Chunk - Add optimised traverse_ for StackSafeMonad.

[diesalbla]

If our Applicative F is actually an instance of StackSafeMonad, we can avoid the default implementation of traverse_, which is based on a foldRight method of Foldable and has to allocate a set of Eval objects. Instead, we can just loop on the monad itself.

Note Given that in practice Streams are mostly used with IO-like datatypes which are stack-safe, this should have some impact.

[armanbilge]

Linking to:

• Improve traverse performance through increased specialization cats#4408

Actually, if we made this optimization in Cats, we probably wouldn't need to repeat it here?

[diesalbla]

Actually, if we made this optimization in Cats, we probably wouldn't need to repeat it here?

As it happens I was taking a look at the cats implementation, but the Foldable type class seems to provide little. With Chunk we can optimise it right away. Note that the ticket refers to the traverse method, not the procedural traverse_. It is so inconvenient we never got around to renaming it typelevel/cats#1723.

[armanbilge]

Note that the ticket refers to the traverse method, not the procedural traverse_

Yes indeed, but we can make the described optimizations for both traverse and traverse_ upstream in Cats.

[diesalbla]

Yes indeed, but we can make the described optimizations for both traverse and traverse_ upstream in Cats.

It may take a while for those to get released, if and when they are done (the link is to an issue). This PR is ready as of now.

[armanbilge]

Sorry, I didn't mean it as a blocker here 🙂 rather, to further justify landing these changes in Cats.