(define newlines 0) ; Should be encapsulated somehow.

(define (make-newline-counting-input-port port)
  (make-input-port
   (lambda ()                                   ; read-char
     (let ((c (read-char port)))
       (if (not (eq? c #\newline))
           c
           (begin
             (set! newlines (add1 newlines))
             c))))
   char-ready?                                  ; char-ready?
   (lambda ()                                   ; close
     (close-input-port port))))