shell.nix

let pkgs = import <nixpkgs> { };
    top-level = import ./top-level.nix { haskellPackages = pkgs.haskellPackages;
                                         dontCheck = pkgs.haskell.lib.dontCheck;
                                         cabal-install = pkgs.cabal-install;
                                         testTopLevel = false; };
in
{ haskell-env = pkgs.stdenv.mkDerivation {
    name = "haskell-env";
    buildInputs = [ pkgs.cabal-install top-level.frank.env ];
  };
}