anchor.diff:    For(this.init, this.test, this.incr, Statement body) : super(body);
   
     accept(NodeVisitor visitor) => visitor.visitFor(this);
  +  void visitChildren(NodeVisitor visitor) {
  +    init.accept(visitor);
  +    test.accept(visitor);
  +    incr.accept(visitor);
  +    body.accept(visitor);
  +  }
   }
   
   class ForIn extends Loop {
  
positive.code:   const StringLiteral(this.value);
  
    accept(NodeVisitor visitor) => visitor.visitStringLiteral(this);
  }
  
  class NumberLiteral extends Literal {
  
negative.code:   Block(this.elements);
  
    accept(NodeVisitor visitor) => visitor.visitBlock(this);
    void visitChildren(NodeVisitor visitor) {
      for (Statement statement in elements) statement.accept(visitor);
    }
  }
  
  class VariableDeclarationList extends Statement {
  