% reply
0> use Set
1> my $s = Set->new
$res[0] = bless( {
         'items' => []
       }, 'Set' )

2> $s->has(42)
$res[1] = 0

3> $s->add(42)
$res[2] = 1

4> $s->has(42)
$res[3] = 1