Chapter 17

Exercise: OTP-Servers-1, 2, 4, 5

defmodule Stack.Server do
  use GenServer

  def start_link(stack) do
    GenServer.start_link(__MODULE__, stack, name: __MODULE__)
  end

  def pop do
    GenServer.call(__MODULE__, :pop)
  end

  def push(value) do
    GenServer.cast(__MODULE__, {:push, value})
  end

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

  def handle_call(:pop, _from, [head | tail]) do
    {:reply, head, tail}
  end

  def handle_cast({:push, value}, _state) when is_integer(value) and value < 10 do
    System.halt(1)
  end

  def handle_cast({:push, value}, current_stack) do
    {:noreply, [value | current_stack]}
  end

  def terminate(reason, state) do
    IO.puts("""
    Stack server terminated.
      reason: #{inspect(reason)}
      state: #{inspect(state)}
    """)
  end
end

{:ok, pid} = GenServer.start_link(Stack.Server, [5, "cat", 9])
5 = GenServer.call(pid, :pop)
"cat" = GenServer.call(pid, :pop)
9 = GenServer.call(pid, :pop)
GenServer.cast(pid, {:push, :hello})
GenServer.cast(pid, {:push, "world"})
"world" = GenServer.call(pid, :pop)
:hello = GenServer.call(pid, :pop)
GenServer.stop(pid)

Exercise: OTP-Servers-3

{:ok, pid} = GenServer.start_link(Stack.Server, ["hello", 42, :world], name: :stack)
"hello" = GenServer.call(:stack, :pop)
GenServer.stop(:stack)

Exercise: OTP-Servers-5

Stack.Server.start_link([])
Stack.Server.pop()