What is the correct way to transform an `Iterable&...

# arrow

[Cody Mikol]

What is the correct way to transform an Iterable<Either<L,R>> into a Validated<Nel<L>, R> ?

For more context, I’m using parTraverse on a collection, returning an Either<L,R> for each item. I’d like to collect that into a Validated<Nel<L>,R to that I can take the left path if there are any errors and collect that into some useful log message.

It looks something like

items
  .parTraverse { doWork(it, foo) }
  .toValidated() // This is what I'm trying to figure out.
  .mapLeft { makeErrorMessage(it) // where it is Nel<L> }

fun doWork() : Either<L,R>

[Alex Johnson]

something like this? https://arrow-kt.io/docs/next/apidocs/arrow-fx-coroutines/arrow.fx.coroutines/kotlin.collections.-iterable/par-traverse-validated.html

[simon.vergauwen]

A short rewrite of your snippet with parTraverseValidated.

items  .parTraverseValidated(Semigroup.nonEmptyList()) {
  doWork(it, foo).toValidatedNel()
}

[Cody Mikol]

This is exactly what I was looking for, thank you 🙂