Can we optimize this `futureOr` function: ``` suspend fun fu(i: Int): Boolean = TODO() suspen...

# arrow

[thanh]

Can we optimize this futureOr function:

suspend fun fu(i: Int): Boolean = TODO()
    suspend fun futureOr(fs: List<Int>): Boolean =
        fs.parTraverse { fu(it) }.reduce { acc, b -> acc || b }

Now it needs to wait for all of suspend function completed. But we know that if there is one of the fu(it) return false we can return false and cancel the rest. Not sure how to do it nicely here.

[simon.vergauwen]

Hey @thanh,

You can do:

[simon.vergauwen]

suspend fun fu(i: Int): Boolean = TODO()

suspend fun futureOr(fs: List<Int>): Boolean =
  effect<Unit, Unit> {
    fs.parTraverse {
      if(fu(it)) Unit else shift(Unit)
    }    
  }.fold({ false }, { true })

[simon.vergauwen]

You can change the types in whatever way you want, but here shift makes the parTraverse short-circuit.

[simon.vergauwen]

This also works with either { } from 1.x.x

[thanh]

It works great, thanks @simon.vergauwen

[simon.vergauwen]

My pleasure @thanh 🙌

[julian]

shift , effect - These are new to me. Where may I read more about them?

[julian]

I found this.

[simon.vergauwen]

Here is a small blog about when I first discovered this new abstraction: https://nomisrev.github.io/continuation-monad-in-kotlin/
The other blogs also use the Effect type, and might give you some more insights.

It's new, but also not new 😄 It works 95% the same as either { } , and either { } is now build on top of effect { } .

[simon.vergauwen]

TL;DR suspend fun <E, A> either(f: suspend EffectScope<E>.() -> A): Either<E, A> = effect(f).toEither() and shift(e) <~~> e.left().bind()

[simon.vergauwen]

If you feel something is missing please create an issue so we can improve the documentation over time, and absolutely feel free to create PRs with suggestions 😁 🙏

[julian]

Thank you @simon.vergauwen!