Parsing LALR

Question

If LALR(1) parser have shift reduce conflict then CLR(1) parser must have shift reduce conflict, why?

Comments

In CLR(1) we are just clubbing the states with same productions which differ in look-aheads in order to obtain LALR(1), so there is no chance of avoiding SR conflict if it is there in CLR(1) and vice-versa.

There might be a chance of producing RR conflict in LALR(1), which is not there in SLR(1)

Answer 1

1. First we make CLR(1) table and then we check for SR and RR conflicts.
2. If SR or RR conflict is there then it is not CLR(1) => it is also not LALR(1).
3. If we don't find any SR and RR conflict in CLR(1) then we compress the table of CLR(1) to make the LALR(1) table by merging the states which have same production and different look ahead symbols.
4. Since we have already checked for SR and RR conflict in CLR(1) so there is no chance of SR conflict in LALR(1) but reduce reduce conflict may be there ( due to merging of states ).

=> In order to have a SR conflict in LALR(1) , CLR(1) should also have SR conflict.

If LALR(1) parser have shift reduce conflict then CLR(1) parser must have shift reduce conflict.

Comments

Thank you Very much for this explaination

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also if there are no S-R conflicts in CLR then there will be no S-R conflict in LALR. It is an implication of above explanation