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Windows Support

Many projects, including the OCaml compiler itself, rely on the Unix shell and its various utilities. Windows doesn’t include these utilities or any of their substitutes (or even a built-in compiler), making it much harder to support a complex library on Windows.

Nevertheless, OCaml is gradually making a transition towards full Windows support.

For newcomers the simplest option is to download and run the latest DkML Windows 64-bit Native Installer.

Options

  • DkML: A distribution of OCaml that uses MSYS2 for Unix utilities and Microsoft Visual Studio 2019 for 100% Windows library compatibility, and has a traditional setup.exe to install. The distribution transparently uses Unix utilities so that Windows users do not need to learn Unix.

    The disadvantages of DkML are:

    • Visual Studio 2019, even though it is automatically installed, is a multi-gigabyte program that requires Administrator permissions to install
    • Only OCaml 4.14.0 is officially supported. OCaml 5.x does not yet support Visual Studio.

  • OCaml on WSL (Windows Subsystem for Linux) - Windows 10 supports Ubuntu or any other Linux distribution natively.

    The disadvantages of this approach are:

    • By default, you’ll be creating Linux binaries, which can only be run on Linux or on another Windows 10 machine that has WSL activated. However, this can be mitigated by using and following the instructions at opam-cross-windows, which can create Windows OCaml programs from Linux.
    • WSL on Windows has no direct graphical support. It thus requires communication via the X protocol, using an X server such as Xming) on the Windows side. Again, by using opam-cross-windows, this barrier can be eliminated.

  • Similar to WSL above, you can create OCaml programs on Linux proper, and cross-compile them so they work on Windows using opam-cross-windows.

  • OCaml for Windows: A cygwin-based Ocaml distribution, with opam support. Keep in mind that cygwin is a translation layer for unix commands, and thus slows down compilation performance. However, the binaries produced can be run in Windows proper without cygwin, if they’re built with the right compiler (mingw).
    • sys2cyg is a tool that allows you to install up-to-date packages from MSYS2 (a lightweight fork of cygwin). MSYS2 by itself is incapable of building OCaml packages, but has better-maintained libraries, which could be useful for building OCaml libraries.
  • esy: a build tool similar to npm and OPAM created by the Reason community. esy operates on top of cygwin but hides it away, making OCaml feel completely native to windows. It therefore also inherits cygwin’s slow compilation speed. Not all OPAM packages are available yet, but support is rapidly growing.

OPAM is being extended to support a Windows environment. See this post for details.

Resources