Compilers: Principles and Practice by Pearson

Syntax Analyzer 107

Now we have to consider what follows A in the sentential form if we take transition from state 1

to state 4. This qualified FOLLOW() we write as FOLLOW(1, A) = {d} = LA(3, A → e). As

FOLLOW(1, A) = {d} ∩ {c} = ∅, so if we take a look-ahead of 1 symbol and see ‘d’ after ‘e’, we

can reduce ‘e’ to A; otherwise, we should shift on ‘c’.

C

1

ec

d

A

reduce

C

4

(C

3

) (C

7

)

The technique we have just illustrated is known as look-ahead LR(1) or LALR(1) technique, which

is discussed more fully in the next sections.

4.3.10 Conflict Situations

Consider another example grammar:

0. S −> G # 4. E −> E + T

1. G −> E = E 5. T −> f

2. G −> f 6. T ...