文件给出一个cfg如何判断字符串否属于它定义语言

PrinciplesofCompiler6PrinciplesofCompiler6AnalysisLecturer:HaiNotethatmostoftheseslideswerecreatedProf.Wen-junLI(SchoolofDr.Zhong-meiSHU(DepartmentofComputerScience)Dr.HanLIN(DepartmentofComputerScience)CourseWebsite:问问Recursive-Recursive-ChooseanA-productionA X1X2Xkfor(i=1tok)if(Xiisanonterminal&&!Xi())returnfalse;elseif isaif(Xiequalsthecurrentinputtokent)getthenexttokent;elsereturn}}return}EliminationofLeftEliminationofLeftEliminationofLeftAEliminationofLeftAgrammarisleftrecursiveifithasanonterminalsuchthatthereisastringforGenerally,Generally,However,ThisHowever,Thisprocedureeliminatesimmediaterecursion,butdoesnoteliminateleftrecursioninvolvingderivationsoftwoormoresteps.TheAlgorithmTheAlgorithmforEliminationofDragon,Dragon,••Whyis••WhyisthealgorithmWhatwillhappeniftheinputgrammarhasacycle?Whatwillhappeniftheinputgrammarhasanє-productions?••Giveanalgorithmtoconvertagrammarintoan•Giveanalgorithmtoconvertagrammarintoanequivalentgrammarthathasnoє-GiveanalgorithmtoconvertagrammarintoanequivalentgrammarthathasnoSeeExercise4.4.6and4.4.7(DragonBook•Recursive-Recursive-对于字符串对于字符串cabdcad回MoreEfficientMoreEfficient••BacktrackingisWeneedmoreefficientRecursive-Recursive-SASAcAd|ab|LeftLeftleftleftIsleftIsleftfactoringenoughforpredictiveSAbc|BdaIfweonlylookaheadonlyonecharacter,wedonotknowwhichproductionshouldbechosen.FIRSTConsiderFIRSTConsidertwoA-productionsAα|β,whereFIRST(α)andaredisjoint.WecanthenchoosebetweentheseA-productionsbylookingatthenextinputsymbola,sinceacanbeinatmostoneofFIRST(α)andFIRST(β),notboth.ComputingComputingComputetheComputetheFIRST(X)foreachnonterminalSaA|є,SaA|є,ifthenextinputsymbolisnot‘a’,thenwillwillchooseSє;otherwisebothproductionscanbeifAcanbetherightmostsymbolinsomesententialform,then$isinFOLLOW(A).ComputingComputingComputetheComputetheFOLLOW(X)foreachnonterminalConstructionofConstructionofaParsingPredictiveParsingPredictiveParsingLL(1)LL(1)SinceM[S’,SinceM[S’,e]containsmorethanoneproduction,thegrammarisnotLL(1).作作ImplementingtheTwo•ImplementingtheTwo••Non-table-CodingforRecursivePredictiveCodingforRecursivePredictive•CodingforRecursiveCodingforRecursivePredictive•CodingforRecursiveCodingforRecursivePredictive•CodingforRecursiveCodingforRecursivePredictiveModelofModelofaTable-PredictiveTabl