(define (mode entry)
  (let ((inc 0))
    (define k #f)
    (set! entry (call/cc (lambda (n)
                           (set! k n)
                           entry)))
    (set! inc (+ inc entry))
    (write inc)
    (newline)
    k))

(define a (mode 1))
(a 2)
;((mode 1) 2)