nix pls play nice ;0;

rf.nix

@@ -2,7 +2,7 @@ let
    
    rev = "d7c0d9a7f83b7f80e08888c040ea8a2ab7ca5f71";
    np = builtins.fetchTarball {
-     url = https://github.com/nixos/nixpkgs/archive/$rev.tar.gz;
+     url = "https://github.com/nixos/nixpkgs/archive/${rev}.tar.gz";
      sha256 = "1i5a0si7m80w1a987crm9xmbin35jpmdcsk3113xxp9xcw0v23rn";
    };
    config = {