use strict;
use warnings;
use Data::Dump qw/pp dd/;


my @a = 1 .. 3;
my @b = "a".."b";
my @c =([]);                            # init one empty row 

for my $l (@a) {
   my @old = @c;
   @c =();
   for my $r (@b) {
      for my $row (@old) {
         push @c, [ @$row , [$l,$r] ];
         #push @c, [ (map [@$_], @$row) , [$l,$r] ]; # copy old-pairs to new arrays
      }
   }
   #pp "old $l: ",@old;
}

warn "final:\n";
pp $_ for @c;

pp \@c;