#!/usr/bin/perl

use warnings;
use strict;

my $src = [['A', 'B', 'C', 'D'],['P', 'Q', 'R'],['1', '2', '3', '4', '5']];

my $products = [''];
for my $level (@$src) {
	my $old_products = $products;
	$products = [];
	for my $prefix (@$old_products) {
		for (@$level) {
			push(@$products, "$prefix$_");
		}
	}
}

print "$_\n" for @$products;