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 String _message;
  
    Failure(buffer, position, this._message) : super(buffer, position);
  
    bool isFailure() => true;
  
  
negative.code: 
    final Dynamic _result;
  
    const Success(buffer, position, this._result) : super(buffer, position);
  
    bool isSuccess() => true;
  
  