Hermes: A Tutorial and Reference Manual - Researcher - IBM
Hermes: A Tutorial and Reference Manual - Researcher - IBM
Hermes: A Tutorial and Reference Manual - Researcher - IBM
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it.Avariableisconstantataparticularprogrampointif: 10.6Constants Althoughweusetheterm\variable"todenoteacellwhichcanholdavalue <strong>and</strong>appearasanoper<strong>and</strong>,sometimes\variables"are\constant"!Thatis, sometimesitisonlylegaltoaccessthevalueofavariablebutnottochange 8810.5.Coercions<br />
Itisabasevariable,<strong>and</strong>anenclosingblockstatementliststhatbase Itisacomponentofaninitializedcallmessage,<strong>and</strong>thecallmessage Itisabasevariablewhichwasinitializedtoaconstantcopy.(See Theprogrampointisinsideanexpressionblock<strong>and</strong>thebasevariable typedenitionliststhatcomponentasaconstant. selector,inspect,forstatements.) variableasconstant.<br />
typestatetoitssuccessorstatements: Herearethestepsincheckingasinglestatement<strong>and</strong>propagatinganew 10.7HowtoApplytheTypestateRules Itisacomponentofaconstant. wasdeclaredoutsidethatexpressionblock.<br />
2.Ifanyrequiredattributeismissing,thisisanerror. 3.Introducecoercionswhichdropattributeswhicharepresentbutare 1.Determinethepreconditionfortheoperation.Thereisatablegiving<br />
forbidden.Ifwecannotaddcoercionswithoutalsodroppingrequired exceptions. asetofpreconditionrulesforeachoperation.Theserulesdetermine:<br />
attributes,thenthisisanerror.Otherwise,wehavesucceededin (1)asetofrequiredattributes,(2)asetofforbiddenattributes,<br />
generatingatypestatewhichisconsistentwiththepreconditions. (3)theoper<strong>and</strong>smodiedbytheoperation,(4)possibleadditional<br />
4.Generateanerrorifanyvariablesmodiedbytheoperationareconstantseral\exception"outcomes.Thetableentryforeachoperationdenemal"outcomeforalloperations(exceptexit),<strong>and</strong>therecanbesev-<br />
whichexceptionoutcomestheoperationhas.Thetablemaylistaddi-<br />
5.Determinethesetofoutcomesoftheoperation.Thereisa\nortionalexceptionswhichtheoperationhasundercertaincircumstances
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