Learn First and Follow , Constructing LL(1) parsing tables and Example on First and follow
22 February, 2016
Construction of LL(1) Parsing table:
- Using First and follow we can construct parsing table.
- Parsing table help us to parse the tree and till now we are directly using the parsing table now we will learn how to construct Parsing table.
- First gives set of all terminals that may derived from alpha.
- If First is a terminal like a,b,(,+,*,id etc..then it is first including empty set element .
Eg2: S-> AaAb | BBBa
A-> a
B-> B
Compute First S, A,B ???
Ans: First(S)= AaAb
First of A that is a and first of BbBa that is b
so first (S)= a,b
First(A)= a
First(B)= b
- Follow always find on the right side of the production rule.
- Like we have to find follow(E) so we have to look E->TE. This E is our element which we need to find.
- Follow(A)= Set of all terminals that may follow immediately to the right of A.
- like A->Aaaa These are terminals , they are follow of A.
- Follow (A) is $ if A is start symbol.
- If follow(A) is null or empty set then we will move to left side non-terminal set .
- S->BA.. Find follow(A). So in this case we will find the value of Follow(A) is Follow(S).
- if b is empty set because follow never contain empty set.
Que: Find First and follow
S->aBDh
B->cC
C->bC|empty
D->EF
E->g|empty
F->f|empty
Solve the question nai toh move to next chapters so till den have fun bye tc..
