有限状態機械のサンプルコード

fsm.ex

defmodule StateServer do
  @transitions %{
    initial: %{ receive_order: :check_stock },
    check_stock: %{ purchase: :ready_for_snipment },
    ready_for_snipment: %{ snipment: :package_arrive },
    package_arrive: %{ initial: :initial }
  }

  def run do
    spawn(fn -> server(:initial) end)
  end

  def server(state) do
    receive do
      { :msg, type, from } ->
        next = Map.get(@transitions, state) |> Map.get(type, state)
        send(from, next)
        server(next)
    end
  end
end

# client
server_pid = StateServer.run()
send(server_pid, { :msg, :receive_order, self() })
send(server_pid, { :msg, :purchase, self() })
send(server_pid, { :msg, :snipment, self() })
send(server_pid, { :msg, :initial, self() })