1、文法G(Z):Z→aZb|ab定义的是什么样的语言?
G(Z):Z→aZb|ab
Z→aZb→aaZbb→a...Z...b→a....ab....b→a^nb^n(n≥1)
则:L(G)={anbn|n≥1 }
2.写出教材22页例2.2中标识符的文法四元组形式。
文法G={VN,VT,P,S},其中,VN={标识符,字母,数字},VT={a,b,c....x,y,z,0,1....,9}
数字:A, 字母:B, 标识符:C
VN={C,A,B} ,VT={A,B}
P={<C>→<B>
<C>→<C><B>
<C>→<C><A>
<B>→a
<B>→b
•
•
•
<B>→9
<A>→0
•
•
•
<A>→9
}
S→<C>
3.写出下列表达式的最左推导、最右推导和语法树。
G(E): E=> E + T | T
T=>T * F | F
F=>(E)| i
i*i+i
i+i*i
i+(i+i)
(1)i*i+i
最左推导:
E=>E+T=>T*F+T=>F*F+T=>i*F+T=>i*i+T=>i*i+F=>i*i+i
最右推导:
E=>E+T=>E+F=>E+i=>T*i=>T*F+i=>T*T+i=>T*T+i=>T*i+i=>i*i+i
语法树
(2)i+i*i
最左推导:
E=>E+T=>T+T=>F+T=>i+T=>i+T*F=>i+F*F=>i+i*i
最右推导:
E=>E+T=>E+F=>E+E=>E+E+T=>E+T*F=>E+T*F=>E+T*i=>E+F*i=>E+i*i=>T+i*i=>F+i*i=>i+i*i
语法树
(3)i+(i+i)
最左推导:
E=>E+T=>T+T=>F+T=>i+T=>i+F=>i+(E)=>i+(E+T)=>i+(T+T)=>i+(F+T)=>i+(i+T)=>i+(i+F)=>i+(i+i)
最右推导:
E=>E+T=>E+F=>E+(E)=>E+(E+T)=>E+(E+F)=>E+(E+i)=>E+(T+i)=>E+(F+i)=>E+(i+i)=>T+(i+i)=>F+(i+i)=>i+(i+i)
语法树