class ActiveSupport::Callbacks::CallbackChain

def compile(key=nil, object=nil)
  method = []
  method << "value = nil"
  method << "halted = false"
  each do |callback|
    method << callback.start(key, object)
  end
  if config[:rescuable]
    method << "rescued_error = nil"
    method << "begin"
  end
  method << "value = yield if block_given? && !halted"
  if config[:rescuable]
    method << "rescue Exception => e"
    method << "rescued_error = e"
    method << "end"
  end
  reverse_each do |callback|
    method << callback.end(key, object)
  end
  method << "raise rescued_error if rescued_error" if config[:rescuable]
  method << "halted ? false : (block_given? ? value : true)"
  method.compact.join("\n")
end

def initialize(name, config)
  @name = name
  @config = {
    :terminator => "false",
    :rescuable => false,
    :scope => [ :kind ]
  }.merge(config)
end