parse method

Implementation

@override
Result<O2>? parse(State<I> state) {
  final pos = state.pos;
  final r1 = start.fastParse(state);
  if (r1) {
    final r2 = p.parse(state);
    if (r2 != null) {
      final r3 = end.fastParse(state);
      if (r3) {
        return r2;
      }
    }
  }

  state.pos = pos;
  return null;
}