sicp习题2.1

(define (gcd x y)
  (if (= y 0)
     x
     (gcd y (remainder x y))))
(define (make-rat n d)
  (let ((g (gcd (abs n) (abs d)))
        (s (signum d)))
    (cons (/ n (* g s)) (/ d (* g s)))))

(define (signum x)
  (if (= x 0 )
     0
     (/ x (abs x))))

(define (numer x) (car x))
(define (denom x) (cdr x))

(define (print-rat x)
  (newline)
  (display (numer x))
  (display "/")
  (display (denom x)))

(define hehe (make-rat -1 2))