Installing OCaml

This guide will walk you through a minimum installation of OCaml. That includes installing a package manager and the compiler itself. We'll also install some platform tools like a build system, support for your editor, and a few other important ones.

On this page, you'll find installation instructions for Linux, macOS, and *BSD for recent OCaml versions. For Docker, Linux instructions apply, except when setting up opam. For Windows, we recommend using WSL but also provide instructions for installing OCaml 4.14.0 via the Diskuv OCaml Installer. If you are setting up OCaml on Windows and are unsure which installation method to use, you might be interested in reading OCaml on Windows first.

Note: You'll be installing OCaml and its tools through a command line interface (CLI), or shell

Installation on Unix and macOS

OCaml has an official package manager, opam, which allows users to download and install OCaml tools and libraries. Opam also makes it practical to deal with different projects which require different versions of OCaml.

Opam also installs the OCaml compiler. Alternatives exist, but opam is the best way to install OCaml. Although OCaml is available as a package in most Linux distributions, it is often outdated.

1. Install opam

To install opam, you can use your system package manager or download the binary distribution. The details are available in these links, but for convenience, we use package distributions:

For macOS

If you're installing with Homebrew:

$ brew install opam

Or if you're using MacPorts:

$ port install opam

Note: While it's rather straightforward to install opam using macOS, it's possible you'll run into problems later with Homebrew because it has changed the way it installs. The executable files cannot be found in ARM64, the M1 processor used in newer Macs. Addressing this can be a rather complicated procedure, so we've made a short ARM64 Fix doc explaining this so as not to derail this installation guide.

For Linux

It's preferable to install opam with your system's package manager on Linux. On the opam site, find details of all installation methods. All supported Linux distributions package versions of opam above 2.0. If you are using an unsupported Linux distribution, please either download a precompiled binary or build opam from sources.

If you are installing in Debian or Ubuntu:

$ apt install opam

If you are installing in Arch Linux:

$ pacman -S opam

Binary Distribution

If you want the latest release of opam, install it through the binary distribution. For that, you'll need to install the following system packages first: gcc, build-essential, curl, bubblewrap, and unzip. Note that they might have different names depending on your operating system or distribution.

The following command will install the latest version of opam that applies to your system:

$ bash -c "sh <(curl -fsSL https://raw.githubusercontent.com/ocaml/opam/master/shell/install.sh)"

2. Initialise opam on Unix

After you install opam, you'll need to initialise it. To do so, run the following command. This might take a few minutes to complete.

$ opam init -y

Note: In case you are running opam init inside a Docker container, you will need to disable sandboxing, which is done by running opam init --disable-sandboxing -y. This is necessary, unless you run a privileged Docker container.

Make sure you follow the instructions provided at the end of the output of opam init to complete the initialisation. Typically, this is:

$ eval $(opam env)

Opam is now installed and configured! You can now move to installing the OCaml Platform development tools in the section below.

Note: opam can manage something called switches. This is key when switching between several OCaml projects. However, in this “getting started” series of tutorials, switches are not needed. If interested, you can read an introduction to opam switches here.

Installation on Windows

In this section, we'll describe using the Diskuv OCaml (DKML) Windows installer. Expect to see another officially-supported Windows installation provided directly by opam in the coming months; it will be compatible with your DKML installation.

Note that only OCaml version 4.14.0 is available via Diskuv OCaml.

Advanced Users: If you are familiar with Cygwin or WSL2, there are other installation methods described on the OCaml on Windows page.

1. Use the DKML Installer

Before using the DKML installer, briefly review the following:

• Do not use the installer if you have a space in your username (ex. C:\Users\Jane Smith).

• You need to stay at your computer and press "Yes" for any Windows security popups. After the DKML installer finishes installing two programs (Visual Studio Installer and Git for Windows), you can leave your computer for the remaining one and a half (1.5) hours.

• First time installations may get a notification printed in red. If you see it, reboot your computer and then restart your installation so that Visual Studio Installer can complete. The notification looks like:

  - FATAL [118acf2a]. The machine needs rebooting.
  - ...
  - >>  The machine needs rebooting. <<<
  -         ...
  -         FATAL [5f927a8b].
  -         A transient failure occurred.
  -         ...
  -         >>  A transient failure occurred. <<<
  

• You may be asked to accept a certificate from Open Source Developer, Gerardo Grignoli for the gsudo executable that was issued by Certum Code Signing CA SHA2.

Now, download and run:

• OCaml 4.14.0 with Git and Visual Studio compiler: setup-diskuv-ocaml-windows_x86_64-1.2.0.exe

2. Create an opam Switch

This step is necessary only if you want to create a new independent environment. dkml init already set up a default opam switch for you to work in.

You can create a new switch with the dkml init command. The only compiler version available is 4.14.0. Use PowerShell or a Command Prompt to create a directory anywhere and then create a switch:

C:\Users\frank> mkdir someproject
C:\Users\frank> cd someproject
C:\Users\frank\someproject> dkml init

# PowerShell only
C:\Users\frank\someproject> (& opam env) -split '\r?\n' | ForEach-Object { Invoke-Expression $_ }

# Command Prompt only
C:\Users\frank\someproject> for /f "tokens=*" %i in ('opam env') do @%i

To learn more about Diskuv OCaml, see the official Diskuv OCaml documentation.

Install Platform Tools

Now that we've successfully installed the OCaml compiler and the opam package manager, let's install some of the OCaml Platform tools, which you'll need to get the full developer experience in OCaml:

• UTop, a modern interactive toplevel (REPL: Read-Eval-Print Loop)
• Dune, a fast and full-featured build system
• ocaml-lsp-server implements the Language Server Protocol to enable editor support for OCaml, e.g., in VS Code, Vim, or Emacs. Under the hood, it uses Merlin.
• odoc to generate documentation from OCaml code
• OCamlFormat to automatically format OCaml code

All these tools can be installed using a single command:

$ opam install dune ocaml-lsp-server odoc ocamlformat utop

You're now all set and ready to start hacking.

Check Installation

To check that everything is working properly, you can start the UTop toplevel:

$ utop
────────┬─────────────────────────────────────────────────────────────┬─────────
        │ Welcome to utop version 2.13.1 (using OCaml version 5.1.0)! │
        └─────────────────────────────────────────────────────────────┘

Type #utop_help for help about using utop.

─( 00:00:00 )─< command 0 >──────────────────────────────────────{ counter: 0 }─
utop #

You're now in an OCaml toplevel, and you can start typing OCaml expressions. For instance, try typing 21 * 2;; at the # prompt, then hit Enter. You'll see the following:

# 21 * 2;;
- : int = 42

Congratulations! You've installed OCaml! 🎉

Join the Community

Make sure you join the OCaml community. You'll find many community members on Discuss or Discord. These are great places to ask for help if you have any issues.