From: "yarl baudig" <yarl-baudig@mailoo.org>
To: jean@abou-samra.fr, "Maxime Devos" <maximedevos@telenet.be>,
guile-devel@gnu.org
Subject: Re: define-module, #:export and export
Date: Fri, 6 Jan 2023 14:31:43 +0100 (CET) [thread overview]
Message-ID: <ea-mime-63b822bf-593a-70287a42@www.mailo.com> (raw)
In-Reply-To: <b5718ab1-57b0-ef9c-093c-73f50248b4ba@abou-samra.fr>
>
> That is also my understanding, confirmed by
>
> $ cat lib.scm
> (define-module (lib)
> #:export (test))
>
> (define-syntax test
> (lambda (sintax)
> (syntax-case sintax ()
> ((test id)
> (datum->syntax sintax (free-identifier=? #'id #'thing))))))
>
> $ cat test.scm
> (define-module (main)
> #:use-module (lib)
> #:export (thing)
> )
>
> (display (test thing))
> (newline)
>
> (define thing 5)
>
> $ guile3.0 -L . test.scm
> #f
>
>
> If you comment out #:export (thing), the result changes to #t.
>
> To put it perhaps more simply, the use of #:export causes Guile to
> understand early that there will be a variable 'thing' in this module,
> and makes the identifier 'thing' refer to this variable that is not yet
> defined. However, hygiene implies that you want to be able to use
> keywords as if they were not keywords if they are rebound, e.g. the
> 'else' here doesn't cause the cond clause to be taken:
>
> (let ((else #f)) (cond (#f 'bla) (else 'foo) (#t 'bar)))
> $1 = bar
>
> The way this is done is by comparing with the original identifier given
> to syntax-rules. Technically, they are compared with free-identifier=? .
> This means that a use of the identifier matches the keyword iff both are
> unbound, or both are bound to the same lexical binding. However, this
> isn't the case here, as the keyword in the macro was unbound, but at the
> point of use, it has been bound by #:export.
>
> Honestly, I think it is better to choose a different way of writing
> these macros that avoids this confusing issue. Try defining the
> operations at the same time as the enum so that the macro giving an enum
> member refers to the bindings of the operators. If you give more context
> on what you're trying to do, we could help more.
>
> Best,
> Jean
>
>
Thank you both. I am trying to process this. I (re-)read 6.8 Macros and read tspl4. I don't understand why you use "datum->syntax".
I heard your suggestion. I am only trying to grasp things for now. I realize I don't know enough (on guile and on guix) to go on a concrete goal yet.
I need to work more on this in order to understand but I wanted to thank you for answering that quickly!
next prev parent reply other threads:[~2023-01-06 13:31 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-04 15:11 define-module, #:export and export yarl baudig
2023-01-04 17:28 ` Maxime Devos
2023-01-05 2:07 ` Jean Abou Samra
2023-01-06 13:31 ` yarl baudig [this message]
2023-01-06 13:55 ` Maxime Devos
2023-01-07 16:24 ` Jean Abou Samra
2023-01-08 9:46 ` yarl baudig
2023-01-08 13:19 ` Jean Abou Samra
2023-01-08 15:18 ` yarl baudig
2023-01-08 15:23 ` Jean Abou Samra
2023-01-13 7:58 ` yarl baudig
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