fibonacci.scala

def fib(n: Int): Int = {
  n match {
    case 0 => 0
    case 1 => 1
    case n => fib(n - 1) + fib(n - 2)
  }
}

println(fib(10))

fibonacci_go.scala

def fib(n: Int): Int = {
  @annotation.tailrec
  def go(n: Int, a: Int, b: Int): Int =
    n match {
      case 0 => 0
      case 1 => a
      case n => go(n - 1, a + b, a)
    }

  go(n, 1, 0)
}

println(fib(10))