2.1.2-abstract-bar.rkt

#lang sicp
(define (make-rat n d)
  (cons n d))

(define (numer x)
  (let ((g (gcd (car x) (cdr x))))
    (/ (car x) g)))

(define (denom x)
  (let ((g (gcd (car x) (cdr x))))
    (/ (cdr x) g)))