2023-08-08

Setting up ANTLR with IntelliJ IDEA

Install the ANTLR plugin
Open a new project and create a simple grammar file g.g4

grammar g;
s   : 'hello' ID;
ID  : [a-z]+ ;
WS  : [ \t\r\n]+ -> skip ;

This grammar has 3 rules - 2 lexer rule and 1 parser rule
Lexer rules are written in uppercase whereas parser rules are written in lowercase
You can test this grammar by clicking on the button at the bottom

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Given the following input, a parse tree will be generated

hello c

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ANTLR Code Generation

You can generate codes for a given grammar by right clicking anywhere with the .g4 file open and then selecting Generate ANTLR Recognizer

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By default this will generate the code in a seperate folder. To change this behavior right click -> Configure ANTLR and choose the current working directory as the output path

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Note that relative paths like ./ or ../ may not work. You have to select the absolute path to the src directory
By default the code generated is in Java. This too can be changed following a similar method to above.

Sample ANTLR Project

Create a new Java Project
Create a Hello.g4 file inside the src/ directory

lexer grammar Hello;
IF: 'if';
ID : ('a'..'z')('a'..'z'| '0'..'9'|'_')*;
WS : [ \r\n\t]+ -> skip;

You can either configure antlr to generate files directly to the src directory or mark the gen directory as Generated Sources Root

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Now press ⌘ + ;(or whatever the shortcut is in Windows) to open the Project Structure
Go to Libraries
Click on the + icon and then click on From Maven
Search for org.antlr:antlr4-runtime:x.x.x
Please check your plugin version to see what is bundled with it
Both of them should match

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create a Main.java file with the following

import java.io.IOException;

import org.antlr.v4.runtime.CharStream;
import org.antlr.v4.runtime.CharStreams;
import org.antlr.v4.runtime.Token;

public class Main {

    public static void main(String[] args) throws IOException {
        CharStream input = CharStreams.fromFileName(args[0]);
        Hello lex = new Hello(input);
        Token token;
        while ((token = lex.nextToken()).getType() != -1) {
            System.out.printf("%s:%d:%d: token <%s, %s>\n", args[0],
                    token.getLine(), token.getStartIndex(),
                    token.getType(), token.getText());
        }
    }
}

Create a file input with

if186 if addfggh 33455 erry
ggjhj 1234dfff ffggg

Build and run to get the following

input:1:0: token <2, if186>
input:1:6: token <1, if>
input:1:9: token <2, addfggh>
input:1:23: token <2, erry>
input:2:28: token <2, ggjhj>
input:2:38: token <2, dfff>
input:2:43: token <2, ffggg>
line 1:17 token recognition error at: '3'
line 1:18 token recognition error at: '3'
line 1:19 token recognition error at: '4'
line 1:20 token recognition error at: '5'
line 1:21 token recognition error at: '5'
line 2:6 token recognition error at: '1'
line 2:7 token recognition error at: '2'
line 2:8 token recognition error at: '3'
line 2:9 token recognition error at: '4'

Process finished with exit code 0