I don't see why it would be particularly difficult beyond not already having a lot of IO libraries (like Kafka connectors or whatever). Pure functional programming in Scala with IO monads is quite pleasant.

I did write small programs myself, but mostly with Claude Code. It was very pleasant to work in it with Claude Code. Implemented a shell and 40 of coreutils. Did not really get very far with proving properties of them, but had working programs. Reading Lean4 is pretty nice. Nicer to read than OCaml, almost as nice as Haskell.