parse method
Parses the input and returns a result wrapped in Result if successful,
null
otherwise.
Implementation
@override
Result<O1>? parse(State<I> state) {
final pos = state.pos;
final r1 = p.parse(state);
if (r1 != null) {
final r2 = end.fastParse(state);
if (r2) {
return r1;
}
state.pos = pos;
}
return null;
}