state_machine.rb

#http://github.com/pluginaweek/state_machine
require 'state_machine'
class A
	state_machine :initial=>:stop do

		event :change do
			transition :stop=>:start,:start=>:stop
		end	
		
		before_transition do |a,_|
			p [:before,a.state]
		end	
		after_transition :on=>:change do |a,t|
			a.info
		end				
		
	end	
	def info
		p [:after,@state]
	end	
end	
a=A.new	
p a.state
2.times do	
	a.change	
end