Higher Order Procedures

higher_order_procedures.scm

  
(define (sum term a next b)
  (accumulate + 0 term a next b))

(define (product term a next b)
  (accumulate * 1 term a next b))

(define (factorial n)
  (product identity 1 inc n))

(define (accumulate combiner base-case term a next b)
  (define (iter a result)
    (if (> a b)
        result
        (iter (next a) (combiner (term a) result))))
  (iter a base-case))

(define (identity x) x)
(define (inc x) (+ 1 x))

(accumulate * 1 identity 1 inc 5)  ; 120
(factorial 5)                      ; 120