rotate.rb

module IntegerAssertions
  
  def negative?
    self < 0
  end
  
  def positive?
    self > 0
  end
  
end

module Rotate
  
  def rotate(index)
    range = if index.positive?
              (0..index).to_a
            elsif index.negative?
              (index..0).to_a
            else
              []
            end
    
    rotated_indexes = range.to_a.inject([]) do |rotated, i|
      (v = self.pop).nil? ? rotated : rotated.push(v)
    end
    
    self + rotated_indexes
  end
  
end

Integer.send(:include, IntegerAssertions)
Array.send(:include, Rotate)

puts [1,2,3,4,5].rotate(-5).inspect