ANTLR

ANTLR takes as input a grammar that specifies a language and generates as output source code for a recognizer of that language. While Version 3 supported generating code in the programming languages Ada95, ActionScript, C, C#, Java, JavaScript, Objective-C, Perl, Python, Ruby, and Standard ML,[1] the current release at present only targets Java, C#, C++ [2], JavaScript, Python, Swift, and Go. A language is specified using a context-free grammar expressed using Extended Backus–Naur Form (EBNF).

ANTLR can generate lexers, parsers, tree parsers, and combined lexer-parsers. Parsers can automatically generate parse trees or abstract syntax trees, which can be further processed with tree parsers. ANTLR provides a single consistent notation for specifying lexers, parsers, and tree parsers.

By default, ANTLR reads a grammar and generates a recognizer for the language defined by the grammar (i.e., a program that reads an input stream and generates an error if the input stream does not conform to the syntax specified by the grammar). If there are no syntax errors, the default action is to simply exit without printing any message. In order to do something useful with the language, actions can be attached to grammar elements in the grammar. These actions are written in the programming language in which the recognizer is being generated. When the recognizer is being generated, the actions are embedded in the source code of the recognizer at the appropriate points. Actions can be used to build and check symbol tables and to emit instructions in a target language, in the case of a compiler.

Other than lexers and parsers, ANTLR can be used to generate tree parsers. These are recognizers that process abstract syntax trees, which can be automatically generated by parsers. These tree parsers are unique to ANTLR and help processing abstract syntax trees.

ANTLR 3 and ANTLR 4 are free software, published under a three-clause BSD License.[3] Prior versions were released as public domain software.[4] Documentation, derived from Parr's book The Definitive ANTLR 4 Reference, is included with the BSD-licensed ANTLR 4 source.[3][5]

Various plugins have been developed for the Eclipse development environment to support the ANTLR grammar, including ANTLR Studio, a proprietary product, as well as the "ANTLR 2"[6] and "ANTLR 3"[7] plugins for Eclipse hosted on SourceForge.

ANTLR 4 deals with left recursion correctly (except for indirect left recursion, i.e., grammars rules x that refer to y that refer to x)[8] and supports actions and attributes flexibly. That is, actions can be defined separately from the grammar, allowing for easier targeting of multiple languages.

Here is a non-comprehensive list of software built using ANTLR:

• Groovy.[11]
• Jython.[12]
• Hibernate.
• OpenJDK Compiler Grammar project experimental version of the javac compiler based upon a grammar written in ANTLR.
• Apex, Salesforce.com's programming language.
• The expression evaluator in Numbers, Apple's spreadsheet.
• Twitter's search query language.
• Weblogic server.
• Apache Cassandra.
• Processing.
• JabRef.
• Presto (SQL query engine)
• MySQL Workbench

Over 200 grammars implemented in ANTLR 4 are available on Github.[13] They range from grammars for a URL to grammars for entire languages like C, Java and Go.

In the following example, a parser in ANTLR describes the sum of expressions can be seen in the form of "1 + 2 + 3":

 // Common options, for example, the target language
 options
 {
  language = "CSharp";
 }
 // Followed by the parser 
 class SumParser extends Parser;
 options
 {
   k = 1; // Parser Lookahead: 1 Token
 }
 // Definition of an expression
 statement: INTEGER (PLUS^ INTEGER)*;
 // Here is the Lexer
 class SumLexer extends Lexer;
 options
 {
   k = 1; // Lexer Lookahead: 1 characters
 }
 PLUS: '+';
 DIGIT: ('0'..'9');
 INTEGER: (DIGIT)+;

The following listing demonstrates the call of the parser in a program:

 TextReader reader;
 // (...) Fill TextReader with character
 SumLexer lexer = new SumLexer(reader);
 SumParser parser = new SumParser(lexer);

 parser.statement();

• Coco/R
• DMS Software Reengineering Toolkit
• JavaCC
• Modular Syntax Definition Formalism
• Parboiled (Java)
• Parsing expression grammar
• SableCC

• Official website
• ANTLR (mega) Tutorial
• Why Use ANTLR?
• ANTLR Studio