$debug = bungee;

if ($debug eq bungee) {
  $debug = SPELUNK;
}
else {
  $debug = bungee;
}

##</code><code>##

if ($debug) {
  # $debug is true
}
else {
  # $debug is false
}

$debug = 1;
$debug = !$debug;  # flip-flop

##</code><code>##

package boolean;

use overload (
  '+0' => sub { $_[0][0] },
  fallback => 1,
);

sub new { bless [ $_[1] ? 1 : 0 ], $_[0] }
sub flip { $_[0][0] = 1 - $_[0][0] }

##</code><code>##

use boolean;

$debug = boolean->new(1);
print "hi\n" if $debug;
$debug->flip;
print "bye\n" if $debug;