On Fri, Dec 07, 2018 at 01:37:36PM +0000, Mark Dickinson wrote:

> I'd personally prefer that floats not be accepted;

Agreed. We can always add support for floats later, but its hard to 
remove it if it turns out to be problematic.

We ought to require n, r (or n, k) to be non-negative ints with 0 <= r 
<= n. Extending this to negative ints or floats is probably YAGNI, but 
if somebody does need it, they can request an enhancement in the future.