ANTLR

In computer-based language recognition, ANTLR (pronounced antler), or ANother Tool for Language Recognition, is a parser generator that uses LL(*) for parsing. ANTLR is the successor to the Purdue Compiler Construction Tool Set (PCCTS), first developed in 1989, and is under active development. Its maintainer is Professor Terence Parr of the University of San Francisco.

ANTLR
Original author(s)Terence Parr and others
Initial releaseFebruary 1992 (1992-02)
Stable release
4.8 / 16 January 2020 (2020-01-16)
Repository
Written inJava
PlatformCross-platform
LicenseBSD License
Websitewww.antlr.org

Usage

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.

Licensing

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

ANTLR 4 deals with left recursion correctly (except for indirect left recursion, i.e., grammar 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.

Development

As reported on the tools[9] page of the ANTLR project, plug-ins that enable features like syntax highlighting, syntax error checking and code completion are freely available for the most common IDEs (Intellij IDEA, NetBeans, Eclipse, Visual Studio[10] and Visual Studio Code).

Projects

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

Over 200 grammars implemented in ANTLR 4 are available on Github.[14] They range from grammars for a URL to grammars for entire languages like C, Java and Go.

Example

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();
gollark: You also pay for markup and quite possibly extra stuff you don't need.
gollark: Also, you generally need pricier CPUs and whatnot.
gollark: Server mainboards are overly expensive compared to consumer-grade ones.]
gollark: Well, out of band remote management, SSH works fine still.
gollark: You'll lose stuff like remote management/IPMI, but it's very cost-effective.

See also

References
  1. SML/NJ Language Processing Tools: User Guide
  2. https://soft-gems.net/the-antlr4-c-runtime-reached-home
  3. "antlr4/LICENSE.txt". GitHub. 2017-03-30.
  4. Parr, Terence (2004-02-05). "licensing stuff". antlr-interest (Mailing list). Archived from the original on 2011-07-18. Retrieved 2009-12-15.
  5. "ANTLR 4 Documentation". GitHub. 2017-03-30.
  6. http://antlreclipse.sourceforge.net
  7. http://antlrv3ide.sourceforge.net
  8. What is the difference between ANTLR 3 & 4
  9. http://www.antlr.org/tools.html
  10. https://marketplace.visualstudio.com/items?itemName=SamHarwell.ANTLRLanguageSupport
  11. http://docs.groovy-lang.org/2.4.0/html/api/org/codehaus/groovy/antlr/parser/GroovyRecognizer.html
  12. https://hg.python.org/jython/rev/31d97f0de5fe
  13. Ebersole, Steve (2018-12-06). "Hibernate ORM 6.0.0.Alpha1 released". In Relation To, The Hibernate team blog on everything data. Retrieved 2020-07-11.
  14. Grammars written for ANTLR v4; expectation that the grammars are free of actions.: antlr/grammars-v4, Antlr Project, 2019-09-25, retrieved 2019-09-25

Bibliography

Further reading
  • Parr, T.J.; Quong, R.W. (July 1995). "ANTLR: A Predicated-LL(k) Parser Generator". Software: Practice and Experience. 25 (7): 789–810. CiteSeerX 10.1.1.54.6015. doi:10.1002/spe.4380250705.
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