We use it extensively at Verizon, and it exists just fine with 'impure' code, Akka code, or whatever else various teams decide to also pull in. Codebases that don't use Scalaz end up re-inventing it, usually in a more buggy way and at a waste of developer effort.
Reinventing is fine on your own for a learning exercise and I certainly did it a few times, but in production code, just use Scalaz. Or sure, I suppose if you want to use a copy and pasted into a new repo version of Scalaz, go for Cats. I don't even know why Shapeless is brought into the conversation, it has a much more narrow use case and I almost never reach for it.
I've also found the Scalaz community and chat room on IRC quite helpful, whereas I've had some really unpleasant interactions with Cats committers. To go around spreading FUD and promoting an alpha level library that's less than half as popular as Scalaz (according to Github stars) is just irresponsible.
The main thing scalaz has that cats doesn't is scalaz.concurrent.Task, and there are multiple typelevel-endorsed alternatives to it being worked on as well (in monix and fs2). Task is wonderful btw.
fwiw we use scalaz at work and haven't upgraded to cats because it isn't ready. cats just fixed a performance bug that would have destroyed us (Map union mappend was ridiculously unoptimized compared to scalaz's). We .foldMap(/* make a small Map*/) all the time and it's one of our favorite parts of scalaz. see https://github.com/typelevel/cats/issues/1290 for the bug.
Typelevel didn't even want to fork Scalaz to begin with. That was only their plan B, plan A was to take over the community with code of conduct/social justice shenanigans, and then expel people they didn't like. The fork is just what they came up with after dibblegate failed.
They need to move their lazy asses to Haskell and start fixing and implementing the tooling there instead of enjoying their free ride in Scala while constantly shitting on the language and its community.
https://groups.google.com/forum/#!topic/scalaz/9X_putSGoCY
https://groups.google.com/forum/#!searchin/scalaz/code$20of$...
Calling Tony Morris a rapist was probably the highlight of the affair: https://twitter.com/shajra/status/544712807220908032
Up until they realized they couldn't take over the community, Lars Hupel and Miles Sabin had no publicly stated plans to leave Scalaz.
Cats initial commit is early 2015.
https://github.com/typelevel/cats/commits/master?page=74
I have no idea why everyone dislikes them so much. I use Scalaz, and it's pretty great. From what I've seen Cats is nearly the same thing, I just saw no reason to switch. In what way do you believe Cats is significantly different from Scalaz, beyond the fact that you apparently dislike the people involved?
Incidentally, scalaz-streaming was also pretty nice - mathematically I liked it but it was simply not as performant as Akka streaming. I'd love to use it if it becomes fast.
Why would they create cats while they still had hope to save scalaz from its community? No need to spin some crazy conspiracy.
> you apparently dislike the people involved
LOL WTF? That guy has single-handedly destroyed more than one community already. It's not like it's some unfortunate thing that accidentally happens. It has happened before, and will keep happening until he is shown the door for good.
The rest of the scalaz community are enabling him to keep doing his toxic shit. The faster scalaz goes the way of Lift, the better.
I judge people for using scalaz. If you think it is acceptable to keep enabling him, you are a bad human being.
it's desperate desire to turn Scala into Haskell ends up turning an awesome ML-inspired language into a vastly inferior religious (...ahem, pure) language. But Cats and Shapeless aren't Scalaz.
I claim that from a technical perspective they are more or less equivalent and they only forked due to a feud. So if you want to avoid Haskell-inspired constructs in Scalaz, Cats won't be much to your liking either.
Glad we are on the same page!
I don't have issues with Haskell-inspired constructs, I have issues with Haskell-inspired behavior.
I'm fully on board with you...I think Scalaz as a library is a virus, and it's community is toxic, and it's desperate desire to turn Scala into Haskell ends up turning an awesome ML-inspired language into a vastly inferior religious (...ahem, pure) language.
But Cats and Shapeless aren't Scalaz. They have concepts that happen to exist in Haskell, but they aren't Haskell's concepts to own any more than C owns imperative programming. If anything, Mathematics owns the concepts and Haskell happened to borrow them to make a terrible purist concept slightly more practical. It turns out that when you need the concepts (and I have, on a couple of occasions), it makes Scala slightly more practical as well.