is it possible to provide async versions of `.map`...

# arrow

[Pratik Tandel]

is it possible to provide async versions of .map / .flatMap from arrow? right now it seems i will have to write extension functions that do something similar

[Pratik Tandel]

This is what an extension function looks like:

suspend fun <A, B, C> Either<A, B>.flatMapAsync(fn: suspend (B) -> Either<A, C>): Either<A, C> {
    return when (this) {
        is Either.Left -> this
        is Either.Right -> fn(this.b)
    }
}

[carbaj0]

Which version are you using?

[carbaj0]

in latest versions, it’s an inline function, allowing you to make asynchronous calls

[simon.vergauwen]

All inline functions allow for suspend from inside the lambda, and Arrow Fx Coroutines contains some more utilities if you’re looking for parallel operators such as parZip, race or parTraverse, etc

[Pratik Tandel]

i’m on 0.11.0

[simon.vergauwen]

Oh, that’s a rather old version. Any reason you use 0.11.0 ?

[Pratik Tandel]

might be challenging to upgrade to kotlin 1.5

[Pratik Tandel]

(other dependencies we need to wait for). i’m not sure if those libraries are backwards compat? perhaps — i hope it’s better than scala 😅

[simon.vergauwen]

Oh okay. Ye, that can be a pickle 😅

[simon.vergauwen]

This is the new approach Arrow takes for this issue instead of declaring it as flatMapAsync.

https://github.com/arrow-kt/arrow/blob/main/arrow-libs/core/arrow-core/src/commonMain/kotlin/arrow/core/Either.kt#L1103

[simon.vergauwen]

And comprehensions now work over suspending code also. https://arrow-kt.io/docs/patterns/monad_comprehensions/#comprehensions-over-coroutines

[simon.vergauwen]

The suspending either DSL could be back-ported to 0.11.0

[Pratik Tandel]

neat! i will look at what it’d take to upgrade — do you know what version this was introduced in?

[simon.vergauwen]

This was introduced in 0.12.0, which should be compatible with 0.11.0. You can try bumping to 0.12.1 and then you should have this available

[simon.vergauwen]

If you cannot upgrade, I can help you backport the either { } DSL so you can use it instead of flatMap (& co) for suspending code.