Teknik Kompilasi - Pertemuan 4 (Top Down Parsing - Brute Force)

Summary

In this session, we explored parsing methods, focusing on top-down parsing and its techniques, such as backtracking. Top-down parsing begins with the initial symbol and seeks to derive terminal symbols, illustrating its workings through examples. However, backtracking can lead to inefficiencies, complicate error handling, and consume significant memory. We also addressed the issue of left recursion in grammars, discussing methods to eliminate it for improved parsing efficiency. Overall, understanding these parsing strategies is essential for effective language processing and compiler design.

Takeaways

• 😀 Parsing is the process of converting a string into a terminal representation.
• 😀 There are two main parsing methods: top-down and bottom-up.
• 😀 Top-down parsing starts from the initial symbol and traces down to terminals.
• 😀 Bottom-up parsing works in the opposite direction, starting from terminals to reach the initial symbol.
• 😀 Top-down parsing includes techniques like backtracking, recursive descent, and predictive parsing (LL1).
• 😀 Backtracking involves storing previous states in memory to retry different parsing paths when faced with a mismatch.
• 😀 Each parsing attempt in backtracking consumes memory, as it keeps backups of previous states.
• 😀 Left recursion in grammars can cause infinite loops in certain parsing methods.
• 😀 To eliminate left recursion, a method is presented involving the separation of productions with and without left recursion.
• 😀 Overall, backtracking can be slow and memory-intensive, making it less efficient for large grammars.

Q & A

What is the primary focus of the meeting discussed in the transcript?

The meeting focuses on parsing methods, particularly top-down parsing.

How is parsing defined in the context of this discussion?

Parsing is described as the process of transforming a string from a starting symbol to a terminal symbol.

What are the two main types of parsing methods mentioned?

The two main types are top-down parsing and bottom-up parsing.

What is top-down parsing and how does it work?

Top-down parsing starts from the root or starting symbol and explores the derivation until it reaches terminal symbols.

What is bottom-up parsing?

Bottom-up parsing begins with terminal symbols and works its way up to the starting symbol.

What are some techniques included in top-down parsing?

Techniques include backtracking, recursive descent parsing, and LL(1) parsing.

What are the limitations of backtracking in parsing?

Backtracking can be slow, requires significant memory for storing backups, and can struggle with left recursion in grammar.

What is left recursion and why is it problematic in parsing?

Left recursion occurs when a variable appears on the leftmost side of its own production rules, which can lead to infinite loops in parsing.

How can left recursion be eliminated from grammar?

Left recursion can be eliminated by separating the rules into those that exhibit left recursion and those that do not, and then reformulating the grammar.

What example is provided in the transcript to illustrate backtracking?

An example is given where a string 'a-b-c-d' is parsed using backtracking methods, demonstrating how the parser explores different derivations.