Question

implicit val odkaz = head;
def vypis(implicit odkaz:Prvek):String = {
    odkaz match{
        case null => ""
        case e => e.cislo + " " + e.pocet + "\n" + vypis(e.dalsi)
    }
}

…

def main(args:Array[String]){
    val q = new MyQueue() // insert some values
    println(q.vypis)
}

This method(vypis) is a member of an queue-class so I’ll always want to implicity start the recursion from the start of the queue, when calling the method from outside. Is there a way how to write it, that the method from outside calling, there’s no paramter, but in inside, there’s a parameter – for recursion…?
The compiler complains that the parameter is not defined when called from outside

---

Or is there are way how can specify the default value for a method’s parameter?

Answer 1

Using a nested method

def sum(list: List[Int]) = {
  @annotation.tailrec
  def sum(ls: List[Int], s: Int): Int = ls match { 
     case x :: xs => sum(xs, x + s)
     case _ => s
  }
  sum(list, 0)
}

Using a default parameter for the accumulator

@annotation.tailrec
def sum(list: List[Int], s: Int = 0): Int = list match { 
   case x :: xs => sum(xs, x + s)
   case _ => s
}

The second approach (only possible with Scala 2.8) unneccesarily broadens the public API, so I would recommend the first.