Hermes: A Tutorial and Reference Manual - Researcher - IBM
Hermes: A Tutorial and Reference Manual - Researcher - IBM
Hermes: A Tutorial and Reference Manual - Researcher - IBM
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6.Determinethepostconditionsforeachpossibleoutcomeoftheoperation.Foreachoutcome,usetherulesgiveninthetabletodetermine<br />
exceptionoutcomeprovideditsoper<strong>and</strong>isakeyedtable. |forexample,itmaysaythattheoperationhasaDuplicateKey 10.TypestateChecking89 whichattributestoaddtoordropfromthetypestate. 7.Checkthatafteradding<strong>and</strong>droppingtheappropriateattributesthe 8.Wheneachtypestateiscomputed,propagatethattypestatetothe resultingtypestateisvalid.<br />
tions: NamedProgram:record(A:Charstring,B:Program); Let'sapplythesestepstoanexample.SupposeIhavethesetypedeniercionoperationstolowerthetypestatetothatmeettypestate.<br />
youhavejustcomputedforthispathtothatdestination.Insertco-<br />
destination.Ifthatdestinationalreadyhasatypestate,computethe<br />
ProgramRepository:tableofRffullgkeys(A); meet(asdenedabove)ofitsprevioustypestate<strong>and</strong>thetypestate<br />
init(R),init(P),init(P.A),init(P.B),checked(P.B)g.Supposethe oftypeProgramRepository.Supposethecurrenttypestateis:finit(I), therearethreerulesrelevanttotypestatechecking.Theseare:thepreconditionrules,thepostconditionrules,<strong>and</strong>theexceptionlist.Forinsert,<br />
statementbeingcheckedis: LookatthetableofoperationrulesinAppendixB.Aftertheclassrules, insertPintoR; NowsupposeIisoftypeinteger,PisoftypeNamedProgram<strong>and</strong>Ris<br />
thepreconditionrulesare (init(table),lowestelementstate(element,table),var(table), var(element),duplicatekey(table))<br />
attributesareforbidden.SectionB.4explainshowtoapplyeachpreconditionfunctiontodeterminetherequired<strong>and</strong>forbiddenattributes.<br />
attributesarerequired:finit(R),init(P),init(P.A),init(P.B)g.This attributeisforbidden:checked(P.B).Sincealltherequiredattributes init(P.B)g.AnyattributesofPorofitscomponentsotherthantheabove Ruleinit(table)saysthatthetableoper<strong>and</strong>mustbeinitialized.Rule SubstitutingPintothisformaltypestateyieldsfinit(P),init(P.A), lowestelementstate(element,table)saysthattheelementoper<strong>and</strong>must beinthelowesttypestateconsistentwiththeelementtypestateofthetable. isffullg,whichisanabbreviationoffinit(*),init(A),init(B)g. (Elementtypestateisdenedbelowinsection11.6.)Theelementtypestate Thersttwomembersofthelistaretypestatepreconditionfunctions.<br />
Asaresultofapplyingthepreconditionrules,itisdeterminedthatthese
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