gistfile1.js

// y-combinator
macro $y {
    rule {( $var )} => {
        function(){
            return function (f){
                return f(f)
            }(function(f){
                return $var(function(x){
                    return f(f)(x);
                })
            });
        }()
    }
    rule {( function $pars $body )} => {
        function(){
            return function(f){
                return f(f)
            }(function(f){
                return function $pars $body(function(x){
                    return f(f)(x);
                })
            });
        }()
    }
}

// factorial
var x = $y(function(fac){ return function(n){ if(n == 1) return 1; return n * fac(n-1); }});
console.log(x(5));

// This should also work
var fac_for_y = function(fac){ return function(n){ if(n == 1) return 1; return n * fac(n-1); }};
var x2 = $y(fac_for_y);
console.log(x2(6));