SICP - Solution: Exercise 1.30

October 23, 2018

Exercise 1.30 #

The sum procedure above generates a linear recursion. The procedure can be rewritten so that the sum is performed iteratively. Show how to do this by filling in the missing expressions in the following definition:

(define (sum term a next b)
  (define (iter a result)
    (if ⟨??⟩
        ⟨??⟩
        (iter ⟨??⟩ ⟨??⟩)))
  (iter ⟨??⟩ ⟨??⟩))

Solution #

The solution is:

(define (sum-iter term a next b)
  (define (iter a result)
    (if (> a b)
        result
        (iter (next a) (+ result (term a)))))
  (iter a 0))