ALTER TABLE ... SET DEFAULT

I have a field called 'updated' of type 'integer' in a table. I have
created a function called 'since_epoch' which is declared with iscacheable
and returns the value of 'extract(epoch from now())'. I want to make
'updated' have a default of 'since_epoch()'. I cannot get it to work with
the following command:

alter table foo alter column updated set default 'since_epoch()' ;

this gets the error:

ERROR: pg_atoi: error in "since_epoch()": can't parse "since_epoch()"

I tried using 'since_epoch()::integer', but that failed as well.
Is it possible to make the default value of an integer field use a
function similar to how we use 'now()' for date and timestamp fields?

- brian

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