Hermes: A Tutorial and Reference Manual - Researcher - IBM

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inspectanelementormergeatableataparticularposition,locatethe subtablefromatable,ndthesizeofthetable,anditerate(repeataset ofstatementsonceforeachelementofthetable). positionofanelementwithparticularcontents,anditerateinorder. Orderedtablesadditionallysupporttheseoperations:insert,remove,or InBoundedBuffer,thesingleactionofthePutserviceconsistsofinsertingthedesignatedlineintotheendofthetableQueue.Theinsert 1.IntroductiontoHermes29 ifyouwish,bywriting: isordered.However,youmayinsertelementsatanypositioninthetable statementinsertsanelementintotheendofatablebydefaultifthetable toinsertsomethingatposition3,theremustbeanelementatposition2, anelementpreviouslyatposition3,itmovestoposition4,andsimilarly orelseyouwillgetaRangeErrorexception. allelementsathigherpositionshavetheirpositionsincremented.Ifyoutry youspecifyposition3,thenewelementappearsatposition3.Iftherewas insertElementintoTableat(Position); Inthiscase,youmustsupplyaninteger-valuedposition.Forexample,if thepositionsofalltheotherelementsmoveupbyone,sotheprevious wewrotetheexpressioncopyof. inGetCM.Line.Whenyouremovetherstelementfromanorderedtable, discardPutCM.Line|inthedenitionofPutLineInterface,parameter intothetable,ratherthancopyingit.Thismeansthatafterthestatement Lineisconstant|wemustmoveacopyofPutCM.Line.Thatexplainswhy isexecuted,thesourceoperandisdiscarded.Sincewe'renotallowedto TheGetserviceclauseremovestherstentryfromthetableandplacesit Onemoretechnicalpointaboutinsert:thestatementmovesitsoperand meanssimplythrowingitaway.Callmessagesandportsaretreatedspecially:Whenacallmessage,oranyvaluewhichcancontaincallmessages TheQuitservicecallterminatestheloop,andhenceterminatesthe nalized|thatis,theirvaluesarediscarded.InBoundedBuffer,thatwould bethequeue,thebooleanvariableRunning,thethreeserviceports,and secondelementnowbecomesrst. theinitializationport.FormostHermesdatatypes,discardingthevalue process. executingitslaststatement.Allvariableswhichremaininitializedare- discarded,thecallmessagesarereturned.EachcallmessagetypehasadefaultDiscardedexception,e.g.GetLineInterface.Discarded.Whenan Disconnectedexception.Anyprocesswhichbecomesisolatedbecauseall itsconnectionstotheoutsideworldarebrokenisequivalenttoaterminated inputportisdiscarded,connectionstothatportarebroken;attemptsto (e.g.aninputportwhichmayhaveseveralcallmessagesonitsqueue)is Let'slookmorecloselyatprocesstermination.Aprocessterminatesafter processandcanbesafelygarbage-collectedbytheimplementation. sendmessagesoverthoseconnectionswillfailandthecallerwillreceivea
toaservice,whileretainingtheabilitytorevokeaccess,giveoutaconnectiontoalterprocesswhichalsosupportsaQuitservicethatyoucall Summary:Wehaveshownthestructureofatypicalserver:anin- Thishasthefollowingconsequences:Togiveaprocesstemporaryaccess whenyouwanttorevokeaccess.Ifyou'reprogrammingashellwhichis mightrunwild,makesurethatoninitialization,youonlypassrevocable 301.6.ASimpleServer outputports.Thenifyourevokealltheports,theprocesswillbecome isolated,eectivelycancellingtheprocess. goingtocreateprocessesrunningarbitraryprogramswhichyou'reafraid putportperservice,somelocalstate,andaniteratedselectstatement. informationhidingofdataabstractionandobject-orientedlanguagesbut Booleanguardsmaybeusedtoprioritizethecallsortoconditionallydisablecertainservices.Wehaveclaimedthatserverprocessesachievethe withadditionaladvantages.Youhavelearnedaboutthetableandordered tabletypefamilies.Youhavelearnedwhathappenswhenprocessesterminate,andthatyoucanusetheabilitytoterminateltersasameans foraccessrevocationandterminationofchildprocesses.Youhavelearned booleanguard,eventguard,Discardedexception,Disconnectedexception,RangeErrorexception,processtermination,theselect,insertand thefollowingHermesconcepts:alternativeclauses,enableanddisable, removestatements,thecopyofandsizeofoperations.
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
Page 13 and 14: 61.2.GettingStarted|ASimpleHermesPr
Page 15 and 16: 81.2.GettingStarted|ASimpleHermesPr
Page 17 and 18: 101.2.GettingStarted|ASimpleHermesP
Page 19 and 20: 121.4.PuttingProcessesTogether thec
Page 21 and 22: 141.4.PuttingProcessesTogether newI
Page 23 and 24: fullycheckedfortypeandtypestateerro
Page 25 and 26: constructs:thenewinput-port,connect
Page 27 and 28: 201.5.DeclarationsandDenitions whil
Page 29 and 30: 221.5.DeclarationsandDenitions Stan
Page 31 and 32: whichtheoutputportconnects|calledth
Page 33 and 34: 261.6.ASimpleServer begin QuitCM:Qu
Page 35: 281.6.ASimpleServer towritedataabst
Page 39 and 40: 322.1.Requirements PutLine PutLine
Page 41 and 42: 342.3.Interfaces WMInterface:callme
Page 43 and 44: asmallchangetotheinterfaceFilter.Re
Page 45 and 46: 382.5.Front-endProcess callParms.Ge
Page 47 and 48: 402.5.Front-endProcess paringavalue
Page 49 and 50: ationtable[expr].Wehaveencounteredt
Page 51 and 52: ishiddenandinnowayaectsthesemantics
Page 53 and 54: 462.7.TheWindowManager callCurrentW
Page 55 and 56: name.Ifwewaitedtobuildtheapplicatio
Page 57 and 58: 502.8.CreatingaWindowApplication re
Page 59 and 60: 522.8.CreatingaWindowApplication be
Page 61 and 62: examplesillustratedhere. errorhandl
Page 63 and 64: 563.TypeandTypestateChecking anerro
Page 65 and 66: 583.TypeandTypestateChecking Therei
Page 67 and 68: 604.1.ExpressionBlocks anexpression
Page 69 and 70: 624.3.Variants thevariantcomponents
Page 71 and 72: thetypestate(i.e.addattributes),but
Page 73 and 74: accesscontrol{anyonecangetit. 664.4
Page 75 and 76: 685.ResearchDirectionsinHermes
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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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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