def eval(self, construct):
        """Evaluate an expression returning its value.

        The Python equivalent of the CLIPS eval command.

        """
        data = clips.data.DataObject(self._env)

        if lib.EnvEval(self._env, construct.encode(), data.byref) != 1:
            raise CLIPSError(self._env)

        return data.value
Evaluate an expression returning its value.

        The Python equivalent of the CLIPS eval command.