anchor.diff:        s,"flac","${flac.bin}/bin/flac",
         s,"mp3val","${mp3val}/bin/mp3val",
       }' beetsplug/badfiles.py
  +  '' + optionalString enableConvert ''
  +    sed -i -e 's,\(util\.command_output(\)\([^)]\+\)),\1[b"${ffmpeg.bin}/bin/ffmpeg" if args[0] == b"ffmpeg" else args[0]] + \2[1:]),' beetsplug/convert.py 
     '' + optionalString enableReplaygain ''
       sed -i -re '
         s!^( *cmd *= *b?['\'''"])(bs1770gain['\'''"])!\1${bs1770gain}/bin/\2!
  
positive.code:               || enableEmbyupdate
                || enableAcousticbrainz)
                                     pythonPackages.requests2
      ++ optional enableDiscogs      pythonPackages.discogs_client
      ++ optional enableEchonest     pythonPackages.pyechonest
      ++ optional enableLastfm       pythonPackages.pylast
  
negative.code: 
  assert enableAcoustid    -> pythonPackages.pyacoustid     != null;
  assert enableBadfiles    -> flac != null && mp3val != null;
  assert enableConvert     -> ffmpeg != null;
  assert enableDiscogs     -> pythonPackages.discogs_client != null;
  assert enableEchonest    -> pythonPackages.pyechonest     != null;
  assert enableFetchart    -> pythonPackages.responses      != null;
  