def new_scope(names)
      values = names.map { |n| self[n] }
      self.class.new(names, values + extras, self)
    end
def new_scope(names)
      values = names.map { |n| self[n] }
      self.class.new(names, values + extras, self)
    end
Create a new argument scope using the prerequisite argument
 names.