Use the typedef arity to know how to invoke a closure given by the dom.

dart/lib/compiler/implementation/elements/elements.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.
 
 #library('elements');
 
 #import('../tree/tree.dart');
 #import('../scanner/scannerlib.dart');
 #import('../leg.dart');  // TODO(karlklose): we only need type.
 #import('../util/util.dart');
@@ skipping 336 matching lines @@
       super(prefix, ElementKind.PREFIX, enclosing);
 
   lookupLocalMember(SourceString memberName) => imported[memberName];
 
   Type computeType(Compiler compiler) => compiler.types.dynamicType;
 
   Token position() => firstPosition;
 }
 
 class TypedefElement extends Element {
-  final Token token;
   Type cachedType;
+  Typedef cachedNode;
 
-  TypedefElement(SourceString name, Element enclosing, this.token)
-      : super(name, ElementKind.TYPEDEF, enclosing) {
-    cachedType = new InterfaceType(this);
+  TypedefElement(SourceString name, Element enclosing)
+      : super(name, ElementKind.TYPEDEF, enclosing);
+
+  Type computeType(Compiler compiler) {

[ahe, 2012/05/29 13:21:50]

I'm absolutely 100% lukewarm on this approach. This looks like a copy of some
code I have seen in a different place.

+    if (cachedType !== null) return cachedType;
+    compiler.withCurrentElement(this, () {
+      FunctionSignature signature = compiler.resolveTypedef(this);
+      LinkBuilder<Type> parameterTypes = new LinkBuilder<Type>();
+      for (Link<Element> link = signature.requiredParameters;
+           !link.isEmpty();
+           link = link.tail) {
+         parameterTypes.addLast(link.head.computeType(compiler));
+         // TODO(karlklose): optional parameters.
+      }
+      cachedType = new FunctionType(compiler.types.dynamicType,
+                                    parameterTypes.toLink(),
+                                    this);
+    });
+    return cachedType;
   }
-
-  position() => findMyName(token);
-
-  Type computeType(Compiler compiler) => cachedType;
 }
 
 class VariableElement extends Element {
   final VariableListElement variables;
   Expression cachedNode; // The send or the identifier in the variables list.
 
   Modifiers get modifiers() => variables.modifiers;
 
   VariableElement(SourceString name,
                   VariableListElement this.variables,
@@ skipping 668 matching lines @@
   final Node node;
   Type bound;
   Type type;
   TypeVariableElement(name, Element enclosing, this.node, this.type,
                       [this.bound])
     : super(name, ElementKind.TYPE_VARIABLE, enclosing);
   Type computeType(compiler) => type;
   Node parseNode(compiler) => node;
   toString() => "${enclosingElement.toString()}.${name.slowToString()}";
 }