Hermes: A Tutorial and Reference Manual - Researcher - IBM

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Connect Theconnectstatementhastwooperands.Therstoperand(beforethe keywordto)isanoutportvariable.Thesecondisaninportvariable.The simple{statement ::=connectoutport{variabletoinport{variable 11.HermesOperations121 inportvariablemustbeofthematchinginporttypeoftheoutportvariable outportvariableisassignedtoaconnectiontotheinportwhichisthe type,andmustbeinitialized. currentvalueoftheinportvariable. Call Thepreviousvalueoftheoutportvariable,ifany,isdiscarded.The simple{statement function{reference ::=calloutport{variablecall{arguments ::=call(outport{expression)call{arguments arguments.Theoutportmustbeinitialized.Thematchinginporttypemust haveanelementtypewhichisacallmessage.Theargumentsarematched guages.Theoperandsofthecallstatementareanoutportandalistof Thecallstatementcorrespondstoaprocedurecallinconventionallan- association associated{pair ::=outport{primarycall{arguments used,thenthereshouldbeonefewerargumentthanparameter,themissingparameterbeingtheresult,whichispassedasanunnamedvariable.If uptothecallmessagecomponentseitherbyposition,ifpositionalnotation isused,orbyname,ifassociationnotationisused.Iffunctionnotationis positionalnotationisusedwithafunctioncall,thenthelastcallmessage componentistheresult.Ifassociationnotationisused,thentheomitted constantparameterswillbeloweredtoexactlymatchtheentrytypestate Eachargumentmusthaveatypestateatleastashighastheentrytypestate ofthecorrespondingparameter.Thetypestatesofargumentsmatching constantparameterswillremainunchanged. ofthecorrespondingparameter.Thetypestateofargumentsmatchingnon- call.Twovariablesoverlapifoneoftheirnamesisaprexoftheotheror theyarethesame. Eachargumentmusthaveatypematchingitscorrespondingparameter. Overlappingvariablescannotbepassedastwoormoreargumentsofa
12211.8.ProcessCreationandCommunicationOperations ingtheargumentsintothecallmessage,(3)sendingthecallmessageto theinputporttowhichtheoutputportisconnected,(4)waitingforthe nofunctioncallcanhaveanymodiableparameterexceptitsresult. arepartsofexpressions,andexpressionsmaynotmodifytheiroperands, procedurereturns4,youwillnotchangethevalueof3.)Sincefunctioncalls ables.Ifthesevariablesarepassedtomodiableparameters,themodica- tionsarelost.(Forexample,ifyoupass3toaninoutparameter,andthe Thecallisexecutedby:(1)creatinganewcallmessagevalue;(2)mov- Itshouldbenotedthatexpressionsareevaluatedintotemporaryvari- callmessagetobereturned,(5)movingthecallmessagecomponentsback theneventuallythemessagewillbereceived. ismade,andthereceivingprocessrepeatedlyissuesreceivestatements, arereturnedinthesametypestatetheyweresent. ontheseoutputportsaremergedfairly.Thismeansthatifacallorsend intotheargumentvariables,(6)throwingawaythecallmessage. aportconnection,theDisconnectedexceptionisraised.Thearguments riedoutasinaregularcall,butadditionally,theexceptionisraisedinthe Ifthecallisreturnedwithanexception,thenalltheabovestepsarecar- Ifseveraloutputportsareconnectedtothesameinputport,thencalls caller.Thiscanonlyhappenifthereexistsadeclarationofthatexceptionin thecallmessagetypedenition.Thefullnamefortheexceptionincludesthe callmessagetypeandtheexceptionname|.. Iftheinputporthasbeenthrownaway,leavingtheoutputportwithout parametersareaddedanddropped.Theseaddsanddropsareappliedto betweentheentryandreturntypestatesdeneswhichattributesofthe .Discardedisraisedinthecaller.Thecallmessageisreturned withtheparametersintheminimumtypestateasdenedinthecallmessage tatejustpriortothecall,fromtheentrytypestate,andfromthetypestate denedforthenormalorexceptionalreturnbeingmade.Thedierence Thetypestateafterexecutingacallstatementisderivedfromthetypes- Iftheprocessowningthecallmessagediscardsit,thentheexception theargumentsmatchingtheparameters. Forexample tionsampleinterface.Failure,thetypestatewillbefinit(p),init(a), constantparametersecond,itcannotretainitsattributeeven(b),which even(b),init(c)g.Sinceamatchestheconstantparameterfirst,it mayretainitsadditionalattributeeven(a).Sincebmatchesthenon- isdroppedpriortothecall.Onnormalreturnfromthecall,thetypestate willbefinit(p),init(a),even(a),init(b),init(d)g.Onexcep- typestatepriortothecallis:finit(p),init(a),even(a),init(b), callp(a,b,c,d); even(a),negative(a),init(b),init(c)g. Supposethetypeofpissampleoutport,denedabove.Supposethe
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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
Page 78 and 79: 6Introduction Thereferencemanualpre
Page 80 and 81: 7LexicalandSyntacticRules lectionso
Page 82 and 83: 8Resolution name,attributename,exce
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Page 142 and 143: A.1LexicalRules Webeginwiththerules
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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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