For a fallible void function, do you use Option<Exception> or Either<Exception, Unit>?

[petejodo]

I couldn't find anything on this topic. Title covers it pretty well, basically I'm looking to determine what the arrow devs and community typically do for a function like

fun foo(): Option<Exception> {}

// vs

fun foo(): Either<Exception, Unit> {}

I ask this because different communities do different things. For example, the Rust community uses Result<Err, ()> (Either) which I personally prefer but the naming of "Result" is better suited towards that than Either and then in Haskell they use Maybe (Option). What does the kotlin/arrow community prefer?

[nomisRev]

Hey @petejodo,
I've never seen Option<Exception> in Haskell 🤔 Typically Option is used for modelling abscene of a value, and most often nullable types are preferred for this.

In Kotlin with Arrow I would suggest using Either, since operators like Either.catch automatically take care of CancellationException and fatal exceptions. You could introduce typealias Result<E, A> = Either<E, A> if you prefer that name.

Alternatively you can use kotlin.Result and Arrow has support for kotlin.Result in it's APIs exposing result { } DSL similarly to either { } DSL. Take care though since kotlin.Result's runCatching will swallow CancellationException and fatal exceptions so you need to manually deal with them.

[petejodo]

hmm yeah... take my note about Haskell and put it in a Maybe 😏 but ok yeah that's how I was thinking about it but wasn't entirely sure. I also asked this before I noticed the void() method on result and so I was doing an ugly .map { }. I found that to be a clue into the preference of Either in such cases

Also, I did not know that about arrow's support around kotlin's result, thanks for the tip!