Vim plugin for Haskell development

hdevtools Vim Plugin

Vim plugin for Haskell development powered by the lightnight fast hdevtools background server.


hdevtools is a command line program powered by the GHC API, that provides services for Haskell development. hdevtools works by running a persistent process in the background, so that your Haskell modules remain in memory, instead of having to reload everything each time you change only one file. This is just like :reload in GHCi - with hdevtools you get the speed of GHCi as well as tight integration with your editor.

This is the Vim plugin that integrates Vim with hdevtools.


  1. You must install the hdevtools command line program, It can be found here:, or from Hackage:

    $ cabal install hdevtools
  2. Install this plugin. pathogen.vim is the recommended way:

    cd ~/.vim/bundle
    git clone
  3. Configure your keybindings in your .vimrc file. I recommend something like:

    au FileType haskell nnoremap <buffer> <F1> :HdevtoolsType<CR>
    au FileType haskell nnoremap <buffer> <silent> <F2> :HdevtoolsClear<CR>


Type Checking

The best feature of the hdevtools command is near-instant checking of Haskell source files for errors - it's fast even for huge projects.

This Vim plugin does not have direct support for interacting with this feature. Instead, I recommend using the excellent Syntastic plugin.

Type Information

Position the cursor anywhere in a Haskell source file, and execute HdevtoolsType (or press the <F1>) key if you have configured as above).

The type for the expression under the cursor will be printed, and the expression will be highlighted. Repeated presses will expand the expression that is examined.

You can execute HdevtoolsClear to get rid of the highlighting.


You can set the g:hdevtools_options variable to pass custom options to hdevtools.

This is useful for passing options through to GHC with the hdevtools -g flag. For example, if your project source code is in a src directory, and you want to use the GHC option -Wall, then stick the following somewhere appropriate (such as your project's Session.vim):

let g:hdevtools_options = '-g-isrc -g-Wall'

Make sure that each GHC option has its own -g prefix (don't group multiple options like this: "-g-isrc\ -Wall")


Parts of the design of this plugin were inspired by ghcmod-vim, and large amounts of code were also taken.