From mboxrd@z Thu Jan  1 00:00:00 1970
From: ludo@gnu.org (Ludovic =?utf-8?Q?Court=C3=A8s?=)
Subject: Re: guix-package --roll-back
Date: Sun, 13 Jan 2013 21:40:58 +0100
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To: Nikita Karetnikov <nikita@karetnikov.org>
Cc: bug-guix@gnu.org

Nikita Karetnikov <nikita@karetnikov.org> skribis:

>> It actually does, but it has no side effect.
>
> I know that printing is a side effect.  Why do you recommend to use
> 'alist-cons'?  If it's not possible to display anything, then
> 'roll-back' won't be able to print the following messages.

It=E2=80=99s just the /option handler/ (the procedure passed to SRFI-37
=E2=80=98option=E2=80=99) that should not print anything.  It is then OK to=
 print
things, of course, like is done for other options.

Check how the other options are handled: during =E2=80=98args-fold=E2=80=99=
, the option
handler just adds to RESULT an element saying that this option was
passed.  Once =E2=80=98args-fold=E2=80=99 has completed, we check its resul=
t: if it
contains a pair whose key is =E2=80=98install=E2=80=99, then it means we wa=
nt to install
something, and so on.

>> When =E2=80=98--profile=E2=80=99 is passed, the result of =E2=80=98parse=
-options=E2=80=99 contains a
>> pair whose key is =E2=80=98profile=E2=80=99.  The (assoc-ref opts 'profi=
le) calls that
>> you see retrieve the argument given to =E2=80=98--profile=E2=80=99.
>
> It's clear.  But where should I call (assoc-ref opts 'profile)?  Should
> I do it in 'process-query'?

In =E2=80=98process-actions=E2=80=99 more precisely, because roll-back is a=
n action, not
a query.  And =E2=80=98process-actions=E2=80=99 already does that.

HTH,
Ludo=E2=80=99.