nixpkgs/pkgs/misc/bleeding-edge-fetch-info/cabal.nix

 args: with args; fetchurl { 
  url = http://mawercer.de/~nix/repos/cabal.tar.gz;
  sha256 = "62b0059cd57e1fb96930858cb575c379bb129f9f2ba94d9e65a8f2e96b4db04e";}