Doom Emacs with the doom-one-light theme

Quick summary

• This assumes you already have Doom Emacs installed.
• We’ll need to install ghcup which is a Haskell toolchain.
• And lastly we’ll make small changes to your doom config file

Install GHCup

Follow the install instructions from the official source https://www.haskell.org/ghcup/

Run the terminal user interface.

ghcup tui

Use the up and down arrows to pick your desired version and install by pressing i, then make sure to also press s after installing to “set” that version.

Doom init.el

Within your doom folder (usually located in ~/.doom.d/) open your init.el file. Make sure to uncomment this line and then run doom sync in your terminal to install the packages.

(haskell +lsp)    ; a language that's lazier than I am

eglot vs lsp-mode

I am familiar with eglot especially since it’s been added to emacs’ core in version 29. I’m sure the haskell language server will work with it but I haven’t put in the time to set that up and I’ve got it working with lsp-mode anyway 🤷🏾‍♂️

Doom config.el

Next open the config.el file, also located in your doom folder. We’ll be adding two snippets.

The first is setting up hooks to turn on the language server when emacs detects haskel-mode.

;; HASKELL
;; Hooks so haskell and literate haskell major modes trigger LSP setup
(add-hook 'haskell-mode-hook #'lsp)
(add-hook 'haskell-literate-mode-hook #'lsp)

Supply environment variables

If you start emacs through a GUI like me, your emacs will likely not have the same environment as your terminal. This will cause an issue where emacs cannot find the haskell-language-server program you installed with ghcup.

For example:

Failed to find a HLS version for GHC 9.4.5
Executable names we failed to find: haskell-language-server-9.4.5,haskell-language-server

This second snippet will ensure that the language server binaries will be available to emacs. It adds the ghcup bin folder to the exec-path list and the PATH environment variable. Put this code block in your config.el as well!

;; Put this in your emacs config
;; Add haskell lsp to path for emacs subprocesses
(add-to-list 'exec-path (expand-file-name "~/.ghcup/bin"))
;; Add haskell tools to path for emacs environment
(setenv "PATH" (concat (expand-file-name "~/.ghcup/bin") ":" (getenv "PATH")))

Hope this helps!