anchor.diff:      };
       "head" = {
         fetchzipversion = 3;
  -      version = "2017-09-01";
  -      rev = "95c48711f60092ad9108fe78d4b84c5a3eac84ad";
  -      sha256 = "2f5e993dfef17ee621804730e4f1db14dc75ac03f69ee6483b3fff709c81230d";
  +      version = "2017-10-08";
  +      rev = "43dfdc08ba57ce164e99e11226bcfad31db413e4";
  +      sha256 = "3ae356d19d0b6248615088ad36b3dad3c05114b787828c94eb17872bc2171fac";
       };
     };
     source = sources."${channel}";
  
positive.code: { stdenv
  , autoreconfHook
  , fetchgit
  , fetchurl
  , lib
  
  
negative.code: 
    src =
      if channel == "head" then
        fetchFromGitHub {
          version = source.fetchzipversion;
          owner = "xiph";
          repo = "opus";
          inherit (source) rev sha256;
        }
      else
  