anchor.diff:  , gnutls
   , gtk
   , libgcrypt
  +, libice
   , libjpeg
   , libnotify
   , libsecret
  +, libsm
   , libsoup
  +, libx11
  +, libxext
  +, libxtst
   , telepathy_glib
  -, xorg
  +, xorgproto
   , zlib
   
   , channel
   }:
  -
  -assert xorg != null ->
  -  xorg.libICE != null
  -  && xorg.libSM != null
  -  && xorg.libX11 != null
  -  && xorg.libXext != null
  -  && xorg.libXtst != null
  -  && xorg.xproto != null;
   
   let
     inherit (stdenv.lib)
  
positive.code:     gnutls
      gtk
      libgcrypt
      libjpeg
      libnotify
      libsecret
      libsoup
      telepathy_glib
      zlib
    ] ++ optionals (xorg != null) [
      xorg.libICE
      xorg.libSM
      xorg.libX11
      xorg.libXext
      xorg.libXtst
      xorg.xproto
    ];
  
    configureFlags = [
  
negative.code:     "--enable-schemas-compile"
      "--${boolWt (telepathy_glib != null)}-telepathy"
      "--${boolWt (libsecret != null)}-secret"
      "--${boolWt (libxll != null)}-x"
      "--${boolWt (gnutls != null)}-gnutls"
      "--${boolWt (libgcrypt != null)}-gcrypt"
      "--${boolWt (avahi != null)}-avahi"
  