>  >  def count(lower, upper, incr)
>  >   raise "Require lower <= upper" if lower > upper
>  >   raise "Require incr > 0" unless incr > 0
>  >   while lower <= upper do
>  >     yield lower
>  >     lower += incr
>  >   end
>  >  end
> 
>  Isn't that Numeric#step (ignoring exceptions)?

Why, yes, it would appear to be so... Learn something every day, I do.
=)