FunServer is a GenServer in which instead of passing parameters to GenServer.call/3 or GenServer.cast/2 and then writing the corresponding callbacks with the necessary functionality you pass functions (i.e. handlers).

Essentially FunServer is just a simple wrapper over GenServer, which takes the approach of passing down functions instead of messages.

example

Example

Basically instead of using handle_call or handle_cast callbacks, functions are being passed that get executed in the corresponding callback.

This is an example of a simple FunServer Stack Server.

defmodule Server do
  use FunServer

  def start_link(_args) do
    FunServer.start_link(__MODULE__, handle_init([]), name: __MODULE__)
  end

  def push(value) do
    value
    |> handle_push()
    |> FunServer.async(__MODULE__)
  end

  def pop(value) do
    value
    |> handle_pop()
    |> FunServer.sync(__MODULE__)
  end

  defp handle_init(args) do
    fn -> {:ok, args} end
  end

  defp handle_push(value) do
    fn state ->
      {:noreply, [value | state]}
    end
  end

  defp handle_pop(value) do
    fn _from, [value | new_state] ->
      {:noreply, value, new_state}
    end
  end
end

The callbacks FunServer wraps around are the following:

• init/1
• handle_call/3
• handle_cast/2
• handle_continue/2

The rest of the callbacks for GenServer can be handled normally:

• handle_info/2
• terminate/2
• code_change/3
• format_status/2