9 Using external formatters

You can enable stylish-haskell by installing it:

$ cabal install stylish-haskell

And by enabling it with a customization

(custom-set-variables
 '(haskell-stylish-on-save t))

Now when you run save-buffer (or C-x C-s) the module will be automatically formatted.

Alternatively, you can run the function directly on demand with M-x haskell-mode-stylish-buffer.