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An LALR(1) parser for a grammar G can have shift-reduce (S-R) conflicts if and only if
- a)the SLR(1) parser for G has S-R conflicts
- b)the LR(1) parser for G has S-R conflicts
- c)the LR(0) parser for G has S-R conflicts
- d)the LALR(1) parser for G has reduce-reduce conflicts
Correct answer is option 'B'. Can you explain this answer?
Verified Answer
An LALR(1) parser for a grammar G can have shift-reduce (S-R) conflict...
Both LALR(1) and LR(1) parser uses LR(1) set of items to form their parsing tables. And LALR(1) states can be find by merging LR(1) states of LR(1) parser that have the same set of first components of their items. i.e. if LR(1) parser has 2 states I and J with items A->a.bP,x and A->a.bP,y respectively, where x and y are look ahead symbols, then as these items are same with respect to their first component, they can be merged together and form one single state, let's say K. Here we have to take union of look ahead symbols. After merging, State K will have one single item as A->a.bP,x,y . This way LALR(1) states are formed (i.e. after merging the states of LR(1)). Now, S-R conflict in LR(1) items can be there whenever a state has items of the form :
A-> a.bB , p
C-> d. , b
i.e. it is getting both shift and reduce at symbol b, hence a conflict.
Now, as LALR(1) have items similar to LR(1) in terms of their first component, shift-reduce form will only take place if it is already there in LR(1) states. If there is no S-R conflict in LR(1) state it will never be reflected in the LALR(1) state obtained by combining LR(1) states. Note: But this process of merging may introduce R-R conflict, and then the Grammar won't be LALR(1).
A-> a.bB , p
C-> d. , b
i.e. it is getting both shift and reduce at symbol b, hence a conflict.
Now, as LALR(1) have items similar to LR(1) in terms of their first component, shift-reduce form will only take place if it is already there in LR(1) states. If there is no S-R conflict in LR(1) state it will never be reflected in the LALR(1) state obtained by combining LR(1) states. Note: But this process of merging may introduce R-R conflict, and then the Grammar won't be LALR(1).
Most Upvoted Answer
An LALR(1) parser for a grammar G can have shift-reduce (S-R) conflict...
Explanation:
The LR(1) parsing algorithm is more powerful than the SLR(1) parsing algorithm because it uses more lookahead symbols to make parsing decisions. Similarly, the LALR(1) parsing algorithm is more powerful than the SLR(1) parsing algorithm because it combines states from the LR(1) parsing table to reduce the number of states.
Shift-Reduce Conflicts:
A shift-reduce conflict occurs in a parsing table when both a shift and a reduce action are possible for the current input symbol and stack state. In other words, the parser does not know whether to shift the input symbol onto the stack or to reduce the stack using a production rule.
SLR(1) Parser:
An SLR(1) parser is the simplest form of LR(1) parser. It uses a simplified parsing table that is generated from an LR(0) automaton with additional lookahead information. However, this simplification can lead to more shift-reduce conflicts in the parsing table.
LR(1) Parser:
An LR(1) parser uses a parsing table that is generated from an LR(1) automaton. The LR(1) automaton has more states than the LR(0) automaton because it considers more lookahead symbols. Therefore, the LR(1) parser is more powerful than the SLR(1) parser and can resolve more shift-reduce conflicts.
LALR(1) Parser:
An LALR(1) parser is a further simplification of the LR(1) parser. It combines states from the LR(1) automaton to reduce the number of states. This reduction can lead to fewer states and fewer shift-reduce conflicts compared to the LR(1) parser.
Conclusion:
Based on the above explanations, it can be concluded that an LALR(1) parser for a grammar G can have shift-reduce conflicts if and only if the LR(1) parser for G has shift-reduce conflicts. This is because the LALR(1) parser is a simplification of the LR(1) parser and inherits its conflicts. Therefore, option B is the correct answer.
The LR(1) parsing algorithm is more powerful than the SLR(1) parsing algorithm because it uses more lookahead symbols to make parsing decisions. Similarly, the LALR(1) parsing algorithm is more powerful than the SLR(1) parsing algorithm because it combines states from the LR(1) parsing table to reduce the number of states.
Shift-Reduce Conflicts:
A shift-reduce conflict occurs in a parsing table when both a shift and a reduce action are possible for the current input symbol and stack state. In other words, the parser does not know whether to shift the input symbol onto the stack or to reduce the stack using a production rule.
SLR(1) Parser:
An SLR(1) parser is the simplest form of LR(1) parser. It uses a simplified parsing table that is generated from an LR(0) automaton with additional lookahead information. However, this simplification can lead to more shift-reduce conflicts in the parsing table.
LR(1) Parser:
An LR(1) parser uses a parsing table that is generated from an LR(1) automaton. The LR(1) automaton has more states than the LR(0) automaton because it considers more lookahead symbols. Therefore, the LR(1) parser is more powerful than the SLR(1) parser and can resolve more shift-reduce conflicts.
LALR(1) Parser:
An LALR(1) parser is a further simplification of the LR(1) parser. It combines states from the LR(1) automaton to reduce the number of states. This reduction can lead to fewer states and fewer shift-reduce conflicts compared to the LR(1) parser.
Conclusion:
Based on the above explanations, it can be concluded that an LALR(1) parser for a grammar G can have shift-reduce conflicts if and only if the LR(1) parser for G has shift-reduce conflicts. This is because the LALR(1) parser is a simplification of the LR(1) parser and inherits its conflicts. Therefore, option B is the correct answer.
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An LALR(1) parser for a grammar G can have shift-reduce (S-R) conflicts if and only ifa)the SLR(1) parser for G has S-R conflictsb)the LR(1) parser for G has S-R conflictsc)the LR(0) parser for G has S-R conflictsd)the LALR(1) parser for G has reduce-reduce conflictsCorrect answer is option 'B'. Can you explain this answer? for Computer Science Engineering (CSE) 2025 is part of Computer Science Engineering (CSE) preparation. The Question and answers have been prepared according to the Computer Science Engineering (CSE) exam syllabus. Information about An LALR(1) parser for a grammar G can have shift-reduce (S-R) conflicts if and only ifa)the SLR(1) parser for G has S-R conflictsb)the LR(1) parser for G has S-R conflictsc)the LR(0) parser for G has S-R conflictsd)the LALR(1) parser for G has reduce-reduce conflictsCorrect answer is option 'B'. Can you explain this answer? covers all topics & solutions for Computer Science Engineering (CSE) 2025 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for An LALR(1) parser for a grammar G can have shift-reduce (S-R) conflicts if and only ifa)the SLR(1) parser for G has S-R conflictsb)the LR(1) parser for G has S-R conflictsc)the LR(0) parser for G has S-R conflictsd)the LALR(1) parser for G has reduce-reduce conflictsCorrect answer is option 'B'. Can you explain this answer?.
An LALR(1) parser for a grammar G can have shift-reduce (S-R) conflicts if and only ifa)the SLR(1) parser for G has S-R conflictsb)the LR(1) parser for G has S-R conflictsc)the LR(0) parser for G has S-R conflictsd)the LALR(1) parser for G has reduce-reduce conflictsCorrect answer is option 'B'. Can you explain this answer? for Computer Science Engineering (CSE) 2025 is part of Computer Science Engineering (CSE) preparation. The Question and answers have been prepared according to the Computer Science Engineering (CSE) exam syllabus. Information about An LALR(1) parser for a grammar G can have shift-reduce (S-R) conflicts if and only ifa)the SLR(1) parser for G has S-R conflictsb)the LR(1) parser for G has S-R conflictsc)the LR(0) parser for G has S-R conflictsd)the LALR(1) parser for G has reduce-reduce conflictsCorrect answer is option 'B'. Can you explain this answer? covers all topics & solutions for Computer Science Engineering (CSE) 2025 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for An LALR(1) parser for a grammar G can have shift-reduce (S-R) conflicts if and only ifa)the SLR(1) parser for G has S-R conflictsb)the LR(1) parser for G has S-R conflictsc)the LR(0) parser for G has S-R conflictsd)the LALR(1) parser for G has reduce-reduce conflictsCorrect answer is option 'B'. Can you explain this answer?.
Solutions for An LALR(1) parser for a grammar G can have shift-reduce (S-R) conflicts if and only ifa)the SLR(1) parser for G has S-R conflictsb)the LR(1) parser for G has S-R conflictsc)the LR(0) parser for G has S-R conflictsd)the LALR(1) parser for G has reduce-reduce conflictsCorrect answer is option 'B'. Can you explain this answer? in English & in Hindi are available as part of our courses for Computer Science Engineering (CSE).
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