Retrieve the instructions for the rule.

def instructions(self):
        """
        Retrieve the instructions for the rule.
        """

        if self._instructions is None:
            # Compile the rule into an Instructions instance; we do
            # this lazily to amortize the cost of the compilation,
            # then cache that result for efficiency...
            self._instructions = parser.parse_rule(self.name, self.text)

        return self._instructions