restructure + lecutre 07

lectures/06/two_list_queue.ml

@@ -0,0 +1,42 @@
+(* queue is empty iff the first list is empty *)
+type 'a t = 'a list * 'a list;;
+
+exception Empty;;
+
+let empty = ([], []);;
+
+let is_empty (l, _) = l = [];;
+
+let enqueue x (l1, l2) =
+  match l1 with
+  | [] -> [x], l2
+  | _ -> (l1, x :: l2);;
+
+let dequeue (l1, l2) =
+  match l1 with
+  | [] -> raise Empty
+  | [_] -> (List.rev l2, [])
+  | _ :: xs -> (xs, l2);;
+
+let dequeue_opt q =
+  try
+    Some (dequeue q)
+  with
+  | Empty -> None;;
+
+let front (l, _) =
+  match l with
+  | [] -> raise Empty
+  | x :: _ -> x;;
+
+let front_opt (l, _) =
+  match l with
+  | [] -> None
+  | x :: _ -> Some x;;
+
+let of_list l = 
+  List.fold_left (Fun.flip enqueue) empty l;;
+
+let to_list (l1, l2) =
+  l1 @ List.rev l2;;
+