add - add a value to a slot in a frame
add value to slot of frame
A predicate that adds a new value to a slot in a frame. If the slot is not present, it is created.
Slots can normally only contain a single value unless they have been declared multivalued.
Triggers the if_added dæmon.
Given the generic definition of cylinder, some instances can be defined as:
c isa cylinder with height: 2; radius: 4! add red to colour of c?
If an attempt is made to add a value to an already existing slot that is not declared multivalued, the call fails with an error.
multivalued, if_added