sub fib {
    my $a = 0;
    my $b = 1;
    
    sub {
        my $out = $a;
        my $c = $a + $b;
        $a = $b;
        $b = $c;
        
        $out;
    }
}

my $f = fib();

my @arr = (0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89);

loop (my $i = 0; $i < @arr.elems; $i++) {
    $f() == @arr[$i] or die "Wrong value";
}