purefunctor / learning-melange

melange-opam-template

A simple project template using Melange with opam.

If you are looking for a template with esy, check melange-esy-template.

Quick Start

npm run init

# In separate terminals:
npm run watch
npm run serve

React

React support is provided by reason-react. The entry point of the sample React app is src/ReactApp.re.

Commands

All the build commands are defined in the scripts field of package.json. This is completely optional, and other tools like make could be used.

You can see all available commands by running npm run. There are explanations on each command in the scriptsComments field of the package.json file. Here are a few of the most useful ones:

• npm run init: set up opam local switch and download OCaml, Melange and JavaScript dependencies
• npm run install-opam-npm: install OCaml, Melange and JavaScript dependencies
• npm run watch: watch for the filesystem and have Melange rebuild on every change
• npm run serve: serve the application with a local HTTP server

JavaScript output

Since Melange compiles source files into JavaScript files, it can be used for projects on any JavaScript platform - not just the browser.

The template includes two melange.emit stanza for two separate apps. This stanza tells Dune to generate JavaScript files using Melange, and specifies in which folder the JavaScript files should be placed, by leveraging the target field:

• The React app JavaScript files will be placed in _build/default/src/output/*.
• The NodeJS app JavaScript files will be placed in _build/default/src/node/*.

So for example, src/Hello.ml (using OCaml syntax) can be run with node:

node _build/default/src/node/src/Hello.js

Similarly, _build/default/src/output/src/ReactApp.js can be passed as entry to a bundler like Webpack:

webpack --mode production --entry ./_build/default/src/output/src/ReactApp.js