Home » Java » Enterprise Java » ANTLR: Getting Started

About Swathi V

Swathi V
Loves Art and Technology! Would like to blog and share.. Involved in Apache Hadoop and its ecosystem. Eager to be a part of Big Data Revolution.

ANTLR: Getting Started

This post drives you towards the basics of ANTLR. Previously, we had learnt about setting up of ANTLR as an external tool.RECAP! It’s here: ANTLR External Tool
:)
So, here we go….

What is ANTLR?

• ANother Tool for Language Recognition, is a language tool that provides a framework for constructing recognizers, interpreters, compilers, and translators from grammatical descriptions containing actions.

What can be the target languages? 

• Action Script, Ada
• C
• C#; C#2
• C#3
• D
• Emacs ELisp
• Objective C
• Java
• Java Script
• Python
• Ruby
• Perl6
• Perl
• PHP
• Oberon
• Scala
 
What does ANTLR support?

• Tree construction
• Error recovery
• Error handling
• Tree walking
• Translation
 
What environment does it support? 

ANTLRWorks is the IDE for ANTLR. It is the graphical grammar editor and debugger, written by Jean Bovet using Swing.

What for ANTLR can be used?

• “”REAL”” programming languages
• domain-specific languages [DSL]  
Who is using ANTLR?

• Programming languages :Boo, Groovy, Mantra, Nemerle, XRuby etc.
• Other Tools: HIbernate, Intellij IDEA, Jazillian, JBoss Rules, Keynote(Apple), WebLogic(Oracle) etc.
 
Where is that you can look for ANTLR?

You can always follow here http://www.antlr.org
• to download ANTLR and ANTLRWorks, which are free and open source
• docs,articles,wiki,mailing list,examples…. You can catch everything here!

Row your Boat….
 

  • Basic terms

Lexer : converts a stream of characters to a stream of tokens.
Parser : processes of tokens, possibly creating AST
Abstract Syntax Tree(AST): an intermediate tree representation of the parsed input that is simpler to process than the stream of tokens. It can as well be processed multiple times.
Tree Parser: It processes an AST
String Template: a library that supports using templates with placeholders for outputting text

  • General Steps

• Write Grammar in one or more files
• Write string templates[optional] • Debug your grammar with ANTLRWorks
• Generate classes from grammar
• Write an application that uses generated classes
• Feed the application text that conforms to the grammar


A Bit Further….

Lets write a simple grammar which consists of
• Lexer
• Parser
Lexer: Breaks the input stream into tokens
Lets take the example of simple declaration type in C of the form “int a,b;” or “int a;” and same with float. As we see we can write lexer as follows:

//TestLexer.g
grammar TestLexer;
ID : (‘a’..’z’|’A’..’Z’|’_’) (‘a’..’z’|’A’..’Z’|’0′..’9’|’_’|’.’|’a’..’z’|’A’..’Z’)*; COMMA: ‘,';
SEMICOLON:';';
DATATYPE: ‘int’ | ‘float';

As we could see, these were the characters that were to be converted to tokens.
So, now lets write some rules which processes these tokens generated and may it create a parse tree accordingly.

//TestParser.g
grammar TestParser;
options {language : Java;}
decl:DATATYPE ID (‘,’ ID)* ;

Running ANTLR on the grammar just generates the lexer and parser,TestParser and TestLexer. To actually try the grammar on some input, we
need a test rig with a main( ) method as follows:
// Test.java

import org.antlr.runtime.*;
public class Test {

public static void main(String[] args) throws Exception {

// Create an input character stream from standard in
ANTLRFileStream input = new ANTLRFileStream("input"); // give path to the file input
// Create an ExprLexer that feeds from that stream
TestLexer lexer = new TestLexer(input);
// Create a stream of tokens fed by the lexer
CommonTokenStream tokens = new CommonTokenStream(lexer);
// Create a parser that feeds off the token stream
TestParser parser = new TestParser(tokens);
// Begin parsing at rule decl
parser.decl();
}}

We shall see how to create an AST and walk over the tree in the next blog post…
Happy learning….! :)

Reference: Getting Started With ANTLR:Basics from our JCG partner Swathi V at the * Techie(S)pArK * blog.

Do you want to know how to develop your skillset to become a Java Rockstar?

Subscribe to our newsletter to start Rocking right now!

To get you started we give you our best selling eBooks for FREE!

1. JPA Mini Book

2. JVM Troubleshooting Guide

3. JUnit Tutorial for Unit Testing

4. Java Annotations Tutorial

5. Java Interview Questions

6. Spring Interview Questions

7. Android UI Design

and many more ....

 

One comment

  1. Hey Swathi,

    I’m an engineering student working on a mini project on ANTLR, supposed to use string templates to emit Java code that does CRUD operations on a file, database and the like. I’m stuck with the template machinery, all i get are errors. Is there any way you can help me out ??

    Thank You

Leave a Reply

Your email address will not be published. Required fields are marked *

*


one + 8 =

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong>

Want to take your Java Skills to the next level?
Grab our programming books for FREE!
  • Save time by leveraging our field-tested solutions to common problems.
  • The books cover a wide range of topics, from JPA and JUnit, to JMeter and Android.
  • Each book comes as a standalone guide (with source code provided), so that you use it as reference.
Last Step ...

Where should we send the free eBooks?

Good Work!
To download the books, please verify your email address by following the instructions found on the email we just sent you.