[racket-dev] A strange problem with namespaces

Oh! So the evaluator module is available in phase 0 in 'ns', but not
in 'namespace'. Is that right?

Robby

On Wed, May 7, 2014 at 9:58 AM, Matthew Flatt <mflatt at cs.utah.edu> wrote:
> I think the right change might be
>
>  (module evaluator racket
>    ....
>    (define (prep!)
>      (parameterize ([current-namespace namespace])
>        (dynamic-require (variable-reference->module-path-index
>                          (#%variable-reference))
>                         0)))
>    ....
>    (define-syntax phase1-phase0-eval
>      (syntax-parser
>       [(_ form:expr ...)
>        #'(begin
>            (prep!)
>            (eval-syntax .....))])))
>
> The `prep!` function ensures that the enclosing module is available.
>
> At Wed, 7 May 2014 10:11:49 -0400, Sam Tobin-Hochstadt 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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