string_state_machine.rb

require 'rubygems'
require 'state_machine'

class StringStateMachine

  state_machine :state, :initial => :s do

    event :a do
      transition :s => :q
    end

    event :b do
      transition :q => :r
      transition :r => same
    end

    event :c do
      transition :q => :v
      transition :r => :t
      transition :v => :u
      transition :u => same
    end

    event :d do
      transition :q => :t
      transition :v => :t
      transition :u => :t
    end
    
  end

end