Type annotations and checking with Sweet.js

annotations.sjs

macroclass typedef {
	pattern { $x:ident : $type:ident }
	pattern { $x:ident : $type:lit }
}

let function = macro {
	rule { $name ($params:typedef ...) { $body ... } } => {
		function $name ($params$x ...) {
			$(if (typeof $params$x !== typeof $params$type) {
				throw new Error('Found type ' + (typeof $params$x) + ' but expected ' + typeof $params$type);
	  		}) ...
			$body ...
		}
	}
}

function foo (a : 0) {
	console.log(a);
}

foo(1);

foo('a');