Return a unicode object with the MATCH representation of this expression.

def to_match(self):
        """Return a unicode object with the MATCH representation of this expression."""
        self.validate()

        mark_name, field_name = self.location.get_location_name()
        validate_safe_string(mark_name)

        if field_name is not None:
            raise AssertionError(u'Vertex location has non-None field_name: '
                                 u'{} {}'.format(field_name, self.location))

        return mark_name