contracts.coffee is a dialect of CoffeeScript with contract support.
Contracts allow you to write powerful runtime assertions about your code. Like types but less painful, like assert but more useful.
square :: (Num) -> Num
square = (x) -> x * x
# throws a run-time error
square "a string"
Documentation, usage, and more examples: http://disnetdev.com/contracts.coffee/
Install via npm:
npm install -g contracts.coffee
Use the compiler:
coffee -c --contracts /path/to/script.coffee
If you are running in the browser then you'll need to load the contracts library (found in lib/contracts/contracts.js)
<script type="text/javascript" src="contracts.js"></script>
If you are running in node.js then you'll need to install the contracts.js package
npm install contracts.js
Note that contracts.coffee requires some pretty new features of JavaScript (Proxies in particular) so it currently only works on Firefox 4+ and node 0.5.10 (but not 0.6 yet) but other JavaScript engines should be adding support soon.