TSS rember-beyond-first, rember-up-to-last, let/cc, call/cc

let/cc ・・・、これは便利。

極端に言うとただのジャンプです。でもなんというか goto や break, continue, throw などのジャンプ文を知った時は別段感動などありませんが、let/cc の方は衝撃というか夢がヒロガリングというか・・・・。左手で字を書くような妙な感覚です。

パラダイムがシフトしそうなのかもしれません。

初めてクロージャを実用的な意味で理解した時とか、interface や abstract クラスの存在意義を初めて理解した時とか、そういうのと似た、いわゆる「悟り体験」的な感覚でしょうか。

let/cc は call/cc （call-with-current-continutation）により実現されていますが、The Seasoned Schemer では call/cc はまだほとんど出てきません。
しばらく let/cc が続きそう。

• vallog: TSS let/cc, try
  

少し大げさになった気もしますが、取り合えず以下コード。

	; rember
	(use srfi-1)
	; fold
	(define (multirember a lat)
	(fold (lambda (e acc)
	(if (eq? e a)
	acc
	(cons e acc)))
	'()
	lat))
	(multirember 'a '(a b c a b c))
	; -> (c b c b)
	; The Little Schemer
	(define rember
	(lambda (a lat)
	(cond ((null? lat) '())
	((eq? a (car lat))(cdr lat))
	(else (cons (car lat)
	(rember a (cdr lat)))))))
	(rember 'a '(a b c a b c))
	; -> (b c a b c)
	; The Seasoned Schemer
	(define rember
	(letrec
	((R (lambda (lat)
	(cond ((null? lat) '())
	((eq? a (car lat))(cdr lat))
	(else (cons (car lat)
	(rember (cdr lat))))))))
	(R lat)))
	(rember 'a '(a b c a b c))

view raw 13.Hop,Skip,andJump.scm hosted with ❤ by GitHub

	; rember-beyond-first
	; (rember-beyond-first 'roots '(noodles spaghetti spatzle bean-thread roots potatoes yam others rice))
	; -> (noodles spaghetti spatzle bean-thread)
	; fold
	(define (rember-beyond-first a lat)
	(reverse
	(let/cc hop
	(fold (lambda (e acc)
	(if (eq? e a)
	(hop acc)
	(cons e acc)))
	'()
	lat))))
	(rember-beyond-first 'roots '(noodles
	spaghetti spatzle bean-thread
	roots
	potatoes yam
	others rice))
	; -> (noodles spaghetti spatzle bean-thread)
	(rember-beyond-first 'others '(noodles
	spaghetti spatzle bean-thread
	roots
	potatoes yam
	others
	rice))
	; -> (noodles spaghetti spatzle bean-thread roots potatoes yam)
	(rember-beyond-first 'sweetthing '(noodles
	spaghetti spatzle bean-thread
	roots
	potatoes yam
	others
	rice))
	; -> (noodles spaghetti spatzle bean-thread roots potatoes yam others rice)
	; The Seasoned Schemer
	(define rember-beyond-first
	(lambda (a lat)
	(letrec
	((R (lambda (lat)
	(cond
	((null? lat)(quote ()))
	((eq? (car lat) a)
	(quote ()))
	(else (cons (car lat)
	(R (cdr lat))))))))
	(R lat))))
	(rember-beyond-first 'roots '(noodles
	spaghetti spatzle bean-thread
	roots
	potatoes yam
	others rice))
	; -> (noodles spaghetti spatzle bean-thread)
	(rember-beyond-first 'others '(noodles
	spaghetti spatzle bean-thread
	roots
	potatoes yam
	others
	rice))
	; -> (noodles spaghetti spatzle bean-thread roots potatoes yam)
	(rember-beyond-first 'sweetthing '(noodles
	spaghetti spatzle bean-thread
	roots
	potatoes yam
	others
	rice))
	; -> (noodles spaghetti spatzle bean-thread roots potatoes yam others rice)

view raw 13.Hop,Skip,andJump.scm hosted with ❤ by GitHub

	; rember-up-to-last
	; The Seasoned Schemer
	(define rember-up-to-last
	(lambda (a lat)
	(let/cc skip
	(letrec
	((R (lambda (lat)
	(cond
	((null? lat)(quote ()))
	((eq? (car lat) a)
	(skip (R (cdr lat))))
	(else (cons (car lat)
	(R (cdr lat))))))))
	(R lat)))))
	(rember-up-to-last 'cookies '(cookies
	chocolate mins
	caramel delight ginger snaps
	desserts
	chocolate mousse
	vannilla ice cream
	German chocolate cake
	more cookies
	gingerbreaddman chocolate
	chips brownies))
	; -> (gingerbreaddman chocolate chips brownies)

view raw 13.Hop,Skip,andJump.scm hosted with ❤ by GitHub