Hermes: A Tutorial and Reference Manual - Researcher - IBM

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ecordsandcallmessages)containpartscalledcomponentswhicharenamed usingthedotnotationcommontomanyprocedurallanguages.Thetype names.Theseidentiersarecalledbasevariables.Structuredvariables(e.g. endprocess Youonlyneedtodeclarethetypeofsimpleidentiersusedasvariable --codeforprocesscompound1.IntroductiontoHermes21 ofacomponentlikeParms.GetLineisinferredfromthetypeofthebase variableParms. writedownischeckedagainstthetypethatisinferred. maywriteboolean#'true'insteadof'true'.Inthatcase,thetypeyou maywriteatypespecierevenwhenitisnotnecessary|forexample,you usinginferencerules.Incertaincases,thetypeofanexpressioncannotbe inferred,andyoumustprecedetheexpressionwithatypespecier.You raryvariabletoholdtheresultofthatexpression.Examplesofexpressions arefunctioncalls(e.g.Parms.GetLine()),arithmeticoperations(e.g.A+B) andliterals(e.g.'true').Thecompilerinfersthetypeofanexpression Whenyouwriteanexpression,youareimplicitlydeclaringatempo- denitionsdescribingwhatastandardclientispassedoninitialization,and theinterfacestothestandardservicesGetLine,PutLine,andGetProgram: 1.5.2Definitions Nowlet'slookatthedenitionsmodules.Let'sbeginwithStandard|the Standard:using()definitions PutLineInterface:callmessage( Line:Charstring) constant(Line) GetLineIn:inportofGetLineInterfacefg; GetLineInterface:callmessage( PutLineOut:outportofPutLineIn; PutLineIn:inportofPutLineInterfaceffullg; Line:Charstring) exitfinit(Line)g exceptionEndStreamfg; exitffullg; StandardInterface:callmessage( GetLineOut:outportofGetLineIn; PutLine:PutLineOut, GetProgram:GetProgramOut, ParmString:Charstring) constant(GetLine,PutLine,GetProgram,ParmString) GetLine:GetLineOut,
221.5.DeclarationsandDenitions StandardIn:inportofStandardInterfaceffullg; GetProgramInterface:callmessage( StandardOut:outportofStandardIn; exitffullg; Name:Charstring, TheProgram:Program) onlyrefertotypesdenedwithinStandarditself,ortopredenedtypes. GetProgramOut:outportofGetProgramIn; enddefinitions ModuleStandarddoesnotimportanyotherdenitionsmodules.Itmay GetProgramIn:inportofGetProgramInterfacefinit(Name)g; exceptionNotFoundfinit(Name)g; constant(Name) Thismoduledenesfourcallinterfaces.Inourpreviousanalogyofprocessesaselectricalcomponentswithplugsandsockets,interfacesdenitions exitfinit(Name),full(TheProgram)g informationthatcanbecommunicatedbetweentwoprocesses. describetheshapesoftheplugsandsockets.Acallinterfacedenesthe facesmustbedenedindefinitionsmodulesandprocessesinprocess modules.Thisseparationmakesaninterfaceavailabletoanyprocessthat wantstouseit.Thecompilerrequiresthataprocessmodulewhichuses evenmoreinformationonainterface. inoutparameters([Ada83]).Hermesallows(andrequires)youtospecify andtypeofaprocedure'sparameters.Pascalalsoletsaprogrammerdistinguishconstantandvarparameters;Adaletsyoudistinguishin,out,and Youdeneaninterfaceseparatelyfromtheprocessesthatuseit;inter- Mosthigh-levellanguagesprovideamechanismfordeningthenumber conformtothesameinterfacecancommunicate. thecallerexpectstoreceiveuponreturn).Anycallerandreceiverwhich ilarlyitdeneswhatareceiverpromisestoreturn(andthereforewhat promisestosend(andthereforewhatthereceiverexpectstoreceive);sim- aninterfaceconformtotheinterface.Theinterfacedeneswhatacaller sage,aninputport,andanoutputport. eachparameter.Inthecallingprocess,youmustsupplyalistofarguments selectedcomponentnotation,e.g.Parms.PutLine. ofmatchingtype.Inthecalledprocess,younametheparametersusing alistofthoseparameterswhosevaluesmustnotchangeduringthecall. EachinterfacetypicallyincludesthreeHermestypedenitions:acallmes- calledprocess. Acallmessagedenitioncontainsadeclarationofthenameandtypeof fortypestatechecking.Atypestateisasetofprogramattributesknown Youmayincludeaconstantslistinthecallmessagedenition.Thisis Younowneedtosupplytheadditionalinformationwhichisrequired Youmustsupplyalistoftheexceptionswhichmaybereturnedbythe
Page 1 and 2: DavidF.BaconArthurP.GoldbergAndyLow
Page 3 and 4: Preface Thisdocumentcontainsatutori
Page 5 and 6: iv3TypeandTypestateChecking 5Resear
Page 8: Tutorial PartI 1
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Page 39 and 40: 322.1.Requirements PutLine PutLine
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6Introduction Thereferencemanualpre
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7LexicalandSyntacticRules lectionso
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8Resolution name,attributename,exce
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8.1.2ComponentNames eachhaveacompon
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onthehandlerandusedontheexitstateme
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theelementwillalsobeknownbyapplying
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documentationpurposesevenwheretheya
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ments.Therstargumenttocasemustbeava
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Ifinit(CM)ispresentandCMisacallmess
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6.Determinethepostconditionsforeach
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droppedattributesafternormalcomplet
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11 HermesOperations Throughoutthere
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Thediscardstatementremovesthevaluef
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Ifnoneoftheclausescanexitsnormally,
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Ifthereisanoptionalselectexpression
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stmemberisanatomwithprintnamematchi
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types.Additionally,theoperations\an
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Less,Less-equal,Greater,Greater-equ
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RecordTypeFamily 11.5RecordOperatio
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valueofthetable,ifany,isdiscarded.
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thetableisordered,theelementisinser
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notallowedonconstantcopies.Avariabl
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thereisnoselectedelement,aNotFounde
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willbeuninitialized,andthedestinati
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Itistheabilityforprogramstosendandr
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Connect Theconnectstatementhastwoop
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possible,andstoresitinadestinationv
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incompatiblewiththeinputporttypeoft
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Inspect-polymorph willincludefinit(
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theprogramwhichembedsit.Thereforeth
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type).Ifthecheckfails,theexceptionD
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isusuallygeneratedasacoercionwhenme
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A.1LexicalRules Webeginwiththerules
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accuracy against andy assert drop e
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Thesimplestatements: simple{stateme
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oolean{guard event{guard::=eventinp
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::=(expression)AppendixA.HermesConc
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user{exception constant{parameters
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formal{variable module{name::=ident
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Typestatesappearinginparticularcont
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destination,source,andposition.Some
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operandwillnolongerbeinitialized. B
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Followingaretheinferencefunctionsap
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lowestentrycondition(message,port):
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copy(source,destination):Foreachatt
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assert(continued) Description:Evalu
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case(continued) Description:Copythe
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copy(continued) Preconditions: unco
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drop(continued) SpecialRules:Thenum
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exists(continued) SpecialRules:Thes
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forall(continued) Description:Ifeve
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greater(continued) Description:Ifso
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insert{at(table,element,position) T
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integer{literal(result) TypeRules:
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merge{at(continued) Description:Rem
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not(result,source) TypeRules: Appen
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print(variable) TypeRules:None Prec
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emove(element,table) TypeRules: App
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select(continued) SpecialRules:Allt
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subtract(result,source1,source2) Ty
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unary{minus(result,source) TypeRule
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wrap(continued) Preconditions: var(
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definitions predefined:using() Appe
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);'named'->typename:typenameffullg
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{{Specicinformationneededtocomplete
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attrdefinition:record( attributeid:
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statement:record( id:statementid, o
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{{Ablockstatementqualieridentiesthe
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{{expressionisfalse. ifqualifier:re
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{{expression.The'element'rootvariab
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[ASU88]AlfredV.Aho,RaviSethi,andJer
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[SYB87a]RobertE.Strom,ShaulaAlexand
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AppendixC.PredenedModule215 coercio
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AppendixC.PredenedModule217 dening,
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variablename discarded,29 variant,6
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