First common lisp function

gistfile1.lisp

;Add all the natural numbers below one thousand that are multiples of 3 or 5.
(defun sum-to-last (x)
  (cond ((eql x 0)
         0)
        (t
          (let ((mod3 (eql (mod x 3) 0))
                (mod5 (eql (mod x 5) 0))
                )
          (cond ((or mod3 mod5) 
                 (+ x (sum-to-last (1- x)))
                 )    
               (t (sum-to-last (1- x))) 
                
          )))))