Re: Range Types: << >> -|- ops vs empty range

On Fri, February 11, 2011 19:02, Josh Berkus wrote:
>
>> "empty range"
>> =============
>> Zero length?
>>   If so, is it fixed at some point, but empty?
>>     '(x,x)'?
>>     '[x,x)'?
>
> Neither of the above should be possible, I think.  The expression "(x"
> logically excludes the expression "x)".
>
> However, "[x,x]" would be valid, and would be a zero-length interval at
> the point "x".
>
>> Is it everything?
>>   '[-inf,+inf]'?
>
> No, that's "everything" which is a different concept.  The above also
> ought to be possible, and overlap everything.
>
>> Is it really meaningfully distinct from NULL?
>
> Yes.  NULL means "I don't know".  If a range type IS NULL, then any
> operation performed with it ought to be NULL.  Hence:
>
> IF y > x, THEN:
>
> [x,x] << [y,z) == TRUE
> [x,x] -|- (x,y] == TRUE
> NULL << [y,z} IS NULL
> [-inf,+inf] << [y,z) == FALSE
>
> I can imagine using all of these constructs in actual applications.  In
> fact, I have *already* used [-inf,+inf]
>

You say yes, but you don't mention "empty range".

Maybe we can indeed do without the concept of an empty-range?;
it might simplify implementation as well as usage.

I'm not decided, but I do find it hard to find a plausible use-case for it.