# File lib/ruby_parser_extras.rb, line 504
  def backref_assign_error ref
    # TODO: need a test for this... obviously
    case ref.first
    when :nth_ref then
      raise "write a test 2"
      raise SyntaxError, "Can't set variable %p" % ref.last
    when :back_ref then
      raise "write a test 3"
      raise SyntaxError, "Can't set back reference %p" % ref.last
    else
      raise "Unknown backref type: #{ref.inspect}"
    end
  end