I want to write acts_as List instead of acts_as_list. Also it help to abstract self.included idiom

acts_as.rb

module ActsAs
end

class ActiveRecord::Base
  def self.const_missing name
    if ActsAs.const_defined?(name)
      ActsAs.const_get(name.to_s)
    else
      raise NameError.new("uninitialized constant #{name}", name)
    end
  end

  def self.acts_as const, *options, &block
    extend(const.const_get('ClassMethods')) if const.const_defined?('ClassMethods')
    include const.const_get('InstanceMethods') if const.const_defined?('InstanceMethods')

    const.send(:setup, self, *options, &block) if const.respond_to?(:setup)
  end
end

acts_as_list.rb

module ActsAs
  module List
    def self.setup cl, options={}, &block
      cl.class_eval <<-EOV
        def default_position
          #{options[:default_position]}
        end
      EOV
    end

    module ClassMethods
      def acts_as_list_class
        "::#{self.name}"
      end
    end

    module InstanceMethods
      def insert_at number
        @position = number
      end
    end
  end
end

models.rb

class TodoItem < ActiveRecord::Base
  belongs_to :todo_list
  acts_as List, :scope => :todo_list
end

class TodoList < ActiveRecord::Base
  has_many :todo_items, :order => "position"
end