4. How to use Cabal in Windows

This document describes how to use Cabal in a Windows system. See the Further reading section for some other references that might provide some more explanations. For a TL;DR, jump to the Complete configuration.

4.1. Install the Haskell environment

Haskell development on Windows makes use of the MSYS2 tools.

The recommended way of setting up a Haskell environment in Windows is by using GHCup. Follow the steps outlined in its webpage to install at least GHC and Cabal. GHCup will install its own MSYS2 system in your computer unless told not to do so: refer to its documentation for more information.

Note

Stack is another tool you can use to set up a Haskell environment on Windows. Stack can be installed on its own or via GHCup. See Stack’s webpage and/or GHCup’s section on Stack integration, in particular the Windows related subsection.

4.2. Ensure that Cabal can call the tools it needs

Cabal sometimes needs to call tools that do not come with Windows (such as make or even git). The MSYS2 project makes many of them available on Windows. The directories where those are located need to be made visible in the PATH when executing cabal. For that, Cabal provides the extra-prog-path configuration option. Your global configuration should include this option:

extra-prog-path: <msys-dir>\<environment>\bin
                 <msys-dir>\usr\bin

Where <msys-dir> points to the location of your MSYS2 installation. Refer to GHCup’s documentation on the default location of this directory. <environment> has to be one of the environments of MSYS2, which for GHCup is mingw64. You can learn more about the different environments in the MSYS2 documentation.

Note

Unless told otherwise, the GHCup bootstrap script already adds these directories to extra-prog-path by default.

4.3. Ensure that Cabal can use system libraries

Third-party libraries can be installed using the pacman package manager on the MSYS2 installation. When installing a third party package its libraries and header files will (usually) be placed in <msys-dir>\<environment>\{lib,include} respectively. These directories need to be specified in the extra-lib-dirs and extra-include-dirs respectively. Your global configuration should include these options:

extra-include-dirs: <msys-dir>\<environment>\include
extra-lib-dirs: <msys-dir>\<environment>\lib

Note

Unless told otherwise, the GHCup bootstrap script already adds these directories to extra-include-dirs and extra-lib-dirs by default.

Warning

Packages in the msys/ repo are not native Windows libraries and will probably not work when one tries to link to them. Install the packages for your selected environment, which for GHCup is mingw64/. Refer to MSYS2’s package management documentation for more information.

4.4. Ensure that Cabal can call Haskell tools

Haskell tools are located in two places:

  • <ghcup-dir>\bin for standard Haskell tools such as GHC, Cabal, Haddock, hsc2hs

  • The installdir that Cabal is configured with for user-installed Haskell tools.

For Cabal to be able to invoke these tools, those directories need to be made visible in the PATH. Your global configuration should include these options:

installdir: <installdir>
extra-prog-path: ...
                 <ghcup-dir>\bin
                 <installdir>

Note

Unless told otherwise, the GHCup bootstrap script already adds these directories to extra-prog-path by default.

4.5. Complete configuration

The complete global configuration should finally look like this:

installdir: <installdir>
extra-include-dirs: <msys-dir>\<environment>\include
extra-lib-dirs: <msys-dir>\<environment>\lib
extra-prog-path: <ghcup-dir>\bin
                 <installdir>
                 <msys-dir>\<environment>\bin
                 <msys-dir>\usr\bin

Note

Unless told otherwise, the GHCup bootstrap script already sets this configuration file to the right values by default.

4.6. Further reading