* Bruce Lester | I am looking for Lisp code to calculate and format date values in a variety | of formats. Does anyone have suggestions on where I might look for this?
It is actually too simple. First you have to forget tiemzones, because they do not generally work, not even your local one, since Common Lisp does not interface to your operating system's timezone database in any standard way and many implementations are severely confused outside the state where its authors live. That makes the whole problem a lot simpler than it really is, so you are relieved of lots of minor problems.
Then you just use decoded-universal-time and bind the values like this:
(multiple-value-bind (ss mm hh d m y dow dst zone) (decode-universal-time X) ...)
Now, the _only_ correct way to print a date is this:
(format <stream> "~4,'0D-~2,'0D-~2,'0D" y m d)
and the _only_ correct way to print a time is this:
(format <stream "~2,'0D:~2,'0D:~2,'0D" hh mm ss)
and if you have to write both in a row, use a space or a T between them.
Drop the "culturally correct" ways to write dates and times and just get with the program. Just like floating point numbers are _not_ written with a stupid decimal comma, and times of day are _not_ written in some ancient 12-hours system, nor with hour, minute, second in any other order, you write year, month, and day of month in that order. No variation, no need to do it abstractly, just do it right.
If you need to compute with days, remember that (floor <universal-time> 86400) always decomposes into a day since 1900-01-01 and the seconds the start of the current day. There are exactly 86400 seconds in a day, all year round. -- Guide to non-spammers: If you want to send me a business proposal, please be specific and do not put "business proposal" in the Subject header. If it is urgent, do not use the word "urgent". If you need an immediate answer, give me a reason, do not shout "for your immediate attention". Thank you.
Erik Naggum <e...@naggum.net> writes: > If you need to compute with days, remember that (floor > <universal-time> 86400) always decomposes into a day since > 1900-01-01 and the seconds the start of the current day. There > are exactly 86400 seconds in a day, all year round.
Except for leap seconds, no? (Or is that not an issue with <universal-time>?)
> If you need to compute with days, remember that (floor <universal-time> > 86400) always decomposes into a day since 1900-01-01 and the seconds the > start of the current day.
* Raymond Wiker | Except for leap seconds, no?
Do you think I would lie about this or withhold essential facts or make a claim that would be true "most of the time"? "There are exactly 86400 seconds in a day, all year round" was phrased that way in order to avoid mention of the leap-second mess, but it should _still_ be crystal clear.
| (Or is that not an issue with <universal-time>?)
I think you should look this up and not believe me. This comes up again and again because some people have heard of leap seconds and get all confused, and unless they do some work to figure it out, they just keep asking. -- Guide to non-spammers: If you want to send me a business proposal, please be specific and do not put "business proposal" in the Subject header. If it is urgent, do not use the word "urgent". If you need an immediate answer, give me a reason, do not shout "for your immediate attention". Thank you.
"Bruce Lester" <bruce_les...@email.com> writes: > I am looking for Lisp code to calculate and format date values in a > variety of formats. Does anyone have suggestions on where I might > look for this?
See: Calendrical Calculations, Nachum Dershowitz and Edward M. Reingold. Software-Practice and Experience 20 (1990), 899-928.
You can get the paper and the corresponding code in Common Lisp, C++, and GNU Emacs Lisp from:
-- Christian Lemburg, <lemb...@aixonix.de>, http://www.clemburg.com/ Whenever you find that you are on the side of the majority, it is time to reform. -- Mark Twain
> * In message <eE1S8.2$d%6.2...@news7.onvoy.net> > * On the subject of "Lisp Date arithmetic library" > * Sent on Tue, 25 Jun 2002 17:21:14 GMT > * Honorable "Bruce Lester" <bruce_les...@email.com> writes:
> I am looking for Lisp code to calculate and format date values in a > variety of formats. Does anyone have suggestions on where I might > look for this?
> and the _only_ correct way to print a time is this:
> (format <stream "~2,'0D:~2,'0D:~2,'0D" hh mm ss)
Why are these the _only_ correct ways of displaying date and time? This Euro-format date and "military" time is quite common in Europe. (I do not like 2002-6-26... I keep using 26.6.2002 just as I speak) But in the USA it is common to use a.m./p.m. for times (ok, it's really cumbersome, but they like it *g*) and "their" date format. Who cares?
> > If you need to compute with days, remember that (floor > > <universal-time> 86400) always decomposes into a day since > > 1900-01-01 and the seconds the start of the current day. There > > are exactly 86400 seconds in a day, all year round.
> Except for leap seconds, no? (Or is that not an issue with > <universal-time>?)
no, length of the day is always 86400 seconds. the leap second insertion is a synchronization device to keep the difference between the solar time and atomic time small. earth's rotation is slowing down, so a day is about 2.5ms longer than it was in 1820. that is about 1s per year, thus the (more or less regular) insertion of a leap second.
oz --- the dots can only be numbered after the fact - bruce schneier
* Julian Stecklina | Why are these the _only_ correct ways of displaying date and time?
ISO 8601.
| This Euro-format date and "military" time is quite common in Europe.
Right, pretend it is "Euro-format". *sigh* It was used in Japan before Europe adopted it.
| (I do not like 2002-6-26... I keep using 26.6.2002 just as I speak)
YECCH! Yeah, I hate that, too. However, 2002-06-26 is correct.
I reply "fem på halv" if somebody asks me the time of day and my watch says 18:24:15. Writing times in this spoken manner is retarded, because it lacks all the context of the verbal communication. (Note that I did not say which hour it was, and rounded off to the nearest 5-minute interval.) Writing is all about retaining _more_ context than voice communication normally does. This is why it is hard to write as you speak and speak as you write, and why nobody should _ever_ try to do it, either.
| But in the USA it is common to use a.m./p.m. for times (ok, it's really | cumbersome, but they like it *g*) and "their" date format. Who cares?
Provincialism at its worst. We have international standards to avoid the problem of trying to figure out more context than we need to use a value. Like, I have to know which goddamn country some English writer is from in order to figure out which day of the year he is talking about. I mean, did anything interesting happen on November 9? I cannot recall _anything_ from November 9. Why are you Americans so upset over November 9? I don't get it.
However, some people appear to be generally context-free, and are completely unaware of the total lack of value in writing down things just like they say them to people who regularly have to ask for or already know major parts of the answer.
But who cares? I tell you who cares. There are lots of people around the world who care about international standards in all sorts of areas, and they have actually made serious headway into many areas previously left to random local decisions. And, in time, standards will save mankind from its local follies. But first, Microsoft must be destroyed. -- Guide to non-spammers: If you want to send me a business proposal, please be specific and do not put "business proposal" in the Subject header. If it is urgent, do not use the word "urgent". If you need an immediate answer, give me a reason, do not shout "for your immediate attention". Thank you.
Erik Naggum <e...@naggum.net> writes: > * Julian Stecklina > | Why are these the _only_ correct ways of displaying date and time?
> ISO 8601.
I recall DIN 44300 which told us poor Germans to name this thing turning mnemonics into machine code "Assemblierer" instead of the established "Assembler".
> | This Euro-format date and "military" time is quite common in Europe.
> Right, pretend it is "Euro-format". *sigh* It was used in Japan before > Europe adopted it.
OK. Learnt something new.
> | (I do not like 2002-6-26... I keep using 26.6.2002 just as I speak)
> YECCH! Yeah, I hate that, too. However, 2002-06-26 is correct.
2002-6-26 and 26.6.2002 are as easily recognized by a computer programme as by human eye.
> I reply "fem på halv" if somebody asks me the time of day and my watch says > 18:24:15. Writing times in this spoken manner is retarded, because it lacks > all the context of the verbal communication. (Note that I did not say which > hour it was, and rounded off to the nearest 5-minute interval.) Writing is > all about retaining _more_ context than voice communication normally does. > This is why it is hard to write as you speak and speak as you write, and why > nobody should _ever_ try to do it, either.
I think dates are not subject to "information loss" either spoken or written. (At least in the named examples)
> | But in the USA it is common to use a.m./p.m. for times (ok, it's really > | cumbersome, but they like it *g*) and "their" date format. Who cares?
> Provincialism at its worst. We have international standards to avoid the > problem of trying to figure out more context than we need to use a value. > Like, I have to know which goddamn country some English writer is from in > order to figure out which day of the year he is talking about. I mean, did > anything interesting happen on November 9? I cannot recall _anything_ from > November 9. Why are you Americans so upset over November 9? I don't get it.
What about countries that do not share the Gregorian calendar?
I doubt it is in much use, but nevertheless it is there.
> But who cares? I tell you who cares. There are lots of people around the > world who care about international standards in all sorts of areas, and they > have actually made serious headway into many areas previously left to random > local decisions. And, in time, standards will save mankind from its local > follies. But first, Microsoft must be destroyed.
It is said that IBM is the only company violating their own standards. :)
* Julian Stecklina | I recall DIN 44300 which told us poor Germans to name this thing turning | mnemonics into machine code "Assemblierer" instead of the established | "Assembler".
Well, I have also experienced personal tragedies, but try to keep those away from completely irrelevant topics and not to let my impression of society or any particular subgroup thereof be formed by my personal experiences. If you have some grievances with a particular DIN standard, you have to be pretty fucked up to take that out on standards in general. Maybe most people get fucked up after traumatizing experiences, what do I know, but try to get a grip on your emotional response and try not fuck up other people, too.
* Erik Naggum
> YECCH! Yeah, I hate that, too. However, 2002-06-26 is correct.
| 2002-6-26 and 26.6.2002 are as easily recognized by a computer programme as | by human eye.
Are you blind or something? 2002-06-26 contains a leading zero so the number of characters in the format is constant, the position of the start of each element is predictable, etc. Some people seem to be really upset with the use of leading zeros numbers. Why is this? Another personal tragedy inter- fering with your normal reasoning?
You have tell the computer which format you use in order for it to get it right. The various forms of "parse-by-hunch" that are used for dates get some dates written by some sloppy humans or computers on their behalf wrong.
The fact is, that some people use a month-day order and some people use a day-month order. This would be perfectly OK if the month-day people could at least have the mental wherewithal to do year-month-day and the day-month people could use day-month-year, and they both wrote their years with four digits, but the month-day people are screwed up and use month-day-year, with only two-digit years, so for the next 30 years, many dates will be ambiguous. Sort of like because you say "ten to five" for 16:50, you would write it 50:16 or maybe -10:17 and maybe -10:17:23 to be precise. How come people do not do this? (Well, they are so nutty that they think 12 is 0, too, so just how much can you trust such people, anyway? They even produce household appliances that, when they are used in Europe with 24-hour clocks, they show 24:10 instead 00:10. Since many journalists spend most of their time after midnight staring into microwave ovens, they also report TV programs to begin at 24:30.)
The only reason to have fun with this topic is that it is so tragic that if we took it seriously, we would have to reinvent time as we know it. Oh, wait, some Swiss clock-maker did just that, and thought, brilliantly, we could use 1000 units per day instead of 86400, while other people were busy trying to divide the second into billions if not trillions of tiny little pieces so each interesting thing could have its own little time unit, so clearly, nothing much happens in the life of people who have space for 1000 events per day. Still, it was pretty clever. But 86.4 seconds per beat is like, sloooow, man, it's like you stab someone and it won't bleed until the next beat, man. Not to mention the ultra-high precision that you would need in order to synchronize these things. With an off-beat beat like that, you would need high-precision clocks that could synchronize at any beat instead of having to wait for every fifth beat to line up with a precise second. And they cleverly made their 000 beat some stupid non-Greenwich meridian just to piss people off. They got the idea of a world-wide uniform beat right, though. It is time for such a thing, except it needs to be at a million beats per day, conveniently grouped in hundreds, so sloppy people can still use only two digits to refer to their synchronized events and precision people can use all six digits. This has worked so well to distinguish sloppy from precision people in the past, we should not just randomly let go of such a simple way to gauge people. Besides, 100 large units per day would line up pretty nicely with the good old "quarter hour". This could work! Yeah! (I need to contact Matt Groening and have him make a new Futurama episode. Ever noticed how a thousand years from now, they _still_ use AM/PM? *sigh* There goes my desire to be cryogenically preserved.)
| It is said that IBM is the only company violating their own standards. :)
You just scored much lower. -- Guide to non-spammers: If you want to send me a business proposal, please be specific and do not put "business proposal" in the Subject header. If it is urgent, do not use the word "urgent". If you need an immediate answer, give me a reason, do not shout "for your immediate attention". Thank you.
> The only reason to have fun with this topic is that it is so tragic that if > we took it seriously, we would have to reinvent time as we know it. Oh, > wait, some Swiss clock-maker did just that, and thought, brilliantly, we > could use 1000 units per day instead of 86400, while other people were busy > trying to divide the second into billions if not trillions of tiny little > pieces so each interesting thing could have its own little time unit, so > clearly, nothing much happens in the life of people who have space for 1000 > events per day.
"I've got them," said the Starbuck. "Two centons out!"
"Frak! We don't have two centons!" yelled Apollo.
A few microns beyond the burning spot, Lt. Adama pulled back on the stick...
Erik Naggum <e...@naggum.net> writes: > | 2002-6-26 and 26.6.2002 are as easily recognized by a computer programme as > | by human eye.
> Are you blind or something? 2002-06-26 contains a leading zero so the number > of characters in the format is constant, the position of the start of each > element is predictable, etc. Some people seem to be really upset with the > use of leading zeros numbers. Why is this? Another personal tragedy inter- > fering with your normal reasoning?
No. (I remember you posting: "we have lots of small things that are black to some people and white to others" <3225130472400...@naggum.net>)
I just drop a character that is redundant. I personally try to write computer programmes which adapt to humans and do not try to force humans to adapt to the programme in most aspects. Parsing a date that could, but not has to, contain leading zeros is of course more work for computers and slightly more complex to implement. The result will nevertheless be more versatile.
(Actually dates found in data files will usually be either binary representations or in some format that is constant throughout the file.)
> The only reason to have fun with this topic is that it is so tragic that if > we took it seriously, we would have to reinvent time as we know it.
I would most certainly support this, but it seems to be quite impossible to achieve this.
> | It is said that IBM is the only company violating their own standards. :)
> You just scored much lower.
Ok. Remind me of not telling anymore jokes in future. Perhaps I should learn from others and restrict myself to cynicism...
* Julian Stecklina | I just drop a character that is redundant.
Oh, christ. That you think it is redundant does not make it redundant, it only means you have not figured things out, yet. Drop the "I know better than everyone else because I am ignorant and have a freer mind" attitude.
| Ok. Remind me of not telling anymore jokes in future. Perhaps I should | learn from others and restrict myself to cynicism...
Wrong lesson. Try telling good jokes, instead. -- Guide to non-spammers: If you want to send me a business proposal, please be specific and do not put "business proposal" in the Subject header. If it is urgent, do not use the word "urgent". If you need an immediate answer, give me a reason, do not shout "for your immediate attention". Thank you.
> I just drop a character that is redundant. I personally try to write > computer programmes which adapt to humans and do not try to force > humans to adapt to the programme in most aspects. Parsing a date that > could, but not has to, contain leading zeros is of course more work for > computers and slightly more complex to implement. The result will > nevertheless be more versatile.
You're trading off a moment's convenience for a lifetime of ambiguity and maintenance problems.
> (Actually dates found in data files will usually be either binary > representations or in some format that is constant throughout the > file.)
I recently had the pleasure of seeing a whole bunch of "nightly backup" files which had, quite consistently, included the date of backup in the file name in a "user friendly" way. The backups for this week, when looked at by almost any standard tool, would be ordered "28, 24, 29, 30, 27, 25, 26". Of course, you'd probably never have noticed this, since ALL Fridays came at the top of the list, and ALL Wednesdays come last. With April as the first month, and September last. And the 10th comes before the 9th, obviously. Some, in fact many, of these "nightly backup" files were missing. Which ones, and was there a pattern?
My, how I did laugh.
-- Emacs tells me it's 10 Messidor aR 210, but won't give me the stardate!
> I am looking for Lisp code to calculate and format date values in a > variety of formats. Does anyone have suggestions on where I might > look for this?
I don't know about formatting, but the local-time library (on cliki) does a good job of calculations.
>> I am looking for Lisp code to calculate and format date values in a >> variety of formats. Does anyone have suggestions on where I might >> look for this? > I don't know about formatting, but the local-time library (on cliki) > does a good job of calculations.
