#!/usr/bin/perl -wl
sub gen_counter {
    my $a = shift;
    return sub { ++$a }, sub { $a = shift };
}

my ($counter, $modifier) = gen_counter(3);
print $counter->();
print $counter->();

$modifier->(8);

print $counter->();
print $counter->();

# which prints:
4
5
9
10

##</code><code>##

#!/usr/bin/perl -wl
sub gen_counter {
    my $a = shift;
    return sub { @_ ? $a = shift : ++$a };
}

my $counter = gen_counter(3);
print $counter->();
print $counter->();
$counter->(8);
print $counter->();
print $counter->();

##</code><code>##

sub gen_closure {
    my ($a, $b, $c) = @_;
    return sub {
        if ($some_trigger) {
            # Calculate new $a, $b, $c based on e.g. the
            # new @_ and the old $a, $b and $c. 
            return gen_closure($new_a, $new_b, $new_c);
        }
        # Do the normal closure action on $a, $b and $c here
     }
}