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) |