diff --git a/README.md b/README.md
index 638d48ba..3da70fbb 100644
--- a/README.md
+++ b/README.md
@@ -373,8 +373,8 @@ val map : string IntMap.t = <abstr>
     (IntMap.pp CCFormat.int CCFormat.string_quoted)
     map;;
 map =
-  1->"1", 2->"2", 3->"3", 4->"4", 5->"5",
-  6->"6", 7->"7", 8->"8", 9->"9"
+  1 -> "1", 2 -> "2", 3 -> "3", 4 -> "4", 5
+  -> "5", 6 -> "6", 7 -> "7", 8 -> "8", 9 -> "9"
 - : unit = ()
 
 # (* options are good *)
diff --git a/src/core/CCArray.ml b/src/core/CCArray.ml
index baed3d57..fd1b6595 100644
--- a/src/core/CCArray.ml
+++ b/src/core/CCArray.ml
@@ -506,17 +506,23 @@ let random_non_empty g st =
   let n = 1 + Random.State.int st 1_000 in
   random_len n g st
 
-let pp ?(sep=", ") pp_item out a =
+let pp ?(pp_start=fun _ () -> ()) ?(pp_stop=fun _ () -> ())
+    ?(pp_sep=fun out () -> Format.fprintf out ",@ ") pp_item out a =
+  pp_start out ();
   for k = 0 to Array.length a-1 do
-    if k > 0 then (Format.pp_print_string out sep; Format.pp_print_cut out ());
+    if k > 0 then pp_sep out ();
     pp_item out a.(k)
-  done
+  done;
+  pp_stop out ()
 
-let pp_i ?(sep=", ") pp_item out a =
+let pp_i ?(pp_start=fun _ () -> ()) ?(pp_stop=fun _ () -> ())
+    ?(pp_sep=fun out () -> Format.fprintf out ",@ ") pp_item out a =
+  pp_start out ();
   for k = 0 to Array.length a - 1 do
-    if k > 0 then (Format.pp_print_string out sep; Format.pp_print_cut out ());
+    if k > 0 then pp_sep out ();
     pp_item k out a.(k)
-  done
+  done;
+  pp_stop out ()
 
 let to_string ?(sep=", ") item_to_string a =
   Array.to_list a
diff --git a/src/core/CCArray.mli b/src/core/CCArray.mli
index 76e7842d..6620cddd 100644
--- a/src/core/CCArray.mli
+++ b/src/core/CCArray.mli
@@ -202,15 +202,22 @@ val to_gen : 'a t -> 'a gen
 
 (** {2 IO} *)
 
-val pp: ?sep:string -> 'a printer -> 'a t printer
-(** [pp ~sep pp_item ppf a] formats the array [a] on [ppf].
-    Each element is formatted with [pp_item] and elements are separated
-    by [sep] (defaults to ", "). *)
+val pp: ?pp_start:unit printer -> ?pp_stop:unit printer -> ?pp_sep:unit printer ->
+  'a printer -> 'a t printer
+(** [pp ~pp_start ~pp_stop ~pp_sep pp_item ppf a] formats the array [a] on [ppf].
+    Each element is formatted with [pp_item], [pp_start] is called at the beginning,
+    [pp_stop] is called at the end, [pp_sep] is called between each elements.
+    By defaults [pp_start] and [pp_stop] does nothing and [pp_sep] defaults to
+    (fun out -> Format.fprintf out ",@ "). *)
 
-val pp_i: ?sep:string -> (int -> 'a printer) -> 'a t printer
-(** [pp_i ~sep pp_item ppf a] prints the array [a] on [ppf].
+val pp_i: ?pp_start:unit printer -> ?pp_stop:unit printer -> ?pp_sep:unit printer ->
+  (int -> 'a printer) -> 'a t printer
+(** [pp_i ~pp_start ~pp_stop ~pp_sep pp_item ppf a] prints the array [a] on [ppf].
     The printing function [pp_item] is giving both index and element.
-    Elements are separated by [sep] (defaults to ", "). *)
+    [pp_start] is called at the beginning,
+    [pp_stop] is called at the end, [pp_sep] is called between each elements.
+    By defaults [pp_start] and [pp_stop] does nothing and [pp_sep] defaults to
+    (fun out -> Format.fprintf out ",@ "). *)
 
 val rev : 'a t -> 'a t
 (** [rev a] copies the array [a] and reverses it in place.
diff --git a/src/core/CCArrayLabels.mli b/src/core/CCArrayLabels.mli
index d8043b96..4cde8cf4 100644
--- a/src/core/CCArrayLabels.mli
+++ b/src/core/CCArrayLabels.mli
@@ -208,15 +208,22 @@ val to_gen : 'a t -> 'a gen
 
 (** {2 IO} *)
 
-val pp: ?sep:string -> 'a printer -> 'a t printer
-(** [pp ~sep pp_item ppf a] formats the array [a] on [ppf].
-    Each element is formatted with [pp_item] and elements are separated
-    by [sep] (defaults to ", "). *)
+val pp: ?pp_start:unit printer -> ?pp_stop:unit printer -> ?pp_sep:unit printer ->
+  'a printer -> 'a t printer
+(** [pp ~pp_start ~pp_stop ~pp_sep pp_item ppf a] formats the array [a] on [ppf].
+    Each element is formatted with [pp_item], [pp_start] is called at the beginning,
+    [pp_stop] is called at the end, [pp_sep] is called between each elements.
+    By defaults [pp_start] and [pp_stop] does nothing and [pp_sep] defaults to
+    (fun out -> Format.fprintf out ",@ "). *)
 
-val pp_i: ?sep:string -> (int -> 'a printer) -> 'a t printer
-(** [pp_i ~sep pp_item ppf a] prints the array [a] on [ppf].
+val pp_i: ?pp_start:unit printer -> ?pp_stop:unit printer -> ?pp_sep:unit printer ->
+  (int -> 'a printer) -> 'a t printer
+(** [pp_i ~pp_start ~pp_stop ~pp_sep pp_item ppf a] prints the array [a] on [ppf].
     The printing function [pp_item] is giving both index and element.
-    Elements are separated by [sep] (defaults to ", "). *)
+    [pp_start] is called at the beginning,
+    [pp_stop] is called at the end, [pp_sep] is called between each elements.
+    By defaults [pp_start] and [pp_stop] does nothing and [pp_sep] defaults to
+    (fun out -> Format.fprintf out ",@ "). *)
 
 val map2 : f:('a -> 'b -> 'c) -> 'a t -> 'b t -> 'c t
 (** [map2 ~f a b] applies function [f] to all elements of [a] and [b],
diff --git a/src/core/CCHashtbl.ml b/src/core/CCHashtbl.ml
index 9ba920dc..64b9145a 100644
--- a/src/core/CCHashtbl.ml
+++ b/src/core/CCHashtbl.ml
@@ -138,17 +138,19 @@ module Poly = struct
     ()
   *)
 
-  let pp pp_k pp_v fmt m =
-    Format.fprintf fmt "@[<hov2>tbl {@,";
+  let pp ?(pp_start=fun _ () -> ()) ?(pp_stop=fun _ () -> ())
+      ?(pp_sep=fun fmt () -> Format.fprintf fmt ",@ ")
+      ?(pp_arrow=fun fmt () -> Format.fprintf fmt "@ -> ") pp_k pp_v fmt m =
+    pp_start fmt ();
     let first = ref true in
     Hashtbl.iter
       (fun k v ->
-         if !first then first := false else Format.fprintf fmt ",@ ";
+         if !first then first := false else pp_sep fmt ();
          pp_k fmt k;
-         Format.pp_print_string fmt " -> ";
+         pp_arrow fmt ();
          pp_v fmt v;
       ) m;
-    Format.fprintf fmt "@,}@]"
+    pp_stop fmt ()
 end
 
 include Poly
@@ -266,7 +268,8 @@ module type S = sig
       to [tbl] and [v] is returned.
       @since 1.0 *)
 
-  val pp : key printer -> 'a printer -> 'a t printer
+  val pp : ?pp_start:unit printer -> ?pp_stop:unit printer -> ?pp_sep:unit printer ->
+    ?pp_arrow:unit printer -> key printer -> 'a printer -> 'a t printer
   (** Printer for tables.
       Renamed from [print] since 2.0.
       @since 0.13 *)
@@ -393,17 +396,18 @@ module Make(X : Hashtbl.HashedType)
     List.iter (fun (k,v) -> add tbl k v) l;
     tbl
 
-  let pp pp_k pp_v fmt m =
-    Format.fprintf fmt "@[<hov2>tbl {@,";
+  let pp ?(pp_start=fun _ () -> ()) ?(pp_stop=fun _ () -> ())
+      ?(pp_sep=fun fmt () -> Format.fprintf fmt ",@ ")
+      ?(pp_arrow=fun fmt () -> Format.fprintf fmt "@ -> ") pp_k pp_v fmt m =
+    pp_start fmt ();
     let first = ref true in
     iter
       (fun k v ->
-         if !first then first := false else Format.pp_print_string fmt ", ";
+         if !first then first := false else pp_sep fmt ();
          pp_k fmt k;
-         Format.pp_print_string fmt " -> ";
+         pp_arrow fmt ();
          pp_v fmt v;
-         Format.pp_print_cut fmt ()
       ) m;
-    Format.fprintf fmt "}@]"
+    pp_stop fmt ()
 end
 
diff --git a/src/core/CCHashtbl.mli b/src/core/CCHashtbl.mli
index 3ed4eefd..a7a4d4a0 100644
--- a/src/core/CCHashtbl.mli
+++ b/src/core/CCHashtbl.mli
@@ -132,9 +132,14 @@ module Poly : sig
       to [tbl] and [v] is returned.
       @since 1.0 *)
 
-  val pp : 'a printer -> 'b printer -> ('a, 'b) Hashtbl.t printer
-  (** [pp pp_k pp_v] returns a table printer given a [pp_k] printer
+  val pp : ?pp_start:unit printer -> ?pp_stop:unit printer -> ?pp_sep:unit printer ->
+    ?pp_arrow:unit printer -> 'a printer -> 'b printer -> ('a, 'b) Hashtbl.t printer
+  (** [pp ~pp_start ~pp_stop ~pp_sep ~pp arrow pp_k pp_v] returns a table printer
+      given a [pp_k] printer
       for individual key and a [pp_v] printer for individual value.
+      [pp_start] and [pp_stop] control the opening and closing delimiters,
+      by default print nothing. [pp_sep] control the separator between binding.
+      [pp_arrow] control the arrow between the key and value.
       Renamed from [print] since 2.0.
       @since 0.13 *)
 end
@@ -260,9 +265,14 @@ module type S = sig
       to [tbl] and [v] is returned.
       @since 1.0 *)
 
-  val pp : key printer -> 'a printer -> 'a t printer
-  (** [pp pp_k pp_v] returns a table printer given a [pp_k] printer
+  val pp : ?pp_start:unit printer -> ?pp_stop:unit printer -> ?pp_sep:unit printer ->
+    ?pp_arrow:unit printer -> key printer -> 'a printer -> 'a t printer
+  (** [pp ~pp_start ~pp_stop ~pp_sep ~pp arrow pp_k pp_v] returns a table printer
+      given a [pp_k] printer
       for individual key and a [pp_v] printer for individual value. 
+      [pp_start] and [pp_stop] control the opening and closing delimiters,
+      by default print nothing. [pp_sep] control the separator between binding.
+      [pp_arrow] control the arrow between the key and value.
       Renamed from [print] since 2.0.
       @since 0.13 *)
 end
diff --git a/src/core/CCHeap.ml b/src/core/CCHeap.ml
index 8042e03f..69d0cc64 100644
--- a/src/core/CCHeap.ml
+++ b/src/core/CCHeap.ml
@@ -213,7 +213,8 @@ module type S = sig
   (**  Print the heap in a string
        @since 2.7 *)
 
-  val pp : ?sep:string -> elt printer -> t printer
+  val pp : ?pp_start:unit printer -> ?pp_stop:unit printer -> ?pp_sep:unit printer ->
+    elt printer -> t printer
   (** Printer.
       Renamed from {!print} since 2.0
       @since 0.16 *)
@@ -434,13 +435,16 @@ module Make(E : PARTIAL_ORD) : S with type elt = E.t = struct
         = (List.sort Stdlib.compare l |> List.map string_of_int |> String.concat " "))
   *)
 
-  let pp ?(sep=",") pp_elt out h =
+  let pp ?(pp_start=fun _ () -> ()) ?(pp_stop=fun _ () -> ())
+      ?(pp_sep=fun out () -> Format.fprintf out ",") pp_elt out h =
     let first=ref true in
+    pp_start out ();
     iter
       (fun x ->
-         if !first then first := false else Format.fprintf out "%s@," sep;
+         if !first then first := false else pp_sep out ();
          pp_elt out x)
-      h
+      h;
+    pp_stop out ();
 end
 
 module Make_from_compare(E : TOTAL_ORD) =
diff --git a/src/core/CCHeap.mli b/src/core/CCHeap.mli
index 35e71040..b3da17d4 100644
--- a/src/core/CCHeap.mli
+++ b/src/core/CCHeap.mli
@@ -164,9 +164,13 @@ module type S = sig
        (converted to a string using [f]).
        @since 2.7 *)
 
-  val pp : ?sep:string -> elt printer -> t printer
-  (** [pp ?sep ppf h] prints [h] on [ppf].
-      Elements are separated by [sep] (default ",").
+  val pp : ?pp_start:unit printer -> ?pp_stop:unit printer -> ?pp_sep:unit printer ->
+    elt printer -> t printer
+  (** [pp ?pp_start ?pp_stop ?pp_sep ppf h] prints [h] on [ppf].
+      Each element is formatted with [ppf], [pp_start] is called at the beginning,
+      [pp_stop] is called at the end, [pp_sep] is called between each elements.
+      By defaults [pp_start] and [pp_stop] does nothing and [pp_sep] defaults to
+      (fun out -> Format.fprintf out ",@ ").
       Renamed from {!print} since 2.0
       @since 0.16 *)
 end
diff --git a/src/core/CCList.ml b/src/core/CCList.ml
index 362e7689..84ec3402 100644
--- a/src/core/CCList.ml
+++ b/src/core/CCList.ml
@@ -1790,24 +1790,25 @@ include Infix
 
 (** {2 IO} *)
 
-let pp ?(start="") ?(stop="") ?(sep=", ") pp_item fmt l =
+let pp ?(pp_start=fun _ () -> ()) ?(pp_stop=fun _ () -> ())
+    ?(pp_sep=fun fmt () ->Format.fprintf fmt ",@ ") pp_item fmt l =
   let rec print fmt l = match l with
     | x::((_::_) as l) ->
       pp_item fmt x;
-      Format.pp_print_string fmt sep;
-      Format.pp_print_cut fmt ();
+      pp_sep fmt ();
       print fmt l
     | x::[] -> pp_item fmt x
     | [] -> ()
   in
-  Format.pp_print_string fmt start;
+  pp_start fmt ();
   print fmt l;
-  Format.pp_print_string fmt stop
+  pp_stop fmt ()
 
 (*$= & ~printer:(fun s->s)
   "[1, 2, 3]" \
       (CCFormat.to_string \
-        (CCFormat.hbox(CCList.pp ~start:"[" ~stop:"]" CCFormat.int)) \
+        (CCFormat.hbox(CCList.pp ~pp_start:(fun fmt () -> Format.fprintf fmt "[") \
+                         ~pp_stop:(fun fmt () -> Format.fprintf fmt "]") CCFormat.int)) \
         [1;2;3])
 *)
 
diff --git a/src/core/CCList.mli b/src/core/CCList.mli
index 7863d77e..f273181f 100644
--- a/src/core/CCList.mli
+++ b/src/core/CCList.mli
@@ -822,6 +822,6 @@ include CCShimsMkLet_.S with type 'a t_let := 'a list
 
 (** {2 IO} *)
 
-val pp : ?start:string -> ?stop:string -> ?sep:string ->
+val pp : ?pp_start:unit printer -> ?pp_stop:unit printer -> ?pp_sep:unit printer ->
   'a printer -> 'a t printer
-(** [pp ?start ?stop ?sep ppf l] prints the contents of a list. *)
+(** [pp ?pp_start ?pp_stop ?pp_sep ppf l] prints the contents of a list. *)
diff --git a/src/core/CCListLabels.mli b/src/core/CCListLabels.mli
index 083b3b4a..761047f3 100644
--- a/src/core/CCListLabels.mli
+++ b/src/core/CCListLabels.mli
@@ -784,7 +784,7 @@ val to_gen : 'a t -> 'a gen
 val of_gen : 'a gen -> 'a t
 (** [of_gen gen] builds a list from a given [gen].
     In the result, elements appear in the same order as they did in the source [gen]. *)
-    
+
 (** {2 Infix Operators}
     It is convenient to {!open CCList.Infix} to access the infix operators
     without cluttering the scope too much.
@@ -798,7 +798,7 @@ module Infix : sig
   val (@) : 'a t -> 'a t -> 'a t
   (** [l1 @ l2] concatenates two lists [l1] and [l2].
       As {!append}. *)
-      
+
   val (<*>) : ('a -> 'b) t -> 'a t -> 'b t
   (** [funs <*> l] is [product (fun f x -> f x) funs l]. *)
 
@@ -826,6 +826,6 @@ include CCShimsMkLet_.S with type 'a t_let := 'a list
 
 (** {2 IO} *)
 
-val pp : ?start:string -> ?stop:string -> ?sep:string ->
+val pp : ?pp_start:unit printer -> ?pp_stop:unit printer -> ?pp_sep:unit printer ->
   'a printer -> 'a t printer
-(** [pp ?start ?stop ?sep ppf l] prints the contents of a list. *)
+(** [pp ?pp_start ?pp_stop ?pp_sep ppf l] prints the contents of a list. *)
diff --git a/src/core/CCMap.ml b/src/core/CCMap.ml
index 71569760..d5283f88 100644
--- a/src/core/CCMap.ml
+++ b/src/core/CCMap.ml
@@ -99,9 +99,8 @@ module type S = sig
 
   val to_list : 'a t -> (key * 'a) list
 
-  val pp :
-    ?start:string -> ?stop:string -> ?arrow:string -> ?sep:string ->
-    key printer -> 'a printer -> 'a t printer
+  val pp : ?pp_start:unit printer -> ?pp_stop:unit printer -> ?pp_arrow:unit printer ->
+    ?pp_sep:unit printer -> key printer -> 'a printer -> 'a t printer
 end
 
 module Make(O : Map.OrderedType) = struct
@@ -223,19 +222,18 @@ module Make(O : Map.OrderedType) = struct
   let to_list m =
     fold (fun k v acc -> (k,v)::acc) m []
 
-  let pp ?(start="") ?(stop="") ?(arrow="->") ?(sep=", ") pp_k pp_v fmt m =
-    Format.pp_print_string fmt start;
+  let pp ?(pp_start=fun _ () -> ()) ?(pp_stop=fun _ () -> ())
+      ?(pp_arrow=fun fmt () -> Format.fprintf fmt "@ -> ")
+      ?(pp_sep=fun fmt () -> Format.fprintf fmt ",@ ") pp_k pp_v fmt m =
+    pp_start fmt ();
     let first = ref true in
     iter
       (fun k v ->
          if !first then first := false
-         else (
-           Format.pp_print_string fmt sep;
-           Format.pp_print_cut fmt ()
-         );
+         else pp_sep fmt ();
          pp_k fmt k;
-         Format.pp_print_string fmt arrow;
+         pp_arrow fmt ();
          pp_v fmt v)
       m;
-    Format.pp_print_string fmt stop
+    pp_stop fmt ()
 end
diff --git a/src/core/CCMap.mli b/src/core/CCMap.mli
index 39bc0bc7..84f1d24a 100644
--- a/src/core/CCMap.mli
+++ b/src/core/CCMap.mli
@@ -128,10 +128,10 @@ module type S = sig
   val to_list : 'a t -> (key * 'a) list
   (** [to_list m] builds a list of the bindings of the given map [m]. *)
 
-  val pp :
-    ?start:string -> ?stop:string -> ?arrow:string -> ?sep:string ->
-    key printer -> 'a printer -> 'a t printer
-  (** [pp ?start ?stop ?arrow ?sep pp_key pp_v m] pretty-prints the contents of the map. *)    
+  val pp : ?pp_start:unit printer -> ?pp_stop:unit printer -> ?pp_arrow:unit printer ->
+    ?pp_sep:unit printer -> key printer -> 'a printer -> 'a t printer
+  (** [pp ?pp_start ?pp_stop ?pp_arrow ?pp_sep pp_key pp_v m] pretty-prints the
+      contents of the map. *)
 end
 
 module Make(O : Map.OrderedType) : S
diff --git a/src/core/CCPair.ml b/src/core/CCPair.ml
index ea1a9a2c..329c6e82 100644
--- a/src/core/CCPair.ml
+++ b/src/core/CCPair.ml
@@ -47,5 +47,10 @@ let to_string ?(sep=", ") a_to_string b_to_string (x,y) =
 
 type 'a printer = Format.formatter -> 'a -> unit
 
-let pp ?(sep=", ") pa pb out (x,y) =
-  Format.fprintf out "%a%s@,%a" pa x sep pb y
+let pp ?(pp_start=fun _ () -> ()) ?(pp_stop=fun _ () -> ())
+    ?(pp_sep=fun out () -> Format.fprintf out ",@ ") pa pb out (x,y) =
+  pp_start out ();
+  pa out x;
+  pp_sep out ();
+  pb out y;
+  pp_stop out ()
diff --git a/src/core/CCPair.mli b/src/core/CCPair.mli
index b82ecfa8..a105767c 100644
--- a/src/core/CCPair.mli
+++ b/src/core/CCPair.mli
@@ -73,5 +73,7 @@ val to_string : ?sep:string -> ('a -> string) -> ('b -> string) -> ('a * 'b) ->
 
 type 'a printer = Format.formatter -> 'a -> unit
 
-val pp : ?sep:string -> 'a printer -> 'b printer -> ('a * 'b) printer
-(** Print a pair given an optional separator and a method for printing each of its elements. *)
+val pp : ?pp_start:unit printer -> ?pp_stop:unit printer -> ?pp_sep:unit printer ->
+  'a printer -> 'b printer -> ('a * 'b) printer
+(** Print a pair given an optional separator, an optional start and stop and a
+    method for printing each of its elements. *)
diff --git a/src/core/CCSeq.ml b/src/core/CCSeq.ml
index 69221e47..1b3aacd9 100644
--- a/src/core/CCSeq.ml
+++ b/src/core/CCSeq.ml
@@ -527,15 +527,19 @@ end
 
 (** {2 IO} *)
 
-let pp ?(sep=",") pp_item fmt l =
+let pp ?(pp_start=fun _ () -> ()) ?(pp_stop=fun _ () -> ())
+    ?(pp_sep=fun out () -> Format.fprintf out ",@ ") pp_item fmt l =
+  pp_start fmt ();
   let rec pp fmt l = match l() with
     | Nil -> ()
     | Cons (x,l') ->
-      Format.pp_print_string fmt sep;
+      pp_sep fmt ();
       Format.pp_print_cut fmt ();
       pp_item fmt x;
       pp fmt l'
   in
-  match l() with
+  begin match l() with
     | Nil -> ()
     | Cons (x,l') -> pp_item fmt x; pp fmt l'
+  end;
+  pp_stop fmt ()
diff --git a/src/core/CCSeq.mli b/src/core/CCSeq.mli
index 7fda8dee..c2ea70b8 100644
--- a/src/core/CCSeq.mli
+++ b/src/core/CCSeq.mli
@@ -272,6 +272,10 @@ val of_gen : 'a gen -> 'a t
 
 (** {2 IO} *)
 
-val pp : ?sep:string -> 'a printer -> 'a t printer
-(** Print the list with the given separator (default ",").
-    Do not print opening/closing delimiters. *)
+val pp : ?pp_start:unit printer -> ?pp_stop:unit printer -> ?pp_sep:unit printer ->
+  'a printer -> 'a t printer
+(** [pp ~pp_start ~pp_stop ~pp_sep pp_item ppf s] formats the sequence [s] on [ppf].
+    Each element is formatted with [pp_item], [pp_start] is called at the beginning,
+    [pp_stop] is called at the end, [pp_sep] is called between each elements.
+    By defaults [pp_start] and [pp_stop] does nothing and [pp_sep] defaults to
+    (fun out -> Format.fprintf out ",@ "). *)
diff --git a/src/core/CCSet.ml b/src/core/CCSet.ml
index ae4c3039..c801a740 100644
--- a/src/core/CCSet.ml
+++ b/src/core/CCSet.ml
@@ -81,8 +81,7 @@ module type S = sig
   (**  Print the set in a string
        @since 2.7 *)
 
-  val pp :
-    ?start:string -> ?stop:string -> ?sep:string ->
+  val pp : ?pp_start:unit printer -> ?pp_stop:unit printer -> ?pp_sep:unit printer ->
     elt printer -> t printer
     (** Print the set. *)
 end
@@ -182,17 +181,15 @@ module Make(O : Map.OrderedType) = struct
            |> List.map string_of_int |> String.concat " "))
   *)
 
-  let pp ?(start="") ?(stop="") ?(sep=", ") pp_x fmt m =
-    Format.pp_print_string fmt start;
+  let pp ?(pp_start=fun _ () -> ()) ?(pp_stop=fun _ () -> ())
+      ?(pp_sep=fun fmt () -> Format.fprintf fmt ",@ ") pp_x fmt m =
+    pp_start fmt ();
     let first = ref true in
     iter
       (fun x ->
          if !first then first := false
-         else (
-           Format.pp_print_string fmt sep;
-           Format.pp_print_cut fmt ()
-         );
+         else pp_sep fmt ();
          pp_x fmt x)
       m;
-    Format.pp_print_string fmt stop
+    pp_stop fmt ()
 end
diff --git a/src/core/CCSet.mli b/src/core/CCSet.mli
index 6779e710..9cc84d74 100644
--- a/src/core/CCSet.mli
+++ b/src/core/CCSet.mli
@@ -73,14 +73,12 @@ module type S = sig
   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 ->
+  val to_string : ?start:string -> ?stop:string -> ?sep:string ->
     (elt -> string) -> t -> string
   (**  Print the set in a string
        @since 2.7 *)
 
-  val pp :
-    ?start:string -> ?stop:string -> ?sep:string ->
+  val pp : ?pp_start:unit printer -> ?pp_stop:unit printer -> ?pp_sep:unit printer ->
     elt printer -> t printer
     (** Print the set. *)
 end
diff --git a/src/core/CCVector.ml b/src/core/CCVector.ml
index 39f602ad..b2588a37 100644
--- a/src/core/CCVector.ml
+++ b/src/core/CCVector.ml
@@ -1069,14 +1069,15 @@ let to_gen v =
 let to_string ?(start="") ?(stop="") ?(sep=", ") item_to_string v =
   start ^ (to_list v |> List.map item_to_string |> String.concat sep) ^ stop
 
-let pp ?(start="") ?(stop="") ?(sep=", ") pp_item fmt v =
-  Format.pp_print_string fmt start;
+let pp ?(pp_start=fun _ () -> ()) ?(pp_stop=fun _ () -> ())
+    ?(pp_sep=fun fmt () -> Format.fprintf fmt ",@ ") pp_item fmt v =
+  pp_start fmt ();
   iteri
     (fun i x ->
-       if i > 0 then (Format.pp_print_string fmt sep; Format.pp_print_cut fmt());
+       if i > 0 then pp_sep fmt ();
        pp_item fmt x
     ) v;
-  Format.pp_print_string fmt stop
+  pp_stop fmt ()
 
 include CCShimsMkLet_.Make2(struct
     type nonrec ('a,'e) t = ('a,'e) t
diff --git a/src/core/CCVector.mli b/src/core/CCVector.mli
index 037bbec4..f799e956 100644
--- a/src/core/CCVector.mli
+++ b/src/core/CCVector.mli
@@ -347,8 +347,13 @@ val to_string :
 (**  Print the vector in a string
      @since 2.7 *)
 
-val pp : ?start:string -> ?stop:string -> ?sep:string ->
+val pp : ?pp_start:unit printer -> ?pp_stop:unit printer -> ?pp_sep:unit printer ->
   'a printer -> ('a,_) t printer
+(** [pp ~pp_start ~pp_stop ~pp_sep pp_item ppf v] formats the vector [v] on [ppf].
+    Each element is formatted with [pp_item], [pp_start] is called at the beginning,
+    [pp_stop] is called at the end, [pp_sep] is called between each elements.
+    By defaults [pp_start] and [pp_stop] does nothing and [pp_sep] defaults to
+    (fun out -> Format.fprintf out ",@ "). *)
 
 (** Let operators on OCaml >= 4.08.0, nothing otherwise
     @since 2.8 *)
diff --git a/src/data/CCHashSet.ml b/src/data/CCHashSet.ml
index a120661f..b5d6ad50 100644
--- a/src/data/CCHashSet.ml
+++ b/src/data/CCHashSet.ml
@@ -85,7 +85,7 @@ module type S = sig
 
   val add_iter : t -> elt iter -> unit
 
-  val pp : ?sep:string -> elt printer -> t printer
+  val pp : ?pp_sep:unit printer -> elt printer -> t printer
   (** [pp pp_elt] returns a set printer, given a printer for
       individual elements *)
 end
@@ -221,17 +221,14 @@ module Make(E : ELEMENT) : S with type elt = E.t = struct
     seq (insert s);
     s
 
-  let pp ?(sep=",") pp_x out s =
+  let pp ?(pp_sep=fun out () -> Format.fprintf out ",@ ") pp_x out s =
     Format.pp_print_string out "{";
     let first = ref true in
     Tbl.iter
       (fun x _ ->
          if !first
          then first := false
-         else (
-           Format.pp_print_string out sep;
-           Format.pp_print_cut out ();
-         );
+         else pp_sep out ();
          pp_x out x
       ) s;
     Format.pp_print_string out "}"
diff --git a/src/data/CCHashSet.mli b/src/data/CCHashSet.mli
index b0dd376a..6bf97dcf 100644
--- a/src/data/CCHashSet.mli
+++ b/src/data/CCHashSet.mli
@@ -89,7 +89,7 @@ module type S = sig
 
   val add_iter : t -> elt iter -> unit
 
-  val pp : ?sep:string -> elt printer -> t printer
+  val pp : ?pp_sep:unit printer -> elt printer -> t printer
   (** [pp pp_elt] returns a set printer, given a printer for
       individual elements. *)
 end
diff --git a/src/data/CCImmutArray.ml b/src/data/CCImmutArray.ml
index 86144911..fca18714 100644
--- a/src/data/CCImmutArray.ml
+++ b/src/data/CCImmutArray.ml
@@ -118,14 +118,11 @@ let to_gen a =
 
 type 'a printer = Format.formatter -> 'a -> unit
 
-let pp ?(start="") ?(stop="") ?(sep=", ") pp_item out a =
-  Format.pp_print_string out start;
+let pp ?(pp_start=fun _ () -> ()) ?(pp_stop=fun _ () -> ())
+    ?(pp_sep=fun out () -> Format.fprintf out ",@ ") pp_item out a =
+  pp_start out ();
   for k = 0 to Array.length a - 1 do
-    if k > 0 then (
-      Format.pp_print_string out sep;
-      Format.pp_print_cut out ()
-    );
+    if k > 0 then pp_sep out ();
     pp_item out a.(k)
   done;
-  Format.pp_print_string out stop;
-  ()
+  pp_stop out ()
diff --git a/src/data/CCImmutArray.mli b/src/data/CCImmutArray.mli
index b9bceb78..ae97d01e 100644
--- a/src/data/CCImmutArray.mli
+++ b/src/data/CCImmutArray.mli
@@ -88,7 +88,12 @@ val to_gen : 'a t -> 'a gen
 
 type 'a printer = Format.formatter -> 'a -> unit
 
-val pp :
-  ?start:string -> ?stop:string -> ?sep:string ->
+val pp: ?pp_start:unit printer -> ?pp_stop:unit printer -> ?pp_sep:unit printer ->
   'a printer -> 'a t printer
+(** [pp ~pp_start ~pp_stop ~pp_sep pp_item ppf a] formats the array [a] on [ppf].
+    Each element is formatted with [pp_item], [pp_start] is called at the beginning,
+    [pp_stop] is called at the end, [pp_sep] is called between each elements.
+    By defaults [pp_start] and [pp_stop] does nothing and [pp_sep] defaults to
+    (fun out -> Format.fprintf out ",@ "). *)
+
 
diff --git a/src/data/CCPersistentHashtbl.ml b/src/data/CCPersistentHashtbl.ml
index af9ff54f..b682b193 100644
--- a/src/data/CCPersistentHashtbl.ml
+++ b/src/data/CCPersistentHashtbl.ml
@@ -110,7 +110,8 @@ module type S = sig
 
   val equal : 'a equal -> 'a t equal
 
-  val pp : ?sep:string -> ?arrow:string -> key printer -> 'a printer -> 'a t printer
+  val pp : ?pp_start:unit printer -> ?pp_stop:unit printer -> ?pp_sep:unit printer ->
+    ?pp_arrow:unit printer -> key printer -> 'a printer -> 'a t printer
 
   val stats : _ t -> Hashtbl.statistics
   (** Statistics on the internal table.
@@ -633,15 +634,20 @@ module Make(H : HashedType) : S with type key = H.t = struct
          | Some v' -> eq v v'
       ) t1
 
-  let pp ?(sep=",") ?(arrow="->") pp_k pp_v fmt t =
+  let pp ?(pp_start=fun _ () -> ()) ?(pp_stop=fun _ () -> ())
+      ?(pp_sep=fun fmt () -> Format.fprintf fmt ",@ ")
+      ?(pp_arrow=fun fmt () -> Format.fprintf fmt "@ -> ") pp_k pp_v fmt t =
     let first = ref true in
+    pp_start fmt ();
     iter t
       (fun k v ->
          if !first then first:=false
-         else (Format.pp_print_string fmt sep; Format.pp_print_cut fmt ());
-         Format.fprintf fmt "%a %s %a" pp_k k arrow pp_v v
+         else pp_sep fmt ();
+         pp_k fmt k;
+         pp_arrow fmt ();
+         pp_v fmt v
       );
-    ()
+    pp_stop fmt ()
 
   let stats t =
     let a = reroot_ t in
diff --git a/src/data/CCPersistentHashtbl.mli b/src/data/CCPersistentHashtbl.mli
index d7af21d0..efe5a619 100644
--- a/src/data/CCPersistentHashtbl.mli
+++ b/src/data/CCPersistentHashtbl.mli
@@ -117,7 +117,8 @@ module type S = sig
 
   val equal : 'a equal -> 'a t equal
 
-  val pp : ?sep:string -> ?arrow:string -> key printer -> 'a printer -> 'a t printer
+  val pp : ?pp_start:unit printer -> ?pp_stop:unit printer -> ?pp_sep:unit printer ->
+    ?pp_arrow:unit printer -> key printer -> 'a printer -> 'a t printer
 
   val stats : _ t -> Hashtbl.statistics
   (** Statistics on the internal table.
diff --git a/src/data/CCRAL.ml b/src/data/CCRAL.ml
index 43594e6c..6daeda1c 100644
--- a/src/data/CCRAL.ml
+++ b/src/data/CCRAL.ml
@@ -624,14 +624,11 @@ include Infix
 
 type 'a printer = Format.formatter -> 'a -> unit
 
-let pp ?(sep=", ") pp_item fmt l =
+let pp ?(pp_sep=fun fmt () -> Format.fprintf fmt ",@ ") pp_item fmt l =
   let first = ref true in
   iter l
     ~f:(fun x ->
-      if !first then first := false else (
-        Format.pp_print_string fmt sep;
-        Format.pp_print_cut fmt ();
-      );
+      if !first then first := false else pp_sep fmt ();
       pp_item fmt x
     );
   ()
diff --git a/src/data/CCRAL.mli b/src/data/CCRAL.mli
index 1abdc2bb..6f5bcbad 100644
--- a/src/data/CCRAL.mli
+++ b/src/data/CCRAL.mli
@@ -187,4 +187,4 @@ include module type of Infix
 
 type 'a printer = Format.formatter -> 'a -> unit
 
-val pp : ?sep:string -> 'a printer -> 'a t printer
+val pp : ?pp_sep:unit printer -> 'a printer -> 'a t printer
diff --git a/src/data/CCWBTree.ml b/src/data/CCWBTree.ml
index 39aa4f6a..de659897 100644
--- a/src/data/CCWBTree.ml
+++ b/src/data/CCWBTree.ml
@@ -161,7 +161,8 @@ module type S = sig
 
   val to_gen : 'a t -> (key * 'a) gen
 
-  val pp : key printer -> 'a printer -> 'a t printer
+  val pp : ?pp_start:unit printer -> ?pp_stop:unit printer -> ?pp_arrow:unit printer ->
+    ?pp_sep:unit printer -> key printer -> 'a printer -> 'a t printer
 
   (**/**)
   val node_ : key -> 'a -> 'a t -> 'a t -> 'a t
@@ -588,19 +589,21 @@ module MakeFull(K : KEY) : S with type key = K.t = struct
           Some (k,v)
     in next
 
-  let pp pp_k pp_v fmt m =
-    let start = "[" and stop = "]" and arrow = "->" and sep = ","in
-    Format.pp_print_string fmt start;
+  let pp ?(pp_start=fun _ () -> ()) ?(pp_stop=fun _ () -> ())
+      ?(pp_arrow=fun fmt () -> Format.fprintf fmt "@ -> ")
+      ?(pp_sep=fun fmt () -> Format.fprintf fmt ",@ ")
+      pp_k pp_v fmt m =
+    pp_start fmt ();
     let first = ref true in
     iter m
       ~f:(fun k v ->
-        if !first then first := false else Format.pp_print_string fmt sep;
+        if !first then first := false else pp_sep fmt ();
         pp_k fmt k;
-        Format.pp_print_string fmt arrow;
+        pp_arrow fmt ();
         pp_v fmt v;
         Format.pp_print_cut fmt ()
       );
-    Format.pp_print_string fmt stop
+    pp_stop fmt ();
 end
 
 module Make(X : ORD) = MakeFull(struct
diff --git a/src/data/CCWBTree.mli b/src/data/CCWBTree.mli
index 71e0a719..4518ff81 100644
--- a/src/data/CCWBTree.mli
+++ b/src/data/CCWBTree.mli
@@ -126,7 +126,8 @@ module type S = sig
 
   val to_gen : 'a t -> (key * 'a) gen
 
-  val pp : key printer -> 'a printer -> 'a t printer
+  val pp : ?pp_start:unit printer -> ?pp_stop:unit printer -> ?pp_arrow:unit printer ->
+    ?pp_sep:unit printer -> key printer -> 'a printer -> 'a t printer
   (** Renamed from [val print].
       @since 2.0 *)