Questions and Answers
Which phase of the compiler uses context-free grammar recognized by push-down automata?
What are the two types of parsers mentioned in the text?
What do the two 'L's in LL parser stand for?
How are production rules represented in a context-free grammar?
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What are the components of a context-free grammar?
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What is the main purpose of a parser in the context of a compiler?
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In syntax analysis, what does a parser do with the string of tokens obtained from the lexical analyzer?
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What is the consequence if the input sentence is not syntactically correct according to the parser?
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Which process does a parser undertake to attempt constructing a top-down parse tree?
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What represents the set of all token strings that can be derived from a grammar's start symbol?
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Study Notes
The Role of the Parser
- Syntax analysis or parsing is the second phase of a compiler
- Parsing is the process of finding a parse tree for a string of tokens
- A parser verifies whether a string of tokens belongs to the language generated by a given grammar
- A parser creates a parse tree if the input sentence is syntactically correct
- If the input sentence is not syntactically correct, the parser produces a syntax error
Types of Parsers
- Top-down parser (LL parser)
- Builds parse trees from top (root) to bottom (leaves)
- Scans the input string from left to right
- Performs left-most derivation
- Bottom-up parser (LR parser)
- Builds parse trees from leaves to root
- Scans the input string from left to right
- Performs right-most derivation
Context Free Grammar
- A context-free grammar (CFG) is recognized by push-down automata
- A CFG has four components: G={V,P,Σ,S}
- V: set of non-terminals (syntactic variables)
- P: set of productions (specify how terminals and non-terminals combine to form strings)
- Σ: set of tokens (terminal symbols)
- S: start symbol (where production begins)
Productions
- Each production consists of a non-terminal (left side) and a sequence of tokens and/or non-terminals (right side)
- Production rule: Non-terminal → Non-terminals. (Or) Non-terminal → terminals
- Example: A → β A1 and A1 → α A1 | ε
Eliminating Left-Recursion
- Example: Eliminating left-recursion for the grammar E → E+T|T, T → T*F|F, F → (E)|id
- Apply the formula A → β A' and A' → αA' | ε to eliminate left-recursion
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Description
Explore the concepts of syntax analysis, context-free grammar, predictive parsing, and operator precedence parsing in the context of compiler design. Learn about the role of the parser in the compilation process and how it generates parse trees for strings of tokens.
