anchor.diff:  in
   
   assert withQt5 -> qtbase != null;
  -assert withQt5 -> qtquick1 != null;
   assert withQt5 -> qttools != null;
   
   stdenv.mkDerivation rec {
  
positive.code: 
    buildInputs =
      [ mesa libpulseaudio ]
      ++ (if withQt5 then [ qtbase qtquick1 qttools ] else [ qt4 ]);
  
    nativeBuildInputs = [ cmake pkgconfig ] ++ optional withQt5 extra-cmake-modules;
  
  
negative.code: { stdenv, lib, fetchurl, cmake, mesa, pkgconfig, libpulseaudio
  , qt4 ? null, extra-cmake-modules ? null, qtbase ? null, qttools ? null
  , debug ? false }:
  
  with lib;
  