How can I do applicative traverse collecting failu...

# arrow

[Satyam Agarwal]

How can I do applicative traverse collecting failures on left hand side ?
it was possible in 0.11.0 if I remember correctly, but I can’t seem to write it in the new version.
from List<A> to Either<List<B>, List<C>> just like we do for validated
We only have parTraverse and parTraverseEither.
So I can either get List<Either<B, C>> or Either<B, List<C>>

[raulraja]

Hi @Satyam Agarwal do you have a small example of the code you are trying to port from 0.11? traverse is available for a few data types and it no longer requires the applicative instance because it always ends in List<F<A>>

[Satyam Agarwal]

I’ll check if I can find it. all my apps are now on 0.13.1 😅

[Satyam Agarwal]

Actually I had it wrong.
With applicative there was always mapN/tupledN, so I was doing something like this :

val re: Either<NonEmptyList<Int>, Tuple3<Int, Nothing, Nothing>> = Validated
    .applicative(NonEmptyList.semigroup<Int>())
    .mapN(1.valid(), 2.invalidNel(), 3.invalidNel()) { (a, b, c) -> Tuple3(a, b, c)}
    .fix()
    .toEither()

But I am looking something like this for parTraverse as I have a list to traverse over.

[raulraja]

those are now called zip and the ones for ValidatedNel already imply you are using the Nel semigroup so you no longer ni to add it as argument

[raulraja]

https://github.com/arrow-kt/arrow/blob/f5a7ca60e9ad91532810e4391673fc3a605b9ce6/ar[…]ow-libs/core/arrow-core/src/main/kotlin/arrow/core/Validated.kt

[raulraja]

There is also https://github.com/arrow-kt/arrow/blob/91470902acd47cee9cd5022211204ea617f6a17e/ar[…]nes/src/main/kotlin/arrow/fx/coroutines/ParTraverseValidated.kt

[Satyam Agarwal]

Yes, I can go from parTraverseValidated and then convert to either. Thank you 🙂