M.E test

Question

Let G be a grammar with the following productions.

If LR(1) Parser is used to construct the DFA using the above productions, then how many look-a-heads are present for an  item  in the initial state?

Comments

yes 4 is the correct answer as given

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We find the lookaheads by finding the follow.

When we start with E' -> .E, $

E -> .E + T should contain follow(E,\$) = follow(E) = { \$, + , )}

Please rectify me, where am I wrong?

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can someone post the entire solution?

Answer 1

(1) E'->.E, $

(2) E->.E+T, $/+                //because of line 1 and 2

 (3) E->.T , $/+                   //because of line 1 and 2

(4) T-> .T*F, $/+/*/-             // because of line 3,4 and 7

(5) T-> .F , $/+/*/-               // because of line 3,4 and 7

(6) F->.(E) , $/+/*/-             // because of line 5 

(7) F->.T-F,  $/+/*/-            // because of line 5 

(8) F->.id , $/+/*/-              // because of line 5

for T->.T*F we have  four Look a heads  {$,+,*,-}

Comments

 Neeraj Mehta why u are add + in second line?

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it will be like

i) E'->.E , $

ii) E->.E+T, $  // because of line 1

now in second line we have .E on the right  side so we need to write for this also and it will be

iii) E->.E+T, +  // this because of E in second line

from (ii) and (iii) we can write  E->.E+T, $/+

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anyone, please provide complete LR(1) DFA for above grammar.

Answer 2

There are 5 lookaheads  ),+,$,-,*

Answer 3

The states are given as :

E' -> .E , $           ( initial look-ahead symbol)

E -> .E+T , $,+

        .T     , $,+       

( look-ahead symbol $ comes because of the production E' -> .E  & look-ahead symbol + comes because of the production E -> .E+T , because of the extra .E all productions of E has to written again with their new look-ahead symbol + and hence merged )

T -> .T*F , $,+,*,-

        .F     , $,+,*,-

        .(E)   , $,+,*,-

        .T-F  , $,+,*,-

( similar to the above one )

F -> .id    , $,+,*,-

Comments

https://www.youtube.com/watch?v=Lfw9tr4g93Q

TRY THIS VIDEO , IT WILL EXPLAIN PROPERLY