<<>> <> <> <> <> <> DIRECTORY UndoEvent; UndoEventImpl: CEDAR PROGRAM EXPORTS UndoEvent = BEGIN OPEN UndoEvent; Create: PUBLIC PROC RETURNS [Event] = { RETURN [NEW[EventRep ¬ [NIL]]] }; Note: PUBLIC PROC [event: Event, undoProc: UndoProc, undoRef: REF Change] = { IF event = NIL THEN RETURN; event.subevents ¬ NEW[SubEventBody ¬ [event.subevents,undoProc,undoRef]] }; Undo: PUBLIC PROC [undoEvent: Event, currentEvent: Event ¬ NIL] = { <> <> sub: SubEvent; IF undoEvent=NIL THEN RETURN; sub ¬ undoEvent.subevents; undoEvent.subevents ¬ NIL; UNTIL sub=NIL DO sub.undoProc[sub.undoRef,currentEvent]; sub ¬ sub.next; ENDLOOP }; Reset: PUBLIC PROC [event: Event] = { IF event # NIL THEN event.subevents ¬ NIL }; Empty: PUBLIC PROC [event: Event] RETURNS [BOOL] = { RETURN [event=NIL OR event.subevents=NIL] }; END.