for $i (0..1) {
  for $j ($i+1..3) {
    for $k ($j+1..5) {
      for $l ($k+1..7) {
[download]

The obvious approach

my $depth = 4;
my $loop = [[0..1]];
my $val = 3;
for my $i (1..$depth-1) {
    push @$loop, sub {[$_+1..$val]};
    $val+=2;
}
my $iter = NestedLoops($loop);
while (my @list = $iter->()) {
  output(@list);
}

sub output {
  my @args = @_;
  print join '', @args, "\n";
}
[download]

fails because $val isn't evaluated when the subroutine is defined; it's evaluated when it's run, such that they all get its last value, 9.

Trying to be more clever by using an iterator:

my $n = shift;
sub plustwo_iter {
  my $val = 1;
  return sub  {
    $val +=2;
    return $val;
  }
}

my $p = plustwo_iter();

my $loop = [[0..1], (sub {[$_+1..&$p]}) x ($n-2)];

my $iter = NestedLoops($loop);
while (my @list = $iter->()) {
  output(@list);
}
[download]

fails because NestedLoops seems to end up calling the iterator more than exactly once per loop (not that I'd want to depend on the assumption it did call it exactly once per loop.)