coproduto / melange

A mixture of tooling combined to produce JavaScript from OCaml & Reason

Melange

A mixture of tooling combined to produce JS from OCaml / Reason.

This project is a fork of the ReScript compiler with a focus on compatibility with the wider OCaml ecosystem. A small write-up with more details on the motivation behind this project can be found in this blog post.

Installation

This project is currently unreleased. Currently, the most straightforward way to use it is via Esy.

1. Make sure you have Esy installed (npm install -g esy should cover most workflows)
2. Use an esy.json file like the following:

{
  "name": "melange-project",
  "dependencies": {
    "ocaml": "4.12.x",
    "melange": "melange-re/melange",
    "@opam/ocaml-lsp-server": "*"
  },
  "esy": {
    "buildsInSource": "unsafe",
    "build": ["ln -sfn #{melange.install} node_modules/bs-platform"]
  },
  "installConfig": {
    "pnp": false
  }
}

3. Run npm install (or yarn) followed by just esy and after they finish installing and building, you should be able to use bsb commands via esy esy bsb -make-world

4. Reach out on the ReasonML Discord if you can't figure it out!

FAQ

How does this project relate to other tools?

Name	Purpose	Dependencies	Notes
Esy	Package manager	Installed with NPM	Obtaining dependencies (e.g. dune or reason)
Dune	Build tool	Installed with esy	Well-known OCaml build tool; supports custom rules that can be composed to build anything
Reason	Syntax	Installed with esy	a library that implements an alternative syntax to OCaml
Melange	Compiler that emits JavaScript	Esy (to install), Dune (to build), Reason (used as a library)	Supports OCaml, Reason and ReScript syntaxes; derived from ReScript, focused on compatibility with the wider OCaml ecosystem
ReScript	The brand around a syntax and a compiler that emits JavaScript	None	Distributed via NPM as prebuilt binaries; previously called BuckleScript

Can I use ReScript syntax?

Yes! ReScript syntax is supported, but beware that it's stuck on an ancient OCaml version (4.06, released in 2018), and it won't have as many features as the OCaml or Reason syntaxes (e.g. letop binding operators, generalized module open expressions, or local substitutions in signatures).

Where has the refmt flag gone?

Upstream removed the refmt flag, which used to allow configuring the path to a custom Reason binary. This was a welcome change for this repo too, so we cherry-picked it. The rationale: this project uses Reason as a library, so you can simply depend on the Reason version that you'd like in the usual way, via your preferred package manager.

Contributing

See CONTRIBUTING.md.

Acknowledgments

See Credits.md.

Licensing

See COPYING and COPYING.LESSER

See Credits for more details.