//typeclass example

//Note : List already has a sum method working the same way
//List(1,2,3).sum returns 6
//but this example is simpler

trait Summable[T] {
  def sum(a: T, b: T): T
}

//default instances
object Summable {
  implicit val intSummable: Summable[Int] = (a: Int, b: Int) => a +b
  implicit val stringSummable: Summable[String] = (a: String, b: String) => a +b
}

//add sumAll method to Scala List type
implicit class ListWithSumAll[T](list: List[T]){
  def sumAll()(implicit summable: Summable[T]): T = {
    list.reduceLeft((sum, element) => summable.sum(sum, element))
  }
}

List(1,2,3).sumAll //6

// add your instances here
case class Color(red: Int, green: Int, blue: Int)

implicit val colorSummable: Summable[Color] = (c1: Color, c2: Color) => {
  val red = (c1.red + c2.red) /2
  val green = (c1.green + c2.green) /2
  val blue = (c1.blue + c2.blue) /2
  Color(red, blue, green)
}

List(Color(10,10,10), Color(200, 255, 10), Color(20, 55, 1)).sumAll // Color(62,66,32)