Differentiate Top Down Parser And Bottom Up Parser?

Top-Down Parser and Bottom-Up Parser are two types of parsers used in syntax analysis phase of a compiler. Here are the differences between them:

1. Starting Point: A Top-Down Parser starts parsing from the start symbol and tries to transform it to the input. On the other hand, a Bottom-Up Parser starts parsing from the input and tries to reach the start symbol.

2. Parsing Technique: Top-Down Parser uses a technique called Recursive Descent Parsing and Predictive Parsing, while Bottom-Up Parser uses techniques like Operator Precedence Parsing, LR Parsing (SLR, LALR, CLR), and Shift-Reduce Parsing.

3. Left Recursion: Top-Down Parser cannot handle left recursion and needs to eliminate it before parsing. However, Bottom-Up Parser can handle left recursion.

4. Use of Stack: In Top-Down Parser, the stack is used to hold the grammar symbols, whereas in Bottom-Up Parser, the stack is used to hold input symbols.

5. Error Detection: Top-Down Parser can detect errors as soon as possible (on the first invalid input symbol). Bottom-Up Parser, however, detects errors at the end (after scanning the whole input).

6. Efficiency: Top-Down Parsers are generally less efficient than Bottom-Up Parsers.

7. Grammar Suitability: Top-Down Parsers are suitable for LL grammars, while Bottom-Up Parsers are suitable for LR grammars.

8. Predictability: Top-Down Parsers predict the production to be applied by looking at the next few tokens, whereas Bottom-Up Parsers reduce the already seen tokens to productions.