Self doubt

Question

S -> AB | BAB

A -> SA | ba

B -> a | $\epsilon$

What are the follow of S, A, B?

Comments

S -> AB | BAB
A -> SA | ba
B -> a | ϵ

• Follow(S) { a, b, $}
• Follow(A) { a, b, $}
• Follow(B) { a, b, $ }

Answer 1

To find Follow, we have to find First first

First are the terminals that a variable can have including ϵ

First of S = {a,b,ϵ}

First of A = {a,b,ϵ}

First of B = {a,ϵ}

Now, we find the follow. Follow means "what are the terminals that could follow a variable in the process of derivation". In Follow, ϵ is not allowed. Follow of start symbol is always $  but not limited to $(reference symbol).

Follow of S = {$,a,b} = First of A, Follow of A , First of B

Follow of A = {$,a,b} = First of B, Follow of S

Follow of B = {$,a,b} = First of A, Follow of A