add Wheel.iter for arbitrary order iteration

lib/data/test_wheel.ml

@@ -25,6 +25,11 @@ let%expect_test _ =
   Wheel.add wh 6 |> ignore;
   (* t=3 *)
   print_ints_nl (Wheel.tick wh); [%expect {| [] |}];
+
+  let every = ref [] in
+  Wheel.iter (fun x -> every := x :: !every) wh;
+  print_ints_nl (List.sort compare !every); [%expect {| [1;2;3;4;5;6] |}];
+
   (* t=0 *)
   print_ints_nl (Wheel.tick wh); [%expect {| [1;2;3] |}];
   (* t=1 *)

lib/data/wheel.ml

@@ -22,3 +22,8 @@ let[@tail_mod_cons] rec empty t =
 let tick t =
   t.index <- (t.index + 1) mod Array.length t.entries;
   empty t
+
+let iter f t =
+  for i = 0 to Array.length t.entries - 1 do
+    Dllist.iter_l f t.entries.(i)
+  done