Great that you want to use Reason with React Native! To get everything running are just a couple of steps. Let's assume that you already have a React Native project. Otherwise follow the React Native instructions until you have your app running.

1. Install Bucklescript (the Reason -> JS compiler), Reason-React and bs-react-native:

# substitute yarn with npm if you prefer
yarn add bs-platform reason-react bs-react-native

2. Create a re folder (there will be your Reason code)
3. Create a bsconfig.json with the following content file in your project root

{
    "name": "my-awesome-app",
    "reason": {
        "react-jsx": 2
    },
    "bsc-flags": ["-bs-super-errors"],
    "bs-dependencies": ["bs-react-native", "reason-react"],
    "sources": [{
        "dir": "re"
    }],
    "refmt": 3
}

4. You are nearly done, the last configuration before we get to the fun stuff. In your package.json add to the "scripts" section two scripts:

"scripts": {
  ...
  "build": "bsb -make-world -clean-world",
  "watch": "bsb -make-world -clean-world -w"
}

5. Now you can build all your (so far nonexsisting) Reason in two modes:

• yarn build performs a single build
• yarn watch enters the watch mode

6. Now we come to the fun stuff! Create a new file re/app.re and make it look like this:

open BsReactNative;

let app = () =>
  <View style=Style.(style([flex(1.), justifyContent(Center), alignItems(Center)]))>
    <Text value="Reason is awesome!" />
  </View>;

and start the watcher with yarn run watch if you haven't done it yet.

7. We are nearly done! We now have to adopt the index.ios.js / index.android.js to look like this

import { app } from "./lib/js/re/app.js";
import React from "react";
import {
  AppRegistry
} from 'react-native';

AppRegistry.registerComponent('MyAwesomeProject', () => app);

Note: Make sure that the first argument to AppRegistry.registerComponent is your correct project name.

If you are using react-native-scripts, then you will need to modify App.js to be like this

import { app } from "./lib/js/re/app.js";

export default app;

8. Now go to a new tab and start your app with react-native run-ios or react-native run-android.

9. Great you are all set up! Check the source of bs-react-native to find out more about the implemented APIs and Components. If you get stuck just ask on our Discord Server! Happy Hacking!

Here are some more things which will be probably useful for you:

• Reason-React Documentation
• Bucklescript Manual

Yes! Check out the Seattle JS Conf App for a real world App written with Reason.

There are some components and APIs missing. You can find an overview of the implemented components and APIs here. Contributions of Components and APIs are very welcome! The bindings are targeted to React Native 0.46+.

Since we have a proper type system we can make styles typesafe! Therefore styles are a little bit different declared than in JavaScript:

open BsReactNative;

/* inline styles */
<View
  style=(
    Style.style([
      Style.flexDirection(Column),
      Style.backgroundColor("#6698FF"),
      Style.marginTop(Pt(5.))
    ])
  )
/>;

/* inline styles with a local open */
<View style=Style.(style([flexDirection(Column), backgroundColor("#6698FF"), marginTop(Pt(5.))])) />;

/* StyleSheets with a local open */
let styles =
  StyleSheet.create(
    Style.({"wrapper": style([flexDirection(Column), backgroundColor("#6698FF"), marginTop(Pt(5.))])})
  );

<View style=styles##wrapper />;

open BsReactNative;

[...]
type state = {animatedValue: Animated.Value.t};
let component = ReasonReact.reducerComponent("Example");

initialState: () => {animatedValue: Animated.Value.create((-100.))},

/* Start animation in method */
Animated.CompositeAnimation.start(
  Animated.Timing.animate(
    ~value=state.animatedValue,
    ~toValue=`raw(0.),
    ()
  ),
  ()
);
[...]

/* Styles with an animated value */

<Animated.View
  style=Style.(style([flexDirection(Column), backgroundColor("#6698FF"), top(Animated(state.animatedValue))]))
  )
/>;

Currently BuckleScript can generate import * as ReactNative from 'react-native', which breaks create-react-native-app. To get around this you can force BuckleScript to generate CommonJS modules instead of ES Modules using:

/* bsconfig.json */
{
  /* ... */
  "package-specs": [
    {
      "module": "commonjs"
    }
  ]
}