From mboxrd@z Thu Jan  1 00:00:00 1970
From: iyzsong@member.fsf.org (=?utf-8?B?5a6L5paH5q2m?=)
Subject: Re: Change defaults of 'define-record-type*' need invalidate
	auto-compilation caches
Date: Mon, 08 Jan 2018 20:49:58 +0800
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In-Reply-To: <87po6khc0o.fsf@gnu.org> ("Ludovic
	\=\?utf-8\?Q\?Court\=C3\=A8s\=22'\?\=
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To: Ludovic =?utf-8?Q?Court=C3=A8s?= <ludo@gnu.org>
Cc: guix-devel@gnu.org

ludo@gnu.org (Ludovic Court=C3=A8s) writes:

> Hi!
>
> iyzsong@member.fsf.org (=E5=AE=8B=E6=96=87=E6=AD=A6) skribis:
>
>> [...]
>>
>> Only with '--fresh-auto-compile' or delete the cache of x.scm, I will
>> get the output "y".
>>
>> Is this a bug?
>
> It=E2=80=99s a feature.  :-)
>
> Namely, default value resolution happens at macro-expansion time:
>
> 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 =3D (let* ((x "x")
>        (s ((@@ (srfi srfi-9) allocate-struct) <foo> 1)))
>   ((@@ (srfi srfi-9) struct-set!) s 0 x)
>   s)
>
> 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!

Get it, thanks for the explanation!