style: improve new code

src/data/CCDeque.ml

@@ -264,9 +264,10 @@ let update_front d f =
         | Some x -> d.cur.cell <- Two (x,y)
       end
     | Three (x,y,z) ->
-       match f x with
+      begin match f x with
         | None -> d.cur.cell <- Two (y,z)
         | Some x -> d.cur.cell <- Three (x,y,z)
+      end
 
 (*$T update_front
   let q = of_list [1;2;3;4;5;6;7] in update_front q (fun _ -> None); to_list q = [2;3;4;5;6;7]
@@ -301,9 +302,10 @@ let update_back d f =
         | Some y -> n.cell <- Two (x,y)
       end
     | Three (x,y,z) ->
-       match f z with
+      begin match f z with
         | None -> n.cell <- Two (x,y)
         | Some z -> n.cell <- Three (x,y,z)
+      end
 
 (*$T update_back
   let q = of_list [1;2;3;4;5;6;7] in update_back q (fun _ -> None); to_list q = [1;2;3;4;5;6]

src/data/CCDeque.mli

@@ -83,10 +83,13 @@ val take_front_opt : 'a t -> 'a option
 
 val update_back : 'a t -> ('a -> 'a option) -> unit
 (** Update last value. If the deque is empty do nothing.
+    If the function returns [None], remove last element;
+    if it returns [Some x], replace last element with [x].
     @since NEXT_RELEASE *)
 
 val update_front : 'a t -> ('a -> 'a option) -> unit
 (** Update first value. If the deque is empty do nothing.
+    Similar to {!update_back} but for the first value.
     @since NEXT_RELEASE *)
 
 val append_front : into:'a t -> 'a t -> unit