Does Arrow have something equivalent to Parallel i...

# arrow

[julian]

Does Arrow have something equivalent to Parallel in Cats, that abstracts over Monads but also supports parallel composition?

[simon.vergauwen]

So such an abstraction currently doesn’t exist

[simon.vergauwen]

What is your use-case?

[julian]

@simon.vergauwen No use case. I attended the 47 Degrees Academy session today on "Functional Error Handling and Validation with Cats" and Parallel was mentioned. I was just curious if such a thing existed in Arrow.

[pakoito]

Isn’t that our Concurrent?

[simon.vergauwen]

Not really. Cats exposes Parallel to describe a relationship between two F. For Concurrent that’d be IO <~> IO.Par, but it also has an instance for EitherNel <~> ValidatedNel.

[simon.vergauwen]

interface Parallel<F, G> {
  val applicative: Applicative<G>
  val transform: FunctionK<F, G> 
  val back: FunctionK<G, F>

  fun parTupledN(fa: Kind<F, A>, fb: Kind<F, B>): Kind<F, Pair<A, B>> = 
     back(applicative.mapN(transform(fa), transform(fb)))
}

Conceptually something like this.