SICP学习笔记 2.1.1 实例: 有理数的算术运算

    练习 2.1

(define (make-rat n d)
  (let ((g (gcd n d)))
    (if (and (< d 0) (> g 0))
	(cons (/ (- n) g) (/ (- d) g))
	(cons (/ n g) (/ d g)))))
	
1 ]=> (print-rat (make-rat 6 -7))
-6/7

1 ]=> (print-rat (make-rat -6 -7))
6/7