Scala list folding

Question

I'm trying to learn scala. It's hard.

I currently have a tree in the form

class Node(children:List[Node], value:Int){

}

I want to calculate a total cost defined by value + the sum of the totalcost of the children. My java background made me do this:

def totalCost() {
  var total = value
  for (child <- children){
    total = total+child.totalCost
  }
  return total
}

now I know I should be folding or reducing, but it's not coming out. Could some of you frendly helpers give me a hand here?

Answer 1

There is already a sum function:

def totalCost = value + children.map(_.totalCost).sum

Answer 2

A left-fold is an elegant solution too:

class Node (children:List[Node], value:Int) {
  def totalCost : Int = (value /: children) (_ + _.totalCost)
}