;;;; Under Creative Commons Attribution-ShareAlike 4.0
;;;; International. See
;;;; <https://creativecommons.org/licenses/by-sa/4.0/>.

(define-module (net ricketyspace sicp one twentythree)
  #:use-module (net ricketyspace sicp utils)
  #:export (smallest-divisor))

(define (square x)
  (expt x 2))

(define (divides? a b)
  (= (remainder b a) 0))

(define (next n)
  (cond ((= n 2) 3)
        (else (+ n 2))))

(define (find-divisor n test-divisor)
  (cond ((> (square test-divisor) n) n)
        ((divides? test-divisor n) test-divisor)
        (else (find-divisor n (next test-divisor)))))

(define (smallest-divisor n)
  (find-divisor n 2))