Ondra Pelech

@kitlangton I've put you as the assignee because you seem to understand this the most of us.

@guizmaii Could you please fix this to work with Scala 3.1.2? :pray:

I'm no category theorist, so please excuse me if I say something nonsensical. Natural transformations are morphisms between functors, right? In that case we don't have them in ZIO Prelude...

So we now have 2 PRs implementing this https://github.com/zio/zio-prelude/pull/442 has * identity * sequentialFusion * purity * naturality * parallelFusion https://github.com/zio/zio-prelude/pull/449 has * identity * composition (for some predefined functors)...

If what @Badmoonz says is correct, than let's just have the one commutativity law. If all the other laws follow from that (+ the Covariant laws), then we don't need...

For the record, here are papers discussing laws for Traversable: * [M. Jaskelioff and O. Rypacek. An investigation of the laws of traversals. 2012.](https://arxiv.org/pdf/1202.2919.pdf) * [Richard Bird, Jeremy Gibbons, Stefan...

There have been some changes in the codebase, like renaming `Traversable` to `ForEach` and others, so the PR(s) might be outdated. But our need for laws for `ForEach` (aka Traversable)...

Looking at the builds again, some were not spurious failures. 2.11 may need more explicit type arguments and dotty seems to need more parentheses. Do you think you could have...

Please run `sbt fix` to fix the problems (formatting in this case, I think).

It may be the cases that this is actually not possible in Scala 3: https://docs.scala-lang.org/scala3/reference/dropped-features/type-projection.html