;;;case-B
(define continuation #f)

(let loop ((counter 1))
(if (< counter 2)
(begin
(if (= counter 1)
(call-with-current-continuation
(lambda (k) (set! continuation k))))
(write counter) (newline)　
(set! counter (+ counter 1))
(loop counter))
'finished))　;==> 1finished

(continuation #t)　;==> 2finished
(continuation #t)　;==> 3finished
(continuation #t)　;==> 4finished