Introduction to Lexical Analyser & Grammars Video Lecture | Compiler Design - Computer Science Engineering (CSE)

A lexical analyzer, also known as a lexer, is a component of a compiler or interpreter that reads the source code and breaks it down into a sequence of tokens. It performs lexical analysis, which involves scanning the source code for lexemes (units of meaning) and categorizing them into different token types, such as identifiers, keywords, operators, and literals. The lexical analyzer is responsible for removing unnecessary white spaces and comments, as well as identifying any lexical errors in the source code.

A lexical analyzer works by using a set of rules defined by a grammar to analyze the source code. It starts by reading the source code character by character and grouping them into lexemes based on the defined rules. The lexemes are then categorized into different token types. This process continues until the entire source code is analyzed. The lexical analyzer also handles any errors, such as encountering an invalid character or an unknown lexeme, and reports them to the compiler or interpreter.

Grammars play a crucial role in lexical analysis. A grammar defines the rules and patterns that determine how the source code is structured and how the lexemes are formed. It provides a formal description of the syntax of a programming language. The lexical analyzer uses these grammar rules to identify and categorize the lexemes into appropriate token types. By following the grammar rules, the lexical analyzer ensures that the source code is correctly parsed and analyzed.

A lexical analyzer identifies various token types in the source code. Some common token types include: 1. Identifiers: These are names defined by the programmer, such as variable names or function names. 2. Keywords: Reserved words in the programming language that have a specific meaning, such as "if," "for," or "while." 3. Operators: Symbols used to perform operations, such as arithmetic operators (+, -, *, /) or logical operators (&&, ||). 4. Literals: Constants or values, such as numbers or strings, used in the source code. 5. Delimiters: Symbols used to separate different parts of the code, such as parentheses, commas, or semicolons.

A lexical analyzer can report various errors encountered during lexical analysis. Some common errors include: 1. Invalid characters: When the lexical analyzer encounters a character that is not a part of the defined character set for the programming language. 2. Unknown lexemes: When the lexical analyzer comes across a lexeme that does not match any defined token type in the grammar. 3. Missing or mismatched delimiters: When there are missing or mismatched delimiters, such as missing closing parentheses or brackets. 4. Improperly formed numbers or strings: When the lexical analyzer encounters a number or string that does not adhere to the syntax rules defined by the grammar. 5. Reserved words used as identifiers: When the lexical analyzer identifies a reserved word being used as an identifier, which is not allowed in most programming languages.