GATE CS 2016 Set 2 — Question 55
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Compiler Design → Syntax Analysis → Left Recursion Elimination
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Question
Which one of the following grammars is free from left recursion?
Correct answer
(B) S → Ab Bb c A → Bd ε B → e
Solution
We check each grammar for left recursion (direct or indirect):(A) . This has direct left recursion in the production .(B)
Substitute into : .
Substitute and into : .
None of the productions exhibit left recursion. This grammar is free from left recursion.(C)
Consider . This is indirect left recursion ().(D)
Substitute into : .
This introduces direct left recursion in ().Therefore, only grammar (B) is free from left recursion.
Substitute into : .
Substitute and into : .
None of the productions exhibit left recursion. This grammar is free from left recursion.(C)
Consider . This is indirect left recursion ().(D)
Substitute into : .
This introduces direct left recursion in ().Therefore, only grammar (B) is free from left recursion.
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