package Private;

use Exporter;
@ISA = 'Exporter';
@EXPORT = 'is_private';

use strict;
use warnings;

use Carp;

sub is_private()
{
    my %c0; @c0{qw( pkg fn l sub )} = caller 0;
    my %c1; @c1{qw( pkg fn l sub )} = caller 1;

    if ( $c0{'pkg'} ne $c1{'pkg'} ) # throw an exception:
    {
        my %c2; @c2{qw( pkg fn l sub )} = caller 2;
        my $caller = $c2{'sub'} || $c2{'pkg'} || 'main';
        croak "$caller cannot call $c1{'sub'} (private to $c0{'pkg'})";
    }
}

1;