Hermes: A Tutorial and Reference Manual - Researcher - IBM

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select(continued) SpecialRules:Allthevariablesidentiedintheeventguardsassociatedwiththeclauseslistedinthestatementqualiermustbeinclass AppendixB.HermesOperations187 resultvariableidentiedineachbooleanguardassociatedwithaclause inport.Ifthereisanoperand,itstypemustbethesameasthatofthe onnormalexitfromtheirassociatedtestclauses.Theentrytypestate foreachbooleanguardclauseisidenticaltotheentrytypestateforthe ment.Allbooleanguardresultvariablesmusthavetheinitattribute theotherwiseclause,isthemeetofthenormalexittypestatefromall thebooleanguardtestclauses(ortheselectstatemententrytypestateiftherearenobooleanguards).Thenormalexittypestatefrom mustbeoftypepredefined!boolean.Allvariablesassociatedwith selectstatement.Theentrytypestateforeachselectclause,including eventguardsmusthavetheinitattributeonentrytotheselectstate- listedinthequalier.Otherwise,eachbooleanguardresultvariable Description:Theinstructionqualiercontainsatableofselectclauses, eachofwhichspeciesoneorbothofaneventguardandaboolean astatementclause.Theselectoperationrstexecutesallthestatementsinclausesidentiedbybooleanguards,yieldingvaluesforallthe guard,aswellasanassociatedstatementclause.Aneventguardis theselectstatementisthemeetofthenormalexittypestatesofall theselectclauses,includingtheotherwiseclause. aninputportvariable,whileabooleanguardidentiesavariableand eventguardwhoseassociatedinputportisnonempty,isselected.The booleanguardvariables.Iftheselectoperationhasanoperand,itis statementsinthestatementclauseassociatedwiththeselectedclause arethenexecuted.Iftherearenoenabledselectclauses,thenthestatementsinthe\otherwise"clause(identiedintheinstructionqualier) outport2outport messagetypeof(outport) Exceptions:Depletion,Disconnected selectclauseswithtruebooleanguardvaluesareenabled.Inaddition, selectclauseswithoutbooleanguardsareenabled.Ifanyselectclause erationhasnooperands,thebooleanguardvaluesmustbeboolean,and isenabled,oneenabledclausewitheithernoeventguard,orwithan clauseforwhichthetestsucceedsbecomes\enabled."Iftheselectop- testedforequalitywitheachbooleanguardvariable,andeachselect Qualier:select send(outport,message) TypeRules: areexecuted. Seex11.3,p.98
188B.6.OperationDescriptions send(continued) Preconditions: Description:Addmessagetothequeueassociatedwiththeinputport Qualier:absent var(message) init(outport) lowestentrycondition(message,outport) connectedtooutport,leavingmessageuninitialized. Postconditions: makeuninit(message) size(result,table) TypeRules: Preconditions: table2table predefined!integer Exceptions:Depletion Seex11.8,p.124 Description:Setresultequaltothenumberofelementsintable. Qualier:absent string{literal(result) init(table) var(result) Postconditions: makeinit(result) TypeRules: Preconditions: SeealsoSpecialRules result2string Exceptions:Depletion,(DuplicateKey) Seex11.6,p.114 SpecialRules:Eachelementofthetableappearinginthestatement Description:Copythestringstoredintheinstructionqualierandstore duplicatekey(result) var(result) qualiermustcorrespondtooneoftheenumerationvaluesappearing inthedenitionoftheelementtypeofresult.Thatis,asingletontable containingtheelementmustequaloneoftheenumerationvalues. Postconditions: thecopyinresult. makeinit(result) Qualier:literal Seex11.6,p.109
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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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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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Page 172 and 173: copy(continued) Preconditions: unco
Page 174 and 175: drop(continued) SpecialRules:Thenum
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Page 180 and 181: greater(continued) Description:Ifso
Page 182 and 183: insert{at(table,element,position) T
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Page 186 and 187: merge{at(continued) Description:Rem
Page 188 and 189: not(result,source) TypeRules: Appen
Page 190 and 191: print(variable) TypeRules:None Prec
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Page 196 and 197: subtract(result,source1,source2) Ty
Page 198 and 199: unary{minus(result,source) TypeRule
Page 200 and 201: wrap(continued) Preconditions: var(
Page 202 and 203: definitions predefined:using() Appe
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Page 224 and 225: AppendixC.PredenedModule217 dening,
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