.visit(($0 == null ? null : $0.assert$TreeVisitor()));
 };
 // ********** Code for MapExpression **************
 function MapExpression(isConst, type, items, span) {
@@ -20818,7 +21228,7 @@ MapExpression.prototype.visit = function(visitor) {
   return visitor.visitMapExpression(this);
 }
 MapExpression.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$TreeVisitor()));
+  return this.visit(($0 == null ? null : $0.assert$TreeVisitor()));
 };
 // ********** Code for ConditionalExpression **************
 function ConditionalExpression(test, trueBranch, falseBranch, span) {
@@ -20833,7 +21243,7 @@ ConditionalExpression.prototype.visit = function(visitor) {
   return visitor.visitConditionalExpression(this);
 }
 ConditionalExpression.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$TreeVisitor()));
+  return this.visit(($0 == null ? null : $0.assert$TreeVisitor()));
 };
 // ********** Code for IsExpression **************
 function IsExpression(isTrue, x, type, span) {
@@ -20852,7 +21262,7 @@ IsExpression.prototype.visit = function(visitor) {
   return visitor.visitIsExpression(this);
 }
 IsExpression.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$TreeVisitor()));
+  return this.visit(($0 == null ? null : $0.assert$TreeVisitor()));
 };
 // ********** Code for ParenExpression **************
 function ParenExpression(body, span) {
@@ -20867,7 +21277,7 @@ ParenExpression.prototype.visit = function(visitor) {
   return visitor.visitParenExpression(this);
 }
 ParenExpression.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$TreeVisitor()));
+  return this.visit(($0 == null ? null : $0.assert$TreeVisitor()));
 };
 // ********** Code for DotExpression **************
 function DotExpression(self, name, span) {
@@ -20877,7 +21287,7 @@ function DotExpression(self, name, span) {
   lang_Expression.call(this, span);
 }
 $inherits(DotExpression, lang_Expression);
-DotExpression.prototype.is$DotExpression = function(){return this;};
+DotExpression.prototype.assert$DotExpression = function(){return this};
 DotExpression.prototype.get$self = function() { return this.self; };
 DotExpression.prototype.set$self = function(value) { return this.self = value; };
 DotExpression.prototype.get$name = function() { return this.name; };
@@ -20886,7 +21296,7 @@ DotExpression.prototype.visit = function(visitor) {
   return visitor.visitDotExpression(this);
 }
 DotExpression.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$TreeVisitor()));
+  return this.visit(($0 == null ? null : $0.assert$TreeVisitor()));
 };
 // ********** Code for VarExpression **************
 function VarExpression(name, span) {
@@ -20895,14 +21305,14 @@ function VarExpression(name, span) {
   lang_Expression.call(this, span);
 }
 $inherits(VarExpression, lang_Expression);
-VarExpression.prototype.is$VarExpression = function(){return this;};
+VarExpression.prototype.assert$VarExpression = function(){return this};
 VarExpression.prototype.get$name = function() { return this.name; };
 VarExpression.prototype.set$name = function(value) { return this.name = value; };
 VarExpression.prototype.visit = function(visitor) {
   return visitor.visitVarExpression(this);
 }
 VarExpression.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$TreeVisitor()));
+  return this.visit(($0 == null ? null : $0.assert$TreeVisitor()));
 };
 // ********** Code for ThisExpression **************
 function ThisExpression(span) {
@@ -20914,7 +21324,7 @@ ThisExpression.prototype.visit = function(visitor) {
   return visitor.visitThisExpression(this);
 }
 ThisExpression.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$TreeVisitor()));
+  return this.visit(($0 == null ? null : $0.assert$TreeVisitor()));
 };
 // ********** Code for SuperExpression **************
 function SuperExpression(span) {
@@ -20926,7 +21336,7 @@ SuperExpression.prototype.visit = function(visitor) {
   return visitor.visitSuperExpression(this);
 }
 SuperExpression.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$TreeVisitor()));
+  return this.visit(($0 == null ? null : $0.assert$TreeVisitor()));
 };
 // ********** Code for NullExpression **************
 function NullExpression(span) {
@@ -20938,7 +21348,7 @@ NullExpression.prototype.visit = function(visitor) {
   return visitor.visitNullExpression(this);
 }
 NullExpression.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$TreeVisitor()));
+  return this.visit(($0 == null ? null : $0.assert$TreeVisitor()));
 };
 // ********** Code for LiteralExpression **************
 function LiteralExpression(value, type, text, span) {
@@ -20959,7 +21369,7 @@ LiteralExpression.prototype.visit = function(visitor) {
   return visitor.visitLiteralExpression(this);
 }
 LiteralExpression.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$TreeVisitor()));
+  return this.visit(($0 == null ? null : $0.assert$TreeVisitor()));
 };
 // ********** Code for NameTypeReference **************
 function NameTypeReference(isFinal, name, names, span) {
@@ -20970,7 +21380,7 @@ function NameTypeReference(isFinal, name, names, span) {
   TypeReference.call(this, span);
 }
 $inherits(NameTypeReference, TypeReference);
-NameTypeReference.prototype.is$NameTypeReference = function(){return this;};
+NameTypeReference.prototype.assert$NameTypeReference = function(){return this};
 NameTypeReference.prototype.get$isFinal = function() { return this.isFinal; };
 NameTypeReference.prototype.set$isFinal = function(value) { return this.isFinal = value; };
 NameTypeReference.prototype.get$name = function() { return this.name; };
@@ -20981,7 +21391,7 @@ NameTypeReference.prototype.visit = function(visitor) {
   return visitor.visitNameTypeReference(this);
 }
 NameTypeReference.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$TreeVisitor()));
+  return this.visit(($0 == null ? null : $0.assert$TreeVisitor()));
 };
 // ********** Code for GenericTypeReference **************
 function GenericTypeReference(baseType, typeArguments, depth, span) {
@@ -20992,7 +21402,7 @@ function GenericTypeReference(baseType, typeArguments, depth, span) {
   TypeReference.call(this, span);
 }
 $inherits(GenericTypeReference, TypeReference);
-GenericTypeReference.prototype.is$GenericTypeReference = function(){return this;};
+GenericTypeReference.prototype.assert$GenericTypeReference = function(){return this};
 GenericTypeReference.prototype.get$baseType = function() { return this.baseType; };
 GenericTypeReference.prototype.set$baseType = function(value) { return this.baseType = value; };
 GenericTypeReference.prototype.get$depth = function() { return this.depth; };
@@ -21001,7 +21411,7 @@ GenericTypeReference.prototype.visit = function(visitor) {
   return visitor.visitGenericTypeReference(this);
 }
 GenericTypeReference.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$TreeVisitor()));
+  return this.visit(($0 == null ? null : $0.assert$TreeVisitor()));
 };
 // ********** Code for FunctionTypeReference **************
 function FunctionTypeReference(isFinal, func, span) {
@@ -21011,7 +21421,7 @@ function FunctionTypeReference(isFinal, func, span) {
   TypeReference.call(this, span);
 }
 $inherits(FunctionTypeReference, TypeReference);
-FunctionTypeReference.prototype.is$FunctionTypeReference = function(){return this;};
+FunctionTypeReference.prototype.assert$FunctionTypeReference = function(){return this};
 FunctionTypeReference.prototype.get$isFinal = function() { return this.isFinal; };
 FunctionTypeReference.prototype.set$isFinal = function(value) { return this.isFinal = value; };
 FunctionTypeReference.prototype.get$func = function() { return this.func; };
@@ -21020,7 +21430,7 @@ FunctionTypeReference.prototype.visit = function(visitor) {
   return visitor.visitFunctionTypeReference(this);
 }
 FunctionTypeReference.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$TreeVisitor()));
+  return this.visit(($0 == null ? null : $0.assert$TreeVisitor()));
 };
 // ********** Code for ArgumentNode **************
 function ArgumentNode(label, value, span) {
@@ -21030,7 +21440,7 @@ function ArgumentNode(label, value, span) {
   lang_Node.call(this, span);
 }
 $inherits(ArgumentNode, lang_Node);
-ArgumentNode.prototype.is$ArgumentNode = function(){return this;};
+ArgumentNode.prototype.assert$ArgumentNode = function(){return this};
 ArgumentNode.prototype.get$label = function() { return this.label; };
 ArgumentNode.prototype.set$label = function(value) { return this.label = value; };
 ArgumentNode.prototype.get$value = function() { return this.value; };
@@ -21039,7 +21449,7 @@ ArgumentNode.prototype.visit = function(visitor) {
   return visitor.visitArgumentNode(this);
 }
 ArgumentNode.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$TreeVisitor()));
+  return this.visit(($0 == null ? null : $0.assert$TreeVisitor()));
 };
 // ********** Code for FormalNode **************
 function FormalNode(isThis, isRest, type, name, value, span) {
@@ -21062,7 +21472,7 @@ FormalNode.prototype.visit = function(visitor) {
   return visitor.visitFormalNode(this);
 }
 FormalNode.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$TreeVisitor()));
+  return this.visit(($0 == null ? null : $0.assert$TreeVisitor()));
 };
 // ********** Code for CatchNode **************
 function CatchNode(exception, trace, body, span) {
@@ -21083,7 +21493,7 @@ CatchNode.prototype.visit = function(visitor) {
   return visitor.visitCatchNode(this);
 }
 CatchNode.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$TreeVisitor()));
+  return this.visit(($0 == null ? null : $0.assert$TreeVisitor()));
 };
 // ********** Code for CaseNode **************
 function CaseNode(label, cases, statements, span) {
@@ -21104,7 +21514,7 @@ CaseNode.prototype.visit = function(visitor) {
   return visitor.visitCaseNode(this);
 }
 CaseNode.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$TreeVisitor()));
+  return this.visit(($0 == null ? null : $0.assert$TreeVisitor()));
 };
 // ********** Code for TypeParameter **************
 function TypeParameter(name, extendsType, span) {
@@ -21122,7 +21532,7 @@ TypeParameter.prototype.visit = function(visitor) {
   return visitor.visitTypeParameter(this);
 }
 TypeParameter.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$TreeVisitor()));
+  return this.visit(($0 == null ? null : $0.assert$TreeVisitor()));
 };
 // ********** Code for lang_Identifier **************
 function lang_Identifier(name, span) {
@@ -21131,14 +21541,14 @@ function lang_Identifier(name, span) {
   lang_Node.call(this, span);
 }
 $inherits(lang_Identifier, lang_Node);
-lang_Identifier.prototype.is$lang_Identifier = function(){return this;};
+lang_Identifier.prototype.assert$lang_Identifier = function(){return this};
 lang_Identifier.prototype.get$name = function() { return this.name; };
 lang_Identifier.prototype.set$name = function(value) { return this.name = value; };
 lang_Identifier.prototype.visit = function(visitor) {
   return visitor.visitIdentifier(this);
 }
 lang_Identifier.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$TreeVisitor()));
+  return this.visit(($0 == null ? null : $0.assert$TreeVisitor()));
 };
 // ********** Code for DeclaredIdentifier **************
 function DeclaredIdentifier(type, name, span) {
@@ -21148,7 +21558,7 @@ function DeclaredIdentifier(type, name, span) {
   lang_Expression.call(this, span);
 }
 $inherits(DeclaredIdentifier, lang_Expression);
-DeclaredIdentifier.prototype.is$DeclaredIdentifier = function(){return this;};
+DeclaredIdentifier.prototype.assert$DeclaredIdentifier = function(){return this};
 DeclaredIdentifier.prototype.get$type = function() { return this.type; };
 DeclaredIdentifier.prototype.set$type = function(value) { return this.type = value; };
 DeclaredIdentifier.prototype.get$name = function() { return this.name; };
@@ -21157,17 +21567,19 @@ DeclaredIdentifier.prototype.visit = function(visitor) {
   return visitor.visitDeclaredIdentifier(this);
 }
 DeclaredIdentifier.prototype.visit$1 = function($0) {
-  return this.visit(($0 && $0.is$TreeVisitor()));
+  return this.visit(($0 == null ? null : $0.assert$TreeVisitor()));
 };
 // ********** Code for lang_Type **************
 function lang_Type(name) {
-  this.isTested = false;
+  this.isTested = false
+  this.isChecked = false
   this._resolvedMembers = $map([]);
+  this.varStubs = $map([]);
   // Initializers done
   lang_Element.call(this, name, null);
 }
 $inherits(lang_Type, lang_Element);
-lang_Type.prototype.is$lang_Type = function(){return this;};
+lang_Type.prototype.assert$lang_Type = function(){return this};
 lang_Type.prototype.get$isTested = function() { return this.isTested; };
 lang_Type.prototype.set$isTested = function(value) { return this.isTested = value; };
 lang_Type.prototype.get$typeCheckCode = function() { return this.typeCheckCode; };
@@ -21180,9 +21592,9 @@ lang_Type.prototype.markUsed = function() {
 lang_Type.prototype.get$typeMember = function() {
   var $0;
   if (this._typeMember == null) {
-    this._typeMember = new TypeMember((this && this.is$DefinedType()));
+    this._typeMember = new TypeMember((this == null ? null : this.assert$DefinedType()));
   }
-  return (($0 = this._typeMember) && $0.is$TypeMember());
+  return (($0 = this._typeMember) == null ? null : $0.assert$TypeMember());
 }
 lang_Type.prototype.getMember = function(name) {
   return null;
@@ -21260,7 +21672,7 @@ lang_Type.prototype.get$typeArgsInOrder = function() {
   return null;
 }
 lang_Type.prototype.get$genericType = function() {
-  return (this && this.is$DefinedType());
+  return (this == null ? null : this.assert$DefinedType());
 }
 lang_Type.prototype.get$interfaces = function() {
   return null;
@@ -21284,13 +21696,13 @@ lang_Type.prototype._checkOverride = function(member) {
   var parentMember = this._getMemberInParents(member.name);
   if ($notnull_bool($ne(parentMember, null))) {
     if (!$notnull_bool(member.get$isPrivate()) || $eq(member.get$library(), parentMember.get$library())) {
-      member.override((parentMember && parentMember.is$Member()));
+      member.override((parentMember == null ? null : parentMember.assert$Member()));
     }
   }
 }
 lang_Type.prototype._createNotEqualMember = function() {
   var $0;
-  var eq = (($0 = this.get$members().$index('\$eq')) && $0.is$MethodMember());
+  var eq = (($0 = this.get$members().$index('\$eq')) == null ? null : $0.assert$MethodMember());
   if (eq == null) {
     $globals.world.internalError('INTERNAL: object does not define ==', this.get$definition().span);
   }
@@ -21311,7 +21723,7 @@ lang_Type.prototype._getMemberInParents = function(memberName) {
       if (memberName == '\$ne') {
         var ret = this._createNotEqualMember();
         this.get$members().$setindex(memberName, ret);
-        return (ret && ret.is$Member());
+        return (ret == null ? null : ret.assert$Member());
       }
       return null;
     }
@@ -21323,7 +21735,7 @@ lang_Type.prototype._getMemberInParents = function(memberName) {
         var i = $list.$index($i);
         var ret = i.getMember$1(memberName);
         if ($notnull_bool($ne(ret, null))) {
-          return (ret && ret.is$Member());
+          return (ret == null ? null : ret.assert$Member());
         }
       }
       return null;
@@ -21335,7 +21747,7 @@ lang_Type.prototype._getMemberInParents = function(memberName) {
 }
 lang_Type.prototype.resolveMember = function(memberName) {
   var $0;
-  var ret = (($0 = this._resolvedMembers.$index(memberName)) && $0.is$MemberSet());
+  var ret = (($0 = this._resolvedMembers.$index(memberName)) == null ? null : $0.assert$MemberSet());
   if (ret != null) return ret;
   var member = this.getMember(memberName);
   if (member == null) {
@@ -21353,12 +21765,12 @@ lang_Type.prototype.resolveMember = function(memberName) {
       if (!$notnull_bool(this.get$isClass()) && $notnull_bool(t.get$isClass())) {
         var m = t.getMember$1(memberName);
         if ($notnull_bool($ne(m, null)) && ret.members.indexOf(m) == -1) {
-          ret.add((m && m.is$Member()));
+          ret.add((m == null ? null : m.assert$Member()));
         }
       }
       else {
         var m = t.get$members().$index(memberName);
-        if ($notnull_bool($ne(m, null))) ret.add((m && m.is$Member()));
+        if ($notnull_bool($ne(m, null))) ret.add((m == null ? null : m.assert$Member()));
       }
     }
     return ret;
@@ -21424,7 +21836,7 @@ lang_Type.prototype.isSubtypeOf = function(other) {
   var call = this.getCallMethod();
   var otherCall = other.getCallMethod();
   if ($notnull_bool($ne(call, null)) && $notnull_bool($ne(otherCall, null))) {
-    return lang_Type._isFunctionSubtypeOf((call && call.is$MethodMember()), (otherCall && otherCall.is$MethodMember()));
+    return lang_Type._isFunctionSubtypeOf((call == null ? null : call.assert$MethodMember()), (otherCall == null ? null : otherCall.assert$MethodMember()));
   }
   if ($eq(this.get$genericType(), other.get$genericType()) && $notnull_bool($ne(this.get$typeArgsInOrder(), null)) && $notnull_bool($ne(other.get$typeArgsInOrder(), null)) && $notnull_bool($eq(this.get$typeArgsInOrder().length, other.get$typeArgsInOrder().length))) {
     var t = this.get$typeArgsInOrder().iterator$0();
@@ -21462,38 +21874,38 @@ lang_Type._isFunctionSubtypeOf = function(t, s) {
   return true;
 }
 lang_Type.prototype.addDirectSubtype$1 = function($0) {
-  return this.addDirectSubtype(($0 && $0.is$lang_Type()));
+  return this.addDirectSubtype(($0 == null ? null : $0.assert$lang_Type()));
 };
 lang_Type.prototype.ensureSubtypeOf$3 = function($0, $1, $2) {
-  return this.ensureSubtypeOf(($0 && $0.is$lang_Type()), ($1 && $1.is$SourceSpan()), $assert_bool($2));
+  return this.ensureSubtypeOf(($0 == null ? null : $0.assert$lang_Type()), ($1 == null ? null : $1.assert$SourceSpan()), $assert_bool($2));
 };
 lang_Type.prototype.getConstructor$1 = function($0) {
   return this.getConstructor($assert_String($0));
 };
 lang_Type.prototype.getFactory$2 = function($0, $1) {
-  return this.getFactory(($0 && $0.is$lang_Type()), $assert_String($1));
+  return this.getFactory(($0 == null ? null : $0.assert$lang_Type()), $assert_String($1));
 };
 lang_Type.prototype.getMember$1 = function($0) {
   return this.getMember($assert_String($0));
 };
 lang_Type.prototype.getOrMakeConcreteType$1 = function($0) {
-  return this.getOrMakeConcreteType(($0 && $0.is$List_Type()));
+  return this.getOrMakeConcreteType(($0 == null ? null : $0.assert$List_Type()));
 };
 lang_Type.prototype.isAssignable$1 = function($0) {
-  return this.isAssignable(($0 && $0.is$lang_Type()));
+  return this.isAssignable(($0 == null ? null : $0.assert$lang_Type()));
 };
 lang_Type.prototype.isString$0 = function() {
   return this.get$isString()();
 };
 lang_Type.prototype.isSubtypeOf$1 = function($0) {
-  return this.isSubtypeOf(($0 && $0.is$lang_Type()));
+  return this.isSubtypeOf(($0 == null ? null : $0.assert$lang_Type()));
 };
 lang_Type.prototype.markUsed$0 = lang_Type.prototype.markUsed;
 lang_Type.prototype.resolveMember$1 = function($0) {
   return this.resolveMember($assert_String($0));
 };
 lang_Type.prototype.resolveTypeParams$1 = function($0) {
-  return this.resolveTypeParams(($0 && $0.is$ConcreteType()));
+  return this.resolveTypeParams(($0 == null ? null : $0.assert$ConcreteType()));
 };
 // ********** Code for ParameterType **************
 function ParameterType(name, typeParameter) {
@@ -21502,7 +21914,7 @@ function ParameterType(name, typeParameter) {
   lang_Type.call(this, name);
 }
 $inherits(ParameterType, lang_Type);
-ParameterType.prototype.is$ParameterType = function(){return this;};
+ParameterType.prototype.assert$ParameterType = function(){return this};
 ParameterType.prototype.get$typeParameter = function() { return this.typeParameter; };
 ParameterType.prototype.set$typeParameter = function(value) { return this.typeParameter = value; };
 ParameterType.prototype.get$extendsType = function() { return this.extendsType; };
@@ -21539,7 +21951,7 @@ ParameterType.prototype.getOrMakeConcreteType = function(typeArgs) {
 }
 ParameterType.prototype.resolveTypeParams = function(inType) {
   var $0;
-  return (($0 = inType.typeArguments.$index(this.name)) && $0.is$lang_Type());
+  return (($0 = inType.typeArguments.$index(this.name)) == null ? null : $0.assert$lang_Type());
 }
 ParameterType.prototype.addDirectSubtype = function(type) {
   $globals.world.internalError('no subtypes of type parameters yet', this.get$span());
@@ -21553,23 +21965,23 @@ ParameterType.prototype.resolve = function() {
   }
 }
 ParameterType.prototype.addDirectSubtype$1 = function($0) {
-  return this.addDirectSubtype(($0 && $0.is$lang_Type()));
+  return this.addDirectSubtype(($0 == null ? null : $0.assert$lang_Type()));
 };
 ParameterType.prototype.getConstructor$1 = function($0) {
   return this.getConstructor($assert_String($0));
 };
 ParameterType.prototype.getOrMakeConcreteType$1 = function($0) {
-  return this.getOrMakeConcreteType(($0 && $0.is$List_Type()));
+  return this.getOrMakeConcreteType(($0 == null ? null : $0.assert$List_Type()));
 };
 ParameterType.prototype.isSubtypeOf$1 = function($0) {
-  return this.isSubtypeOf(($0 && $0.is$lang_Type()));
+  return this.isSubtypeOf(($0 == null ? null : $0.assert$lang_Type()));
 };
 ParameterType.prototype.resolve$0 = ParameterType.prototype.resolve;
 ParameterType.prototype.resolveMember$1 = function($0) {
   return this.resolveMember($assert_String($0));
 };
 ParameterType.prototype.resolveTypeParams$1 = function($0) {
-  return this.resolveTypeParams(($0 && $0.is$ConcreteType()));
+  return this.resolveTypeParams(($0 == null ? null : $0.assert$ConcreteType()));
 };
 // ********** Code for NonNullableType **************
 function NonNullableType(type) {
@@ -21617,11 +22029,11 @@ NonNullableType.prototype.getMember = function(name) {
 }
 NonNullableType.prototype.getConstructor = function(name) {
   var $0;
-  return (($0 = this.type.getConstructor(name)) && $0.is$MethodMember());
+  return (($0 = this.type.getConstructor(name)) == null ? null : $0.assert$MethodMember());
 }
 NonNullableType.prototype.getFactory = function(t, name) {
   var $0;
-  return (($0 = this.type.getFactory(t, name)) && $0.is$MethodMember());
+  return (($0 = this.type.getFactory(t, name)) == null ? null : $0.assert$MethodMember());
 }
 NonNullableType.prototype.getOrMakeConcreteType = function(typeArgs) {
   return this.type.getOrMakeConcreteType(typeArgs);
@@ -21661,7 +22073,7 @@ NonNullableType.prototype.get$factories = function() {
 }
 NonNullableType.prototype.get$typeArgsInOrder = function() {
   var $0;
-  return (($0 = this.type.get$typeArgsInOrder()) && $0.is$Collection_Type());
+  return (($0 = this.type.get$typeArgsInOrder()) == null ? null : $0.assert$Collection_Type());
 }
 NonNullableType.prototype.get$genericType = function() {
   return this.type.get$genericType();
@@ -21679,29 +22091,29 @@ NonNullableType.prototype.get$isNative = function() {
   return this.type.get$isNative();
 }
 NonNullableType.prototype.addDirectSubtype$1 = function($0) {
-  return this.addDirectSubtype(($0 && $0.is$lang_Type()));
+  return this.addDirectSubtype(($0 == null ? null : $0.assert$lang_Type()));
 };
 NonNullableType.prototype.getConstructor$1 = function($0) {
   return this.getConstructor($assert_String($0));
 };
 NonNullableType.prototype.getFactory$2 = function($0, $1) {
-  return this.getFactory(($0 && $0.is$lang_Type()), $assert_String($1));
+  return this.getFactory(($0 == null ? null : $0.assert$lang_Type()), $assert_String($1));
 };
 NonNullableType.prototype.getMember$1 = function($0) {
   return this.getMember($assert_String($0));
 };
 NonNullableType.prototype.getOrMakeConcreteType$1 = function($0) {
-  return this.getOrMakeConcreteType(($0 && $0.is$List_Type()));
+  return this.getOrMakeConcreteType(($0 == null ? null : $0.assert$List_Type()));
 };
 NonNullableType.prototype.isSubtypeOf$1 = function($0) {
-  return this.isSubtypeOf(($0 && $0.is$lang_Type()));
+  return this.isSubtypeOf(($0 == null ? null : $0.assert$lang_Type()));
 };
 NonNullableType.prototype.markUsed$0 = NonNullableType.prototype.markUsed;
 NonNullableType.prototype.resolveMember$1 = function($0) {
   return this.resolveMember($assert_String($0));
 };
 NonNullableType.prototype.resolveTypeParams$1 = function($0) {
-  return this.resolveTypeParams(($0 && $0.is$ConcreteType()));
+  return this.resolveTypeParams(($0 == null ? null : $0.assert$ConcreteType()));
 };
 // ********** Code for ConcreteType **************
 function ConcreteType(name, genericType, typeArguments, typeArgsInOrder) {
@@ -21715,7 +22127,7 @@ function ConcreteType(name, genericType, typeArguments, typeArgsInOrder) {
   lang_Type.call(this, name);
 }
 $inherits(ConcreteType, lang_Type);
-ConcreteType.prototype.is$ConcreteType = function(){return this;};
+ConcreteType.prototype.assert$ConcreteType = function(){return this};
 ConcreteType.prototype.get$genericType = function() { return this.genericType; };
 ConcreteType.prototype.get$typeArgsInOrder = function() { return this.typeArgsInOrder; };
 ConcreteType.prototype.set$typeArgsInOrder = function(value) { return this.typeArgsInOrder = value; };
@@ -21754,7 +22166,7 @@ ConcreteType.prototype.resolveTypeParams = function(inType) {
     newTypeArgs.add$1(newType);
   }
   if (!$notnull_bool(needsNewType)) return this;
-  return this.genericType.getOrMakeConcreteType((newTypeArgs && newTypeArgs.is$List_Type()));
+  return this.genericType.getOrMakeConcreteType((newTypeArgs == null ? null : newTypeArgs.assert$List_Type()));
 }
 ConcreteType.prototype.getOrMakeConcreteType = function(typeArgs) {
   return this.genericType.getOrMakeConcreteType(typeArgs);
@@ -21800,7 +22212,7 @@ ConcreteType.prototype.getAllMembers = function() {
       result.$setindex(memberName, myMember);
     }
   }
-  return (result && result.is$Map_String$Member());
+  return (result == null ? null : result.assert$Map_String$Member());
 }
 ConcreteType.prototype.markUsed = function() {
   this.genericType.markUsed();
@@ -21827,7 +22239,7 @@ ConcreteType.prototype.getConstructor = function(constructorName) {
   }
   if ($notnull_bool(genericMember.get$isFactory())) {
     ret = new ConcreteMember($assert_String(genericMember.get$name()), this, genericMember);
-    this.factories.addFactory(this.name, constructorName, (ret && ret.is$Member()));
+    this.factories.addFactory(this.name, constructorName, (ret == null ? null : ret.assert$Member()));
   }
   else {
     ret = new ConcreteMember(this.name, this, genericMember);
@@ -21837,7 +22249,7 @@ ConcreteType.prototype.getConstructor = function(constructorName) {
 }
 ConcreteType.prototype.getMember = function(memberName) {
   var $0;
-  var member = (($0 = this.members.$index(memberName)) && $0.is$Member());
+  var member = (($0 = this.members.$index(memberName)) == null ? null : $0.assert$Member());
   if (member != null) {
     this._checkOverride(member);
     return member;
@@ -21852,29 +22264,29 @@ ConcreteType.prototype.getMember = function(memberName) {
 }
 ConcreteType.prototype.resolveType = function(node, isRequired) {
   var ret = this.genericType.resolveType(node, isRequired);
-  return (ret && ret.is$lang_Type());
+  return (ret == null ? null : ret.assert$lang_Type());
 }
 ConcreteType.prototype.addDirectSubtype = function(type) {
   this.genericType.addDirectSubtype(type);
 }
 ConcreteType.prototype.addDirectSubtype$1 = function($0) {
-  return this.addDirectSubtype(($0 && $0.is$lang_Type()));
+  return this.addDirectSubtype(($0 == null ? null : $0.assert$lang_Type()));
 };
 ConcreteType.prototype.getConstructor$1 = function($0) {
   return this.getConstructor($assert_String($0));
 };
 ConcreteType.prototype.getFactory$2 = function($0, $1) {
-  return this.getFactory(($0 && $0.is$lang_Type()), $assert_String($1));
+  return this.getFactory(($0 == null ? null : $0.assert$lang_Type()), $assert_String($1));
 };
 ConcreteType.prototype.getMember$1 = function($0) {
   return this.getMember($assert_String($0));
 };
 ConcreteType.prototype.getOrMakeConcreteType$1 = function($0) {
-  return this.getOrMakeConcreteType(($0 && $0.is$List_Type()));
+  return this.getOrMakeConcreteType(($0 == null ? null : $0.assert$List_Type()));
 };
 ConcreteType.prototype.markUsed$0 = ConcreteType.prototype.markUsed;
 ConcreteType.prototype.resolveTypeParams$1 = function($0) {
-  return this.resolveTypeParams(($0 && $0.is$ConcreteType()));
+  return this.resolveTypeParams(($0 == null ? null : $0.assert$ConcreteType()));
 };
 // ********** Code for DefinedType **************
 function DefinedType(name, library, definition, isClass) {
@@ -21891,7 +22303,7 @@ function DefinedType(name, library, definition, isClass) {
   this.setDefinition(definition);
 }
 $inherits(DefinedType, lang_Type);
-DefinedType.prototype.is$DefinedType = function(){return this;};
+DefinedType.prototype.assert$DefinedType = function(){return this};
 DefinedType.prototype.get$definition = function() { return this.definition; };
 DefinedType.prototype.set$definition = function(value) { return this.definition = value; };
 DefinedType.prototype.get$library = function() { return this.library; };
@@ -21918,18 +22330,18 @@ DefinedType.prototype.get$isNative = function() { return this.isNative; };
 DefinedType.prototype.set$isNative = function(value) { return this.isNative = value; };
 DefinedType.prototype.setDefinition = function(def) {
   var $0;
-  $assert(this.definition == null, "definition == null", "type.dart", 725, 12);
+  $assert(this.definition == null, "definition == null", "type.dart", 726, 12);
   this.definition = def;
   if ((this.definition instanceof TypeDefinition) && $notnull_bool($ne(this.definition.get$nativeType(), null))) {
     this.isNative = true;
   }
   if (this.definition != null && $notnull_bool($ne(this.definition.get$typeParameters(), null))) {
     this._concreteTypes = $map([]);
-    this.typeParameters = (($0 = this.definition.get$typeParameters()) && $0.is$List_ParameterType());
+    this.typeParameters = (($0 = this.definition.get$typeParameters()) == null ? null : $0.assert$List_ParameterType());
   }
 }
 DefinedType.prototype.get$isHiddenNativeType = function() {
-  return $eq(this.library, $globals.world.get$dom()) || ($notnull_bool($ne(this.definition.get$nativeType(), null)) && $notnull_bool(this.definition.get$nativeType().get$isConstructorHidden()));
+  return (this.definition != null && $notnull_bool($ne(this.definition.get$nativeType(), null)) && $notnull_bool(this.definition.get$nativeType().get$isConstructorHidden()));
 }
 DefinedType.prototype.get$typeArgsInOrder = function() {
   if (this.typeParameters == null) return null;
@@ -21967,7 +22379,7 @@ DefinedType.prototype.get$isGeneric = function() {
 }
 DefinedType.prototype.get$span = function() {
   var $0;
-  return (($0 = this.definition == null ? null : this.definition.span) && $0.is$SourceSpan());
+  return (($0 = this.definition == null ? null : this.definition.span) == null ? null : $0.assert$SourceSpan());
 }
 DefinedType.prototype.get$typeofName = function() {
   if (!$notnull_bool(this.library.get$isCore())) return null;
@@ -21982,7 +22394,7 @@ DefinedType.prototype.get$isNum = function() {
 }
 DefinedType.prototype.getCallMethod = function() {
   var $0;
-  return (($0 = this.members.$index('\$call')) && $0.is$MethodMember());
+  return (($0 = this.members.$index('\$call')) == null ? null : $0.assert$MethodMember());
 }
 DefinedType.prototype.getAllMembers = function() {
   return HashMapImplementation.HashMapImplementation$from$factory(this.members);
@@ -21994,7 +22406,7 @@ DefinedType.prototype.markUsed = function() {
     var $list = orderValuesByKeys(this._lazyGenMethods);
     for (var $i = 0;$i < $list.length; $i++) {
       var method = $list.$index($i);
-      $globals.world.gen.genMethod((method && method.is$Member()));
+      $globals.world.gen.genMethod((method == null ? null : method.assert$Member()));
     }
     this._lazyGenMethods = null;
   }
@@ -22015,14 +22427,14 @@ DefinedType.prototype._resolveInterfaces = function(types) {
   var interfaces = [];
   for (var $i = 0;$i < types.length; $i++) {
     var type = types.$index($i);
-    var resolvedInterface = this.resolveType((type && type.is$TypeReference()), true);
+    var resolvedInterface = this.resolveType((type == null ? null : type.assert$TypeReference()), true);
     if ($notnull_bool(resolvedInterface.get$isClosed()) && !($notnull_bool(this.library.get$isCore()) || $notnull_bool(this.library.get$isCoreImpl()))) {
-      $globals.world.error(('can not implement "' + resolvedInterface.get$name() + '": ') + 'only native implementation allowed', (($0 = type.get$span()) && $0.is$SourceSpan()));
+      $globals.world.error(('can not implement "' + resolvedInterface.get$name() + '": ') + 'only native implementation allowed', (($0 = type.get$span()) == null ? null : $0.assert$SourceSpan()));
     }
     resolvedInterface.addDirectSubtype$1(this);
     interfaces.add$1(resolvedInterface);
   }
-  return (interfaces && interfaces.is$List_Type());
+  return (interfaces == null ? null : interfaces.assert$List_Type());
 }
 DefinedType.prototype.addDirectSubtype = function(type) {
   $assert(this._subtypes == null, "_subtypes == null", "type.dart", 841, 12);
@@ -22036,7 +22448,7 @@ DefinedType.prototype.get$subtypes = function() {
     for (var $i = this.directSubtypes.iterator(); $i.hasNext$0(); ) {
       var st = $i.next$0();
       this._subtypes.add(st);
-      this._subtypes.addAll((($0 = st.get$subtypes()) && $0.is$Collection_E()));
+      this._subtypes.addAll((($0 = st.get$subtypes()) == null ? null : $0.assert$Collection_E()));
     }
   }
   return this._subtypes;
@@ -22086,24 +22498,24 @@ DefinedType.prototype._cycleInInterfaceExtends = function() {
 DefinedType.prototype.resolve = function() {
   var $0;
   if ((this.definition instanceof TypeDefinition)) {
-    var typeDef = (($0 = this.definition) && $0.is$TypeDefinition());
+    var typeDef = (($0 = this.definition) == null ? null : $0.assert$TypeDefinition());
     if ($notnull_bool(this.isClass)) {
       if (typeDef.extendsTypes != null && typeDef.extendsTypes.length > 0) {
         if (typeDef.extendsTypes.length > 1) {
-          $globals.world.error('more than one base class', (($0 = typeDef.extendsTypes.$index(1).get$span()) && $0.is$SourceSpan()));
+          $globals.world.error('more than one base class', (($0 = typeDef.extendsTypes.$index(1).get$span()) == null ? null : $0.assert$SourceSpan()));
         }
         var extendsTypeRef = typeDef.extendsTypes.$index(0);
         if ((extendsTypeRef instanceof GenericTypeReference)) {
-          var g = (extendsTypeRef && extendsTypeRef.is$GenericTypeReference());
+          var g = (extendsTypeRef == null ? null : extendsTypeRef.assert$GenericTypeReference());
           this.set$parent(this.resolveType(g.baseType, true));
         }
-        this.set$parent(this.resolveType((extendsTypeRef && extendsTypeRef.is$TypeReference()), true));
+        this.set$parent(this.resolveType((extendsTypeRef == null ? null : extendsTypeRef.assert$TypeReference()), true));
         if (!$notnull_bool(this.get$parent().get$isClass())) {
-          $globals.world.error('class may not extend an interface - use implements', (($0 = typeDef.extendsTypes.$index(0).get$span()) && $0.is$SourceSpan()));
+          $globals.world.error('class may not extend an interface - use implements', (($0 = typeDef.extendsTypes.$index(0).get$span()) == null ? null : $0.assert$SourceSpan()));
         }
         this.get$parent().addDirectSubtype(this);
         if ($notnull_bool(this._cycleInClassExtends())) {
-          $globals.world.error(('class "' + this.name + '" has a cycle in its inheritance chain'), (($0 = extendsTypeRef.get$span()) && $0.is$SourceSpan()));
+          $globals.world.error(('class "' + this.name + '" has a cycle in its inheritance chain'), (($0 = extendsTypeRef.get$span()) == null ? null : $0.assert$SourceSpan()));
         }
       }
       else {
@@ -22119,12 +22531,12 @@ DefinedType.prototype.resolve = function() {
     }
     else {
       if (typeDef.implementsTypes != null && typeDef.implementsTypes.length > 0) {
-        $globals.world.error('implements not allowed on interfaces (use extends)', (($0 = typeDef.implementsTypes.$index(0).get$span()) && $0.is$SourceSpan()));
+        $globals.world.error('implements not allowed on interfaces (use extends)', (($0 = typeDef.implementsTypes.$index(0).get$span()) == null ? null : $0.assert$SourceSpan()));
       }
       this.interfaces = this._resolveInterfaces(typeDef.extendsTypes);
       var res = this._cycleInInterfaceExtends();
       if (res >= 0) {
-        $globals.world.error(('interface "' + this.name + '" has a cycle in its inheritance chain'), (($0 = typeDef.extendsTypes.$index(res).get$span()) && $0.is$SourceSpan()));
+        $globals.world.error(('interface "' + this.name + '" has a cycle in its inheritance chain'), (($0 = typeDef.extendsTypes.$index(res).get$span()) == null ? null : $0.assert$SourceSpan()));
       }
       if (typeDef.factoryType != null) {
         this.factory_ = this.resolveType(typeDef.factoryType, true);
@@ -22177,7 +22589,7 @@ DefinedType.prototype.addMethod = function(methodName, definition) {
       $globals.world.error(('duplicate factory definition of "' + method.get$name() + '"'), definition.span);
       return;
     }
-    this.factories.addFactory($assert_String(method.get$constructorName()), $assert_String(method.get$name()), (method && method.is$Member()));
+    this.factories.addFactory($assert_String(method.get$constructorName()), $assert_String(method.get$name()), (method == null ? null : method.assert$Member()));
     return;
   }
   if (methodName.startsWith('get\$') || methodName.startsWith('set\$')) {
@@ -22262,11 +22674,11 @@ DefinedType.prototype._tryCreateDefaultConstructor = function(name) {
     }
     else {
       body = null;
-      inits = [new CallExpression(new SuperExpression((span && span.is$SourceSpan())), [], (span && span.is$SourceSpan()))];
+      inits = [new CallExpression(new SuperExpression((span == null ? null : span.assert$SourceSpan())), [], (span == null ? null : span.assert$SourceSpan()))];
     }
-    var typeDef = (($0 = this.definition) && $0.is$TypeDefinition());
-    var c = new FunctionDefinition(null, null, typeDef.name, [], null, inits, native_, body, (span && span.is$SourceSpan()));
-    this.addMethod(null, (c && c.is$FunctionDefinition()));
+    var typeDef = (($0 = this.definition) == null ? null : $0.assert$TypeDefinition());
+    var c = new FunctionDefinition(null, null, typeDef.name, [], null, inits, native_, body, (span == null ? null : span.assert$SourceSpan()));
+    this.addMethod(null, (c == null ? null : c.assert$FunctionDefinition()));
     this.constructors.$index('').resolve$0();
     return this.constructors.$index('');
   }
@@ -22274,7 +22686,7 @@ DefinedType.prototype._tryCreateDefaultConstructor = function(name) {
 }
 DefinedType.prototype.getMember = function(memberName) {
   var $0;
-  var member = (($0 = this.members.$index(memberName)) && $0.is$Member());
+  var member = (($0 = this.members.$index(memberName)) == null ? null : $0.assert$Member());
   if (member != null) {
     this._checkOverride(member);
     return member;
@@ -22282,7 +22694,7 @@ DefinedType.prototype.getMember = function(memberName) {
   if ($notnull_bool(this.get$isTop())) {
     var libType = this.library.findTypeByName(memberName);
     if ($notnull_bool($ne(libType, null))) {
-      return (($0 = libType.get$typeMember()) && $0.is$Member());
+      return (($0 = libType.get$typeMember()) == null ? null : $0.assert$Member());
     }
   }
   return this._getMemberInParents(memberName);
@@ -22302,45 +22714,44 @@ DefinedType.prototype.getOrMakeConcreteType = function(typeArgs) {
     names.add$1(typeArgs.$index(i).get$name());
     jsnames.add$1(typeArgs.$index(i).get$jsname());
   }
-  var jsname = ('' + this.get$jsname() + '_' + Strings.join((jsnames && jsnames.is$List_String()), '\$'));
-  var simpleName = ('' + this.name + '<' + Strings.join((names && names.is$List_String()), ', ') + '>');
-  var key = Strings.join((names && names.is$List_String()), '\$');
+  var jsname = ('' + this.get$jsname() + '_' + Strings.join((jsnames == null ? null : jsnames.assert$List_String()), '\$'));
+  var simpleName = ('' + this.name + '<' + Strings.join((names == null ? null : names.assert$List_String()), ', ') + '>');
+  var key = Strings.join((names == null ? null : names.assert$List_String()), '\$');
   var ret = this._concreteTypes.$index(key);
   if ($notnull_bool(ret == null)) {
     ret = new ConcreteType($assert_String(simpleName), this, typeMap, typeArgs);
     ret._jsname = $assert_String(jsname);
     this._concreteTypes.$setindex(key, ret);
   }
-  return (ret && ret.is$lang_Type());
+  return (ret == null ? null : ret.assert$lang_Type());
 }
 DefinedType.prototype.getCallStub = function(args) {
   $assert(this.get$isFunction(), "isFunction", "type.dart", 1184, 12);
   var name = _getCallStubName('call', args);
-  if (this.varStubs == null) this.varStubs = $map([]);
   var stub = this.varStubs.$index(name);
   if ($notnull_bool(stub == null)) {
     stub = new VarFunctionStub($assert_String(name), args);
     this.varStubs.$setindex(name, stub);
   }
-  return (stub && stub.is$VarFunctionStub());
+  return (stub == null ? null : stub.assert$VarFunctionStub());
 }
 DefinedType.prototype.addDirectSubtype$1 = function($0) {
-  return this.addDirectSubtype(($0 && $0.is$lang_Type()));
+  return this.addDirectSubtype(($0 == null ? null : $0.assert$lang_Type()));
 };
 DefinedType.prototype.addMethod$2 = function($0, $1) {
-  return this.addMethod($assert_String($0), ($1 && $1.is$FunctionDefinition()));
+  return this.addMethod($assert_String($0), ($1 == null ? null : $1.assert$FunctionDefinition()));
 };
 DefinedType.prototype.getConstructor$1 = function($0) {
   return this.getConstructor($assert_String($0));
 };
 DefinedType.prototype.getFactory$2 = function($0, $1) {
-  return this.getFactory(($0 && $0.is$lang_Type()), $assert_String($1));
+  return this.getFactory(($0 == null ? null : $0.assert$lang_Type()), $assert_String($1));
 };
 DefinedType.prototype.getMember$1 = function($0) {
   return this.getMember($assert_String($0));
 };
 DefinedType.prototype.getOrMakeConcreteType$1 = function($0) {
-  return this.getOrMakeConcreteType(($0 && $0.is$List_Type()));
+  return this.getOrMakeConcreteType(($0 == null ? null : $0.assert$List_Type()));
 };
 DefinedType.prototype.isString$0 = function() {
   return this.get$isString()();
@@ -22348,10 +22759,10 @@ DefinedType.prototype.isString$0 = function() {
 DefinedType.prototype.markUsed$0 = DefinedType.prototype.markUsed;
 DefinedType.prototype.resolve$0 = DefinedType.prototype.resolve;
 DefinedType.prototype.resolveTypeParams$1 = function($0) {
-  return this.resolveTypeParams(($0 && $0.is$ConcreteType()));
+  return this.resolveTypeParams(($0 == null ? null : $0.assert$ConcreteType()));
 };
 DefinedType.prototype.setDefinition$1 = function($0) {
-  return this.setDefinition(($0 && $0.is$Definition()));
+  return this.setDefinition(($0 == null ? null : $0.assert$Definition()));
 };
 // ********** Code for NativeType **************
 function NativeType(spec) {
@@ -22375,10 +22786,10 @@ function FixedCollection(value, length) {
   this.length = length;
   // Initializers done
 }
-FixedCollection.prototype.is$Collection_E = function(){return this;};
-FixedCollection.prototype.is$Collection_Object = function(){return this;};
-FixedCollection.prototype.is$Collection_Type = function(){return this;};
-FixedCollection.prototype.is$Iterable = function(){return this;};
+FixedCollection.prototype.assert$Collection_E = function(){return this};
+FixedCollection.prototype.assert$Collection_Object = function(){return this};
+FixedCollection.prototype.assert$Collection_Type = function(){return this};
+FixedCollection.prototype.assert$Iterable = function(){return this};
 FixedCollection.prototype.get$value = function() { return this.value; };
 FixedCollection.prototype.iterator = function() {
   return new FixedIterator_E(this.value, this.length);
@@ -22419,10 +22830,10 @@ function FixedCollection_lang_Type(value, length) {
   // Initializers done
 }
 $inherits(FixedCollection_lang_Type, FixedCollection);
-FixedCollection_lang_Type.prototype.is$Collection_E = function(){return this;};
-FixedCollection_lang_Type.prototype.is$Collection_Object = function(){return this;};
-FixedCollection_lang_Type.prototype.is$Collection_Type = function(){return this;};
-FixedCollection_lang_Type.prototype.is$Iterable = function(){return this;};
+FixedCollection_lang_Type.prototype.assert$Collection_E = function(){return this};
+FixedCollection_lang_Type.prototype.assert$Collection_Object = function(){return this};
+FixedCollection_lang_Type.prototype.assert$Collection_Type = function(){return this};
+FixedCollection_lang_Type.prototype.assert$Iterable = function(){return this};
 // ********** Code for FixedIterator **************
 function FixedIterator(value, length) {
   this._index = 0
@@ -22430,7 +22841,7 @@ function FixedIterator(value, length) {
   this.length = length;
   // Initializers done
 }
-FixedIterator.prototype.is$Iterator_T = function(){return this;};
+FixedIterator.prototype.assert$Iterator_T = function(){return this};
 FixedIterator.prototype.get$value = function() { return this.value; };
 FixedIterator.prototype.hasNext = function() {
   return this._index < this.length;
@@ -22449,7 +22860,7 @@ function FixedIterator_E(value, length) {
   // Initializers done
 }
 $inherits(FixedIterator_E, FixedIterator);
-FixedIterator_E.prototype.is$Iterator_T = function(){return this;};
+FixedIterator_E.prototype.assert$Iterator_T = function(){return this};
 // ********** Code for Value **************
 function Value(type, code, span, needsTemp) {
   this.isSuper = false
@@ -22475,7 +22886,7 @@ Value.type$ctor = function(type, span) {
   if (this.type == null) $globals.world.internalError('type passed as null', this.span);
 }
 Value.type$ctor.prototype = Value.prototype;
-Value.prototype.is$Value = function(){return this;};
+Value.prototype.assert$Value = function(){return this};
 Value.prototype.get$type = function() { return this.type; };
 Value.prototype.set$type = function(value) { return this.type = value; };
 Value.prototype.get$code = function() { return this.code; };
@@ -22503,7 +22914,7 @@ Value.prototype.get_ = function(context, name, node) {
   var $0;
   var member = this._resolveMember(context, name, node, false);
   if ($notnull_bool($ne(member, null))) {
-    return (($0 = member._get$3(context, node, this)) && $0.is$Value());
+    return (($0 = member._get$3(context, node, this)) == null ? null : $0.assert$Value());
   }
   else {
     return this.invokeNoSuchMethod(context, ('get:' + name), node);
@@ -22541,7 +22952,7 @@ Value.prototype.invoke = function(context, name, node, args, isDynamic) {
     return this.invokeNoSuchMethod(context, name, node, args);
   }
   else {
-    return (($0 = member.invoke$5(context, node, this, args, isDynamic)) && $0.is$Value());
+    return (($0 = member.invoke$5(context, node, this, args, isDynamic)) == null ? null : $0.assert$Value());
   }
 }
 Value.prototype.canInvoke = function(context, name, args) {
@@ -22646,7 +23057,7 @@ Value.prototype.convertTo = function(context, toType, node, isDynamic) {
     if ($notnull_bool(myCall == null) || $notnull_bool($ne(myCall.get$parameters().length, arity))) {
       var stub = $globals.world.functionType.getCallStub(Arguments.Arguments$bare$factory(arity));
       var val = new Value(toType, ('to\$' + stub.name + '(' + this.code + ')'), node.span, true);
-      return (($0 = $notnull_bool(this._isDomCallback(toType)) && !$notnull_bool(this._isDomCallback(this.type)) ? val._wrapDomCallback(toType, arity) : val) && $0.is$Value());
+      return (($0 = $notnull_bool(this._isDomCallback(toType)) && !$notnull_bool(this._isDomCallback(this.type)) ? val._wrapDomCallback(toType, arity) : val) == null ? null : $0.assert$Value());
     }
     else if ($notnull_bool(this._isDomCallback(toType)) && !$notnull_bool(this._isDomCallback(this.type))) {
       return this._wrapDomCallback(toType, arity);
@@ -22664,7 +23075,7 @@ Value.prototype.convertTo = function(context, toType, node, isDynamic) {
     this.convertWarning(toType, node);
   }
   if ($notnull_bool($globals.options.enableTypeChecks)) {
-    return this._typeAssert(context, toType, node);
+    return this._typeAssert(context, toType, node, isDynamic);
   }
   else {
     return this;
@@ -22682,23 +23093,26 @@ Value.prototype._wrapDomCallback = function(toType, arity) {
   }
   return new Value(toType, ('\$wrap_call\$' + arity + '(' + this.code + ')'), this.span, true);
 }
-Value.prototype._typeAssert = function(context, toType, node) {
+Value.prototype._typeAssert = function(context, toType, node, isDynamic) {
   if ((toType instanceof ParameterType)) {
-    var p = (toType && toType.is$ParameterType());
+    var p = (toType == null ? null : toType.assert$ParameterType());
     toType = p.extendsType;
   }
-  if (toType.getCallMethod() != null || $eq(toType.get$library(), $globals.world.get$dom())) {
-    return this;
-  }
   if ($notnull_bool(toType.get$isObject()) || $notnull_bool(toType.get$isVar())) {
     $globals.world.internalError(('We thought ' + this.type.name + ' is not a subtype of ' + toType.name + '?'));
   }
+  var typeError = $globals.world.corelib.types.$index('TypeError');
+  var typeErrorCtor = typeError.getConstructor$1('_internal');
+  $globals.world.gen.corejs.ensureTypeNameOf();
+  var result = typeErrorCtor.invoke$5(context, node, new Value.type$ctor(typeError, null), new Arguments(null, [new Value($globals.world.objectType, 'this', null, true), new Value($globals.world.stringType, ('"' + toType.name + '"'), null, true)]), isDynamic);
+  $globals.world.gen.corejs.useThrow = true;
+  var throwTypeError = ('\$throw(' + result.get$code() + ')');
   if ($notnull_bool(toType.get$isNum())) toType = $globals.world.numType;
   var check;
   if ($notnull_bool(toType.get$isVoid())) {
     check = ('\$assert_void(' + this.code + ')');
     if (toType.typeCheckCode == null) {
-      toType.typeCheckCode = "function $assert_void(x) {\n  return x == null ? x : x.is$void(); // throws TypeError\n}";
+      toType.typeCheckCode = ("function $assert_void(x) {\n  if (x == null) return null;\n  " + throwTypeError + "\n}");
     }
   }
   else if ($eq(toType, $globals.world.nonNullBool)) {
@@ -22708,15 +23122,19 @@ Value.prototype._typeAssert = function(context, toType, node) {
   else if ($notnull_bool(toType.get$library().get$isCore()) && toType.get$typeofName() != null) {
     check = ('\$assert_' + toType.name + '(' + this.code + ')');
     if (toType.typeCheckCode == null) {
-      toType.typeCheckCode = ("function $assert_" + toType.name + "(x) {\n  if (x == null || typeof(x) == \"" + toType.get$typeofName() + "\") return x;\n  throw new TypeError(\"'\" + x + \"' is not a " + toType.name + ".\");\n}");
+      toType.typeCheckCode = ("function $assert_" + toType.name + "(x) {\n  if (x == null || typeof(x) == \"" + toType.get$typeofName() + "\") return x;\n  " + throwTypeError + "\n}");
     }
   }
   else {
-    toType.isTested = true;
+    toType.isChecked = true;
+    var checkName = 'assert\$' + toType.get$jsname();
     var temp = context.getTemp(this);
-    check = ('(' + context.assignTemp((temp && temp.is$Value()), this).code + ' &&');
-    check = check + (' ' + temp.get$code() + '.is\$' + toType.get$jsname() + '())');
-    if ($ne(this, temp)) context.freeTemp((temp && temp.is$Value()));
+    check = ('(' + context.assignTemp((temp == null ? null : temp.assert$Value()), this).code + ' == null ? null :');
+    check = check + (' ' + temp.get$code() + '.' + checkName + '())');
+    if ($ne(this, temp)) context.freeTemp((temp == null ? null : temp.assert$Value()));
+    if (!$globals.world.objectType.varStubs.containsKey(checkName)) {
+      $globals.world.objectType.varStubs.$setindex(checkName, new VarMethodStub(checkName, null, Arguments.get$EMPTY(), throwTypeError));
+    }
   }
   return new Value(toType, check, this.span, true);
 }
@@ -22739,7 +23157,7 @@ Value.prototype.instanceOf = function(context, toType, span, isTrue, forceCheck)
       testCode = ("(typeof(" + this.code + ") " + ($notnull_bool(isTrue) ? '==' : '!=') + " '" + typeofName + "')");
     }
   }
-  if ($notnull_bool(toType.get$isClass()) && !(toType instanceof ConcreteType)) {
+  if ($notnull_bool(toType.get$isClass()) && !(toType instanceof ConcreteType) && !$notnull_bool(toType.get$isHiddenNativeType())) {
     toType.markUsed();
     testCode = ('(' + this.code + ' instanceof ' + toType.get$jsname() + ')');
     if (!$notnull_bool(isTrue)) {
@@ -22749,15 +23167,19 @@ Value.prototype.instanceOf = function(context, toType, span, isTrue, forceCheck)
   if (testCode == null) {
     toType.isTested = true;
     var temp = context.getTemp(this);
-    testCode = ('(' + context.assignTemp((temp && temp.is$Value()), this).code + ' &&');
-    testCode = testCode + (' ' + temp.get$code() + '.is\$' + toType.get$jsname() + ')');
+    var checkName = ('is\$' + toType.get$jsname());
+    testCode = ('(' + context.assignTemp((temp == null ? null : temp.assert$Value()), this).code + ' &&');
+    testCode = testCode + (' ' + temp.get$code() + '.' + checkName + '())');
     if ($notnull_bool(isTrue)) {
       testCode = '!!' + testCode;
     }
     else {
       testCode = '!' + testCode;
     }
-    if ($ne(this, temp)) context.freeTemp((temp && temp.is$Value()));
+    if ($ne(this, temp)) context.freeTemp((temp == null ? null : temp.assert$Value()));
+    if (!$globals.world.objectType.varStubs.containsKey(checkName)) {
+      $globals.world.objectType.varStubs.$setindex(checkName, new VarMethodStub(checkName, null, Arguments.get$EMPTY(), 'return false'));
+    }
   }
   return new Value($globals.world.nonNullBool, testCode, span, true);
 }
@@ -22773,14 +23195,14 @@ Value.prototype.invokeNoSuchMethod = function(context, name, node, args) {
      i < args.get$length(); i++) {
       argsCode.add$1(args.values.$index(i).get$code());
     }
-    pos = Strings.join((argsCode && argsCode.is$List_String()), ", ");
+    pos = Strings.join((argsCode == null ? null : argsCode.assert$List_String()), ", ");
   }
   var noSuchArgs = [new Value($globals.world.stringType, ('"' + name + '"'), node.span, true), new Value($globals.world.listType, ('[' + pos + ']'), node.span, true)];
-  return (($0 = this._resolveMember(context, 'noSuchMethod', node, false).invoke$4(context, node, this, new Arguments(null, noSuchArgs))) && $0.is$Value());
+  return (($0 = this._resolveMember(context, 'noSuchMethod', node, false).invoke$4(context, node, this, new Arguments(null, noSuchArgs))) == null ? null : $0.assert$Value());
 }
 Value.prototype.invokeSpecial = function(name, args, returnType) {
-  $assert(name.startsWith('\$'), "name.startsWith('\\$')", "value.dart", 496, 12);
-  $assert(!$notnull_bool(args.get$hasNames()), "!args.hasNames", "value.dart", 497, 12);
+  $assert(name.startsWith('\$'), "name.startsWith('\\$')", "value.dart", 519, 12);
+  $assert(!$notnull_bool(args.get$hasNames()), "!args.hasNames", "value.dart", 520, 12);
   var argsString = args.getCode();
   if (name == '\$index' || name == '\$setindex') {
     return new Value(returnType, ('' + this.code + '.' + name + '(' + argsString + ')'), this.span, true);
@@ -22792,37 +23214,37 @@ Value.prototype.invokeSpecial = function(name, args, returnType) {
   }
 }
 Value.prototype.checkFirstClass$1 = function($0) {
-  return this.checkFirstClass(($0 && $0.is$SourceSpan()));
+  return this.checkFirstClass(($0 == null ? null : $0.assert$SourceSpan()));
 };
 Value.prototype.convertTo$3 = function($0, $1, $2) {
-  return this.convertTo(($0 && $0.is$MethodGenerator()), ($1 && $1.is$lang_Type()), ($2 && $2.is$lang_Node()), false);
+  return this.convertTo(($0 == null ? null : $0.assert$MethodGenerator()), ($1 == null ? null : $1.assert$lang_Type()), ($2 == null ? null : $2.assert$lang_Node()), false);
 };
 Value.prototype.convertTo$4 = function($0, $1, $2, $3) {
-  return this.convertTo(($0 && $0.is$MethodGenerator()), ($1 && $1.is$lang_Type()), ($2 && $2.is$lang_Node()), $assert_bool($3));
+  return this.convertTo(($0 == null ? null : $0.assert$MethodGenerator()), ($1 == null ? null : $1.assert$lang_Type()), ($2 == null ? null : $2.assert$lang_Node()), $assert_bool($3));
 };
 Value.prototype.get_$3 = function($0, $1, $2) {
-  return this.get_(($0 && $0.is$MethodGenerator()), $assert_String($1), ($2 && $2.is$lang_Node()));
+  return this.get_(($0 == null ? null : $0.assert$MethodGenerator()), $assert_String($1), ($2 == null ? null : $2.assert$lang_Node()));
 };
 Value.prototype.instanceOf$3$isTrue$forceCheck = function($0, $1, $2, isTrue, forceCheck) {
-  return this.instanceOf(($0 && $0.is$MethodGenerator()), ($1 && $1.is$lang_Type()), ($2 && $2.is$SourceSpan()), $assert_bool(isTrue), $assert_bool(forceCheck));
+  return this.instanceOf(($0 == null ? null : $0.assert$MethodGenerator()), ($1 == null ? null : $1.assert$lang_Type()), ($2 == null ? null : $2.assert$SourceSpan()), $assert_bool(isTrue), $assert_bool(forceCheck));
 };
 Value.prototype.instanceOf$4 = function($0, $1, $2, $3) {
-  return this.instanceOf(($0 && $0.is$MethodGenerator()), ($1 && $1.is$lang_Type()), ($2 && $2.is$SourceSpan()), $assert_bool($3), false);
+  return this.instanceOf(($0 == null ? null : $0.assert$MethodGenerator()), ($1 == null ? null : $1.assert$lang_Type()), ($2 == null ? null : $2.assert$SourceSpan()), $assert_bool($3), false);
 };
 Value.prototype.invoke$4 = function($0, $1, $2, $3) {
-  return this.invoke(($0 && $0.is$MethodGenerator()), $assert_String($1), ($2 && $2.is$lang_Node()), ($3 && $3.is$Arguments()), false);
+  return this.invoke(($0 == null ? null : $0.assert$MethodGenerator()), $assert_String($1), ($2 == null ? null : $2.assert$lang_Node()), ($3 == null ? null : $3.assert$Arguments()), false);
 };
 Value.prototype.invoke$4$isDynamic = function($0, $1, $2, $3, isDynamic) {
-  return this.invoke(($0 && $0.is$MethodGenerator()), $assert_String($1), ($2 && $2.is$lang_Node()), ($3 && $3.is$Arguments()), $assert_bool(isDynamic));
+  return this.invoke(($0 == null ? null : $0.assert$MethodGenerator()), $assert_String($1), ($2 == null ? null : $2.assert$lang_Node()), ($3 == null ? null : $3.assert$Arguments()), $assert_bool(isDynamic));
 };
 Value.prototype.invoke$5 = function($0, $1, $2, $3, $4) {
-  return this.invoke(($0 && $0.is$MethodGenerator()), $assert_String($1), ($2 && $2.is$lang_Node()), ($3 && $3.is$Arguments()), $assert_bool($4));
+  return this.invoke(($0 == null ? null : $0.assert$MethodGenerator()), $assert_String($1), ($2 == null ? null : $2.assert$lang_Node()), ($3 == null ? null : $3.assert$Arguments()), $assert_bool($4));
 };
 Value.prototype.needsConversion$1 = function($0) {
-  return this.needsConversion(($0 && $0.is$lang_Type()));
+  return this.needsConversion(($0 == null ? null : $0.assert$lang_Type()));
 };
 Value.prototype.set_$4 = function($0, $1, $2, $3) {
-  return this.set_(($0 && $0.is$MethodGenerator()), $assert_String($1), ($2 && $2.is$lang_Node()), ($3 && $3.is$Value()), false);
+  return this.set_(($0 == null ? null : $0.assert$MethodGenerator()), $assert_String($1), ($2 == null ? null : $2.assert$lang_Node()), ($3 == null ? null : $3.assert$Value()), false);
 };
 // ********** Code for EvaluatedValue **************
 function EvaluatedValue() {}
@@ -22852,7 +23274,7 @@ function ConstListValue() {}
 ConstListValue._internal$ctor = function(type, values, actualValue, canonicalCode, span, code) {
   this.values = values;
   // Initializers done
-  EvaluatedValue._internal$ctor.call(this, (type && type.is$lang_Type()), actualValue, canonicalCode, (span && span.is$SourceSpan()), $assert_String(code));
+  EvaluatedValue._internal$ctor.call(this, (type == null ? null : type.assert$lang_Type()), actualValue, canonicalCode, (span == null ? null : span.assert$SourceSpan()), $assert_String(code));
 }
 ConstListValue._internal$ctor.prototype = ConstListValue.prototype;
 $inherits(ConstListValue, EvaluatedValue);
@@ -22866,7 +23288,7 @@ function ConstMapValue() {}
 ConstMapValue._internal$ctor = function(type, values, actualValue, canonicalCode, span, code) {
   this.values = values;
   // Initializers done
-  EvaluatedValue._internal$ctor.call(this, (type && type.is$lang_Type()), actualValue, canonicalCode, (span && span.is$SourceSpan()), $assert_String(code));
+  EvaluatedValue._internal$ctor.call(this, (type == null ? null : type.assert$lang_Type()), actualValue, canonicalCode, (span == null ? null : span.assert$SourceSpan()), $assert_String(code));
 }
 ConstMapValue._internal$ctor.prototype = ConstMapValue.prototype;
 $inherits(ConstMapValue, EvaluatedValue);
@@ -22885,7 +23307,7 @@ function ConstObjectValue() {}
 ConstObjectValue._internal$ctor = function(type, fields, actualValue, canonicalCode, span, code) {
   this.fields = fields;
   // Initializers done
-  EvaluatedValue._internal$ctor.call(this, (type && type.is$lang_Type()), actualValue, canonicalCode, (span && span.is$SourceSpan()), $assert_String(code));
+  EvaluatedValue._internal$ctor.call(this, (type == null ? null : type.assert$lang_Type()), actualValue, canonicalCode, (span == null ? null : span.assert$SourceSpan()), $assert_String(code));
 }
 ConstObjectValue._internal$ctor.prototype = ConstObjectValue.prototype;
 $inherits(ConstObjectValue, EvaluatedValue);
@@ -22918,12 +23340,12 @@ function GlobalValue(type, code, isConst, field, name, exp, canonicalCode, span,
   for (var $i = 0;$i < _dependencies.length; $i++) {
     var dep = _dependencies.$index($i);
     this.dependencies.add(dep);
-    this.dependencies.addAll((($0 = dep.get$dependencies()) && $0.is$Collection_E()));
+    this.dependencies.addAll((($0 = dep.get$dependencies()) == null ? null : $0.assert$Collection_E()));
   }
 }
 $inherits(GlobalValue, Value);
-GlobalValue.prototype.is$GlobalValue = function(){return this;};
-GlobalValue.prototype.is$Comparable = function(){return this;};
+GlobalValue.prototype.assert$GlobalValue = function(){return this};
+GlobalValue.prototype.assert$Comparable = function(){return this};
 GlobalValue.GlobalValue$fromStatic$factory = function(field, exp, dependencies) {
   var $0;
   var code = ($notnull_bool(exp.get$isConst()) ? exp.get$canonicalCode() : exp.code);
@@ -22931,7 +23353,7 @@ GlobalValue.GlobalValue$fromStatic$factory = function(field, exp, dependencies)
   return new GlobalValue(exp.type, $assert_String(codeWithComment), $assert_bool(field.get$isFinal()), field, null, exp, code, exp.span, (($0 = dependencies.filter$1((function (d) {
     return (d instanceof GlobalValue);
   })
-  )) && $0.is$List_GlobalValue()));
+  )) == null ? null : $0.assert$List_GlobalValue()));
 }
 GlobalValue.GlobalValue$fromConst$factory = function(uniqueId, exp, dependencies) {
   var $0;
@@ -22940,7 +23362,7 @@ GlobalValue.GlobalValue$fromConst$factory = function(uniqueId, exp, dependencies
   return new GlobalValue(exp.type, $assert_String(codeWithComment), true, null, name, exp, name, exp.span, (($0 = dependencies.filter$1((function (d) {
     return (d instanceof GlobalValue);
   })
-  )) && $0.is$List_GlobalValue()));
+  )) == null ? null : $0.assert$List_GlobalValue()));
 }
 GlobalValue.prototype.get$field = function() { return this.field; };
 GlobalValue.prototype.set$field = function(value) { return this.field = value; };
@@ -22988,7 +23410,7 @@ GlobalValue.prototype.compareTo = function(other) {
   }
 }
 GlobalValue.prototype.compareTo$1 = function($0) {
-  return this.compareTo(($0 && $0.is$GlobalValue()));
+  return this.compareTo(($0 == null ? null : $0.assert$GlobalValue()));
 };
 // ********** Code for BareValue **************
 function BareValue(home, outermost, span) {
@@ -23008,7 +23430,7 @@ BareValue.prototype._ensureCode = function() {
   }
 }
 BareValue.prototype._tryResolveMember = function(context, name) {
-  $assert($eq(context, this.home), "context == home", "value.dart", 717, 12);
+  $assert($eq(context, this.home), "context == home", "value.dart", 740, 12);
   var member = this.type.resolveMember(name);
   if ($notnull_bool($ne(member, null))) {
     this._ensureCode();
@@ -23053,11 +23475,11 @@ function World(files) {
 }
 World.prototype.get$coreimpl = function() {
   var $0;
-  return (($0 = this.libraries.$index('dart:coreimpl')) && $0.is$Library());
+  return (($0 = this.libraries.$index('dart:coreimpl')) == null ? null : $0.assert$Library());
 }
 World.prototype.get$dom = function() {
   var $0;
-  return (($0 = this.libraries.$index('dart:dom')) && $0.is$Library());
+  return (($0 = this.libraries.$index('dart:dom')) == null ? null : $0.assert$Library());
 }
 World.prototype.get$dynamicType = function() { return this.dynamicType; };
 World.prototype.set$dynamicType = function(value) { return this.dynamicType = value; };
@@ -23068,18 +23490,18 @@ World.prototype.init = function() {
   this.corelib = new Library(this.readFile('dart:core'));
   this.libraries.$setindex('dart:core', this.corelib);
   this._todo.add(this.corelib);
-  this.voidType = (($0 = this._addToCoreLib('void', false)) && $0.is$DefinedType());
-  this.dynamicType = (($0 = this._addToCoreLib('Dynamic', false)) && $0.is$DefinedType());
+  this.voidType = (($0 = this._addToCoreLib('void', false)) == null ? null : $0.assert$DefinedType());
+  this.dynamicType = (($0 = this._addToCoreLib('Dynamic', false)) == null ? null : $0.assert$DefinedType());
   this.varType = this.dynamicType;
-  this.objectType = (($0 = this._addToCoreLib('Object', true)) && $0.is$DefinedType());
-  this.numType = (($0 = this._addToCoreLib('num', false)) && $0.is$DefinedType());
-  this.intType = (($0 = this._addToCoreLib('int', false)) && $0.is$DefinedType());
-  this.doubleType = (($0 = this._addToCoreLib('double', false)) && $0.is$DefinedType());
-  this.boolType = (($0 = this._addToCoreLib('bool', false)) && $0.is$DefinedType());
-  this.stringType = (($0 = this._addToCoreLib('String', false)) && $0.is$DefinedType());
-  this.listType = (($0 = this._addToCoreLib('List', false)) && $0.is$DefinedType());
-  this.mapType = (($0 = this._addToCoreLib('Map', false)) && $0.is$DefinedType());
-  this.functionType = (($0 = this._addToCoreLib('Function', false)) && $0.is$DefinedType());
+  this.objectType = (($0 = this._addToCoreLib('Object', true)) == null ? null : $0.assert$DefinedType());
+  this.numType = (($0 = this._addToCoreLib('num', false)) == null ? null : $0.assert$DefinedType());
+  this.intType = (($0 = this._addToCoreLib('int', false)) == null ? null : $0.assert$DefinedType());
+  this.doubleType = (($0 = this._addToCoreLib('double', false)) == null ? null : $0.assert$DefinedType());
+  this.boolType = (($0 = this._addToCoreLib('bool', false)) == null ? null : $0.assert$DefinedType());
+  this.stringType = (($0 = this._addToCoreLib('String', false)) == null ? null : $0.assert$DefinedType());
+  this.listType = (($0 = this._addToCoreLib('List', false)) == null ? null : $0.assert$DefinedType());
+  this.mapType = (($0 = this._addToCoreLib('Map', false)) == null ? null : $0.assert$DefinedType());
+  this.functionType = (($0 = this._addToCoreLib('Function', false)) == null ? null : $0.assert$DefinedType());
   this.nonNullBool = new NonNullableType(this.boolType);
 }
 World.prototype._addMember = function(member) {
@@ -23109,7 +23531,7 @@ World.prototype._addTopName = function(named) {
       }
       else {
         this._topNames.$setindex(named.get$jsname(), named);
-        this._addJavascriptTopName((existing && existing.is$lang_Element()));
+        this._addJavascriptTopName((existing == null ? null : existing.assert$lang_Element()));
       }
     }
     else if ($notnull_bool(named.get$library().get$isCore())) {
@@ -23118,7 +23540,7 @@ World.prototype._addTopName = function(named) {
       }
       else {
         this._topNames.$setindex(named.get$jsname(), named);
-        this._addJavascriptTopName((existing && existing.is$lang_Element()));
+        this._addJavascriptTopName((existing == null ? null : existing.assert$lang_Element()));
       }
     }
     else {
@@ -23210,7 +23632,7 @@ World.prototype.runCompilationPhases = function() {
       for (var $i = mainMembers.get$members().iterator$0(); $i.hasNext$0(); ) {
         var m = $i.next$0();
         main = m;
-        $this.error('more than one main member (using last?)', (($0 = main.get$span()) && $0.is$SourceSpan()));
+        $this.error('more than one main member (using last?)', (($0 = main.get$span()) == null ? null : $0.assert$SourceSpan()));
       }
     }
     else {
@@ -23245,7 +23667,7 @@ World.prototype.readFile = function(filename) {
 }
 World.prototype.getOrAddLibrary = function(filename) {
   var $0;
-  var library = (($0 = this.libraries.$index(filename)) && $0.is$Library());
+  var library = (($0 = this.libraries.$index(filename)) == null ? null : $0.assert$Library());
   if (library == null) {
     library = new Library(this.readFile(filename));
     this.info(('read library ' + filename));
@@ -23453,7 +23875,7 @@ function FrogOptions(homedir, args, files) {
 
         if ($notnull_bool(arg.endsWith$1('.dart'))) {
           this.dartScript = $assert_String(arg);
-          this.childArgs = (($0 = args.getRange(i + 1, args.length - i - 1)) && $0.is$List_String());
+          this.childArgs = (($0 = args.getRange(i + 1, args.length - i - 1)) == null ? null : $0.assert$List_String());
           break loop;
         }
         else if ($notnull_bool(arg.startsWith$1('--out='))) {
@@ -23504,7 +23926,7 @@ function VarMember(name) {
   this.name = name;
   // Initializers done
 }
-VarMember.prototype.is$VarMember = function(){return this;};
+VarMember.prototype.assert$VarMember = function(){return this};
 VarMember.prototype.get$name = function() { return this.name; };
 VarMember.prototype.get$returnType = function() {
   return $globals.world.varType;
@@ -23513,10 +23935,10 @@ VarMember.prototype.invoke = function(context, node, target, args) {
   return new Value(this.get$returnType(), ('' + target.code + '.' + this.name + '(' + args.getCode() + ')'), node.span, true);
 }
 VarMember.prototype.generate$1 = function($0) {
-  return this.generate(($0 && $0.is$CodeWriter()));
+  return this.generate(($0 == null ? null : $0.assert$CodeWriter()));
 };
 VarMember.prototype.invoke$4 = function($0, $1, $2, $3) {
-  return this.invoke(($0 && $0.is$MethodGenerator()), ($1 && $1.is$lang_Node()), ($2 && $2.is$Value()), ($3 && $3.is$Arguments()));
+  return this.invoke(($0 == null ? null : $0.assert$MethodGenerator()), ($1 == null ? null : $1.assert$lang_Node()), ($2 == null ? null : $2.assert$Value()), ($3 == null ? null : $3.assert$Arguments()));
 };
 // ********** Code for VarFunctionStub **************
 function VarFunctionStub(name, callArgs) {
@@ -23526,7 +23948,7 @@ function VarFunctionStub(name, callArgs) {
   $globals.world.gen.corejs.useGenStub = true;
 }
 $inherits(VarFunctionStub, VarMember);
-VarFunctionStub.prototype.is$VarFunctionStub = function(){return this;};
+VarFunctionStub.prototype.assert$VarFunctionStub = function(){return this};
 VarFunctionStub.prototype.generate = function(code) {
   if ($notnull_bool(this.args.get$hasNames())) {
     this.generateNamed(code);
@@ -23557,7 +23979,7 @@ VarFunctionStub.prototype.generateNamed = function(w) {
   w.exitBlock('}');
 }
 VarFunctionStub.prototype.generate$1 = function($0) {
-  return this.generate(($0 && $0.is$CodeWriter()));
+  return this.generate(($0 == null ? null : $0.assert$CodeWriter()));
 };
 // ********** Code for VarMethodStub **************
 function VarMethodStub(name, member, args, body) {
@@ -23569,30 +23991,51 @@ function VarMethodStub(name, member, args, body) {
 }
 $inherits(VarMethodStub, VarMember);
 VarMethodStub.prototype.get$body = function() { return this.body; };
+VarMethodStub.prototype.get$isHidden = function() {
+  return $assert_bool(this.member != null ? this.member.declaringType.get$isHiddenNativeType() : false);
+}
 VarMethodStub.prototype.get$returnType = function() {
   var $0;
-  return (($0 = this.member != null ? this.member.get$returnType() : $globals.world.varType) && $0.is$lang_Type());
+  return (($0 = this.member != null ? this.member.get$returnType() : $globals.world.varType) == null ? null : $0.assert$lang_Type());
 }
-VarMethodStub.prototype.get$typeName = function() {
-  return this.member != null ? this.member.declaringType.get$jsname() : 'Object';
+VarMethodStub.prototype.get$declaringType = function() {
+  var $0;
+  return (($0 = this.member != null ? this.member.declaringType : $globals.world.objectType) == null ? null : $0.assert$lang_Type());
 }
 VarMethodStub.prototype.generate = function(code) {
-  code.write(('' + this.get$typeName() + '.prototype.' + this.name + ' = '));
-  this.generateBody(code, ';');
-}
-VarMethodStub.prototype.generateBody = function(code, end) {
-  if ($notnull_bool(this._useDirectCall(this.member, this.args))) {
-    code.writeln(('' + this.get$typeName() + '.prototype.' + this.member.get$jsname() + end));
+  code.write($globals.world.gen._prototypeOf(this.get$declaringType(), this.name) + ' = ');
+  if (!$notnull_bool(this.get$isHidden()) && $notnull_bool(this._useDirectCall(this.args))) {
+    code.writeln(('' + this.get$declaringType().get$jsname() + '.prototype.' + this.member.get$jsname() + ';'));
+  }
+  else if ($notnull_bool(this._needsExactTypeCheck())) {
+    code.enterBlock(('function(' + this.args.getCode() + ') {'));
+    code.enterBlock(('if (Object.getPrototypeOf(this).hasOwnProperty("' + this.name + '")) {'));
+    code.writeln(('' + this.body + ';'));
+    code.exitBlock('}');
+    var argsCode = this.args.getCode();
+    if (argsCode != '') argsCode = ', ' + argsCode;
+    code.writeln(('return Object.prototype.' + this.name + '.call(this' + argsCode + ');'));
+    code.exitBlock('};');
   }
   else {
     code.enterBlock(('function(' + this.args.getCode() + ') {'));
-    code.writeln(('return ' + this.body.code + ';'));
-    code.exitBlock(('}' + end));
+    code.writeln(('' + this.body + ';'));
+    code.exitBlock('};');
   }
 }
-VarMethodStub.prototype._useDirectCall = function(member, args) {
-  if ((member instanceof MethodMember) && !$notnull_bool(member.declaringType.get$isHiddenNativeType()) && !$notnull_bool(member.declaringType.get$hasNativeSubtypes())) {
-    var method = (member && member.is$MethodMember());
+VarMethodStub.prototype._needsExactTypeCheck = function() {
+  var $this = this; // closure support
+  if (this.member == null || $notnull_bool(this.member.declaringType.get$isObject())) return false;
+  var members = this.member.declaringType.resolveMember(this.member.name).members;
+  return members.filter$1((function (m) {
+    return $notnull_bool($ne(m, $this.member)) && $notnull_bool(m.get$declaringType().get$isHiddenNativeType());
+  })
+  ).length >= 1;
+}
+VarMethodStub.prototype._useDirectCall = function(args) {
+  var $0;
+  if ((this.member instanceof MethodMember) && !$notnull_bool(this.member.declaringType.get$hasNativeSubtypes())) {
+    var method = (($0 = this.member) == null ? null : $0.assert$MethodMember());
     if ($notnull_bool(method.needsArgumentConversion(args))) {
       return false;
     }
@@ -23609,13 +24052,11 @@ VarMethodStub.prototype._useDirectCall = function(member, args) {
   }
 }
 VarMethodStub.prototype.generate$1 = function($0) {
-  return this.generate(($0 && $0.is$CodeWriter()));
-};
-VarMethodStub.prototype.generateBody$2 = function($0, $1) {
-  return this.generateBody(($0 && $0.is$CodeWriter()), $assert_String($1));
+  return this.generate(($0 == null ? null : $0.assert$CodeWriter()));
 };
 // ********** Code for VarMethodSet **************
 function VarMethodSet(name, members, callArgs, returnType) {
+  this.invoked = false
   this.members = members;
   this.returnType = returnType;
   this.args = callArgs.toCallStubArgs();
@@ -23633,66 +24074,40 @@ VarMethodSet.prototype.invoke = function(context, node, target, args) {
   return VarMember.prototype.invoke.call(this, context, node, target, args);
 }
 VarMethodSet.prototype._invokeMembers = function(context, node) {
-  if (this._fallbackStubs != null) return;
-  var objectStub = null;
-  this._fallbackStubs = [];
+  if ($notnull_bool(this.invoked)) return;
+  this.invoked = true;
+  var hasObjectType = false;
   var $list = this.members;
   for (var $i = 0;$i < $list.length; $i++) {
     var member = $list.$index($i);
-    var target = new Value(member.get$declaringType(), 'this', node.span, true);
-    var result = member.invoke$4$isDynamic(context, node, target, this.args, true);
-    var stub = new VarMethodStub(this.name, member, this.args, result);
     var type = member.get$declaringType();
-    if ($notnull_bool(type.get$isObject())) {
-      objectStub = stub;
-    }
-    else if (!$notnull_bool(type.get$isHiddenNativeType())) {
-      VarMethodSet._addVarStub((type && type.is$lang_Type()), (stub && stub.is$VarMember()));
-    }
-    else {
-      this._fallbackStubs.add(stub);
-    }
+    var target = new Value(type, 'this', node.span, true);
+    var result = member.invoke$4$isDynamic(context, node, target, this.args, true);
+    var stub = new VarMethodStub(this.name, member, this.args, 'return ' + result.get$code());
+    type.get$varStubs().$setindex(stub.get$name(), stub);
+    if ($notnull_bool(type.get$isObject())) hasObjectType = true;
   }
-  if ($notnull_bool(objectStub == null)) {
+  if (!$notnull_bool(hasObjectType)) {
     var target = new Value($globals.world.objectType, 'this', node.span, true);
     var result = target.invokeNoSuchMethod(context, this.get$baseName(), node, this.args);
-    objectStub = new VarMethodStub(this.name, null, this.args, result);
-  }
-  if (this._fallbackStubs.length == 0) {
-    VarMethodSet._addVarStub($globals.world.objectType, (objectStub && objectStub.is$VarMember()));
-  }
-  else {
-    this._fallbackStubs.add(objectStub);
-    $globals.world.gen.corejs.useVarMethod = true;
+    var stub = new VarMethodStub(this.name, null, this.args, 'return ' + result.get$code());
+    $globals.world.objectType.varStubs.$setindex(stub.get$name(), stub);
   }
 }
-VarMethodSet._addVarStub = function(type, stub) {
-  if (type.varStubs == null) type.varStubs = $map([]);
-  type.varStubs.$setindex(stub.name, stub);
-}
 VarMethodSet.prototype.generate = function(code) {
-  if (this._fallbackStubs.length == 0) return;
-  code.enterBlock(('\$varMethod("' + this.name + '", {'));
-  var lastOne = this._fallbackStubs.last();
-  var $list = this._fallbackStubs;
-  for (var $i = 0;$i < $list.length; $i++) {
-    var stub = $list.$index($i);
-    code.write(('"' + stub.get$typeName() + '": '));
-    stub.generateBody$2(code, $notnull_bool($eq(stub, lastOne)) ? '' : ',');
-  }
-  code.exitBlock('});');
+
 }
 VarMethodSet.prototype.generate$1 = function($0) {
-  return this.generate(($0 && $0.is$CodeWriter()));
+  return this.generate(($0 == null ? null : $0.assert$CodeWriter()));
 };
 VarMethodSet.prototype.invoke$4 = function($0, $1, $2, $3) {
-  return this.invoke(($0 && $0.is$MethodGenerator()), ($1 && $1.is$lang_Node()), ($2 && $2.is$Value()), ($3 && $3.is$Arguments()));
+  return this.invoke(($0 == null ? null : $0.assert$MethodGenerator()), ($1 == null ? null : $1.assert$lang_Node()), ($2 == null ? null : $2.assert$Value()), ($3 == null ? null : $3.assert$Arguments()));
 };
 // ********** Code for top level **************
 function map(source, mapper) {
   var result = new ListFactory();
-  if (!!(source && source.is$List)) {
-    var list = (source && source.is$List());
+  if (!!(source && source.is$List())) {
+    var list = (source == null ? null : source.assert$List());
     result.length = list.length;
     for (var i = 0;
      i < list.length; i++) {
@@ -23720,7 +24135,7 @@ function reduce(source, callback, initialValue) {
 }
 function orderValuesByKeys(map) {
   var $0;
-  var keys = (($0 = map.getKeys()) && $0.is$List());
+  var keys = (($0 = map.getKeys()) == null ? null : $0.assert$List());
   keys.sort((function (x, y) {
     return x.compareTo$1(y);
   })
@@ -23816,7 +24231,7 @@ function _getCallStubName(name, args) {
 function main() {
   var homedir = path.dirname(fs.realpathSync($assert_String(process.argv.$index(1))));
   var argv = ListFactory.ListFactory$from$factory(process.argv);
-  if ($notnull_bool(lang_compile($assert_String(homedir), (argv && argv.is$List_String()), new NodeFileSystem()))) {
+  if ($notnull_bool(lang_compile($assert_String(homedir), (argv == null ? null : argv.assert$List_String()), new NodeFileSystem()))) {
     var code = $globals.world.getGeneratedCode();
     if (!$notnull_bool($globals.options.compileOnly)) {
       process.argv = [argv.$index(0), argv.$index(1)];