How Can I Create a Simple Four-Operation Calculator Using ANTLR?

Is There a Simple ANTLR Example?

Creating a simple ANTLR example involving a four-operation calculator requires understanding the process of converting grammar to Java source code.

Creating the Grammar File

Begin with a grammar file like "Exp.g":

grammar Exp;

eval
    : additionExp EOF
    ;

additionExp
    : multiplyExp(+ multiplyExp
                | - multiplyExp
                )*
    ;

multiplyExp
    : atomExp(* atomExp
             | / atomExp
             )*
    ;

atomExp
    : Number
    | '(' additionExp ')'
    ;

Number
    : ('0'..'9')+ ('.' ('0'..'9')+)?
    ;

WS
    :   (' ' | '\t' | '\r'| '\n') {$channel=HIDDEN;}
    ;

Generating the Lexer and Parser

Use the command below to generate the lexer and parser:

java -cp antlr-3.2.jar org.antlr.Tool Exp.g

Creating the Test Class

Create a test class like "ANTLRDemo.java":

import org.antlr.runtime.*;

public class ANTLRDemo {
    public static void main(String[] args) throws Exception {
        ANTLRStringStream in = new ANTLRStringStream("12*(5-6)");
        ExpLexer lexer = new ExpLexer(in);
        CommonTokenStream tokens = new CommonTokenStream(lexer);
        ExpParser parser = new ExpParser(tokens);
        parser.eval();
    }
}

Adding Java Code to the Grammar

To enable the parser to perform actions, add Java code within {...} blocks:

grammar Exp;

eval returns [double value]
    : additionExp { System.out.println("value equals: "+$value); }
    ;
    
// ...

Executing the Example

Compile the classes, generate the lexer and parser, and run ANTLRDemo to evaluate the expression "12*(5-6)".

This example demonstrates a basic grammar for a simple four-operation calculator, illustrating the process of defining a grammar, generating the necessary components, and adding Java code to control the parser's behavior.

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