eratosthenes.lisp

(defun eratosthenes (n)
  (loop
     :for lst = (loop :for i from 2 to n :collect i) then lst
     :for x = (car lst)
     :while lst
     :collect x
     :do
     (setf lst
	   (delete-if
	    #'(lambda (n) (zerop (mod n x)))
	    lst))))