Setup ANTLR in Java Project and Write Grammar for Parsing Boolean Algebra Expressions

ANTLR (Another Tool for Language Recognition) is a powerful parser generator used for reading, processing, and executing or translating structured text or binary files. In this post, you'll learn how to:

• Set up ANTLR in a Java project using Gradle.
• Write a grammar for parsing Boolean algebra expressions.
• Generate lexer and parser code using the Gradle plugin.

Step 1: Add ANTLR Plugin to build.gradle

First, apply the ANTLR plugin and add required dependencies.

plugins {
    id 'java'
    id 'antlr'
}

group = 'com.vkpapps'
version = '1.0-SNAPSHOT'

repositories {
    mavenCentral()
}

dependencies {
    antlr "org.antlr:antlr4:4.13.1"
    implementation "org.antlr:antlr4-runtime:4.13.1"
    // other dependencies
}

generateGrammarSource {
    maxHeapSize = "64m"
    arguments += ["-visitor", "-long-messages"]
    outputDirectory = file("build/generated/antlr/main/com/vkpapps")
}

sourceSets {
    main {
        java {
            srcDir "$buildDir/generated/antlr/main"
        }
        antlr {
            srcDirs = ['src/main/antlr']
        }
    }
}

This config tells Gradle to:

• Use ANTLR for grammar processing.
• Output generated sources in a specific directory.
• Include those sources in the main source set.

Step 2: Create ANTLR Grammar Directory

Create a folder named antlr under src/main to store your grammar files:

src/
└── main/
    └── antlr/
        └── BooleanAlgebra.g4

Step 3: Define the Boolean Algebra Grammar

Create a file named BooleanAlgebra.g4 and define your grammar:

grammar BooleanAlgebra;

@header {
package com.vkpapps;
}

expr
    : expr (OPERATION expr)+
    | '{' expr '}'
    | '[' expr ']'
    | '(' expr ')'
    | VARIABLE
    | (VARIABLE)? '(' expr ')' (VARIABLE)?
    | WS
    ;

VARIABLE
    : [a-z]+
    | [a-z]+'\'' (WS)*
    | [0-1]
    ;

OPERATION
    : OR
    | PRODUCT
    ;

OR      : 'OR' | 'or' | '+' ;
PRODUCT : '*' ;

WS : [\t\r\n]+ -> skip ;

This grammar handles:

• Parentheses and brackets
• Single-letter variables (like a, b')
• Basic operations (+, *, OR, etc.)

Step 4: Generate Parser and Lexer Code

Use the following Gradle command to generate the parser and lexer classes:

./gradlew generateGrammarSource

This will generate Java classes for the lexer, parser, and visitor pattern under build/generated/antlr/main/com/vkpapps.

What's Next?

With the parser and lexer in place, you can now write a Java program to:

• Parse Boolean expressions.
• Traverse the parse tree using the generated visitor classes.
• Evaluate or transform expressions for your specific use case (e.g., simplification, circuit generation, etc.)