编译原理与实践 第六 七章 答案

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1、TheExercisesofChapterSix6.2应该在num→digit产生式中再加一条语义规则：numd.count=1用来进行初始化。6.46.7ConsiderthefollowinggrammarforsimplePascal-styledeclarations:delc→var-list:typevar-list→var-list,id

2、idtype→integer

3、realWriteanattributegrammarforthetypeofavariable.[Solution]GrammarRuleSemanticRulesdelc→var-list:typev

4、ar-list.type=type.typevar-list1→var-list2,idval-list2.type=var-list1.typeid.type=var-list1.typevar-list→idid.type=var-list.typetype→integertype.type=INTERGERtype→realtype.type=REAL6.10a.DrawdependencygraphscorrespondingtoeachgrammarruleofExample6.14(Page283),andfortheexpression5/2/2.0.b.Describ

5、ethetwopassesrequiredtocomputetheattributesonthesyntaxtreeof5/2/2.0,includingapossibleorderinwhichthenodescouldbevisitedandtheattributevaluescomputedateachpoint.c.Writepseudcodeforproceduresthatwouldperformthecomputationsdescribedinpart(b).[Solution]a.ThegrammarrulesofExample6.14S→expexp→exp/ex

6、p

7、num

8、num.numThedependencygraphsforeachgrammarrule:S→expvalSisFloatetypevalexpexp→exp/expisFloatetypevalexpisFloatetypevalexp/isFloatetypevalexpexp→numisFloatetypevalexpvalnumexp→num.numisFloatetypevalexpvalnum.numThedependencygraphsfortheexpression:5/2/2.0valSIsFloatetypevalexpisFloatetypevale

9、xp/isFloatetypevalexpisFloatetypevalexp/isFloatetypevalexpvalnum.num(2.0)valnumvalnum(5)(2)b.ThefirstpassistocomputetheetypefromisFloat.Thesecondpassistocomputethevalfrometype.Thepossibleorderisasfollows:valS122IsFloatetype3val11exp1isFloat4etypeval9exp/isFloatetypeval10expisFloat5etypeval6exp/

10、isFloat7etypeval8expvalnum.num(2.0)valnumvalnum(5)(2)c.ThepseudcodeprocedureforthecomputationoftheisFloat.FunctionEvalisFloat(T:treenode):BooleanVartemp1,temp2:BooleanBeginCasenodekindofTofexp:temp1=EvalisFloat(leftchildofT);ifrightchildofTisnotnilthentemp2=EvalisFloat(rightchildofT)returntemp1

11、ortemp2elsereturntemp1;num:returnfalse;num.num:returntrue;endFunctionEvalval(T:treenode,etype:integer):VALUEVartemp1,temp2:VALUEBeginCasenodekindofTofS:Return(Evalval(leftchildofT,etype));Exp:Ifetype=EMPTYthenIfEvalisFloat(T)thene