The lisp-way to solve Fibonnaci

Question

I wanted to try and learn Lisp, but I very quickly gave up. I figured I\'d try again. I\'m looking at Problem 2 on Project Euler - finding the sum of all even Fibonacci numbers

Answer 1

(defun fib (x &optional (y 0) (z 1))
           (if (< x z)
               nil
               (append (list z) (fib x z (+ y z)))))

CL-USER> (reduce #'+ (remove-if-not #'evenp (fib 1000000)))