                     %Entry{value: value, expires_at: now() + expires_in})
     {:reply, value, state}
   end
+
+  defp now do
+    :os.system_time(:second)
+  end
 end

  end

  defp get(key) do
    case GenServer.call(__MODULE__, {:get, key}) do
      :error -> {:not_found}
      {:ok, result} -> if now() >= result.expires_at do
        {:not_found}

        {:found, result.value}
      end
    end
    {:reply, value, state}
  end

  def handle_call({:set, key, value, expires_in}, _from, state) do
