Recently on haskell-cafe I asked
if there is an easy way to get the Haddock documentation url for a given identifier in Haskell. I discovered
that it's not completely straightforward, for example if we look up
we are told that it's defined in
$ ghc-mod info foo.hs Foo String type String = [Char] -- Defined in `GHC.Base'
Then we can find the Haddock url for the base package:
$ ghc-pkg find-module GHC.Base /home/carlo/opt/ghc-7.6.3_build/lib/ghc-7.6.3/package.conf.d base-188.8.131.52 /home/carlo/.ghc/x86_64-linux-7.6.3/package.conf.d $ ghc-pkg field base-184.108.40.206 haddock-html haddock-html: /home/carlo/opt/ghc-7.6.3_build/share/doc/ghc/html/libraries/base-220.127.116.11
so we'd expect to be able to view
but this file doesn't exist because
GHC.Base is an
internal module and does not have a Haddock page. This happens with
some other packages too, not just
In the haskell-cafe thread, Roman Cheplyaka
pointed out that I should be asking for where a thing is imported from,
as opposed to defined. For the
String example we would prefer to send the user to
the Haddock page for the
This turns out to be a bit tricky as well, but I think I have a reasonable prototype working now, which I have unimaginatively called ghc-imported-from. There are some very rough edges, for example parsing of language extensions and GHC options, but these should be easy to fix either by following how ghc-mod does the same thing, or perhaps by adding my code to a fork of ghc-mod. We'll see.
Here's a short screencast of ghc-imported-from in action, along with my forked version of ghcmod-vim:
Make sure that the video plays fullscreen in 720p otherwise the text is illegible.