DIRECTORY Pipal, RefTab;PipalModify: CEDAR DEFINITIONS = BEGINWorld: TYPE = REF WorldRec;WorldRec: TYPE = RECORD [object: Pipal.Object,state: REF _ NIL,undoEvents: Events _ NIL, -- first undoable event head of listredoEvents: Events _ NIL, -- first redoable event head of listselected: LIST OF Pipal.Object _ NIL  --  must be children of the object];Event: TYPE = REF EventRec;EventRec: TYPE = RECORD [message: Pipal.ROPE,object: Pipal.Object _ NIL,state: REF _ NIL];Events: TYPE = LIST OF Event;Undo: PROC [world: World];Redo: PROC [world: World];Reset: PROC [world: World];Commit: PROC [world: World];Do: PROC [world: World, message: Pipal.ROPE, newObject: Pipal.Object _ NIL, newState: REF _ NIL];Reachable: PROC [root, candidate: Pipal.Object] RETURNS [BOOL];ReachableFromRoots: PROC [roots: Pipal.Objects, candidate: Pipal.Object] RETURNS [BOOL];replaceMethod: Pipal.Method;ReplaceProc: TYPE = PROC [parent: Pipal.Object, table: RefTab.Ref] RETURNS [newParent: Pipal.Object];Replace: ReplaceProc;TransitiveReplace: PROC [oldRoots: Pipal.Objects, table: RefTab.Ref] RETURNS [newRoots: Pipal.Objects];ReplaceInWorld: PROC [world: World, oldChild, newChild: Pipal.Object _ NIL];END.   ò  PipalModify.mesa	Copyright Ó 1988 by Xerox Corporation.  All rights reserved.Bertrand Serlet January 26, 1988 1:22:24 am PSTLouis Monier January 25, 1988 9:41:33 am PSTTheoryThis modules define how to modify Pipal "worlds".WorldGeneric Operations on WorldsUndoes while possible.Flushes undoEvents and redoEvents.Stacks a new event containing the current object and state on the undo list and modifies current state and object.Transitive ClosureTransitive closure is a common operation that has to be efficient. Is candidate object reachable by enumeration from the root object?Is candidate object reachable by enumeration from any root object?ReplacementReplaces each child of parent found in table.Table maps [old child] -> [new child].No replaceMethod method => crash and burn.If no child of parent is found in table, it is possible but not imperative that newParent=parent.Short cut for applying the replace method.No replace method => crash and burn.Replaces every child by its matching object everywhere reachable from oldRoots.  Recursively replaces each parent.  If no first is reachable from oldRoots then newRoots=oldRoots.Temporary Hack ....Short cut for applying the replacing everywhere in world oldChild by newChild.Ê  ˜ –"Cedar" stylešœ™Jšœ<™<Icodešœ/™/K™,—J˜ šÏk	œ˜J˜ —JšÏnœœœ˜&head™Ibodyšœ1™1—™Kšœœœ
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