GATE CSE 2014 Set 1 | Question: 34

Question

A canonical set of items is given below

• $S \to L .> R $
• $Q \to R.$

On input symbol $<$ the set has

• A. a shift-reduce conflict and a reduce-reduce conflict.
• B. a shift-reduce conflict but not a reduce-reduce conflict.
• C. a reduce-reduce conflict but not a shift-reduce conflict.
• D. neither a shift-reduce nor a reduce-reduce conflict.

Comments

A rare example, when the question setter decided to conduct a small prank, and the answer key along with the answer prints the line “Look at the camera and say Hi!” You’ve been pranked.

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@Souvik33 hahaha

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I think the given state itself is invalid.

Which means we can not have that as a state in any parsing.

$S \rightarrow L .> R :$ This item indicates that the parser is in a state where it has derived the L.

$Q \rightarrow R.$ : This item indicates that the parser is in a state where it has derived the R.

Having both items in the same state is not possible and violates the rules of a valid parsing state.

Answer 1

The question is asked with respect to the symbol  ' $<$ '  which is not present in the given canonical set of items. Hence it is neither a shift-reduce conflict nor a reduce-reduce conflict on symbol '$<$'. Hence D is the correct option. But if the question would have asked with respect to the symbol  ' $>$ '  then it would have been a shift-reduce conflict.

Comments

@abir_banerjee Why do you think so? It is a collection of LR(0) items, then?

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I also think @abir_banerjee is correct

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I also think that there will not be any shift reduce conflict even if they had asked about  '>'. It's because, on input '>', only first production rulw gets into next item(state). Isn't that right ?

Answer 2

Ans : The given input symbol no where in the given grammar so with given symbol we have neither a shift-reduce nor a reduce-reduce conflict. So, correct answer is (D.) ...

Comments

Even if the question had ">", there won't be any conflict on its canonical collection. There will only be shift to $S\rightarrow L>.R$  and enumerations of R. The current state itself is in SR conflict, and that's a different matter.

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Can someone send some resources for this topic?

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may be printing mistake in the question?
but according to the question Option D is right

Answer 3

The input symbol is “<” which is not in canonical set of item, so it is neither a shift-reduce nor a reduce-reduce conflict with reference to “<” symbol.
But if it would have asked about “>” then it will be a SR conflict.

Answer 4

d ans as <. is not in the grammer

Comments

this question is just to trap students marking in a hurry!