SICP ex. 1.31

ex131.scm

;helpers
(define (identity x) x)
(define (plus1 x) (+ 1 x))

; recursive
(define (product term a next b)
  (if (> a b) 
      1
      (* (term a)
         (product term (next a) next b))))

(display (product identity 3 plus1 6)) ; 360
(newline)

; iterator
(define (product-i term a next b)

  (define (prod-iter a current_prod) 
    (if (> a b)
        current_prod
        (prod-iter (next a) (* current_prod (term a)))))
  (prod-iter a 1))

(display (product-i identity 3 plus1 6))  ; 360
(newline)