add CCDeque.{filter,filter_map}

src/data/CCDeque.ml

@@ -411,6 +411,23 @@ let filter_in_place (d:_ t) f : unit =
     (filter_in_place q f; to_list q) = (List.filter f l))
   *)
 
+let filter f q =
+  let q' = create() in
+  iter (fun x -> if f x then push_back q' x) q;
+  q'
+
+(*$Q
+  Q.(list small_nat) (fun l -> \
+    let f = fun x -> x mod 2=0 in \
+    let q = filter f (of_list l) in \
+    (to_list q) = (List.filter f l))
+  *)
+
+let filter_map f q =
+  let q' = create() in
+  iter (fun x -> match f x with None -> () | Some y -> push_back q' y) q;
+  q'
+
 let rec gen_iter_ f g = match g() with
   | None -> ()
   | Some x -> f x; gen_iter_ f g

src/data/CCDeque.mli

@@ -123,6 +123,14 @@ val to_rev_list : 'a t -> 'a list
 (** Efficient conversion to list, in reverse order.
     @since 0.13 *)
 
+val filter : ('a -> bool) -> 'a t -> 'a t
+(** Filter into a new copy.
+    @since NEXT_RELEASE *)
+
+val filter_map : ('a -> 'b option) -> 'a t -> 'b t
+(** Filter map into a new copy
+    @since NEXT_RELEASE *)
+
 val filter_in_place : 'a t -> ('a -> bool) -> unit
 (** Keep only elements that satisfy the predicate.
     @since NEXT_RELEASE *)