Extensible Haskell pretty printer. Both a library and an executable.

$ stack install

hindent is used in a pipeline style:

$ cat path/to/sourcefile.hs | hindent > outfile.hs

In elisp/hindent.el there is hindent-mode, which provides keybindings to reindent parts of the buffer:

• M-q reformats the current declaration. When inside a comment, it fills the current paragraph instead, like the standard M-q.
• C-M-\ reformats the current region.

To enable it, add the following to your init file:

(add-to-list 'load-path "/path/to/hindent/elisp")
(require 'hindent)
(add-hook 'haskell-mode-hook #'hindent-mode)

The 'formatprg' option lets you use an external program (like hindent) to format your text. Put the following line into ~/.vim/ftplugin/haskell.vim to set this option for Haskell files:

setlocal formatprg=hindent

Then you can format with hindent using gq. Read :help gq and help 'formatprg' for more details.

Note that unlike in emacs you have to take care of selecting a sensible buffer region as input to hindent yourself. If that is too much trouble you can try vim-textobj-haskell which provides a text object for top level bindings.

Basic support is provided through atom/hindent.coffee. Mode should be installed as package into .atom\packages\${PACKAGE_NAME}, here is simple example of atom package.