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Chapter 3
Lexical Analysis
Page 2


Chapter 3
Lexical Analysis
Outline
? Role of lexical analyzer
? Specification of tokens
? Recognition of tokens
? Lexical analyzer generator
? Finite automata
? Design of lexical analyzer generator
Page 3


Chapter 3
Lexical Analysis
Outline
? Role of lexical analyzer
? Specification of tokens
? Recognition of tokens
? Lexical analyzer generator
? Finite automata
? Design of lexical analyzer generator
The role of lexical analyzer
Lexical
Analyzer
Parser
Source
program
token
getNextToken
Symbol
table
To semantic
analysis
Page 4


Chapter 3
Lexical Analysis
Outline
? Role of lexical analyzer
? Specification of tokens
? Recognition of tokens
? Lexical analyzer generator
? Finite automata
? Design of lexical analyzer generator
The role of lexical analyzer
Lexical
Analyzer
Parser
Source
program
token
getNextToken
Symbol
table
To semantic
analysis
Why to separate Lexical analysis
and parsing
1. Simplicity of design
2. Improving compiler efficiency
3. Enhancing compiler portability
Page 5


Chapter 3
Lexical Analysis
Outline
? Role of lexical analyzer
? Specification of tokens
? Recognition of tokens
? Lexical analyzer generator
? Finite automata
? Design of lexical analyzer generator
The role of lexical analyzer
Lexical
Analyzer
Parser
Source
program
token
getNextToken
Symbol
table
To semantic
analysis
Why to separate Lexical analysis
and parsing
1. Simplicity of design
2. Improving compiler efficiency
3. Enhancing compiler portability
Tokens, Patterns and Lexemes
? A token is a pair a token name and an optional token
value
? A pattern is a description of the form that the lexemes
of a token may take
? A lexeme is a sequence of characters in the source
program that matches the pattern for a token
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FAQs on PPT: Lexical Analysis - Compiler Design - Computer Science Engineering (CSE)

1. What is lexical analysis in computer science engineering (CSE)?
Ans. Lexical analysis in computer science engineering (CSE) is the process of converting a sequence of characters into a sequence of tokens or lexemes. It is the first phase of the compiler design, where the input program is scanned to identify the basic units, such as keywords, identifiers, literals, and operators.
2. What is the role of lexical analysis in the compilation process?
Ans. The role of lexical analysis in the compilation process is to analyze the source code and break it down into meaningful tokens. It helps in identifying and categorizing the different elements of the code, such as keywords, identifiers, literals, and operators. The tokens generated by lexical analysis are then used in subsequent phases of the compiler, such as parsing and semantic analysis.
3. What are tokens in lexical analysis?
Ans. In lexical analysis, tokens are the smallest meaningful units of a programming language. They represent the various elements of the source code, such as keywords, identifiers, literals, and operators. Tokens are generated by the lexer or scanner, which scans the input program character by character, identifying and categorizing the elements based on predefined rules.
4. What is the purpose of using regular expressions in lexical analysis?
Ans. Regular expressions are used in lexical analysis to define the patterns for identifying different tokens in the source code. Each token type is associated with a regular expression that describes its structure and characteristics. These regular expressions are used by the lexer or scanner to match and extract the tokens from the input program.
5. How does lexical analysis contribute to compiler optimization?
Ans. Lexical analysis plays a role in compiler optimization by identifying and eliminating unnecessary or redundant tokens from the source code. By removing such redundant tokens, the compiler can reduce the size of the intermediate representation and improve the efficiency of subsequent compilation phases. Additionally, lexical analysis can also detect and report lexical errors, helping in the early detection and resolution of issues in the code.
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