CAST ON NEW TYPE - Mailing list pgsql-hackers

Hi,

I create a new type that work well, but when
i use the cast function on my new type like this i have an error:
(other fucntion like substring don't work too )

select bare_code::text from ean_article;
ERROR:  Cannot cast type 'ean13' to 'text'

What can i do in my new type in order to use cast ???

Best regards,

PEJAC Pascal