Reason Scripts provides a JS-like development environment for developing web apps with the Reason programming language and React. It bootstraps an environment to automatically compile all Reason code to JS, provide features like reloading and bundling, and seamlessly use JS code from Reason.

Getting Started

Using Yarn

Note that using yarn create requires Yarn 0.25 or later

To create a new app using Reason and React, run:

$ npm install -g bs-platform
$ yarn create react-app <app-name> -- --scripts-version reason-relay-scripts
$ cd <app-name>
$ yarn start

Using npm

$ npm install -g bs-platform create-react-app
$ create-react-app <app-name> --scripts-version reason-relay-scripts
$ cd <app-name>
$ npm start

Directory Layout

Creating a new app makes an <app-name> directory with the following layout:

<app-name>/
  README.md
  node_modules/
  package.json
  bsconfig.json
  .gitignore
  public/
    favicon.ico
    index.html
  src/
    index.re
    index.css
    app.re
    app.css
    logo.svg

Features

Everything from Create React App

• Highly-optimized build configuration
• Pre-configured test runner
• Friendly developer environment
• "eject" Webpack config
• Environment variable configuration
• Automatic PWA configuration
• Low configuration builds

Reason Entrypoint

The entry point to the app is src/index.re. From the start your new app will be based on Reason, but can seamlessly interop with existing JS files and projects!

Automatic Compilation of Reason/Ocaml files

Any Reason/Ocaml file will be automatically compiled to a JS file. For example, a file called math_fns.re can be required by a JS file:

import { add } from './math_fns.re'

const sum = add(1, 4)

Jest Integration

Reason Scripts will automatically configure a Jest environment to test Reason code. Any code found in a file ending with _test.re, _test.ml or test.js will be considered a test and run with Jest. From these files, the normal Jest API can be used interacting with any other modules defined in your app. For example:

/* math_fns.re */

let add x y => x + y;

/* math_fns_test.re */

open Jest;

test "addition" (fun () => {
  let num_1 = 10;
  let num_2 = 12;

  expect (Math_fns.add num_1 num_2) |> toBe 22;
});

Or if you prefer writing your tests in JavaScript, just don't forget to import the tested module:

/* maths_fns.test.js */

import Math_fns from './math_fns.re'

test('addition', () => {
  const num1 = 10
  const num2 = 12

  expect(Math_fns.add(num1, num2)).toBe(22)
})

For more documentation on the Jest API, see bs-jest

Importing non-Reason files

You can require CSS files with:

[%bs.raw {|require('./App.css')|}];

or any other kind of file (like SVG's) with:

let logo : string = [%bs.raw {|require('./logo.svg')|}];

Help, Tips, and Tricks

Editor support is provided by Merlin. To generate a .merlin file, run the app with npm start or yarn start.

See our full editor integration guide here: https://reasonml.github.io/guide/editor-tools/editors-plugins

Use FORCE_COLOR=true react-scripts start | cat - as your start command instead

Checkout our fancy website: https://reasonml.github.io/!

We also have a very active Discord to come talk about Reason, and ask for help: https://discordapp.com/invite/reasonml