cats VS Shapeless

Is that the pure from the Cats library? https://github.com/typelevel/cats/blob/main/alleycats-core/src/main/scala/alleycats/Pure.scala

Cats is a library which provides abstractions for functional programming in the Scala programming language. The name is a playful shortening of the word category. https://typelevel.org/cats/

Obviamente que teoria de categorias https://typelevel.org/cats/

Akka HTTP, Cats, Quill, ninny, Monix Observable, mill.

Have a look at Profunctor. Specifically at rmap

Example of how it makes life worse

But not so long ago he was doing releases for Cats even though he was officially out of TL. And when he had some outburst I saw more support from TL-related people than scolding. Unless he really went over the top (like the time he ranted some guy on GitHub) there was no action.

Scala really shines for more advanced FP (compared to Java, Kotlin, C#, Swift etc.) so I would suggest learning more about that. For example look into ZIO or Cats (or Cats Effect). You can find many tutorial videos on YouTube for these libraries.

I know that libraries like Scodec and shapeless were rewritten practically from scratch for Scala 3, taking advantage of the next syntax and internals, as well as protoquill - a Scala 3 implementation of Quill.

please show me something like this: https://akka.io/ or this: https://zio.dev/ or this: https://github.com/milessabin/shapeless

That largely depends on the type system. Languages like Haskell and Scala which have much more powerful type systems than C/Java/Go/etc absolutely do allow you to do those sorts of things. It is a bit harder to wrap your head around to be sure and there are some rough edges, but once you get the hang of it you can get the benefits of static typing with the flexibility of dynamic typing. See https://github.com/milessabin/shapeless or a project that I've been working on a lot lately https://github.com/zio/zio-schema.

Just use cats and use the apply syntax .mapN for this. Seriously. There isn't a way to do it without generating source code that I can see in the api. Scala 3's HList Tuples aren't like Shapeless 2's HLists and I can't figure out a way in the api to reduce the tuple members down from (A, B, C, D) into an E, generically, yet with Scala 3 poly functions, unlike what you could do in Shapeless 2 with HList

Scala has sparked a huge ecosystem of very high quality libraries (Cats, Scalaz, shapeless, to name but a few). I think a major reason for this is that Scala attracts developers who value the advantages of the JVM, but are fed up with the limitations of the Java programming language and understand the benefits of an expressive type system and functional programming.

I also investigated shapeless3 macroses: https://github.com/milessabin/shapeless/tree/shapeless-3/modules, but they are more about derivation than reflection. And probably that is all I found.

Well, that is sometimes possible, depending on a structure of Foo. If you have a List, for instance, you can iterate every element, and if every element is A, then it's safe to cast a list to List[A]. In fact, shapeless provides exactly that, in form of Typeable[List[A]], in a more generic form. I suppose shapeless also can derive a typeable instance for you, but I haven't dug into scala 3 version of it.

I'm not sure where is the line between extensive and basic knowledge. Here is my more detailed exposure:

In commercial context:

* Of strongly typed ones only Scala (with [shapeless]). Can reluctantly throw in Kotlin as well for it's amazing structured concurrency.

In non-commercial context:

* Went through a few chapters of [Software Foundations] doing Coq proofs.

* Worked through most of the [Types and Programming Languages] (writing typecheckers in Ocaml)

* 3 services in Haskell (1 on Scotty, 2 on Servant). Loved persistent+esqueleto for the ORM layer, disliked Opaleye.

* 2 projects in PureScript (1 with Halogen, 1 with React bindings).

* 1 project in ReasonML (Ocaml).

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> I am afraid there is no way back for me

I see where you are coming from. In my case I can alternate between "I want all invariants properly expressed and checked" and "I just want to ship that barely-working piece of junk and iterate on it". I learned to adjust depending on organization needs. IMO, for many orgs, especially startups/scaleups, the latter is often the more fitting way. With that in mind, I'm willing to trade the guiding hand of great type systems for other productivity aspects (amazing runtime and cohesive web framework in Elixir's case).

[shapeless]: https://github.com/milessabin/shapeless

[Software Foundations]: https://softwarefoundations.cis.upenn.edu/

[Types and Programming Languages]: https://www.cis.upenn.edu/~bcpierce/tapl/