fun hd (l) {
  case l of
    h : _ -> h
  esac
}

fun tl (l) {
  case l of
    _ : t -> t
  esac
}

printf ("%s\n", {1, 2, 3}.hd.string);
printf ("%s\n", {1, 2, 3, 4}.tl.string);
printf ("%s\n", {1, {2, 3, 4}, 5, 6}.tl.hd.hd.string)