Scala.NotImplementedError: an implementation is missing?

Question

Here is my code:

package example

object Lists {

  def max(xs: List[Int]): Int = {
    if(xs.isEmpty){
        throw new java.util.NoSuchElementException()
    }
    else {
        max(xs.tail)
    }
  }
}

When i run it in sbt console:

scala> import example.Lists._
scala> max(List(1,3,2))

I have the following error:

Scala.NotImplementedError: an implementation is missing

How can I fix that?

Thanks.

Answer 1

open example.Lists, you will see below lines:

def sum(xs: List[Int]): Int = ???
def max(xs: List[Int]): Int = ???

use 0 instead of ???.

Answer 2

Also, putting the correct recursive implementation for the max that should work

  def max(xs: List[Int]): Int = {
    if(xs.isEmpty){
      throw new java.util.NoSuchElementException()
    }
    val tailMax =  if (xs.tail.isEmpty)  xs.head else max(xs.tail)
    if (xs.head >= tailMax){
      xs.head
    }
    else  tailMax;
  }