~/.nixpkgs/config.nix

config.nix

{
  packageOverrides = pkgs:
    let
      haskell = pkgs.haskellPackages_ghc704;
      hiPrio  = pkgs.lib.hiPrio;

    in
    rec {
      mathijs = pkgs.buildEnv {
        name = "mathijs";
        paths = [ haskell.haskellPlatform # _2011_2_0_1
                  haskell.uhc
                  haskell.ghcMod
                  pkgs.unison
                  pkgs.nodejs
                  pkgs.auctexWithPreview
                  pkgs.emacs
                  pkgs.emacs23Packages.haskellMode
                  pkgs.dejavu_fonts
                  pkgs.jruby165
                  pkgs.MPlayer
                  hiPrio (pkgs.texLive)
                  pkgs.texLiveBeamer
                  pkgs.texLiveExtra
                ];
      };
    };
}