Implement parsing and resolving of type-variables.

frog/leg/typechecker.dart

Index: frog/leg/typechecker.dart
diff --git a/frog/leg/typechecker.dart b/frog/leg/typechecker.dart
index 55049a4686a0cbf590f746b3e884d3bb2e8e52eb..c3424c3f0c970031f54ef25e160cb291e4fb95db 100644
--- a/frog/leg/typechecker.dart
+++ b/frog/leg/typechecker.dart
@@ -29,6 +29,12 @@ interface Type {
   Element get element();
 }
 
+class TypeVariableType implements Type {
+  final SourceString name;
+  Element element;
+  TypeVariableType(this.name, [this.element]);
+}
+
 /**
  * A statement type tracks whether a statement returns or may return.
  */
@@ -590,6 +596,10 @@ class TypeCheckerVisitor implements Visitor<Type> {
     return type;
   }
 
+  visitTypeVariable(TypeVariable node) {
+    return types.dynamicType;
+  }
+
   Type visitVariableDefinitions(VariableDefinitions node) {
     Type type = analyzeWithDefault(node.type, types.dynamicType);
     if (type == types.voidType) {