Moved to Tumblr

--> http://sneakybits.tumblr.com/

Ruby-Processing and java.lang.ExceptionInInitializerError

rp5 run samples/jwishy.rb 
RubyGlobal.java:135:in `createGlobals': java.lang.ExceptionInInitializerError
    from Ruby.java:939:in `init'
    from Ruby.java:172:in `newInstance'
    from Main.java:199:in `run'
    from Main.java:110:in `run'
    from Main.java:94:in `main'

... the culprit was the alternative version of the JRE I was using (OpenJDK). After swtiching to the standard Sun JDK everything worked fine.

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:

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:

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

python-xml woes

Python ImportErrors like the following (stemming from the recent deprecation of the python-xml library in Ubuntu):

Failed to load application: No module named ext

... can be easily addressed by:

sudo apt-get install python-xml
export PYTHONPATH=$PYTHONPATH:/usr/lib/python2.5/site-packages/oldxml

This caused me a good few hours' grief earlier today.