genType VS melange

I don't really use ts-belt to be certain, but by looking at the source, it seems that it's using genType, which can generate TS types from ReScript values, and that makes interop work really well.

They discuss this in their docs.

https://rescript-lang.org/docs/manual/latest/introduction#di...

Seems like a type system for Javascript, built with a differing set of opinions than Typescript.

Looks like they also offer some form of TS interop:

https://rescript-lang.org/docs/gentype/latest/introduction

TS Belt has been built with ReScript (and its Belt stdlib). ReScript generates highly performant JavaScript code, and with genType it also automatically generates TypeScript types. Moreover, I've added a few codemods to the building process to provide even more code optimizations and cleaner TypeScript signatures.

To interoperate with TypeScript with proper type information you’ll use third-party genType. Add it as a devDependency and annotate the module export you want to generate with @genType (in previous versions you’d surround annotations with square brackets).

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.

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.

TL;DR: Reason is, and always has been, independent of ReScript (formerly BuckleScript) and is still actively maintained. If you want to use Reason or OCaml to make native code you can. If you want to compile JS from OCaml or Reason you also still can, but you'll want to use either js_of_ocaml or a BuckleScript fork named Melange that was made in response to the BuckleScript/ReScript people's shenanigans. And if you only care about JS-like syntax and JS output, you can use ReScript.

While banging my head against the wall trying to understand the Dune build system used with OCaml and the Melange project I came across these great simple videos by @TheEduardoRFS.