编译原理龙书课后部分答案(英文版).doc

编译原理龙书课后部分答案(英文版).doc

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1）Whatisthedifferencebetweenacompilerandaninterpreter?

·Acompilerisaprogramthatcanreadaprograminonelanguage-thesourcelanguage-andtranslateitintoanequivalentprograminanotherlanguage–thetargetlanguageandreportanyerrorsinthesourceprogramthatitdetectsduringthetranslationprocess.

·Interpreterdirectlyexecutestheoperationsspecifiedinthesourceprogramoninputssuppliedbytheuser.

2）Whataretheadvantagesof:

（a）acompileroveraninterpreter

a.Themachine-languagetargetprogramproducedbyacompilerisusuallymuchfasterthananinterpreteratmappinginputstooutputs.

（b）aninterpreteroveracompiler?

b.Aninterpretercanusuallygivebettererrordiagnosticsthanacompiler,becauseitexecutesthesourceprogramstatementbystatement.

3）Whatadvantagesaretheretoalanguage-processingsysteminwhichthecompiler

producesassemblylanguageratherthanmachinelanguage?

Thecompilermayproduceanassembly-languageprogramasitsoutput,because

assemblylanguageiseasiertoproduceasoutputandiseasiertodebug.

4.2.3Designgrammarsforthefollowinglanguages:

a）Thesetofallstringsof0sand1ssuchthatevery0isimmediatelyfollowedbyatleast1.

S->SS|1|01|e

4.3.1Thefollowingisagrammarfortheregularexpressionsoversymbolsaandbonly,using+inplaceof|forunions,toavoidconflictwiththeuseofverticalbarasmeta-symbolingrammars:

rexpr->rexpr+rterm|rterm

rterm->rtermrfactor|rfactor

rfactor->rfactor*|rprimary

rprimary->a|b

a）Leftfactorthisgrammar.

rexpr->rexpr+rterm|rterm

rterm->rtermrfactor|rfactor

rfactor->rfactor*|rprimary

rprimary->a|b

b）Doesleftfactoringmakethegrammarsuitablefortop-downparsing?

No,leftrecursionisstillinthegrammar.

c）Inadditiontoleftfactoring,eliminateleftrecursionfromtheoriginalgrammar.

rexpr->rtermrexpr’

rexpr’->+rtermrexpr|e

rterm->rfactorrterm’

rterm’->rfactorrterm|e

rfactor->rprimaryrfactor’

rfactor’->*rfactor’|e

rprimary->a|b

d）Istheresultinggrammarsuitablefortop-downparsing?

Yes.

Exercise4.4.1Foreachofthefollowinggrammars,derivepredictiveparsersandshowtheparsingtables.Youmayleft-factorand/oreliminateleft-recursionfromyourgrammarsfirst.Apredictiveparsermaybederivedbyrecursivedecentorbythetabledrivenapproach.Eitherwayyoumustalsoshowthepredictiveparsetable.

a）Thegrammarofexercise4.2.2（a）.

4.2.2a）S->0S1|01

Thisgrammarhasnoleftrecursion.Itcouldpossiblybenefitfromleftfactoring.HereistherecursivedecentPPcode.

s（）{

match（‘0’）;

if（lookahead==‘0’）

s（）;

match（‘1’）;

}

Or

Leftfactoringthegrammarfirst:

S->0S’

S’->S1|1

s（）{

match（‘0’）;s’（）;

}

s’（）{

if（lookahead==‘0’）

s（）;match（‘1’）;

else

match（‘1’）;

}NowwewillbuildthePPtable

S->0S’

S’->S1|1

First（S）={0}

First（S’）={0,1}

Follow（S）={1,$}

Follow（S’）={1,$}

Non-Terminal

InputSymbol

0

1

$

S

S->0S’

S’

S’->S1

S’->1

Thepredictiveparsingalgorithmonpage227（fig4.19and4.20）canusethistablefornon-recursivepredictiveparsing.

b）Thegrammarofexercise4.2.2（b）.

4.2.2b）S->+SS|*SS|awithstring+*aaa.

Leftfactoringdoesnotapplyandthereisnoleftrecursiontoremove.

s（）{

if（lookahead==‘+’）

match（‘+’）;s（）;s（）;

elseif（lookahead==‘*’）

match（‘*’）;s（）;s（）;

elseif（lookahead==‘a’）

match（‘a’）;

else

report（“syntaxerror”）;

}

First（S）={+,*,a}

Follow（S）={$,+,*,a}

Non-Terminal

InputSymbol

+

*

a

$

S

S->+SS

S->*SS

S->a

Thepredictiveparsingalgorithmonpage227（fig4.19and4.20）canusethistablefornon-recursivepredictiveparsing.

5.1.1a,b,c:

InvestigatingGraphVizasasolutiontopresentingtrees

5.1.2:

 ExtendtheSDDofFig.5.4tohandleexpressionsasinFig.5.1:

1.L->EN

1.L.val=E.syn

2.E->FE'

1.E.syn=E'.syn

2.E'.inh=F.val

3.E'->+TEsubone'

1.Esubone'.inh=E'.inh+T.syn

2.E'.syn=Esubone'.syn

4.T->FT'

1.T'.inh=F.val

2.T.syn=T'.syn

5.T'->*FTsubone'

1.Tsubone'.inh=T'.inh*F.val

2.T'.syn=Tsubone'.syn

6.T'->epsilon

1.T'.syn=T'.inh

7.E'->epsilon

1.E'.syn=E'.inh

8.F-> digit

1.F.val= digit.lexval

9.F->（E）

1.F.val=E.syn

10.E->T

1.E.syn=T.syn

5.1.3a,b,c:

InvestigatingGraphVizasasolutiontopresentingtrees

5.2.1:

 WhatareallthetopologicalsortsforthedependencygraphofFig.5.7?

1.1,2,3,4,5,6,7,8,9

2.1,2,3,5,4,6,7,8,9

3.1,2,4,3,5,6,7,8,9

4.1,3,2