Lol, Scheme

(define i (open-input-file "in.txt"))
(define o (open-output-file "out.txt"))
(define (bbc)
  (if (eof-object? (peek-char i))
      (begin (newline o) (close-output-port o))
      (case (peek-char i)
        ((#\<) (display #\[ o) (bbc))
        ((#\>) (display #\] o) (bbc))
        (else (display (read-char i) o)))))

This is supposed to be an EXPERT BBCODE UTILITY to convert HTML tags to BBCode, but when I run it, it never stops. I am only a beginner, but I've analysed it and noticed no errors. A little help here?

$ php -r "file_put_contents("out.txt",str_replace(array("<",">"),array("[","]"),file_get_contents("in.txt")));"