Scala Problem

example.scala

    def reverse[A](as: List[A]): List[A] = {
    foldLeft(as, List[A]())((acc, x) => x::acc)
  }
  
  def foldRightFromFoldLeft[A,B](as: List[A], z:B)(f:(B, A) => B):B ={
    foldLeft(reverse(as), z)((onlyNil, x) =>f(onlyNil, x) )
  }
  
  // The Problem Child
  // Type checker has a problem with both x.toString :: onlyNil or as seen below.
  def doubleToString(as: List[Double]): List[String] ={
    foldRightFromFoldLeft(as, List[String]())((onlyNil, x) => x.toString :: onlyNil)
  }