anchor.diff:   */
   class Result extends Context {
   
  -  Result(buffer, position) : super(buffer, position);
  +  const Result(buffer, position) : super(buffer, position);
   
     /** Returns the parse result of the current context. */
     abstract Dynamic getResult();
  
positive.code:   final Dynamic _buffer;
    final int _position;
  
    Context(this._buffer, this._position);
  
    /** The buffer we are working on. */
    Dynamic get buffer() => _buffer;
  
negative.code: 
    final Dynamic _result;
  
    const Success(buffer, position, this._result) : super(buffer, position);
  
    bool isSuccess() => true;
  
  