my $value = $it->();

##</code><code>##

my $value->it();

##</code><code>##

#!/usr/bin/perl
use warnings;
use strict;
use feature qw{ say };

sub Iterator(&) { $_[0] }

sub upto {
    my ($m, $n) = @_;
    return Iterator {
        $m <= $n ? $m++ : undef
    }
}

my $it = upto(3,5);
while (my $value = $it->()) {
    say $value;
}