Simulacrum VS interop-cats

The Cats ecosystem offers mature named abstractions providing algebraic laws virtually identical to those offered by Haskell and PureScript and that have stood the test of time, at the cost of relying on a "design pattern" approach to implementation you have to squint a bit to see ("typeclasses" based on higher-kinded types and implicit arguments) and that sometimes doesn't play nicely with Scala's colored local type inference. The selling point of this, coupled with parametricity ("tagless-final style"), is the ability to reason algebraically about your code.

If you're using http4s, don't use ZIO. Yes, ZIO has an interop-cats module, so you can do this. But using http4s means you're working in the conceptual framework the Typelevel ecosystem is based on (and what interop-cats does can be characterized as "describe ZIO's implementation in those terms, so the Typelevel ecosystem can make heads or tails of it.") This is essentially all cost and no benefit: you can't avoid understanding the Typelevel ecosystem if you use http4s (at least, no more than you can by using cats-effect), and you don't get any of the value proposition of ZIO (interop-cats gives you Typelevel typeclass instances for the RIO type alias, which means your error channel is rooted in Throwable, and you're faced with the most complex part of the ZIO ecosystem: ZLayer, which the Typelevel ecosystem doesn't use and doesn't need). Finally the ZIO ecosystem is still quite immature, and this brings us to documentation. There is not (yet!) anything comparable to:

These are necessarily oversimplifications. In particular, the ZIO ecosystem offers the relevant instances of cats-effect typeclasses to support use of the ZIO type in the cats-effect ecosystem.

However, ZIO continues to offer cats-effect type classes and I certainly have no doubt cats-effect 3 continues to benefit from John's contributions. Furthermore, I likewise don't doubt the value of the ZIO ecosystem generally, and John's success in building the ZIO community speaks for itself. I personally have chosen to remain closer to the other, let's say "classical," pure FP ecosystems, partially for historical (or, if you prefer, "sunk cost") reasons, but partially because I'm satisfied the value of the Haskell/Typelevel/PureScript/fp-ts/etc. interplay warrants it.

It seems that zio/interop-cats faces a similar issue.