SICP Exercise 1.30
The sum procedure is given as:
(define (sum term a next b)
(if (> ab)
0
(+ (term a)
(sum term (next a) next b))))
It can be changed to act iteratively as:
(define (sum term a next b)
(define (iter a result)
(if (> a b)
result
(iter (next a) (+ result (term a)))))
(iter a 0))