Casting macaddr types to text

I'm trying to do this:

hdb=> select * from interface where mac like '08:%';
ERROR:  Unable to identify an operator '~~' for types 'macaddr' and
'unknown'
        You will have to retype this query using an explicit cast

There's no like operator (~~) defined for mac. Ok, fine. *BUT*, nor is there
a cast to text either:

hdb=> select * from interface where mac::text like '08:%';
ERROR:  Cannot cast type 'macaddr' to 'text'

Why? It seems clear to me that there is a well-defined cast to text type,
and in the absence of a like operator...

Advice?

Regards,
Phil

+----------------------------------+
| Phil Mayers, Network Support     |
| Centre for Computing Services    |
| Imperial College                 |
+----------------------------------+