Programmer Passport: OTP

Anatomy of a GenServer

In the last chapter, we built a basic calculator, with and without a GenServer. Let’s look back at that program. We’ll focus on a a couple major messages: add and state:

def start(initial_state) do
  spawn(fn -> run(initial_state) end)
end

def run(state) do
  state
  |> listen
  |> run
end

def listen(state) do
  receive do
    {:add, number} ->
      Core.add(state, number)

    {:state, pid} ->
      send(pid, {:state, state})
      state
  end
end

This program has the same basic shape of many other Elixir programs. There are two major parts, the lifecycle management and the message process. Our lifecycle management is a simple start function to start a process. The run and listen messages ...