<div dir="ltr">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.<div>
<br></div><div>But Matthias's advice is probably a better route.<br><div><br>Robby</div></div></div><div class="gmail_extra"><br><br><div class="gmail_quote">On Sat, Dec 28, 2013 at 1:43 AM, Alexander D. Knauth <span dir="ltr"><<a href="mailto:alexander@knauth.org" target="_blank">alexander@knauth.org</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word"><div>The problem isn't with defining the function, the problem is with making a contract for it. </div>
<div><br></div><div>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. </div>
<div><br></div><div>The actual concrete example is that I'm making my own version of send that works with method-like procedures. </div><div><br></div><div><span style="font-family:'Courier New'">#lang racket</span></div>
<div><span style="font-family:'Courier New'"><br></span></div><div><span style="font-family:'Courier New'">(define/contract current-send-object (parameter/c (or/c object? #f))</span></div><div><font face="'Courier New'"> (make-parameter #f))</font></div>
<div><font face="'Courier New'"><br></font></div><div><font face="'Courier New'"><div style="font-family:Helvetica"><font face="'Courier New'">(define my-send</font></div><div style="font-family:Helvetica">
<font face="'Courier New'"> (make-keyword-procedure</font></div><div style="font-family:Helvetica"><font face="'Courier New'"> (lambda (kws kw-args object proc . rest-args)</font></div><div style="font-family:Helvetica">
<font face="'Courier New'"> (parameterize ([current-send-object object])</font></div><div style="font-family:Helvetica"><font face="'Courier New'"> (keyword-apply proc kws kw-args rest-args)))))</font></div>
</font></div><div><font face="'Courier New'"><br></font></div><div><font face="'Courier New'">(define point%</font></div><div><font face="'Courier New'"> (class object%</font></div><div><font face="'Courier New'"> (super-new)</font></div>
<div><font face="'Courier New'"> (init-field [x 0] [y 0])</font></div><div><font face="'Courier New'"> (define/public (get-x) x)</font></div><div><font face="'Courier New'"> (define/public (get-y) y)</font><span style="font-family:'Courier New'">))</span></div>
<div><font face="'Courier New'"><br></font></div><div><font face="'Courier New'">(define (get-vector)</font></div><div><font face="'Courier New'"> (let* ([object (current-send-object)]</font></div>
<div><font face="'Courier New'"> [x (send object get-x)]</font></div><div><font face="'Courier New'"> [y (send object get-y)])</font></div><div><font face="'Courier New'"> (vector x y)))</font></div>
<div><font face="'Courier New'"><br></font></div><div><font face="'Courier New'">(define p (new point% [x 3] [y 5]))</font></div><div><font face="'Courier New'"><br></font></div><div><font face="'Courier New'">(require rackunit)</font></div>
<div><font face="'Courier New'"><br></font></div><div><font face="'Courier New'">(check-equal? (my-send p get-vector)</font></div><div><font face="'Courier New'"> (vector 3 5))</font></div>
<div><font face="'Courier New'"><br></font></div><div><font face="'Courier New'">(check-equal? (my-send p (compose vector->list get-vector))</font></div><div><font face="'Courier New'"> (list 3 5))</font></div>
<div><font face="'Courier New'"><br></font></div><div>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. </div>
<div class="im"><br><div><div>On Dec 27, 2013, at 1:03 PM, Matthias Felleisen wrote:</div><br><blockquote type="cite"><div><br>This is a bit vague. Can you clarify the question with a concrete example? <br><br><br>On Dec 26, 2013, at 7:45 PM, "Alexander D. Knauth" <<a href="mailto:alexander@knauth.org" target="_blank">alexander@knauth.org</a>> wrote:<br>
<br><blockquote type="cite">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?____________________<br>
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