anchor.diff:        (mkFlag mmsSupport "mms")
         (mkFlag mpg123Support "mpg123")
         (mkFlag aacSupport "aac")
  +      (mkFlag lameSupport "lame-encoder")
         (mkFlag (!stdenv.isDarwin && pulseaudioSupport) "pulse")
         (mkFlag (!stdenv.isDarwin && jackSupport) "jack")
         (mkFlag stdenv.isDarwin "osx")
  
positive.code: , mmsSupport ? true, libmms
  , mpg123Support ? true, mpg123
  , aacSupport ? true, faad2
  , pulseaudioSupport ? true, libpulseaudio
  , jackSupport ? true, libjack2
  , gmeSupport ? true, game-music-emu
  
negative.code:     ++ opt mmsSupport libmms
      ++ opt mpg123Support mpg123
      ++ opt aacSupport faad2
      ++ opt lameSupport lame
      ++ opt zipSupport zziplib
      ++ opt (!stdenv.isDarwin && pulseaudioSupport) libpulseaudio
      ++ opt (!stdenv.isDarwin && jackSupport) libjack2
  