Overview

CongoCC generates parsers in Java, Python, C#, and Rust from a single grammar. The grammar language, the parsing behavior, and the shape of the syntax tree are the same whichever target you choose; what changes is the language of any code you embed, the layout and naming of the generated output, and how you build and run it. This guide covers those differences.

Choosing a target

The -lang flag selects the target; Java is the default:

$ java -jar congocc.jar -lang python  MyGrammar.ccc
$ java -jar congocc.jar -lang csharp  MyGrammar.ccc
$ java -jar congocc.jar -lang rust -d my-parser MyGrammar.ccc

The same grammar can be generated for every target, provided it contains no embedded target-language code. Embedded actions and INJECT blocks are written in one language and must be ported or guarded to support others — see Injected Code Across Languages.

What differs between targets

For a grammar with PARSER_PACKAGE = "demo.lang", the four targets produce noticeably different output:

Target	Output layout	Start production call	Root of the tree
Java	a package directory tree (demo/lang/… plus an ast/ subpackage)	parser.NumberList()	parser.rootNode()
Python	a package, langparser/ (*.py modules)	parser.parse_NumberList()	parser.root_node()
C#	a project, cs-langparser/ (with a .csproj)	parser.ParseNumberList()	parser.RootNode
Rust	a self-contained crate (Cargo.toml plus *.rs, flat in -d)	Parser::parse(input, Some("name"))	ast.root()

The conventions follow each language: production methods are bare in Java, parse_-prefixed and snake_case in Python, Parse-prefixed and PascalCase in C#, and folded into a single Parser::parse entry point for Rust’s arena-based AST.

Self-contained output

Whichever target you pick, the generated code is self-contained: it includes its own lexer, parser, token, and node types and does not depend on a CongoCC runtime library. Rust crates have zero external dependencies (with optional serde); the others rely only on their standard libraries. The per-language chapters — Java, Python, C#, Rust — give the details, and Build and Runtime Matrix summarizes how to build and run each.