anchor.diff:  
     # Purity: Waf is normally downloaded by bootstrap.py, but
     # for purity reasons this behavior should be avoided.
  +  wafVersion = "1.8.12";
     waf = fetchurl {
  -    url = http://ftp.waf.io/pub/release/waf-1.8.5;
  -    sha256 = "0gh266076pd9fzwkycskyd3kkv2kds9613blpxmn9w4glkiwmmh5";
  +    urls = [ "http://ftp.waf.io/pub/release/waf-${wafVersion}"
  +             "http://waf.io/waf-${wafVersion}" ];
  +    sha256 = "12y9c352zwliw0zk9jm2lhynsjcf5jy0k1qch1c1av8hnbm2pgq1";
     };
   in
   
   stdenv.mkDerivation rec {
  -  name = "mpv-${version}";
  -  version = "0.9.2";
  +
  +  name = "mpv-${meta.version}";
   
     src = fetchurl {
  -    url = "https://github.com/mpv-player/mpv/archive/v${version}.tar.gz";
  -    sha256 = "0la7pmy75mq92kcrawdiw5idw6a46z7d15mlkgs0axyivdaqy560";
  +    url = "https://github.com/mpv-player/mpv/archive/v${meta.version}.tar.gz";
  +    sha256 = "1i3cinyjg1k7rp93cgf641zi8j98hl6qd6al9ws51n29qx22096z";
     };
   
     patchPhase = ''
  
positive.code:     '';
    };
  }
  
negative.code:   '';
  
    meta = with stdenv.lib; {
      version = "0.12.0";
      description = "A media player that supports many video formats (MPlayer and mplayer2 fork)";
      homepage = http://mpv.io;
      license = licenses.gpl2Plus;
  