[Nix-dev] Re: Building an old GHC for a new Cabal...

[Yury G. Kudryashov]

Marc Weber wrote:

>>   I do have GHC 6.10 still installed; but why does it not build
>>   against the new GHC?
> 
> Because of a design decision Andres Loeh once made:
> 
> try cat `which ghc`. You'll see that ghc finds the packages containing
> ghc libraries by iterating over $PATH.
Marc, did you see the command in the original message? It was `nix-env --
install cabal-install-0.8.0`, and the real question was "why nix-env -i 
cabal-install pulls cabal-install from ghc-6.10 packages?"

The answer is: because of "haskellPackages_ghc6122 = lowPrio" in all-
packages.nix. You need to select haskellPackages_ghc6122.cabalInstall 
manually.

And, as Marc said, it is not usefull to have two ghc versions in the same 
environment (at least, in the current setup).