Is there a way to represent a function that either does an action successfully (no return value) or ...

# arrow

[dave08]

Is there a way to represent a function that either does an action successfully (no return value) or has a failure one can bind() to in an either? Is there only Either<SomeFailure, Unit> or maybe something made for this purpose?

[simon.vergauwen]

Either<SomeFailure, Unit> is the best accurate return type for this.

[Stylianos Gakis]

What about a function that does something, may fail (but I don’t want/can’t know why it failed) and it may also succeed but without any result? Is Either<Unit, Unit> normal, or just an indicator that I probably want something more smart for Left?

[simon.vergauwen]

I've not really come across cases where I have no idea at all what went wrong. I would probably create a marker object Failed that at some point you mapLeft to align errors into a different error hierarchy, or Throwable with Either.catch in case I don't know what goes wrong. Being aware that with Throwable you don't swallow, and/or send an alert/log to a metric service.

In any other case where there is some result but no clear error, so Either<Unit, A> is a good indication you probably want A?.