<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div><br></div><div>YC, this can all work out IF you organize your program like this: </div><div><br></div><div> module A: define functions, export with contracts and only with contracts </div><div> module B: import A and create the assoc lists from here </div><div> module C: the client imports from B only and performs all ops on the assoc list via B operations </div><div><br></div><div>Then the keys are contracted procedures and lookup works out fine. </div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div><br><div><div>On Jul 22, 2010, at 12:48 AM, YC wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div>Hi Robby - </div><div><br></div><div>What I am trying to do is to look up a key/value pair where the key happens to be the procedure.  The struct idea will work only if I can serialize/hash the procedure into a unique key, which means I will still have to rely on a procedure matching itself (otherwise it's too much work for the client). </div> <div><br></div><div>The scenario really boils down to - why does a contracted procedure not eq itself?  </div><div><br></div><div>The same script above shows that a contracted procedure returns #f with eq?, but a plain procedure returns #t in REPL (both returns #t in module). </div> <div><br></div><div><div>> (eq? test? test?) ;; test? is contracted. </div><div>#f</div><div>> (eq? test2? test2?) ;; test2? is not contracted </div><div>#t</div></div><div><br></div><div>Looking at the <a href="http://docs.racket-lang.org/reference/booleans.html#%28def._%28%28quote._~23~25kernel%29._eq~3f%29%29">definition of eq?</a> shows that eq? is for determining whether two objects are the same.  And since both test? and test2? are exposed via a module, i.e. they are "fixed" once exposed outside of module, whether contracted or not - I would have expected eq? would return #t for both cases in REPL. </div> <div><br></div><div>Am I misunderstand what eq? is all about?  Thanks. </div><div><br></div><div>yc</div><div><br></div><div class="gmail_quote">On Wed, Jul 21, 2010 at 5:40 PM, Robby Findler <span dir="ltr"><<a href="mailto:robby@eecs.northwestern.edu" target="_blank">robby@eecs.northwestern.edu</a>></span> wrote:<br> <blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">You seem to be relying on identity of procedures (which is a bad<br> idea). Contracts on functions are implemented with wrappers which<br> breaks that by making fewer things equal but compiler optimizations<br> can take things the other direction making more things equal than you<br> might expect.<br> <br> Overall I think you should just avoid relying on the identity of<br> procedures. One way to do that (without knowing more about your code)<br> would be to use struct procedures and put an extra field on the struct<br> that gives you the key for a comparison.<br> <br> Hth,<br> <font color="#888888">Robby<br> </font><div><div></div><div><br> On Wednesday, July 21, 2010, YC <<a href="mailto:yinso.chen@gmail.com" target="_blank">yinso.chen@gmail.com</a>> wrote:<br> > Hi all -<br> ><br> > I am running into an interesting issue where an alist of procedures in REPL, the ones without a contract works with assoc, but the ones with contract do not work with assoc.<br> ><br> > What I have is an alist where the keys are procedures.  Some of these procedures have contracts attached to them, and some do not.  Then I tried to use assoc to match the procedures.  If the code are run within the module itself - both types match, but within REPL only the ones without contract matches.<br> ><br> > Here's an simplified example, where foo.ss defines the procedures, and the test.ss uses foo.ss to construct the alist.<br> ><br> > ;; foo.ss<br> > #lang scheme<br> > (define (test? v) #t) ;; provided with contract<br> ><br> > (define (test2? v) #t) ;; provided without contract<br> ><br> > (provide/contract<br> >  (test? (-> any/c boolean?))<br> >  )<br> ><br> > (provide test2?)<br> ><br> > ;; test.ss<br> > #lang scheme<br> > (require "foo.ss")<br> ><br> > (define table `((,test2? . 1) (,test? . 2)))<br> ><br> > (assoc test? table) ;; works in module setting but not in REPL<br> ><br> > (assoc test2? table) ;; works in module setting AND in REPL<br> ><br> > Both the assoc test above returns the correct result.  But if I try to copy and run (assoc test? table) in REPL again, it will not match, whereas (assoc test2? table) continues to match.<br> ><br> > Is there any particular reason for the divergence of the behaviors?  I verified the behavior in both v4.2.5 and v5.0.  Thanks.<br> ><br> > yc<br> ><br> ><br> ><br> ><br> ><br> </div></div></blockquote></div><br><br clear="all"><br>-- <br>Cheers,<br>yc<br><br>Taming the software dragon - <a href="http://dragonmaestro.com/" target="_blank">http://dragonmaestro.com</a><br><br> _________________________________________________<br>  For list-related administrative tasks:<br>  <a href="http://lists.racket-lang.org/listinfo/users">http://lists.racket-lang.org/listinfo/users</a></blockquote></div><br></body></html>