A)For Windows

Filename: hello.g4

Scanner || Lexer :

antlr4 file.g4 javac file*.java grun file tokens -tokens

Parser: prog(This is the starting expression of the production rules)

antlr4 file.g4 compile file*.java grun hello prog -gui

1. Sample Lexer Code (`lex.g4`)

The lexer identifies tokens like keywords, identifiers, and numbers. Here’s an example of a simple lexer grammar.

Lexer Grammar (`lex.g4`):

lexer grammar lex;

// Tokens
IF: 'if';                       // IF keyword
ID: [a-z]+;                      // Identifier (sequence of lowercase letters)
DIGIT: [0-9]+;                   // Digit (one or more numbers)

// Whitespace - skip spaces, tabs, and newlines
WS: [ \\\\t\\\\r\\\\n]+ -> skip;

Sample Input for Lexer (`test_input.txt`):

if abc 123

How to Run the Lexer :

Generate the lexer files:
```
antlr4 lex.g4
```
Compile the lexer files:
```
javac lex*.java
```

Run the lexer:

grun lex tokens test_input.txt -tokens

Expected Output:

[@0,0:1='if',<'if'>,1:0]
[@1,3:5='abc',<ID>,1:3]
[@2,7:9='123',<DIGIT>,1:7]
[@3,10:9='<EOF>',<EOF>,1:10]

2. Sample Parser Code with Embedded Lexer (`file.g4`)

Here’s an example that combines the lexer and parser into one grammar file. This parser will process simple assignment and if statements.

A)For Windows

1. Sample Lexer Code (lex.g4)

Lexer Grammar (lex.g4):