Hermes: A Tutorial and Reference Manual - Researcher - IBM

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willbeuninitialized,andthedestinationvariablewillhavethetypestate thenmovedintothedestinationvariable.Aftertheoperation,thevariant attributesofthevariantcomponent. Reveal 11.HermesOperations117 Therevealstatementrevealsahiddenvariantcomponent.Theoperand coercedbacktohidden. exists,thenthatcomponentisrevealed.Ifthecaseofthevariantissuch thatthecomponentbeingrevealeddoesnotexist,theexceptionCaseError isavariantcomponent.Thevariantmustbehidden|ifitisrevealed,itis Ifthecaseofthevariantissuchthatthecomponentbeingrevealed simple{statement israised,andthevariantremainshidden. ::=revealvariant{component usually)generatedautomaticallyasaresultofacoercionwhichdropsthe caseattribute. Thehideoperationisacoercion.Itcanbeexplicitlycoded,or(more Hide Itmustbeinitialized.Afterexecutingthestatement,thevariantwillbe hidden. Thesingleoperandofahidestatementisavariableofvarianttype. simple{statement ::=hidevariant{variable Thecaseofoperatortakesavariantasoperandandreturnsthecaseof Case thevariant.Theresultisavalueofthevariant'scasetype. secondary::=caseofsecondary
InputPort,OutputPort,CallmessageTypeFamilies 11811.7.VariantOperations 11.8ProcessCreationandCommunication type{construction ::=callmessage( ::=inportofcallmessage{typeentry{typestate ...] )[constant{parameters] exitexit{typestate [user{exception]... [minimum] [component{declaration[,component{declaration] constant{parameters ::=constant([component{name[,component{name]... ::=outportofinport{type Thetypefamiliesinputport,outputport,andcallmessageareusedin \programming-in-the-large"|thatis,thedivisionofsystemsintoprocesses, minimum::=minimumminimum{typestate user{exception ::=exceptionuser{exception{nameexception{typestate ]) thecreationofprocesses,thecreationofbindingsbetweenprocesses,and type,and(2)aformaltypestate,calledtheentrytypestate. portsorentriesarenotvaluesofvariables. inportvaluesarestoredininportvariablesjustasintegerorstringvalues made.ItshouldbeemphasizedthatinHermesinportsarevalues,andthat arestoredinintegerorstringvariables.Thisiscompletelyconsistentwith therestofHermes,butmightappear\dierent"becauseinmanylanguages thecommunicationbetweenprocesses. Usuallythemessagetypewillbeacallmessagetype.However,themessagetypecanbeanytype,sincesendcanbeusetotransmitanyvalueto aninport. callmessage,sinceallcallstatementswillgenerateinitializedcallmessages, willhavewhensent.Youmayomitinit(*)fromtheformaltypestateofa andusingsendtodeliveranuninitializedcallmessageispointless. Aninporttypedenitionspecies(1)atypename,calledthemessage Aninputportorinportisamessagequeuetowhichconnectionscanbe Theentrytypestateisthetypestatethatvaluesofthemessagetype
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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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Page 78 and 79: 6Introduction Thereferencemanualpre
Page 80 and 81: 7LexicalandSyntacticRules lectionso
Page 82 and 83: 8Resolution name,attributename,exce
Page 84 and 85: 8.1.2ComponentNames eachhaveacompon
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Page 96 and 97: 6.Determinethepostconditionsforeach
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Page 100 and 101: 11 HermesOperations Throughoutthere
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Page 128 and 129: Connect Theconnectstatementhastwoop
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Page 142 and 143: A.1LexicalRules Webeginwiththerules
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Page 154 and 155: formal{variable module{name::=ident
Page 156 and 157: Typestatesappearinginparticularcont
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Page 160 and 161: operandwillnolongerbeinitialized. B
Page 162 and 163: Followingaretheinferencefunctionsap
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Page 166 and 167: copy(source,destination):Foreachatt
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Page 172 and 173: 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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