parse method
Implementation
@override
Tuple1? parse(ParseInput<I> input, ParseState state) {
final pos = input.pos;
for (var i = 0; i < ps.length; i++) {
final p = ps[i];
if (p.parse(input, state) == null) {
return null;
}
return const Tuple1(null);
}
input.pos = pos;
}