example of how I manage packages with Nix

config.nix

{
    packageOverrides = super: rec {
        /*
        haskell = super.haskell // {
            compiler = super.haskell.compiler // {
                ghc801 = super.stdenv.lib.overrideDerivation super.haskell.compiler.ghc801 (oldAttrs: {
                    patches = oldAttrs.patches ++ [./ghc.801.patch];
                });
            };
        };
        */
        my-packages = [
            #haskell.compiler.ghc801
            super.cabal2nix
            super.cabal-install
            super.nix-repl
            super.nox
            super.patchelf
            super.stack
            super.haskellPackages.djinn
            super.haskellPackages.ghc-events-analyze
            super.haskellPackages.ghcid
            super.haskellPackages.haskdogs
            super.haskell.packages.ghc801.hasktags
            super.haskellPackages.hlint
            super.haskellPackages.hoogle
            super.haskellPackages.pointfree
            super.haskellPackages.pointful
            super.haskellPackages.stylish-haskell
        ];
    };

}

I put use this file as ~/.nixpkgs/config.nix and then install packages with

$ nix-env -i -A nixpkgs.my-packages