mapVialfoldRightViaFoldLeft.scala

def reverse[A](as: List[A]): List[A] = as match {
  case Nil => Nil
  case Cons(x, xs) => foldLeft(xs, Cons(x,Nil))((a,b) => Cons(b, a))
}

def foldRightViaFoldLeft[A,B](as: List[A], z: B)(f: (B, A) => B): B = 
  foldLeft(reverse(as), z)((b,a) => f(b,a))

def map[A,B](as: List[A])(f: A => B): List[B] = 
  foldRightViaFoldLeft(as, Nil:List[B])((t,h) => Cons(f(h),t))