[racket-dev] A strange problem with namespaces

From: Sam Tobin-Hochstadt (samth at cs.indiana.edu)
Date: Wed May 7 10:31:38 EDT 2014

Well, to quote from the docs for `dynamic-require`:

"When provided is a symbol, the value of the module’s export with the
given name is returned, and still the module is not visited or made
available in higher phases."

That's why I think the extra line is needed.

You're right that the error message refers to phase 0, but I'm not
sure who's phase 0 that is.


On Wed, May 7, 2014 at 10:27 AM, Robby Findler
<robby at eecs.northwestern.edu> wrote:
> When I look at this code I can't figure out why (submod "weird.rkt"
> evaluator) _isn't_ available at phase 0! Could this be a bug?
> Robby
> On Wed, May 7, 2014 at 9:11 AM, Sam Tobin-Hochstadt
> <samth at cs.indiana.edu> wrote:
>> This program: https://gist.github.com/samth/e7b55fcef66da9b8416a works
>> when line 33 is uncommented, otherwise it gives the error:
>> ?: module mismatch;
>>  attempted to use a module that is not available
>>   possible cause:
>>    using (dynamic-require .... #f)
>>    but need (dynamic-require .... 0)
>>   module: (submod "weird.rkt" evaluator)
>>   phase: 0
>>   in: phase1-phase0-run
>>   context...:
>>    weird.rkt: [running body]
>> From reading the docs on `dynamic-require`, I can see that
>> `(dynamic-require m 'f)` doesn't make anything available for higher
>> phases.  However, the actual `dynamic-require` in the program is just
>> for a function -- the need for higher phases is an implementation
>> detail that's leaking in because it doesn't behave like a regular
>> value wrt `dynamic-require`.
>> Is there something I can change in the implementation of the internals
>> of `f` so that clients of `f` don't need to do the extra
>> `(dynamic-require m 0)` in order for `f` to work?
>> Sam
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