cache - a flag to indicate if an if_needed value should be stored.
SlotName:
cache yes
Normally, when an if_needed dæmon is triggered, its value is returned and when the same dæmon is triggered again, the value is recomputed. If you wish the value to be remembered, add a cache flag to the slot. The next time and if_needed dæmon is triggered, its result will stored in the corresponding slot of the instance frame that invoked the if_needed dæmon.