Hermes: A Tutorial and Reference Manual - Researcher - IBM

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Inspect-polymorph willincludefinit(name)g.Componentnamewillbediscardedbeforemovingthewrappedvalueintox.Theresultingtypestatewillbefinit(x), Thetypeswillmatch,buttheformaltypestateinthewrapperofy 11.HermesOperations127 init(x.id),positive(x.id)g. compound{statement ::=inspectdeclaration morphisconstant. ceptthatinsteadofmovingthewrappedvalue,aconstantcopyismade. Theinspect-polymorphstatementbehaveslikeanunwrapstatementex- Thisallowsthevalueofapolymorphtobeexamined,evenifthepoly- endinspect begin [statement;]... frompolymorph{expressioninspect{typestate whichwouldbelegalevenifthepolymorphywereconstant: Hereisanalternativeversionoftheunwrapstatementshownabove, wouldnotbeaccessible,sincethetypestateinsidethestatementwouldbe thatcomponentwouldnotbediscardedintheconstantcopyx,butit inspectx:personfromyfinit(*),init(id),positive(id)g operation. simplyfinit(y)init(x),init(x.id),positive(x.id)g. Assumingthatthewrappedvaluehadaninitializedcomponentname, TheexceptionPolymorphMismatchisraisedexactlyasforanunwrap endinspect; begin .../*statementsreferringtox*/ Type morphwrapper.Thisisaninitializedvalueoftypepredefined!typeofvalue. Thetypeofoperationevaluatestothetypeinformationstoredinthepoly- Thevalueincludesthetypename,thedenitionsmoduledeningthetype name,andalltheimporteddenitionsmodules. Theoperandmustbeaninitializedpolymorph. secondary::=typeofsecondary Typestate secondary::=typestateofsecondary
12811.9.PolymorphOperations Thevalueincludesthetypestate,thedenitionsmoduledeningthetypestate,andalltheimporteddenitionsmodules. Thetypestateofoperationevaluatestothetypestateinformationstored inthepolymorphwrapper.Thisisaninitializedvalueoftypepredefined!typestateofvalue. intocheckedprogramvalues.Alternatively,youcancreateprogramvalues, linearsourceformandpassthemtotheHermescompilerforconversion 11.10ProgramOperations InHermes,youcancreateprogramsintwoways:Youcanwritethemin Theoperandmustbeaninitializedpolymorph. either\fromscratch",orbycomposingormodifyingotherprogramvalues. pilingitintomachinecodeforthemachineormachinesonwhichthepro- statement ingacheckedprogramwillbemissingthepredefined!checkedattribute. Tocheckafullyinitializedinstanceofprogramvariablepgm,executethe tributepredefined!checked.Aprogrambuiltfromscratchorbymodify- assertchecked(pgm); InmostimplementationsofHermes,checkingaprogramalsoentailscom- Aprogramvalueobtainedfromthecompilerwillhavethetypestateat- instantiateaprogramwhichisnotchecked. predefined!program. ProgramLiteral gramwillbeinstantiated.Thisisanoptionalandmachine-dependentop- timization;theprogrammercannotdirectlymanipulatethemachinecode. Thechecking,however,isnotoptional.Itisatypestateerrortotryto Theoperationsinthissectionareusedtoconstructobjectsoftype Thepredefined!programdenitionisshownintheappendix. program{literal ::=process(declaration) begin [declaration{section] [pragma] Thecompilerwillchecktheprogramliteralatthesametimethatitchecks Aprogramliteraloperationiscodedasaself-deningvalue.Thevalueof theliteralisthevalueoftheprogramaftertranslationbythecompiler. ::=processlink{name endprocess [handler]... [statement;]...
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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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Page 96 and 97: 6.Determinethepostconditionsforeach
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Page 100 and 101: 11 HermesOperations Throughoutthere
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Page 142 and 143: A.1LexicalRules Webeginwiththerules
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Page 154 and 155: formal{variable module{name::=ident
Page 156 and 157: Typestatesappearinginparticularcont
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Page 162 and 163: Followingaretheinferencefunctionsap
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Page 172 and 173: copy(continued) Preconditions: unco
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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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