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