Charpter12.bak

#|【Scheme Basic Functions by Kevin&poi~】|#



;function: ture if input is a vowel, false if not.

;argument: 1 character

(define (vowel? char)

  (member? char '(a e i o u)))

;square the number

;argument: 1 number

(define (square num)

  (* num num))

;cube the number

;argument: 1 number

(define (cube num)

  (* num num num))

;find the second word/character in a string/word

;argument: word/string

(define (second x)

  (first (bf x)))

;reverse the order of the word

;argument:word
;——————————————————————————————————————————practice problems————————————————————————————————————————————————————————————————
(define (factorial x)
   (if (<= x 1)
       1
       (* x(factorial (- x 1)))))
(define (fib x)
  (if (or (= x 1)(= x 2))
      1
      (+ (fib(- x 1)) (fib(- x 2)))))
;———————————————————————————————————————————exercise problems———————————————————————————————————————————————————————————————
#|12.1  Here is a definition of a procedure that returns the sum of the numbers in its argument sentence: 

(define (addup nums)
  (if (empty? (bf nums))
      (first nums)
      (+ (first nums) (addup (bf nums)))))
Although this works, it could be simplified by changing the base case. Do that.|#
  (define (addup nums)
    (if (empty? nums)
      0
      (+ (first nums) (addup (bf nums)))))
#|12.2  Fix the bug in the following definition: 

(define (acronym sent)                       ;; wrong
  (if (= (count sent) 1)
      (first sent)
      (word (first (first sent))
	    (acronym (bf sent)))))|#
(define (acronym sent)                       ;; wrong
  (if (= (count sent) 1)
      (first (first (sent)))
      (word (first (first sent))
	    (acronym (bf sent)))))