First class lazy Interval

[Andrei Alexandrescu]

Daniel Keep wrote:
> I don't think this should be in the language... it just feels like there
> isn't enough use for it.  Especially not when you can implement it as a
> library.
> 
> As proof, I've attached an implementation of an integral interval.
> Here's a sample of usage (the program prints this if you run it):

This is pretty darn cool!

Andrei