<<-- UndoEventImpl.mesa>> <<-- written by Bill Paxton, June 1981>> <<-- last edit by Bill Paxton, April 5, 1982 12:38 pm>> DIRECTORY UndoEvent, TextNode; UndoEventImpl: CEDAR PROGRAM IMPORTS TextNode EXPORTS UndoEvent = BEGIN OPEN UndoEvent; Create: PUBLIC PROC RETURNS [Ref] = { RETURN [TextNode.pZone.NEW[EventBody]] }; Note: PUBLIC PROC [event: Ref, undoProc: UndoProc, undoRef: REF Change] = { IF event = NIL THEN RETURN; event.subevents _ TextNode.pZone.NEW[SubEventBody _ [event.subevents,undoProc,undoRef]] }; Undo: PUBLIC PROC [undoEvent: Ref, currentEvent: Ref _ NIL] = { <<-- calls undoProc[undoRef] for each subevent >> <<-- in reverse order that subevents originally happened>> 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: Ref] = { IF event # NIL THEN event.subevents _ NIL }; Empty: PUBLIC PROC [event: Ref] RETURNS [BOOLEAN] = { RETURN [event=NIL OR event.subevents=NIL] }; Start: PUBLIC PROC = { }; END.