See https://groups.google.com/forum/#!topic/elixir-lang-talk/8wn5RM-stwk.

case_error.exs

defmodule Test do
  def test(a, b, c) do
    case true do
      a == b && b == c -> :equilateral
      a == b || b == c -> :isosceles
      _ -> :scalene
    end
  end
end