OT: need help with library versioning conflicts (on BSD)

[David Fries <djf@gmx.ch>]

Hi Debian guys,

I have been working on porting the Haskell-Platform to the FreeBSD
operating system for a while now and some issues have come up. I've
asked the same questions on the Haskell Café & the Arch Linux Haskell
mailing list hoping someone would give me some cues, but I didn't get
any replies what so ever. I guess the guys are all busy with other stuff
at the moment. So I thought I maybe the Debian camp might help out. I
know this is way off topic, but we *nix guys must stick together,
right ;)

The haskell-platform has been released over a year ago and it still
isn't available on FreeBSD. So I decided to do it myself. However I've
run into problems. Let me begin by giving you an idea of the situation
(in the example below I'm talking about the 2009ner version of the
Platform, but the same issues persist with the latest version):

Our approach is very compiler-centric. We're still running on GHC-6.10.4
(6.12 is in the testing phase). Our ghc compiler package contains a
couple of "builtin" (i.e. not available as separate separate packages)
libraries that it requires. For instance, network-2.2.1.2 is one of
them. The problem is that the Haskell-Platform requires version 2.2.1.4.
Under normal circumstances I would port network-2.2.1.4 to FreeBSD and
then specify it as a dependency of the Platform port (Currently, the
plan is to make it a meta package). But then we would end up with two
(exposed) versions of the network library installed on the system. 

For example, let's assume that I have the following Haskell source
(Networking.hs):

module Networking where

import Data.ByteString.Lazy
import Data.Maybe
import Network.HTTP
import Network.Stream
import Network.URI

getBinary :: String -> IO ByteString
getBinary url = do
  uri <- return $ fromJust $ parseURI url
  rsp <- simpleHTTP $ request uri
  getResponseBody rsp
    where
      request uri = Request
        { rqURI = uri
        , rqMethod = GET
        , rqHeaders = []
        , rqBody = empty }


When I try to compile it (`ghc --make Networking.hs`) I get the
following:

Networking.hs:12:30:
    Couldn't match expected type `network-2.2.1.2:Network.URI.URI'
           against inferred type `URI'
    In the first argument of `request', namely `uri'
    In the second argument of `($)', namely `request uri'
    In a stmt of a 'do' expression: rsp <- simpleHTTP $ request uri

However, the following thing could help:

$ ghc --make Networking.hs -package network-2.2.1.2

The above workaround ain't acceptable to the FreeBSD committers, so I
have to come up with something better to get the Port into the official
repository.

The way things are setup, there is no way for me to replace the
network-2.2.1.2 library which is part of our ghc compiler package.

In a perfect world, I'd be able to install the required HP dependencies
without tripping ghc up. Then we could switch over to the platform and
use that as a foundation for GHC-6.12. 

Currently the attitude in our camp is that cabal packages/libraries that
were installed together with the compiler is simply are off limits and
shouldn't be tampered with. Do you have a similar policy? 

I've been also reading the this mailing list's archives. It seems you
have been facing similar version discrepancies. And dealt with it by
patching the setup to make cabal shut up [1]. How did that approach work
out for you?

Do you have a strategy to avoid future conflicts? By marking certain
libraries as off limits perhaps?

I'm grateful for any comments

regards and TIA,
dave

[1] http://lists.debian.org/debian-haskell/2009/10/msg00007.html