diff --git a/CHANGELOG.md b/CHANGELOG.md
index d97d3d9ff..687660ebf 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,18 @@
 # Changelog
 
+## 3.6
+
+- rename `CCOpt` to `CCOption` and deprecate `CCOpt`
+- add iterator functions to `CCIO`
+- `CCOrd`: add `poly`, deprecate `compare`
+- add `CCIO.File.walk_iter`
+- `CCParse`: heavy refactoring, many new functions
+  * backtracking by default
+  * add `slice` and the ability to recurse on them
+  * expose Position module, add `or_`, `both`, `lookahead`, `U.bool`
+  * example Sexpr parser, and a test
+  * example and test of an IRC log parser
+
 ## 3.5
 
 - add `CCHash.map` and `CCHash.bytes`
diff --git a/containers-data.opam b/containers-data.opam
index f79e53ab9..7eab3a458 100644
--- a/containers-data.opam
+++ b/containers-data.opam
@@ -1,5 +1,5 @@
 opam-version: "2.0"
-version: "3.5"
+version: "3.6"
 author: "Simon Cruanes"
 maintainer: "simon.cruanes.2007@m4x.org"
 synopsis: "A set of advanced datatypes for containers"
diff --git a/containers-thread.opam b/containers-thread.opam
index cab02dc06..d13c57517 100644
--- a/containers-thread.opam
+++ b/containers-thread.opam
@@ -1,5 +1,5 @@
 opam-version: "2.0"
-version: "3.5"
+version: "3.6"
 author: "Simon Cruanes"
 maintainer: "simon.cruanes.2007@m4x.org"
 license: "BSD-2-Clause"
diff --git a/containers.opam b/containers.opam
index 419f11c33..14dc7f527 100644
--- a/containers.opam
+++ b/containers.opam
@@ -1,6 +1,6 @@
 opam-version: "2.0"
 name: "containers"
-version: "3.5"
+version: "3.6"
 author: "Simon Cruanes"
 maintainer: "simon.cruanes.2007@m4x.org"
 license: "BSD-2-Clause"
diff --git a/src/core/CCIO.mli b/src/core/CCIO.mli
index c0d8efb5b..dfeffd135 100644
--- a/src/core/CCIO.mli
+++ b/src/core/CCIO.mli
@@ -80,7 +80,7 @@ val read_chunks_seq : ?size:int -> in_channel -> string Seq.t
 
 val read_chunks_iter : ?size:int -> in_channel -> string iter
 (** Read the channel's content into chunks of size at most [size]
-    @since NEXT_RELEASE *)
+    @since 3.6 *)
 
 val read_line : in_channel -> string option
 (** Read a line from the channel. Returns [None] if the input is terminated.
@@ -99,7 +99,7 @@ val read_lines_seq : in_channel -> string Seq.t
 
 val read_lines_iter : in_channel -> string iter
 (** Read all lines.
-    @since NEXT_RELEASE *)
+    @since 3.6 *)
 
 val read_lines_l : in_channel -> string list
 (** Read all lines into a list. *)
@@ -146,7 +146,7 @@ val write_lines : out_channel -> string gen -> unit
 
 val write_lines_iter : out_channel -> string iter -> unit
 (** Write every string on the output, followed by "\n".
-    @since NEXT_RELEASE *)
+    @since 3.6 *)
 
 val write_lines_seq : out_channel -> string Seq.t -> unit
 (** Write every string on the output, followed by "\n".
@@ -265,7 +265,7 @@ module File : sig
 
   val walk_iter : t -> walk_item iter
   (** Like {!walk} but with an imperative iterator.
-      @since NEXT_RELEASE *)
+      @since 3.6 *)
 
   val walk_l : t -> walk_item list
   (** Like {!walk} but returns a list (therefore it's eager and might
@@ -274,7 +274,7 @@ module File : sig
 
   val walk_seq : t -> walk_item Seq.t
   (** Like {!walk} but returns a Seq
-      @since NEXT_RELEASE *)
+      @since 3.6 *)
 
   val show_walk_item : walk_item -> string
 
diff --git a/src/core/CCOption.mli b/src/core/CCOption.mli
index 22b8e31f5..8ae501184 100644
--- a/src/core/CCOption.mli
+++ b/src/core/CCOption.mli
@@ -3,7 +3,7 @@
 (** Options
 
    This module replaces `CCOpt`.
-   @since NEXT_RELEASE *)
+   @since 3.6 *)
 
 type +'a t = 'a option
 
diff --git a/src/core/CCOrd.mli b/src/core/CCOrd.mli
index 11c816ba5..c4e2fed78 100644
--- a/src/core/CCOrd.mli
+++ b/src/core/CCOrd.mli
@@ -9,12 +9,12 @@ type 'a t = 'a -> 'a -> int
 val poly : 'a t
 (** Polymorphic "magic" comparison. Use with care, as it will fail on
     some types.
-    @since NEXT_RELEASE *)
+    @since 3.6 *)
 
 val compare : 'a t
 [@@deprecated "use CCOrd.poly instead, this name is too general"]
 (** Polymorphic "magic" comparison.
-    @deprecated since NEXT_RELEASE in favor of {!poly}. The reason is that
+    @deprecated since 3.6 in favor of {!poly}. The reason is that
     [compare] is easily shadowed, can shadow other comparators, and is just
     generally not very descriptive. *)
 
diff --git a/src/core/CCParse.mli b/src/core/CCParse.mli
index 274d4852a..25c6a6aef 100644
--- a/src/core/CCParse.mli
+++ b/src/core/CCParse.mli
@@ -67,7 +67,7 @@ type position
 
 (** {2 Positions in input}
 
-    @since NEXT_RELEASE *)
+    @since 3.6 *)
 module Position : sig
   type t = position
 
@@ -85,11 +85,11 @@ module Position : sig
 end
 
 (** {2 Errors}
-    @since NEXT_RELEASE *)
+    @since 3.6 *)
 module Error : sig
   type t
   (** A parse error.
-      @since NEXT_RELEASE *)
+      @since 3.6 *)
 
   val position : t -> position
   (** Returns position of the error *)
@@ -123,7 +123,7 @@ type 'a t
 (** The abstract type of parsers that return a value of type ['a] (or fail).
 
     @raise ParseError in case of failure.
-    @since NEXT_RELEASE the type is private.
+    @since 3.6 the type is private.
 *)
 
 val return : 'a -> 'a t
@@ -141,19 +141,19 @@ val map3 : ('a -> 'b -> 'c -> 'd) -> 'a t -> 'b t -> 'c t -> 'd t
 val bind : ('a -> 'b t) -> 'a t -> 'b t
 (** [bind f p] results in a new parser which behaves as [p] then,
     in case of success, applies [f] to the result.
-    @since NEXT_RELEASE
+    @since 3.6
 *)
 
 val ap : ('a -> 'b) t -> 'a t -> 'b t
 (** Applicative.
-    @since NEXT_RELEASE *)
+    @since 3.6 *)
 
 val eoi : unit t
 (** Expect the end of input, fails otherwise. *)
 
 val empty : unit t
 (** Succeed with [()].
-    @since NEXT_RELEASE *)
+    @since 3.6 *)
 
 val fail : string -> 'a t
 (** [fail msg] fails with the given message. It can trigger a backtrack. *)
@@ -163,7 +163,7 @@ val failf: ('a, unit, string, 'b t) format4 -> 'a
 
 val fail_lazy : (unit -> string) -> 'a t
 (** Like {!fail}, but only produce an error message on demand.
-    @since NEXT_RELEASE *)
+    @since 3.6 *)
 
 val parsing : string -> 'a t -> 'a t
 (** [parsing s p] behaves the same as [p], with the information that
@@ -176,24 +176,24 @@ val set_error_message : string -> 'a t -> 'a t
 (** [set_error_message msg p] behaves like [p], but if [p] fails,
     [set_error_message msg p] fails with [msg] instead and at the current
     position. The internal error message of [p] is just discarded.
-    @since NEXT_RELEASE *)
+    @since 3.6 *)
 
 val with_pos : 'a t -> ('a * position) t
 (** [with_pos p] behaves like [p], but returns the (starting) position
     along with [p]'s result.
 
     {b EXPERIMENTAL}
-    @since NEXT_RELEASE *)
+    @since 3.6 *)
 
 val any_char : char t
 (** [any_char] parses any character.
     It still fails if the end of input was reached.
-    @since NEXT_RELEASE *)
+    @since 3.6 *)
 
 val any_char_n : int -> string t
 (** [any_char_n len] parses exactly [len] characters from the input.
     Fails if the input doesn't contain at least [len] chars.
-    @since NEXT_RELEASE *)
+    @since 3.6 *)
 
 val char : char -> char t
 (** [char c] parses the character [c] and nothing else. *)
@@ -215,10 +215,10 @@ type slice
     not at line 1.
 
     {b EXPERIMENTAL}
-    @since NEXT_RELEASE *)
+    @since 3.6 *)
 
 (** Functions on slices.
-    @since NEXT_RELEASE *)
+    @since 3.6 *)
 module Slice : sig
   type t = slice
 
@@ -243,13 +243,13 @@ val recurse : slice -> 'a t -> 'a t
     the slice.
 
     {b EXPERIMENTAL}
-    @since NEXT_RELEASE *)
+    @since 3.6 *)
 
 val set_current_slice : slice -> unit t
 (** [set_current_slice slice] replaces the parser's state with [slice].
 
     {b EXPERIMENTAL}
-    @since NEXT_RELEASE *)
+    @since 3.6 *)
 
 val chars_fold :
   f:('acc -> char ->
@@ -273,7 +273,7 @@ val chars_fold :
     It can also be useful as a base component for a lexer.
 
    @return a pair of the final accumular, and the slice matched by the fold.
-   @since NEXT_RELEASE *)
+   @since 3.6 *)
 
 val chars_fold_transduce :
   f:('acc -> char ->
@@ -289,22 +289,22 @@ val chars_fold_transduce :
     - new case [`Yield (acc, c)] adds [c] to the returned string
       and continues parsing with [acc].
 
-    @since NEXT_RELEASE *)
+    @since 3.6 *)
 
 val take : int -> slice t
 (** [take len] parses exactly [len] characters from the input.
     Fails if the input doesn't contain at least [len] chars.
-    @since NEXT_RELEASE *)
+    @since 3.6 *)
 
 val take_if : (char -> bool) -> slice t
 (** [take_if f] takes characters as long as they satisfy the predicate [f].
-    @since NEXT_RELEASE *)
+    @since 3.6 *)
 
 val take1_if : ?descr:string -> (char -> bool) -> slice t
 (** [take1_if f] takes characters as long as they satisfy the predicate [f].
     Fails if no character satisfies [f].
     @param descr describes what kind of character was expected, in case of error
-    @since NEXT_RELEASE *)
+    @since 3.6 *)
 
 val char_if : ?descr:string -> (char -> bool) -> char t
 (** [char_if f] parses a character [c] if [f c = true].
@@ -363,7 +363,7 @@ val string : string -> string t
 
 val exact : string -> string t
 (** Alias to {!string}.
-    @since NEXT_RELEASE *)
+    @since 3.6 *)
 
 val many : 'a t -> 'a list t
 (** [many p] parses [p] repeatedly, until [p] fails, and
@@ -374,21 +374,21 @@ val optional : _ t -> unit t
     succeeded or failed. Cannot fail itself.
     It consumes input if [p] succeeded (as much as [p] consumed), but
     consumes not input if [p] failed.
-    @since NEXT_RELEASE *)
+    @since 3.6 *)
 
 val try_ : 'a t -> 'a t
 [@@deprecated "plays no role anymore, just replace [try foo] with [foo]"]
 (** [try_ p] is just like [p] (it used to play a role in backtracking
     semantics but no more).
 
-    @deprecated since NEXT_RELEASE it can just be removed. See {!try_opt} if you want
+    @deprecated since 3.6 it can just be removed. See {!try_opt} if you want
     to detect failure. *)
 
 val try_opt : 'a t -> 'a option t
 (** [try_opt p] tries to parse using [p], and return [Some x] if [p]
     succeeded with [x] (and consumes what [p] consumed).
     Otherwise it returns [None] and consumes nothing. This cannot fail.
-    @since NEXT_RELEASE *)
+    @since 3.6 *)
 
 val many_until : until:_ t -> 'a t -> 'a list t
 (** [many_until ~until p] parses as many [p] as it can until
@@ -399,7 +399,7 @@ val many_until : until:_ t -> 'a t -> 'a list t
 
     {b EXPERIMENTAL}
 
-    @since NEXT_RELEASE *)
+    @since 3.6 *)
 
 val try_or : 'a t -> f:('a -> 'b t) -> else_:'b t -> 'b t
 (** [try_or p1 ~f ~else_:p2] attempts to parse [x] using [p1],
@@ -407,7 +407,7 @@ val try_or : 'a t -> f:('a -> 'b t) -> else_:'b t -> 'b t
     If [p1] fails, then it becomes [p2]. This can be useful if [f] is expensive
     but only ever works if [p1] matches (e.g. after an opening parenthesis
     or some sort of prefix).
-    @since NEXT_RELEASE
+    @since 3.6
 *)
 
 val try_or_l :
@@ -429,16 +429,16 @@ val try_or_l :
     @param msg error message if all options fail
 
     {b EXPERIMENTAL}
-    @since NEXT_RELEASE *)
+    @since 3.6 *)
 
 val or_ : 'a t -> 'a t -> 'a t
 (** [or_ p1 p2] tries to parse [p1], and if it fails, tries [p2]
     from the same position.
-    @since NEXT_RELEASE *)
+    @since 3.6 *)
 
 val both : 'a t -> 'b t -> ('a * 'b) t
 (** [both a b] parses [a], then [b], then returns the pair of their results.
-    @since NEXT_RELEASE *)
+    @since 3.6 *)
 
 val many1 : 'a t -> 'a list t
 (** [many1 p] is like [many p] excepts it fails if the
@@ -454,7 +454,7 @@ val sep : by:_ t -> 'a t -> 'a list t
 
 val sep_until: until:_ t -> by:_ t -> 'a t -> 'a list t
 (** Same as {!sep} but stop when [until] parses successfully.
-    @since NEXT_RELEASE *)
+    @since 3.6 *)
 
 val sep1 : by:_ t -> 'a t -> 'a list t
 (** [sep1 ~by p] parses a non empty list of [p], separated by [by]. *)
@@ -463,7 +463,7 @@ val lookahead : 'a t -> 'a t
 (** [lookahead p] behaves like [p], except it doesn't consume any input.
 
     {b EXPERIMENTAL}
-    @since NEXT_RELEASE *)
+    @since 3.6 *)
 
 val lookahead_ignore : 'a t -> unit t
 (** [lookahead_ignore p] tries to parse input with [p],
@@ -472,25 +472,25 @@ val lookahead_ignore : 'a t -> unit t
     whether [p] succeeds, e.g. in {!try_or_l}.
 
     {b EXPERIMENTAL}
-    @since NEXT_RELEASE *)
+    @since 3.6 *)
 
 val fix : ('a t -> 'a t) -> 'a t
 (** Fixpoint combinator. *)
 
 val line : slice t
 (** Parse a line, ['\n'] excluded, and position the cursor after the ['\n'].
-    @since NEXT_RELEASE *)
+    @since 3.6 *)
 
 val line_str : string t
 (** [line_str] is [line >|= Slice.to_string].
     It parses the next line and turns the slice into a string.
     The state points to the character immediately after the ['\n'] character.
-    @since NEXT_RELEASE *)
+    @since 3.6 *)
 
 val each_line : 'a t -> 'a list t
 (** [each_line p] runs [p] on each line of the input.
     {b EXPERIMENTAL}
-    @since NEXT_RELEASE *)
+    @since 3.6 *)
 
 val split_1 : on_char:char -> (slice * slice option) t
 (** [split_1 ~on_char] looks for [on_char] in the input, and returns a
@@ -506,14 +506,14 @@ val split_1 : on_char:char -> (slice * slice option) t
     The parser is now positioned at the end of the input.
 
     {b EXPERIMENTAL}
-    @since NEXT_RELEASE *)
+    @since 3.6 *)
 
 val split_list : on_char:char -> slice list t
 (** [split_list ~on_char] splits the input on all occurrences of [on_char],
     returning a list of slices.
 
     {b EXPERIMENTAL}
-    @since NEXT_RELEASE *)
+    @since 3.6 *)
 
 val split_list_at_most : on_char:char -> int -> slice list t
 (** [split_list_at_most ~on_char n] applies [split_1 ~on_char] at most
@@ -522,24 +522,24 @@ val split_list_at_most : on_char:char -> int -> slice list t
     amount of work done by {!split_list}.
 
     {b EXPERIMENTAL}
-    @since NEXT_RELEASE *)
+    @since 3.6 *)
 
 
 val split_2 : on_char:char -> (slice * slice) t
 (** [split_2 ~on_char] splits the input into exactly 2 fields,
     and fails if the split yields less or more than 2 items.
     {b EXPERIMENTAL}
-    @since NEXT_RELEASE *)
+    @since 3.6 *)
 
 val split_3 : on_char:char -> (slice * slice * slice) t
 (** See {!split_2}
     {b EXPERIMENTAL}
-    @since NEXT_RELEASE *)
+    @since 3.6 *)
 
 val split_4 : on_char:char -> (slice * slice * slice * slice) t
 (** See {!split_2}
     {b EXPERIMENTAL}
-    @since NEXT_RELEASE *)
+    @since 3.6 *)
 
 val each_split : on_char:char -> 'a t -> 'a list t
 (** [split_list_map ~on_char p] uses [split_list ~on_char] to split
@@ -554,7 +554,7 @@ val each_split : on_char:char -> 'a t -> 'a list t
     basically [each_split ~on_char:'\n' p].
 
     {b EXPERIMENTAL}
-    @since NEXT_RELEASE *)
+    @since 3.6 *)
 
 val all : slice t
 (** [all] returns all the unconsumed input as a slice, and consumes it.
@@ -563,20 +563,20 @@ val all : slice t
     Note that [lookahead all] can be used to {i peek} at the rest of the input
     without consuming anything.
 
-    @since NEXT_RELEASE *)
+    @since 3.6 *)
 
 val all_str : string t
 (** [all_str] accepts all the remaining chars and extracts them into a
     string. Similar to {!all} but with a string.
 
     {b EXPERIMENTAL}
-    @since NEXT_RELEASE *)
+    @since 3.6 *)
 
 (* TODO
 val trim : slice t
 (** [trim] is like {!all}, but removes whitespace on the left and right.
    {b EXPERIMENTAL}
-    @since NEXT_RELEASE *)
+    @since 3.6 *)
  *)
 
 val memo : 'a t -> 'a t
@@ -641,7 +641,7 @@ module Infix : sig
   val (|||) : 'a t -> 'b t -> ('a * 'b) t
   (** Alias to {!both}.
       [a ||| b] parses [a], then [b], then returns the pair of their results.
-      @since NEXT_RELEASE *)
+      @since 3.6 *)
 
   (** Let operators on OCaml >= 4.08.0, nothing otherwise
       @since 2.8 *)
@@ -654,7 +654,7 @@ include module type of Infix
 
 val stringify_result : 'a or_error -> ('a, string) result
 (** Turn a {!Error.t}-oriented result into a more basic string result.
-    @since NEXT_RELEASE *)
+    @since 3.6 *)
 
 val parse_string : 'a t -> string -> ('a, string) result
 (** Parse a string using the parser. *)
@@ -695,29 +695,29 @@ module U : sig
 
   val in_paren : 'a t -> 'a t
   (** [in_paren p] parses an opening "(",[p] , and then ")".
-      @since NEXT_RELEASE *)
+      @since 3.6 *)
 
   val in_parens_opt : 'a t -> 'a t
   (** [in_parens_opt p] parses [p] in an arbitrary number of nested
       parenthesis (possibly 0).
-      @since NEXT_RELEASE *)
+      @since 3.6 *)
 
   val option : 'a t -> 'a option t
   (** [option p] parses "Some <x>" into [Some x]  if [p] parses "<x>" into [x],
       and parses "None" into [None].
-      @since NEXT_RELEASE *)
+      @since 3.6 *)
 
   val hexa_int : int t
   (** Parse an int int hexadecimal format. Accepts an optional [0x] prefix,
       and ignores capitalization.
-      @since NEXT_RELEASE *)
+      @since 3.6 *)
 
   val word : string t
   (** Non empty string of alpha num, start with alpha. *)
 
   val bool : bool t
   (** Accepts "true" or "false"
-      @since NEXT_RELEASE *)
+      @since 3.6 *)
 
   (* TODO: quoted string *)
 
@@ -734,7 +734,7 @@ end
 
 (** Debugging utils.
     {b EXPERIMENTAL}
-    @since NEXT_RELEASE *)
+    @since 3.6 *)
 module Debug_ : sig
   val trace_fail : string -> 'a t -> 'a t
   (** [trace_fail name p] behaves like [p], but prints the error message of [p]