euler-1

(defun multiple-of (x y)
  (if (= 0 (rem x y)) t))

(defun check-number (x) 
  (if (multiple-of x 3) (setf answer (+ answer x))
  (if (multiple-of x 5) (setf answer (+ answer x)))))

(setf answer 0)

(loop for i from 1 to 999 do 
     (check-number i))

(print answer)