plpgsql extract epoch problem

Hey all

I am trying to extract the epoch from a timestamp variable in plpgsql.
The function is as follows:

create or replace function test() returns integer as '
declare
_test timestamp with time zone;
_f integer;
begin
_test := current_timestamp;
_f := extract(epoch from timestamp _test);
return _f;
end;' language 'plpgsql';

Any ideas why this will not work????

The error is as follows:
pts=> select test();
WARNING: Error occurred while executing PL/pgSQL function test
WARNING: line 6 at assignment
ERROR: parser: parse error at or near "$1" at character 40

And that is the _test variable

Any help greatly apprechiated
Darren