Challenge 1: An Independent Counter Pair — Possible Solution
====================================================================

use strict;
use warnings;
use feature 'say';

sub make_counter {
    my $count = 0;
    return sub { return ++$count; };
}

my $counter_a = make_counter();
my $counter_b = make_counter();

$counter_a->();
$counter_a->();
$counter_a->();

$counter_b->();

say $counter_a->();   # calling a 4th time to check the current value
say $counter_b->();   # calling a 2nd time to check the current value

Output:
4
2

WHY THIS WORKS AS AN ANSWER
------------------------------
make_counter is reused completely unchanged from the chapter's own
example — each call builds a fresh $count lexical and returns an
anonymous sub that closes over that specific variable.

my $counter_a = make_counter(); and my $counter_b = make_counter();
each invoke make_counter() SEPARATELY, meaning each call creates its
own independent $count — reusing the chapter's own explanation that
"each call to make_counter() creates a genuinely fresh $count," so
$counter_a and $counter_b, despite being built from identical code,
never share state.

Calling $counter_a->() three times advances ITS $count to 3, then a
fourth call (used here to both advance and print in one step) brings
it to 4. Calling $counter_b->() once advances its own, completely
separate $count to 1, and a second call brings it to 2. The two final
printed values, 4 and 2, directly confirm the counters never
interfered with each other — exactly the independence the chapter's
own $counter1/$counter2 example demonstrates.