It's not a problem in practice. OCaml has great concurrency support, which is what you need for applications that do IO, like servers. For CPU-bound application

It's not a problem in practice. OCaml has great concurrency support, which is what you need for applications that do IO, like servers. For CPU-bound applications like number-crunching, you take advantage of existing bindings to C or Fortran libraries. For a thorough discussion, see https://discuss.ocaml.org/t/7-years-after-is-ocaml-suitable-to-write-networking-servers/639 https://discuss.ocaml.org/t/7-years-after-is-ocaml-suitable-... Also remember that with BuckleScript, you're deploying to JavaScript, which is single-threaded by definition. OCaml's runtime model (modular, single-threaded, strictly-evaluated) maps beautifully to JavaScript.