uptoLib.upto : int -> int -> int list
Builds a list of integers.
An invocation upto b t returns the list
[b, b+1, ..., t], if b <= t. Otherwise, the
empty list is returned.
Never fails.
> upto 2 10;
val it = [2, 3, 4, 5, 6, 7, 8, 9, 10]: int list