From mboxrd@z Thu Jan  1 00:00:00 1970
From: ludo@gnu.org (Ludovic =?utf-8?Q?Court=C3=A8s?=)
Subject: Re: New =?utf-8?Q?=E2=80=98--list-generations=E2=80=99?= and
	=?utf-8?Q?=E2=80=98--delete-generations=E2=80=99?= options
Date: Mon, 09 Sep 2013 18:55:30 +0200
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In-Reply-To: <877geq9wx6.fsf@karetnikov.org> (Nikita Karetnikov's message of
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To: Nikita Karetnikov <nikita@karetnikov.org>
Cc: guix-devel@gnu.org

Nikita Karetnikov <nikita@karetnikov.org> skribis:

>> In that case, would you suggest --list-generations=3Drec to specify the
>> recutils output format (with no filtering)?
>
> No need for the =E2=80=98rec=E2=80=99 part.  I propose to output all gene=
rations in the
> recutils format when =E2=80=98--list-generations=E2=80=99 is passed.

OK.

>> Age specifications would only be of the kind =E2=80=9Cat least X days/mo=
nths
>> old=E2=80=9D.  A non-ambiguous syntax is needed, and something more flex=
ible
>> than just =E2=80=98last-month=E2=80=99.  Let=E2=80=99s assume =E2=80=98s=
tring->duration=E2=80=99:
>
>>   "+22"    =E2=87=92 #<time time-duration ...>   ; 22 days
>>   "+2w"    =E2=87=92 #<time time-duration ...>   ; 14 days
>>   "+1m"    =E2=87=92 #<time time-duration ...>   ; 30 days
>
> The plus sign is confusing (we=E2=80=99re subtracting).  I=E2=80=99d rath=
er use =E2=80=9822d=E2=80=99,
> =E2=80=982w=E2=80=99, and =E2=80=981m=E2=80=99.

Fine with me.

> How can I subtract 22 days from (current-time) using SRFI-19?

Note that the above example suggests that =E2=80=98string->duration=E2=80=
=99 returns a
time object with of type =E2=80=98time-duration=E2=80=99 (thus independent =
of the
current time.)

Subtraction is done like this:

--8<---------------cut here---------------start------------->8---
scheme@(guile-user)> (subtract-duration (current-time)
                        (make-time time-duration 0 (* 3600 24 22)))
$3 =3D #<time type: time-utc nanosecond: 357264000 second: 1376844845>
scheme@(guile-user)> (date->string (time-utc->date $3))
$4 =3D "Sun Aug 18 18:54:05+0200 2013"
--8<---------------cut here---------------end--------------->8---

HTH,
Ludo=E2=80=99.