then<R3> method
Returns a parser that consumes the receiver followed by other in
sequence and returns a SequenceParser3 with the 3 positional
parse results.
Flattens into a strictly typed Record with 3 elements, preserving static type information.
For example,
the parser char('a').then(char('b')).then(char('c'))
returns ('a', 'b', 'c')
for the input 'abc'.
Implementation
@useResult
SequenceParser3<R1, R2, R3> then<R3>(Parser<R3> other) =>
SequenceParser3<R1, R2, R3>(parser1, parser2, other);