myAppendUsingPatternMatching.sml

fun append(xs, ys) =
  case xs of
    [] => ys
  | head::tail => head::append(tail, ys)

val testAppend1 = append([1, 2, 3, 4], [5, 6, 7])
(* val testAppend1 = [1,2,3,4,5,6,7] : int list *)

val testAppend2 = append([], [5, 6, 7])
(* val testAppend2 = [5,6,7] : int list *)

val testAppend3 = append([1, 2, 3, 4], [])
(* val testAppend3 = [1,2,3,4] : int list *)