From: ludo@gnu.org (Ludovic Courtès)
To: 宋文武 <iyzsong@member.fsf.org>
Cc: guix-devel@gnu.org
Subject: Re: Change defaults of 'define-record-type*' need invalidate auto-compilation caches
Date: Mon, 08 Jan 2018 11:37:27 +0100 [thread overview]
Message-ID: <87po6khc0o.fsf@gnu.org> (raw)
In-Reply-To: <87o9m7m3es.fsf@member.fsf.org> ("宋文武"'s message of "Sat, 06 Jan 2018 23:07:39 +0800")
Hi!
iyzsong@member.fsf.org (宋文武) skribis:
> For example, in the current directory, I have 'foo.scm':
>
> (define-module (foo)
> #:use-module (guix records)
> #:export (foo foo-x))
>
> (define-record-type* <foo>
> foo make-foo foo?
> (x foo-x (default "x")))
>
>
>
> And 'x.scm':
>
> (use-modules (foo))
> (display (foo-x (foo)))
>
>
> Run 'guile -L . x.scm', will output "x".
>
> Then I change the '(default "x")' to '(default "y")' in foo.scm, and
> re-run 'guile -L x.scm', it still output "x", I would expect it to
> change to "y".
>
> Only with '--fresh-auto-compile' or delete the cache of x.scm, I will
> get the output "y".
>
> Is this a bug?
It’s a feature. :-)
Namely, default value resolution happens at macro-expansion time:
--8<---------------cut here---------------start------------->8---
scheme@(guile-user)> ,use(guix records)
scheme@(guile-user)> (define-record-type* <foo>
foo make-foo foo?
(x foo-x (default "x")))
scheme@(guile-user)> ,expand (foo)
$2 = (let* ((x "x")
(s ((@@ (srfi srfi-9) allocate-struct) <foo> 1)))
((@@ (srfi srfi-9) struct-set!) s 0 x)
s)
--8<---------------cut here---------------end--------------->8---
That way, we can check at macro-expansion time that all the required
fields are present, which is nice.
The downside is what you write: that everything that uses the record
type must be recompiled when it is changed (IOW, the record type is part
of the ABI).
HTH!
Ludo’.
next prev parent reply other threads:[~2018-01-08 10:37 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-06 14:55 Change defaults of 'define-record-type*' need invalidate auto-compilation caches 宋文武
2018-01-06 15:07 ` 宋文武
2018-01-08 10:37 ` Ludovic Courtès [this message]
2018-01-08 12:49 ` 宋文武
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