Install Esy

We recommend using Esy as your package manager in native Reason projects. Esy is a native, npm-esque package manager with built-in dependency isolation and fast, incremental builds.

The easiest way to install Esy is with npm:

npm install -g esy

Create a fresh project

First, clone a copy of the esy-ocaml/hello-reason project:

git clone https://github.com/esy-ocaml/hello-reason.git
cd hello-reason

Then, run esy to install relevant dependencies and build your app:

esy

Run your first app

Run

esy x Hello.exe # runs Hello.exe

If everything went as expected, you should see the following output:

Running Test Program:
Hello, World!

Believe it or not, you're already using two Reason Native packages!

Pastel

Open up lib/Util.re and you might see something interesting:

/* lib/Util.re */
let hello = () =>
  Pastel.(
    <Pastel>
      <Pastel color=Red> "Hello" </Pastel>
      ", "
      <Pastel color=Green> "World" </Pastel>
      "!"
    </Pastel>
  );

Pastel is a React-like text formatting library for the terminal; one of its core features is the ability to format console text with ANSI Escape Codes.

Let's try making Hello yellow:

/* lib/Util.re */
/* ... */
    <Pastel>
      <Pastel color=Yellow> "Hello" </Pastel>
      ", "
/* ... */

Run esy build to rebuild your app, and run esy x Hello.exe to see your changes:

Running Test Program:
Hello, World!

Console

Similarly, let's take a look at bin/Hello.re:

/* bin/Hello.re */
Console.log("Running Test Program:");
let () = print_endline(Lib.Util.hello());

The Console package allows you to log nearly anything without having to define any printers. Let's try logging a nested tuple:

/* bin/Hello.re */
Console.log((1, (2, 3)));
let () = print_endline(Lib.Util.hello());

Running esy build && esy x Hello.exe should produce the following:

{1, {2, 3}}
Hello, World!