Portage slots for GHC?

[Duncan Coutts]

Oops, I sent this previously from my @gentoo address so it got rejected
by the mailing list. Re-sending my reply in case anyone other than
Dinko Tenev is interested.

On Thu, 2007-12-13 at 11:25 +0200, Dinko Tenev wrote:
> Hi,
> 
> I'm using GHC on Gentoo, and so far I've had to stay clear of GHC 6.6,
> because I've also installed stuff depending on 6.4.2, like wxHaskell,
> for instance. 

On that specific issue, we prodded the wxHaskell team the other day
complaining that the current release only works with ghc-6.4.2 and old
with old versions of wxGTK. They are apparently looking at doing a
release that'll work with recent wxGTK and ghc-6.6 and 6.8.

> Now I see a new version of mtl, which I also have
> installed, depends on 6.6.1, while all of the rest of the stuff is
> "lagging behind" with a dependency on 6.4.2. 

Yes, it's annoying. The only things left that do not work with 6.6 are
hs-plugins and wxHaskell.

> Of course, I can easily solve the problem partially by masking out the
> new version for mtl, but this is going to become a major inconvenience
> with new versions of GHC and its dependents.

Yep.

> What I'm getting at is, can we please have separate slots for GHC
> 6.4.2 and 6.6 on portage?

Sadly not because portage is not clever enough to deal with the kind of
dependencies you end up with by doing that. Portage does not know that
some libs are installed for one ghc and some for another, so it'd try
and satisfy a dependency for mtl using the mtl you'd installed for
ghc-6.4.2 when in fact you were building something for 6.6.1.

You may have heard of other new portage features that sound like they'd
help, they don't. We've thought about this a lot and it is not feasible
in with the current portage.

We could slot multiple versions of a lib for the same ghc, but not slot
ghc itself.


-- 
Duncan Coutts : Gentoo Developer (Haskell team)