ZIO VS Vert.x

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.

> It's a weakness of functional programming, not the language.

I would strongly object this.

Have you seen ZIO?

https://zio.dev/

But overall, I'm happier with Scala. It has not one, but two lively FP communities. I recommend that you pick one of them: ZIO or TypeLevel (Cats Effect, fs2, http4s, ...). To some extent, you can mix TypeLevel libraries in ZIO projects.

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.

I actually think Scala is in the best position it's ever been.

There is a commitment to making the language simpler, easier and cleaner.

On the backend, ZIO [1] is the best concurrency library on any platform. On the frontend you have really interesting Scala.js projects like Laminar [2].

The biggest issue really is the tooling. SBT is simply awful.

[1] https://zio.dev

Scala? With some help from additional libs such as Zio (https://zio.dev/) it allows you to write production quality programs like you would in Haskell on top of the JVM quite quickly...

Eclipse Vert.x - Add amazing Async to any Java stack

Vert.X example: https://github.com/eclipse-vertx/vert.x/blob/master/src/main/java/examples/EventBusExamples.java#L106 (couldn't even find docs)

In fact, it builds on top of proven standards such as Eclipse MicroProfile or frameworks such as Vert.x or JAX‑RS.

If you’ve used NodeJS & ExpessJS, in Java world, Vert.x, Helidon and Javalin should be familiar.

Vert.x is a toolkit for writing asynchronous and reactive applications on the JVM. The Vert.x ecosystem has high-quality libraries providing support for web services, database drivers, authentication, and more.

If FP is scaring you off then maybe consider Vertx.

For performance and good support for asynchronous programming, I think the best option is Vert.x. It's the fastest Java option by far according to TechEmpower ranking.