optionalWith method
Returns new parser that accepts the receiver, if possible. The resulting
parser returns the result of the receiver, or value
if not applicable.
For example, the parser letter().optionalWith('!')
accepts a letter as
input and returns that letter. When given something else the parser
succeeds as well, does not consume anything and returns '!'
.
Implementation
@useResult
Parser<R> optionalWith(R value) => OptionalParser<R>(this, value);