diff --git a/README.md b/README.md
index b18bc559..edf35ecc 100644
--- a/README.md
+++ b/README.md
@@ -351,14 +351,14 @@ module IntMap = CCMap.Make(CCInt)
   let map : string IntMap.t =
     l2
     |> List.map (fun x -> x, string_of_int x)
-    |> CCList.to_seq
-    |> IntMap.of_seq;;
+    |> CCList.to_iter
+    |> IntMap.of_iter;;
 val map : string IntMap.t = <abstr>
 
-# CCList.to_seq ;; (* check the type *)
-- : 'a list -> 'a CCList.sequence = <fun>
-# IntMap.of_seq ;;
-- : (int * 'a) CCMap.sequence -> 'a IntMap.t = <fun>
+# CCList.to_iter;; (* check the type *)
+- : 'a list -> 'a CCList.iter = <fun>
+# IntMap.of_iter ;;
+- : (int * 'a) CCMap.iter -> 'a IntMap.t = <fun>
 
 # (* we can print, too *)
   Format.printf "@[<2>map =@ @[<hov>%a@]@]@."
@@ -448,7 +448,7 @@ module IntHeap = CCHeap.Make(struct type t = int let leq = (<=) end);;
 ```
 
 ```ocaml
-# let h = v2 |> CCVector.to_seq |> IntHeap.of_seq ;;
+# let h = v2 |> CCVector.to_iter |> IntHeap.of_iter ;;
 val h : IntHeap.t = <abstr>
 
 # (* We can print the content of h
diff --git a/src/core/CCArray.ml b/src/core/CCArray.ml
index 86c5ef06..668389e2 100644
--- a/src/core/CCArray.ml
+++ b/src/core/CCArray.ml
@@ -2,6 +2,7 @@
 
 (** {1 Array utils} *)
 
+type 'a iter = ('a -> unit) -> unit
 type 'a sequence = ('a -> unit) -> unit
 type 'a klist = unit -> [`Nil | `Cons of 'a * 'a klist]
 type 'a gen = unit -> 'a option
@@ -559,7 +560,21 @@ let to_string ?(sep=", ") item_to_string a =
   (to_string string_of_int [|1|]) "1"
 *)
 
-let to_seq a k = iter k a
+let to_std_seq a =
+  let rec aux i () =
+    if i>= length a then Seq.Nil
+    else Seq.Cons (a.(i), aux (i+1))
+  in
+  aux 0
+
+(*$=
+  [] (to_std_seq [||] |> CCList.of_std_seq)
+  [1;2;3] (to_std_seq [|1;2;3|] |> CCList.of_std_seq)
+  CCList.(1 -- 1000) (to_std_seq (1--1000) |> CCList.of_std_seq)
+*)
+
+let to_iter a k = iter k a
+let to_seq = to_iter
 
 let to_gen a =
   let k = ref 0 in
diff --git a/src/core/CCArray.mli b/src/core/CCArray.mli
index af710ac7..454e823a 100644
--- a/src/core/CCArray.mli
+++ b/src/core/CCArray.mli
@@ -1,10 +1,16 @@
-(*  AUTOGENERATED FROM CCArrayLabels.mli  *)
 
 (* This file is free software, part of containers. See file "license" for more details. *)
 
 (** {1 Array utils} *)
 
+(* TODO: remove for 3.0 *)
 type 'a sequence = ('a -> unit) -> unit
+(** @deprecated use ['a iter] instead *)
+
+type 'a iter = ('a -> unit) -> unit
+(** Fast internal iterator.
+    @since NEXT_RELEASE *)
+
 type 'a klist = unit -> [`Nil | `Cons of 'a * 'a klist]
 type 'a gen = unit -> 'a option
 type 'a equal = 'a -> 'a -> bool
@@ -251,16 +257,31 @@ val to_string : ?sep:string -> ('a -> string) -> 'a array -> string
     between elements of [a].
     @since 2.7 *)
 
-val to_seq : 'a t -> 'a sequence
-(** [to_seq a] returns a [sequence] of the elements of an array [a].
+val to_iter : 'a t -> 'a iter
+(** [to_iter a] returns an [iter] of the elements of an array [a].
     The input array [a] is shared with the sequence and modification of it will result
-    in modification of the sequence. *)
+    in modification of the iterator.
+    @since NEXT_RELEASE *)
+
+val to_std_seq : 'a t -> 'a Seq.t
+(** [to_std_seq a] returns a [Seq.t] of the elements of an array [a].
+    The input array [a] is shared with the sequence and modification of it will result
+    in modification of the sequence.
+    @since NEXT_RELEASE
+*)
+
+val to_seq : 'a t -> 'a sequence
+(** Same as {!to_iter}.
+    @deprecated use {!to_iter} instead *)
+[@@ocaml.deprecated "use to_iter or to_std_seq"]
 
 val to_gen : 'a t -> 'a gen
 (** [to_gen a] returns a [gen] of the elements of an array [a]. *)
 
 val to_klist : 'a t -> 'a klist
-(** [to_klist] returns a [klist] of the elements of an array [a]. *)
+(** [to_klist] returns a [klist] of the elements of an array [a].
+    @deprecated use {!to_std_seq} *)
+[@@ocaml.deprecated "use to_std_seq"]
 
 (** {2 IO} *)
 
diff --git a/src/core/CCArrayLabels.mli b/src/core/CCArrayLabels.mli
index 76684e5b..97c56ec8 100644
--- a/src/core/CCArrayLabels.mli
+++ b/src/core/CCArrayLabels.mli
@@ -2,7 +2,15 @@
 
 (** {1 Array utils} *)
 
+
+(* TODO: remove for 3.0 *)
 type 'a sequence = ('a -> unit) -> unit
+(** @deprecated use ['a iter] instead *)
+
+type 'a iter = ('a -> unit) -> unit
+(** Fast internal iterator.
+    @since NEXT_RELEASE *)
+
 type 'a klist = unit -> [`Nil | `Cons of 'a * 'a klist]
 type 'a gen = unit -> 'a option
 type 'a equal = 'a -> 'a -> bool
@@ -249,16 +257,31 @@ val to_string : ?sep:string -> ('a -> string) -> 'a array -> string
     between elements of [a].
     @since 2.7 *)
 
-val to_seq : 'a t -> 'a sequence
-(** [to_seq a] returns a [sequence] of the elements of an array [a].
+val to_iter : 'a t -> 'a iter
+(** [to_iter a] returns an [iter] of the elements of an array [a].
     The input array [a] is shared with the sequence and modification of it will result
-    in modification of the sequence. *)
+    in modification of the iterator.
+    @since NEXT_RELEASE *)
+
+val to_std_seq : 'a t -> 'a Seq.t
+(** [to_std_seq a] returns a [Seq.t] of the elements of an array [a].
+    The input array [a] is shared with the sequence and modification of it will result
+    in modification of the sequence.
+    @since NEXT_RELEASE
+*)
+
+val to_seq : 'a t -> 'a sequence
+(** Same as {!to_iter}.
+    @deprecated use {!to_iter} instead *)
+[@@ocaml.deprecated "use to_iter or to_std_seq"]
 
 val to_gen : 'a t -> 'a gen
 (** [to_gen a] returns a [gen] of the elements of an array [a]. *)
 
 val to_klist : 'a t -> 'a klist
-(** [to_klist] returns a [klist] of the elements of an array [a]. *)
+(** [to_klist] returns a [klist] of the elements of an array [a].
+    @deprecated use {!to_std_seq} *)
+[@@ocaml.deprecated "use to_std_seq"]
 
 (** {2 IO} *)
 
@@ -298,13 +321,13 @@ val filter_map : f:('a -> 'b option) -> 'a t -> 'b t
     of all elements [bi] such as [~f ai = Some bi]. When [~f] returns [None], the corresponding
     element of [a] is discarded. *)
 
-val flat_map : f:('a -> 'b t) -> 'a t -> 'b array
-(** [flat_map ~f a] transforms each element of [a] into an array, then flattens. *)
-
 val monoid_product : f:('a -> 'b -> 'c) -> 'a t -> 'b t -> 'c t
 (** All combinaisons of tuples from the two arrays are passed to the function
     @since NEXT_RELEASE *)
 
+val flat_map : f:('a -> 'b t) -> 'a t -> 'b array
+(** [flat_map ~f a] transforms each element of [a] into an array, then flattens. *)
+
 val (>>=) : 'a t -> ('a -> 'b t) -> 'b t
 (** [a >>= f] is the infix version of {!flat_map}. *)
 
diff --git a/src/core/CCArray_slice.ml b/src/core/CCArray_slice.ml
index a9db0cab..53118d85 100644
--- a/src/core/CCArray_slice.ml
+++ b/src/core/CCArray_slice.ml
@@ -5,6 +5,7 @@
 
 open CCShims_
 
+type 'a iter = ('a -> unit) -> unit
 type 'a sequence = ('a -> unit) -> unit
 type 'a klist = unit -> [`Nil | `Cons of 'a * 'a klist]
 type 'a gen = unit -> 'a option
@@ -264,6 +265,9 @@ let _to_gen a i j =
       Some x
     ) else None
 
+let rec _to_std_seq a i j () =
+  if i=j then Seq.Nil else Seq.Cons (a.(i), _to_std_seq a (i+1) j)
+
 let rec _to_klist a i j () =
   if i=j then `Nil else `Cons (a.(i), _to_klist a (i+1) j)
 
@@ -413,10 +417,12 @@ let pp ?(sep=", ") pp_item buf a = _pp ~sep pp_item buf a.arr a.i a.j
 let pp_i ?(sep=", ") pp_item out a =
   _pp_i ~sep (fun k out x -> pp_item (k-a.i) out x) out a.arr a.i a.j
 
-let to_seq a k = iter k a
+let to_iter a k = iter k a
+let to_seq = to_iter
 
 let to_gen a = _to_gen a.arr a.i a.j
 
+let to_std_seq a = _to_std_seq a.arr a.i a.j
 let to_klist a = _to_klist a.arr a.i a.j
     
 
diff --git a/src/core/CCArray_slice.mli b/src/core/CCArray_slice.mli
index f79fcb78..aa7beb07 100644
--- a/src/core/CCArray_slice.mli
+++ b/src/core/CCArray_slice.mli
@@ -5,7 +5,15 @@
 
 (** {1 Array Slice} *)
 
+
+(* TODO: remove for 3.0 *)
 type 'a sequence = ('a -> unit) -> unit
+(** @deprecated use ['a iter] instead *)
+
+type 'a iter = ('a -> unit) -> unit
+(** Fast internal iterator.
+    @since NEXT_RELEASE *)
+
 type 'a klist = unit -> [`Nil | `Cons of 'a * 'a klist]
 type 'a gen = unit -> 'a option
 type 'a equal = 'a -> 'a -> bool
@@ -237,16 +245,33 @@ val random_choose : 'a t -> 'a random_gen
 (** [random_choose as rs] randomly chooses an element of [as].
     @raise Not_found if the array/slice is empty. *)
 
+val to_iter : 'a t -> 'a iter
+(** [to_iter a] returns an [iter] of the elements of a slice [a].
+    The input array [a] is shared with the sequence and modification of it will result
+    in modification of the iterator.
+    @since NEXT_RELEASE *)
+
+val to_std_seq : 'a t -> 'a Seq.t
+(** [to_std_seq a] returns a [Seq.t] of the elements of a slice [a].
+    The input array [a] is shared with the sequence and modification of it will result
+    in modification of the sequence.
+    @since NEXT_RELEASE
+*)
+
 val to_seq : 'a t -> 'a sequence
 (** [to_seq as] returns a [sequence] of the elements of a slice [as].
     The input slice [as] is shared with the sequence and modification of it will result
-    in modification of the sequence. *)
+    in modification of the sequence.
+    @deprecated use {!to_iter} instead *)
+[@@ocaml.deprecated "use to_iter or to_std_seq"]
 
 val to_gen : 'a t -> 'a gen
 (** [to_gen as] returns a [gen] of the elements of a slice [as]. *)
 
 val to_klist : 'a t -> 'a klist
-(** [to_klist as] returns a [klist] of the elements of a slice [as]. *)
+(** [to_klist as] returns a [klist] of the elements of a slice [as].
+    @deprecated use {!to_std_seq} *)
+[@@ocaml.deprecated "use to_std_seq"]
 
 (** {2 IO} *)
 
diff --git a/src/core/CCArray_sliceLabels.mli b/src/core/CCArray_sliceLabels.mli
index 41b59667..8fecce9c 100644
--- a/src/core/CCArray_sliceLabels.mli
+++ b/src/core/CCArray_sliceLabels.mli
@@ -3,7 +3,14 @@
 
 (** {1 Array Slice} *)
 
+(* TODO: remove for 3.0 *)
 type 'a sequence = ('a -> unit) -> unit
+(** @deprecated use ['a iter] instead *)
+
+type 'a iter = ('a -> unit) -> unit
+(** Fast internal iterator.
+    @since NEXT_RELEASE *)
+
 type 'a klist = unit -> [`Nil | `Cons of 'a * 'a klist]
 type 'a gen = unit -> 'a option
 type 'a equal = 'a -> 'a -> bool
@@ -235,10 +242,25 @@ val random_choose : 'a t -> 'a random_gen
 (** [random_choose as rs] randomly chooses an element of [as].
     @raise Not_found if the array/slice is empty. *)
 
+val to_iter : 'a t -> 'a iter
+(** [to_iter a] returns an [iter] of the elements of a slice [a].
+    The input array [a] is shared with the sequence and modification of it will result
+    in modification of the iterator.
+    @since NEXT_RELEASE *)
+
+val to_std_seq : 'a t -> 'a Seq.t
+(** [to_std_seq a] returns a [Seq.t] of the elements of a slice [a].
+    The input array [a] is shared with the sequence and modification of it will result
+    in modification of the sequence.
+    @since NEXT_RELEASE
+*)
+
 val to_seq : 'a t -> 'a sequence
 (** [to_seq as] returns a [sequence] of the elements of a slice [as].
     The input slice [as] is shared with the sequence and modification of it will result
-    in modification of the sequence. *)
+    in modification of the sequence.
+    @deprecated use {!to_iter} instead *)
+[@@ocaml.deprecated "use to_iter or to_std_seq"]
 
 val to_gen : 'a t -> 'a gen
 (** [to_gen as] returns a [gen] of the elements of a slice [as]. *)
diff --git a/src/core/CCHashtbl.ml b/src/core/CCHashtbl.ml
index 39fa57a3..ba58413f 100644
--- a/src/core/CCHashtbl.ml
+++ b/src/core/CCHashtbl.ml
@@ -3,6 +3,7 @@
 
 (** {1 Extension to the standard Hashtbl}  *)
 
+type 'a iter = ('a -> unit) -> unit
 type 'a sequence = ('a -> unit) -> unit
 type 'a eq = 'a -> 'a -> bool
 type 'a hash = 'a -> int
@@ -59,22 +60,42 @@ module Poly = struct
       |> List.sort Stdlib.compare = ["1a"; "2b"]
   *)
 
-  let to_seq tbl k = Hashtbl.iter (fun key v -> k (key,v)) tbl
+  let to_iter tbl k = Hashtbl.iter (fun key v -> k (key,v)) tbl
 
-  let add_seq tbl seq = seq (fun (k,v) -> Hashtbl.add tbl k v)
+  let add_iter tbl i = i (fun (k,v) -> Hashtbl.add tbl k v)
 
-  let of_seq seq =
+  let add_std_seq tbl seq = Seq.iter (fun (k,v) -> Hashtbl.add tbl k v) seq
+
+  let of_iter i =
     let tbl = Hashtbl.create 32 in
-    add_seq tbl seq;
+    add_iter tbl i;
     tbl
 
-  let add_seq_count tbl seq = seq (fun k -> incr tbl k)
-
-  let of_seq_count seq =
+  let of_std_seq i =
     let tbl = Hashtbl.create 32 in
-    add_seq_count tbl seq;
+    add_std_seq tbl i;
     tbl
 
+  let add_iter_count tbl i = i (fun k -> incr tbl k)
+
+  let add_std_seq_count tbl seq = Seq.iter (fun k -> incr tbl k) seq
+
+  let of_iter_count i =
+    let tbl = Hashtbl.create 32 in
+    add_iter_count tbl i;
+    tbl
+
+  let of_std_seq_count i =
+    let tbl = Hashtbl.create 32 in
+    add_std_seq_count tbl i;
+    tbl
+
+  let to_seq = to_iter
+  let add_seq = add_iter
+  let of_seq = of_iter
+  let add_seq_count = add_iter_count
+  let of_seq_count = of_iter_count
+
   let to_list tbl =
     Hashtbl.fold
       (fun k v l -> (k,v) :: l)
@@ -145,23 +166,23 @@ module type S = sig
   include Hashtbl.S
 
   val get : 'a t -> key -> 'a option
-  (** Safe version of {!Hashtbl.find} *)
+  (** Safe version of {!Hashtbl.find}. *)
 
   val get_or : 'a t -> key -> default:'a -> 'a
   (** [get_or tbl k ~default] returns the value associated to [k] if present,
-      and returns [default] otherwise (if [k] doesn't belong in [tbl])
+      and returns [default] otherwise (if [k] doesn't belong in [tbl]).
       @since 0.16 *)
 
   val add_list : 'a list t -> key -> 'a -> unit
   (** [add_list tbl x y] adds [y] to the list [x] is bound to. If [x] is
-      not bound, it becomes bound to [[y]].
+      not bound, it becomes bound to [y].
       @since 0.16 *)
 
   val incr : ?by:int -> int t -> key -> unit
   (** [incr ?by tbl x] increments or initializes the counter associated with [x].
       If [get tbl x = None], then after update, [get tbl x = Some 1];
       otherwise, if [get tbl x = Some n], now [get tbl x = Some (n+1)].
-      @param by if specified, the int value is incremented by [by] rather than 1
+      @param by if specified, the int value is incremented by [by] rather than 1.
       @since 0.16 *)
 
   val decr : ?by:int -> int t -> key -> unit
@@ -170,45 +191,96 @@ module type S = sig
       This does nothing if the key is not already present in the table.
       @since 0.16 *)
 
-  val keys : 'a t -> key sequence
-  (** Iterate on keys (similar order as {!Hashtbl.iter}) *)
+  val keys : 'a t -> key iter
+  (** Iterate on keys (similar order as {!Hashtbl.iter}). *)
 
-  val values : 'a t -> 'a sequence
-  (** Iterate on values in the table *)
+  val values : 'a t -> 'a iter
+  (** Iterate on values in the table. *)
 
   val keys_list : _ t -> key list
-  (** [keys t] is the list of keys in [t].
+  (** [keys_list t] is the list of keys in [t].
+      If the key is in the Hashtable multiple times, all occurrences will be returned.
       @since 0.8 *)
 
   val values_list : 'a t -> 'a list
-  (** [values t] is the list of values in [t].
+  (** [values_list t] is the list of values in [t].
       @since 0.8 *)
 
   val map_list : (key -> 'a -> 'b) -> 'a t -> 'b list
-  (** Map on a hashtable's items, collect into a list *)
+  (** Map on a hashtable's items, collect into a list. *)
+
+  val to_iter : 'a t -> (key * 'a) iter
+  (** Iterate on bindings in the table.
+      @since NEXT_RELEASE *)
 
   val to_seq : 'a t -> (key * 'a) sequence
-  (** Iterate on values in the table *)
+  (** Iterate on values in the table.
+      @deprecated use {!to_iter} instead *)
+  [@@ocaml.deprecated "use to_iter"]
 
-  val of_seq : (key * 'a) sequence -> 'a t
-  (** From the given bindings, added in order *)
+  val add_iter : 'a t -> (key * 'a) iter -> unit
+  (** Add the corresponding pairs to the table, using {!Hashtbl.add}.
+      @since NEXT_RELEASE *)
+
+  val add_std_seq : 'a t -> (key * 'a) Seq.t -> unit
+  (** Add the corresponding pairs to the table, using {!Hashtbl.add}.
+      @since NEXT_RELEASE *)
 
   val add_seq : 'a t -> (key * 'a) sequence -> unit
   (** Add the corresponding pairs to the table, using {!Hashtbl.add}.
-      @since 0.16 *)
+      @since 0.16
+      @deprecated use {!add_iter} or {!add_std_seq} *)
+  [@@ocaml.deprecated "use add_iter or add_std_seq"]
+
+  val of_iter : (key * 'a) iter -> 'a t
+  (** From the given bindings, added in order.
+      @since NEXT_RELEASE *)
+
+  val of_std_seq : (key * 'a) Seq.t -> 'a t
+  (** From the given bindings, added in order.
+      @since NEXT_RELEASE *)
+
+  val of_seq : (key * 'a) sequence -> 'a t
+  (** From the given bindings, added in order.
+      @deprecated use {!of_iter} or {!of_std_seq} *)
+  [@@ocaml.deprecated "use of_iter or of_std_seq"]
+
+  val add_iter_count : int t -> key iter -> unit
+  (** [add_iter_count tbl i] increments the count of each element of [i]
+      by calling {!incr}. This is useful for counting how many times each
+      element of [i] occurs.
+      @since NEXT_RELEASE *)
+
+  val add_std_seq_count : int t -> key Seq.t -> unit
+  (** [add_seq_count tbl seq] increments the count of each element of [seq]
+      by calling {!incr}. This is useful for counting how many times each
+      element of [seq] occurs.
+      @since NEXT_RELEASE *)
 
   val add_seq_count : int t -> key sequence -> unit
   (** [add_seq_count tbl seq] increments the count of each element of [seq]
       by calling {!incr}. This is useful for counting how many times each
       element of [seq] occurs.
-      @since 0.16 *)
+      @since 0.16
+      @deprecated use {!add_iter_count} or {!add_std_seq_count} *)
+  [@@ocaml.deprecated "use add_iter_count or add_std_seq_count"]
+
+  val of_iter_count : key iter -> int t
+  (** Like {!add_seq_count}, but allocates a new table and returns it.
+      @since NEXT_RELEASE *)
+
+  val of_std_seq_count : key Seq.t -> int t
+  (** Like {!add_seq_count}, but allocates a new table and returns it.
+      @since NEXT_RELEASE *)
 
   val of_seq_count : key sequence -> int t
-  (** Like {!add_seq_count}, but allocates a new table and returns it
-      @since 0.16 *)
+  (** Like {!add_seq_count}, but allocates a new table and returns it.
+      @since 0.16
+      @deprecated use {!of_iter_count} or {!of_std_seq_count} *)
+  [@@ocaml.deprecated "use add_iter_count or add_std_seq_count"]
 
   val to_list : 'a t -> (key * 'a) list
-  (** List of bindings (order unspecified)  *)
+  (** List of bindings (order unspecified). *)
 
   val of_list : (key * 'a) list -> 'a t
   (** Build a table from the given list of bindings [k_i -> v_i],
@@ -221,7 +293,7 @@ module type S = sig
       [k] was mapped to [v], or [f k None] otherwise; if the call
       returns [None] then [k] is removed/stays removed, if the call
       returns [Some v'] then the binding [k -> v'] is inserted
-      using {!Hashtbl.replace}
+      using {!Hashtbl.replace}.
       @since 0.14 *)
 
   val get_or_add : 'a t -> f:(key -> 'a) -> k:key -> 'a
@@ -232,9 +304,9 @@ module type S = sig
       @since 1.0 *)
 
   val pp : key printer -> 'a printer -> 'a t printer
-  (** Printer for table
-      @since 0.13
-      Renamed from [print] @since 2.0 *)
+  (** Printer for tables.
+      Renamed from [print] since 2.0.
+      @since 0.13 *)
 end
 
 (*$inject
@@ -318,22 +390,42 @@ module Make(X : Hashtbl.HashedType)
       add tbl k v;
       v
 
-  let to_seq tbl k = iter (fun key v -> k (key,v)) tbl
+  let to_iter tbl k = iter (fun key v -> k (key,v)) tbl
 
-  let add_seq tbl seq = seq (fun (k,v) -> add tbl k v)
+  let add_iter tbl i = i (fun (k,v) -> add tbl k v)
 
-  let of_seq seq =
+  let add_std_seq tbl seq = Seq.iter (fun (k,v) -> add tbl k v) seq
+
+  let of_iter i =
     let tbl = create 32 in
-    add_seq tbl seq;
+    add_iter tbl i;
     tbl
 
-  let add_seq_count tbl seq = seq (fun k -> incr tbl k)
-
-  let of_seq_count seq =
+  let of_std_seq i =
     let tbl = create 32 in
-    add_seq_count tbl seq;
+    add_std_seq tbl i;
     tbl
 
+  let add_iter_count tbl i = i (fun k -> incr tbl k)
+
+  let add_std_seq_count tbl seq = Seq.iter (fun k -> incr tbl k) seq
+
+  let of_iter_count seq =
+    let tbl = create 32 in
+    add_iter_count tbl seq;
+    tbl
+
+  let of_std_seq_count i =
+    let tbl = create 32 in
+    add_std_seq_count tbl i;
+    tbl
+
+  let to_seq = to_iter
+  let add_seq = add_iter
+  let of_seq = of_iter
+  let add_seq_count = add_iter_count
+  let of_seq_count = of_iter_count
+
   let to_list tbl =
     fold
       (fun k v l -> (k,v) :: l)
diff --git a/src/core/CCHashtbl.mli b/src/core/CCHashtbl.mli
index 3897ff93..5ce3c219 100644
--- a/src/core/CCHashtbl.mli
+++ b/src/core/CCHashtbl.mli
@@ -5,7 +5,15 @@
 
     @since 0.4 *)
 
+
+(* TODO: remove for 3.0 *)
 type 'a sequence = ('a -> unit) -> unit
+(** @deprecated use ['a iter] instead *)
+
+type 'a iter = ('a -> unit) -> unit
+(** Fast internal iterator.
+    @since NEXT_RELEASE *)
+
 type 'a eq = 'a -> 'a -> bool
 type 'a hash = 'a -> int
 type 'a printer = Format.formatter -> 'a -> unit
@@ -23,10 +31,10 @@ module Poly : sig
       and returns [default] otherwise (if [k] doesn't belong in [tbl]).
       @since 0.16 *)
 
-  val keys : ('a,'b) Hashtbl.t -> 'a sequence
+  val keys : ('a,'b) Hashtbl.t -> 'a iter
   (** Iterate on keys (similar order as {!Hashtbl.iter}). *)
 
-  val values : ('a,'b) Hashtbl.t -> 'b sequence
+  val values : ('a,'b) Hashtbl.t -> 'b iter
   (** Iterate on values in the table. *)
 
   val keys_list : ('a, 'b) Hashtbl.t -> 'a list
@@ -54,30 +62,80 @@ module Poly : sig
       This does nothing if the key is not already present in the table.
       @since 0.16 *)
 
+  val to_iter : ('a,'b) Hashtbl.t -> ('a * 'b) iter
+  (** Iterate on bindings in the table.
+      @since NEXT_RELEASE *)
+
   val to_seq : ('a,'b) Hashtbl.t -> ('a * 'b) sequence
-  (** Iterate on bindings in the table. *)
+  (** Iterate on bindings in the table.
+      @deprecated use {!to_iter} instead *)
+  [@@ocaml.deprecated "use to_iter"]
 
   val add_list : ('a, 'b list) Hashtbl.t -> 'a -> 'b -> unit
   (** [add_list tbl x y] adds [y] to the list [x] is bound to. If [x] is
       not bound, it becomes bound to [y].
       @since 0.16 *)
 
+  val add_iter : ('a,'b) Hashtbl.t -> ('a * 'b) iter -> unit
+  (** Add the corresponding pairs to the table, using {!Hashtbl.add}.
+      @since NEXT_RELEASE *)
+
+  val add_std_seq : ('a,'b) Hashtbl.t -> ('a * 'b) Seq.t -> unit
+  (** Add the corresponding pairs to the table, using {!Hashtbl.add}.
+      @since NEXT_RELEASE *)
+
   val add_seq : ('a,'b) Hashtbl.t -> ('a * 'b) sequence -> unit
   (** Add the corresponding pairs to the table, using {!Hashtbl.add}.
-      @since 0.16 *)
+      @since 0.16
+      @deprecated use {!add_iter} or {!add_std_seq} *)
+  [@@ocaml.deprecated "use add_iter or add_std_seq"]
+
+  val of_iter : ('a * 'b) iter -> ('a,'b) Hashtbl.t
+  (** From the given bindings, added in order.
+      @since NEXT_RELEASE *)
+
+  val of_std_seq : ('a * 'b) Seq.t -> ('a,'b) Hashtbl.t
+  (** From the given bindings, added in order.
+      @since NEXT_RELEASE *)
 
   val of_seq : ('a * 'b) sequence -> ('a,'b) Hashtbl.t
-  (** From the given bindings, added in order. *)
+  (** From the given bindings, added in order.
+      @deprecated use {!of_iter} or {!of_std_seq} *)
+  [@@ocaml.deprecated "use of_iter or of_std_seq"]
+
+  val add_iter_count : ('a, int) Hashtbl.t -> 'a iter -> unit
+  (** [add_iter_count tbl i] increments the count of each element of [i]
+      by calling {!incr}. This is useful for counting how many times each
+      element of [i] occurs.
+      @since NEXT_RELEASE *)
+
+  val add_std_seq_count : ('a, int) Hashtbl.t -> 'a Seq.t -> unit
+  (** [add_seq_count tbl seq] increments the count of each element of [seq]
+      by calling {!incr}. This is useful for counting how many times each
+      element of [seq] occurs.
+      @since NEXT_RELEASE *)
 
   val add_seq_count : ('a, int) Hashtbl.t -> 'a sequence -> unit
   (** [add_seq_count tbl seq] increments the count of each element of [seq]
       by calling {!incr}. This is useful for counting how many times each
       element of [seq] occurs.
-      @since 0.16 *)
+      @since 0.16 
+      @deprecated use {!add_iter_count} or {!add_std_seq_count} *)
+  [@@ocaml.deprecated "use add_iter_count or add_std_seq_count"]
+
+  val of_iter_count : 'a iter -> ('a, int) Hashtbl.t
+  (** Like {!add_seq_count}, but allocates a new table and returns it.
+      @since NEXT_RELEASE *)
+
+  val of_std_seq_count : 'a Seq.t -> ('a, int) Hashtbl.t
+  (** Like {!add_seq_count}, but allocates a new table and returns it.
+      @since NEXT_RELEASE *)
 
   val of_seq_count : 'a sequence -> ('a, int) Hashtbl.t
   (** Like {!add_seq_count}, but allocates a new table and returns it.
-      @since 0.16 *)
+      @since 0.16
+      @deprecated use {!of_iter_count} or {!of_std_seq_count} *)
+  [@@ocaml.deprecated "use add_iter_count or add_std_seq_count"]
 
   val to_list : ('a,'b) Hashtbl.t -> ('a * 'b) list
   (** List of bindings (order unspecified). *)
@@ -142,10 +200,10 @@ module type S = sig
       This does nothing if the key is not already present in the table.
       @since 0.16 *)
 
-  val keys : 'a t -> key sequence
+  val keys : 'a t -> key iter
   (** Iterate on keys (similar order as {!Hashtbl.iter}). *)
 
-  val values : 'a t -> 'a sequence
+  val values : 'a t -> 'a iter
   (** Iterate on values in the table. *)
 
   val keys_list : _ t -> key list
@@ -160,25 +218,75 @@ module type S = sig
   val map_list : (key -> 'a -> 'b) -> 'a t -> 'b list
   (** Map on a hashtable's items, collect into a list. *)
 
-  val to_seq : 'a t -> (key * 'a) sequence
-  (** Iterate on values in the table. *)
+  val to_iter : 'a t -> (key * 'a) iter
+  (** Iterate on bindings in the table.
+      @since NEXT_RELEASE *)
 
-  val of_seq : (key * 'a) sequence -> 'a t
-  (** From the given bindings, added in order. *)
+  val to_seq : 'a t -> (key * 'a) sequence
+  (** Iterate on values in the table.
+      @deprecated use {!to_iter} instead *)
+  [@@ocaml.deprecated "use to_iter"]
+
+  val add_iter : 'a t -> (key * 'a) iter -> unit
+  (** Add the corresponding pairs to the table, using {!Hashtbl.add}.
+      @since NEXT_RELEASE *)
+
+  val add_std_seq : 'a t -> (key * 'a) Seq.t -> unit
+  (** Add the corresponding pairs to the table, using {!Hashtbl.add}.
+      @since NEXT_RELEASE *)
 
   val add_seq : 'a t -> (key * 'a) sequence -> unit
   (** Add the corresponding pairs to the table, using {!Hashtbl.add}.
-      @since 0.16 *)
+      @since 0.16
+      @deprecated use {!add_iter} or {!add_std_seq} *)
+  [@@ocaml.deprecated "use add_iter or add_std_seq"]
+
+  val of_iter : (key * 'a) iter -> 'a t
+  (** From the given bindings, added in order.
+      @since NEXT_RELEASE *)
+
+  val of_std_seq : (key * 'a) Seq.t -> 'a t
+  (** From the given bindings, added in order.
+      @since NEXT_RELEASE *)
+
+  val of_seq : (key * 'a) sequence -> 'a t
+  (** From the given bindings, added in order.
+      @deprecated use {!of_iter} or {!of_std_seq} *)
+  [@@ocaml.deprecated "use of_iter or of_std_seq"]
+
+  val add_iter_count : int t -> key iter -> unit
+  (** [add_iter_count tbl i] increments the count of each element of [i]
+      by calling {!incr}. This is useful for counting how many times each
+      element of [i] occurs.
+      @since NEXT_RELEASE *)
+
+  val add_std_seq_count : int t -> key Seq.t -> unit
+  (** [add_seq_count tbl seq] increments the count of each element of [seq]
+      by calling {!incr}. This is useful for counting how many times each
+      element of [seq] occurs.
+      @since NEXT_RELEASE *)
 
   val add_seq_count : int t -> key sequence -> unit
   (** [add_seq_count tbl seq] increments the count of each element of [seq]
       by calling {!incr}. This is useful for counting how many times each
       element of [seq] occurs.
-      @since 0.16 *)
+      @since 0.16
+      @deprecated use {!add_iter_count} or {!add_std_seq_count} *)
+  [@@ocaml.deprecated "use add_iter_count or add_std_seq_count"]
+
+  val of_iter_count : key iter -> int t
+  (** Like {!add_seq_count}, but allocates a new table and returns it.
+      @since NEXT_RELEASE *)
+
+  val of_std_seq_count : key Seq.t -> int t
+  (** Like {!add_seq_count}, but allocates a new table and returns it.
+      @since NEXT_RELEASE *)
 
   val of_seq_count : key sequence -> int t
   (** Like {!add_seq_count}, but allocates a new table and returns it.
-      @since 0.16 *)
+      @since 0.16
+      @deprecated use {!of_iter_count} or {!of_std_seq_count} *)
+  [@@ocaml.deprecated "use add_iter_count or add_std_seq_count"]
 
   val to_list : 'a t -> (key * 'a) list
   (** List of bindings (order unspecified). *)
diff --git a/src/core/CCHeap.ml b/src/core/CCHeap.ml
index ebc9f1d8..2cab7086 100644
--- a/src/core/CCHeap.ml
+++ b/src/core/CCHeap.ml
@@ -3,6 +3,7 @@
 
 (** {1 Leftist Heaps} *)
 
+type 'a iter = ('a -> unit) -> unit
 type 'a sequence = ('a -> unit) -> unit
 type 'a gen = unit -> 'a option
 type 'a printer = Format.formatter -> 'a -> unit
@@ -130,14 +131,16 @@ module type S = sig
   val delete_one : (elt -> elt -> bool) -> elt -> t -> t
   (** Delete one occurrence of a value if it exist in the heap.
       [delete_one eq x h], use [eq] to find one [x] in [h] and delete it.
-      If [h] do not contain [x] then it return [h]. *)
+      If [h] do not contain [x] then it return [h].
+      @since 2.0 *)
 
   val delete_all : (elt -> elt -> bool) -> elt -> t -> t
   (** Delete all occurrences of a value in the heap.
       [delete_all eq x h], use [eq] to find all [x] in [h] and delete them.
       If [h] do not contain [x] then it return [h].
       The difference with {!filter} is that [delete_all] stops as soon as
-      it enters a subtree whose root is bigger than the element. *)
+      it enters a subtree whose root is bigger than the element.
+      @since 2.0 *)
 
   val iter : (elt -> unit) -> t -> unit
   (** Iterate on elements. *)
@@ -151,7 +154,7 @@ module type S = sig
   (** {2 Conversions}
 
       The interface of [of_gen], [of_seq], [of_klist]
-      has changed @since 0.16 (the old signatures
+      has changed since 0.16 (the old signatures
       are now [add_seq], [add_gen], [add_klist]). *)
 
   val to_list : t -> elt list
@@ -167,26 +170,65 @@ module type S = sig
       @since 0.16 *)
 
   val of_list : elt list -> t
-  (** [of_list l] is [add_list empty l]. *)
+  (** [of_list l] is [add_list empty l]. Complexity: [O(n log n)]. *)
 
-  val add_seq : t -> elt sequence -> t
+  val add_iter : t -> elt iter -> t
   (** Like {!add_list}.
-      @since 0.16 *)
+      @since NEXT_RELEASE *)
+
+  val add_std_seq : t -> elt Seq.t -> t
+  (** Like {!add_list}.
+      @since NEXT_RELEASE *)
+
+  val add_seq : t -> elt sequence -> t (** @since 0.16 *)
+  (** Like {!add_list}.
+      @deprecated use {!add_iter} or {!add_std_seq} instead *)
+  [@@ocaml.deprecated "use add_iter. For the standard Seq, see {!add_std_seq}"]
+
+  val of_iter : elt iter -> t
+  (** Build a heap from a given [iter]. Complexity: [O(n log n)].
+      @since NEXT_RELEASE *)
+
+  val of_std_seq : elt Seq.t -> t
+  (** Build a heap from a given [Seq.t]. Complexity: [O(n log n)].
+      @since NEXT_RELEASE *)
 
   val of_seq : elt sequence -> t
-  (** Build a heap from a given [sequence]. *)
+  (** Build a heap from a given [sequence]. Complexity: [O(n log n)].
+      @deprecated use {!of_iter} or {!of_std_seq} instead *)
+  [@@ocaml.deprecated "use of_iter. For the standard Seq, see {!of_std_seq}"]
+
+  val to_iter : t -> elt iter
+  (** Return a [iter] of the elements of the heap.
+      @since NEXT_RELEASE *)
+
+  val to_std_seq : t -> elt Seq.t
+  (** Return a [Seq.t] of the elements of the heap.
+      @since NEXT_RELEASE *)
 
   val to_seq : t -> elt sequence
-  (** Return a [sequence] of the elements of the heap. *)
+  (** Return a [sequence] of the elements of the heap.
+      @deprecated use {!to_iter} or {!to_std_seq} instead *)
+  [@@ocaml.deprecated "use to_iter. For the standard Seq, see {!to_std_seq}"]
+
+  val to_iter_sorted : t -> elt iter
+  (** Iterate on the elements, in increasing order.
+      @since NEXT_RELEASE *)
+
+  val to_std_seq_sorted : t -> elt Seq.t
+  (** Iterate on the elements, in increasing order.
+      @since NEXT_RELEASE *)
 
   val to_seq_sorted : t -> elt sequence
   (** Iterate on the elements, in increasing order.
-      @since 1.1 *)
+      @since 1.1
+      @deprecated use {!to_iter_sorted} or {!to_std_seq_sorted} instead *)
+  [@@ocaml.deprecated "use to_iter_sorted or to_std_seq_sorted"]
 
   val add_klist : t -> elt klist -> t (** @since 0.16 *)
 
   val of_klist : elt klist -> t
-  (** Build a heap from a given [klist]. *)
+  (** Build a heap from a given [klist]. Complexity: [O(n log n)]. *)
 
   val to_klist : t -> elt klist
   (** Return a [klist] of the elements of the heap. *)
@@ -194,7 +236,7 @@ module type S = sig
   val add_gen : t -> elt gen -> t (** @since 0.16 *)
 
   val of_gen : elt gen -> t
-  (** Build a heap from a given [gen]. *)
+  (** Build a heap from a given [gen]. Complexity: [O(n log n)]. *)
 
   val to_gen : t -> elt gen
   (** Return a [gen] of the elements of the heap. *)
@@ -207,8 +249,9 @@ module type S = sig
        @since 2.7 *)
 
   val pp : ?sep:string -> elt printer -> t printer
-  (** @since 0.16
-      Renamed from {!print} @since 2.0 *)
+  (** Printer.
+      Renamed from {!print} since 2.0
+      @since 0.16 *)
 end
 
 module Make(E : PARTIAL_ORD) : S with type elt = E.t = struct
@@ -340,22 +383,46 @@ module Make(E : PARTIAL_ORD) : S with type elt = E.t = struct
 
   let of_list l = add_list empty l
 
-  let add_seq h seq =
+  let add_iter h i =
     let h = ref h in
-    seq (fun x -> h := insert x !h);
+    i (fun x -> h := insert x !h);
     !h
 
-  let of_seq seq = add_seq empty seq
+  let add_std_seq h seq =
+    let h = ref h in
+    Seq.iter (fun x -> h := insert x !h) seq;
+    !h
 
-  let to_seq h k = iter k h
+  let of_iter i = add_iter empty i
+  let of_std_seq seq = add_std_seq empty seq
 
-  let to_seq_sorted heap =
+  let to_iter h k = iter k h
+
+  let to_std_seq h =
+    (* use an explicit stack [st] *)
+    let rec aux st () =
+      match st with
+      | [] -> Seq.Nil
+      | E :: st' -> aux st' ()
+      | N(_,x,l,r) :: st' -> Seq.Cons (x, aux (l::r::st'))
+    in aux [h]
+
+  let to_iter_sorted heap =
     let rec recurse h k = match take h with
       | None -> ()
       | Some (h',x) -> k x; recurse h' k
     in
     fun k -> recurse heap k
 
+  let rec to_std_seq_sorted h () = match take h with
+    | None -> Seq.Nil
+    | Some (h', x) -> Seq.Cons (x, to_std_seq_sorted h')
+
+  let add_seq = add_iter
+  let of_seq = of_iter
+  let to_seq = to_iter
+  let to_seq_sorted = to_iter_sorted
+
   let rec add_klist h l = match l() with
     | `Nil -> h
     | `Cons (x, l') ->
diff --git a/src/core/CCHeap.mli b/src/core/CCHeap.mli
index b0bc278e..0caab204 100644
--- a/src/core/CCHeap.mli
+++ b/src/core/CCHeap.mli
@@ -5,7 +5,15 @@
     
     Implementation following Okasaki's book. *)
 
+
+(* TODO: remove for 3.0 *)
 type 'a sequence = ('a -> unit) -> unit
+(** @deprecated use ['a iter] instead *)
+
+type 'a iter = ('a -> unit) -> unit
+(** Fast internal iterator.
+    @since NEXT_RELEASE *)
+
 type 'a gen = unit -> 'a option
 type 'a klist = unit -> [`Nil | `Cons of 'a * 'a klist]
 type 'a ktree = unit -> [`Nil | `Node of 'a * 'a ktree list]
@@ -110,18 +118,58 @@ module type S = sig
   val of_list : elt list -> t
   (** [of_list l] is [add_list empty l]. Complexity: [O(n log n)]. *)
 
+  val add_iter : t -> elt iter -> t
+  (** Like {!add_list}.
+      @since NEXT_RELEASE *)
+
+  val add_std_seq : t -> elt Seq.t -> t
+  (** Like {!add_list}.
+      @since NEXT_RELEASE *)
+
   val add_seq : t -> elt sequence -> t (** @since 0.16 *)
-  (** Like {!add_list}. *)
+  (** Like {!add_list}.
+      @deprecated use {!add_iter} or {!add_std_seq} instead *)
+  [@@ocaml.deprecated "use add_iter. For the standard Seq, see {!add_std_seq}"]
+
+  val of_iter : elt iter -> t
+  (** Build a heap from a given [iter]. Complexity: [O(n log n)].
+      @since NEXT_RELEASE *)
+
+  val of_std_seq : elt Seq.t -> t
+  (** Build a heap from a given [Seq.t]. Complexity: [O(n log n)].
+      @since NEXT_RELEASE *)
 
   val of_seq : elt sequence -> t
-  (** Build a heap from a given [sequence]. Complexity: [O(n log n)]. *)
+  (** Build a heap from a given [sequence]. Complexity: [O(n log n)].
+      @deprecated use {!of_iter} or {!of_std_seq} instead *)
+  [@@ocaml.deprecated "use of_iter. For the standard Seq, see {!of_std_seq}"]
+
+  val to_iter : t -> elt iter
+  (** Return a [iter] of the elements of the heap.
+      @since NEXT_RELEASE *)
+
+  val to_std_seq : t -> elt Seq.t
+  (** Return a [Seq.t] of the elements of the heap.
+      @since NEXT_RELEASE *)
 
   val to_seq : t -> elt sequence
-  (** Return a [sequence] of the elements of the heap. *)
+  (** Return a [sequence] of the elements of the heap.
+      @deprecated use {!to_iter} or {!to_std_seq} instead *)
+  [@@ocaml.deprecated "use to_iter. For the standard Seq, see {!to_std_seq}"]
+
+  val to_iter_sorted : t -> elt iter
+  (** Iterate on the elements, in increasing order.
+      @since NEXT_RELEASE *)
+
+  val to_std_seq_sorted : t -> elt Seq.t
+  (** Iterate on the elements, in increasing order.
+      @since NEXT_RELEASE *)
 
   val to_seq_sorted : t -> elt sequence
   (** Iterate on the elements, in increasing order.
-      @since 1.1 *)
+      @since 1.1
+      @deprecated use {!to_iter_sorted} or {!to_std_seq_sorted} instead *)
+  [@@ocaml.deprecated "use to_iter_sorted or to_std_seq_sorted"]
 
   val add_klist : t -> elt klist -> t (** @since 0.16 *)
 
diff --git a/src/core/CCList.ml b/src/core/CCList.ml
index ea09ddf3..48db53c0 100644
--- a/src/core/CCList.ml
+++ b/src/core/CCList.ml
@@ -1608,6 +1608,7 @@ end
 
 (** {2 Conversions} *)
 
+type 'a iter = ('a -> unit) -> unit
 type 'a sequence = ('a -> unit) -> unit
 type 'a gen = unit -> 'a option
 type 'a klist = unit -> [`Nil | `Cons of 'a * 'a klist]
@@ -1651,16 +1652,42 @@ let to_string ?(start="") ?(stop="") ?(sep=", ") item_to_string l =
   (to_string ~sep:" " string_of_int [1;2;3;4]) "1 2 3 4"
 *)
 
-let to_seq l k = List.iter k l
-let of_seq seq =
+let to_iter l k = List.iter k l
+
+let rec to_std_seq l () = match l with
+  | [] -> Seq.Nil
+  | x :: tl -> Seq.Cons (x, to_std_seq tl)
+
+let of_iter i =
   let l = ref [] in
-  seq (fun x -> l := x :: !l);
+  i (fun x -> l := x :: !l);
   List.rev !l
 
+let of_std_seq_rev l =
+  let rec loop acc s = match s() with
+    | Seq.Nil -> acc
+    | Seq.Cons (x,tl) -> loop (x::acc) tl
+  in
+  loop [] l
+
+let of_std_seq l =
+  let rec direct i seq =
+    if i <= 0 then List.rev (of_std_seq_rev seq)
+    else (
+      match seq() with
+        | Seq.Nil -> []
+        | Seq.Cons (x, tl) -> x :: direct (i-1) tl
+    )
+  in
+  direct direct_depth_default_ l
+
 (*$Q
   Q.(list int) (fun l -> of_seq (to_seq l) = l)
 *)
 
+let to_seq = to_iter
+let of_seq = of_iter
+
 let to_gen l =
   let l = ref l in
   fun () ->
diff --git a/src/core/CCList.mli b/src/core/CCList.mli
index 620ca315..64430bb0 100644
--- a/src/core/CCList.mli
+++ b/src/core/CCList.mli
@@ -1,11 +1,17 @@
-(*  AUTOGENERATED FROM CCListLabels.mli  *)
-
 
 (* This file is free software, part of containers. See file "license" for more details. *)
 
 (** {1 Complements to list} *)
 
+
+(* TODO: remove for 3.0 *)
 type 'a sequence = ('a -> unit) -> unit
+(** @deprecated use ['a iter] instead *)
+
+type 'a iter = ('a -> unit) -> unit
+(** Fast internal iterator.
+    @since NEXT_RELEASE *)
+
 type 'a gen = unit -> 'a option
 type 'a klist = unit -> [`Nil | `Cons of 'a * 'a klist]
 type 'a printer = Format.formatter -> 'a -> unit
@@ -691,12 +697,38 @@ val to_string : ?start:string -> ?stop:string -> ?sep:string ->
     [sep] as a separator between elements of [l].
     @since 2.7 *)
 
+val to_iter : 'a t -> 'a iter
+(** Return a [iter] of the elements of the list.
+    @since NEXT_RELEASE *)
+
+val to_std_seq : 'a t -> 'a Seq.t
+(** Return a [Seq.t] of the elements of the list.
+    @since NEXT_RELEASE *)
+
 val to_seq : 'a t -> 'a sequence
-(** Return a [sequence] of the elements of the list. *)
+(** Return a [sequence] of the elements of the list.
+    @deprecated use {!to_iter} or {!to_std_seq} instead *)
+[@@ocaml.deprecated "use to_iter or to_std_seq"]
+
+val of_iter : 'a iter -> 'a t
+(** Build a list from a given [iter].
+    In the result, elements appear in the same order as they did in the source [iter].
+    @since NEXT_RELEASE *)
+
+val of_std_seq_rev : 'a Seq.t -> 'a t
+(** Build a list from a given [Seq.t], in reverse order.
+    @since NEXT_RELEASE *)
+
+val of_std_seq : 'a Seq.t -> 'a t
+(** Build a list from a given [Seq.t].
+    In the result, elements appear in the same order as they did in the source [seq].
+    @since NEXT_RELEASE *)
 
 val of_seq : 'a sequence -> 'a t
 (** Build a list from a given [sequence].
-    In the result, elements appear in the same order as they did in the source [sequence]. *)
+    In the result, elements appear in the same order as they did in the source [sequence].
+    @deprecated use {!of_iter} or {!of_std_seq} instead *)
+[@@ocaml.deprecated "use of_iter or of_std_seq"]
 
 val to_gen : 'a t -> 'a gen
 (** Return a [gen] of the elements of the list. *)
diff --git a/src/core/CCListLabels.mli b/src/core/CCListLabels.mli
index 2b8df038..bc914720 100644
--- a/src/core/CCListLabels.mli
+++ b/src/core/CCListLabels.mli
@@ -3,7 +3,15 @@
 
 (** {1 Complements to list} *)
 
+
+(* TODO: remove for 3.0 *)
 type 'a sequence = ('a -> unit) -> unit
+(** @deprecated use ['a iter] instead *)
+
+type 'a iter = ('a -> unit) -> unit
+(** Fast internal iterator.
+    @since NEXT_RELEASE *)
+
 type 'a gen = unit -> 'a option
 type 'a klist = unit -> [`Nil | `Cons of 'a * 'a klist]
 type 'a printer = Format.formatter -> 'a -> unit
@@ -689,12 +697,38 @@ val to_string : ?start:string -> ?stop:string -> ?sep:string ->
     [sep] as a separator between elements of [l].
     @since 2.7 *)
 
+val to_iter : 'a t -> 'a iter
+(** Return a [iter] of the elements of the list.
+    @since NEXT_RELEASE *)
+
+val to_std_seq : 'a t -> 'a Seq.t
+(** Return a [Seq.t] of the elements of the list.
+    @since NEXT_RELEASE *)
+
 val to_seq : 'a t -> 'a sequence
-(** Return a [sequence] of the elements of the list. *)
+(** Return a [sequence] of the elements of the list.
+    @deprecated use {!to_iter} or {!to_std_seq} instead *)
+[@@ocaml.deprecated "use to_iter or to_std_seq"]
+
+val of_iter : 'a iter -> 'a t
+(** Build a list from a given [iter].
+    In the result, elements appear in the same order as they did in the source [iter].
+    @since NEXT_RELEASE *)
+
+val of_std_seq_rev : 'a Seq.t -> 'a t
+(** Build a list from a given [Seq.t], in reverse order.
+    @since NEXT_RELEASE *)
+
+val of_std_seq : 'a Seq.t -> 'a t
+(** Build a list from a given [Seq.t].
+    In the result, elements appear in the same order as they did in the source [seq].
+    @since NEXT_RELEASE *)
 
 val of_seq : 'a sequence -> 'a t
 (** Build a list from a given [sequence].
-    In the result, elements appear in the same order as they did in the source [sequence]. *)
+    In the result, elements appear in the same order as they did in the source [sequence].
+    @deprecated use {!of_iter} or {!of_std_seq} instead *)
+[@@ocaml.deprecated "use of_iter or of_std_seq"]
 
 val to_gen : 'a t -> 'a gen
 (** Return a [gen] of the elements of the list. *)
diff --git a/src/core/CCMap.ml b/src/core/CCMap.ml
index 214b00e7..5f68e0b7 100644
--- a/src/core/CCMap.ml
+++ b/src/core/CCMap.ml
@@ -3,6 +3,7 @@
 
 (** {1 Extensions of Standard Map} *)
 
+type 'a iter = ('a -> unit) -> unit
 type 'a sequence = ('a -> unit) -> unit
 type 'a printer = Format.formatter -> 'a -> unit
 
@@ -12,11 +13,11 @@ module type S = sig
   include Map.S
 
   val get : key -> 'a t -> 'a option
-  (** Safe version of {!find} *)
+  (** Safe version of {!find}. *)
 
   val get_or : key -> 'a t -> default:'a -> 'a
   (** [get_or k m ~default] returns the value associated to [k] if present,
-      and returns [default] otherwise (if [k] doesn't belong in [m])
+      and returns [default] otherwise (if [k] doesn't belong in [m]).
       @since 0.16 *)
 
   val update : key -> ('a option -> 'a option) -> 'a t -> 'a t
@@ -26,19 +27,19 @@ module type S = sig
       [add k v' m] is returned. *)
 
   val choose_opt : 'a t -> (key * 'a) option
-  (** Safe version of {!choose}
+  (** Safe version of {!choose}.
       @since 1.5 *)
 
   val min_binding_opt : 'a t -> (key * 'a) option
-  (** Safe version of {!min_binding}
+  (** Safe version of {!min_binding}.
       @since 1.5 *)
 
   val max_binding_opt : 'a t -> (key * 'a) option
-  (** Safe version of {!max_binding}
+  (** Safe version of {!max_binding}.
       @since 1.5 *)
 
   val find_opt : key -> 'a t -> 'a option
-  (** Safe version of {!find}
+  (** Safe version of {!find}.
       @since 1.5 *)
 
   val find_first : (key -> bool) -> 'a t -> key * 'a
@@ -47,7 +48,7 @@ module type S = sig
       @since 1.5 *)
 
   val find_first_opt : (key -> bool) -> 'a t -> (key * 'a) option
-  (** Safe version of {!find_first}
+  (** Safe version of {!find_first}.
       @since 1.5 *)
 
   val merge_safe :
@@ -58,16 +59,46 @@ module type S = sig
 
   val union : (key -> 'a -> 'a -> 'a option) -> 'a t -> 'a t -> 'a t
   (** Union of both maps, using the function to combine bindings
-      that belong to both inputs
+      that belong to both inputs.
       @since 1.4 *)
 
+  val of_iter : (key * 'a) iter -> 'a t
+  (** Like {!of_list}.
+      @since NEXT_RELEASE *)
+
+  val add_std_seq : 'a t -> (key * 'a) Seq.t -> 'a t
+  (** Like {!add_list}.
+      @since NEXT_RELEASE *)
+
+  val of_std_seq : (key * 'a) Seq.t -> 'a t
+  (** Like {!of_list}.
+      @since NEXT_RELEASE *)
+
+  val add_iter : 'a t -> (key * 'a) iter -> 'a t
+  (** Like {!add_list}.
+      @since NEXT_RELEASE *)
+
+  val of_iter : (key * 'a) iter -> 'a t
+  (** Like {!of_list}.
+      @since NEXT_RELEASE *)
+
+  val to_iter : 'a t -> (key * 'a) iter
+  (** Like {!to_list}.
+      @since NEXT_RELEASE *)
+
   val of_seq : (key * 'a) sequence -> 'a t
-  (** Like {!of_list} *)
+  (** Like {!of_list}.
+      @deprecated use {!of_iter} instead. *)
+  [@@ocaml.deprecated "use of_iter instead"]
 
   val add_seq : 'a t -> (key * 'a) sequence -> 'a t
-  (** @since 0.14 *)
+  (** @since 0.14
+      @deprecated use {!add_iter} instead. *)
+  [@@ocaml.deprecated "use add_iter instead"]
 
   val to_seq : 'a t -> (key * 'a) sequence
+  (** @deprecated use {!to_iter} instead. *)
+  [@@ocaml.deprecated "use to_iter instead"]
 
   val of_list : (key * 'a) list -> 'a t
   (** Build a map from the given list of bindings [k_i -> v_i],
@@ -78,12 +109,12 @@ module type S = sig
   val add_list : 'a t -> (key * 'a) list -> 'a t
   (** @since 0.14 *)
 
-  val keys : _ t -> key sequence
-  (** Iterate on keys only
+  val keys : _ t -> key iter
+  (** Iterate on keys only.
       @since 0.15 *)
 
-  val values : 'a t -> 'a sequence
-  (** Iterate on values only
+  val values : 'a t -> 'a iter
+  (** Iterate on values only.
       @since 0.15 *)
 
   val to_list : 'a t -> (key * 'a) list
@@ -182,16 +213,27 @@ module Make(O : Map.OrderedType) = struct
          | Some v1, Some v2 -> f k (`Both (v1,v2)))
       a b
 
-  let add_seq m s =
+  let add_std_seq m s =
+    let m = ref m in
+    Seq.iter (fun (k,v) -> m := add k v !m) s;
+    !m
+
+  let of_std_seq s = add_std_seq empty s
+
+  let add_iter m s =
     let m = ref m in
     s (fun (k,v) -> m := add k v !m);
     !m
 
-  let of_seq s = add_seq empty s
+  let of_iter s = add_iter empty s
 
-  let to_seq m yield =
+  let to_iter m yield =
     iter (fun k v -> yield (k,v)) m
 
+  let add_seq = add_iter
+  let of_seq = of_iter
+  let to_seq = to_iter
+
   let keys m yield =
     iter (fun k _ -> yield k) m
 
diff --git a/src/core/CCMap.mli b/src/core/CCMap.mli
index b241a30c..71158f3d 100644
--- a/src/core/CCMap.mli
+++ b/src/core/CCMap.mli
@@ -6,7 +6,15 @@
     Provide useful functions and iterators on [Map.S]
     @since 0.5 *)
 
+
+(* TODO: remove for 3.0 *)
 type 'a sequence = ('a -> unit) -> unit
+(** @deprecated use ['a iter] instead *)
+
+type 'a iter = ('a -> unit) -> unit
+(** Fast internal iterator.
+    @since NEXT_RELEASE *)
+
 type 'a printer = Format.formatter -> 'a -> unit
 
 module type OrderedType = Map.OrderedType
@@ -65,13 +73,43 @@ module type S = sig
       that belong to both inputs.
       @since 1.4 *)
 
+  val of_iter : (key * 'a) iter -> 'a t
+  (** Like {!of_list}.
+      @since NEXT_RELEASE *)
+
+  val add_std_seq : 'a t -> (key * 'a) Seq.t -> 'a t
+  (** Like {!add_list}.
+      @since NEXT_RELEASE *)
+
+  val of_std_seq : (key * 'a) Seq.t -> 'a t
+  (** Like {!of_list}.
+      @since NEXT_RELEASE *)
+
+  val add_iter : 'a t -> (key * 'a) iter -> 'a t
+  (** Like {!add_list}.
+      @since NEXT_RELEASE *)
+
+  val of_iter : (key * 'a) iter -> 'a t
+  (** Like {!of_list}.
+      @since NEXT_RELEASE *)
+
+  val to_iter : 'a t -> (key * 'a) iter
+  (** Like {!to_list}.
+      @since NEXT_RELEASE *)
+
   val of_seq : (key * 'a) sequence -> 'a t
-  (** Like {!of_list}. *)
+  (** Like {!of_list}.
+      @deprecated use {!of_iter} instead. *)
+  [@@ocaml.deprecated "use of_iter instead"]
 
   val add_seq : 'a t -> (key * 'a) sequence -> 'a t
-  (** @since 0.14 *)
+  (** @since 0.14
+      @deprecated use {!add_iter} instead. *)
+  [@@ocaml.deprecated "use add_iter instead"]
 
   val to_seq : 'a t -> (key * 'a) sequence
+  (** @deprecated use {!to_iter} instead. *)
+  [@@ocaml.deprecated "use to_iter instead"]
 
   val of_list : (key * 'a) list -> 'a t
   (** Build a map from the given list of bindings [k_i -> v_i],
@@ -82,11 +120,11 @@ module type S = sig
   val add_list : 'a t -> (key * 'a) list -> 'a t
   (** @since 0.14 *)
 
-  val keys : _ t -> key sequence
+  val keys : _ t -> key iter
   (** Iterate on keys only.
       @since 0.15 *)
 
-  val values : 'a t -> 'a sequence
+  val values : 'a t -> 'a iter
   (** Iterate on values only.
       @since 0.15 *)
 
diff --git a/src/core/CCOpt.mli b/src/core/CCOpt.mli
index b3e3467d..2231ff5a 100644
--- a/src/core/CCOpt.mli
+++ b/src/core/CCOpt.mli
@@ -205,6 +205,8 @@ val to_iter : 'a t -> 'a sequence
 
 val to_seq : 'a t -> 'a sequence
 (** Previous name for {!to_iter}
-    @deprecated use {!to_iter} instead *)
+    @deprecated use {!to_iter} or {!to_std_seq} instead *)
+[@@ocaml.deprecated "use to_iter or to_std_seq"]
+
 
 val pp : 'a printer -> 'a t printer
diff --git a/src/core/CCResult.ml b/src/core/CCResult.ml
index 99b2f07e..20ad028a 100644
--- a/src/core/CCResult.ml
+++ b/src/core/CCResult.ml
@@ -2,6 +2,7 @@
 
 (** {1 Error Monad} *)
 
+type 'a iter = ('a -> unit) -> unit
 type 'a sequence = ('a -> unit) -> unit
 type 'a equal = 'a -> 'a -> bool
 type 'a ord = 'a -> 'a -> int
@@ -323,10 +324,16 @@ let of_opt = function
   | None -> Error "of_opt"
   | Some x -> Ok x
 
-let to_seq e k = match e with
+let to_std_seq e () = match e with
+  | Ok x -> Seq.Cons (x, Seq.empty)
+  | Error _ -> Seq.Nil
+
+let to_iter e k = match e with
   | Ok x -> k x
   | Error _ -> ()
 
+let to_seq = to_iter
+
 type ('a, 'b) error = [`Ok of 'a | `Error of 'b]
 
 let of_err = function
diff --git a/src/core/CCResult.mli b/src/core/CCResult.mli
index 320cbec9..61984ac2 100644
--- a/src/core/CCResult.mli
+++ b/src/core/CCResult.mli
@@ -6,7 +6,15 @@
 
     @since 0.16 *)
 
+
+(* TODO: remove for 3.0 *)
 type 'a sequence = ('a -> unit) -> unit
+(** @deprecated use ['a iter] instead *)
+
+type 'a iter = ('a -> unit) -> unit
+(** Fast internal iterator.
+    @since NEXT_RELEASE *)
+
 type 'a equal = 'a -> 'a -> bool
 type 'a ord = 'a -> 'a -> int
 type 'a printer = Format.formatter -> 'a -> unit
@@ -246,7 +254,15 @@ val to_opt : ('a, _) t -> 'a option
 val of_opt : 'a option -> ('a, string) t
 (** Convert an option to a result. *)
 
+val to_iter : ('a, _) t -> 'a iter
+(** @since NEXT_RELEASE *)
+
+val to_std_seq : ('a, _) t -> 'a Seq.t
+(** @since NEXT_RELEASE *)
+
 val to_seq : ('a, _) t -> 'a sequence
+(** @deprecated use {!to_iter} or {!to_std_seq} *)
+[@@ocaml.deprecated "use to_iter or to_std_seq"]
 
 type ('a, 'b) error = [`Ok of 'a | `Error of 'b]
 
diff --git a/src/core/CCSet.ml b/src/core/CCSet.ml
index 36f21a2e..4bfa7d04 100644
--- a/src/core/CCSet.ml
+++ b/src/core/CCSet.ml
@@ -3,6 +3,7 @@
 
 (** {1 Wrapper around Set} *)
 
+type 'a iter = ('a -> unit) -> unit
 type 'a sequence = ('a -> unit) -> unit
 type 'a printer = Format.formatter -> 'a -> unit
 
@@ -19,43 +20,62 @@ module type S = sig
   include Set.S
 
   val min_elt_opt : t -> elt option
-  (** Safe version of {!min_elt}
+  (** Safe version of {!min_elt}.
       @since 1.5 *)
 
   val max_elt_opt : t -> elt option
-  (** Safe version of {!max_elt}
+  (** Safe version of {!max_elt}.
       @since 1.5 *)
 
   val choose_opt : t -> elt option
-  (** Safe version of {!choose}
+  (** Safe version of {!choose}.
       @since 1.5 *)
 
   val find_opt : elt -> t -> elt option
-  (** Safe version of {!find}
+  (** Safe version of {!find}.
       @since 1.5 *)
 
   val find_first : (elt -> bool) -> t -> elt
-  (** Find minimum element satisfying predicate
+  (** Find minimum element satisfying predicate.
       @since 1.5 *)
 
   val find_first_opt : (elt -> bool) -> t -> elt option
-  (** Safe version of {!find_first}
+  (** Safe version of {!find_first}.
       @since 1.5 *)
 
   val find_last : (elt -> bool) -> t -> elt
-  (** Find maximum element satisfying predicate
+  (** Find maximum element satisfying predicate.
       @since 1.5 *)
 
   val find_last_opt : (elt -> bool) -> t -> elt option
-  (** Safe version of {!find_last}
+  (** Safe version of {!find_last}.
       @since 1.5 *)
 
+  val of_iter : elt iter -> t
+  (** Build a set from the given [iter] of elements.
+      @since NEXT_RELEASE *)
+
+  val add_iter : t -> elt iter -> t
+  (** @since NEXT_RELEASE *)
+
+  val to_iter : t -> elt iter
+  (** [to_iter t] converts the set [t] to a [iter] of the elements.
+      @since NEXT_RELEASE *)
+
   val of_seq : elt sequence -> t
+  (** Build a set from the given [sequence] of elements.
+      @deprecated use {!of_iter} instead. *)
+  [@@ocaml.deprecated "use of_iter instead"]
 
   val add_seq : t -> elt sequence -> t
-  (** @since 0.14 *)
+  (** @since 0.14
+      @deprecated use {!add_iter} instead. *)
+  [@@ocaml.deprecated "use add_iter instead"]
 
   val to_seq : t -> elt sequence
+  (** [to_seq t] converts the set [t] to a [sequence] of the elements.
+      @deprecated use {!to_iter} instead. *)
+  [@@ocaml.deprecated "use to_iter instead"]
 
   val of_list : elt list -> t
   (** Build a set from the given list of elements,
@@ -65,6 +85,7 @@ module type S = sig
   (** @since 0.14 *)
 
   val to_list : t -> elt list
+  (** [to_list t] converts the set [t] to a list of the elements. *)
 
   val to_string :
     ?start:string -> ?stop:string -> ?sep:string ->
@@ -75,6 +96,7 @@ module type S = sig
   val pp :
     ?start:string -> ?stop:string -> ?sep:string ->
     elt printer -> t printer
+    (** Print the set. *)
 end
 
 module Make(O : Map.OrderedType) = struct
@@ -133,14 +155,24 @@ module Make(O : Map.OrderedType) = struct
 
   include S
 
-  let add_seq set seq =
+  let add_std_seq set seq =
     let set = ref set in
-    seq (fun x -> set := add x !set);
+    Seq.iter (fun x -> set := add x !set) seq;
     !set
 
-  let of_seq s = add_seq empty s
+  let of_std_seq s = add_std_seq empty s
 
-  let to_seq s yield = iter yield s
+  let add_iter set i =
+    let set = ref set in
+    i (fun x -> set := add x !set);
+    !set
+
+  let of_iter s = add_iter empty s
+  let to_iter s yield = iter yield s
+
+  let add_seq = add_iter
+  let of_seq = of_iter
+  let to_seq = to_iter
 
   let add_list = List.fold_left (fun set x -> add x set)
 
diff --git a/src/core/CCSet.mli b/src/core/CCSet.mli
index f31246ef..47e9d8de 100644
--- a/src/core/CCSet.mli
+++ b/src/core/CCSet.mli
@@ -5,7 +5,15 @@
 
     @since 0.9 *)
 
+
+(* TODO: remove for 3.0 *)
 type 'a sequence = ('a -> unit) -> unit
+(** @deprecated use ['a iter] instead *)
+
+type 'a iter = ('a -> unit) -> unit
+(** Fast internal iterator.
+    @since NEXT_RELEASE *)
+
 type 'a printer = Format.formatter -> 'a -> unit
 
 module type OrderedType = Set.OrderedType
@@ -46,14 +54,31 @@ module type S = sig
   (** Safe version of {!find_last}.
       @since 1.5 *)
 
+  val of_iter : elt iter -> t
+  (** Build a set from the given [iter] of elements.
+      @since NEXT_RELEASE *)
+
+  val add_iter : t -> elt iter -> t
+  (** @since NEXT_RELEASE *)
+
+  val to_iter : t -> elt iter
+  (** [to_iter t] converts the set [t] to a [iter] of the elements.
+      @since NEXT_RELEASE *)
+
   val of_seq : elt sequence -> t
-  (** Build a set from the given [sequence] of elements. *)
+  (** Build a set from the given [sequence] of elements.
+      @deprecated use {!of_iter} instead. *)
+  [@@ocaml.deprecated "use of_iter instead"]
 
   val add_seq : t -> elt sequence -> t
-  (** @since 0.14 *)
+  (** @since 0.14
+      @deprecated use {!add_iter} instead. *)
+  [@@ocaml.deprecated "use add_iter instead"]
 
   val to_seq : t -> elt sequence
-  (** [to_seq t] converts the set [t] to a [sequence] of the elements. *)
+  (** [to_seq t] converts the set [t] to a [sequence] of the elements.
+      @deprecated use {!to_iter} instead. *)
+  [@@ocaml.deprecated "use to_iter instead"]
 
   val of_list : elt list -> t
   (** Build a set from the given list of elements,
@@ -75,7 +100,6 @@ module type S = sig
     ?start:string -> ?stop:string -> ?sep:string ->
     elt printer -> t printer
     (** Print the set. *)
-
 end
 
 module Make(O : Set.OrderedType) : S
diff --git a/src/core/CCString.ml b/src/core/CCString.ml
index f947184c..ab36d1c4 100644
--- a/src/core/CCString.ml
+++ b/src/core/CCString.ml
@@ -5,6 +5,7 @@
 
 open CCShims_
 
+type 'a iter = ('a -> unit) -> unit
 type 'a gen = unit -> 'a option
 type 'a sequence = ('a -> unit) -> unit
 type 'a klist = unit -> [`Nil | `Cons of 'a * 'a klist]
@@ -44,23 +45,59 @@ module type S = sig
   type t
 
   val length : t -> int
+  (** Return the length (number of characters) of the given string. *)
 
   val blit : t -> int -> Bytes.t -> int -> int -> unit
   (** Like {!String.blit}.
       Compatible with the [-safe-string] option.
-      @raise Invalid_argument if indices are not valid *)
+      @raise Invalid_argument if indices are not valid. *)
+
+  (*
+  val blit_immut : t -> int -> t -> int -> int -> string
+  (** Immutable version of {!blit}, returning a new string.
+      [blit a i b j len] is the same as [b], but in which
+      the range [j, ..., j+len] is replaced by [a.[i], ..., a.[i + len]].
+      @raise Invalid_argument if indices are not valid. *)
+     *)
 
   val fold : ('a -> char -> 'a) -> 'a -> t -> 'a
+  (** Fold on chars by increasing index.
+      @since 0.7 *)
 
   (** {2 Conversions} *)
 
   val to_gen : t -> char gen
+  (** Return the [gen] of characters contained in the string. *)
+
+  val to_iter : t -> char iter
+  (** Return the [iter] of characters contained in the string.
+      @since NEXT_RELEASE *)
+
+  val to_std_seq : t -> char Seq.t
+  (** [to_std_seq s] returns a [Seq.t] of the bytes in [s].
+      @since NEXT_RELEASE
+  *)
+
   val to_seq : t -> char sequence
+  (** Return the [sequence] of characters contained in the string.
+      @deprecated use {!to_iter} instead *)
+  [@@ocaml.deprecated "use to_iter or to_std_seq"]
+
   val to_klist : t -> char klist
+  (** Return the [klist] of characters contained in the string.
+      @deprecated use {!to_std_seq} instead *)
+  [@@ocaml.deprecated "use to_std_seq"]
+
   val to_list : t -> char list
+  (** Return the list of characters contained in the string. *)
 
   val pp_buf : Buffer.t -> t -> unit
+  (** Renamed from [pp] since 2.0. *)
+
   val pp : Format.formatter -> t -> unit
+  (** Print the string within quotes.
+
+      Renamed from [print] since 2.0. *)
 end
 
 let equal (a:string) b = Stdlib.(=) a b
@@ -458,6 +495,20 @@ module Split = struct
     Split.list_cpy ~by:" " "hello  world aie" = ["hello"; ""; "world"; "aie"]
   *)
 
+  let _mkseq ~drop ~by s k =
+    let by = Find.compile by in
+    let rec make state () = match _split ~by s state with
+      | None -> Seq.Nil
+      | Some (state', 0, 0) when drop.first -> make state' ()
+      | Some (_, i, 0) when drop.last && i=length s -> Seq.Nil
+      | Some (state', i, len) ->
+        Seq.Cons (k s i len , make state')
+    in make (SplitAt 0)
+
+  let std_seq ?(drop=default_drop) ~by s = _mkseq ~drop ~by s _tuple3
+
+  let std_seq_cpy ?(drop=default_drop) ~by s = _mkseq ~drop ~by s String.sub
+
   let _mkklist ~drop ~by s k =
     let by = Find.compile by in
     let rec make state () = match _split ~by s state with
@@ -472,7 +523,7 @@ module Split = struct
 
   let klist_cpy ?(drop=default_drop) ~by s = _mkklist ~drop ~by s String.sub
 
-  let _mkseq ~drop ~by s f k =
+  let _mk_iter ~drop ~by s f k =
     let by = Find.compile by in
     let rec aux state = match _split ~by s state with
       | None -> ()
@@ -481,8 +532,11 @@ module Split = struct
       | Some (state', i, len) -> k (f s i len); aux state'
     in aux (SplitAt 0)
 
-  let seq ?(drop=default_drop) ~by s = _mkseq ~drop ~by s _tuple3
-  let seq_cpy ?(drop=default_drop) ~by s = _mkseq ~drop ~by s String.sub
+  let iter ?(drop=default_drop) ~by s = _mk_iter ~drop ~by s _tuple3
+  let iter_cpy ?(drop=default_drop) ~by s = _mk_iter ~drop ~by s String.sub
+
+  let seq = iter
+  let seq_cpy = iter_cpy
 
   let left_exn ~by s =
     let i = find ~sub:by s in
@@ -516,7 +570,6 @@ module Split = struct
     Split.right ~by:"_" "abcde" = None
     Split.right ~by:"a_" "abcde" = None
   *)
-
 end
 
 let split_on_char c s: _ list =
@@ -822,13 +875,28 @@ let of_gen g =
     | Some c -> Buffer.add_char b c; aux ()
   in aux ()
 
-let to_seq s k = String.iter k s
+let to_iter s k = String.iter k s
 
-let of_seq seq =
-  let b= Buffer.create 32 in
-  seq (Buffer.add_char b);
+let to_seq = to_iter
+
+let rec _to_std_seq s i len () =
+  if len=0 then Seq.Nil
+  else Seq.Cons (s.[i], _to_std_seq s (i+1)(len-1))
+
+let to_std_seq s = _to_std_seq s 0 (String.length s)
+
+let of_iter i =
+  let b = Buffer.create 32 in
+  i (Buffer.add_char b);
   Buffer.contents b
 
+let of_std_seq seq =
+  let b = Buffer.create 32 in
+  Seq.iter (Buffer.add_char b) seq;
+  Buffer.contents b
+
+let of_seq = of_iter
+
 let rec _to_klist s i len () =
   if len=0 then `Nil
   else `Cons (s.[i], _to_klist s (i+1)(len-1))
@@ -1149,8 +1217,10 @@ module Sub = struct
   *)
 
   let to_gen (s,i,len) = _to_gen s i len
-  let to_seq (s,i,len) k =
-    for i=i to i+len-1 do k s.[i] done
+  let to_iter (s,i,len) k = for i=i to i+len-1 do k s.[i] done
+  let to_std_seq (s,i,len) = _to_std_seq s i len
+
+  let to_seq = to_iter
   let to_klist (s,i,len) = _to_klist s i len
   let to_list (s,i,len) = _to_list s [] i len
 
diff --git a/src/core/CCString.mli b/src/core/CCString.mli
index 74379a0f..9beacbed 100644
--- a/src/core/CCString.mli
+++ b/src/core/CCString.mli
@@ -5,8 +5,16 @@
 
 (** {1 Basic String Utils} *)
 
-type 'a gen = unit -> 'a option
+
+(* TODO: remove for 3.0 *)
 type 'a sequence = ('a -> unit) -> unit
+(** @deprecated use ['a iter] instead *)
+
+type 'a iter = ('a -> unit) -> unit
+(** Fast internal iterator.
+    @since NEXT_RELEASE *)
+
+type 'a gen = unit -> 'a option
 type 'a klist = unit -> [`Nil | `Cons of 'a * 'a klist]
 
 (** {2 Common Signature} *)
@@ -39,11 +47,24 @@ module type S = sig
   val to_gen : t -> char gen
   (** Return the [gen] of characters contained in the string. *)
 
+  val to_iter : t -> char iter
+  (** Return the [iter] of characters contained in the string.
+      @since NEXT_RELEASE *)
+
+  val to_std_seq : t -> char Seq.t
+  (** [to_std_seq s] returns a [Seq.t] of the bytes in [s].
+      @since NEXT_RELEASE
+  *)
+
   val to_seq : t -> char sequence
-  (** Return the [sequence] of characters contained in the string. *)
+  (** Return the [sequence] of characters contained in the string.
+      @deprecated use {!to_iter} instead *)
+  [@@ocaml.deprecated "use to_iter or to_std_seq"]
 
   val to_klist : t -> char klist
-  (** Return the [klist] of characters contained in the string. *)
+  (** Return the [klist] of characters contained in the string.
+      @deprecated use {!to_std_seq} instead *)
+  [@@ocaml.deprecated "use to_std_seq"]
 
   val to_list : t -> char list
   (** Return the list of characters contained in the string. *)
@@ -94,11 +115,23 @@ val of_char : char -> string
 val of_gen : char gen -> string
 (** Convert a [gen] of characters to a string. *)
 
+val of_iter : char iter -> string
+(** Convert a [iter] of characters to a string.
+    @since NEXT_RELEASE *)
+
+val of_std_seq : char Seq.t -> string
+(** Convert a [sequence] of characters to a string.
+    @since NEXT_RELEASE *)
+
 val of_seq : char sequence -> string
-(** Convert a [sequence] of characters to a string. *)
+(** Convert a [sequence] of characters to a string.
+    @deprecated use {!of_iter} instead *)
+[@@ocaml.deprecated "use of_iter"]
 
 val of_klist : char klist -> string
-(** Convert a [klist] of characters to a string. *)
+(** Convert a [klist] of characters to a string.
+    @deprecated use {!of_std_seq} instead *)
+[@@ocaml.deprecated "use of_std_seq"]
 
 val of_list : char list -> string
 (** Convert a list of characters to a string. *)
@@ -379,9 +412,19 @@ module Split : sig
 
   val gen : ?drop:drop_if_empty -> by:string -> string -> (string*int*int) gen
 
+  val iter : ?drop:drop_if_empty -> by:string -> string -> (string*int*int) sequence
+  (** @since NEXT_RELEASE *)
+
+  val std_seq : ?drop:drop_if_empty -> by:string -> string -> (string*int*int) Seq.t
+  (** @since NEXT_RELEASE *)
+
   val seq : ?drop:drop_if_empty -> by:string -> string -> (string*int*int) sequence
+  (** deprecated, use {!iter} instead *)
+  [@@ocaml.deprecated "use iter"]
 
   val klist : ?drop:drop_if_empty -> by:string -> string -> (string*int*int) klist
+  (** deprecated, use {!std_seq} instead *)
+  [@@ocaml.deprecated "use std_seq"]
 
   (** {4 Copying functions}
 
@@ -392,9 +435,19 @@ module Split : sig
 
   val gen_cpy : ?drop:drop_if_empty -> by:string -> string -> string gen
 
+  val iter_cpy : ?drop:drop_if_empty -> by:string -> string -> string sequence
+  (** @since NEXT_RELEASE *)
+
+  val std_seq_cpy : ?drop:drop_if_empty -> by:string -> string -> string Seq.t
+  (** @since NEXT_RELEASE *)
+
   val seq_cpy : ?drop:drop_if_empty -> by:string -> string -> string sequence
+  (** deprecated, use {!iter_cpy} instead *)
+  [@@ocaml.deprecated "use iter_cpy"]
 
   val klist_cpy : ?drop:drop_if_empty -> by:string -> string -> string klist
+  (** deprecated, use {!std_seq_cpy} instead *)
+  [@@ocaml.deprecated "use std_seq_cpy"]
 
   val left : by:string -> string -> (string * string) option
   (** Split on the first occurrence of [by] from the leftmost part of
diff --git a/src/core/CCStringLabels.mli b/src/core/CCStringLabels.mli
index 87b710d4..041e4780 100644
--- a/src/core/CCStringLabels.mli
+++ b/src/core/CCStringLabels.mli
@@ -3,8 +3,15 @@
 
 (** {1 Basic String Utils} *)
 
-type 'a gen = unit -> 'a option
+(* TODO: remove for 3.0 *)
 type 'a sequence = ('a -> unit) -> unit
+(** @deprecated use ['a iter] instead *)
+
+type 'a iter = ('a -> unit) -> unit
+(** Fast internal iterator.
+    @since NEXT_RELEASE *)
+
+type 'a gen = unit -> 'a option
 type 'a klist = unit -> [`Nil | `Cons of 'a * 'a klist]
 
 (** {2 Common Signature} *)
@@ -37,11 +44,24 @@ module type S = sig
   val to_gen : t -> char gen
   (** Return the [gen] of characters contained in the string. *)
 
+  val to_iter : t -> char iter
+  (** Return the [iter] of characters contained in the string.
+      @since NEXT_RELEASE *)
+
+  val to_std_seq : t -> char Seq.t
+  (** [to_std_seq s] returns a [Seq.t] of the bytes in [s].
+      @since NEXT_RELEASE
+  *)
+
   val to_seq : t -> char sequence
-  (** Return the [sequence] of characters contained in the string. *)
+  (** Return the [sequence] of characters contained in the string.
+      @deprecated use {!to_iter} instead *)
+  [@@ocaml.deprecated "use to_iter or to_std_seq"]
 
   val to_klist : t -> char klist
-  (** Return the [klist] of characters contained in the string. *)
+  (** Return the [klist] of characters contained in the string.
+      @deprecated use {!to_std_seq} instead *)
+  [@@ocaml.deprecated "use to_std_seq"]
 
   val to_list : t -> char list
   (** Return the list of characters contained in the string. *)
@@ -92,11 +112,23 @@ val of_char : char -> string
 val of_gen : char gen -> string
 (** Convert a [gen] of characters to a string. *)
 
+val of_iter : char iter -> string
+(** Convert a [iter] of characters to a string.
+    @since NEXT_RELEASE *)
+
+val of_std_seq : char Seq.t -> string
+(** Convert a [sequence] of characters to a string.
+    @since NEXT_RELEASE *)
+
 val of_seq : char sequence -> string
-(** Convert a [sequence] of characters to a string. *)
+(** Convert a [sequence] of characters to a string.
+    @deprecated use {!of_iter} instead *)
+[@@ocaml.deprecated "use of_iter"]
 
 val of_klist : char klist -> string
-(** Convert a [klist] of characters to a string. *)
+(** Convert a [klist] of characters to a string.
+    @deprecated use {!of_std_seq} instead *)
+[@@ocaml.deprecated "use of_std_seq"]
 
 val of_list : char list -> string
 (** Convert a list of characters to a string. *)
@@ -375,24 +407,44 @@ module Split : sig
       a string from the slice.
       @raise Failure if [by = ""]. *)
 
-  val gen : ?drop:drop_if_empty -> by:(string [@keep_label]) -> string -> (string*int*int) gen
+  val gen : ?drop:drop_if_empty -> by:string -> string -> (string*int*int) gen
 
-  val seq : ?drop:drop_if_empty -> by:(string [@keep_label]) -> string -> (string*int*int) sequence
+  val iter : ?drop:drop_if_empty -> by:string -> string -> (string*int*int) sequence
+  (** @since NEXT_RELEASE *)
 
-  val klist : ?drop:drop_if_empty -> by:(string [@keep_label]) -> string -> (string*int*int) klist
+  val std_seq : ?drop:drop_if_empty -> by:string -> string -> (string*int*int) Seq.t
+  (** @since NEXT_RELEASE *)
+
+  val seq : ?drop:drop_if_empty -> by:string -> string -> (string*int*int) sequence
+  (** deprecated, use {!iter} instead *)
+  [@@ocaml.deprecated "use iter"]
+
+  val klist : ?drop:drop_if_empty -> by:string -> string -> (string*int*int) klist
+  (** deprecated, use {!std_seq} instead *)
+  [@@ocaml.deprecated "use std_seq"]
 
   (** {4 Copying functions}
 
       Those split functions actually copy the substrings, which can be
       more convenient but less efficient in general. *)
 
-  val list_cpy : ?drop:drop_if_empty -> by:(string [@keep_label]) -> string -> string list
+  val list_cpy : ?drop:drop_if_empty -> by:string -> string -> string list
 
-  val gen_cpy : ?drop:drop_if_empty -> by:(string [@keep_label]) -> string -> string gen
+  val gen_cpy : ?drop:drop_if_empty -> by:string -> string -> string gen
 
-  val seq_cpy : ?drop:drop_if_empty -> by:(string [@keep_label]) -> string -> string sequence
+  val iter_cpy : ?drop:drop_if_empty -> by:string -> string -> string sequence
+  (** @since NEXT_RELEASE *)
 
-  val klist_cpy : ?drop:drop_if_empty -> by:(string [@keep_label]) -> string -> string klist
+  val std_seq_cpy : ?drop:drop_if_empty -> by:string -> string -> string Seq.t
+  (** @since NEXT_RELEASE *)
+
+  val seq_cpy : ?drop:drop_if_empty -> by:string -> string -> string sequence
+  (** deprecated, use {!iter_cpy} instead *)
+  [@@ocaml.deprecated "use iter_cpy"]
+
+  val klist_cpy : ?drop:drop_if_empty -> by:string -> string -> string klist
+  (** deprecated, use {!std_seq_cpy} instead *)
+  [@@ocaml.deprecated "use std_seq_cpy"]
 
   val left : by:(string [@keep_label]) -> string -> (string * string) option
   (** Split on the first occurrence of [by] from the leftmost part of
diff --git a/src/core/CCUtf8_string.ml b/src/core/CCUtf8_string.ml
index 2fc60809..71a0c422 100644
--- a/src/core/CCUtf8_string.ml
+++ b/src/core/CCUtf8_string.ml
@@ -9,6 +9,7 @@ open CCShims_
 
 type uchar = Uchar.t
 type 'a gen = unit -> 'a option
+type 'a iter = ('a -> unit) -> unit
 type 'a sequence = ('a -> unit) -> unit
 
 let equal (a:string) b = Stdlib.(=) a b
@@ -113,7 +114,7 @@ let to_gen ?(idx=0) str : uchar gen =
 
 exception Stop
 
-let to_seq ?(idx=0) s : uchar sequence =
+let to_iter ?(idx=0) s : uchar iter =
   fun yield ->
     let st = Dec.make ~idx s in
     try
@@ -124,7 +125,41 @@ let to_seq ?(idx=0) s : uchar sequence =
       done
     with Stop -> ()
 
-let iter ?idx f s = to_seq ?idx s f
+let to_seq = to_iter
+
+let to_std_seq ?(idx=0) s : uchar Seq.t =
+  let rec loop st =
+    let r = ref None in
+    fun () ->
+      match !r with
+      | Some c -> c
+      | None ->
+        let c = next_ st ~yield:(fun x -> Seq.Cons (x, loop st))
+            ~stop:(fun () -> Seq.Nil) ()
+        in
+        r := Some c;
+        c
+  in
+  let st = Dec.make ~idx s in
+  loop st
+
+(*$= & ~cmp:(=) ~printer:Q.Print.(list (fun c -> string_of_int@@ Uchar.to_int c))
+  (to_list (of_string_exn "aébõ😀")) (to_std_seq (of_string_exn "aébõ😀") |> CCList.of_std_seq)
+  *)
+
+(* make sure it's persisted correctly *)
+(*$R
+  let s = (of_string_exn "aébõ😀") in
+  let seq = to_std_seq s in
+  let l = to_list s in
+  let testeq seq = assert_equal ~cmp:(=) l (CCList.of_std_seq seq) in
+  testeq seq;
+  testeq seq;
+  testeq seq;
+  *)
+
+
+let iter ?idx f s = to_iter ?idx s f
 
 let fold ?idx f acc s =
   let st = Dec.make ?idx s in
@@ -181,11 +216,18 @@ let of_gen g : t =
   in
   aux ()
 
-let of_seq seq : t =
+let of_std_seq seq : t =
   let buf = Buffer.create 32 in
-  seq (code_to_string buf);
+  Seq.iter (code_to_string buf) seq;
   Buffer.contents buf
 
+let of_iter i : t =
+  let buf = Buffer.create 32 in
+  i (code_to_string buf);
+  Buffer.contents buf
+
+let of_seq = of_iter
+
 let of_list l : t =
   let buf = Buffer.create 32 in
   List.iter (code_to_string buf) l;
diff --git a/src/core/CCUtf8_string.mli b/src/core/CCUtf8_string.mli
index f174bf97..12875459 100644
--- a/src/core/CCUtf8_string.mli
+++ b/src/core/CCUtf8_string.mli
@@ -18,7 +18,15 @@
 
 type uchar = Uchar.t
 type 'a gen = unit -> 'a option
+
+(* TODO: remove for 3.0 *)
 type 'a sequence = ('a -> unit) -> unit
+(** @deprecated use ['a iter] instead *)
+
+type 'a iter = ('a -> unit) -> unit
+(** Fast internal iterator.
+    @since NEXT_RELEASE *)
+
 
 type t = private string
 (** A UTF8 string *)
@@ -41,9 +49,22 @@ val to_gen : ?idx:int -> t -> uchar gen
 (** Generator of unicode codepoints.
     @param idx offset where to start the decoding. *)
 
+val to_iter : ?idx:int -> t -> uchar iter
+(** Iterator of unicode codepoints.
+    @param idx offset where to start the decoding.
+    @since NEXT_RELEASE *)
+
 val to_seq : ?idx:int -> t -> uchar sequence
 (** Iter of unicode codepoints.
-    @param idx offset where to start the decoding. *)
+    @param idx offset where to start the decoding.
+    @deprecated use {!to_iter} or {!to_std_seq} instead *)
+[@@ocaml.deprecated "use to_iter or to_std_seq instead"]
+
+val to_std_seq : ?idx:int -> t -> uchar Seq.t
+(** Iter of unicode codepoints.
+    @param idx offset where to start the decoding.
+    @since NEXT_RELEASE
+*)
 
 val to_list : ?idx:int -> t -> uchar list
 (** List of unicode codepoints.
@@ -69,7 +90,17 @@ val append : t -> t -> t
 
 val concat : t -> t list -> t
 
+val of_std_seq : uchar Seq.t -> t
+(** Build a string from unicode codepoints
+    @since NEXT_RELEASE *)
+
+val of_iter : uchar sequence -> t
+(** Build a string from unicode codepoints
+    @since NEXT_RELEASE *)
+
 val of_seq : uchar sequence -> t
+(** @deprecated use {!of_seq} or {!of_std_seq} instead *)
+[@@ocaml.deprecated "use of_iter or of_std_seq instead"]
 
 val of_gen : uchar gen -> t
 
@@ -87,5 +118,8 @@ val is_valid : string -> bool
 
 val unsafe_of_string : string -> t
 (** Conversion from a string without validating.
-    Upon iteration, if an invalid substring is met, Malformed will be raised. *)
+    {b CAUTION} this is unsafe and can break all the other functions
+    in this module. Use only if you're sure the string is valid UTF8.
+    Upon iteration, if an invalid substring is met, Malformed will be raised.
+*)
 
diff --git a/src/core/CCVector.ml b/src/core/CCVector.ml
index 09d03729..df941e27 100644
--- a/src/core/CCVector.ml
+++ b/src/core/CCVector.ml
@@ -6,6 +6,7 @@ type rw = [`RW]
 type ro = [`RO]
 
 type 'a sequence = ('a -> unit) -> unit
+type 'a iter = ('a -> unit) -> unit
 type 'a klist = unit -> [`Nil | `Cons of 'a * 'a klist]
 type 'a gen = unit -> 'a option
 type 'a equal = 'a -> 'a -> bool
@@ -256,8 +257,9 @@ let remove v i =
   v.size <- v.size - 1;
   fill_with_junk_ v.vec v.size 1
 
-let append_seq a seq =
-  seq (fun x -> push a x)
+let append_iter a i = i (fun x -> push a x)
+
+let append_std_seq a seq = Seq.iter (fun x -> push a x) seq
 
 let append_array a b =
   let len_b = Array.length b in
@@ -801,12 +803,21 @@ let flat_map f v =
   iter (fun x -> iter (push v') (f x)) v;
   v'
 
-let flat_map_seq f v =
+let flat_map_iter f v =
   let v' = create () in
   iter
     (fun x ->
        let seq = f x in
-       append_seq v' seq)
+       append_iter v' seq)
+    v;
+  v'
+
+let flat_map_std_seq f v =
+  let v' = create () in
+  iter
+    (fun x ->
+       let seq = f x in
+       append_std_seq v' seq)
     v;
   v'
 
@@ -899,22 +910,46 @@ let capacity v = Array.length v.vec
 
 let unsafe_get_array v = v.vec
 
-let of_seq ?(init=create ()) seq =
-  append_seq init seq;
+let of_iter ?(init=create ()) seq =
+  append_iter init seq;
+  init
+
+let of_std_seq ?(init=create ()) seq =
+  append_std_seq init seq;
   init
 
 (*$T
   of_seq Iter.(1 -- 10) |> to_list = CCList.(1 -- 10)
 *)
 
-let to_seq v k = iter k v
+let to_iter v k = iter k v
 
-let to_seq_rev v k =
+let to_iter_rev v k =
   let n = v.size in
   for i = n - 1 downto 0 do
     k (Array.unsafe_get v.vec i)
   done
 
+let to_std_seq v =
+  let rec aux i () =
+    if i>= size v then Seq.Nil
+    else Seq.Cons (v.vec.(i), aux (i+1))
+  in
+  aux 0
+
+let to_std_seq_rev v =
+  let rec aux i () =
+    if i<0 || i > size v then Seq.Nil
+    else Seq.Cons (v.vec.(i), aux (i-1))
+  in
+  aux (size v-1)
+
+let of_seq = of_iter
+let to_seq = to_iter
+let to_seq_rev = to_iter_rev
+let append_seq = append_iter
+let flat_map_seq = flat_map_iter
+
 (*$Q
   Q.(list int) (fun l -> \
     let v= of_list l in v |> to_seq_rev |> Iter.to_rev_list = l)
diff --git a/src/core/CCVector.mli b/src/core/CCVector.mli
index e02d53fb..715911fd 100644
--- a/src/core/CCVector.mli
+++ b/src/core/CCVector.mli
@@ -18,7 +18,14 @@ type 'a ro_vector = ('a, ro) t
 (** Alias for immutable vectors.
     @since 0.15 *)
 
+(* TODO: remove for 3.0 *)
 type 'a sequence = ('a -> unit) -> unit
+(** @deprecated use ['a iter] instead *)
+
+type 'a iter = ('a -> unit) -> unit
+(** Fast internal iterator.
+    @since NEXT_RELEASE *)
+
 type 'a klist = unit -> [`Nil | `Cons of 'a * 'a klist]
 type 'a gen = unit -> 'a option
 type 'a equal = 'a -> 'a -> bool
@@ -79,6 +86,14 @@ val append : ('a, rw) t -> ('a, _) t -> unit
 val append_array : ('a, rw) t -> 'a array -> unit
 (** Like {!append}, with an array. *)
 
+val append_iter : ('a, rw) t -> 'a iter -> unit
+(** Append content of iterator.
+    @since NEXT_RELEASE *)
+
+val append_std_seq : ('a, rw) t -> 'a Seq.t -> unit
+(** Append content of iterator.
+    @since NEXT_RELEASE *)
+
 val append_seq : ('a, rw) t -> 'a sequence -> unit
 (** Append content of sequence. *)
 
@@ -198,10 +213,20 @@ val filter_map_in_place : ('a -> 'a option) -> ('a,_) t -> unit
 val flat_map : ('a -> ('b,_) t) -> ('a,_) t -> ('b, 'mut) t
 (** Map each element to a sub-vector. *)
 
+val flat_map_iter : ('a -> 'b sequence) -> ('a,_) t -> ('b, 'mut) t
+(** Like {!flat_map}, but using {!iter} for intermediate collections.
+    @since NEXT_RELEASE *)
+
+val flat_map_std_seq : ('a -> 'b Seq.t) -> ('a,_) t -> ('b, 'mut) t
+(** Like {!flat_map}, but using [Seq] for intermediate collections.
+    @since NEXT_RELEASE *)
+
 val flat_map_seq : ('a -> 'b sequence) -> ('a,_) t -> ('b, 'mut) t
 (** Like {!flat_map}, but using {!sequence} for
     intermediate collections.
+    @deprecated use {!flat_map_iter} or {!flat_map_std_seq}
     @since 0.14 *)
+[@@ocaml.deprecated "use flat_map_iter or flat_map_std_seq"]
 
 val flat_map_list : ('a -> 'b list) -> ('a,_) t -> ('b, 'mut) t
 (** Like {!flat_map}, but using {!list} for
@@ -277,14 +302,47 @@ val to_list : ('a,_) t -> 'a list
 (** Return a list with the elements contained in the vector. *)
 
 val of_seq : ?init:('a,rw) t -> 'a sequence -> ('a, rw) t
+(** Convert an Iterator to a vector.
+    @deprecated use of_iter *)
+[@@ocaml.deprecated "use of_iter. For the standard Seq, see {!of_std_seq}"]
+
+val of_std_seq : ?init:('a,rw) t -> 'a Seq.t -> ('a, rw) t
+(** Convert an Iterator to a vector.
+    @deprecated use of_iter *)
+[@@ocaml.deprecated "use of_iter. For the standard Seq, see {!of_std_seq}"]
+
+val to_iter : ('a,_) t -> 'a iter
+(** Return a [iter] with the elements contained in the vector.
+    @since NEXT_RELEASE
+*)
+
+val to_iter_rev : ('a,_) t -> 'a iter
+(** [to_iter_rev v] returns the sequence of elements of [v] in reverse order,
+    that is, the last elements of [v] are iterated on first.
+    @since NEXT_RELEASE
+*)
+
+val to_std_seq : ('a,_) t -> 'a Seq.t
+(** Return an iterator with the elements contained in the vector.
+    @since NEXT_RELEASE
+*)
+
+val to_std_seq_rev : ('a,_) t -> 'a Seq.t
+(** [to_seq v] returns the sequence of elements of [v] in reverse order,
+    that is, the last elements of [v] are iterated on first.
+    @since NEXT_RELEASE
+*)
 
 val to_seq : ('a,_) t -> 'a sequence
-(** Return a [sequence] with the elements contained in the vector. *)
+(** @deprecated use to_iter *)
+[@@ocaml.deprecated "use to_iter. For the standard Seq, see {!to_std_seq}"]
 
 val to_seq_rev : ('a, _) t -> 'a sequence
 (** [to_seq_rev v] returns the sequence of elements of [v] in reverse order,
     that is, the last elements of [v] are iterated on first.
-    @since 0.14 *)
+    @since 0.14
+    @deprecated use {!to_iter_rev} *)
+[@@ocaml.deprecated "use to_iter_rev. For the standard Seq, see {!to_std_seq_rev}"]
 
 val slice : ('a,rw) t -> ('a array * int * int)
 (** Vector as an array slice. By doing it we expose the internal array, so
diff --git a/src/data/CCSimple_queue.ml b/src/data/CCSimple_queue.ml
index 01150d33..25ecf393 100644
--- a/src/data/CCSimple_queue.ml
+++ b/src/data/CCSimple_queue.ml
@@ -3,6 +3,7 @@
 
 (** {1 Functional queues (fifo)} *)
 
+type 'a iter = ('a -> unit) -> unit
 type 'a sequence = ('a -> unit) -> unit
 type 'a printer = Format.formatter -> 'a -> unit
 type 'a klist = unit -> [`Nil | `Cons of 'a * 'a klist]
@@ -107,14 +108,18 @@ let to_list q = fold (fun acc x->x::acc) [] q |> List.rev
 let add_list q l = List.fold_left snoc q l
 let of_list l = add_list empty l
 
-let to_seq q = fun k -> iter k q
+let to_iter q = fun k -> iter k q
 
-let add_seq q seq =
+let add_iter q seq =
   let q = ref q in
   seq (fun x -> q := push x !q);
   !q
 
-let of_seq s = add_seq empty s
+let of_iter s = add_iter empty s
+
+let of_seq = of_iter
+let to_seq = to_iter
+let add_seq = add_iter
 
 (*$Q
   Q.(list small_int) (fun l -> \
@@ -125,6 +130,19 @@ let of_seq s = add_seq empty s
     l = (of_list l |> to_seq |> Iter.to_list))
 *)
 
+let add_std_seq q l = add_iter q (fun k -> Seq.iter k l)
+let of_std_seq l = add_std_seq empty l
+
+let to_std_seq q =
+  let rec aux1 l () = match l with
+    | [] -> aux2 (List.rev q.tl) ()
+    | x :: tl -> Seq.Cons (x, aux1 tl)
+  and aux2 l () = match l with
+    | [] -> Seq.Nil
+    | x :: tl -> Seq.Cons (x, aux2 tl)
+  in
+  aux1 q.hd
+
 let rec klist_iter_ k f = match k() with
   | `Nil -> ()
   | `Cons (x,tl) -> f x; klist_iter_ tl f
diff --git a/src/data/CCSimple_queue.mli b/src/data/CCSimple_queue.mli
index a49232bb..236bddf7 100644
--- a/src/data/CCSimple_queue.mli
+++ b/src/data/CCSimple_queue.mli
@@ -6,7 +6,15 @@
 (** Simple implementation of functional queues
     @since 1.3 *)
 
+
+(* TODO: remove for 3.0 *)
 type 'a sequence = ('a -> unit) -> unit
+(** @deprecated use ['a iter] instead *)
+
+type 'a iter = ('a -> unit) -> unit
+(** Fast internal iterator.
+    @since NEXT_RELEASE *)
+
 type 'a printer = Format.formatter -> 'a -> unit
 type 'a klist = unit -> [`Nil | `Cons of 'a * 'a klist]
 type 'a gen = unit -> 'a option
@@ -76,13 +84,31 @@ val to_list : 'a t -> 'a list
 val add_list : 'a t -> 'a list -> 'a t
 val of_list : 'a list -> 'a t
 
+val to_iter : 'a t -> 'a iter
+val add_iter : 'a t -> 'a iter -> 'a t
+val of_iter : 'a iter -> 'a t
+
 val to_seq : 'a t -> 'a sequence
+[@@ocaml.deprecated "use to_iter"]
+
 val add_seq : 'a t -> 'a sequence -> 'a t
+[@@ocaml.deprecated "use add_iter"]
+
 val of_seq : 'a sequence -> 'a t
+[@@ocaml.deprecated "use of_iter"]
+
+val to_std_seq : 'a t -> 'a Seq.t
+val add_std_seq : 'a t -> 'a Seq.t -> 'a t
+val of_std_seq : 'a Seq.t -> 'a t
 
 val to_klist : 'a t -> 'a klist
+[@@ocaml.deprecated "use to_std_seq"]
+
 val add_klist : 'a t -> 'a klist -> 'a t
+[@@ocaml.deprecated "use add_std_seq"]
+
 val of_klist : 'a klist -> 'a t
+[@@ocaml.deprecated "use of_std_seq"]
 
 val of_gen : 'a gen -> 'a t
 val add_gen : 'a t -> 'a gen -> 'a t