(define (filtered-accumulate filter? combiner null-value term a next b)
(define (iter a result)
(cond ((> a b) result)
((filter? a) (iter (next a)
(combiner (term a) result)))
(else (iter (next a)
result))))
(iter a null-value))
(define (smallest-divisor n)
(find-divisor n 2))
(define (find-divisor n test-divisor)
(cond ((> (square test-divisor) n) n)
((divides? n test-divisor) test-divisor)
(else (find-divisor n (+ test-divisor 1)))))
(define (divides? a b)
(= (remainder a b) 0))
(define (prime? n)
(if (< n 2)
#f
(= n (smallest-divisor n))))
(define (square x)
(* x x))
(define (primes-sum a b)
(filtered-accumulate prime?
+
0
(lambda (x) x)
a
(lambda (x) (+ x 1))
b))
(primes-sum 1 10)
转载于:https://www.cnblogs.com/R4mble/p/7893713.html
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