Re: Range Types: empty ranges

On Fri, 2011-02-11 at 13:08 -0600, Kevin Grittner wrote:
> It makes more sense in the context of a range of some type with a
> clearly defined granularity.  Our accounting system, for example,
> can assign a new range of receipt IDs for each calendar year.  If
> you want a variable to represent the receipts for traffic receipts
> for 2012, you might, in preparation for the upcoming year, define
> something to declare the range as '[12TR000001,12TR000001)'.  When
> the first receipt is assigned as 12TR000001, that is updated to
> '[12TR000001,12TR000002)'.  Just as an off-the-cuff example.
>  
> Basically, with a type having well-defined granularity, a [) range
> could usefully represent, "start to last used", and start out empty.

I think this is trying to make a range into something that's not. A
range is a set of values with the additional constraint that there are
no "gaps".

Trying to incorporate a "start value" is adding extra information in
there, and it's not really a part of the same algebra. It sounds more
like a contiguous sequence with a "start value" and a "current value" to
me.

Sequences have other useful operations, like "next", and things like
"overlaps" don't really seem to make sense (at least not in a practical
way that I can tell).

Regards,Jeff Davis