Excluding null return values from functions

How do I give a condition on the return value of a function (for
example plperl)?

I have a perl search function that returns either a bigint, or undef
if nothing is found. I want to exclude the undef/null return values
from my select statement, something like:

sql> select search(data, 'field', 'value') as result from mydata where
result is not null;

--
Jason Armstrong