then<R4> method
Returns a parser that consumes the receiver followed by other in
sequence and returns a SequenceParser4 with the 4 positional
parse results.
Flattens into a strictly typed Record with 4 elements, preserving static type information.
For example,
the parser char('a').then(char('b')).then(char('c')).then(char('d'))
returns ('a', 'b', 'c', 'd')
for the input 'abcd'.
Implementation
@useResult
SequenceParser4<R1, R2, R3, R4> then<R4>(Parser<R4> other) =>
SequenceParser4<R1, R2, R3, R4>(parser1, parser2, parser3, other);