traffic_light.rb

# State Machine - http://en.wikipedia.org/wiki/State_machine
# Traffic Light - http://en.wikipedia.org/wiki/Traffic_light
#      Workflow - http://en.wikipedia.org/wiki/Workflow
#        Wizard - http://en.wikipedia.org/wiki/Wizard_%28software%29
# state_machine - https://github.com/pluginaweek/state_machine
# traffic_light - https://gist.github.com/735281

class TrafficLight
  WAIT_TIME_IN_SECONDS = 5

  state_machine :state, :initial => :red
    state :red
    state :yellow
    state :green
    state :blinking_red
    state :blinking_yellow

    after_transition :on => :slow, :do => :wait_then_stop
    
    event :go do
      transition :from => :red, :to => :green
    end
    
    event :slow do
      transition :from => :green, :to => :yellow
    end
    
    event :stop do
      transition :from => [:yellow, :blinking_yellow, :blinking_red], :to => :red
    end
    
    event :proceed_with_caution do
      transition :from => any, :to => :blinking_yellow
    end
    
    event :stop_before_proceeding do
      transition :from => any, :to => :blinking_red
    end
  end

  def wait_then_stop
    sleep WAIT_TIME_IN_SECONDS
    stop
  end
end  

State Machine (Finite-State Machine) - http://en.wikipedia.org/wiki/State_machine

Traffic Light - http://en.wikipedia.org/wiki/Traffic_light

Workflow - http://en.wikipedia.org/wiki/Workflow

Wizard - http://en.wikipedia.org/wiki/Wizard_%28software%29

state_machine - https://github.com/pluginaweek/state_machine

traffic_light - https://gist.github.com/735281