CLR VS LALR Parsing

Question

confuse among clr and lalr??

what is necessary and sufficient condition for clr??

what is necessary and sufficient condition for lalr???

when it's clr & when not??

when it's lalr & when not??

Comments

Plz have a look at this https://gateoverflow.in/37184/lalr-vs-clr-vs-slr 

Answer 1

i havnt understood ur question properly but let me try

both CLR(1) and LALR(1) have one lookahead....if u will construct the parsing table for CLR(1)...it will contain the maximum no of rows...because here we divide each state based on its lookahead....there will be more spaces in the table and hence more error detecting capacity...we move from LR(0) to SLR(1) to CLR(1) so that error handling can be increased...

if u get two states in CLR(1) parsing table like
1.S->a.,$
  S->a.a,$

2.S->a.,b
   S->a.a,$/b

u have to place both in different states since lookaheads are different...
but if u merge them in LALR(1)...u will get one state as

  S->a.,$/b
  S->a.a,$/b
so if u could merge two states with different lookaheads we get LALR(1)

one more thing...if a grammar  is not CLR(1)..its definitly not  LALR(1) also...
but if it is CLR(1)...it doent mean it is always LALR(1) because it is possible that with different lookaheads u will not get ant SR or RR conflict in CLR(1) but when u will merge them there could be an error in LALR(1)..

for more clearance on this u can watch this...how we can merge different states

https://gateoverflow.in/72198/made-easy-test-series

Comments

i understand your explaination u say  if grammer is not clr then it's not lalr but if it's clr then may or may not lalr???

my ques is what is the suficient condition for lalr grammer??

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yes ur right of grammar is clr..it may or may  not be lalr;;

m not getting ur second question.....i think if u can merge two states with different lookaheads and there is no sr or rr conflict then it is lalr grammar...

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u said if a grammar  is not CLR(1)..its definitly not  LALR(1) so why CLR(1) is more powerful than LALR(1) ?