StateServer

Opinionated :gen_statem shim for Elixir

A foolish consistency is the hobgoblin of little minds, adored by little statemen and philosophers and divines. With consistency a great soul has simply nothing to do.

-- Ralph Waldo Emerson

The unusual callback pattern of :gen_statem exists to allow code organization which we have better ways of achieving in Elixir (versus erlang). On the other hand we want to make sure users are using the canonical :gen_statem to leverage and prove out its battle-testedness

This library makes :gen_statem more consistent with how Elixir architects its GenServers.

There are three major objectives:

• Fanout the callback handling
• Unify callback return type with that of GenServer, and sanitize
• Enforce the use of a programmer-defined state graph.

Installation

The package can be installed by adding state_server to your list of dependencies in mix.exs:

def deps do
  [
    {:state_server, "~> 0.4.7"}
  ]
end

The docs can be found at https://hexdocs.pm/state_server.

Example

defmodule Demo do
  use StateServer, on: [flip: :off],
                   off: [flip: :on]

  def start_link(_), do: StateServer.start_link(__MODULE__, [], name: Demo)

  def init(state), do: {:ok, []}

  def handle_call(:flip, _from, state, data) do
    {:reply, data, transition: :flip, update: [state | data], timeout: {:foo, 100}}
  end

  def handle_transition(start, tr, data) do
    IO.puts("transitioned from #{start} through #{tr}")
    :noreply
  end

  def handle_timeout(_, _, _) do
    IO.puts("timed out!")
    :noreply
  end
end


iex(2)> Demo.start_link(:ok)
{:ok, #PID<0.230.0>}
iex(3)> GenServer.call(Demo, :flip)
transitioned from on through flip
[]
timed out!
iex(4)> GenServer.call(Demo, :flip)
transitioned from off through flip
[:on]
timed out!
iex(5)> GenServer.call(Demo, :flip)
transitioned from on through flip
[:off, :on]
timed out!