module Sass::Callbacks

def define_callback(name)
  class_eval <<RUBY
on_#{name}(&block)
sass_callbacks ||= {}
_sass_callbacks[#{name.inspect}] ||= []) << block
run_#{name}(*args)
turn unless @_sass_callbacks
turn unless @_sass_callbacks[#{name.inspect}]
sass_callbacks[#{name.inspect}].each {|c| c[*args]}
ate :run_#{name}

end