Scala concatenate lists with foldRight

Question

I making function of list to list adding.

I can't understand why it's doesn't working

def lconcat(l: List[List[Int]]): List[Int] = {
    return l.foldRight(1)((x:List[Int], y:List[Int]) => x ++ y)
  }

and I call function like

println(lconcat(List(List(1, 2, 3), List(4, 5, 6))))

I want result like List[Int] = List(1, 2, 3, 4, 5, 6)

Answer 1

Since you want to return List of Integers, the parameter of foldRight should be an empty list that the input lists will be concatenated to it.

Your code should be:

  def lconcat(l: List[List[Int]]): List[Int] = {
    l.foldRight(List.empty[Int])((x:List[Int], y: List[Int]) => {
      x ++ y
    })
  }