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dart/frog/leg/resolver.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.
 
 interface TreeElements {
   Element operator[](Node node);
 }
 
 class TreeElementMapping implements TreeElements {
   Map<Node, Element> map;
@@ skipping 790 matching lines @@
     }
     for (Link<Node> link = node.interfaces.nodes;
          !link.isEmpty();
          link = link.tail) {
       element.interfaces = element.interfaces.prepend(visit(link.head));
     }
     return element.computeType(compiler);
   }
 
   Type visitTypeAnnotation(TypeAnnotation node) {
-    Identifier name = node.typeName;
+    Identifier name = node.typeName.asIdentifier();
+    if (name === null) {
+      compiler.unimplemented("prefixes", node: node.typeName);
+    }
     Element element = context.lookup(name.source);
     if (element === null) {
       compiler.reportError(node,
           new ResolutionError(MessageKind.CANNOT_RESOLVE_TYPE, [name]));
     } else if (element.kind !== ElementKind.CLASS) {
       compiler.reportError(node,
           new ResolutionError(MessageKind.NOT_A_TYPE, [name]));
     } else {
       compiler.resolver.toResolve.add(element);
       // TODO(ngeoffray): Use type variables.
@@ skipping 177 matching lines @@
 class TopScope extends Scope {
   Universe universe;
 
   TopScope(Universe this.universe) : super(null, null);
   Element lookup(SourceString name) => universe.find(name);
 
   Element add(Element element) {
     throw "Cannot add an element in the top scope";
   }
 }