[Nix-dev] overview about hack-nix and how it works

[Andres Loeh]

If you say

$ nix-env -iA nixpkgs_sys.haskellPackages.leksah

or

$ nix-env -f /etc/nixos/nixpkgs -iA haskellPackages.leksah

then it will be built for the current GHC default version, which is now 7.0.4.
You can also do

$ nix-env -f /etc/nixos/nixpkgs -iA haskellPackages_ghc703.leksah

in order to get it built with GHC-7.0.3.

Alternatively, you can go via the package rather than attribute names:

$ nix-env -i haskell-leksah-ghc7.0.4
$ nix-env -i haskell-leksah-ghc7.0.3

HTH,
  Andres