State machine driving registrations

registartion.rb

  state_machine do 
    state :email, :exit => lambda {|reg| reg.errors.clear }
    state :age, :exit => lambda {|reg| reg.errors.clear }
    state :complete, :enter => :register_user 

    event :next do 
      transitions :from => :email, :to => :age, :guard => :guard_to_age
      transitions :from => :age, :to => :complete, :guard => :guard_to_complete
      # do not allow complete => complete
    end 
  end