第十次作业

1.将以下文法消除左递归,分析符号串 i*i+i 。

   并分别求FIRST集、FOLLOW集,和SELECT集

     E -> E+T | T

     T -> T*F | F

     F -> (E) | i

 

first集:

 FIRST(TE')={ (, i }

  FIRST(+TE')={+}

  FIRST(ε)={ε}

  FIRST(FT')={ (, i }

  FIRST(*FT')={*}

  FIRST((E))={ ( }

  FIRST(i)={i}

follow集:

  FOLLOW(E)={ ),# }

  FOLLOW(E')={ ),# }

  FOLLOW(T)={+,),#}

  FOLLOW(T')={+,),#}

  FOLLOW(F)={*,+,),#}

select集:

  SELECT(E->TE')=FIRST(TE')={ (, i }

  SELECT(E'->+TE')=FIRST(+TE')={+}

  SELECT(E'->ε)=FIRST(ε)-{ε}UFOLLOW(E')=FOLLOW(E')={ ),# }

  SELECT(T->FT')=FIRST(FT')={ (,i }

  SELECT(T'->*FT')=FIRST(*FT')={*}

  SELECT(T'->ε)=FIRST(ε)-{ε}UFOLLOW(T')=FOLLOW(T')={ +,),# }

  SELECT(F->(E))=FIRST((E))={ ( }

  SELECT(F->i)=FIRST(i)={i}

 

2.P101练习7(2)(3)文法改写,并分别求FIRST集、FOLLOW集,和SELECT集

            A->aABe | a

    B->Bb | d

   文法改写:

   A->aA'

     A'->ABe | ε

     B->dB'

     B'->bB' | ε  

  FIRST集:

  FIRST(aA')={a}

  FIRST(ABe)={a}

  FIRST(ε)={ε}

  FIRST(dB')={d}

  FIRST(bB')={b}

  FOLLOW集:

  FOLLOW(A)={d,#}

  FOLLOW(A')={d,#}

  FOLLOW(B)={e}

  FOLLOW(B')={e}

  SELECT集:

  SELECT(A->aA')=FIRST(aA')={a}

  SELECT(A'->ABe)=FIRST(ABe)={a}

  SELECT(A'->ε)=FIRST(ε)-{ε}UFOLLOW(A')=FOLLOW(A')={d,#}

  SELECT(B->dB')=FIRST(dB')={d}

  SELECT(B'->bB')=FIRST(bB')={b}

  SELECT(B'->ε)=FIRST(ε)-{ε}UFOLLOW(B')=FOLLOW(B')={e}

  

  (3)S->Aa | b

    A->SB

      B->ab

      文法改写:

   S->bS'

      S'->BaS' | ε

      B->ab 

  FIRST集:

  FIRST(bS')={b}

  FIRST(BaS')={a}

  FIRST(ε)={ε}

  FIRST(ab)={a}

  FOLLOW集:

  FOLLOW(S)={#}

  FOLLOW(S')={#}

  FOLLOW(B)={a}

  SELECT集:

  SELECT(S->bS')=FIRST(bS')={b}

  SELECT(S'->BaS')=FIRST(BaS')={a}

  SELECT(S'->ε)=FIRST(ε)-{ε}UFOLLOW(S')=FOLLOW(S')={#}

  SELECT(B->ab)=FIRST(ab)={a}

 

课堂练习:

求以下文法的FIRST集、FOLLOW集和SELECT集。

(1)S->Ap
A->a |ε
A->cA

A->aA

 

 

 

(1)FIRST集:

FIRST(S)={a,c,p}

FIRST(A)={a}

FIRST(A)={c}

FIRST(A)={a}

 

FOLLOW集:

FOLLOW(S)={#}

FOLLOW(A)={p}

 

SELECT集:

SELECT(S->Ap)={a,c,p}

SELECT(A->a)={a}

SELECT(A->ε)={p}

SELECT(A->cA)={c}

SELECT(A->aA)={a}

 

(2)S->Ap
S->Bq
A->a
A->cA
B->b
B->dB

(2)FIRST集:

FIRST(S)={a,c}

FIRST(S)={b,d}

FIRST(A)={a}

FIRST(A)={c}

FIRST(B)={b}

FIRST(B)={d}

 

FOLLOW集:

FOLLOW(S)={#}

FOLLOW(A)={p}

FOLLOW(B)={q}

 

SELECT集:

S->Ap

S->Bq

A->a

A->cA

B->b

B->dB

 

SELECT()={}

 

SELECT(S->Ap)={a,c}

SELECT(S->Bq)={b,d}

SELECT(A->a)={a}

SELECT(A->cA)={c}

SELECT(B->b)={b}

SELECT(B->dB)={d}

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