call-cc.scm

;;; call/cc を理解しよう！

;; 一見すると普通にかけぬけている
(call/cc (lambda (c) "Just invoke")) ; "Just invoke"

(define boundval (call/cc (lambda (c) "Just invoke")))
boundval ; "Just invoke

;; だが…

(define frozenval ())
(begin
  (print "before call/cc...")
  (call/cc (lambda (c) (set! frozenval c)))
  (print "after call/cc..."))

;; としてから…

(frozenval) ; "after call/cc"
(frozenval) ; "after call/cc"

(begin
  (frozenval)
  (print "after frozenval")) ; 何も表示しない

;; 他の例

(define pokemonGetDaze ())

(string-append
 (call/cc
  (lambda (c)
	(set! pokemonGetDaze c) ; とりあえず現在位置を保存しとく
	"Pikachu"))
 " Get daze!") ; Pikachu Get daze!

;; 上のコードの部分のcall/ccにあたる部分の結果を"Hitokage"に置き換える感じ
(pokemonGetDaze "Hitokage") ; Hitokage Get daze!

(string-append (pokemonGetDaze "Fushigidane")
			   "!????") ; もちろんstring-appendは実行されない


;; レキシカルかな？
(define accumlator ())

(let ((cnt 0))
  (call/cc (lambda (c) (set! accumlator c)))
  (set! cnt (+ cnt 1))) ; 1
(accumlator) ; 2
(accumlator) ; 3 レキシカルですね。


;; 繰り返し
;; GOTO みたいなもんですわ
(let ((i 10)
	  (frozen ()))
  (call/cc (cut set! frozen <>))
  (cond ((= i 0)
		 (print "Done!"))
		(else
		 (print i)
		 (set! i (- i 1))
		 (frozen)))) ; 10 9 ... 1 Done!


;; call/ccだけど呼び戻してもらう

(define reflector ())

(let ((startFromHere
	   (call/cc (lambda (c)
				  (set! reflector c)
				  (lambda ())))))
  (print "Reflect!")
  (startFromHere)
  (print "After reflection"))

(let ((called #f)
	  (frozen (call/cc (lambda (c) c))))
  (cond
   ((not called)
	(set! called #t)
	(print "Call reflect")
	(reflector frozen))
   (else
	(print "Reversed!")
	"Yeah")))
;; Call reflect -> Reflect! -> Reversed! -> "Yeah"