def new(self, val):
        """Add a new value to me.

        Args:
            val (LispVal): The value to be added.

        Returns:
            LispVal: The added value.

        Raises:
            ~parthial.errs.LimitationError: If I already contain the maximum
                number of elements.
        """
        if len(self.things) >= self.max_things:
            raise LimitationError('too many things')
        self.things.add(val)
        return val
Add a new value to me.

        Args:
            val (LispVal): The value to be added.

        Returns:
            LispVal: The added value.

        Raises:
            ~parthial.errs.LimitationError: If I already contain the maximum
                number of elements.