PL/Perl function signatures

Hi all,
is there any way to exploit sub signatures in PL/Perl?
The following is not working, I suspect it is not possible due to the
way PL/Perl compiles the code.

testdb=# create or replace function f( a int )
returns text
as $$
use feature 'signatures';

elog( INFO, "Perl version $^V" );
elog(INFO, "A = $a" );
return "A=$a";
$$
language plperlu;

testdb=# select f( 10 );
INFO: Perl version v5.32.1
INFO: A =
f
----
A=
(1 row)