Tail recursion in scala explainer

tail.sc

def sumNonTail(ints: List[Int]): Int = {
  ints match {
    case Nil => 0
    case x :: xs => x + sumNonTail(xs)
  }

  // bytecode
  // temp = sumNonTail(i) <-- recursive call not in tail position, the result of the recursive call is being 'post-processed' and has to be stored on the stack as it cant return out
  // return x + temp

}

//to refactor move the variables that would be stored on stack to be function args as 'accumulator vars'

@tailrec
def sumTail(ints: List[Int], acc: Int = 0) : Int = {
  ints match {
    case Nil => acc
    case x :: xs => sumTail(xs, acc + x) // sum tail is in tail position
  }
}