From: Maxime Devos <maximedevos@telenet.be>
To: Zelphir Kaltstahl <zelphirkaltstahl@posteo.de>
Cc: Guile User <guile-user@gnu.org>
Subject: Re: Contracts macro example
Date: Wed, 20 Jul 2022 10:55:53 +0200 [thread overview]
Message-ID: <40733751-fe8e-1e01-4a41-23b83a0c6e35@telenet.be> (raw)
In-Reply-To: <b580b558-9e07-d7b1-94bf-37f343bf0374@posteo.de>
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On 20-07-2022 10:39, Zelphir Kaltstahl wrote:
>> It would also be nice to define a global 'require' and 'ensure' and
>> '<?>' somewhere (e.g.: (define-syntax require (identifier-syntax
>> (syntax-error "'require' can only be used as part of a contract
>> construct")))), that way, require / ensure / <?> can be renamed during
>> importing, so all contract things could be prefixed with, say,
>> contract:.
>
> I thought about implementing <?> for the insertion location of the
> result in a predicate, but initially wanted to keep it simple and get
> a simple version to work. I think I have seen this for pipelining in
> an SRFI before … *checks* … Maybe in
> https://srfi.schemers.org/srfi-197/srfi-197.html, or
> https://srfi.schemers.org/srfi-26/srfi-26.html, or maybe in some other
> repository.
>
> Now that the basic version works, I can try to introduce the placeholder.
>
> The idea is to define these globally in the module, so that they can
> be exported separately, so that they can be renamed upon import, correct?
Yes.
>
> How could a macro check, whether it is used inside something else? If
> the pattern matching only looks at the form of the macro itself, how
> can I get the "context", in which it was used and check, whether that
> is inside a `define-with-contract`? I think I have not yet unlocked
> that knowledge yet : )
That's one way to implement things (syntax-parameterize sounds useful
here), but that sounds way more complicated than needs to be. All you
need to do is:
* keep the original code
* Add:
(define <?> "consider define-syntax+identifier-syntax+syntax-error
for better error messages but this will do for now)
* Export <?> (at least, once your code is turned into a module, if the
users of define-with-contract are in the same module as
define-with-contract then exporting isn't required though harmless)
* Likewise for 'require' and 'ensure'
By doing that, syntax-rules knows that its '<?>', 'require' and 'ensure'
is not just the symbol '<?>' 'require' and 'ensure', but the
_identifier_ (which keeps being the same identifier after renaming)
'<?>', 'require' and 'ensure'.
(Note that as a consequence, if you do that, (let ((require 0))
(define-with-contract foo (require) (ensure) (lambda _ 0))) will be a
syntax error, because the 'require' in define-with-contract now refers
to the variable 'require' from the let, not the identifier from your
RnRS module).
That's all you need to do (untested)!
Greetings,
Maxime
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next prev parent reply other threads:[~2022-07-20 8:55 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-14 23:55 Contracts macro example Zelphir Kaltstahl
2022-07-19 15:20 ` Maxime Devos
2022-07-20 8:39 ` Zelphir Kaltstahl
2022-07-20 8:55 ` Maxime Devos [this message]
2022-07-24 1:21 ` Zelphir Kaltstahl
2022-08-04 16:19 ` Maxime Devos
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