Melange
Melange compiles OCaml / Reason to JavaScript
Powered by the versatile OCaml type system, with best-in-class type inference, Melange produces robust JavaScript code.
Sponsored by:
Installation
OPAM
Melange is released to OPAM. Install it with:
$ opam install melangeTemplate
melange-re/melange-opam-template provides a GitHub template repository that can be used as a project starter.
Nix
Melange has good support for Nix:
github:melange-re/melangecan be added as a flake input- the melange flake provides a
melange.overlays.defaultoverlay that adds melange topkgs.ocamlPackages.melange - the
melcbinary can be run withnix run github:melange-re/melange, e.g.nix run github:melange-re/melange/1.0.0 -- --help
Esy
Get Esy on NPM:
npm install -g esyinstalls Esy globally- if
npmis installed,npx esycan be used to run Esy locally
An Esy project starter also exists.
After cloning the template, run esy in the project root.
OCaml version compatibility
Melange >= v1.0 can build projects on OCaml >= 4.13 (including OCaml 5.x).
Editor integration only works on OCaml 4.14, because Melange emits
.cmt artifacts
targeting the OCaml 4.14 binary format.
Editor integration
Melange has first class support in Dune.
ocaml-lsp or
Merlin works as usual. In VSCode, the
VSCode OCaml Platform
extension is recommended.
Community
- There's a
#melangechannel in the ReasonML Discord
FAQ
How does this project relate to other tools?
This project is forked from the ReScript compiler, focused on a deeper integration with the OCaml ecosystem. This allows sharing code between backend and frontend using Dune's virtual libraries.
Melange also introduces a ReScript compatibility layer to maintain compatibility with ReScript syntax - preserving access to ReScript's package ecosystem. It's only recommended to use it with Melange v1, as both ReScript and Melange have diverged significantly since then.
A small write-up with more details on the motivation behind this project can be found in the announcement blog post.
Below is a quick comparison between Melange and other tools:
| Name | Purpose | Dependencies | Notes |
|---|---|---|---|
| Esy | Package manager | Installed with NPM | Obtaining dependencies such as dune or reason |
| OPAM | Package manager | None | Obtaining dependencies such as dune or reason |
| Dune | Build tool | Installed with e.g. esy or opam |
Composable build tool for OCaml; supports composing custom rules to build any project |
| Reason | Syntax | Installed with e.g. esy or opam |
Alternative syntax to OCaml |
| Melange | Compiler that emits Script | Esy / OPAM (to install), Dune (to build) | Supports OCaml, Reason and ReScript syntax; derived from ReScript, focused on deeper integration with OCaml |
| ReScript | The brand around a syntax and a compiler that emits JavaScript | None | Distributed via NPM as prebuilt binaries; previously called BuckleScript |
Contributing
See CONTRIBUTING.md.
Acknowledgments
- Thanks to the ReScript project, its author and maintainer @bobzhang, and its many contributors. Melange is a fork of ReScript, and continues to incorporate patches to ReScript on a regular basis.
- Thanks to the OCaml team, obviously, without such a beautiful yet practical language, this project would not exist.
- Thanks to Bloomberg and Facebook. The ReScript project began at Bloomberg and was published in 2016; without the support of Bloomberg, it would not have happened. ReScript was funded by Facebook since July 2017.
See also Credits.md concerning some individual components of Melange.
Licensing
See COPYING and COPYING.LESSER
See Credits for more details.