Question

%token A B C D E F G H
%%
x : y H y | z H z
;

y : G | t |  y B G | y B t
;

z : w | z D w
;

w : C | t | E z F
;

t : A
;

There is a reduce/reduce conflict because of t. How can we solve it?

Answer 1

By default the conflict between y: t and w: t is resolved in favor of y: t. If you want it the other way, reorder the corresponding rules. Or you can expand one of them like this :-

%token A B C D E F G H
%%
x : y H y | z H z
;

w : C | A | E z F
;

z : w | z D w
;

y : G |  A B G | A B A | y B G | y B A
;

Note that I’ve got rid of the t rule and removed the y: A rule by expanding it :-

Step 1: Eliminate the t: A rule

%token A B C D E F G H
%%
x : y H y | z H z
;

y : G | A |  y B G | y B A
;

z : w | z D w
;

w : C | A | E z F
;

Step 2:

%token A B C D E F G H
%%
x : y H y | z H z
;

y : G | A |  A B G | A B A | y B G | y B A
;

z : w | z D w
;

w : C | A | E z F
;