SICP Exercise 1.33
The procedure filtered-accumulator:
(define (filtered-accumulate combiner null-value term a next b filter)
(if (> a b)
null-value
combiner (if (filter a)
(term a)
null-value)
(filtered-accumulate combiner null-value term (next a) next b filter)))
Part A:
Borrowing prime? from earlier:
(define (sum-of-prime-squares a b)
(filtered-accumulate + 0 square a inc b prime?))
Part B:
(define (gcd m n)
(cond ((< m n) (gcd (n m)))
((= n 0) m)
(else (gcd n (remainder m n)))))
(define (relatively-prime? m n)
(= (gcd m n) 1))
(define (product-of-relative-primes n)
(define (filter x)
(relative-prime? x n))
(filtered-accumulate * 1 identity 1 inc n filter))