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

 args: with args; fetchurl { 
  url = http://mawercer.de/~nix/repos/cabal.tar.gz;
  sha256 = "33bdbe8f0c213dcc28da88a2775f81f72e89209806e26b412699220c3db206ec";}