From mboxrd@z Thu Jan  1 00:00:00 1970
From: =?utf-8?Q?Ludovic_Court=C3=A8s?= <ludo@gnu.org>
Subject: Re: using package-for-guile2.0 outside of guile.scm
Date: Tue, 29 Jan 2019 23:15:26 +0100
Message-ID: <87k1inm7pd.fsf@gnu.org>
References: <877eepssan.fsf@elephly.net> <87va29rlr5.fsf@gnu.org>
Mime-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: quoted-printable
Return-path: <guix-devel-bounces+gcggd-guix-devel=m.gmane.org@gnu.org>
Received: from eggs.gnu.org ([209.51.188.92]:35075)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <ludo@gnu.org>) id 1gobfV-0007tE-0n
	for guix-devel@gnu.org; Tue, 29 Jan 2019 17:15:46 -0500
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <ludo@gnu.org>) id 1gobfU-0000ne-9L
	for guix-devel@gnu.org; Tue, 29 Jan 2019 17:15:45 -0500
Received: from hera.aquilenet.fr ([2a0c:e300::1]:45410)
	by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32)
	(Exim 4.71) (envelope-from <ludo@gnu.org>) id 1gobfT-0000fl-Og
	for guix-devel@gnu.org; Tue, 29 Jan 2019 17:15:44 -0500
In-Reply-To: <87va29rlr5.fsf@gnu.org> ("Ludovic
	\=\?utf-8\?Q\?Court\=C3\=A8s\=22'\?\=
	\=\?utf-8\?Q\?s\?\= message of "Mon, 28 Jan 2019 13:48:30 +0100")
List-Id: "Development of GNU Guix and the GNU System distribution."
	<guix-devel.gnu.org>
List-Unsubscribe: <https://lists.gnu.org/mailman/options/guix-devel>,
	<mailto:guix-devel-request@gnu.org?subject=unsubscribe>
List-Archive: <http://lists.gnu.org/archive/html/guix-devel/>
List-Post: <mailto:guix-devel@gnu.org>
List-Help: <mailto:guix-devel-request@gnu.org?subject=help>
List-Subscribe: <https://lists.gnu.org/mailman/listinfo/guix-devel>,
	<mailto:guix-devel-request@gnu.org?subject=subscribe>
Errors-To: guix-devel-bounces+gcggd-guix-devel=m.gmane.org@gnu.org
Sender: "Guix-devel" <guix-devel-bounces+gcggd-guix-devel=m.gmane.org@gnu.org>
To: Ricardo Wurmus <rekado@elephly.net>
Cc: guix-devel@gnu.org

Hi!

Ludovic Court=C3=A8s <ludo@gnu.org> skribis:

> Ricardo Wurmus <rekado@elephly.net> skribis:
>
>> I tried to move most of the packages in gnu/packages/guile.scm to a new
>> module gnu/packages/guile-xyz.scm.
>>
>> The only problem with this is that package-for-guile2.0 cannot be used
>> in guile-xyz.scm.  I cannot compile the module when there=E2=80=99s a re=
ference
>> to package-for-guile2.0, even when the definition is in guile-xyz.scm.
>> The definition of package-for-guile2.0 refers to guile-2.2, which is
>> located in guile.scm.
>>
>> What to do?
>
> The problem is that =E2=80=98package-with-guile-2.0=E2=80=99 needs to res=
olve
> =E2=80=98guile-2.0=E2=80=99.  So if you use it at the top-level, then (gn=
u packages
> guile) has to be fully loaded, or you have to be in (gnu packages guile)
> itself and =E2=80=98guile-2.0=E2=80=99 has been defined above.
>
> I think we can get around it using this cute hack.  I=E2=80=99ll commit i=
t if
> that=E2=80=99s fine with you.

As you found out, that=E2=80=99s not enough.  The reason is that
=E2=80=98package-input-rewriting=E2=80=99 is inherently greedy, not lazy.  =
For example:

  (let ((rewrite (package-input-rewriting `((,p . ,q)))))
    (eq? q (rewrite p)))
  =3D> #t

This works only because the replacement alist is traversed as soon as
=E2=80=98rewrite=E2=80=99 is called.

Needs more thought=E2=80=A6

Ludo=E2=80=99.