Multicore OCaml comes with native support for concurrency through algebraic effect handlers which generalize common control flow abstractions such as exceptions, async/await, generators, non-determinism, backtracking. All of these mechanisms can be implemented directly in OCaml. [0] introduces the model, [1,2] has examples, and for further reading see [3].

[0]: http://kcsrk.info/ocaml/multicore/2015/05/20/effects-multico...

[1]: http://kcsrk.info/ocaml/multicore/effects/2015/05/27/more-ef...

[2]: https://github.com/kayceesrk/effects-examples

[3]: See recent pubs here http://kcsrk.info/.