Section serializer.
Variables A : Type.
Variable sA :Serializer A.
(* Now we're ready to serialize trees. First, we serialize their shape. *)
Fixpoint serialize_tree_shape (t : tree A) : IOStreamWriter.t :=
let fix serialize_list_tree_shape (l : list (tree A)) : IOStreamWriter.t :=
match l with
| [] => IOStreamWriter.empty
| x :: xs => IOStreamWriter.append (fun _ => serialize_tree_shape x)
(fun _ => serialize_list_tree_shape xs)
end in
match t with
| atom _ => serialize x00 (* ignore the data, since we're just focused on the shape *)
| node l => IOStreamWriter.append (fun _ => serialize x01)
(fun _ => (IOStreamWriter.append
(fun _ => serialize_list_tree_shape l)
(fun _ => serialize x02)))
end.
Definition serialize_list_tree_shape :=
fix serialize_list_tree_shape (l : list (tree A)) : IOStreamWriter.t :=
match l with
| [] => IOStreamWriter.empty
| x :: xs => IOStreamWriter.append (fun _ => serialize_tree_shape x)
(fun _ => serialize_list_tree_shape xs)
end.
Definition deserialize_tree_shape_step (b : byte) (s : list (list (tree unit))) :
fold_state (list (list (tree unit))) (tree unit) :=
match b with
| x00 => match s with
| [] => Done (atom tt)
| ts :: s => More ((atom tt :: ts) :: s)
end
| x01 => More ([] :: s)
| x02 => match s with
| [] => Error
| ts :: s => let t := node (rev' ts) in
match s with
| [] => Done t
| ts :: acc => More ((t :: ts) :: acc)
end
end
| _ => Error
end.

Lemma shape_aux :
forall t acc bytes,
ByteListReader.unwrap (ByteListReader.fold deserialize_tree_shape_step acc)
(IOStreamWriter.unwrap (serialize_tree_shape t) ++ bytes) =
match acc with
| [] => Some (shape t, bytes)
| j :: js => ByteListReader.unwrap
(ByteListReader.fold deserialize_tree_shape_step
((shape t :: j) :: js)) bytes
end.