I think you probably could make a contract that did what you were talking about in the first message in this thread, but you cannot do it with any of the existing contract combinators (->, ->*, case->, ->i, etc). You would have to use the lower-level, projection-based api to make a new combinator.
But Matthias's advice is probably a better route. Robby On Sat, Dec 28, 2013 at 1:43 AM, Alexander D. Knauth <alexan...@knauth.org>wrote: > 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" <alexan...@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 > > > > > ____________________ > Racket Users list: > http://lists.racket-lang.org/users > >
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