Hi Robby - 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).
The scenario really boils down to - why does a contracted procedure not eq itself? 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). > (eq? test? test?) ;; test? is contracted. #f > (eq? test2? test2?) ;; test2? is not contracted #t Looking at the definition of eq?<http://docs.racket-lang.org/reference/booleans.html#%28def._%28%28quote._~23~25kernel%29._eq~3f%29%29>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. Am I misunderstand what eq? is all about? Thanks. yc On Wed, Jul 21, 2010 at 5:40 PM, Robby Findler <ro...@eecs.northwestern.edu>wrote: > You seem to be relying on identity of procedures (which is a bad > idea). Contracts on functions are implemented with wrappers which > breaks that by making fewer things equal but compiler optimizations > can take things the other direction making more things equal than you > might expect. > > Overall I think you should just avoid relying on the identity of > procedures. One way to do that (without knowing more about your code) > would be to use struct procedures and put an extra field on the struct > that gives you the key for a comparison. > > Hth, > Robby > > On Wednesday, July 21, 2010, YC <yinso.c...@gmail.com> wrote: > > Hi all - > > > > 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. > > > > 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. > > > > Here's an simplified example, where foo.ss defines the procedures, and > the test.ss uses foo.ss to construct the alist. > > > > ;; foo.ss > > #lang scheme > > (define (test? v) #t) ;; provided with contract > > > > (define (test2? v) #t) ;; provided without contract > > > > (provide/contract > > (test? (-> any/c boolean?)) > > ) > > > > (provide test2?) > > > > ;; test.ss > > #lang scheme > > (require "foo.ss") > > > > (define table `((,test2? . 1) (,test? . 2))) > > > > (assoc test? table) ;; works in module setting but not in REPL > > > > (assoc test2? table) ;; works in module setting AND in REPL > > > > 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. > > > > Is there any particular reason for the divergence of the behaviors? I > verified the behavior in both v4.2.5 and v5.0. Thanks. > > > > yc > > > > > > > > > > > -- Cheers, yc Taming the software dragon - http://dragonmaestro.com
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