Please note that now, one can have more than just one loop var, like a "pointy block" in Perl6.

The cheat is that $a has to be global here to work under strict.*

Using my $a wouldn't work, because the scope only starts after the statements semicolon, and the body-sub is defined before.

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


sub iter (&$;@) {
    my $gen = shift;
    my $body = pop;

    for (my $it = $gen->(@_) ; $it->(@_); ) {
        $body->();
    }
}


for my $limit (reverse 1..5) {

    iter { countdown($limit) } $a => sub  {
        print "$a: ";
    };

    print "\n";
}



sub countdown{
    my $val = shift;

    my $it = sub {
        if ($val--) {
            $_[0]=$val;
            return 1;
        }
        return;                         # stop iteration
    };

    return $it;

}
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4: 3: 2: 1: 0: 
3: 2: 1: 0: 
2: 1: 0: 
1: 0: 
0:
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update

Renamed loop to iter ... the loop construct in Perl6 is another beast, and wanted to avoid confusion.

*) remember $a and $b are global to allow sort to work.