[racket] Com Service with ffi

Ok,

I make this:

(define _ULONG _ulong)
(define _CATID _GUID)
(define _REFCATID _GUID-pointer)
(define-cstruct _CATEGORYINFO ( [catid _CATID]
                                [lcid _LCID]
                                [szDescription (_array _short 128)]))        
(define IID_ICustomList
            (string->iid "{3039E12D-6CEF-4F91-AE9B-E609481C8824}"))
(define-com-interface (_ICustomList _IUnknown)
    ([Next/ci (_mfun (_ULONG = 1)
                 (catinfo : (_ptr o _CATEGORYINFO))
                (got : (_ptr o _ULONG))
                -> (r : _HRESULT)
                -> (cond
                [(zero? r) catinfo]
                [(= r 1) #f]
                [else (windows-error "Next/ci
    failed" r)]))]
        [Skip _fpointer]
        [Reset _fpointer]
        [Clone _fpointer]))


But I dont know how to use it, especially in invoking the desired function??

Yours,