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ANTLR (ANother Tool for Language Recognition) is a powerful parser generator for reading, processing, executing, or translating structured text or binary files.

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Quick Overview

ANTLR (ANother Tool for Language Recognition) is a powerful parser generator for reading, processing, executing, or translating structured text or binary files. It's widely used to build languages, tools, and frameworks. ANTLR takes as input a grammar that specifies a language and generates as output source code for a recognizer for that language.

Pros

  • Supports a wide range of target languages (Java, C#, Python, JavaScript, Go, C++, Swift)
  • Provides an easy-to-use, human-readable grammar syntax
  • Includes built-in support for parse tree generation and traversal
  • Offers excellent documentation and a large, active community

Cons

  • Learning curve can be steep for beginners
  • Generated parsers may be slower than hand-written ones for some use cases
  • Large runtime library size for some target languages
  • Can be overkill for simple parsing tasks

Code Examples

  1. Simple arithmetic expression grammar:
grammar Arithmetic;
expr : expr ('*'|'/') expr
     | expr ('+'|'-') expr
     | INT
     | '(' expr ')'
     ;
INT : [0-9]+ ;
WS : [ \t\r\n]+ -> skip ;
  1. Using the generated parser in Java:
String input = "2 * (3 + 4)";
ArithmeticLexer lexer = new ArithmeticLexer(CharStreams.fromString(input));
CommonTokenStream tokens = new CommonTokenStream(lexer);
ArithmeticParser parser = new ArithmeticParser(tokens);
ParseTree tree = parser.expr();
  1. Traversing the parse tree with a listener:
ParseTreeWalker walker = new ParseTreeWalker();
MyArithmeticListener listener = new MyArithmeticListener();
walker.walk(listener, tree);

Getting Started

  1. Install ANTLR:

    pip install antlr4-tools

  2. Write your grammar (e.g., Arithmetic.g4)

  3. Generate parser:

    antlr4 Arithmetic.g4

  4. Compile and run (Java example):

    javac *.java
java YourMainClass

For other languages, refer to the ANTLR documentation for specific setup instructions.

Competitor Comparisons

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javacc

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JavaCC - a parser generator for building parsers from grammars. It can generate code in Java, C++ and C#.

Pros of JavaCC

  • Simpler syntax and easier to learn for beginners
  • Better integration with Java, allowing direct embedding of Java code
  • More flexible in terms of grammar specification

Cons of JavaCC

  • Limited support for target languages (primarily Java)
  • Less powerful in handling complex grammars
  • Smaller community and fewer resources compared to ANTLR

Code Comparison

ANTLR4 grammar example:

grammar Example;
expr: term (('+' | '-') term)*;
term: factor (('*' | '/') factor)*;
factor: NUMBER | '(' expr ')';
NUMBER: [0-9]+;
WS: [ \t\r\n]+ -> skip;

JavaCC grammar example:

PARSER_BEGIN(Example)
public class Example {}
PARSER_END(Example)

TOKEN:
{
  < NUMBER: (["0"-"9"])+ >
| < WHITESPACE: [" ","\t","\n","\r"] > {SPC()}
}

void expr():
{}
{
  term() (("+" | "-") term())*
}

void term():
{}
{
  factor() (("*" | "/") factor())*
}

void factor():
{}
{
  <NUMBER> | "(" expr() ")"
}

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README

ANTLR v4

Java 11+ License

ANTLR (ANother Tool for Language Recognition) is a powerful parser generator for reading, processing, executing, or translating structured text or binary files. It's widely used to build languages, tools, and frameworks. From a grammar, ANTLR generates a parser that can build parse trees and also generates a listener interface (or visitor) that makes it easy to respond to the recognition of phrases of interest.

Dev branch build status

MacOSX, Windows, Linux (github actions)

Versioning

ANTLR 4 supports 10 target languages (Cpp, CSharp, Dart, Java, JavaScript, PHP, Python3, Swift, TypeScript, Go), and ensuring consistency across these targets is a unique and highly valuable feature. To ensure proper support of this feature, each release of ANTLR is a complete release of the tool and the 10 runtimes, all with the same version. As such, ANTLR versioning does not strictly follow semver semantics:

  • a component may be released with the latest version number even though nothing has changed within that component since the previous release
  • major version is bumped only when ANTLR is rewritten for a totally new "generation", such as ANTLR3 -> ANTLR4 (LL(*) -> ALL(*) parsing)
  • minor version updates may include minor breaking changes, the policy is to regenerate parsers with every release (4.11 -> 4.12)
  • backwards compatibility is only guaranteed for patch version bumps (4.11.1 -> 4.11.2)

If you use a semver verifier in your CI, you probably want to apply special rules for ANTLR, such as treating minor change as a major change.

Repo branch structure

The default branch for this repo is master, which is the latest stable release and has tags for the various releases; e.g., see release tag 4.9.3. Branch dev is where development occurs between releases and all pull requests should be derived from that branch. The dev branch is merged back into master to cut a release and the release state is tagged (e.g., with 4.10-rc1 or 4.10.) Visually our process looks roughly like this:

The Go target now has its own dedicated repo:

$ go get github.com/antlr4-go/antlr

Note The dedicated Go repo is for go get and import only. Go runtime development is still performed in the main antlr/antlr4 repo.

Authors and major contributors

Useful information

You might also find the following pages useful, particularly if you want to mess around with the various target languages.

The Definitive ANTLR 4 Reference

Programmers run into parsing problems all the time. Whether it’s a data format like JSON, a network protocol like SMTP, a server configuration file for Apache, a PostScript/PDF file, or a simple spreadsheet macro language—ANTLR v4 and this book will demystify the process. ANTLR v4 has been rewritten from scratch to make it easier than ever to build parsers and the language applications built on top. This completely rewritten new edition of the bestselling Definitive ANTLR Reference shows you how to take advantage of these new features.

You can buy the book The Definitive ANTLR 4 Reference at amazon or an electronic version at the publisher's site.

You will find the Book source code useful.

Additional grammars

This repository is a collection of grammars without actions where the root directory name is the all-lowercase name of the language parsed by the grammar. For example, java, cpp, csharp, c, etc...

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