anchor.diff:      ++ lib.optional enableFfmpeg ffmpeg
       ++ lib.optionals enableGStreamer (with gst_all_1; [ gstreamer gst-plugins-base ])
       ++ lib.optional enableEigen eigen
  -    ++ lib.optional enableCuda [ cudatoolkit gcc49 ]
  +    ++ lib.optional enableCuda [ cudatoolkit gcc5 ]
       ;
   
     propagatedBuildInputs = lib.optional enablePython pythonPackages.numpy;
  
positive.code:     rev = version;
      sha256 = "1l0w12czavgs0wzw1c594g358ilvfg2fn32cn8z7pv84zxj4g429";
    };
  
    preConfigure =
      let ippicvVersion = "20151201";
  
negative.code: { lib, stdenv, fetchurl, fetchpatch, fetchFromGitHub, cmake, pkgconfig, unzip
  , zlib
  , enableIpp ? false
  , enableContrib ? false
  