Golem Statemachine

Following a frustrating week with the acts_as_state_machine/AASM plugin, I ended up writing my own finite state machine library for Ruby.

It's called Golem, and it's now on Github, here: http://github.com/zuk/golem_statemachine/tree/master

The code is cleaner than AASM's (or at least I think so), which should make debugging less frustrating. There's also a nice DSL for defining the state machine.

For example, to implement this statemachine:

You would define it like so:

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1. define_statemachine do  
2.   initial_state :HUNGRY  
3.   
4.   state :HUNGRY do  
5.     on :eat do  
6.       transition :to => :SATIATED, :if => :likes?  
7.       transition do  
8.         action do |monster|   
9.           puts "#{monster} says BLAH!!"  
10.         end  
11.       end  
12.     end  
13.   end  
14.   
15.   state :SATIATED do  
16.     enter do |monster|  
17.       puts "#{monster} says BURP!!!"  
18.     end  
19.   end  
20. end  

define_statemachine do
  initial_state :HUNGRY

  state :HUNGRY do
    on :eat do
      transition :to => :SATIATED, :if => :likes?
      transition do
        action do |monster| 
          puts "#{monster} says BLAH!!"
        end
      end
    end
  end

  state :SATIATED do
    enter do |monster|
      puts "#{monster} says BURP!!!"
    end
  end
end

The state machine definition goes inside your Ruby class (or ActiveRecord model), endowing the class with finite state machine behavior:

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1. require 'golem'  
2.   
3. class Monster  
4.   include Golem  
5.   
6.   attr_accessor :state  
7.   
8.   def initialize(name)  
9.     @name = name  
10.   end  
11.   
12.   def to_s  
13.     @name  
14.   end  
15.   
16.   def likes?(food)  
17.     food.kind_of?(String)  
18.   end  
19.   
20.   define_statemachine do  
21.     # ...  
22.   end  
23. end  
24.   
25. m = Monster.new("Stringosaurus")  
26. puts m.current_state # ==> :HUNGRY  
27. m.eat(12345)         # ==> "Stringosaurus says BLAH!!"  
28. puts m.current_state # ==> :HUNGRY  
29. m.eat("abcde")       # ==> "Stringosaurus says BURP!!"  
30. puts m.current_state # ==> :SATIATED  

require 'golem'

class Monster
  include Golem

  attr_accessor :state

  def initialize(name)
    @name = name
  end

  def to_s
    @name
  end

  def likes?(food)
    food.kind_of?(String)
  end

  define_statemachine do
    # ...
  end
end

m = Monster.new("Stringosaurus")
puts m.current_state # ==> :HUNGRY
m.eat(12345)         # ==> "Stringosaurus says BLAH!!"
puts m.current_state # ==> :HUNGRY
m.eat("abcde")       # ==> "Stringosaurus says BURP!!"
puts m.current_state # ==> :SATIATED