use Algorithm::Loops qw( NestedLoops );

my $level = 3;

my @indices = NestedLoops(
   [
      (['A'..'D']) x $level
   ],
   sub { join '', map { "${_}1" } @_ }
);

foreach my $val (@indices) {
   print($val\n")
]

##</code><code>##

use Algorithm::Loops qw( NestedLoops );

my $level = 3;

my $iter = NestedLoops(
   [
      (['A'..'D']) x $level
   ]
);

while (my @values = $iter->()) {
   my $val = join '', map { "${_}1" } @values;

   print("$val\n");
}