nitin-motiani

def Y (g): 
    r =  lambda f : lambda n : g(f(f))(n)
    return r(r);

def fact (f) : 
    return lambda n : n if n < 2 else  n * f(n - 1)

factorial = Y(fact)
print(factorial(7))

nitin-motiani

var Y = function(g) {
    var recur = function (f) {
        return function(n) {
            return g(f(f))(n);
        };
    };
    return recur(recur);
};

var fact = function(rec) {

nitin-motiani

(setf Y (lambda (g) 
            (funcall (lambda (f) (lambda (n) (funcall (funcall g (funcall f f)) n)))
                    (lambda (f) (lambda (n) (funcall (funcall g (funcall f f) n)))))))

(setf factorial (funcall Y 
                    (lambda (f) 
                    (lambda (n)
                        (if (< n 2) n
                        (* n (funcall f (- n 1))))))))