Haddock version during build

[Claus Reinke]

>> I was more hoping for a way to ask GHCi for *its libpath*, so that I can 
>> stuff that into a GHC API session *running in that GHCi*,
>> and similarly for a GHC-compiled GHC API session.
> 
> I don't get it - why not just do 'ghc --print-libdir'?  It sounds like GHCi 
> is a red herring here.  You have to know the libdir regardless of whether 
> you're using the GHC API from within GHCi or in a compiled program.

because the 'ghc' first in $PATH might not be the 'ghc' in use. GHCi
is just a good way to illustrate the issue:

    $ /cygdrive/c/ghc/ghc-6.9.20080217/bin/ghcii.sh
    GHCi, version 6.9.20080217: http://www.haskell.org/ghc/  :? for help
    Loading package base ... linking ... done.
    Prelude> :!ghc --print-libdir
    c:/ghc/ghc-6.6.1
    Prelude>

It is yet another incarnation of the "how does ghc find its other parts"
issue (considering multiple OSs, multiple ghcs per platform, mix of
installed/uninstalled ghcs): 

1 someone gives you $GHC with the path to a ghc: how do you
    find the matching ghc-pkg?

    GHC_PKG="${GHC}-pkg" has a chance of working, well, 
    modulo ".exe", and modulo 'ghc' sometimes being a script
    to arrange for local-platform-specific settings..

    perhaps "find `dirname $GHC` -name 'ghc-pkg*'" instead?

    life would be easier if 'ghc-pkg' was 'ghc --manage-packages',
    just as 'ghci' is 'ghc --interactive' - then there'd be a single entry 
    point to all of ghc/ghci/ghc-pkg.

2 someone dumps you into a GHCi session: how do you find the
    matching ghc-pkg?

    perhaps 'System.Environment.getProgname' and back to (1)?
    no - see haddocks for 'System.Environment.getProgname'.

    perhaps ':!ghc-pkg'?
    wrong again, if that finds a program, that might be the 'ghc-pkg'
    for a different ghc installation..

3 you write code to the GHC API: how do you write calls to
    'newSession' without hardcoding the libpath, so that the code 
    works with whatever ghc compiles it?

    perhaps:
    ghcDir = "ghc --print-libdir" |> (fmap dropLineEnds . hGetContents)
    as I have used, naively, to avoid fixed paths?
    wrong again, see above.

4 someone gives you a $GHC: how do you find the matching
    html docs and manpage?

    'haskell_doc.vim' in my haskellmode plugins for Vim does a
    lot of guesswork to try and find the docs, and still has to have
    a manual override option for when it fails to guess correctly.

Life for 2/3/4 would be easier if there was a GHC.Paths module
to import, with the paths relevant for the host ghc. Having that
module in a package ghc-paths, with fields describing the paths,
would be a useful bonus for tools/scripting.

Any clearer?-)
Claus

PS. If this isn't clearer, perhaps someone else could jump
    in and try to explain it better? Unless, of course, I'm the
    only one experiencing these issues?-)