Implement parsing and resolving of type-variables.

frog/leg/tree/visitors.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 AbstractVisitor<R> implements Visitor<R> {
   abstract R visitNode(Node node);
 
   R visitBlock(Block node) => visitStatement(node);
   R visitBreakStatement(BreakStatement node) => visitGotoStatement(node);
   R visitCatchBlock(CatchBlock node) => visitNode(node);
@@ skipping 43 matching lines @@
   R visitStringInterpolation(StringInterpolation node) => visitExpression(node);
   R visitStringInterpolationPart(StringInterpolationPart node) {
     return visitNode(node);
   }
   R visitSwitchCase(SwitchCase node) => visitNode(node);
   R visitSwitchStatement(SwitchStatement node) => visitStatement(node);
   R visitThrow(Throw node) => visitStatement(node);
   R visitTryStatement(TryStatement node) => visitStatement(node);
   R visitTypeAnnotation(TypeAnnotation node) => visitNode(node);
   R visitTypedef(Typedef node) => visitNode(node);
+  R visitTypeVariable(TypeVariable node) => visitNode(node);
   R visitVariableDefinitions(VariableDefinitions node) => visitStatement(node);
   R visitWhile(While node) => visitLoop(node);
 }
 
 /**
  * This visitor takes another visitor and applies it to every
  * node in the tree. There is currently no way to control the
  * traversal.
  */
 class TraversingVisitor extends AbstractVisitor {
   final Visitor visitor;
 
   TraversingVisitor(Visitor this.visitor);
 
   visitNode(Node node) {
     node.accept(visitor);
     node.visitChildren(this);
   }
 }