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Description:

larkjs 0.1.4

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!" --
// 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
Examples
Online IDE
Gitter chat - A place to ask questions and discuss
Lark - The Python library

Install Lark.js
Install lark-js on Python:
pip install lark-js --upgrade

Generate a Javascript LALR(1) parser
lark-js my_grammar.lark -o my_parser.js

For help, run:
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
vscode
Intellij & PyCharm
Vim
Atom

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.
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 ❤️
If you like Lark, and want to see it grow, please consider sponsoring us!