Re: [racket-users] Macros expanding to require forms

[Veit Heller]

Hello,

This is very useful information, thank you! I still have trouble 
understanding _why_ this works, though; I guess I’m a little confused as to 
how the scope-flipping influences things.

For instance, I don’t quite understand why the example from the docs works, 
but if you define the module to import in the macro (no matter whether it’s 
wrapped in `syntax-local-introduce` or not, it won’t. Example:

```
(module example racket (provide require-mod)
   (define-syntax (require-mod stx)
 #`(begin
  (module mod racket (provide hi) (define (hi) 1))
  #,(syntax-local-introduce #'(require 'mod
)
(require-mod) ; works fine, without an error
(hi) ; is still undefined
```

I’m not sure that this is supposed to work, but I’m using these to 
highlight my lack of understanding for the big picture here. What is going 
on? What am I missing?

V
On Thursday, 12 November 2020 at 13:26:48 UTC+1 sorawe...@gmail.com wrote:

> See 
> https://docs.racket-lang.org/reference/stxtrans.html#%28def._%28%28quote._~23~25kernel%29._syntax-local-introduce%29%29
>  for 
> an example program that requires a library via a macro.
>
> On Thu, Nov 12, 2020 at 3:09 AM Veit Heller  wrote:
>
>>
>> Hello,
>>
>> I’m suspecting I’m getting a little turned around by phase levels and 
>> where `require` comes in: it seems to be impossible to write a macro that 
>> expands to a valid `require` (it doesn’t throw an error, but the functions 
>> aren’t defined either). What am I missing? At what phase level does 
>> `require` do its magic? And can I tap into this magic from within a macro?
>>
>> An example to illustrate my point:
>>
>> ```
>> (define-syntax require-distributed ()
>>   ((_)
>> (require racket/place/distributed))) ; could be anything, really
>> (require-distributed) ; expands and runs fine, but no symbols :(
>> ```
>>
>> I know that this is somewhat of an odd thing to want, and I understand if 
>> it’s not possible.
>>
>> V
>>
>> -- 
>> You received this message because you are subscribed to the Google Groups 
>> "Racket Users" group.
>> To unsubscribe from this group and stop receiving emails from it, send an 
>> email to racket-users...@googlegroups.com.
>> To view this discussion on the web visit 
>> https://groups.google.com/d/msgid/racket-users/a49ab428-ae49-45ce-9d16-8a77d27f5a85n%40googlegroups.com
>>  
>> 
>> .
>>
>

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Re: [racket-users] Macros expanding to require forms

[Sorawee Porncharoenwase]

See
https://docs.racket-lang.org/reference/stxtrans.html#%28def._%28%28quote._~23~25kernel%29._syntax-local-introduce%29%29
for
an example program that requires a library via a macro.

On Thu, Nov 12, 2020 at 3:09 AM Veit Heller  wrote:

>
> Hello,
>
> I’m suspecting I’m getting a little turned around by phase levels and
> where `require` comes in: it seems to be impossible to write a macro that
> expands to a valid `require` (it doesn’t throw an error, but the functions
> aren’t defined either). What am I missing? At what phase level does
> `require` do its magic? And can I tap into this magic from within a macro?
>
> An example to illustrate my point:
>
> ```
> (define-syntax require-distributed ()
>   ((_)
> (require racket/place/distributed))) ; could be anything, really
> (require-distributed) ; expands and runs fine, but no symbols :(
> ```
>
> I know that this is somewhat of an odd thing to want, and I understand if
> it’s not possible.
>
> V
>
> --
> You received this message because you are subscribed to the Google Groups
> "Racket Users" group.
> To unsubscribe from this group and stop receiving emails from it, send an
> email to racket-users+unsubscr...@googlegroups.com.
> To view this discussion on the web visit
> https://groups.google.com/d/msgid/racket-users/a49ab428-ae49-45ce-9d16-8a77d27f5a85n%40googlegroups.com
> 
> .
>

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[racket-users] Macros expanding to require forms

[Veit Heller]

Hello,

I’m suspecting I’m getting a little turned around by phase levels and where 
`require` comes in: it seems to be impossible to write a macro that expands 
to a valid `require` (it doesn’t throw an error, but the functions aren’t 
defined either). What am I missing? At what phase level does `require` do 
its magic? And can I tap into this magic from within a macro?

An example to illustrate my point:

```
(define-syntax require-distributed ()
  ((_)
(require racket/place/distributed))) ; could be anything, really
(require-distributed) ; expands and runs fine, but no symbols :(
```

I know that this is somewhat of an odd thing to want, and I understand if 
it’s not possible.

V

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