[racket] struct contract violation problem

It is extremely unlikely that out of date .zo files could cause this, altho
it is, in theory, possible.

Robby


On Wed, Oct 23, 2013 at 7:55 PM, Erik Pearson <erik at adaptations.com> wrote:

> Thanks Robby, a nice teaching gift.
>
> I think the problem has "gone away". Realizing my ad-hoc test was run from
> the file in which url triggers the error, I set about to embed the test in
> the file / dr racket window that generates url.
>
> I ran a test function, starting very simple and step by step getting
> closer to the one which fails, but was unable to trigger the error. Finally
> I returned to the original function, and now I can't trigger the error with
> it either, even with all the test code removed.
>
> Could it have been a stuck compiled file? Overwritten finally when I was
> running the tests? I see that my Dr Racket's "Populate 'compiled'
> directories" is enabled. From my CL days, if I ran into something like this
> I might blow away all the compiled files and recompile everything from
> scratch.. Anyway it works now and I'm back to working on the real problems
> ...
>
> Thanks again for all the lightening fast help!
>
> Erik.
>
>
> On Wed, Oct 23, 2013 at 4:58 PM, Robby Findler <
> robby at eecs.northwestern.edu> wrote:
>
>> Since there's little background here, I thought I'd just add that this
>> feature you're coming across is one of the critical things that underpins
>> Racket and differentiates it from languages like python and ruby. That is,
>> what you're seeing is that Racket has a way to make unforgeable values.
>> This ability is (in addition to lots of stuff, notably macros) is what
>> makes it possible for Racket's class system to be a library and lots of
>> other things that you'd expect to be built into a language to also be
>> libraries.
>>
>> As a little example, if you have these files:
>>
>> ;; a.rkt
>> #lang racket
>> (struct url (stuff more-stuff))
>>
>> ;; b.rkt
>> #lang racket
>> (struct url (stuff more-stuff))
>>
>> ;; c.rkt
>> #lang racket
>> (require (prefix-in a: "a.rkt") (prefix-in b: "b.rkt"))
>> (b:url-stuff (a:url 1 2))
>>
>>
>> you'll see an error message very similar to the one you reported.
>>
>> It is the struct declaration's location (technically when it is evaluated
>> -- you can even stick them inside functions and each time you call the
>> function you get a different notion of "url") that determines which is
>> which.
>>
>> This is why, for example, you cannot see the hidden stuff inside the
>> class and object structs. Or, for that matter functions! The "lambda" that
>> #lang racket exports is a lot fancier than the low-level built-in lambda,
>> and that is all implemented with structs. Indeed, you cannot tell what is
>> primitive and what is implemented with a struct in some private file
>> (unless you read the source code). Or, to put it another way: everything is
>> implemented with struct and the runtime system is just good at optimizing a
>> small subset of the structs where performance matters.
>>
>> Robby
>>
>>
>>
>> On Wed, Oct 23, 2013 at 5:38 PM, Erik Pearson <erik at adaptations.com>wrote:
>>
>>> On Wed, Oct 23, 2013 at 3:31 PM, Jay McCarthy <jay.mccarthy at gmail.com>wrote:
>>>
>>>> Here are two ideas.
>>>>
>>>> 1) You simply have an old use of the original net/url. When #<url> is
>>>> printed, it uses the symbolic name and you can't really figure out
>>>> what the underlying code came from. I would do a grep to make sure
>>>> this is not the case.
>>>>
>>>
>>> Would the operative places to look be the point at which the url object
>>> is created and then where it is used? In other words, if it is created in
>>> the context of net/url (i.e. a module where net/url is required) and used
>>> in a module with adaptnet/url required, it will look like a #<url> (when
>>> printed) but not be a url? according to adaptnet/url's url-structs, and
>>> where the object travels in between doesn't make a difference?
>>>
>>>
>>>> 2) You are using namespaces somewhere and actually have two instances
>>>> of the same module somewhere where a value produced by copy 1 is going
>>>> to copy 2. This is possible with the Web server if you don't set up
>>>> the servlet namespace properly:
>>>>
>>>>
>>>> http://docs.racket-lang.org/web-server-internal/dispatch-servlets.html#(part._namespace)
>>>>
>>>> On Wed, Oct 23, 2013 at 4:25 PM, Erik Pearson <erik at adaptations.com>
>>>> wrote:
>>>> > Excuse my poor experience with contracts, this is probably an easy
>>>> one.
>>>> >
>>>> > I'm using a copy of net/url and have a strange problem. The copied
>>>> library
>>>> > is working fine in general, but this problem cropped up today:
>>>> >
>>>> > struct:exn:fail:contract:blame url-port: contract violation
>>>> > expected: url?
>>>> > given: #<url>
>>>> > in: the 1st argument of
>>>> > (-> url? (or/c #f number?))
>>>> > contract from:
>>>> > /home/epearson/work/racket/github/adaptnet/url-structs.rkt
>>>> > blaming: /home/epearson/work/racket/github/racqueb/httpc.rkt
>>>> > at: /home/epearson/work/racket/github/adaptnet/url-structs.rkt:4.28
>>>> >
>>>> > The error is thrown in my usage of url-port which is being passed a
>>>> > perfectly good url struct object. The file is requiring the copied
>>>> > url-structs. If I play with the function that is being blamed in
>>>> httpc.rkt
>>>> > via the repl in dr racket, this specific error is not thrown. The
>>>> call to
>>>> > (url-port url) succeeds without throwing this contract exception.
>>>> >
>>>> > From my primitive understanding, I'm flummoxed: Why is a #<url> not a
>>>> url?
>>>> >
>>>> > I suspected that there may have been a leftover require of net/url
>>>> confusing
>>>> > things, but I can't find any in my code.
>>>> >
>>>> > Using racket head from github 5.90.0.9--2013-10-20(d6610289/d)
>>>> >
>>>> > Help!
>>>> >
>>>> > Thanks,
>>>> > Erik.
>>>> >
>>>> >
>>>> >
>>>> > ____________________
>>>> >   Racket Users list:
>>>> >   http://lists.racket-lang.org/users
>>>> >
>>>>
>>>>
>>>>
>>>> --
>>>> Jay McCarthy <jay at cs.byu.edu>
>>>> Assistant Professor / Brigham Young University
>>>> http://faculty.cs.byu.edu/~jay
>>>>
>>>> "The glory of God is Intelligence" - D&C 93
>>>>
>>>
>>>
>>>
>>> --
>>> Erik Pearson
>>> Adaptations
>>> ;; web form and function
>>>
>>> ____________________
>>>   Racket Users list:
>>>   http://lists.racket-lang.org/users
>>>
>>>
>>
>
>
> --
> Erik Pearson
> Adaptations
> ;; web form and function
>
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