There's gotta be a better way than this:

use strict;
use warnings;

sub genIterator_helper($\@) {
   my ($base, $list) = @_;
   my $i = $#$list;
   for (;;) {
      last if (++$$list[$i] < $base);
      $$list[$i] = 0;
      return undef unless $i;
      $i--;
   }
   return 1;
}

sub genIterator {
   my ($max_digits, $base) = @_;
   my @list;
   foreach my $num_digits (1..4) {
      my @digits = (0) x $num_digits;
      do {
         push(@list, join('', @digits));
      } while (genIterator_helper($base, @digits));
   }
   @list = sort { $a cmp $b } @list;
   return sub { shift(@list) };
}

my $iter = genIterator(4, 3);
print "$_$/" while defined ($_ = $iter->());
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