; Performs the sieve of Eratosthenes over a list of numbers.
; Further explanation is contained on the zlisp documentation page zlispdoc.html
; Alejandro Luque Estepa, 1999

(defun divisible  (n m) (zerop (mod n m)))
(defun cribe (list) (subset '(lambda (x) (not (divisible x (car list)))) (cdr list)))
(defun sieve (list) 
     (cond 
      ((null list) nil) 
      (t (cons (car list) (sieve (cribe list)))) 
     ) 
)
(defun numbers (n m)
 (do ((i m (sub1 i)) (l nil (cons i l))) ((! (> i n)) l))
)
(msg "Usage: (sieve list), where list is a set of numers over wich" t 
     "you want to perform the sieve of Erathostenes." t 
     "(numbers n m) returns a list of all integer numbers between n and m," t
     " so (sieve (numbers 2 100)) will return a list of all prime numbers below 100")