Rantlr

The Modern, Lightweight Parser Generator.
No Java. No Boilerplate. Just Clean Code.

Rantlr turns readable .gr grammars into idiomatic parsers for TypeScript, Python, Go, and Java — powered by a single Rust binary.

Why Rantlr?

Universal — Generates clean, idiomatic code for TS, Python, Go, Java, and more.
Fast — Written in Rust. Single binary, minimal host dependencies.
Modern Syntax — .gr files are easier to read than EBNF / ANTLR4.
Smart — Built-in linter with auto-suggestions for common grammar mistakes (including left recursion).
Zero runtime lock-in — Generated parsers embed a tiny BaseParser helper; copy the folder and go.

Installation

# From crates.io
cargo install rantlr

# From this repository
cargo install --path crates/rantlr-cli

# Or build locally
cargo build -p rantlr --release
# binary: target/release/rantlr

Quick Start (The `.gr` format)

Create a calculator.gr:

grammar Calculator;

token Num = Number;
token Ws = " " -> skip;

rule expr {
    term
    repeat {
        match "+" | "-"
        term
    }
}

rule term {
    Num
}

example "simple_add" {
    input: `1+2`
    expect: expr
}

Usage

1. Parse and validate

rantlr parse calculator.gr

2. Diagnose (JSON for editors / LSP)

rantlr diagnose calculator.gr
# or: rantlr parse calculator.gr --json   # AST on success; diagnostics on failure

3. Generate code

rantlr gen --target ts --out ./parser calculator.gr
# targets: ts | py | go | java

Project Structure

Path	Role
`crates/rantlr-core`	Rust engine — Lexer, Parser, Linter, in-process runtime
`crates/rantlr-cli`	Command-line interface (crate `rantlr`)
`crates/rantlr-gen`	Code generation for TS / Python / Go / Java
`editors/vscode`	Visual Studio Code extension
`playground`	Tauri + React visual debugger
`examples/`	Sample `.gr` / `.g4` grammars
`docs/`	Language notes (e.g. left recursion)

VS Code Extension

cd editors/vscode
npm install
npm run compile
# Then: F5 in VS Code, or install the extension from the folder

Features:

TextMate syntax highlighting for .gr
On-save diagnostics via rantlr diagnose (red squiggles)
Quick Fix for left recursion → opens docs/left-recursion.md

Set rantlr.cliPath if the binary is not on PATH (defaults to target/debug/rantlr in the workspace).

Playground (Tauri)

cd playground
npm install
npm run tauri dev

Left: Monaco editor for the .gr grammar
Right top: test input
Right bottom: live parse tree (or error)
Backend command analyze_grammar validates the grammar and interprets the test input in Rust

`.gr` vs ANTLR4

Concept	ANTLR4	Rantlr
Repetition	`*` / `+`	`repeat { … }`
Optionality	`?`	`optional { … }`
Choice	`a \| b`	`match a \| b`
Lexer types	Char classes	`Number`, `QuotedString`, …
Tests	External	`example` blocks

Contributing

Rantlr is built for the community. See CONTRIBUTING.md to add new target languages, improve the linter, or extend the playground.

License

MIT — see repository metadata. Author: Roberto de Souza <rabbittrix@hotmail.com>

rantlr-core 0.1.0