cs416 compiler design - ankith m s：cs416编译器设计ankith m s

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1、Syntax-DirectedTranslationGrammarsymbolsareassociatedwithattributestoassociateinformationwiththeprogramminglanguageconstructsthattheyrepresent.Valuesoftheseattributesareevaluatedbythesemanticrulesassociatedwiththeproductionrules.Evaluationofthesesemanticrules:maygenerateinterme

2、diatecodesmayputinformationintothesymboltablemayperformtypecheckingmayissueerrormessagesmayperformsomeotheractivitiesinfact,theymayperformalmostanyactivities.Anattributemayholdalmostanything.astring,anumber,amemorylocation,acomplexrecord.1CS416CompilerDesignSyntax-DirectedDefin

3、itionsandTranslationSchemesWhenweassociatesemanticruleswithproductions,weusetwonotations:Syntax-DirectedDefinitionsTranslationSchemesSyntax-DirectedDefinitions:givehigh-levelspecificationsfortranslationshidemanyimplementationdetailssuchasorderofevaluationofsemanticactions.Weass

4、ociateaproductionrulewithasetofsemanticactions,andwedonotsaywhentheywillbeevaluated.TranslationSchemes:indicatetheorderofevaluationofsemanticactionsassociatedwithaproductionrule.Inotherwords,translationschemesgivealittlebitinformationaboutimplementationdetails.2CS416CompilerDes

5、ignSyntax-DirectedDefinitionsAsyntax-directeddefinitionisageneralizationofacontext-freegrammarinwhich:Eachgrammarsymbolisassociatedwithasetofattributes.Thissetofattributesforagrammarsymbolispartitionedintotwosubsetscalledsynthesizedandinheritedattributesofthatgrammarsymbol.Each

6、productionruleisassociatedwithasetofsemanticrules.Semanticrulessetupdependenciesbetweenattributeswhichcanberepresentedbyadependencygraph.Thisdependencygraphdeterminestheevaluationorderofthesesemanticrules.Evaluationofasemanticruledefinesthevalueofanattribute.Butasemanticrulemay

7、alsohavesomesideeffectssuchasprintingavalue.3CS416CompilerDesignAnnotatedParseTreeAparsetreeshowingthevaluesofattributesateachnodeiscalledanannotatedparsetree.Theprocessofcomputingtheattributesvaluesatthenodesiscalledannotating(ordecorating)oftheparsetree.Ofcourse,theorderofthe

8、secomputationsdependsonthedependencygraphinducedbythes