Consume both "left" and "right" of Vavr Either?

Question

How can I consume both a "left" or a "right" of a vavr Either in a functional way?

I have a method that returns an Either<RuntimeException, String>. Based on this result, I need to execute a callback to our reporting library, e.g. reportSuccess() or reportFailure(). Consequently, I am looking for a nice, functional way of doing it. If an Either had a biConsumer(Consumer<? super L> leftConsumer, Consumer<? super R> rightConsumer, I could write something like:

Either<RuntimeException, String> result = // get the result from somewhere

result.biConsumer(ex -> {
  reportFailure();
}, str -> {
  repportSuccess();
});

The closest workaround I have found so far is the biMap() method, which would look something like

Either<RuntimeException, String> mappedResult = result.bimap(ex -> {
  reportFailure();
  return ex;
}, str -> {
  reportSuccess();
  return str;
});

Arguably, mapping functions should be used for mapping and not side effects, so even if it works I am looking for alternatives.

Answer 1

There's peek and peekLeft that – in combination – are pretty close to what you are looking for.

void reportFailure(RuntimeException e) {
    System.out.println(e);
}
void reportSuccess(String value) {
    System.out.println(value);
}

....

// prints: some value
Either<RuntimeException, String> right = Either.right("some value");
right.peekLeft(this::reportFailure).peek(this::reportSuccess);

// prints: java.lang.RuntimeException: some error
Either<RuntimeException, String> left = Either.left(
    new RuntimeException("some error")
);
left.peekLeft(this::reportFailure).peek(this::reportSuccess);