Consider the following Scala case class and function definitions: crait Result [+x, +Y] case class Error[+Y] (s:Y) extends Result [Nothing, Y] case class Ok + (n:x) extends Result[x, Nothing] def combine [ U, X, Y] (us : List [ U], f : U=>Result [X, Y] ) : Result [ List [X], List [ Y] ] { = us match f case Nil Ok (Nil) (f (v), combine (vs, f)) match f case (Error (s) Error (ss Error (: SS) case (Ok (n,Error (ss) Error (ss) case (Error sOk case (Ok(n, Ok (ns)> Ok (n: :ns) nsError (List (s)