parse method

Implementation

@override
Result<int>? parse(State<StringReader> state) {
  final input = state.input;
  final pos = state.pos;
  if (pos < input.length) {
    final c = input.readChar(state.pos);
    for (var i = 0; i < chars.length; i++) {
      if (chars.codeUnitAt(i) == c) {
        state.pos += input.count;
        return Result(c);
      }
    }
  }

  return state.fail(ErrorUnexpectedCharacter());
}