OCaml Setup

Installation, Build Tools, and IDEs

Windows 10

If you are using Windows 10, I suggest to install Ubuntu via the Windows Subsystem for Linux, following the same instructions as for setting up the Scala tool chain. Then follow the instructions for Linux below.

Linux and MacOS

Most Linux distributions as well as homebrew on Mac OS come with precompiled packages for OCaml. There is also a Windows installer. However, I suggest to install OCaml using opam, which is a package manager for OCaml that makes it easy to install many other useful tools for developing OCaml programs.

Installing opam on MacOS

Make sure that you have XCode installed; see Scala setup)

Then install opam by executing

brew install ocaml
brew install opam

Installing opam on Ubuntu [Window subsystem for Linux]:

If you are using Ubuntu 18.04 on WSL, it uses an older version of opam by default. To install the latest opam version, first add the latest ppa containing the stable version of opam:

sudo add-apt-repository ppa:avsm/ppa
sudo apt update

After this (or if you are using a newer Ubuntu version), install the latest stable version of opam:

sudo apt install opam

Once you have opam installed, you can install and set up the most recent version of the OCaml language and compiler by first executing the following commands in a terminal:

opam init --disable-sandboxing

then continue with the instructions for all platforms below following the steps after opam init has been executed.

Installing opam on Ubuntu [native]

To install opam execute:

sudo apt install opam

Installing opam on other operating systems

Please read the installation instructions of opam if you have another operating system.

All platforms (after opam is installed)

Once you have opam installed, you can install and set up the most recent version of the OCaml language and compiler by executing the following commands in a terminal:

opam init

If you see a warning related to a missing m4 dependency, then install m4 before you proceed using

brew install m4

respectively

sudo apt install m4

Then you can create a 'switch' for the most recent OCaml release by executing

opam switch create 4.14.0
eval `opam config env`

The installation will take a while since opam will download the sources of the OCaml compiler and compile it from scratch. Follow the instructions provided by the output of these commands to set up your environment variables. Once, the installation has completed, you can execute ocaml, which starts an OCaml REPL session:

        OCaml version 4.14.0

#

You can also install an alternative OCaml REPL called utop that provides additional functionality. To install utop execute:

opam install -y utop

One you have started a REPL session, you can use it to evaluate OCAML expressions. In the REPL, you need to terminate each expression by a double semicolon ;; and then press Enter:

# 3 + 1 ;;
- : int = 4

# let x = 3 + 1 ;;
val x : int = 4

# #quit ;;

These double semicolons are only needed in the REPL but not in source code files that are processed by the compiler.

In addition to the OCaml compiler and runtime, you also want to install the OCaml library manager ocamlfind, the OCaml build tool Dune, and the OCaml unit testing framework OUnit. You can do this via opam:

opam install -y ocamlfind
opam install -y dune
opam install -y ounit2

These tools provide similar functionality as sbt and scalatest do for Scala.

Several IDEs have plugins for OCaml. I suggest to use Merlin which provides IDE support for OCaml in common editors like Emacs and Vim. Merlin can also be integrated into other editors and IDEs via third-party plugins, including Atom, Sublime, and Visual Studio Code. You can install Merlin via opam by executing:

opam install -y merlin

See the installation instructions on Merlin's project website for further details on how to configure various editors.

If you want a modern IDE, Visual Studio Code works well with OCaml in my experience. Follow the installation instructions for your operating system/distribution. For supporting OCaml, you should install the OCaml and Reason IDE extension. You can do this from within Visual Studio Code by selecting

File -> Preferences -> Extensions

Then search for the vscode-reasonml extension and install it. The extension builds on top of Merlin which you can install via opam (see above).