<> <> <> <> <> DIRECTORY PropertyLists; PropertyListsImpl: 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.