[Perl 6] Recursion demo: fibonacci

sub fib(Int $n where $n >= 0) returns Int {
    if $n == 0 {
        return 0;
    } elsif $n == 1 {
        return 1;
    }

    fib($n - 1) + fib($n - 2);
}

fib(10) == 55 or die "Wrong number";