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  • Briefly describe two types of demon used in the frame system described in lectures.

    Answer: Pick any two of:

    if_added
    demons are triggered when a new value is put into a slot.
    if_removed
    demons are triggered when a value is removed from a slot.
    if_replaced
    is triggered when a slot value is replaced.
    if_needed
    demons are triggered when there is no value present in an instance frame and a value must be computed from a generic frame.
    if_new
    is triggered when a new frame is created.
    range
    is triggered when a new value is added. The value must satisfy the range constraint specified for the slot.
    help
    is triggered when the range demon is triggered and returns false.