Elixir example of trapping exit

example_trap_exit.exs

defmodule A do
  def start_link do
    GenServer.start_link(__MODULE__, :ok, name: :A)
  end

  def fun(fun_loving_person) do
    GenServer.call(fun_loving_person, :have_fun)
  end

  def init(:ok) do
    {:ok, %{}}
  end

  def handle_call(:have_fun, _from, state) do
    ######################### Raise an error that will kill process :A
    raise "TooMuchFun"
    #########################
    {:reply, :ok, state}
  end
end

defmodule B do
  def start_link do
    GenServer.start_link(__MODULE__, :ok, name: :B)
  end

  def spread_fun(fun_seeker) do
    GenServer.call(:B, {:spread_fun, fun_seeker})
  end

  def init(:ok) do
    {:ok, %{}}
  end

  def handle_call({:spread_fun, fun_seeker}, _from, state) do
    ######################### Monitor
    Process.monitor(:A)
    #########################
    result = A.fun(fun_seeker)
    {:reply, result, state}
  rescue
    _ -> IO.puts "Too much fun rescued"
    {:reply, :error, state}
  end

  ######################### Receive :DOWN message because I monitor A
  def handle_info({:DOWN, _ref, :process, :A, _reason}, state) do
    IO.puts "################# DOWN DOWN DOWN ###########"
    {:noreply, state}
  end
  #########################

end

{:ok, a} = A.start_link
{:ok, _b} = B.start_link
result = B.spread_fun(a)
IO.puts "#{inspect result}"