#!perl -w
use strict;

package Top;
use Carp;
carp( __PACKAGE__ ." has been loaded" );

package Top::level;
use vars qw( @ISA );
@ISA = ( 'Top' );
carp( __PACKAGE__ ." has been loaded" );

__END__
Output:
Top has been loaded at test.pl line 6
Undefined subroutine &Top::level::carp called at test.pl line 11.