aecor VS cats-effect

Thanks, and thanks for your question! So regarding production use I wish I could tell you that we have load on a service using this, but as of just now it's not the case. It's recent and we're using this in a new micro-service which is not seeing much load yet. However this builds up on experience we've had dealing with Akka clusters for the past three years or so. We've been trying to find a way to have a lean and expressive domain while retaining Akka's power for a while, we actually published this article a while back where we were still using an OOP approach. Then we found out about a library, aecor, which was going full FP with the domain. However, we could not use the library directly for a number of reasons, chiefly because we are attached to keeping the layer above Akka as lightweight as possible and we want to keep a tight control on serialization aspects for rolling deployment. There also are other more differences: for instance we consider command rejections as first-order values, therefore opting for Either for replies. In endless, we’ve also tried to stick close to DDD & Akka nomenclature as much as possible. All in all I'm confident as it's lightweight and there is no magic, we simply delegate to Akka's DSL, we're not re-implementing an actor runtime. The main value in this approach IMO is the separation of concerns: it allows lean and expressive description of the domain, while retaining precise wire protocol handling in the infra layer. We also introduced some cool abstractions to manage side-effects and control passivation explicitly. The downside could be that tagless final isn't necessarily easy to bootstrap in a codebase when you're not used to it. But what I found it is that if someone with experience or time to experiment bootstraps the project, it's not so difficult to get the others on-board afterwards since the domain is easy to read and replicating the patterns isn't so difficult. Where it gets a bit fancy is with the usage of natural transformations internally, for which we rely on cats-tagless. That requires annotating traits involved in entity behavior with `@autofunctorK`. This also prevents us to go to scala 3 for now as `cats-tagless` is blocked on some missing macro feature . The project has a functional sample application that you can play with so that you can get a feel of how it looks in practice. If you do, make sure to let me know how it goes and if you have further questions!

Those benchmarks are using a snapshot version of cats-effect. I don't know where that one comes from, but previously they were using a snapshot from https://github.com/typelevel/cats-effect/pull/3332 which had some issues (3.5-6581dc4, 70% performance degradation), which have since been resolved (see that PR for more info and comparative benchmarks).

Recently, CE3 has had similar issues reported across multiple repositories, almost an epidemic of reports!

The one advantage Rust has over Scala is that it detects data races at compile time, and that's a big time saver if you use low level thread synchronization. However, if you write pure FP code with ZIO or Cats Effect that's basically a non-issue anyway.

See also cats-effect and fs2. cats-effect gives you your IO Monad (and IOApp to run it with on supported platforms). fs2 is the ecosystem’s streaming library, which is much more pervasive in functional Scala than in Haskell. For example, http4s and Doobie are both based on fs2.

On the contrary, switching to the functional mindset, with something like Typelevel Scala3 and respective cats and cats-effect fs2 frameworks, helps to rethink a lot of designs and development approaches.

I think "better Haskell on JVM" (in contrast to "worse Haskell") is a good identity for Scala to have. (Please note that this is an intentional hyperbole.)

Of course, there are areas where Haskell is stronger than Scala (hint: modularity, crucial for good Software Engineering, is not one of them). And Scala has its own way of doing things, so just imitating Haskell won't work well.

Examples of this "better Haskell" are https://typelevel.org/cats-effect/ and https://zio.dev/ .

All together, Scala may be a better choice for you if you want to do Pure Functional Programming. And is definitely less risky (runs on JVM, Java libraries interop, IntelliJ, easy debugging, etc...).

None of the other languages you mentioned are viable in this sense (if also you want a powerful type system, which rules out Clojure).

I agree that Rust's identity is pretty clear: a modern language for use cases where only C or C++ could have been used before.

I would use Scala. I like FP and Scala comes with some awesome libraries for concurrent/async programming like Cats Effect or ZIO. Good choice for creating modern style micro-services to be run in the cloud (or even macro-services, Scala has a powerful module system, so it's made to handle large codebases).

https://typelevel.org/cats-effect/

https://zio.dev/

The language, the community and customs are great. You don't have to worry about nulls, things are immutable by default, domain modelling with ADTs and patter matching is pure joy.

The tooling available is from good to great and Scala is big enough that there are good libraries for typical if not vast majority of stuff and Java libs as a reliable fallback.

What took my interest is this (for both JVM and future multithreaded Scala native): https://github.com/typelevel/cats-effect/discussions/3070 Having the same threads poll available IO events and execute callbacks should improve performance greatly

The author is the creator of Monix and implemented the first version of cats-effect. He knows what he is doing.

You want Kernmantle, which quite honestly shouldn't be hard to implement around Cats and cats-effect. In particular, although Kernmantle doesn't require the use of the Arrow typeclass, there happen to be Arrow (actually ArrowChoice) instances for both Function1 from the standard library and Kleisli from Cats itself, given a Monad instance for the Kleilsi's F[_] type parameter. In other words, we should be able to port Kernmantle from Haskell to Scala (with the Typelevel ecosystem) and instantly be able to use pretty much anything else from the Typelevel ecosystem, or wrapped with it, in our workflow graphs. Pure functions, monadic functions, applicative functions, GADTs with hand-written interpreters, any of it. I think this would be eminently worth doing.