BASIC PARSING TECHNIQUES (COMPILER)

BASIC PARSING TECHNIQUES
PARSER
Parser user se string w leta hai aur grammar ki help se parse tree banata hai or error generate karta hai.

Parser two types ke hote hai
1.Bottom up
2.Top down

Bottom up:

Isse parse tree banate hai jo ki leaves se shuru hoti hai aur start symbol ki taraf move karta hai .

Top down

Isse parse tree banate hai jo ki start symbol se shuru karte hai aur grammar ke production rules ko apply kar string w ko generate karte hai ya error produce karte hai.


Shift Reduce Parser

It is bottom up parsers ja ki leaves se start karke root ya start symbol ki taraf move karti hai.Isko ham string ko start symbol me reduce karne ke liye use karte hain.
Example:

S->aAcBe
A->Ab!b
B->d
and w=abbcde


Solution:

S-->aAcBe
S-->aAcde
S-->aAbcde
S-->abbcde
S-->w

Operator Precedence Grammar

Kisi grammar ko hum operator precedence grammar kahte jab uske production ke right side me na to null ho or na hi do adjacent non-terminal ho.

Left factoring

Kuch grammars recursive descent parsing ke liye suitable nahi hote,left recursion apply karne ke bad bhi.isliye grammar ko recursive descent parser ke liye suitable karne ke liye left facetoring ka use karte hain.

Agar hamara production A->aß|a? ki form main ho to hum use
A->aA'
A'->ß|?