What the heck...I just uploaded another new release of Var::Pairs
(version 0.004000), which lets you write this:

use Var::Pairs;

sub countdown {
    my $n = shift;

    return sub {
        return if $n < 0;  # Indicates iterator exhausted
        return $n--;       # Next value iterated
    }
}

for my $limit (reverse 1..5) {
    while (my ($a) = each_value countdown($limit)) {
        print $a, ':';
    }
    say q{};
}
[download]

...which is very close to what you wanted, I believe.

(And, yes, the each_value() subroutine is doing a lot of very hard paddling
under the surface to correctly ignore all those repeated calls to countdown($limit)
in the while loop. ;-)

for my $limit (reverse 1..5) {
    my $iter = countdown($limit);
    while (my ($a) = each_value $iter) {
        print $a, ':';
    }
    say q{};
}
[download]

Damian