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open Dial
module Turner : sig
val turn : Dial.t -> int -> Dial.direction -> Dial.t * int
(** [turn dial direction] is the new state of the dial after turning [direction] on [dial] *)
end = struct
(** [turn dial direction] is the new state of the dial after turning [direction] on [dial].
Raises: [dial_out_of_range] if the dial is moved to an invalid state. *)
let rec turn dial zero_count direction =
let open Dial in
match direction with
| Left 0 ->
(dial, zero_count)
| Left n ->
let dial' = prev dial in
let zero_count' =
if Dial.is_zero dial' then zero_count + 1 else zero_count
in
turn dial' zero_count' (Left (n - 1))
| Right 0 ->
(dial, zero_count)
| Right n ->
let dial' = next dial in
let zero_count' =
if Dial.is_zero dial' then zero_count + 1 else zero_count
in
turn dial' zero_count' (Right (n - 1))
end
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