anchor.diff:    final int _start;
     final int _stop;
   
  -  Token(this._buffer, this._start, this._stop);
  +  const Token(this._buffer, this._start, this._stop);
   
     bool operator == (Token other) => other is Token
         && _buffer === other._buffer
  
positive.code:     }
      return LINEFEED_PARSER;
    }
  }
  
  /** Non local return. */
  class NonLocalReturn<T> implements Exception {
    final T _value;
    NonLocalReturn(this._value);
    T get value() => _value;
  }
negative.code: // Copyright (c) 2012, Lukas Renggli <renggli@gmail.com>
  
  /** Function interface for parse actions. */
  typedef Dynamic Action(Dynamic argument);
  
  /**
   * A parser that performs a transformation with a given function on the
  