[racket] [realm of racket] contract error with 'smaller' function

I am not sure whether this is a the right list to post this question. Else
please let me know.

I run this in Dr. racket.

#lang racket
(define lower 1)
(define upper 100)

(define (guess)
  (quotient (+ lower upper) 2))

(define (smaller)
  (set! upper (max lower (guess (sub1 guess))))
  (guess))

When i invoke the smaller function in the repl i get:

Welcome to DrRacket, version 5.3.5--2013-06-18(-/f) [3m].
Language: racket; memory limit: 128 MB.
> (smaller)
. . sub1: contract violation
  expected: number?
  given: #<procedure:guess>
>

What am i doing wrong?

- Jo
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.racket-lang.org/users/archive/attachments/20131020/75974655/attachment.html>