default.nix

overrides = let
      composeManyExtensions =
        pkgs.lib.foldr (x: y: pkgs.lib.composeExtensions x y)
        (self: super: { });
      pythonOverides = self: super: {
        python = super.python.override {
          packageOverrides = python-self: python-super: {
            # tests fail on linux
            pyopenssl =
              python-super.pyopenssl.overridePythonAttrs
              (old: { doCheck = false; });

          };
        };
      };

    in composeManyExtensions [
      pythonOverides
      (import foo).haskellOverrides
      (self: super:
        with pkgs.haskell.lib;
        let foo=foo;
        in {};  #etc