alt<L, R> function
Recieves an Either, and if it is a Left value replaces it with an
alternative Either determined by executing the onLeft
callback.
expect(
left('fail').chain(alt((s) => right('caught the $s'))),
right('caught the fail'),
);
expect(
right('yay').chain(alt((s) => right('caught the $s'))),
right('yay'),
);
Implementation
Either<L, R> Function(Either<L, R> either) alt<L, R>(
Either<L, R> Function(L left) onLeft,
) =>
fold(onLeft, right);