Hermes: A Tutorial and Reference Manual - Researcher - IBM

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1.IntroductiontoHermes13 FIGURE1.4.Interfacetothelter FIGURE1.5.Twointerconnectedprocesses PutLine 1.3.Itcreatestheoriginalclient,thelter,andconnectsthemtogether interfaceastheoriginalsingleclientprocess,itcanbefurthercomposed. initiallypasseditsoutputportandtheprexstring. asshownbelowingure1.5.Sincethecompositeprogramhasthesame inputportandoneoutputport,asshowningure1.4.Thelterprogram receivesacallasifitwereaPutLineservice.Eachtimeitiscalledon theoriginallineprecededbyacharacterstringcalledPrefix.Thelteris itsinputportwithalineasparameter,itcallsitsoutputportpassing Thecompositeprogramisaprogramwiththesameinterfaceasingure thedataisnotrestrictedtobeingbytestreamsincontiguousbuers|it socket.Unlikethepipes,lesandsocketsoftraditionaloperatingsystems, typecheckingguaranteesthataroundplugisneverpluggedintoasquare tionsastherstbox.Theinterfacecorrespondstotheshapeoftheplugs; samethreeplugs,andcanthereforebepluggedintothesameconguranentswithplugsandsockets.Wecanthinkoftheprocessingure1.3 oneplugandonesocket.Thecombinationingure1.5isaboxwiththe asacomponentwith3plugs,andtheprocessingure1.4asaboxwith WemakeananalogybetweenHermesprocessesandelectricalcompo- canbeanydatatypesupportedbythelanguage. Let'slookatthelterprogramrst: --initialization receiveParmsfromInit; Out:=Parms.PutLine; Prefix:=Parms.Prefix; GetProgram GetLine PutLine Client Filter PutLine Filter PutLine
141.4.PuttingProcessesTogether newIn; connectParms.ClientPutLinetoIn; aftertheparentinstantiatesthelterandcallstheinitializationport.The returnParms; secondsectionisexecutedrepeatedlyeverytimeacallmessagearriveson --mainloop thelter'sIninputport|thiswillhappenwhentheclientmakesacallon endwhile; Thelterprocesshastwosections.Therstsectionisexecutedjustonce while('true')repeat itsPutLineoutputport. receivePutLineCMfromIn; Let'sbeginwiththeinitialization.Thelter'sinterfaceisdierentfrom returnPutLineCM; callOut(Prefix|":"|PutLineCM.Line); outputport|theconnectiontothePutLineservices|asParms.PutLine, passedthreeoutputportsandastring.Thelter'sparentwillpassone theonewehaveseeninHelloWorldandEcho.Thoseprocesses'parents andaprexstringasParms.Prefix.Itexpectstoreceivebackanoutput variableParms.ClientPutLineaconnectiontotheinputportIn,using In.Thisisdonewiththenewstatement.Itthenassignstheoutputport port,Parms.ClientPutLine,connectedtothelter'sinputportIn. aconnectstatement.TheconnectstatementistheHermesprimitivefor examples,thelterhasrealworktodoafterreturningtheinitialization nolongerbeinitializedafterthereturnstatement.Unliketheprevious call|itmustservicePutLinecallsfromitsclient. intolocalvariables.ThisisnecessarybecausethecallmessageParmswill Aftersavingthetwovariablesitneeds,ittheninitializesitsinputport TheinitializationcoderstcopiesParms.PutLineandParms.Prefix creatingconnectionsbetweenoutputportsandinputports.Itnowreturns connectedtothelter'sinputportIn. theinitializationcallmessage.Thiscallmessagewillcontainanoutputport control"asitwouldinalanguagewithoutmultipleprocesses.Thereturn thesecallswithtransformeddata.Wecodethisasaninnitewhileloop. statementmarkstheendoftheinitializationsectionofthelter,andthe beginningofitsmainsection. withanargumentcomputedbyprexingtheoriginalstringwithastring Ateachiterationoftheloop,wedequeueasinglecallmessageintovariable PutLineCM.Thenweservicethecallbycallingthe`real'PutLineservice Recallthatthereturnstatementreturnsamessage;itdoesnot\transfer prexandacolon.Finally,wereturntheoriginalcallmessage.Thelterwill runindenitelyuntilitsconnectionissevered.We'llseeinalatersection howthisisdone. ThemainjobofthelteristoreceivecallsoninputportIn,andreissue Nowlet'slookatthecodeoftheparentprocess,Compound.Thisprocess
Page 1 and 2: DavidF.BaconArthurP.GoldbergAndyLow
Page 3 and 4: Preface Thisdocumentcontainsatutori
Page 5 and 6: iv3TypeandTypestateChecking 5Resear
Page 8: Tutorial PartI 1
Page 11 and 12: ortransactions.AHermesmoduleisastra
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Page 39 and 40: 322.1.Requirements PutLine PutLine
Page 41 and 42: 342.3.Interfaces WMInterface:callme
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Page 45 and 46: 382.5.Front-endProcess callParms.Ge
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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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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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