How to make a grammar LL(1)?

Asked Feb 14 '18 at 15:06

Active Feb 14 '18 at 15:06

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I have this grammar that has to be transformed to LL(1) grammar:

S->A
A->BC|DBC
B->Bb|epsilon
C->c|epsilon
D->a|b|d

After applying left recursion and left factoring to it, I get the grammar as below:

S->A
A->BCA'|epsilon
A'->D | epsilon
B->B'
B'->bB'|epsilon
C->c|epsilon
D->a|b|d

But the grammar is still ambiguous. Have I done something wrong?

asked Feb 14 '18 at 15:06

eri

I'm pretty sure I can derive epsilon in two different ways with your second grammar. – melpomene Feb 14 '18 at 15:13
1

Your first grammar accepts "abc", but your second grammar doesn't. – melpomene Feb 14 '18 at 15:16
I don't know what LL(1) is, but as a regex your first grammar reduces to `[ad]?b*c?`, which corresponds to `S->DBC; D->a|d|epsilon; B->bB|epsilon; C->c|epsilon`. – melpomene Feb 14 '18 at 15:19
the original grammar is ambiguous. You have to fix that first. – 1010 Feb 20 '18 at 22:35

0 Answers0