Re: Macro for replacing a placeholder in an expression

[Zelphir Kaltstahl <zelphirkaltstahl@posteo.de>]

On 7/28/22 11:48, Maxime Devos wrote:
>
>
> On 28-07-2022 10:39, Zelphir Kaltstahl wrote:
>> I aimed to do everything with syntax-rules, as the simplest means, but when 
>> writing the code I have, I hit the snag, that one could not have multiple 
>> ellipses at the same level of nesting in the patterns.
>
> IIUC, you mean:
>
> (syntax-rules ()
>   ((foo x ... y ...) [the replacement]))
>
> ? If so, such a construct is ambigious.
>
Yep, that is the case I meant : )


>> After some thinking I found the solution to build up a temporary list, which 
>> then is of course 1 deeper level of nesting, where I could then use ellipses 
>> again. I felt quite clever doing that trick. Maybe I could implement a 
>> syntax-map using that trick and then use syntax-map in my macro instead. 
>> I have a question regarding syntax-case:
>>
>> If I use it, does my code become less portable to other Schemes?
>>
>> And regarding syntax-rules:
>>
>> How portable are macros, which exclusively use syntax-rules?
>>
> Everything that supports syntax-case most likely supports syntax-rules too, as 
> syntax-rules can easily be defined in terms of syntax-case, so syntax-rules is 
> at least as portable as syntax-case.
>
> syntax-rules and syntax-case are pretty standard (it's in the R6RS), so I 
> expect them to be available in recent-ish non-minimalistic Schemes.
>
> However, some Schemes (likely Schemes that predate the R6RS, or in Schemes 
> that try new things out), use other syntax systems.
>
> Anyway, I've found a table:
>
>> https://docs.scheme.org/surveys/syntax-definitions/
>
> Looks like syntax-rules is supported by all the tested systems. syntax-case is 
> less supported, but among the 'low-level' macro systems it has the highest 
> support.  It's a bit out-of-date though, syntax-case is supported for Chicken: 
> http://code.call-cc.org/legacy-eggs/3/syntax-case.html,
>
> Decide for yourself of course, but I don't think going for maximal portability 
> is worth the effort here of something making things work with syntax-rules.
>
Hm OK, thanks for that! Well, it is in a repository of guile-examples, so I 
guess I can let go of wanting to do it all with syntax-rules.


>>>
>>> Greetings,
>>> Maxime
>>
>> Thank you again for your help and explanations! Things are much clearer now!
>>
>> Best regards,
>> Zelphir 

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