PEG.js: Parser Generator for JavaScript ======================================= PEG.js is a parser generator for JavaScript based on the [parsing expression grammar](http://en.wikipedia.org/wiki/Parsing_expression_grammar) formalism. It is designed to be used either from your browser or from the command line (using [Rhino](http://www.mozilla.org/rhino/) JavaScript interpreter). Features -------- * Usable [from your browser](http://pegjs.majda.cz/online) or [from a command-line](http://pegjs.majda.cz/documentation#generating-a-parser) * Simple and expressive [grammar syntax](http://pegjs.majda.cz/documentation#grammar) * No separate lexical analysis step—both lexical and syntactical analysis are handled by one tool * Handles wide class of grammars (strict superset of LL(k) and LR(k)) * Precise and human-friendly error reporting Usage ----- To use PEG.js, you need to generate a parser from your grammar and then use the generated parser in your project. ### Generating a Parser A parser can be generated either [online](http://pegjs.majda.cz/online) in your browser or using the command line. Let's look at the second option. You need to follow these steps: 1. Install Java. This is necessary to run [Rhino](http://www.mozilla.org/rhino/) (which is bundled with PEG.js). 2. Generate the parser using `bin/pegjs` script on Unix or `bin/pegjs.bat` batch file on Windows. For example, to generate a parser from an example grammar in the `examples/arithmetics.pegjs` file on Unix, run: $ bin/pegjs arithmeticsParser examples/arithmetics.pegjs This command will create the parser in the `examples/arithmetics.js` file and will make it available in the `arithmeticsParser` global variable. The `bin/pegjs` command has several options that influence the generator—to learn more about them, use the `--help` option. **Note:** In the future, I will probably use [Narwhal](http://narwhaljs.org/) for the command-line version. ### Using the Generated Parser Let's assume that you want to use the parser in a web page. To do this, you need to: 1. Include the generated parser into your page: This creates a variable with the parser object in the global scope (you can choose name of the variable when generating the parser). 2. Use the parser, i.e. call the `parse` method on the parser variable: The `parse` method of the generated parser will return either the result of the parsing (dependent on the actions you specified in the grammar) or throw `PEG.Parser.SyntaxError` exception if the input contains a syntax error. The exception has properties `message`, `line` and `column`, which contain details about the error. Grammar ------- For detailed description of the grammar see the [online documentation](http://pegjs.majda.cz/documentation#grammar). Compatibility ------------- Both the parser generator and generated parsers should run well in IE6+ and recent versions of Firefox, Chrome, Safari and Opera, as well as Rhino JavaScript engine.