[plt-scheme] field contracts?

This is nice.  I'm having trouble using provide/contract with classes:

  (module m mzscheme
    (require (lib "contract.ss") (lib "class.ss"))
    (provide/contract
     (point% (object-contract (field x number?) (field y number?))))
  
    (define point%
      (class* object% ()
        (public set-x! set-y!)
        (field (x 0)) 
        (field (y 0))
        (define (set-x! new-x) (set! x new-x))
        (define (set-y! new-y) (set! y new-y))
        (super-new))))

  (require m)
  (define p1 (make-object point%))

gives:

  top-level: m broke point%'s contract: 
  (object-contract (field x number?) (field y number?)): 
  expected an object, got #<struct:class:point%>

This makes sense, but how do I tell provide/contract that point% is a
class, not an object?

Mike


> From: Robby Findler <robby at cs.uchicago.edu>
> Cc: plt-scheme at list.cs.brown.edu
> Date: Sat, 9 Oct 2004 09:54:06 -0500
> 
> Here's one way to do that:
> 
> (module m mzscheme
>   (provide/contract
>     (struct posn ((x number?) (y number?))))
> 
>   (define-struct posn (x y)))
> 
> Robby
> 
> At Sat,  9 Oct 2004 01:06:14 -0700 (PDT), Michael Vanier wrote:
> >   For list-related administrative tasks:
> >   http://list.cs.brown.edu/mailman/listinfo/plt-scheme
> > 
> > 
> > Quick question:
> > 
> > Is there a reasonably straightforward way to define a struct or object type
> > whose fields are required to be of specific types?  It seems like the
> > contract system should be usable for this, but I don't see any examples in
> > the PLT scheme documentation.
> > 
> > Mike
>