Search code examples
scalaintellij-ideaimplicitscala-cats

How to figure out the functor for cats.Parallel?

Because IntelliJ does not play all that nicely with Cats, I am sometimes explicit about type parameters in my code to avoid ugly red lines. For example, if we assume this gives a red line under IO.pure(x.toString),

List(1, 2, 3).traverse(x => IO.pure(x.toString))

then I can easily add the types and IntelliJ is happy:

List(1, 2, 3).traverse[IO, String](x => IO.pure(x.toString))

Now, with parTraverse it seems a bit more difficult because of the functor parameter:

List(1, 2, 3).parTraverse[IO, ???, String](x => IO.pure(x.toString)) //what is ???

Is there any way to figure out the type of the F[_] parameter here so I can please IntelliJ or is this some partial unification thing and so I'm doomed to ugliness? Thanks

Solution

  • If you go to the scaladoc api of cats-effects, and search for Parallel instances, it lists you just a single implicit method that produces Parallel[IO, ???], namely Parallel[IO, Par] provided by cats.effect.IO.ioParallel. So, it seems that cats.effect.IO.Par should do the trick:

    List(1, 2, 3).parTraverse[IO, Par, String](x => IO.pure(x.toString))