[racket] A macro's `require' works in module but not in REPL

net/uri-codec is not required (directly) into use.rkt. Instead, it is
required at the definition of the macro and then a reference to that
module is inserted into use.rkt. The macro system can track such
references without explicitly having requires.

BTW, the same thing is happening with 'define'...  :)

Robby

On Sat, Oct 20, 2012 at 9:30 AM, Greg Hendershott
<greghendershott at gmail.com> wrote:
> 1. Thank you!
> 2. This works. Hooray.
> 3. I don't understand why it works. Boo.
>
> My reasoning:
>
> In def.rkt, `define-foo' generates syntax. The syntax is a procedure
> definition. The body of the defined procedure needs to use a function
> from another module (in this case net/uri-codec).
>
> When Racket is compiling use.rkt, it substitutes `(define-foo)' with
> the syntax from def.rkt. However, if that new syntax doesn't include a
> `(require net/uri-codec)', how the heck does net/uri-codec get
> required into use.rkt?
>
> On Fri, Oct 19, 2012 at 7:15 PM, Danny Yoo <dyoo at hashcollision.org> wrote:
>> On Fri, Oct 19, 2012 at 9:04 AM, Greg Hendershott
>> <greghendershott at gmail.com> wrote:
>>> I need to fix a bug, https://github.com/greghendershott/gapi/issues/2 .
>>>
>>> I've distilled to a simple case that exhibits the behavior:
>>>
>>> ;; def.rkt
>>> #lang racket
>>> (provide define-foo)
>>> (define-syntax define-foo
>>>   (lambda (stx)
>>>     #`(begin
>>>         (require net/uri-codec)
>>>         (define (#,(datum->syntax stx 'foo))
>>>           (alist->form-urlencoded '([a . "1"]))))))
>>
>>
>>
>> The macro's outputted code appears to require net/uri-codec.  But
>> rather that require be part of the macro's output, you probably should
>> just modify def.rkt so that it requires net/uri-codec directly.
>>
>> Basically, change def.rkt and lift the require up:
>>
>> ;;;;;;;;;;;;;;;;;;;;;;;;
>> #lang racket
>> (provide define-foo)
>>
>> (require net/uri-codec)
>> (define-syntax define-foo
>>   (lambda (stx)
>>     #`(define (#,(datum->syntax stx 'foo))
>>         (alist->form-urlencoded '([a . "1"])))))
>> ;;;;;;;;;;;;;;;;;;;;;;;;
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