Customize

Global variables

g:ghcmod_ghc_options

ghcmod.vim passes these options to GHC via ghc-mod.
By default, ghcmod.vim doesn’t pass any GHC options.

Example: passing -idir1 and -idir2 to GHC

let g:ghcmod_ghc_options = ['-idir1', '-idir2']

g:ghcmod_hlint_options

ghmod.vim passes these options to hlint via ghc-mod.
By default, ghcmod.vim doesn’t pass any hlint options.

Example: passing '--ignore=Redundant $' to hlint

let g:ghcmod_hlint_options = ['--ignore=Redundant $']

g:ghcmod_type_highlight

The highlight group used in :GhcModType.
By default, the Search group is used.
See :help :highlight for details on Vim’s highlighting.

Example: highlighting sub-expressions with yellow background

hi ghcmodType ctermbg=yellow
let g:ghcmod_type_highlight = 'ghcmodType'

Customization tips

Auto-checking on writing

Put the below in your ~/.vimrc.
When you write *.hs buffer to a file, both check and lint are run.

autocmd BufWritePost *.hs call s:check_and_lint()
function! s:check_and_lint()
  let l:qflist = ghcmod#make('check', expand('%'))
  call extend(l:qflist, ghcmod#make('lint', expand('%')))
  call setqflist(l:qflist)
  cwindow
  if empty(l:qflist)
    echo "No errors found"
  endif
endfunction

If you like asynchronous checking, put the below instead.

autocmd BufWritePost *.hs GhcModCheckAndLintAsync

Displaying check/lint status in statusline

ghcmod.vim gather errors into quickfix, so it could be useful to simply display in statusline whether quickfix is empty or not.
Put the below in your ~/.vim/ftplugin/haskell.vim, then the statusline editing Haskell source has [No Errors] or [Errors Found] field.

let &l:statusline = '%{empty(getqflist()) ? "[No Errors]" : "[Errors Found]"}' . (empty(&l:statusline) ? &statusline : &l:statusline)

Autoload functions

These autoload functions would be useful if you want to define a new command using ghcmod.vim.

ghcmod#type()

ghcmod#type() highlights the current sub-expression and returns highlighted region [line1, col1, line2, col2] and its type.

Example return value: [['6', '10', '6', '17'], 'Maybe a']

ghcmod#type_clear()

ghcmod#type_clear() clears the highlight created by ghcmod#type().

ghcmod#parse_make(lines)

ghcmod#parse_make() parses lines (which is ghc-mod’s output) and returns a list of quickfix items which can be used as an argument of setqflist().
This function is used by ghcmod#make() and ghcmod#async_make().

Note that ghc-mod produces NUL-characters. Using the result of split(system('ghc-mod check /path/to/file.hs'), '\n') is not a good idea.

ghcmod#make(type)

ghcmod#make() invokes ghc-mod and returns its output as a list of quckfix items.
type is either check or lint.

Example return value: [{'lnum': '3', 'col': '1', 'filename': 'M.hs', 'type': 'W', 'text': 'Top-level binding with no type signature: foo :: Int'}]

ghcmod#async_make(type, action)

ghcmod#async_make() invokes ghc-mod asynchronously and set its output at quickfix.
action is passed to setqflist()’s second argument.

ghcmod#async#exist_session()

ghcmod#async#exist_session() returns whether running sessions created via ghcmod#async#register() exist.
ghcmod#async_make() uses ghcmod#async#register() internally.
This function is useful when you want to run check/lint automatically. See the definition of :GhcModCheckAndLintAsync as an example.

ghcmod#expand()

ghcmod#expand() returns the result of ghc-mod expand as a list of quickfix items.

Example return value: [{'lnum': '5', 'col': '5', 'filename': 'N.hs', 'text': 'Splicing expression'}, {'text': ' " hello TH " ======> " hello TH "'}]

ghcmod#check_version(version)

ghcmod#check_version() returns whether ghc-mod’s version is higher or equal to version.

ghcmod#build_command(args)

ghcmod#build_command() returns a ghc-mod command.
This function adds g:ghcmod_ghc_options to args .