LL Parser includes both the recursive descent parser and non-recursive descent parser. Its one type uses backtracking while another one uses parsing table. Theses are top down parser.
Example: Given grammar is
S -> Ac A -> ab
where S is start symbol, A is non-terminal and a, b, c are terminals.
Input string: abc
Parse tree generated by LL parser:
LR Parser is one of the bottom up parser which uses parsing table (dynamic programming) to obtain the parse tree form given string using grammar productions.
Example: In the above example, parse tree generated by LR parser:
Difference between LL and LR parser:
|LL Parser||LR Parser|
|First L of LL is for left to right and second L is for leftmost derivation.||L of LR is for left to right and R is for rightmost derivation.|
|It follows the left most derivation.||It follows reverse of right most derivation.|
|Using LL parser parser tree is constructed in top down manner.||Parser tree is constructed in bottom up manner.|
|In LL parser, non-terminals are expanded.||In LR parser, terminals are compressed.|
|Starts with the start symbol(S).||Ends with start symbol(S).|
|Ends when stack used becomes empty.||Starts with an empty stack.|
|Pre-order traversal of the parse tree.||Post-order traversal of the parser tree.|
|Terminal is read after popping out of stack.||Terminal is read before pushing into the stack.|
|It may use backtracking or dynamic programming.||It uses dynamic programming.|
|LL is easier to write.||LR is difficult to write.|
|Example: LL(0), LL(1)||Example: LR(0), SLR(1), LALR(1), CLR(1)|
Attention reader! Don’t stop learning now. Get hold of all the important CS Theory concepts for SDE interviews with the CS Theory Course at a student-friendly price and become industry ready.