Hume

Hume is a library for building event-sourced state machines in Elixir.

It provides a framework for defining state machines that handle events, maintain state, and take snapshots for efficient recovery. The library leverages Elixir's GenServer for process management and supports ETS for event storage, including ownership transfer via a dedicated "heir" process.

Features

• Define state machines using a simple behavior (Hume.Projection)
• Handle and persist events to an event store (in-memory or ETS-based)
• Take snapshots of the current state for efficient recovery
• Transfer ETS table ownership using a dedicated heir process
• Utilities for ordered event sequences via Hume.EventOrder

Usage

To get started with Hume, define a state machine by creating a module that uses Hume.Projection and implements the required callbacks:

defmodule MyProjection do
  use Hume.Projection, use_ets: true, store: Hume.EventStore.ETS

  @impl true
  def init_state(_), do: %{}

  @impl true
  def handle_event({:add, key, value}, state),
    do: {:ok, Map.put(state || %{}, key, value)}

  @impl true
  def handle_event({:remove, key}, state),
    do: {:ok, Map.delete(state || %{}, key)}
end

Hume.EventStore.ETS.start_link([])
{:ok, pid} = Hume.start_link(MyProjection, stream: MyStream)

{:ok, _} = Hume.publish(Hume.EventStore.ETS, MyStream, {:add, :foo, 42})
%{foo: 42} = Hume.state(pid)
{:ok, _} = Hume.publish(Hume.EventStore.ETS, MyStream, {:remove, :foo})
%{} = Hume.state(pid)

Installation

Add hume to your list of dependencies in mix.exs:

def deps do
  [
    {:hume, "~> 0.0.1"}
  ]
end

Documentation

Documentation can be generated with ExDoc:

mix docs

Once published, the docs can be found at https://hexdocs.pm/hume.