Haskell layer

• syntax highlighting for haskell source, cabal files, C– source,
• auto-completion with one of selected backends (intero, ghci or ghc-mod).

This layer is in construction, it needs your contributions and bug reports.

To use this configuration layer, add it to your ~/.spacemacs. You will need to add haskell to the existing dotspacemacs-configuration-layers list in this file.

This layer requires some cabal packages:

• apply-refact (required by hlint-refactor)
• hlint (required by hlint-refactor)
• stylish-haskell (optional for haskell-mode)
• hasktags (optional)
• hoogle (optional for haskell-mode and helm-hoogle)
• ghc-mod (optional for completion)
• intero (optional for completion)

To install them, use following command (or the stack equivalent):

$ cabal install apply-refact hlint stylish-haskell hasktags hoogle

First of all make sure that your $PATH contains the installation path for Haskell tools like ghc, ghci etc. It depends on how you have installed ghc, but you can always check it by running which ghc in your terminal. Stack users should add only the installation path of stack itself. Usually it's ~/.local/bin.

Then make sure that your $PATH contains the installation path for cabal packages. If you are using cabal it should be ~/.cabal/bin or ~/Library/Haskell/bin (for 'Haskell for Mac' users). If you are using stack then it should be ~/.local/bin.

For information about setting up $PATH, check out the corresponding section in the FAQ (SPC h SPC $PATH RET).

This layer provides several completion backends - intero, ghci and ghc-mod. By default ghci (company-ghci) is used as it requires no dependencies and works both with stack and pure cabal projects. In order to manually set completion backend set value of haskell-completion-backend. Note that in order to enable completion you have to enable auto-completion layer as well.

(setq-default dotspacemacs-configuration-layers
              '(auto-completion
                (haskell :variables haskell-completion-backend 'intero)))

The Haskell layer supports some extra features that can be enabled through layer variables.

Documentation commands are prefixed by SPC m h

Debug commands are prefixed by SPC m d:

REPL commands are prefixed by SPC m s:

Intero REPL commands are prefixed by SPC m i:

Cabal commands are prefixed by SPC m c:

This commands are available in a cabal file.

Refactor commands are prefixed by SPC m r:

Only some of the HLint suggestions can be applied.

To apply the intero suggestions, press `C-c C-c` when the window is open, which is also shown in the window that appears.

These commands are only available when ghc-mod is enabled.

For more info, see http://www.mew.org/~kazu/proj/ghc-mod/en/emacs.html

ghc-mod commands are prefixed by SPC m m:

This is the standard spacemacs way to do syntax checking and the most elaborate. You need the syntax-checking layer to enable this. Please the documentation for that layer on how to interact with flycheck.

Flycheck has different Haskell checkers: haskell-ghc, haskell-stack-ghc and haskell-hlint. Normally it can automatically detect the best one to use, but if it doesn't work, you can change it using SPC e s.

HLint is a linter for Haskell. It doesn't detect errors (as long as it can parse the file) but bad coding style and code smell. The HLint checker is called after the flycheck GHC checker.

Ghc-mod, when enabled, also does syntax checking. It doesn't highlight errors but instead displays an exclamation point in the fringe. You can navigate between errors using ghc-goto-next-error (M-n) and ghc-goto-prev-error (M-p).

Finally, interactive haskell-mode (SPC m s b) also displays errors. These errors can be navigated from the interactive buffer (by clicking on the error) or using haskell-goto-next-error (M-n) and haskell-goto-prev-error (M-p).

An alternative to syntax checking is to build your project using flymake-compile. It doesn't highlight error in the buffer but is more reliable. The error navigation is similar to interactive haskell-mode.

Flycheck and ghc-mod can fail silently for miscellaneous reasons. See the 5 for troubleshooting.

Usually haskell-mode is great at figuring out which interactive process to bring up. But if you are experiencing problems with it you can help haskell-mode by setting haskell-process-type as in following code:

(setq-default dotspacemacs-configuration-layers
  '((haskell :variables haskell-process-type 'stack-ghci)))

Available options are:

• ghci
• cabal-repl
• cabal-dev
• cabal-ghci
• stack-ghci

Make sure that when you are typing anything in REPL there is a space between what you type and λ>. When there is no space - REPL will behave as if it's stuck. Usually, when you enter normal state, cursor is moved back, so there is no required space when you switch to insert mode. There is possible workaround - just add following snippet to your dotspacemacs/user-config function:

(when (configuration-layer/package-usedp 'haskell)
  (add-hook 'haskell-interactive-mode-hook
            (lambda ()
              (setq-local evil-move-cursor-back nil))))

It will make cursor stay at the right place in the REPL buffer when you enter normal state. Which in most cases helps you to avoid the problem with 'stuck' REPL.

Also, some users might want to start REPL in insert mode. For this to happen you could place following snippet in your dotspacemacs/user-config function:

(when (configuration-layer/package-usedp 'haskell)
    (defadvice haskell-interactive-switch (after spacemacs/haskell-interactive-switch-advice activate)
      (when (eq dotspacemacs-editing-style 'vim)
        (call-interactively 'evil-insert))))

Make sure that dist directory doesn't exist in your project root. So if it exists, just remove it and try again.

First of all - make sure that the version of ghc matches the version of ghc that was used to build ghc-mod. To get the latter call ghc-mod --version in terminal. If they don't match you have to rebuild ghc-mod.

Stack provides ability to use different ghc versions across different projects. In case you are using this feature you have to rebuild ghc-mod quite often. If you use ghc-mod only for completion and don't want to rebuild ghc-mod every time you switch project you'd better disable ghc-mod support, so company-ghci will be used for completion.

The second thing to do if it's still not working - call ghc-mod debug in the root of project you are currently working on. Make sure that it shows no errors. If there are errors you can't solve - it's better to report them upstream.

This is the intended behavior in haskell-indentation-mode. If you want to reset indentation when pressing return after an empty line, add the following snippet into your dotspacemacs/user-config function.

(defun haskell-indentation-advice ()
  (when (and (< 1 (line-number-at-pos))
             (save-excursion
               (forward-line -1)
               (string= "" (s-trim (buffer-substring (line-beginning-position) (line-end-position))))))
    (delete-region (line-beginning-position) (point))))

(advice-add 'haskell-indentation-newline-and-indent
            :after 'haskell-indentation-advice)

The HLint checker is called after normal flycheck checker even if the checker fails. Check the 5.8 section.

The error list is only set by flycheck. You are probably seeing errors highlighted by either ghc-mode or haskell-mode. Check the 5.8 section.

You can check what is wrong with flycheck with the flycheck-compile command. This will show you the exact command line used and its output.

If you are using stack, check the 5.9 section.

First check that flycheck uses the correct checker and all the paths are properly configured using flycheck-verify-setup (SPC e v). You can force the checker with flycheck-select-checker (SPC e s) to ensure it uses haskell-stack-ghc. If it still doesn't work, it could be one of the following problems:

• The stack build directory is wrong
• The project root is not set properly

Some (most of) the haskell-mode commands only works when haskell-mode is in interactive mode, i.e. as a interactive session associated to it. Load it using SPC m s b.

ghc-mod commands are prefixed with ghc-, haskell-mode ones are prefixed with haskell-.

Commands starting with ghc- are ghc-mod commands. Commands starting with haskell- are haskell-mode commands.