This document describes my setup for working with Haskell on Windows. Notice I don’t know much of the intricacies of Windows but it seems I was able to make it work.

Environment

Git

Install git using scoop in PowerShell:

Set-ExecutionPolicy -ExecutionPolicy RemoteSigned -Scope CurrentUser
Invoke-RestMethod -Uri https://get.scoop.sh | Invoke-Expression
scoop install git

Notice we are installing Git for Windows with this. It seems like it has worked properly for me until now. Some configs:

➜ cat .gitconfig
[user]
  name = ...
  email = ...
[core]
  autocrlf = input
  sshCommand = C:/Windows/System32/OpenSSH/ssh.exe
[gpg]
  program = C:/Program Files (x86)/GnuPG/bin/gpg.exe
[core]
  symlinks = true

For gpg, I use Gpg4win, and for ssh I use Window’s OpenSSH

MSYS2

The developer environment will be based on MSYS2. Download the installer from their webpage and follow the wizard steps.

System upgrade

Run pacman -Syuu twice, to update the runtime and to update the packages.

Setting the $HOME for MSYS2

Add this line to your /etc/nsswitch.conf file from inside MSYS2.

db_home: <whatever-was-here> windows

and restart the terminal.

Choosing an environment

GHC ships a minimal toolchain in order to not depend on the user’s toolchain (currently 0.8 here, check here for the version on your particular GHC).

Before GHC 9.4, the base environment was GCC-based, thus the best way to align things was to use a MINGW64 environment.

After GHC 9.4, the base environment is clang-based. So I would suggest using the CLANG64 environment.

Inheriting the Windows’ PATH

Add the argument -use-full-path to the msys2_shell.cmd (right-click on the icon that appears when you search for MSYS2 in your start menu, and modify the shortcut).

Essential packages

Some packages that I find very useful to have around:

mingw-w64-clang-x86_64-pkgconf: there is a msys2/pkgconf package but it doesn’t understand Windows paths in PKG_CONFIG_PATH… Sadly this means that if you change environments you will have to switch the pkg-config package (or install a new one).
base-devel: generally useful
mingw-w64-clang-x86_64-zlib
mingw-w64-clang-x86_64-openssl

or in one line:

pacman --noconfirm -S base-devel mingw-w64-clang-x86_64-pkgconf mingw-w64-clang-x86_64-zlib mingw-w64-clang-x86_64-fd mingw-w64-clang-x86_64-jq mingw-w64-clang-x86_64-emacs mingw-w64-clang-x86_64-python mingw-w64-clang-x86_64-python-pip

Windows Terminal

I would suggest installing the Windows Terminal and FiraCode Nerd font (make sure to install it for all users or Windows Terminal will complain). There you can configure the different profiles you want to use. My settings are as follows (notice the -use-full-path and the -shell zsh):

"defaultProfile": "<some profile guid from below>",
"profiles":
 {
   "defaults": {},
   "list":
   [
      {
          "commandline": "C:\\msys64\\msys2_shell.cmd -defterm -here -no-start -clang64 -shell zsh -use-full-path",
          ...
          "name": "MSYS2 / CLANG64"
      },
      {
          "commandline": "C:\\Program Files\\PowerShell\\7\\pwsh.exe",
          "name": "Windows PowerShell"
      }
  ]
}

PowerShell

Install the latest PowerShell with winget:

winget install --id Microsoft.WindowsTerminal --source winget

Point your Windows Terminal profile to C:\Program Files\PowerShell\7\pwsh.exe.

Add this to your profile (~/Documents/PowerShell/Microsoft.PowerShell_profile.ps1) to enable movement like emacs on the command line:

Import-Module PSReadLine
Set-PSReadLineOption -EditMode Emacs

Haskell

GHCup

Set the following user variables:

Var	Value
`GHCUP_INSTALL_BASE_PREFIX`	`C:\`
`GHCUP_MSYS2`	`C:\msys64`
`Path`	Add `C:\ghcup\bin` and `C:\Users\Javier\AppData\Roaming\cabal\bin`

Then go to GHCup and get the POSIX install command:

curl --proto '=https' --tlsv1.2 -sSf https://get-ghcup.haskell.org | sh

And run it in an MSYS2 shell. Restart the terminal and run ghcup tui to select the latest versions of cabal, stack and the desired ghc.

Integrate with cabal

GHCup will have modified your cabal global config like this:

extra-include-dirs: C:\msys64\clang64\include
extra-lib-dirs: C:\msys64\clang64\lib
extra-prog-path: C:\ghcup\bin,
                 C:\Users\<USER>\AppData\Roaming\cabal\bin,
                 C:\msys64\clang64\bin,
                 C:\msys64\usr\bin

This might lead to problems sometimes, see this.

I would say leave it if using CLANG64 and GHC >= 9.4, but if using MINGW64 you might need to comment the include and lib dirs.

I use this function to switch environments if needed:

cabal-msys2-env () {
  sed -i "s/\(ucrt\|mingw\|clang\)/$1/g" $(cygpath -u "$(cabal --help | tail -n1 | sed 's_\r__g' | tr -d ' ')")
}

NOTE: while this is fixed, I suggest adding the following to your cabal config
program-default-options
  ghc-options: -optc-Wno-pragma-pack -optc-Wno-macro-redefined -optc-Wno-missing-declarations

Haskell ❤️ Windows