exericse 1.31

gistfile1.lisp

(defun product (term a next b)
  (if (> a b)
      1
    (* (funcall term a)
       (product term (funcall next a) next b))))

(defun product-iter (term a next b)
  (defun iter (a result)
    (if (> a b)
        result
      (iter (funcall next a ) (* result (funcall term a)))))
  (iter a 1))
(product-iter #'(lambda (x) x) 1 #'(lambda (x) (+ x 1)) 3)