age-on-planet exercise in elixir

elixir/space-age/space_age.exs

@@ -0,0 +1,25 @@
+defmodule SpaceAge do
+  @type planet :: :mercury | :venus | :earth | :mars | :jupiter
+                | :saturn | :neptune | :uranus
+
+  @seconds_per_earth_year 31557600
+  @orbit_seconds %{
+   mercury:   0.2408467  * @seconds_per_earth_year,
+   venus:     0.61519726 * @seconds_per_earth_year,
+   earth:     1.00000000 * @seconds_per_earth_year,
+   mars:      1.8808158  * @seconds_per_earth_year,
+   jupiter:  11.862615   * @seconds_per_earth_year,
+   saturn:   29.447498   * @seconds_per_earth_year,
+   uranus:   84.016846   * @seconds_per_earth_year,
+   neptune: 164.79132    * @seconds_per_earth_year,
+  }
+
+  @doc """
+  Return the number of years a person that has lived for 'seconds' seconds is
+  aged on 'planet'.
+  """
+  @spec age_on(planet, pos_integer) :: float
+  def age_on(planet, seconds) do
+    seconds / @orbit_seconds[planet]
+  end
+end