reverse-string.scala

def rev[A](str: List[A]): List[A] = str match {
  case Nil => Nil
  case x :: Nil => x :: Nil
  case x :: y :: Nil => y :: x :: Nil
  case x :: xs => xs.last +: rev(xs.init) :+ x
}

val gus = "Gustavo".toList //gus: List[Char] = List(G, u, s, t, a, v, o)
rev(gus) //res0: List[Char] = List(o, v, a, t, s, u, G)