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Parsing and it’s classification in Compiler Design- Top down parsing/bottom up parsing/Crecursive

Parsing and it’s classification in Compiler Design- Top down parsing/bottom up parsing/Crecursive

https://www.gyanodhan.com/video/7B2.%20GATE%20CSEIT/Compiler%20Design/272.%20Parsing%20and%20it%27s%20classification%20in%20Compiler%20Design-%20Top%20down%20parsing%2C%20bottom%20up%20parsing%2Crecursive%2CLR.mp4

Parsing and Its Classification in Compiler Design

 What is Parsing?

Parsing is the process of analyzing a sequence of tokens (from lexical analysis) to check if they follow the syntax rules of a grammar. It helps in syntax analysis and is a crucial part of a compiler.

 Classification of Parsing

Parsing is broadly classified into two types:
Top-Down Parsing
Bottom-Up Parsing

 Top-Down Parsing

In top-down parsing, the parser starts from the start symbol (S) and tries to derive the input string step by step by applying production rules.

Types of Top-Down Parsing:

 Recursive Descent Parsing

Example:

r
E → T + E | T
T → id

For input id + id, the parser starts from E and applies rules step by step.

 Predictive Parsing (LL(1) Parsing)

Example:
Grammar:

pgsql
E → TE'
E'
→ +TE' | ε
T → id

LL(1) table helps decide which production to apply next.

 Bottom-Up Parsing

In bottom-up parsing, the parser starts with the input string and reduces it step by step to the start symbol using reverse derivations.

Types of Bottom-Up Parsing:

 Shift-Reduce Parsing (LR Parsing)

Example:
Grammar:

r
E → E + T | T
T → id

For input id + id, the parser shifts tokens onto the stack and reduces them using rules.

 Key Differences: Top-Down vs. Bottom-Up Parsing

Feature Top-Down Parsing Bottom-Up Parsing
Start Point From the start symbol From the input string
Direction of Parsing Left-to-right derivation Right-to-left reduction
Backtracking May require (in Recursive Descent) No backtracking
Common Techniques Recursive Descent, Predictive Parsing (LL(1)) Shift-Reduce Parsing (LR, SLR, CLR, LALR)
Complexity Easier to implement More powerful but complex

 Conclusion

Top-Down Parsing is simpler but may not handle all types of grammars.
Bottom-Up Parsing is more powerful and can handle complex grammars.

 Would you like an example of LL(1) or LR(1) parsing? Let me know!

Here’s a clear and concise explanation of:


Parsing and Its Classification in Compiler Design

Includes Top-Down Parsing, Bottom-Up Parsing, and Recursive Descent Parsing


What is Parsing?

Parsing is the process of analyzing a string of symbols (source code) according to the rules of a formal grammar.

It helps in:


Goal of Parsing:

To determine if the input string can be generated by the grammar and to produce a derivation or parse tree.


Classification of Parsing:

Parsing techniques are broadly classified into two categories:

Type Direction Works With
Top-Down Parsing Left-to-right (L→R), builds tree from root LL Parsers
Bottom-Up Parsing Left-to-right (L→R), builds tree from leaves LR Parsers

1. Top-Down Parsing

Definition:

Starts from the start symbol and tries to derive the input string using production rules.

Techniques:

Process:

Issues:


Recursive Descent Parsing

Suitable for:


2. Bottom-Up Parsing

Definition:

Starts from the input string and tries to reduce it to the start symbol using reverse productions.

Techniques:

Process:

Advantages:


Comparison Table

Feature Top-Down Parsing Bottom-Up Parsing
Direction Left-to-right Left-to-right
Tree Construction Root to leaves Leaves to root
Backtracking May need it Not required
Handles Left Recursion No Yes
Examples Recursive Descent, LL LR, SLR, LALR, CLR

Summary:


Bonus:

Would you like:

Let me know what you’d like next!

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