Simplify AST by extending LetNode and replace CommaNode.

runtime/vm/ast.cc

 // 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.
 
 #include "vm/ast.h"
 #include "vm/compiler.h"
 #include "vm/dart_entry.h"
 #include "vm/isolate.h"
 #include "vm/object_store.h"
 #include "vm/resolver.h"
@@ skipping 59 matching lines @@
   for (intptr_t i = 0; i < this->length(); i++) {
     NodeAt(i)->Visit(visitor);
   }
 }
 
 
 LetNode::LetNode(intptr_t token_pos)
   : AstNode(token_pos),
     vars_(1),
     initializers_(1),
-    body_(NULL) { }
+    nodes_(1) { }
 
 
 LocalVariable* LetNode::AddInitializer(AstNode* node) {
   initializers_.Add(node);
   char name[64];
   OS::SNPrint(name, sizeof(name), ":lt%"Pd"_%d", token_pos(), vars_.length());
   LocalVariable* temp_var =
       new LocalVariable(token_pos(),
                         String::ZoneHandle(Symbols::New(name)),
                         Type::ZoneHandle(Type::DynamicType()));
   vars_.Add(temp_var);
   return temp_var;
 }
 
 
 void LetNode::VisitChildren(AstNodeVisitor* visitor) const {
   for (intptr_t i = 0; i < num_temps(); ++i) {
     initializers_[i]->Visit(visitor);
   }
-  body_->Visit(visitor);
+  for (intptr_t i = 0; i < nodes_.length(); ++i) {
+    nodes_[i]->Visit(visitor);
+  }
 }
 
 
 void ArrayNode::VisitChildren(AstNodeVisitor* visitor) const {
   for (intptr_t i = 0; i < this->length(); i++) {
     ElementAt(i)->Visit(visitor);
   }
 }
 
 
@@ skipping 347 matching lines @@
   if (result.IsError() || result.IsNull()) {
     // TODO(turnidge): We could get better error messages by returning
     // the Error object directly to the parser.  This will involve
     // replumbing all of the EvalConstExpr methods.
     return NULL;
   }
   return &Instance::ZoneHandle(Instance::Cast(result).raw());
 }
 
 }  // namespace dart