Chevrotain

Introduction

Chevrotain is a very fast and feature rich Parser Building Toolkit for JavaScript. It can be used to build parsers/compilers/interpreters for various use cases ranging from simple configuration files, to full fledged programing languages.

A more in depth description of Chevrotain can be found in this great article on: Parsing in JavaScript: Tools and Libraries.

It is important to note that Chevrotain is NOT a parser generator. It solves the same kind of problems as a parser generator, just without any code generation. Chevrotain Grammars are pure code which can be created/debugged/edited as any other pure code without requiring any new tools or processes.

TLDR

• Online Playground
• Getting Started Tutorial
• Performance benchmark

Features

1. Parsing DSL.

   • LL(k) grammars support.
   • Useable from JavaScript / TypeScript / CoffeeScript.
   • Separation of grammar and semantics.
   • Customizable Error Reporting with full location information.
   • Strong Error Recovery/Fault-Tolerance capabilities based on Antlr3's algorithms.
   • Supports gates/predicates.
   • Backtracking support.
   • Grammar Inheritance.
   • Multiple starting rules.
   • Parameterized Rules.
   • Syntactic Content Assist.
   • No code generation.
     • The DSL is just JavaScript, not an external language.
     • The grammar is directly debuggable as plain JavaScript source.
     • Short feedback loops.
     • Allows great flexibility for inserting custom Parser actions.
   • Custom APIs.

2. Lexer Engine

   • Based on Regular Expressions.
   • Full position information tracking (lines/columns/offsets).
   • Token skipping (whitespace/comments/...).
   • Prioritise longest match (Keywords vs Identifiers).
   • Multiple Lexer Modes depending on the context.
   • Tokens Grouping.
   • Custom Token patterns(none RegExp) support
   • No code generation The Lexer does not require any code generation phase.

3. High Performance.

4. Railroad Diagrams Generation.

5. Grammar Reflection/Introspection.

   • The Grammar's structure is known and exposed at runtime.
   • Can be used to implement advanced features such as dynamically generated syntax diagrams or Syntactic error recovery.

6. Well tested with ~100% code coverage, Unit & Integration tests

Installation

• npm: npm install chevrotain
• Browser: The npm package contains Chevrotain as concatenated and minified files ready for use in a browser. These can also be accessed directly via UNPKG in a script tag.
  • Latest:
    • https://unpkg.com/chevrotain/lib/chevrotain.js
    • https://unpkg.com/chevrotain/lib/chevrotain.min.js
  • Explicit version number:
    • https://unpkg.com/chevrotain@3.4.0/lib/chevrotain.js
    • https://unpkg.com/chevrotain@3.4.0/lib/chevrotain.min.js

Documentation & Resources

• Getting Started Tutorial.

• Sample Grammars.

• FAQ.

• Other Examples.

• HTML API docs.

  • The Parsing DSL Docs.

Dependencies

There is a single dependency to regexp-to-ast library. This dependency is included in the bundled artifacts, for ease of consumption in browsers.

Compatibility

Chevrotain should run on any modern JavaScript ES5.1 runtime.

• The CI build runs the tests under:

  • Node.js (6 / 8 / 10).
  • Latest stable: Chrome, FireFox, Safari, IE Edge and IE 11.

• Uses UMD to work with common module loaders (browser global / amd / commonjs).

Contributions

Contributions are greatly appreciated. See CONTRIBUTING.md for details.

Where used

Some interesting samples:

• Metabase BI expression parser.
• Eve Programing Language.
• BioModelAnalyzer's ChatBot parser.
• Bombadil Toml Parser