A plugin for PEG.js to use CoffeeScript in your actions.

PEGjs Coffee Plugin

Plugin for PEG.js to use CoffeeScript in actions. Because all I want for christmas is CoffeeScript.

The basic functionality is finished. Please test it and add feature requests and issues here.

$ npm install pegjs-coffee-plugin

Then in your code call

PEG = require 'pegjs'
coffee = require 'pegjs-coffee-plugin'

Download the development or the minified version. Now include all needed scripts in your html file like this.

<script src="peg.js"></script>
<script src="pegjs-coffee-plugin.js"></script>

After you have loaded all scripts you can do

grammar = '' # Define your grammar
parser = PEG.buildParser grammar, plugins: [coffee]

Just pass the pegjs commandline like this

$ pegjs --plugin pegjs-coffee-plugin myGrammar.pegcoffee myCompiledGrammar.js

You now have a save scope shared between all actions and predicates. To begin it is empty, then all declarations from the initializer are added. Afterwards you can add and remove stuff as much as you like. This scope is there even if you don't use the initializer. So you can do something like the following.

start = a { @result }
a = "a" { @result = "awesome" }

And this will correctly return "awesome" if you call parse("a").

Also all variable assignments in an action are safely scoped to the action. { result = "awesome" } becomes { var result; result = "awesome" }. This gives you the ability to explicitly share variables with other actions via this and the security to just assign variables for local use like you are used to when writing CoffeeScript.

There is no need to call return anymore. You can just do

start = a:"a" { "Great Stuff" }

which is the equivalent of

start = a:"a" { return "Great Stuff"; }

If you declare variables in your initializer you set them on this.

  @result = ""
  = awesome / rule { @result }
  = "awesome" { @result = "awesome" }
  = "rule" { @result = "rule }

Clone the repo and run the install

$ git clone
$ cd pegjs-cofee-plugin
$ npm install && npm install pegjs
$ make build

Running the tests

For the Node.js tests run

$ make test

and for the browser tests

$ make test-browser

and open your browser on localhost:3000.


  • more tests
  • make bower package