Support anonymous functions.

frog/leg/resolver.dart

 // Copyright (c) 2012, 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.
 
 interface TreeElements {
   Element operator[](Node node);
   Selector getSelector(Send send);
 }
 
 class TreeElementMapping implements TreeElements {
@@ skipping 413 matching lines @@
       }
     } else {
       ClassElement cls = element;
       compiler.resolver.toResolve.add(element);
       // TODO(ahe): This should be a Type.
       useElement(node, element);
     }
     return element;
   }
 
-  Element defineElement(Node node, Element element) {
+  Element defineElement(Node node, Element element,
+                        [bool doAddToScope = true]) {
     compiler.ensure(element !== null);
     mapping[node] = element;
-    Element existing = context.add(element);
-    if (existing != element) {
-      error(node, MessageKind.DUPLICATE_DEFINITION, [node]);
+    if (doAddToScope) { 
+      Element existing = context.add(element);
+      if (existing != element) {
+        error(node, MessageKind.DUPLICATE_DEFINITION, [node]);
+      }
     }
     return element;
   }
 
   Element useElement(Node node, Element element) {
     if (element === null) return null;
     return mapping[node] = element;
   }
 
   void setupFunction(FunctionExpression node, FunctionElement function) {
@@ skipping 39 matching lines @@
   visitFor(For node) {
     Scope scope = new BlockScope(context);
     visitIn(node.initializer, scope);
     visitIn(node.condition, scope);
     visitIn(node.update, scope);
     visitIn(node.body, scope);
   }
 
   visitFunctionExpression(FunctionExpression node) {
     visit(node.returnType);
+    SourceString name;
     if (node.name === null) {
-      cancel(node, "anonymous functions are not implemented");
+      name = const SourceString("");
+    } else {
+      name = node.name.asIdentifier().source;
     }
-    SourceString name = node.name.asIdentifier().source;
     FunctionElement enclosingElement = new FunctionElement.node(
         name, node, ElementKind.FUNCTION, new Modifiers.empty(),
         context.element);
-    defineElement(node, enclosingElement);
+    defineElement(node, enclosingElement, doAddToScope: node.name !== null);
     setupFunction(node, enclosingElement);
 
     visit(node.body);
     context = context.parent;
     return enclosingElement;
   }
 
   visitIf(If node) {
     visit(node.condition);
     visit(node.thenPart);
@@ skipping 632 matching lines @@
 class TopScope extends Scope {
   LibraryElement get library() => element;
 
   TopScope(LibraryElement library) : super(null, library);
   Element lookup(SourceString name) => library.find(name);
 
   Element add(Element element) {
     throw "Cannot add an element in the top scope";
   }
 }