プログラミングGauche

p.56 listの長さを計算する

#!/usr/bin/env gosh

(define (length lis)
  (define (length-walk lis n)
    (if (null? lis)
	n
	(length-walk (cdr lis) (+ n 1))
    )
  )
  (length-walk lis 0))


(print (length '(1 2 3)))

p.56 リスト内から条件を満たす要素を抜き出したリストを返す

#!/usr/bin/env gosh

(define (find pred lis)
  (if (null? lis)
      #f
      (if (pred (car lis))
	  (car lis)
	  (find pred (cdr lis))
	  )
      ))

(print (find odd? '(2 3 4 5)))

(print (find (lambda (i) (if (and (> i 2) (odd? i))
			     #t 
			     #f))
	     '(1 2 3 4)))

3
3

(define (filter pred lis)
  (define (filter-each pred lis res)
    (if (null? lis)
	res
	(if (pred (car lis))
	    (filter-each pred (cdr lis) (append res (list(car lis))))
	    (filter-each pred (cdr lis) res)
	    )
	)
    )
  (filter-each pred lis '()))

(define data '(2 3 4 5 10 11 34 35 1 2 3))
(print data)
(print (filter odd? data))

(2 3 4 5 10 11 34 35 1 2 3)
(3 5 11 35 1 3)

(define data '(4 10 11 50 "hello work" 5 8))
(print data)
(print (filter 
	(lambda (x) (if (and (number? x) (odd? x)) 
			#t
			#f))
	data))

(4 10 11 50 hello work 5 8)
(11 5)