parse method
Implementation
@override
@inline
Tuple1<O>? parse(ParseInput<I> input, ParseState state) {
final pos = input.pos;
if (open.parse(input, state) != null) {
final r = p.parse(input, state);
if (r != null) {
if (close.parse(input, state) != null) {
return Tuple1(r.$0);
}
}
}
input.pos = pos;
}