1.33 SICP (iterative solution)

filtered-acc.scm

(define (filtered-acc filter combiner null-value term a next b)
  (define (iter a result)
    (if (> a b)
	result
	(if (filter a)
	    (iter (next a) (combiner (term a) result))
	    (iter (next a) result))))
  (iter a null-value))

(define (prime? n)
  (define (iter i) 
    (if (= i 1)
	true
	(if (= (remainder n i) 0)
	    false
	    (iter (- i 1)))))
  (iter (floor (sqrt n))))

(define (square x) (* x x))
(define (inc x) (+ x 1))

(define (sum-squares-of-primes a b)
  (filtered-acc prime? + 0 square a inc b)) 

(define (gcd a b)
  (if (= b 0)
      a
      (gcd b (remainder a b))))

(define (relative-prime-gen? n)
  (lambda (x) (= (gcd n x) 1)))

(define (identity x) x)

(define (product-relative-primes n)
  (filtered-acc (relative-prime-gen? n) * 1 identity 1 inc (- n 1)))