package SuperClass;
sub subclasses {
        return grep {
                UNIVERSAL::isa($_,__PACKAGE__) && 
                $_ ne __PACKAGE__ 
        } main::packages();
}

package SubClass;
@ISA=qw(SuperClass);

package main;
sub packages {
        return packages({},\%main::) unless @_;
        my ($packages,$in) = @_;                        
        while(my ($package,$table) = each %$in) {       
                next unless $package =~ /(.*)::$/;      
                next if exists $packages->{$table};     
                $packages->{$table} = $1;               
                packages($packages,$table);             
        }
        return values %$packages;                       
}

$\=$,="\n";
print SuperClass::subclasses();

##</code><code>##

my @subclasses = grep {
    /^(.*?)::$/ &&                  # it's a package entry
    UNIVERSAL::isa($1,__PACKAGE__)  # entry is subclass of me!
} keys %main:: ;                    # for everything in main namespace