Bit String Manipulation - Mailing list pgsql-general

Hi, I am having problems manipulating bit strings.

CREATE TABLE lookup(
fname TEXT PRIMARY KEY,
digest BIT VARYING
);

I am trying to construct another bit string based on the length of the
first:

SELECT b'1'::bit( bit_length( digest ) ) FROM lookup;

This doesn't work as i had hoped, where am I going wrong?

Thanks!