melange VS lwt

Hey HN, at Ahrefs we have been working on an online book that hopefully helps React developers get up and running with Melange, an OCaml to JavaScript compiler. You can read more about Melange here: https://melange.re/.

There are still a few chapters that we'd like to add before considering it "complete", but it might be already helpful for some folks out there, that's why we decided to publish it early.

The book uses Reason syntax to implement React components using ReasonReact components. You can read more about both in:

https://reasonml.github.io/

In my previous post on trying to use the NextJS App Router and Reason I described some of the problems and limitations of their compatibility with one another. With the release of Melange 2 I decided to see if the new features of Melange 2 could help to increase the compatibility of Reason and the NextJS App Router. I have also documented some of the things learnt after trying Melange (v1) with Astro and Remix.

So it's Reason, not ReasonML which the umbrella project's name, and Rescript is a imcompatible syntax split from the Bucklescript team (that previously transpiled Reason to JS). Bucklescript's new name is... Rescript.

But not everyone agrees with the split and work is being done on Melange to replace Bucklescript : https://github.com/melange-re/melange

Ultimately JsOfOcaml can directly transpile Ocaml to JS.

In reality, most folks that developed BuckleScript frontends with ReasonML switched to ReScript syntax and are happy with it. Some felt more friction because of their reliance on PPXes or FP-heavy libraries (like Relude) and those people tend to use the Melange fork of BuckleScript or they switched to js_of_ocaml.

There is a fork of ReScript that supports ReasonML syntax and with the goal of maintaining Ocaml compatibility: https://github.com/melange-re/melange.

There's also a fork of BuckleScript/ReScript called Melange that guts its build system so that instead of using ninja, it works with more standard tools for the ecosystem, specifically dune and esy. In doing so they managed to also finally get the compiler off of OCaml 4.06: now it can use a newer OCaml compiler and take advantage of four years worth of language and compiler improvements.

For OCaml and ReasonML your options are js_of_ocaml (mentioned here in ReasonML docs) or a fairly new fork of BuckleScript called melange. They differ in implementation and output, with JSOO taking intermediate bytecode generated by ocamlc and turning it into unreadable JS, vs Melange being a patched compiler that builds more human-readable JS.

Here is link number 1 - Previous text "Lwt"

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)