编译原理09-5-6.md

• 五

  G中的规则r	Frist(rhs(r))	Follow(lhs(r))	PS(r)
  $S\rightarrow P$	$(,a$	$\text#$	$(,a$
  $S\rightarrow\epsilon$	$\epsilon$	None	$\text#$
  $P\rightarrow(P)P$	$($	$\text#,)$	$($
  $P\rightarrow a$	$a$	None	$a$

  2. 是LL(1)文法.因为$PS(S\rightarrow P)\cap PS(S\rightarrow\epsilon)=\varnothing$,且$PS(P\rightarrow(P)P)\cap PS(P\rightarrow a)=\varnothing$.

  3. 预测分析表

     	a	(	)	#
     S	$S\rightarrow P$	$S\rightarrow P$		$S\rightarrow\epsilon$
     P	$P\rightarrow a$	$P\rightarrow(P)P$

  4. int ParseP(int P_y) {
       switch (lookahead) {
         case '(': {
           MatchToken('(');
           int P1_y = P_y;
           int P1_x = ParseP(P1_y);
           MatchToken(')');
           int P2_y = P1_x;
           int P2_x = ParseP(P2_y);
           return P1_x + P2_x;
         }
         case 'a': {
           return P_y + 1;
         }
         default:
           reportError();
       }
     }
     int ParseS() {
       switch (lookahead) {
         case '(':
         case 'a': {
           int P_y = 0;
           int P_x = ParseP(P_y);
           return P_x;
         }
         case '#': {
           return 0;
         }
         default: {
           reportError();
         }
       }
     }
     

• 六

  $S\rightarrow{switch} A of \text{{L.val=A.place,L.next=S.next} L end} \ \text{{S.code=A.code//L.code}}$

  $L\rightarrow case \text{{V.failed=newlabel}} V : \text{{S.next=L.next}}; \text{{L1.val=L.val, L1.next=L.next}}\\text{{L.code=gen(if V.val != L.val then goto V.failed)// S.code//gen(goto L.next)//gen(V.failed :)//L.code}}$

  $L\rightarrow default \text{{S.next=L.next}} S \text{{L.code=S.code//gen(goto L.next)}}$

  $V\rightarrow d \text{{V.val=d.lexval}}$

  $S\rightarrow while \text{{E.true=newlabel, E.false=S.next}} E do \ \text{{S1.next=E.newlabel, S1.break=S.next}} S1\ \text{{S.code=gen(S1.next :)//E.code//gen(E.true :)//S1.code//gen(goto S1.next)}}$

  $S\rightarrow \text{{S1.break=S.break, S1.next=newlabel}}S1\text{{S2.break=S.break, S2.next.S.next}}S2\ \text{{S.code=S1.code//gen(S1.next : )// S2.code}}$

  $S\rightarrow break \text{{gen(goto S.break)}}$