lwt

> Also, didn't OCaml have weak support for concurrency? Has that changed recently? OCaml has had Lwt for concurrent IO for long enough that it is now being deprecated in favor of Eio[1]: https://github.com/ocsigen/lwt [1] https://github.com/ocaml-multicore/eio

> It turns out Lwt gained support for let* sytax only in April 2020. I don't understand your point. Monadic let can be done with ppx_let (created in 2016), and even before that there was the older syntax where you write `lwt` instead of `let`. https://github.com/ocsigen/lwt/commit/d28204984646042676570d...

I have to admit I don't know much about ReScript and only have very basic exposure to OCAML, here is how you do await in it: https://github.com/ocsigen/lwt The `let* in` is a generic syntax for monads, it doesn't need a special one just for promise. This was in fact a debate back when async/await was in consideration for ECMAScript, but special syntax is hip so now we have `async/await` for Promise, `.?` for optionals and `flatMap` for arrays, basically the same thing.

Dream doesn't have much of a system call dependency footprint itself. It's basically just a convention for plugging request -> response functions into a web server. Some of its native dependencies will have to be replaced by Node equivalents. Soon after that, it would be portable to Node. There is already work underway to port Dream to Mirage, to run in unikernels: https://github.com/aantron/dream/pull/22 Lwt, Dream's promise library, is itself getting ported to run on top of libuv: https://github.com/ocsigen/lwt/issues/813 libuv is, of course, the I/O library that powers Node, so it might be practical to run Dream as a native node module very soon after doing this. (As an aside, I'm supposed to work on that libuv project, but instead I've been working on Dream :P)

Lwt [1] based web frameworks can be used on MirageOS if they provide an interface that allows someone to swap out the unix dependent pieces. One such framework is Opium [2], that provides most of its features in a unix independent code library `opium_kernel`. Its fairly straightforward to run an opium app on mirage. This example needs to be updated to the newest apis in the released version of Opium but this can provide some hints about how to run an opium app on mirage: https://github.com/anuragsoni/ocaml-opium-unikernel. If a lower level web toolkit is sufficient then ocaml's cohttp [3] library has been available on mirage for quite some time now. [1] https://github.com/ocsigen/lwt/ [2] https://github.com/rgrinberg/opium [3] https://github.com/mirage/ocaml-cohttp/

OCaml has really good libraries for concurrency–e.g. check out https://github.com/ocsigen/lwt There is a GIL (like Node/Python) that means only one thread runs at any moment in time, but multiple threads can still be started. Lwt's Promise abstraction is very similar to Node's, except it's at the library level, not at the runtime level.

OCaml has the equivalent of computation expressions since 2018: http://jobjo.github.io/2019/04/24/ocaml-has-some-new-shiny-s... It definitely has async: https://github.com/ocsigen/lwt It doesn't have units of measure but due to strong abstraction properties of modules we can fairly easily roll abstract types. It doesn't have type providers but it does have plugins for type-directed derivation of JSON codecs, equality, comparison, printing, etc. > The long slog towards multicore for the OCaml community has been kind of embarrassing IMHO it's been refreshing to see the pushback against 'multicore at all costs'. There is a benefit to taking the time to do things the right way. OCaml is a 30+ year-old language with an even longer ML heritage. It's going to be around for a while; it doesn't need to rush into a sub-par implementation. Meanwhile

>Ocaml parallelism/concurrency story was not that good OCaml concurrency is great, and Lwt [1] would be exactly what systemd need: run daemon and poll the answer concurrently. Ada, C++ and D would have been another great choices. [1] https://github.com/ocsigen/lwt

There are several libraries for concurrency: - Lwt: https://github.com/ocsigen/lwt - Async https://realworldocaml.org/v1/en/html/concurrent-programming... However pulling these over more than 1 core is still a problem. OCaml 4.05.0 should have infrastructure for that (although OCaml multicore has been somewhat a `duke-nukem forever` story)