[yawaramin]

> last I heard Ocaml had an issue with being single threaded.

OCaml is single-threaded, yes, but in practice that's not a big deal. There's a great concurrency library (Lwt) and the recently-added monadic (and applicative) bind syntax makes it look almost like sequential code. And if you really need a separate OS thread, there are ways to do that :-)

Last I checked, Swift still does concurrency mostly with Node-style callbacks.