anchor.diff:  , enableE2E ? true
   , enableRST ? true
   , enableSpelling ? true, gtkspell ? null
  +, enableNotifications ? false
   , enableLaTeX ? false, texLive ? null
   }:
   
  
positive.code:   ] ++ optionals enableJingle [ farstream gst_plugins_bad libnice ]
      ++ optional enableE2E pythonPackages.pycrypto
      ++ optional enableRST pythonPackages.docutils
      ++ optional enableLaTeX texLive;
  
    postInstall = ''
  
negative.code: assert enableE2E -> pythonPackages.pycrypto != null;
  assert enableRST -> pythonPackages.docutils != null;
  assert enableSpelling -> gtkspell != null;
  assert enableNotifications -> pythonPackages.notify != null;
  assert enableLaTeX -> texLive != null;
  
  with stdenv.lib;
  