Hi, This is the most invasive change in the hugs directory, and the last one. Split the main loop into invoke (which performs the computation) and prefix (which sets up the required bits). Change the main loop to call while(1){prefix(); invoke();} for the standard hugs. WinHugs now uses the normal windows message pump which gives it much better performance and no polling. It does this by calling invoke directly. If people would like to see revisions to this patch just ask, its a little more violent than I would like, but I'm not sure there is any better way. If you look at the code for the non-winhugs path, it comes out identical to what was being called before. With this patch, on Windows WinHugs now outperforms the standard console version by about 2 times in output intensive programs ([1..]), and is the same for compute intensive ones (nqueens). Thanks Neil