UndoEvent.mesa
Copyright © 1985, 1986 by Xerox Corporation. All rights reserved.
written by Bill Paxton, June 1981
last edit by Bill Paxton, April 5, 1982 12:39 pm
Doug Wyatt, September 5, 1986 3:04:27 pm PDT
An undo event is a series of actions that are to be undone as a unit.
The event record contains sufficient information to undo the actions.
UndoEvent: CEDAR DEFINITIONS
= BEGIN
Event: TYPE = REF EventBody;
EventBody: TYPE = RECORD [subevents: SubEvent];
SubEvent: TYPE = REF SubEventBody;
SubEventBody:
TYPE =
RECORD [
next: SubEvent,
undoProc: UndoProc,
undoRef: REF Change
];
Change:
TYPE;
-- EditNotify.Change
undo list contains changes.
UndoProc:
TYPE =
PROC [undoRef:
REF Change, currentEvent: Event];
procedure supplied by client to undo the effects of a particular subevent
Create:
PROC
RETURNS [Event];
Note:
PROC [event: Event, undoProc: UndoProc, undoRef:
REF Change];
adds <undoProc, undoRef> to list of subevents
Undo:
PROC [undoEvent: Event, currentEvent: Event ←
NIL];
calls undoProc[undoRef, currentEvent] for each subevent
in reverse order that subevents originally happened
currentEvent arg is to record the effects of Undo so it too will be undoable
Reset:
PROC [event: Event];
resets the list of subevents to NIL
Undo automatically does a Reset when it is finished
Empty:
PROC [event: Event]
RETURNS [
BOOL];
returns true if subevents list is empty
END.