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Supported Features

• Multiple state machines per class each of them acting independently
• Find errors in state machine definitions as early as possible
• Transition guards
• Multiple actions executed on transitions
• Multiple actions executed on entering and exiting a state

State Machine Examples

We start implementing the State Machine, by giving some examples of state machines we want to run.

class Microwave
  state_machine :microwave do  # name should be optional, if the name is not present, it should have a default name
                               # we give state machines names, so we can pun many machines inside a class
    initial_state :unplugged # initial state should be optional, if the initial state is not present, the initial state will be the first defined state

    state :unplugged

    state :plugged

    state :door_opened do
      enter :light_on            # enter should be executed on entering the state
      exit  :light_off           # exit method should be executed on exiting the state
    end

    state :door_closed

    state :started_in_grill_mode do
      enter lambda { |t| p "Entering hate" }   # should have support for Procs
      exit  :grill_off
    end

    state :started do
      enter :microwaves_on
      exit  :microwaves_off
    end

    event :plug_in do
      transition :from => :unplugged, :to => :plugged
    end

    event :open_door do
      transition :from => :plugged, :to => :door_opened
    end

    event :close_door do
      transition :from => :door_opened, :to => :door_closed, :on_transition => :put_food_in_the_microwave # we can put many actions in an Array for the on_transition parameter
    end

    event :start do
      transition :from => :door_closed, :to => [:started, :started_in_grill_mode], :on_transition => :start_spinning_the_food, :guard => :grill_button_pressed?    # the method grill_button_pressed? should choose the next state 
    end

    event :stop do
      transition :from => [:started, :started_in_grill_mode], :to => :door_closed
    end
  end  
end 

class Dice

  state_machine do
    state :one
    state :two
    state :three
    state :four
    state :five
    state :six

    event :roll do
      transition :from => [:one, :two, :three, :four, :five, :six],
                 :to => [:one, :two, :three, :four, :five, :six],
                 :guard => :roll_result,
                 :on_transition => :display_dice_rolling_animation
    end
  end

  def roll_result
    # return one of the states
  end

  def display_dice_rolling_animation
    # draw the new position of the dice
  end
end

class User
  state_machine do
    state :pending # first one is initial state
    state :active
    state :blocked # the user in this state can't sign in

    event :activate do
      transition :from => [:pending], :to => :active, :on_transition => :do_activate
    end

    event :block do
      transition :from => [:pending, :active], :to => :blocked
    end
  end    
end

Notes

For classes with multiple state machines, the state names, machine names must be unique per class.

The same thing with the event names.