anchor.diff:   */
   class _SequenceParser extends ListParser {
   
  -  _SequenceParser(parsers) : super(parsers);
  +  factory _SequenceParser(Iterable<Parser> parsers) {
  +    return new _SequenceParser._(new List.from(parsers, growable: false));
  +  }
  +
  +  _SequenceParser._(parsers) : super(parsers);
   
     @override
     Result parseOn(Context context) {
  
positive.code: 
    @override
    Parser or(Parser other) {
      var parsers = new List.from(_parsers);
      parsers.add(other);
      return new _ChoiceParser(parsers);
    }
  
    @override
    Parser copy() => new _ChoiceParser(new List.from(_parsers));
  
  }
  
  
negative.code: 
    @override
    Parser seq(Parser other) {
      return new _SequenceParser(new List()..addAll(_parsers)..add(other));
    }
  
    @override
    Parser copy() => new _SequenceParser(_parsers);
  
  }
  