numerify.js

function numerify(churchNumeral) {
	return churchNumeral(function (x) {
		return x + 1;
	})(0); // f is a function that increments the value by 1; z=0
}

// example
numerify(ZERO) // returns 0
var ONE = SUCC(ZERO)
numerify(ONE) // returns 1
var FOUR = SUCC(SUCC(SUCC(SUCC(ZERO))))
numerify(FOUR) // returns 4