Better runtime type checks.

frog/library.dart

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 class LibraryImport {
   String prefix;
   Library library;
   LibraryImport(this.library, [this.prefix = null]);
 }
 
@@ skipping 96 matching lines @@
       world._addMember(member);
     }
   }
 
   // TODO(jimhug): Cache and share the types as interfaces?
   Type getOrAddFunctionType(String name, FunctionDefinition func, Type inType) {
     final def = new FunctionTypeDefinition(func, null, func.span);
     final type = new DefinedType(name, this, def, false);
     type.addMethod('\$call', func);
     type.members['\$call'].resolve(inType);
-    // Functions should implement Function. See "Function Types" in the spec.
+    // Function types implement the Function interface.
     type.interfaces = [world.functionType];
     return type;
   }
 
   /** Adds a type to the library. */
   Type addType(String name, Node definition, bool isClass) {
     if (types.containsKey(name)) {
       var existingType = types[name];
       if (isCore && existingType.definition == null) {
         // TODO(jimhug): Validate compatibility with natives.
@@ skipping 268 matching lines @@
 
   void visitFunctionDefinition(FunctionDefinition node) {
     currentType.addMethod(node.name.name, node);
   }
 
   void visitFunctionTypeDefinition(FunctionTypeDefinition node) {
     var type = library.addType(node.func.name.name, node, false);
     type.addMethod('\$call', node.func);
   }
 }