sztheory/gen_fsm

Elixir wrapper around OTP's gen_fsm

GenFSM

Elixir wrapper around Erlang's OTP gen_fsm.

Motivation

Elixir deprecated its wrapper around OTP's gen_fsm from the standard library because it is difficult to understand and suggested that developers seek other finite state machine implementations.

This is understandable, but some of us still need/prefer to use the OTP gen_fsm.

I took the basis of Elixir's old GenFSM.Behaviour and added some additional convenience methods. Currently missing are the enter_loop methods.

Usage

The following example implement a simple state machine with two states, martin and paul. The state machine will initialize into the martin state, when the state machine receive :hello as the input it will transition between the states, from martin to paul and "Hello, Paul" will get printed to the console.

defmodule Conversation do
  use GenFSM

  def start_link() do
    GenFSM.start_link(__MODULE__, :na)
  end

  def hello(pid) do
    GenFSM.send_event(pid, :hello)
  end

  def init(:na), do: {:ok, :martin, nil}

  def martin(:hello, nil) do
    IO.puts "Hello, Paul"
    {:next_state, :paul, nil}
  end

  def paul(:hello, nil) do
    IO.puts "Hello, Martin"
    {:next_state, :martin, nil}
  end
end

A conversation could go like this:

iex(2)> {:ok, pid} = Conversation.start_link
{:ok, #PID<0.165.0>}
iex(3)> Conversation.hello pid
Hello, Paul
:ok
iex(4)> Conversation.hello pid
Hello, Martin
:ok
iex(5)>

Installation

If available in Hex, the package can be installed as:

1. Add gen_fsm to your list of dependencies in mix.exs:

   def deps do [{:gen_fsm, "~> 0.1.0"}] end

Documentation

Complete API documentation can be found at http://erlang.org/doc/man/gen_fsm.html and OTP design principal documentation lives at http://erlang.org/doc/man/gen_fsm.html