Refactor of PolymerExpressions. Adds "as" expressions.

pkg/polymer_expressions/lib/eval.dart

 // Copyright (c) 2013, 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.
 
 library polymer_expressions.eval;
 
 import 'dart:async';
 import 'dart:collection';
 
 @MirrorsUsed(
@@ skipping 47 matching lines @@
 }
 
 /**
  * Returns an [ExpressionObserver] that evaluates [expr] in the context of
  * scope] and listens for any changes on [Observable] values that are
  * returned from sub-expressions. When a value changes the expression is
  * reevaluated and the new result is sent to the [onUpdate] stream of the
  * [ExpressionObsserver].
  */
 ExpressionObserver observe(Expression expr, Scope scope) {
-  var observer = new ObserverBuilder(scope).visit(expr);
+  var observer = new ObserverBuilder(/*scope*/).visit(expr);

[Jennifer Messerly, 2014/03/17 23:10:08]

did you mean to remove the scope argument to "observe"?

[justinfagnani, 2014/04/24 00:26:13]

yep

   return observer;
 }
 
 /**
  * Causes [expr] to be reevaluated a returns it's value.
  */
 Object update(ExpressionObserver expr, Scope scope) {
   new Updater(scope).visit(expr);
   return expr.currentValue;
 }
@@ skipping 78 matching lines @@
  */
 class Scope {
   final Scope parent;
   final Object model;
   // TODO(justinfagnani): disallow adding/removing names
   final ObservableMap<String, Object> _variables;
 
   Scope({this.model, Map<String, Object> variables, this.parent})
       : _variables = new ObservableMap.from(variables == null ? {} : variables);
 
+  get variables => _variables;

[Jennifer Messerly, 2014/03/17 23:10:08]

another option is just to make _variables public. Since it's already "final" it
won't have a setter :)

[justinfagnani, 2014/04/24 00:26:13]

Done.

+
   Object operator[](String name) {
     if (name == 'this') {
       return model;
     } else if (_variables.containsKey(name)) {
       return _convert(_variables[name]);
     } else {
       var symbol = smoke.nameToSymbol(name);
       if (model != null && smoke.hasGetter(model.runtimeType, symbol)) {
         return _convert(smoke.read(model, symbol));
       }
@@ skipping 12 matching lines @@
       // seem neccessary
       return null;
     } else if (_variables.containsKey(name)) {
       return _variables;
     } else if (smoke.hasGetter(model.runtimeType, smoke.nameToSymbol(name))) {
       return model;
     }
     if (parent != null) {
       return parent.ownerOf(name);
     }
+    return null;
   }
 
-  bool contains(String name) {
-    if (_variables.containsKey(name) ||
-        smoke.hasGetter(model.runtimeType, smoke.nameToSymbol(name))) {
-      return true;
-    }
-    if (parent != null) {
-      return parent.contains(name);
-    }
-    return false;
-  }
+  String toString() => 'Scope(parent: $parent, model: $model, '
+      'variables: $variables)';
 }
 
 Object _convert(v) {
   if (v is Stream) return new StreamBinding(v);
   return v;
 }
 
 abstract class ExpressionObserver<E extends Expression> implements Expression {
   final E _expr;
   ExpressionObserver _parent;
@@ skipping 42 matching lines @@
 }
 
 class Updater extends RecursiveVisitor {
   final Scope scope;
 
   Updater(this.scope);
 
   visitExpression(ExpressionObserver e) {
     e._observe(scope);
   }
-
-  visitInExpression(InObserver c) {
-    visit(c.right);
-    visitExpression(c);
-  }
 }
 
 class ObserverBuilder extends Visitor {
-  final Scope scope;
+//  final Scope scope;
   final Queue parents = new Queue();
 
-  ObserverBuilder(this.scope);
+  ObserverBuilder(/*this.scope*/);
 
   visitEmptyExpression(EmptyExpression e) => new EmptyObserver(e);
 
   visitParenthesizedExpression(ParenthesizedExpression e) => visit(e.child);
 
   visitGetter(Getter g) {
     var receiver = visit(g.receiver);
     var getter = new GetterObserver(g, receiver);
     receiver._parent = getter;
     return getter;
@@ skipping 67 matching lines @@
     var trueExpr = visit(o.trueExpr);
     var falseExpr = visit(o.falseExpr);
     var ternary = new TernaryObserver(o, condition, trueExpr, falseExpr);
     condition._parent = ternary;
     trueExpr._parent = ternary;
     falseExpr._parent = ternary;
     return ternary;
   }
 
   visitInExpression(InExpression i) {
-    // don't visit the left. It's an identifier, but we don't want to evaluate
-    // it, we just want to add it to the comprehension object
-    var left = visit(i.left);
-    var right = visit(i.right);
-    var inexpr = new InObserver(i, left, right);
-    right._parent = inexpr;
-    return inexpr;
+    throw new UnsupportedError("can't eval an 'in' expression");
   }
+
+  visitAsExpression(AsExpression i) {
+    throw new UnsupportedError("can't eval an 'as' expression");
+  }
+
 }
 
 class EmptyObserver extends ExpressionObserver<EmptyExpression>
     implements EmptyExpression {
 
   EmptyObserver(EmptyExpression value) : super(value);
 
   _updateSelf(Scope scope) {
     _value = scope.model;
     // TODO(justin): listen for scope.model changes?
@@ skipping 257 matching lines @@
                 _invalidate(scope);
               }
             });
       }
     }
   }
 
   accept(Visitor v) => v.visitInvoke(this);
 }
 
-class InObserver extends ExpressionObserver<InExpression>
-    implements InExpression {
-  IdentifierObserver left;
-  ExpressionObserver right;
-
-  InObserver(Expression expr, this.left, this.right) : super(expr);
-
-  _updateSelf(Scope scope) {
-    Identifier identifier = left;
-    var iterable = right._value;
-
-    if (iterable is! Iterable && iterable != null) {
-      throw new EvalException("right side of 'in' is not an iterator");
-    }
-
-    if (iterable is ObservableList) {
-      _subscription = iterable.listChanges.listen((_) => _invalidate(scope));
-    }
-
-    // TODO: make Comprehension observable and update it
-    _value = new Comprehension(identifier.value, iterable);
-  }
-
-  accept(Visitor v) => v.visitInExpression(this);
-}
-
 _toBool(v) => (v == null) ? false : v;
 
-/**
- * A comprehension declaration ("a in b"). [identifier] is the loop variable
- * that's added to the scope during iteration. [iterable] is the set of
- * objects to iterate over.
- */
-class Comprehension {
-  final String identifier;
-  final Iterable iterable;
-
-  Comprehension(this.identifier, Iterable iterable)
-      : iterable = (iterable != null) ? iterable : const [];
-}
-
 class EvalException implements Exception {
   final String message;
   EvalException(this.message);
   String toString() => "EvalException: $message";
 }