1.33 (累积互素数)

(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 (coprime? i n)
  (and (< i n)
       (= 1 (gcd i n))))

(define (product-of-coprimes n)
  (filtered-accumulate (lambda (x) (coprime? x n))
                       *
                       1
                       (lambda (x) x)
                       1
                       (lambda (x) (+ x 1))
                       n))

(product-of-coprimes 10)