help with a mouse events in scheme

[Claudio Gamberini <cgamberini@inwind.it>]

hello, my porblem is to intercept the mouse click into a canvas
i do :

 > >(define clickable-canvas%
 > > (class canvas% args
 > > (override
 > > [on-event
 > > (lambda (evt)
 > > (when (send evt button-up?)
 > > (printf "click at (~a,~a)~n" (send evt get-x) (send evt
 > > get-y))))])
 > > (sequence
 > > (apply super-init args))))
 > >
 > >(define f (make-object frame% "frame" #f 100 100))
 > >(make-object clickable-canvas% f)
 > >(send f show #t)
 >

the algorithm intercept the mouse click into a frame but i have to 
intercept the mouse Click into a canvas.
What i have to change ? Can write me the solution ?
Thanks !