I want to convert an `Either<SomeError, SomeSuc...

# arrow

[Daniel]

I want to convert an Either<SomeError, SomeSuccess> to a SomeError? , discarding the SomeSuccess. Does a function like that exist in arrow?

Right now I'm just doing the below, but I wanted to know if there is a more idiomatic way

return when (result) {
            is Either.Left -> result.a
            is Either.Right -> null
        }

[David Stone]

e.swap().orNull() would give you what you’re looking for

[Daniel]

Thank you! Also, is there a method like map for just doing a side effect? For example

.mapForSideEffect { log(it) }

instead of

.map { log(it); it }

[David Stone]

Side effects?! 😱 😉

So that doesn’t exist in arrow core, but over in arrow fx where you pull in typeclasses that let you do this exact thing. You can read @raulraja’s explanation of this very thing here: https://github.com/arrow-kt/arrow/issues/1361#issuecomment-477113878

[Daniel]

Thanks!

[David Stone]

👍