SICP exercise 1.22

sicp_exercice_1_22.scm

(define (expect actual expectation expected)
  (display "• ")
  (display actual)
  (display " should equal ")
  (display expected)
  (display ": ")
  (expectation actual expected)
  (display "pass\n")
  )
  
(define (to-equal actual expected)
  (assert (= actual expected)))

(define (to-be actual expected)
  (if expected
    (assert actual)
    (assert (not actual))))
  
(define (prime? n)
  (= n (smallest-divisor n)))

(define (smallest-divisor n)
  (find-divisor n 2))
  
(define (find-divisor n test-divisor)
  (cond ((> (square test-divisor) n) n)
        ((divides? test-divisor n) test-divisor)
        (else (find-divisor n (+ test-divisor 1)))))
        
(define (divides? a b)
  (= (remainder b a) 0))
  
(define (square n)
  (* n n))

(expect (prime? 2) to-be #t)
(expect (prime? 3) to-be #t)
(expect (prime? 4) to-be #f)
(expect (prime? 5) to-be #t)
(expect (prime? 6) to-be #f)
(expect (prime? 7) to-be #t)
(expect (prime? 8) to-be #f)
(expect (prime? 9) to-be #f)