import extensions;

fib(n)
{
    if (n < 0)
        { InvalidArgumentException.raise() };

    ^ (n)
        {
            if (n > 1)
            {
                ^ this self(n - 2) + (this self(n - 1))
            }
            else
            {
                ^ n
            }
        }(n)
}

public program()
{
    for (int i := -1, i <= 10, i += 1)
    {
        console.print("fib(",i,")=");
        try
        {
            console.printLine(fib(i))
        }
        catch(Exception e)
        {
            console.printLine:"invalid"
        }
    };

    console.readChar()
}