anchor.diff:  { stdenv, fetchurl, pkgconfig, glib, systemd, boost, darwin
   , alsaSupport ? true, alsaLib
  +, avahiSupport ? true, avahi, dbus
   , flacSupport ? true, flac
   , vorbisSupport ? true, libvorbis
   , madSupport ? true, libmad
  
positive.code:       (mkFlag opusSupport "opus")
        (mkFlag soundcloudSupport "soundcloud")
        "--enable-debug"
      ]
      ++ opt stdenv.isLinux
        "--with-systemdsystemunitdir=$(out)/etc/systemd/system";
  
negative.code:     ++ opt stdenv.isDarwin darwin.apple_sdk.frameworks.CoreAudioKit
      ++ opt stdenv.isLinux systemd
      ++ opt (stdenv.isLinux && alsaSupport) alsaLib
      ++ opt avahiSupport avahi
      ++ opt avahiSupport dbus
      ++ opt flacSupport flac
      ++ opt vorbisSupport libvorbis
      # using libmad to decode mp3 files on darwin is causing a segfault -- there
  