anchor.diff:  
   let
     optionalPlugins = {
  -    beatport = enableBeatport;
       chroma = enableAcoustid;
       discogs = enableDiscogs;
       echonest = enableEchonest;
  
positive.code: { stdenv, fetchFromGitHub, writeScript
  , buildPythonPackage, pythonPackages, python
  
  , enableAcoustid   ? true
  , enableBeatport   ? true
  , enableDiscogs    ? true
  , enableEchonest   ? true
  , enableFetchart   ? true
  , enableLastfm     ? true
  , enableMpd        ? true
  , enableReplaygain ? true
  , enableWeb        ? true
  
  , bashInteractive, bashCompletion
  }:
  
  assert enableAcoustid    -> pythonPackages.pyacoustid     != null;
  assert enableBeatport    -> pythonPackages.responses      != null;
  assert enableDiscogs     -> pythonPackages.discogs_client != null;
  assert enableEchonest    -> pythonPackages.pyechonest     != null;
  assert enableFetchart    -> pythonPackages.responses      != null;
  assert enableLastfm      -> pythonPackages.pylast         != null;
  assert enableMpd         -> pythonPackages.mpd            != null;
  assert enableReplaygain  -> pythonPackages.audiotools     != null;
  assert enableWeb         -> pythonPackages.flask          != null;
  
  
negative.code:     pythonPackages.munkres
      pythonPackages.musicbrainzngs
      pythonPackages.mutagen
      pythonPackages.pathlib
      pythonPackages.pyyaml
      pythonPackages.unidecode
      python.modules.sqlite3
      python.modules.readline
    ] ++ optional enableAcoustid   pythonPackages.pyacoustid
      ++ optional enableFetchart   pythonPackages.requests2
      ++ optional enableDiscogs    pythonPackages.discogs_client
      ++ optional enableEchonest   pythonPackages.pyechonest
      ++ optional enableLastfm     pythonPackages.pylast
      ++ optional enableMpd        pythonPackages.mpd
      ++ optional enableThumbnails pythonPackages.pyxdg
      ++ optional enableReplaygain pythonPackages.audiotools
      ++ optional enableWeb        pythonPackages.flask;
  
    buildInputs = with pythonPackages; [
      beautifulsoup4
  