Question

I’ve installed Haskell on my Mac using Homebrew, that is brew install ghc haskell-platform.

I’m looking for a way to generate a ctags file of the standard Haskell Platform libraries (modules) so I could browse the source while coding in Vim. I specifically need Prelude and the other most popular modules, like Data.List and such.

I am aware that the source is available on the web via Hoogle, but It’ll be easier for me to jump-to-source whenever I need to, for learning purposes.

1. Where is the source located when installing the Haskell Platform?
2. Is the source even installed when installing the Haskell Platform, or just the compiled binaries or something of the sort?
3. How can I make the source available for browsing in Vim? As in put the generated tags file somewhere and tell Vim to read from it. I also understand there’s no need to re-generate the tags file, since these modules are pretty much static and don’t get updated very often.

Answer 1

1) and 2) were answered by permeakra in comments. I’ll try to cover 3) by describing setup similar to the one I’m using. First simple solution for base libraries, then more generic solution for whatever Haskell source package in general.

As a prerequisites we will need a tool which generates tags file for Haskell:

cabal install hothasktags

Instead of hothasktags you might use your favourite one. See for example https://github.com/bitc/lushtags page which enumerates some of these.

Then we need to have sources for base libraries available. Here I’m using the ones from GitHub:

cd /space/haskell/sources/ # tweak to your personal taste
git clone https://github.com/ghc/packages-base.git

Optionally we might switch to particular branch. E.g.:

git checkout ghc-7.4

Run git branch -a to see all possibilities.

Now let’s generate tags for the base libraries (I do not have Mac available and thus have to assume the command works there or you are able to tweak it appropriately):

cd packages-base
export LC_ALL=C # needed for case-sensitive searching
find -type f | egrep \.hs$\|\.lhs$ | xargs -Ii hothasktags i | sort > tags

(Note about sort: My Vim complains when I do not use the sort. For LC_ALL explanation see for example this blog post)

Now we need to let the Vim know about the tags we generated. The easiest way is probably to put the following line into your $HOME/.vimrc:

autocmd FileType haskell setlocal tags+=/space/haskell/sources/packages-base/tags

This way the tags for base libraries will be set for each Haskell file we open. If this is not desirable we can put following Vim command into .vimrc:

autocmd FileType haskell command! SetGHCTags
    \ setlocal tags+=/space/haskell/sources/packages-base/tags

and call :SetGHCTags on demand.

For more generic solution which works with all Haskell sources packages we can use the following function (put into .vimrc or into Vim file dedicated to Haskell filetype):

" Add 'tags' of the given package to the current tag stack. The package sources
" must be available in "/space/haskell/sources/<package>" and the tags must be
" generated for it.
fun! s:SetHaskellTags(pathInHaskellSrcDir) "{{{
  let tagFile = "/space/haskell/sources/" . a:pathInHaskellSrcDir . "/tags"
  if filereadable(tagFile)
    exe "setlocal tags+=" . tagFile
  else
    echoerr "File does not exist or is not readable: " . tagFile
  endif
endfunction "}}}
command! -nargs=1 SetHaskellTags call <SID>SetHaskellTags(<args>)

Utilizing it for example for Shelly.hs library:

cd /space/haskell/sources/
git clone https://github.com/yesodweb/Shelly.hs.git
cd Shelly.hs
regenerate-haskell-tags # [1]

In Vim just call:

:SetHaskellTags "Shelly.hs"

There is space for improvement – SetHaskellTags could generate tags if not exist, or could even fetch the sources, configurable Haskell source code storage, directory completion, etc. But works good enough for me now. So at least sharing the solution I have. Will come back here if I get to some of these improvement done.

[1]: It’s better to store regenerate-haskell-tags in your $PAHT.