Hermes: A Tutorial and Reference Manual - Researcher - IBM

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onthehandlerandusedontheexitstatement. withoutraisingabuiltinexceptionorissuingacall.Exitnamesaredened 8.5ExitNames Theexitstatementallowstheprogrammertojumptoahandlerclause Thedeningoccurrenceofanexitnameisahandlerbeginningonexit. 8.Resolution79 Thenamespaceistheidentierlistappearingafterthewordexit.The visibilityforthesameexitname. nameisvisiblethroughoutthemainclauseoftheblockcontainingthe handler.Unlikebasevariables,therecanbeseveraloverlappingregionsof Aprocessnameisusedonlyintheprogramliteralconstruct: exitname,theinnermostvisibledenitionisused. 8.6ProcessNames resolvinganexitname,ifthereareseveralvisibledenitionsofthesame Theappliedoccurrenceofanexitnameisonanexitstatement.When Theidentierdenotestheprocessmoduleofthatname. programliteral:processidentifier Theidentiermustbepresentinthelinkinglistofthesourcemodule.
isconcerned.Allthe\noisewords",likeof,fromandinto,whichmakethe Hermesprogramvalue.Thisisamuchsimplerformasfarasthecomputer Afteramodulehasbeentokenized,parsed,andresolved,itisstoredasa 9TypeCheckingandInference programeasierforpeopletoreadbutlesssyntacticallyregular,aregone. Statementswithembeddedexpressionsareexpandedouttosequencesof statements.Names,likeX,whoseresolutionmaybecontext-sensitive,have beenremoved.Intheirplaceareuniqueidentiers. clauseisaseriesofstatements,andeachstatementisanoperator,alistof operands(variablenames),anda\qualier",whichiseverythingelse.By ofdeclarations,organizedinto\scopes";(3)acollectionofclauses.Each constraintdenitions,organizedintodenitionsmodules;(2)acollection declared. thistime,allbasevariablenamesexceptexpressiontemporarieshavebeen TheHermesprogramvalueis:(1)acollectionoftypedenitionsand inferencerulesareusedforbothinferenceandchecking.Theclassrulesare rules.Therearetwofamiliesofrules:inferencerules,andclassrules.The typesoftheoperands. theexpressiontemporariessothateverybasevariablewillhaveaknown type;(2)typechecking:tocheckthattheoperationsarelegal,giventhe anextrasetofcheckswhichapplyaftertypeinferenceiscomplete. Bothtypeinferenceandtypecheckingaredrivenfromasingletableof Thejobofthenextphaseis:(1)typeinference:tosupplydeclarationsfor thetypeoftheoperandontheleft. theleft.Thesecondkindofruleisredwhenthetypeoftheoperandon therightbecomesknown.Theruleprovidesafunctionwhichdetermines inferencerule:operand Therstkindofruleunconditionallyassignsatypetotheoperandon Therulesappearintheappendix.Thesyntaxofaninferenceruleis: insertat(table,element,position)absent Thetyperulesinthetableentryforthisoperationlooklikethis: rulename() table2orderedtable rulename(operand) tointherulesastable,element,andposition.Thereisnoqualier.The thattheoperationinsertathasthreeoperands,whichwillbereferred Forexample,let'slookattheoperationinsertat.Theheaderlinestates element elementtypeof(table) predefinedinteger()
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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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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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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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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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