defmodule Haversine do
  @v  :math.pi / 180
  @r  6372.8            # km for the earth radius
  def distance({lat1, long1}, {lat2, long2}) do
    dlat  = :math.sin((lat2 - lat1) * @v / 2)
    dlong = :math.sin((long2 - long1) * @v / 2)
    a = dlat * dlat + dlong * dlong * :math.cos(lat1 * @v) * :math.cos(lat2 * @v)
    @r * 2 * :math.asin(:math.sqrt(a))
  end
end

bna = {36.12,  -86.67}
lax = {33.94, -118.40}
IO.puts Haversine.distance(bna, lax)