let rev = "0d576d7eb875b83ada78dca788981cccf2e4d883"; np = builtins.fetchTarball { url = "https://github.com/nixos/nixpkgs/archive/${rev}.tar.gz"; sha256 = "178j5kp89is5a6vkbj83g0yr4ykgibp1lwhybvgp7sfw9rk9fy5d"; }; config = { allowBroken = true; overlays = []; packageOverrides = pkgs: rec { haskellPackages = pkgs.haskellPackages.override { overrides = haskellPackagesNew: haskellPackagesOld: rec { rf = haskellPackagesNew.callPackage ./cabal.nix { }; }; }; }; }; pkgs = import np { inherit config; }; in rec { inherit pkgs; rf = pkgs.haskellPackages.rf; }