lark-js 0.1.4
An extension to Lark that generates a Javascript standalone
License: MIT

# Lark.js

**Generate LALR(1) parsers in Javascript**

Lark is a popular parsing toolkit for Python.

This project is a live port of the Lark standalone parser to Javascript.

**Lark.js** takes a `.lark` grammar, and from it generates a standalone Javascript parser.

The LALR(1) algorithm guarantees O(n) running time (proportional to input length), and minimal memory consumption.

### Lark grammars

Lark grammars are written in an augmented EBNF (a textual format), and usually use the `.lark` extension.

Because they are purely declarative, and don't contain code, they are entirely portable between languages.

It is now possible to use Lark grammars in 3 languages: Python, Javascript, and Julia.

#### "Hello World" Grammar

The following Lark grammar will match the string "Hello, World!" --

```lark
// A bunch of words
start: word+                

// Allow optional punctuation after each word
word: WORD ["," | "!"]

// imports WORD from library
%import common.WORD   

// Disregard spaces in text
%ignore " "           
```

### Quick links

- [Documentation](https://lark-parser.github.io/Lark.js/index.html)
- [Examples](https://github.com/lark-parser/Lark.js/tree/master/examples)
- [Online IDE](https://lark-parser.github.io/ide)
- [Gitter chat](https://gitter.im/lark-parser/Lobby) - A place to ask questions and discuss
- [Lark](https://github.com/lark-parser/lark) - The Python library

### Install Lark.js

Install lark-js on Python:

```sh
    pip install lark-js --upgrade
```

### Generate a Javascript LALR(1) parser

```sh
	lark-js my_grammar.lark -o my_parser.js
```

For help, run:

```sh
	lark-js --help
```

## Features

 - **LALR(1)** parser - Fast and light
 - **EBNF** grammar
 - Builds a parse-tree (AST) automagically, based on the structure of the grammar
 - Usable in the browser and in Node.js
 - Interactive parsing (step-by-step)
 - Error handling
 - Tree utilities (including transformers & visitors)
 - Line & column tracking
 - Standard library of terminals (strings, numbers, names, etc.)
 - Import grammars from Nearley.js

 Planned features:

 - Support for Earley

### Syntax Highlighting

Lark provides syntax highlighting for its grammar files (\*.lark):

- [Sublime Text & TextMate](https://github.com/lark-parser/lark_syntax)
- [vscode](https://github.com/lark-parser/vscode-lark)
- [Intellij & PyCharm](https://github.com/lark-parser/intellij-syntax-highlighting)
- [Vim](https://github.com/lark-parser/vim-lark-syntax)
- [Atom](https://github.com/Alhadis/language-grammars)

### Live Port

Usually, ports from one language to another are at risk of falling out of sync as time goes on.

But Lark.js wasn't translated by hand -- 98% of the lines were transpiled directly from Lark's Python code!

That means that futures updates to Lark-Python (fixes, features, etc.) will automatically sync to Lark.js.

## License

Lark.js uses the [MIT license](LICENSE).

## Contribute

Lark.js is accepting pull-requests. If you would like to help, open an issue or find us on gitter.

## Sponsoring

Lark.js was made possible with the help of a generous donation by [Smore](https://www.smore.com/) ❤️

If you like Lark, and want to see it grow, please consider [sponsoring us!](https://github.com/sponsors/lark-parser)