class Array
  # Returns the positive ordinal index given
  # a cardinal position, 1 to n or -n to -1.
  #
  #   require 'facet/array/pos'
  #
  #   [1,2,3,4,5].pos(1)   #=> 0
  #   [1,2,3,4,5].pos(-1)  #=> 4
  #
  def pos(i)
    if i > 0
      return i - 1
    else
      self.length + i
    end
  end
end