tap<L, R>  function 
 
Perform a side effect on the Either, if it is a Right.
expect(
  right(1).chain(tap(print)), // Prints '1' to the console
  equals(right(1)),
);
Implementation
Either<L, R> Function(Either<L, R> either) tap<L, R>(
  void Function(R value) f,
) =>
    map((r) {
      f(r);
      return r;
    });