others say typestates, but Scala and Haskell have had IndexedStateT for the purpose of typelevel-state-machinery and it works really well with (somewhat lesser) boilerplate and semantics + FP. To me, it's particularly useful for anything resembling a protocol.

Signal based processing is Observables/reactive streams, which provide a sane interface to use.

This is (one of) the problem with new languages: library ecosystem access. It's why Scala/Clojure/Kotlin is one camp of languages and Zig/Rust is in another - both Java and C have a ton of great libraries written in them, with ones that add signals-first approaches via libraries.