First class lazy Interval

[Don]

Joel C. Salomon wrote:
> Daniel Keep wrote:
>> Yes, a..b is very nice.  It's also a bad syntax for intervals.  As Don
>> keeps pointing out, you can't have an interval that includes int.max
>> with that syntax.
> 
> 4 .. int.$
> 
> —Joel Salomon

I love that real.$ is the number that's even bigger than infinity <g>.
What if the range is stored in variables?

x[a..b];
How can you set b so that it includes x[int.max]?

BTW, I'm not merely being negative, I'd love for one of these schemes to 
work.