class AST::Node

def updated(type=nil, children=nil, properties=nil)
  new_type       = type       || @type
  new_children   = children   || @children
  new_properties = properties || {}
  if @type == new_type &&
      @children == new_children &&
      properties.nil?
    self
  else
    copy = original_dup
    copy.send :initialize, new_type, new_children, new_properties
    copy
  end
end