fun splitAtFirst 0 xs        = ([], xs)
  | splitAtFirst n []        = ([], [])
  | splitAtFirst n (x::xs) =
      let
         val (t, d) = splitAtFirst (n) xs
      in
        if n = x then (x::d, t) else (x::t, d)
      end;

splitAtFirst 8 [3,4,2,~1,15,3,8,3,4,19];
(* Fæ val it = ([3,4,2,~1,15,3,8],[3,4,19])*)
(* Ætti að fá val it = ([3,4,2,~1,15,3],[8,3,4,19])*))