PropertyListsImpl.mesa
Copyright © 1985 by Xerox Corporation. All rights reserved.
Christian Jacobi, September 19, 1985 3:33:07 pm PDT 4:15 pm
Christian Jacobi, March 12, 1986 8:13:23 pm PST
DIRECTORY
PropertyLists;
PropertiesImpl: CEDAR MONITOR
EXPORTS PropertyLists =
BEGIN
PropList: TYPE = PropertyLists.PropList;
GetProp: PUBLIC ENTRY PROC [propList: PropList, prop: REF] RETURNS [REF ← NIL] = {
ENABLE UNWIND => NULL;
WHILE propList # NIL DO
IF propList.first.key = prop THEN RETURN [propList.first.val];
propList ← propList.rest;
ENDLOOP;
};
PutProp: PUBLIC ENTRY PROC [propList: PropList, prop: REF, val: REF ← NIL] RETURNS [PropList] = {
ENABLE UNWIND => NULL;
IF val=NIL THEN RETURN [RemPropInternal[propList, prop]]
ELSE RETURN [PutPropInternal[propList, prop, val]]
};
RemPropInternal: INTERNAL PROC [propList: PropList, prop: REF] RETURNS [PropList] = INLINE {
lst: PropList ← propList;
lag: PropList ← NIL;
UNTIL lst = NIL DO
rest: PropList ← lst.rest;
IF lst.first.key = prop THEN {
IF lag = NIL THEN RETURN [rest];
lag.rest ← rest;
RETURN [propList];
};
lag ← lst;
lst ← rest;
ENDLOOP;
RETURN [propList];
};
PutPropInternal: INTERNAL PROC [propList: PropList, prop: REF, val: REF] RETURNS [PropList] = INLINE {
lst: PropList ← propList;
lag: PropList ← NIL;
WHILE lst # NIL DO
IF lst.first.key = prop THEN {
--Update list element in place
lst.first.val ← val;
RETURN [propList];
};
lag ← lst;
lst ← lst.rest;
ENDLOOP;
--prop not found on property list
lst ← LIST[[key: prop, val: val]];
IF lag = NIL THEN RETURN [lst];
lag.rest ← lst;
RETURN [propList];
};
Enumerate: PUBLIC PROC [propList: PropList, proc: PropertyLists.EachProp] RETURNS [quit: BOOL←FALSE] = {
--yes, this needs no special monitoring...
--but I don't want each user to have to prove again
--that this module never creates a state where Enumerate would fail
FOR l: PropList ← propList, l.rest WHILE l#NIL AND ~quit DO
quit ← proc[l.first.key, l.first.val];
ENDLOOP;
};
END.