function signature dropthrough a bit like case

   1: price_by_age({car,Age}) -> 10 * (10 - Age);

   2: price_by_age({boat,Age}) -> 20 * (20 - Age).

is equivalent to

   1: price_by_age(Vehicle) ->

   2:     case Vehicle of

   3:         {car,Age} -> 10 * (10 - Age);

   4:         {boat,Age} -> 20 * (20 - Age)

   5:     end.