TSS member?

listの中に指定した要素が入ってるかどうかっていうあれです。
letrec の使われ方が微妙に新鮮だったりする。
使われ方というか位置というか。

• vallog: TSS multirember-f letrec, fold
  

	; member?
	; The Little Schemer
	(define member?
	(lambda (a lat)
	(cond ((null? lat) #f)
	((eq? a (car lat)) #t)
	(else (member? a (cdr lat))))))
	(member? 'b '(a b c))
	(member? 'd '(a b c))
	(define member?
	(lambda (a lat)
	(cond ((or (null? lat)
	(not (eq? a (car lat)))) #f)
	(else (member? a (cdr lat))))))
	(member? 3 '(1 2 3 4 5))
	(member? 6 '(1 2 3 4 5))
	; and or
	(define (member? a lat)
	(and (not (null? lat))
	(or (eq? a (car lat))
	(member? a (cdr lat)))))
	(member? 'c '(a b c d e f))
	(member? 1 '(a b c d e f))
	; any
	(use srfi-1)
	(define (member? a lat)
	(any (lambda (e)
	(eq? e a))
	lat))
	(member? 'a '(a b c))
	(member? 'd '(a b c))
	; The Seasoned Schemer
	(define member?
	(lambda (a lat)
	((letrec ((yes? (lambda (l)
	(cond ((null? l) #f)
	((eq? a (car l)) #t)
	(else (yes? (cdr l)))))))
	yes?)
	lat)))
	(member? 'a '(a b c))
	(member? 'd '(a b c))
	(define member?
	(lambda (a lat)
	(letrec ((yes? (lambda (l)
	(cond ((null? l) #f)
	((eq? a (car l)) #t)
	(else (member? a (cdr l)))))))
	(yes? lat))))
	(member? 'a '(a b c))
	(member? 'd '(a b c))

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