SICP 1.33 答案

我的代码有点丑陋。。。不过算了，练习而已

(define (filtered-accumulate combiner null-value filter term a next b)
  (define (filter-work x)
    (if (filter x) (term x)
        null-value))
  (if (> a b)
      null-value
      (combiner (filter-work a) (filtered-accumulate combiner null-value filter term (next a) next b))))

a的答案

(define (sum-range-of-prime a b)
  (define (sum-filter? x)
    (if (or (< x a) (> x b)) false
        true))
  (define (term x)
    (if (prime? x) x
        0))
  (define (adding x)
    (+ x 1))
  (filtered-accumulate + 0 sum-filter? term a adding b))

(sum-range-of-prime 1 10)

b的答案

(define (sum-range-of-gcd n)
  (define (sum-filter? x)
    (if (> x n) false
        true))
  (define (term x)
    (if (= 1 (gcd x n)) x
        0))
  (define (adding x)
    (+ x 1))
  (filtered-accumulate + 0 sum-filter? term 0 adding n))

(sum-range-of-gcd 10)