(define (odd)
  (let ((c (read-char)))
    (if (char-alphabetic? c)
      (let ((r (odd)))
	(write-char c)
	r)
      (lambda () (write-char c) (char=? c #\.)))))

(define (even)
  (let ((c (read-char)))
    (write-char c)
    (if (char-alphabetic? c)
      (even)
      (char=? c #\.))))

(let loop ((i #f))
  (if (if i ((odd)) (even))
    (exit)
    (loop (not i))))