def evaluate_step(step)
      return step if step.is_a? Integer
      return evaluate_step_proc(step) if step.is_a? Proc
      fail ArgumentError, 'step is not an Integer or a Proc'
    end
def evaluate_step(step)
      return step if step.is_a? Integer
      return evaluate_step_proc(step) if step.is_a? Proc
      fail ArgumentError, 'step is not an Integer or a Proc'
    end
Returns the number to add to the current increment

 @param [ Object ] step The +Integer+ to be returned
 or +Proc+ to be evaluated

 @raise [ ArgumentError ] When +step+ is not an +Integer+ or +Proc+

 @return [ Integer ] The number to add to the current increment