10.15.2.1 Events

An FDBG event can (currently) belong to one of the two following major classes:

constraint event

A constraint is woken.

labeling event

Three events belong to this class, namely:

• the labeling of an FD variable is started
• an FD variable gets constrained
• the labeling of an FD variable fails, i.e. all elements of its domain have been tried and caused failure

These events are intercepted by the FDBG core. When any of them occurs, the appropriate visualizer (see FDBG Visualizers) gets called with a representation of the event (a Prolog term) as extra arguments.