self: super: {

  xmonad-with-packages = self.callPackage <nixpkgs>/pkgs/applications/window-managers/xmonad/wrapper.nix {
    inherit (self.haskellPackages) ghcWithPackages;
    packages = self: [ self.haskellPackages.xmonad-contrib ];
  };

  # this gives the error
  # error: value is a path while a set was expected


}