ProXL provides three mechanisms for handling events and activating callbacks. First of all, events are handled whenever Prolog is waiting for input. This includes while Prolog is reading input from the terminal, even under the Quintus User Interface. The also includes while debugging. Events are not handled while Prolog computations are under way (Prolog is not interruped to handle events).
In situations where the program needs to wait while events are being
handled, the predicates handle_events/N are appropriate. For
those cases where more flexibility is required, there are many
predicates described in pxl-evf that will return events.
These can be used in conjunction with dispatch_event/N,
described below, to handle callbacks. Alternatively, callbacks need
not be used: you can handle the event any way you like.