Hermes: A Tutorial and Reference Manual - Researcher - IBM

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possible,andstoresitinadestinationvariable.Theinputportmustbe Receive Thereceivestatementdequeuesamessagefromaninputport,ifthisis simple{statement ::=receivecallmessage{variablefrominport{variable 11.HermesOperations123 initialized. thenthereceivestatementwillblockindenitely. beraised. toreceiveisnon-deterministic. Themessageismovedintothedestinationvariable.Thisvariablewillbein theentrytypestateassociatedwiththeinport.Thechoiceofwhichmessage port.Thepreviouscontentsofthedestinationvariable,ifany,arediscarded. Iftheinporthasconnections,butnomessageiseversenttotheinport, Iftheinporthasnoconnections,thentheDisconnectedexceptionwill Onnormalcompletionofreceive,amessageisdequeuedfromthein- Return Thereturnstatementreturnsacallmessagetoitscallerandresumesexecutionofthecaller.Optionally,anexceptioncanbereturnedtothecaller. simple{statement qualier. inthedenition.Theexceptionnameiswrittenwithoutanytypename ceptionforthatcallmessagetype|eitherDiscarded,oranexceptionlisted Thereturnstatementmustspecifyeithernoexception,oralegalex- ::=returncallmessage{variable Thecallmessagemusthavethetypestateattributesassociatedwiththe [exceptionuser{exception{name] whichisexpectedbythecaller. appropriateexceptiontypestateforareturnwithanexception.Ifthetypestateishigher,coercionsareinsertedtolowerthetypestatetoexactlythat kindofreturn|theexittypestateforareturnwithoutexceptions,orthe theequivalenteectofprocedures,codethereturnstatementasthelast executablestatementoftheprocess,orfollowthereturnstatementwith anexitstatementjumpingtotheendoftheprocess. ment,aswouldbethecaseifprocesseswerepassiveprocedures.Toproduce continuesexecuting. execution.Ifanexceptionisspecied,thatexceptionisraisedinthecaller, notintheprocessissuingthereturnstatement.Theprocessissuingreturn Thereisnoautomaticterminationofaprocessexecutingareturnstate- Afterthereturn,thecallmessageisuninitialized.Thecallerresumes
12411.8.ProcessCreationandCommunicationOperations Send terminedfromthematchinginporttypeoftheoutport.Ifthetypestateis musthavetheentrytypestateorhigher.Thetypeandtypestatearede- higherthantheentrytypestate,itiscoerceddowntotheentrytypestate. inputport.Itsoperandsareasourcevariableandanoutport. Thesendstatementmovesavalueoutofavariableandenqueuesitonan Thevariablewhosevalueistobesentmusthavethecorrecttype,and simple{statement Theoutputportmustbeinitialized. ::=sendsource{expressiontooutport{expression carded,thentheDisconnectedexceptionisraised. Create Iftheinputporttowhichtheoutputportwasconnectedhasbeendis- compiledwithinthemainprogramorwithinotherprocessliterals.Amain setofprocesses.Oneisthemainprogram.Theothersareprocessliterals isavariableoftypepredefined!program.Theresultisanoutport. Thecreateofoperationinstantiatesanewprocess.Theoperandofcreate Theprogrammusthavethetypestatechecked. Theprogramvalueisdenedinthepredefinedmodule.Itconsistsofa secondary::=createofsecondary programistheresultofconvertingtheprocessmoduleproductionofa process.Thismustbeaninputporttype.Whencreateisexecuted,itis sourcemodule. outporttypewhichistheresultofthecreatestatement.Ifitisnot,the checkedthatthisinputporttypeisthematchinginputporttypeofthe exceptionInterfaceMismatchisraised. Theinitializationportisthevariabledeclaredfollowingthekeyword Procedure initializationportwillbeinitialized.Aconnectiontotheinitializationport isreturnedasthevalueofcreate. willexecutetheprogramdenedbythemainprogramintheprogramvalue, beginningatthestatementfollowingthekeywordbegin.Initiallyonlythe Ifthereisnointerfacemismatch,anewprocessiscreated.Thisprocess isacheckedprogram,andtheresultisanoutputport.Aswithcreate, anInterfaceMismatchexceptionisreturnediftheoutputporttypeis Theprocedureofoperationinstantiatesaprocessgenerator.Theoperand secondary::=procedureofsecondary
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DavidF.BaconArthurP.GoldbergAndyLow
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Preface Thisdocumentcontainsatutori
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iv3TypeandTypestateChecking 5Resear
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Tutorial PartI 1
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ortransactions.AHermesmoduleisastra
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61.2.GettingStarted|ASimpleHermesPr
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81.2.GettingStarted|ASimpleHermesPr
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101.2.GettingStarted|ASimpleHermesP
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121.4.PuttingProcessesTogether thec
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141.4.PuttingProcessesTogether newI
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fullycheckedfortypeandtypestateerro
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constructs:thenewinput-port,connect
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201.5.DeclarationsandDenitions whil
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221.5.DeclarationsandDenitions Stan
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whichtheoutputportconnects|calledth
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261.6.ASimpleServer begin QuitCM:Qu
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281.6.ASimpleServer towritedataabst
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toaservice,whileretainingtheability
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322.1.Requirements PutLine PutLine
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342.3.Interfaces WMInterface:callme
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asmallchangetotheinterfaceFilter.Re
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382.5.Front-endProcess callParms.Ge
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402.5.Front-endProcess paringavalue
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ationtable[expr].Wehaveencounteredt
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ishiddenandinnowayaectsthesemantics
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462.7.TheWindowManager callCurrentW
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name.Ifwewaitedtobuildtheapplicatio
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502.8.CreatingaWindowApplication re
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522.8.CreatingaWindowApplication be
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examplesillustratedhere. errorhandl
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563.TypeandTypestateChecking anerro
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583.TypeandTypestateChecking Therei
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604.1.ExpressionBlocks anexpression
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624.3.Variants thevariantcomponents
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thetypestate(i.e.addattributes),but
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accesscontrol{anyonecangetit. 664.4
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685.ResearchDirectionsinHermes
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6Introduction Thereferencemanualpre
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Page 142 and 143: A.1LexicalRules Webeginwiththerules
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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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