[plt-scheme] What is wrong with this program ?

#lang scheme
(define cont (call/cc (lambda (k) 
                        (display 'bonjour)
                        (newline)
                        k))) 

(cont
 (lambda (var) 
   (display 'bonsoir)
   (newline)
   var))

==RESULT==
Bienvenue dans DrScheme, version 4.1.1 [3m].
Langage: Module personnalisé; memory limit: 256 megabytes.
bonjour
define-values: cannot re-define a constant: cont
>