UndoEventImpl.mesa
Copyright Ó 1985, 1986, 1991, 1992 by Xerox Corporation. All rights reserved.
written by Bill Paxton, June 1981
last edit by Bill Paxton, April 5, 1982 12:38 pm
Doug Wyatt, January 30, 1992 5:49 pm PST
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] = {
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: Event] = { IF event # NIL THEN event.subevents ¬ NIL };
Empty: PUBLIC PROC [event: Event] RETURNS [BOOL] = { RETURN [event=NIL OR event.subevents=NIL] };
END.