vallog: TSS multirember-f letrec, fold

2010/02/24

(define hoge (letrec ・・・ってのは見慣れなくて驚いた。

も参考に。

	; multirember -> multirember-f

	; The Seasoned Schemer
	(define multirember-f
	(lambda (test?)
	(lambda (a lat)
	(cond ((null? lat) '())
	((test? a (car lat))((multirember-f test?) a (cdr lat)))
	(else (cons (car lat)
	((multirember-f test?) a (cdr lat))))))))

	((multirember-f eq?) 'a '(a b c a b c))

	; fold
	(define (multirember-f test?)
	(lambda (a lat)
	(fold (lambda (e l)
	(if (test? a e)
	l
	(cons e l)))
	'()
	lat)))

	((multirember-f eq?) 'a '(a b c a b c))

	; 再帰結果は束縛可能 http://beta-reduction.blogspot.com/2010/02/define-multirember-lat-cond-null-lat-eq.html
	(define (multirember-f test?)
	(lambda (a lat)
	(if (null? lat)
	'()
	(let ((b (car lat))
	(mr ((multirember-f test?) a (cdr lat))))
	(if (test? a b)
	mr
	(cons b mr))))))

	((multirember-f eq?) 'a '(a b c d a b c d))


	; letrec multirember-f - The Seasoned Schemer
	(define multirember-f
	(lambda (test?)
	(letrec ((m-f (lambda (a lat)
	(cond ((null? lat) '())
	((test? a (car lat))(m-f a (cdr lat)))
	(else (cons (car lat)
	(m-f a (cdr lat))))))))
	m-f)))

	((multirember-f eq?) 1 '(1 2 3 4 5 1 2 3 1 2 3 1 2))


	; letrec multirember - The Seasoned Schemer
	(define multirember
	(letrec ((multirember
	(lambda (a lat)
	(cond ((null? lat) '())
	((eq? a (car lat))(multirember a (cdr lat)))
	(else (cons (car lat)
	(multirember a (cdr lat))))))))
	multirember))

	(multirember 'a '(a b a b a b c a))

vallog