OCaml on Windows

There is a DkML Windows installer that we recommend for new users. However, while DkML has a modern OCaml 4.14.0 compiler, it does not track the latest OCaml compilers. We will officially support Windows as a Tier 1 platform with a major release of opam in the coming months, and it will be compatible with DkML installations.

Our guidance is when you want:

  • To only run, and not develop, applications, use Docker or WSL2
  • To develop applications and have some familiarity with Unix, use opam-repository-mingw
  • To develop applications and care more about stability and ease-of-use than the latest compiler, use DkML

The guidance is based on the availability table below:

  • Tier 1 is fully supported with the latest compilers.
  • Tier 2 is supported but maintained when possible.
  • Tier 3 is user supported.
│ Tier   │ OCaml Version and Environment     │ Support and Availability                    │
│ ------ │ --------------------------------- │ ------------------------------------------- │
│ Tier 1 │ OCaml 5 with Opam 2.2             │ Full support. Coming in the next few months │
│ Tier 2 │ 4.14.0 with DkML                  │ Supported on select versions. Available now │
│ Tier 3 │ 4.14.0 with opam-repository-mingw │ Deprecated. Available now and mostly works  │
│ Tier 3 │ 4.14.2 with WSL2                  │ User supported. Available now               │
│ Tier 3 │ 4.14.1 with Docker                | User supported. Available now               │

opam 2.2

After the successful release of opam 2.1.0, the next version of opam will focus on closing the gap to fully support Windows. This includes supporting an external dependency installation for Windows and integrating it with the Windows shell. From an opam-repository perspective, the ocaml-base-compiler packages will support the MinGW-w64 and MSVC variants.

Installation Environments


opam-repository-mingw is an opam repository that contains patches for packages to build and install on Windows as well as MinGW-w64 and MSVC compiler variants (in both 32- and 64-bit). For a long time, this has been maintained by @fdopen along with installers to create a custom Cygwin environment with opam and OCaml installed.

As of August 2021, the repository will no longer be updated. However, it is still useful as an overlay to the default opam repository. This means if a package exists in opam-repository-mingw, the opam client will use that information, otherwise it will fall through to opam-repository. To add opam-repository as an underlay to your opam setup (assuming you followed the manual installation from the OCaml for Windows site), you can use:

opam repo add upstream https://opam.ocaml.org --rank 2 --all-switches --set-default

This assumes you only have the opam-repository-mingw repository for this switch set with a priority of 1.


If you only need to run OCaml programs on a Windows machine, the simplest solution is to use the Windows Subsystem for Linux 2 (WSL2). WSL2 is a feature that allows Linux programs to run directly on Windows. WSL2 is substantially easier and faster to use than WSL1. Microsoft has comprehensive installation steps for setting up WSL2.

After you have installed WSL2 and chosen one Linux distribution (we suggest Ubuntu LTS), you can follow the Installing OCaml: Installation for Linux and macOS steps.

Docker Images

The ocaml/opam Docker Hub repository now contains regularly-updated Windows images. This includes images using msvc and mingw. If you are comfortable with Docker, this might be an easier way to get a working Windows environment on your machine.

Editor Support for OCaml on Windows

Visual Studio Code on Windows

If you use the recommended DkML installer, you will need to:

  1. Go to File > Preferences > Settings view (or press Ctrl ,).
  2. Select User > Extensions > OCaml Platform.
  3. Uncheck OCaml: Use OCaml Env.

If you use WSL2, you will remotely connect to your WSL2 instance from Visual Studio Code. Microsoft has a useful blog post covering getting WSL2 and Visual Studio Code connected.

Vim and Emacs on Windows

For Vim and Emacs install the Merlin system using opam:

$ opam install merlin

The installation procedure will print instructions on how to link Merlin with your editor.

If you use Vim, the default Cygwin Vim will not work with Merlin. You will need install Vim separately. In addition to the usual instructions printed when installing Merlin, you may need to set the PATH in Vim:

let $PATH .= ";".substitute(system('opam config var bin'),'\n$','','''')

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