On Thu, Feb 19, 2009 at 05:05:32PM -0600, Dave Rolsky wrote:
> On Thu, 19 Feb 2009, Darren Duncan wrote:
>
>> As per my previous post, I recommend having both, like this:
>>
>> role Instant {
>> has Int $.year;
>> ...
>> has Rat $.second;
>> }
>>
>> role DateTime is Instant where defined $.year ... and defined $.second;
>>
>> role Date is Instant where defined $.year ... and defined $.day;
>>
>> role Time is Instant where defined $.hour ... and defined $.second;
>>
>> So something like that. So Date and Time mean all Date|Time details,
>> and DateTime means all details of both. And Instant means any
>> combination of defined or not of said member attributes. And that's
>> actually why I advocated Instant as a name for that
>> more-broad-than-DateTime thing.
>
> Is there a way in which a class which does the Date role could change the
> type $.year so it was "Int|Undef"?
Doesn't have to. Int already comes with an undefined value known as
Int, aka the protoobject. Only subset types (and their cousins, native
types) can restrict values to being defined, and they do so on the
primarily on basis of constraints, and only secondarily on whether the
underlying storage can represent an undefined value. So an Int can be
undefined, but an int can't. A Num can be undefined, but a num can only
approximate that with NaN.
So the built-in types may certainly represent incomplete information.
That being said, I'm thinking that all actual times represented by
floats in Perl are TAI time, not the Unix pseudo time with hidden
leap seconds. I sure wish they'd done away with civic leap seconds
in 2000 and said we'll put in a leap minute or two on century breaks...
Well, leaving that rant aside, I'm still tempted to say that times
in Perl 6 are TAI seconds since 2000. Standard TAI would work too.
In any case, I think if Perl is to be taken seriously for scientific
computing its native seconds shouldn't be varying in length. And I
also think with the advent of ubiquitous GPS we're getting to the
point where nearly all computers will know the correct atomic time.
Time is on our side, as it were...
Larry
