or method

@useResult ChoiceParser or(Parser other, { FailureJoiner? failureJoiner, })

Returns a parser that accepts the receiver or other. The resulting parser returns the parse result of the receiver, if the receiver fails it returns the parse result of other (exclusive ordered choice).

An optional failureJoiner can be specified that determines which Failure to return in case both parsers fail. By default the last failure is returned selectLast, but selectFarthest is another common choice that usually gives better error messages.

For example, the parser letter().or(digit()) accepts a letter or a digit. An example where the order matters is the following choice between overlapping parsers: letter().or(char('a')). In the example the parser char('a') will never be activated, because the input is always consumed letter(). This can be problematic if the author intended to attach a production action to char('a').

Due to https://github.com/dart-lang/language/issues/1557 the resulting parser cannot be properly typed. Please use ChoiceIterableExtension as a workaround: [first, second].toChoiceParser().

Implementation

@useResult
ChoiceParser<dynamic> or(Parser other, {FailureJoiner? failureJoiner}) =>
    switch (this) {
      ChoiceParser(
        children: final children,
        failureJoiner: final thisFailureJoiner
      ) =>
        [
          ...children,
          other
        ].toChoiceParser(failureJoiner: failureJoiner ?? thisFailureJoiner),
      _ => [this, other].toChoiceParser(failureJoiner: failureJoiner)
    };