On 4/18/07, Philippe Marschall <philippe.marschall at gmail.com> wrote:
>
> 2007/4/17, Hernan Wilkinson <hernan.wilkinson at gmail.com>:
> >
> >
> > On 4/17/07, Philippe Marschall <philippe.marschall at gmail.com> wrote:
> > > You said:
> > > > 5) Chalten is based on a arithmetic model that allows you to
> represent
> > time measurements easily (like 3 days, 5 months, etc)
> > >
> > > So I assumed you meant we could write
> > > 5 months
> > > just the same way we could write
> > > 100 dollars
> > > like the examples in the paper show.
> >
> > No "5 months" but "5 * months" or "moth with: 5". Same for "dollars",
> > "euros", "meters", "liters", "A", "B", etc.
> > That is why I think that measure was not a good word to define this
> > objects... 5*A is not a measure.. what we implemented is really an
> algebra,
> > maybe a limited one, but an algebra at the end.
>
> Maybe I'm just seeing things:
>
> http://www.iam.unibe.ch/~ducasse/Teaching/CoursAnnecy/0506-M1-COO/A%20New%20Object-Oriented%20Model%20of%20the%20Gregorian%20Calendar.pdf
> page 7, figure 11:
> 14 days + 1 week = 1814400000 milliseconds. "Adding measurements of
> the same base unit"
> ((14 days + 1 week) convertTo: days) = 21 days. "Converting the result
> of an operation"
> (1 year + 10 days) = (1 year + 10 days) "Adding measurements of
> different base unit"
> 10 years * 10 = 100 years "Multiplying a measurement by a number"
> 10 years * 12 months = 10 year*year "Multiplying measurements"
> 10 years * 12 months / 24 months = 5 years "The model automatically
> simplifies units"
> 100 kilometers / 1 hour "Represents a speed of 100 km per hour"
> 0.01 / 1 month "Represent an interest rate of 10 % by month"
>
> page 8, figure 12:
> (GregorianYear number: 2005) next: 1 year "Returns GregorianYear number:
> 2006"
> (GregorianYear number: 2005) next: 12 months "Returns GregorianYear
> number: 2006"
> (GregorianYear number: 2005) next: 10 years "Returns GregorianYear number:
> 2015"
> (GregorianYear number: 2005) previous: 5 years "Returns GregorianYear
> number: 2000"
>
> page 8, figure 13:
> (GregorianYear number: 2005) next: 120 days "Signals an exception
> because 120 days can not be
> converted to years"
> '01/2005' asGregorianMonthOfYear next: 120 days "Signals an exception
> because 120 days can not be
> converted to months"
>
> page 8, figure 14:
> GregorianDay monday next: 4 days "Returns Friday"
> GregorianMonth january next: 2 months "Returns March"
> (GregorianMonth january dayNumber: 1) next: 2 days "Returns January 3rd "
>
> page 8, figure 17:
> "Returns an Interval with six elements, the years
> 2005,2007,2009,2011,2013 and 2015 inclusive".
> (GregorianYear number: 2005) to: (GregorianYear number: 2015) by: 2 years
> "Returns an Interval with six elements, the years
> 2005,2004,2003,2002,2001 and 2000 inclusive".
> (GregorianYear number: 2005) to: (GregorianYear number: 2000) by: -1 year
>
> page 10, figure 22:
> "06/01/2005 is a Thursday"
> aTimespan := Timespan from: '06/01/2005' asGregorianDate duration: 48
> hours.


ups... you are right, the papers were written before we implemented the #*
message to create measures... that's why documentation is not good! :-)
(Hey, just kidding, I don't want to get into that discussion again...)

> > > > And there is still the question where year comes from
> > > > > (please no shared pool).
> > > >
> > > > I did not see that question, but the answer is No.  The variable
> "year"
> > is
> > > > global. The same as month, day, January, February, Monday, etc.
> Maybe
> > you
> > > > will not like it,
> > >
> > > Global state sucks, no matter how well intended. I haven't tested it
> > > but I wouldn't be surprised if it causes problems with Monticello.
> >
> > Well, I do not agree... I used to think like that but I've changed my
> > mind... Object should be global if the entity they represent in real
> life is
> > global... but I understand that you don't like them.
> > From an Software Engineering point of view, global variables are not
> good...
> > but if you think software development as a learning process and you see
> the
> > Smalltalk image as the "state" of your knowledge about a specific
> domain(s),
> > having global objects (well know objects) is not bad....
> >
> > > > but I think that the time domain is so important in
> > > > writing software as the arithmetic domain,
> > >
> > > I think time sucks as a domain. Days that don't have 24 hours, minutes
> > > that don't have 60 seconds, years that don't have 365 days, different
> > > calendars, timezones, points in time with timezones and without
> > > timezones, timezones with more than two DST changes, different week
> > > start days, .... For every rule there's an exception and these can
> > > change at basically any time. Seriously, how much worse can it get?
> >
> >
> > I believe it is a really interesting domain!!  because of the things you
> > mention! because the exceptions it has makes it a very interesting and
> > challenging problem to design.
>
> Well, yeah. I just don't see how Chalten addresses many of these. Eg.
> it assumes days have 24 hours and minutes have 60 seconds.


Yes, as I said, it is a model of the GREGORIAN CALENDAR, and  in that
calendar, days have 24 hours and minutes 60 seconds...

> > > so if numbers are global (1, 2,
> > > > 3, etc) why not the time objects? They are well know entities of the
> > real
> > > > life....
> > >
> > > Numbers are literals not global variables.
> >
> > Well... that's an implementation detail... at the end they are global.
> They
> > are not "global variables" but "global objects" because the parser knows
> > about them.... so, at the end, they are global. And I think it is ok for
> > them to be global because it is almost impossible to think about a
> > programming language without numbers.... when we get a programming
> language
> > we are expecting to have at least the math to be model with it... (a
> > programming language without numbers as primitives is a very challenging
> > idea... I don't know if it is feasible...)
>
> I don't agree because they don't have the semantics of globals like
> identify (for everything but SmallIntegers).


I don't understand this... anyhow, at the end, from a conceptual point of
view, they are global objects (no global variables... I see variables just
as names we give to objects...)

The compiler/parser knows
> about them, that's all. But that certainly depends of POV.




> Anyhow, I think that when your knowledge about a problem domain (Smalltalk
> > image) is mature, you will end up with some global objects... We develop
> > financial software and I have to tell you that having "dollar", "euro",
> etc.
> > as global objects would help us a lot...   for example no need to
> declare them
> > on each unit test (of course we use test resources, but still), no need
> for
> > the final user to define them (they expect dollar, euro, peso, etc. as
> part
> > of the "kit")...
>
> Why don't you have them as global objects then?


Because  software evolution is not simple you know... and because not
everybody in the team agrees with me!!! :-).

Well, it was nice to talk about this issues with you.

Bye,
Hernan.



Cheers
> Philippe
>
> > Bye,
> > Hernan.
> >
> > > Cheers
> > > Philippe
> > >
> > > > Bye,
> > > > Hernan.
> > > >
> > > >
> > > > > Cheers
> > > > > Philippe
> > > > >
> > > > > >
> > > >
> >
> http://portal.acm.org/citation.cfm?id=1094964&coll=ACM&dl=ACM&CFID=20205775&CFTOKEN=19800555
> > > > > > )
> > > > > >
> > > > > > Hope this help.
> > > > > > Hernan.
> > > > > >
> > > > > > > Cheers
> > > > > > > Philippe
> > > > > > >
> > > > > > > > > > These objects are
> > > > > > > > > > polymorphic with numbers respect to the arithmetic
> messages
> > such
> > > > as
> > > > > > +,
> > > > > > > > -, *,
> > > > > > > > > > etc., that means that you can use them in arithmetic
> > formulas
> > > > > > > > >
> > > > > > > > > That's true to a certain extent in Chronos for example you
> > can:
> > > > > > > > > Timepoint now - (CalendarDuration months: 1)
> > > > > > > > > (CalendarDuration months: 1) * 5
> > > > > > > > > but you can't:
> > > > > > > > > 5 * (CalendarDuration months: 1)
> > > > > > > >
> > > > > > > > Ok, but it is not only the functionality what it is
> important
> > for
> > > > us...
> > > > > > for
> > > > > > > > us it is also important the way you "write" these things...
> for
> > > > example,
> > > > > > > > with Chalten/Aconcagua you can write:
> > > > > > > >
> > > > > > > > 5 * month ---> Equivalent to 5 * (CalendarDuration months:
> 1)
> > > > > > > > 5 * meter / (second * second) --> A measure of acceleration
> if
> > you
> > > > > > create
> > > > > > > > meter as a unit using Aconcagua
> > > > > > > > 1/10 * year --> Represents an interest rate of 10% yearly.
> > > > > > > >
> > > > > > > > As you can see, time measure are not only related only to
> the
> > time
> > > > > > domain
> > > > > > > > but used in other domains... that is way for us it is
> important
> > to
> > > > > > support
> > > > > > > > this type of behavior and in a DSL way...
> > > > > > > >
> > > > > > > > Bye,
> > > > > > > > Hernan.
> > > > > > > >
> > > > > > > > > > 5) And of course, I like Chalten's model more that
> Chronos
> > :-).
> > > > For
> > > > > > me
> > > > > > > > it is
> > > > > > > > > > easier to use, but this is just a matter of taste...
> > > > > > > > > >
> > > > > > > > > > There is a paper we wrote 2 years ago about the problems
> > that
> > > > the
> > > > > > > > Smalltalk
> > > > > > > > > > date classes have and the advantages of having a better
> > model.
> > > > If
> > > > > > you
> > > > > > > > are
> > > > > > > > > > interested on having better date and time classes, I
> > recommend
> > > > you
> > > > > > to
> > > > > > > > read
> > > > > > > > > > the paper... you may not like it, but at least you will
> see
> > > > other
> > > > > > people
> > > > > > > > > > ideas...
> > > > > > > > > > We use that model (Chalten) in a production system and
> we
> > > > believe it
> > > > > > > > allowed
> > > > > > > > > > us to avoid many common mistakes related to financial
> > > > systems....
> > > > > > but
> > > > > > > > hey,
> > > > > > > > > > that's just a feeling, nothing I can prove formally.
> > > > > > > > > >
> > > > > > > > > > I hope you can do something useful.
> > > > > > > > > > Bye,
> > > > > > > > >
> > > > > > > > > Chronos is a bit ugly in Squeak because Squeak does not
> > support
> > > > > > > > > namespaces which means that classes that model the same
> > concept as
> > > > > > > > > Squeak Chronology classes have different names (unless you
> > mess
> > > > with
> > > > > > > > > shared pools). Also loading it is a bit of a pain with
> > Monticello
> > > > > > > > > (this is the fault of Monticello and not Chronos).
> > > > > > > > >
> > > > > > > > > Cheers
> > > > > > > > > Philippe
> > > > > > > > >
> > > > > > > > > > Hernan.
> > > > > > > > > >
> > > > > > > > > >
> > > > > > > > > > On 4/16/07, J J <azreal1977 at hotmail.com > wrote:
> > > > > > > > > > > I have looked at Cronos but it is really huge, and the
> > classes
> > > > > > that
> > > > > > > > come
> > > > > > > > > > > with the image are already very close.  I will have to
> > look at
> > > > > > > > Chalten,
> > > > > > > > > > but
> > > > > > > > > > > what is wrong with a few upgrades to the classes that
> come
> > > > with
> > > > > > > > Squeak?
> > > > > > > > > > >
> > > > > > > > > > > >From: "Hernan Wilkinson" < hernan.wilkinson at gmail.com
> >
> > > > > > > > > > > >Reply-To: The general-purpose Squeak developers
> > > > > > > > > > > >list<
> > squeak-dev at lists.squeakfoundation.org
> > > > >
> > > > > > > > > > > >To: "The general-purpose Squeak developers
> > > > > > > > > > > >list"<
> > squeak-dev at lists.squeakfoundation.org
> > > > >
> > > > > > > > > > > >Subject: Re: Date classes
> > > > > > > > > > > >Date: Mon, 16 Apr 2007 14:28:09 -0300
> > > > > > > > > > > >
> > > > > > > > > > > >Before doing something with Date, I recommend you to
> take
> > a
> > > > look
> > > > > > at
> > > > > > > > > > > >"Chalten" or "Cronos". Chalten is in SqueakSource....
> I
> > think
> > > > > > Cronos
> > > > > > > > too.
> > > > > > > > > > > >
> > > > > > > > > > > >Hernan.
> > > > > > > > > > > >
> > > > > > > > > > > >On 4/16/07, J J < azreal1977 at hotmail.com> wrote:
> > > > > > > > > > > >>
> > > > > > > > > > > >>Hi all,
> > > > > > > > > > > >>
> > > > > > > > > > > >>I am doing some stuff with dates and I noticed the
> date
> > > > classes
> > > > > > that
> > > > > > > > > > come
> > > > > > > > > > > >>with the default Squeak image are very nice and very
> > close
> > > > to
> > > > > > having
> > > > > > > > > > > >>everything I would want.  But there are a few
> > > > inconsistencies
> > > > > > here
> > > > > > > > and
> > > > > > > > > > > >>there, and things missing that would make things
> easier.
> > > > > > > > > > > >>
> > > > > > > > > > > >>So what is the procedure to updating this?  I think
> it's
> > > > part of
> > > > > > the
> > > > > > > > > > core
> > > > > > > > > > > >>system so I probably can't just do a monicello
> package
> > > > update
> > > > > > > > > > > >>somewhere?  Do
> > > > > > > > > > > >>I have to do it through mantis?
> > > > > > > > > > > >>
> > > > > > > > > > > >>Thanks,
> > > > > > > > > > > >>Jason
> > > > > > > > > > > >>
> > > > > > > > > > >
> > > > > > > > > >
> > > > > > > >
> > > > > >
> > > >
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