setup-dev-env.md

Set Up a Haskell Development Environment in Three Steps

a Haskell Development Environment consist in a compiler (ghc), a language server (hls), a building tool (cabal or stack), and an editor compatible with the language server protocol.

The best way to have a coherent installation of these components is with the ghcup tool.

• Step 1: Install GHCup. You'll be prompted to install some tools. Say yes to hls. Do not install stack yet (see below).
• Step 2: Install vscode
• Step 3: Open vscode and install the haskell extension either using the extension panel or pressing CTRL+P and ext install haskell.haskell.

Integration with other editors

If you want an editor different from vscode, check the documentation here

Integration with stack.

to integrate stack with haskell-language-server, you should configure it properly.

The key point is to prevent stack to install ghc on its own. Follow these steps:

• First, You still need to follow the three steps at the top of this guide. You can't get a proper working environment solely with stack.

• Skip this point if you installed stack independently from ghcup. In a terminal run ghcup install stack

• Configure stack to use system's ghc. Configuration can be either global (recomended) or local

  • Global (recomended)

    # Run on a terminal if you want to set a global configuration
    stack config set install-ghc --global false
    stack config set system-ghc --global true 

  • Local:

    # On stack.yaml add this line if you want to set a local configuration
    system-ghc: true 

• You must use a stack snapshot compatible with the ghc version installed by ghcup. Visit stackage to get the ghc version on each sanpshot. For example lts-18.28 uses ghc-8.10.7. You can check version compatibility with:

  # This prints the ghc's version installed by ghcup
  > ghcup list -c installed -t ghc
  ✔✔ ghc  8.10.7  recommended,base-4.14.3.0 hls-powered
  
  # Your resolver should point to 18.28      ---------------------------------------------------
  > cat stack.yaml    #                                                                    vvvvv    
  resolver:
    url: https://raw.githubusercontent.com/commercialhaskell/stackage-snapshots/master/lts/18/28.yaml
  

What if I need to use a different snapshot?

In case you need to use a different snapshot you have to install it's ghc version with ghcup. For the sake of example, let say you are using lts-16.31, which uses ghc-8.8.4. Then you need to run ghcup install ghc 8.8.4 on a terminal. Also, depending on which snapshot you are using, you might loose integration with hls. Check hls documentation for more info.

I'm interested in what your error is - do you want to share it, if you still have it on hand?

I don't remember well but something like "hls has failed three times in the last five minutes. not restarting".

Here you have a SO addressing this issue.

https://stackoverflow.com/questions/73155847/using-vscode-with-haskell-ghcup-and-stack-hls-crashes-with-newer-versions-of

Actually, if you look at SO's tag haskell-language-server you can find many people having issues with stack/hls

https://stackoverflow.com/questions/tagged/haskell-language-server

Saying no to GHCup HLS (yes to everything else), and then letting the Haskell extension install HLS seems to work fine. Either GHCup or the extension, I don't know which one, creates a stack hook to prevent it from installing its own GHC. There's no further need to mess with stack anyway.
https://www.haskell.org/ghcup/guide/#strategy-1-stack-hooks-new-recommended

Debugging and testing (HSpec) still don't work from VSCode though. The debug adapter extension is $shit.