anchor.diff:   */
   class Success extends Result {
   
  -  final dynamic _value;
  -
  -  const Success(buffer, position, this._value) : super(buffer, position);
  +  const Success(buffer, position, this.value) : super(buffer, position);
   
     @override
     bool get isSuccess => true;
   
     @override
  -  dynamic get value => _value;
  +  final dynamic value;
   
     @override
     String get message => null;
   
     @override
  -  String toString() => 'Success[${toPositionString()}]: $_value';
  +  String toString() => 'Success[${toPositionString()}]: $value';
   
   }
   
  
positive.code:   /**
     * Returns the line:column if the input is a string, otherwise the position.
     */
    String toPositionString() => Token.positionString(_buffer, _position);
  
  }
  
  
negative.code:  */
  class Context {
  
    const Context(this.buffer, this.position);
  
    /**
     * The buffer we are working on.
     */
    final dynamic buffer;
  
    /**
     * The current position in the buffer.
     */
    final int position;
  
    /**
     * Returns [true] if this result indicates a parse success.
  