ANTLR

ANTLR, short for Another Tool for Language Recognition, is a parser generator enabling developers to build language recognizers, compilers, interpreters, and translators from grammatical descriptions. It reads grammar files that define both lexers and parsers and generates source code in multiple target languages that can recognize inputs according to the specified grammar. The generated code produces parse trees that can be further processed by listeners or visitors.

ANTLR was created by Terence Parr and has evolved through several major versions, with ANTLR 4 being the current widely used release. It introduced adaptive LL(*) parsing, which uses dynamic lookahead to decide parsing paths, along with direct left recursion support and operator precedence.

Grammar mechanics: grammar files have .g4 extension; Lexer rules are typically written in uppercase, Parser rules in lowercase; tokens and channels; grammar options; Semantic predicates and actions are allowed in the target language. ANTLR generates recognizers that include a parser and a lexer, plus a runtime library for the chosen language. The project supports multiple targets such as Java, C#, Python, JavaScript, Go, Swift, C++, Dart, among others.

Tooling and usage: developers write a grammar, invoke the ANTLR tool (e.g., antlr4) to produce source code, compile it, and integrate it into applications. It also provides ANTLRWorks, an integrated development environment for editing and debugging grammars. Typical outputs include parse trees and optional listeners or visitors to traverse them. ANTLR is widely used for building programming languages, data formats, DSLs, and translation tools. It is released under a permissive BSD-like license. The official site is antlr.org.

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