Introduction to Lexical Analyzer

Summary

This session provides an in-depth look at the lexical analyzer's working principle, explaining how it processes high-level language code to produce tokens. It covers the types of tokens, the scanning and analyzing phases, and the use of finite state machines (FSM) for pattern recognition. The video also discusses handling comments, whitespace, and macro expansion, emphasizing the analyzer's role in creating symbol table entries and its interaction with the syntax analyzer.

Takeaways

• 📘 The lexical analyzer is a crucial part of a compiler that transforms high-level language code into tokens.
• 🔍 It uses regular expressions and type 3 grammar to recognize tokens, which are the basic elements of the source code.
• 📚 Tokens can be identifiers, operators, constants, keywords, literals, punctuators, and special characters.
• 🔧 The lexical analyzer performs two main functions: scanning to remove non-token elements and analyzing to produce tokens.
• 🌐 It operates on a finite state machine (FSM) to recognize different types of tokens such as keywords, identifiers, and integers.
• 🔄 The FSM can be a non-deterministic finite automata (NFA) which is then converted to a deterministic finite automata (DFA) for implementation.
• 🔑 The DFA recognizes tokens by moving through states based on the input characters until it reaches a final state.
• 🚮 The lexical analyzer also removes comments and white spaces which are considered non-token elements.
• 🔄 It supports macro expansion by replacing macro identifiers with their defined values throughout the code.
• 🔗 The lexical analyzer maintains a symbol table for identifiers and communicates with the syntax analyzer to provide tokens for parsing.

Q & A

What is the primary function of a lexical analyzer?

The primary function of a lexical analyzer is to scan the source code of a high-level programming language and convert it into a sequence of tokens.

What are the different phases of a compiler where lexical analyzer plays a role?

The lexical analyzer plays a role in the lexical analysis phase of a compiler, where it processes the arithmetic expression and produces a stream of tokens.

How does the lexical analyzer use regular expressions?

The lexical analyzer uses regular expressions to recognize tokens by employing regular grammar or type 3 grammar.

What are the types of tokens that a lexical analyzer can produce?

Tokens produced by a lexical analyzer can be identifiers, operators, constants, keywords, literals, punctuators, and special characters.

What is the role of a finite state machine in lexical analysis?

A finite state machine is used by the lexical analyzer to recognize tokens by transitioning between states based on the input characters.

How does the lexical analyzer handle comments in the source code?

The lexical analyzer detects comments and eliminates them as non-token elements, replacing them with whitespace or simply ignoring them.

What is the difference between scanning and analyzing phases in a lexical analyzer?

In the scanning phase, the lexical analyzer eliminates non-token elements like comments and whitespace. In the analyzing phase, it identifies tokens using the finite state machine.

How does the lexical analyzer deal with white spaces?

The lexical analyzer recognizes various types of white spaces such as space, horizontal tab, new line, vertical tab, form feed, and carriage return, and treats them as non-token elements.

What is the significance of the symbol table in the context of a lexical analyzer?

The lexical analyzer creates entries for identifiers in the symbol table, which is crucial for later stages of compilation like semantic analysis.

How does the lexical analyzer communicate with the syntax analyzer?

The lexical analyzer and the syntax analyzer frequently communicate, with the lexical analyzer providing tokens to the syntax analyzer upon request during parsing.

What additional functionality does the lexical analyzer provide besides tokenization?

Apart from tokenization, the lexical analyzer also performs macro expansion, replacing macro identifiers with their defined values in the source code.