1 665c255d 2023-08-04 jrmu (defun product (term a next b)
 2 665c255d 2023-08-04 jrmu   (if (> a b)
 3 665c255d 2023-08-04 jrmu       1
 4 665c255d 2023-08-04 jrmu     (* (funcall term a)
 5 665c255d 2023-08-04 jrmu        (product term (funcall next a) next b))))
 6 665c255d 2023-08-04 jrmu (defun factorial (n)
 7 665c255d 2023-08-04 jrmu   (product #'identity 1 #'1+ n))
 8 665c255d 2023-08-04 jrmu (defun wallis-pi (n)
 9 665c255d 2023-08-04 jrmu   (defun wallis-term (k)
10 665c255d 2023-08-04 jrmu     (let ((nom
11 665c255d 2023-08-04 jrmu 	   (if (evenp k)
12 665c255d 2023-08-04 jrmu 	       (+ k 2)
13 665c255d 2023-08-04 jrmu 	     (+ k 1)))
14 665c255d 2023-08-04 jrmu 	  (denom
15 665c255d 2023-08-04 jrmu 	   (if (evenp k)
16 665c255d 2023-08-04 jrmu 	       (+ k 1)
17 665c255d 2023-08-04 jrmu 	     (+ k 2))))
18 665c255d 2023-08-04 jrmu       (float (/ nom denom))))
19 665c255d 2023-08-04 jrmu   (* (product #'wallis-term 1 #'1+ n)))
20 665c255d 2023-08-04 jrmu 
21 665c255d 2023-08-04 jrmu (defun product-iter (term a next b)
22 665c255d 2023-08-04 jrmu   (defun iter (a result)
23 665c255d 2023-08-04 jrmu     (if (> a b)
24 665c255d 2023-08-04 jrmu 	result
25 665c255d 2023-08-04 jrmu       (iter (funcall next a)
26 665c255d 2023-08-04 jrmu 	    (* (funcall term a) result))))
27 665c255d 2023-08-04 jrmu   (iter a 1))
28 665c255d 2023-08-04 jrmu