Fibonacci using tail recursion

fibonacci.scala

def fib(n: Long): Long = {
    @annotation.tailrec
    def go(n: Long, x: Long, y: Long): Long = 
        n match {
            case 0 => x
            case 1 => y
            case _ => go(n - 1, y, x + y)
        }

    go(n, 0, 1)
}