LISP Programming 1062_ex6

http://erdos.csie.ncnu.edu.tw/~klim/scheme/lisp-1062.html

exercise 6: representing a pair with a number
•Refer to exercise 2.5.
•Note the requirement of nonnegative is removed. Your method 
should accept two integers.

解答:

(define (num-cons a b)
    (* (expt 2 a) (expt 3 b)))

(define (num-car n)
  (if (= 0 (modulo n 2))
      (+ 1 (num-car (/ n 2)))
      0))

(define (num-cdr n)
  (if (= 0 (modulo n 3))
      (+ 1 (num-cdr (/ n 3)))
      0))

執行結果：