[racket] contracts on functions that take arbitrary keyword arguments

The problem isn't with defining the function, the problem is with  
making a contract for it.

I can define the function fine, I just don't know how to write a  
contract for it.  I used make-keyword-procedure to define the  
function, but is there something like make-keyword-procedure- 
contract?  I could write my own error code, but it would be better if  
I could express it as a contract.

The actual concrete example is that I'm making my own version of send  
that works with method-like procedures.

#lang racket

(define/contract current-send-object (parameter/c (or/c object? #f))
   (make-parameter #f))

(define my-send
   (make-keyword-procedure
    (lambda (kws kw-args object proc . rest-args)
      (parameterize ([current-send-object object])
        (keyword-apply proc kws kw-args rest-args)))))

(define point%
   (class object%
     (super-new)
     (init-field [x 0] [y 0])
     (define/public (get-x) x)
     (define/public (get-y) y)))

(define (get-vector)
   (let* ([object (current-send-object)]
          [x (send object get-x)]
          [y (send object get-y)])
     (vector x y)))

(define p (new point% [x 3] [y 5]))

(require rackunit)

(check-equal? (my-send p get-vector)
               (vector 3 5))

(check-equal? (my-send p (compose vector->list get-vector))
               (list 3 5))

that way you can define new "methods" without them being specified by  
the class, and they're first class functions.  I wanted to be able to  
make a contract for my-send (and my-send/apply etc.) that would check  
that object is an object and that proc is a procedure, but still take  
arbitrary keyword arguments and just pass them on to proc.

On Dec 27, 2013, at 1:03 PM, Matthias Felleisen wrote:

>
> This is a bit vague. Can you clarify the question with a concrete  
> example?
>
>
> On Dec 26, 2013, at 7:45 PM, "Alexander D. Knauth" <alexander at knauth.org 
> > wrote:
>
>> I want to make contracts on some apply-like functions that check  
>> some arguments but just passes all the others (including keyword  
>> arguments) on to a function (provided as an argument).  If there  
>> weren't any keyword arguments, I could use a rest argument to do  
>> this, but that wouldn't work with keyword arguments.  Is there a  
>> way to do something like a rest argument for keyword-arguments in a  
>> contract?____________________
>> Racket Users list:
>> http://lists.racket-lang.org/users
>

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