npm package discovery and stats viewer.

Discover Tips

  • General search

    [free text search, go nuts!]

  • Package details

    pkg:[package-name]

  • User packages

    @[username]

Sponsor

Optimize Toolset

I’ve always been into building performant and accessible sites, but lately I’ve been taking it extremely seriously. So much so that I’ve been building a tool to help me optimize and monitor the sites that I build to make sure that I’m making an attempt to offer the best experience to those who visit them. If you’re into performant, accessible and SEO friendly sites, you might like it too! You can check it out at Optimize Toolset.

About

Hi, 👋, I’m Ryan Hefner  and I built this site for me, and you! The goal of this site was to provide an easy way for me to check the stats on my npm packages, both for prioritizing issues and updates, and to give me a little kick in the pants to keep up on stuff.

As I was building it, I realized that I was actually using the tool to build the tool, and figured I might as well put this out there and hopefully others will find it to be a fast and useful way to search and browse npm packages as I have.

If you’re interested in other things I’m working on, follow me on Twitter or check out the open source projects I’ve been publishing on GitHub.

I am also working on a Twitter bot for this site to tweet the most popular, newest, random packages from npm. Please follow that account now and it will start sending out packages soon–ish.

Open Software & Tools

This site wouldn’t be possible without the immense generosity and tireless efforts from the people who make contributions to the world and share their work via open source initiatives. Thank you 🙏

© 2024 – Pkg Stats / Ryan Hefner

cfgrammar-tool

v1.0.0

Published

Work with context-free grammars. Parsing, string generation, and manipulation.

Downloads

38

Readme

CFGrammar-Tool

A JavaScript library for working with context-free grammars. It's also a node.js module (npm install cfgrammar-tool).

Check out the the demo.

Features

  • Parsing. The implementation is Earley's algorithm, so arbitrary CFGs are supported without transformation. Optionally keep track of two parses or all parses, so as to catch ambiguity. Note that tracking all parses can take exponential or infinite time (though the latter possibility can be detected in advance).

  • Generation. Given a grammar, generate a string of length n in its language. All such strings are generated with non-zero probability, and if the grammar is unambiguous and does not contain nullable nonterminals then strings are generated uniformly at random. Requires n^2 preprocessing time, then linear time for each string.

  • Useful for automatic testing when QuickCheck and its ilk aren't generating sufficiently structured data. For example, test.js contains a CFG for CFGs, which was used to automatically test this very application.
  • Diagnostics and manipulation. Find/remove unreachable symbols, symbols which do not generate any string, nullable symbols, duplicate rules, unit productions (A -> B), etc.

Example

var cfgtool = require('cfgrammar-tool');
var types = cfgtool.types;
var parser = cfgtool.parser;
var generatorFactory = cfgtool.generator;

var Grammar = types.Grammar;
var Rule = types.Rule;
var T = types.T;
var NT = types.NT;
var exprGrammar = Grammar([
  Rule('E', [NT('E'), T('+'), NT('T')]),
  Rule('E', [NT('T')]),
  Rule('T', [NT('T'), T('*'), NT('F')]),
  Rule('T', [NT('F')]),
  Rule('F', [T('('), NT('E'), T(')')]),
  Rule('F', [T('n')])
]);

parser.parse(exprGrammar, 'n*(n+n)').length > 0; // true
parser.parse(exprGrammar, 'n(n+n)').length > 0; // false

var generator = generatorFactory(exprGrammar);
generator(21); // something like 'n*((n+(n)*n+n+n*n))*n'

TODO

License

Licensed under the MIT license. If you're making public or commercial use of this library, I encourage (but do not require) you to tell me about it!