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From: <tomas@tuxteam.de>
To: Ricardo Wurmus <rekado@elephly.net>
Cc: guile-user@gnu.org
Subject: Re: timestamp
Date: Sat, 12 Feb 2022 13:32:58 +0100	[thread overview]
Message-ID: <Ygeo+pHmUuLUyTR9@tuxteam.de> (raw)
In-Reply-To: <874k54tia0.fsf@elephly.net>

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On Sat, Feb 12, 2022 at 12:49:10PM +0100, Ricardo Wurmus wrote:
> 
> Hi adriano,
> 
> I’ve got no good answers as to “why” things are the way they are, but
> the manual explains the range of these values:
> 
> > It seesm to be
> >
> > (tm:mon %3)
> >
> > This returns
> >
> > 11
> >
> > I expected 12 but ok, I recognize this kind of weirdness
> 
>  -- Scheme Procedure: tm:mon tm
>  -- Scheme Procedure: set-tm:mon tm val
>      Month (0-11).
> 
> > I'm unhappy with 
> >
> > (tm:year $3)
> >
> > This returns
> >
> > 120
> >
> > it's 2020
> >
> > Why would 120 represent 2020 ?
> 
>  -- Scheme Procedure: tm:year tm
>  -- Scheme Procedure: set-tm:year tm val
>      Year (70-), the year minus 1900.
> 
> I don’t know why this would be useful, but that’s what it is ¯\_(ツ)_/¯

Oh. That is old POSIXy tradition :-)

Guile actually only passes along what libc provides, and I think it is a
good idea, in general. See the man page of localtime(3) on your next Linux-ish
box for all the details. If you prefer an online version, perhaps [1], [2]
convey an idea.

The year... those interfaces were developed well before the year 2000. It was
usual, Back Then (TM) to write down the year as a two-digit number (the 19
prefix was implied). Nobody could predict that the year 2000 was about to
arrive, honestly ;-)

As to the month... zero based numberings ease computations and setting up
name arrays (as in: 0: January, 1: February and so on).

Don't ask me why, though, the day of the month (1..31) is one-based. It is
the only exception :-)

But it makes for an easy calculation where you can add up the year (times
year length, taking leap years into account), the days-in-month so far for
full months and the current month day and things to arrive at the current
Epoch day. Guess one has to be one-based, otherwise you'll have to add 1 at
the end.

(This is all somewhat tongue-in-cheek ;-P

But it illustrates some other point: for folks coming from C and POSIX, (I
do), all that stuff feels "pretty natural", although it isn't, of course.

Cheers

[1] https://en.cppreference.com/w/c/chrono/localtime
[2] https://en.cppreference.com/w/c/chrono/tm

-- 
t

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  reply	other threads:[~2022-02-12 12:32 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-02-12  8:37 timestamp adriano
2022-02-12  8:52 ` timestamp Vivien
2022-02-12  9:43   ` timestamp adriano
2022-02-12 11:49     ` timestamp Ricardo Wurmus
2022-02-12 12:32       ` tomas [this message]
2022-02-12 12:38       ` timestamp Eli Zaretskii
2022-02-12 13:30       ` timestamp adriano
2022-02-12 13:42         ` timestamp adriano
2022-02-12 13:49         ` timestamp Ricardo Wurmus
2022-02-12 13:55           ` timestamp adriano
2022-02-12 14:01             ` Guile cookbook ? adriano
2022-02-12 14:15               ` Ricardo Wurmus
2022-02-12 15:01                 ` adriano
2022-02-12 15:30               ` Olivier Dion via General Guile related discussions
2022-02-12 17:11               ` Zelphir Kaltstahl
2022-02-12 17:32           ` timestamp Eli Zaretskii
2022-02-12 17:48             ` Examples in Guile documentation Zelphir Kaltstahl
2022-02-12  9:01 ` timestamp tomas
2022-02-12  9:49   ` timestamp adriano
2022-02-12 12:50   ` timestamp Eli Zaretskii
2022-02-12 13:01     ` timestamp tomas
2022-02-12 15:23     ` timestamp adriano

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