ex_1_032.scm

(define (accumulate combiner null-value term a next b)
  (define (recursive a)
    (if (> a b) null-value
        (combiner a
                  (recursive (next a)))))
  (recursive a))

(define (increment a)
  (+ a 1))

(define (comb_prod a b)
  (* a b))

(define (comb_sum a b)
  (+ a b))

(define (factorial n)
  (accumulate comb_prod 1 comb_prod 1 increment n))

(factorial 5);120

(define (sum n)
  (accumulate comb_sum 0 comb_sum 1 increment n))

(sum 5);15