diff --git a/core/CCHash.ml b/core/CCHash.ml
index af0b9a3b..e485d228 100644
--- a/core/CCHash.ml
+++ b/core/CCHash.ml
@@ -58,7 +58,7 @@ let hash_triple h1 h2 h3 (x,y,z) = (h1 x) <<>> (h2 y) <<>> (h3 z)
 
 type 'a sequence = ('a -> unit) -> unit
 type 'a gen = unit -> 'a option
-type 'a klist = [`Nil | `Cons of 'a * (unit -> 'a klist)]
+type 'a klist = unit -> [`Nil | `Cons of 'a * 'a klist]
 
 let hash_seq f h seq =
   let h = ref h in
@@ -70,7 +70,6 @@ let rec hash_gen f h g = match g () with
   | Some x ->
       hash_gen f (h <<>> f x) g
 
-let rec hash_klist f h l = match l with
+let rec hash_klist f h l = match l () with
   | `Nil -> h
-  | `Cons (x,l') -> hash_klist f (h <<>> f x) (l' ())
-
+  | `Cons (x,l') -> hash_klist f (h <<>> f x) l'
diff --git a/core/CCHash.mli b/core/CCHash.mli
index 2233e240..e250ed10 100644
--- a/core/CCHash.mli
+++ b/core/CCHash.mli
@@ -57,7 +57,7 @@ val hash_triple : 'a hash_fun -> 'b hash_fun -> 'c hash_fun -> ('a * 'b * 'c) ha
 
 type 'a sequence = ('a -> unit) -> unit
 type 'a gen = unit -> 'a option
-type 'a klist = [`Nil | `Cons of 'a * (unit -> 'a klist)]
+type 'a klist = unit -> [`Nil | `Cons of 'a * 'a klist]
 
 val hash_seq : 'a hash_fun -> t -> 'a sequence hash_fun
 val hash_gen : 'a hash_fun -> t -> 'a gen hash_fun
diff --git a/core/CCList.ml b/core/CCList.ml
index 0d446ed8..a60428db 100644
--- a/core/CCList.ml
+++ b/core/CCList.ml
@@ -388,7 +388,7 @@ end
 
 type 'a sequence = ('a -> unit) -> unit
 type 'a gen = unit -> 'a option
-type 'a klist = [`Nil | `Cons of 'a * (unit -> 'a klist)]
+type 'a klist = unit -> [`Nil | `Cons of 'a * 'a klist]
 type 'a printer = Buffer.t -> 'a -> unit
 type 'a formatter = Format.formatter -> 'a -> unit
 
@@ -422,17 +422,17 @@ let to_klist l =
   let rec make l () = match l with
     | [] -> `Nil
     | x::l' -> `Cons (x, make l')
-  in make l ()
+  in make l
 
 let of_klist l =
   let rec direct i g =
     if i = 0 then safe [] g
-    else match l with
+    else match l () with
       | `Nil -> []
-      | `Cons (x,l') -> x :: direct (i-1) (l' ())
-  and safe acc l = match l with
+      | `Cons (x,l') -> x :: direct (i-1) l'
+  and safe acc l = match l () with
     | `Nil -> List.rev acc
-    | `Cons (x,l') -> safe (x::acc) (l' ())
+    | `Cons (x,l') -> safe (x::acc) l'
   in
   direct _direct_depth l
 
diff --git a/core/CCList.mli b/core/CCList.mli
index 1691ed75..6f9adf77 100644
--- a/core/CCList.mli
+++ b/core/CCList.mli
@@ -171,7 +171,7 @@ end
 
 type 'a sequence = ('a -> unit) -> unit
 type 'a gen = unit -> 'a option
-type 'a klist = [`Nil | `Cons of 'a * (unit -> 'a klist)]
+type 'a klist = unit -> [`Nil | `Cons of 'a * 'a klist]
 type 'a printer = Buffer.t -> 'a -> unit
 type 'a formatter = Format.formatter -> 'a -> unit
 
diff --git a/misc/AVL.ml b/misc/AVL.ml
index 97e53436..592113a1 100644
--- a/misc/AVL.ml
+++ b/misc/AVL.ml
@@ -356,26 +356,26 @@ let rec _before~cmp stack t key = match t with
       else _yield k v (_push_swap l stack)
 
 module KList = struct
-  type 'a t = [ `Nil | `Cons of 'a * (unit -> 'a t) ]
+  type 'a t = unit -> [ `Nil | `Cons of 'a * 'a t ]
 
-  let rec _next (l:('a,'b) explore list) () : ('a*'b) t = match l with
+  let rec _next (l:('a,'b) explore list) () = match l with
     | [] -> `Nil
     | _::_ ->
         let k, v, l' = _pop l in
         `Cons ((k,v), _next l')
 
-  let iter {t; _} = _next (_push t []) ()
+  let iter {t; _} = _next (_push t [])
 
-  let rec _add ~cmp t (l:'a t) = match l with
+  let rec _add ~cmp t (l:'a t) = match l () with
     | `Nil -> t
     | `Cons ((k,v), l') ->
-        _add ~cmp (_insert ~cmp t k v) (l' ())
+        _add ~cmp (_insert ~cmp t k v) l'
 
   let add {cmp; t} l = {cmp; t=_add ~cmp t l}
 
-  let after {cmp; t} key = _next (_after ~cmp [] t key) ()
+  let after {cmp; t} key = _next (_after ~cmp [] t key)
 
-  let before {cmp; t} key = _next (_before ~cmp [] t key) ()
+  let before {cmp; t} key = _next (_before ~cmp [] t key)
 end
 
 module Gen = struct
diff --git a/misc/AVL.mli b/misc/AVL.mli
index 788f2aa1..5ff71ffa 100644
--- a/misc/AVL.mli
+++ b/misc/AVL.mli
@@ -93,7 +93,7 @@ module type ITERATOR = sig
 end
 
 module KList : sig
-  type 'a t = [ `Nil | `Cons of 'a * (unit -> 'a t) ]
+  type 'a t = unit -> [ `Nil | `Cons of 'a * 'a t ]
 
   include ITERATOR with type 'a iter := 'a t
 end
diff --git a/misc/CSM.ml b/misc/CSM.ml
index 158f5b3a..6d72cd7b 100644
--- a/misc/CSM.ml
+++ b/misc/CSM.ml
@@ -210,7 +210,7 @@ module List = struct
   let build state x = Some (x::state, x::state)
 end
 
-module CCGen = struct
+module Gen = struct
   type 'a gen = unit -> 'a option
 
   let map a state gen =
@@ -227,7 +227,7 @@ module CCGen = struct
           end
 end
 
-module CCSequence = struct
+module Sequence = struct
   type 'a sequence = ('a -> unit) -> unit
 
   exception ExitSeq
@@ -244,6 +244,20 @@ module CCSequence = struct
       with ExitSeq -> ()
 end
 
+module KList = struct
+  type 'a klist = unit -> [`Nil | `Cons of 'a * 'a klist]
+
+  let rec map f state (l:'a klist) () =
+    match l () with
+    | `Nil -> `Nil
+    | `Cons (x, l') ->
+        begin match f state x with
+        | None -> `Nil
+        | Some (y, state') ->
+          `Cons (y, map f state' l')
+        end
+end
+
 (** {2 Mutable Interface} *)
 
 module Mut = struct
diff --git a/misc/CSM.mli b/misc/CSM.mli
index abd59af1..0f60cfca 100644
--- a/misc/CSM.mli
+++ b/misc/CSM.mli
@@ -26,10 +26,11 @@ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 (** {1 Composable State Machines}
 
 This module defines state machines that should help design applications
-with a more explicit control of state (e.g. for networking applications. *)
+with a more explicit control of state (e.g. for networking applications). *)
 
 type ('a, 's, 'b) t = 's -> 'a -> ('b * 's) option
-(** transition function that fully describes an automaton *)
+(** transition function that fully describes an automaton. It returns
+    [None] to indicate that it stops. *)
 
 type ('a, 's, 'b) automaton = ('a, 's, 'b) t
 
@@ -140,18 +141,24 @@ module List : sig
   (** build a list from its inputs *)
 end
 
-module CCGen : sig
+module Gen : sig
   type 'a gen = unit -> 'a option
 
   val map : ('a, 's, 'b) t -> 's -> 'a gen -> 'b gen
 end
 
-module CCSequence : sig
+module Sequence : sig
   type 'a sequence = ('a -> unit) -> unit
 
   val map : ('a, 's, 'b) t -> 's -> 'a sequence -> 'b sequence
 end
 
+module KList : sig
+  type 'a klist = unit -> [`Nil | `Cons of 'a * 'a klist]
+
+  val map : ('a, 's, 'b) t -> 's -> 'a klist -> 'b klist
+end
+
 (** {2 Mutable Interface} *)
 
 module Mut : sig
diff --git a/string/levenshtein.ml b/string/levenshtein.ml
index 9aec05c8..cf9b4f9d 100644
--- a/string/levenshtein.ml
+++ b/string/levenshtein.ml
@@ -37,15 +37,15 @@ module type STRING = sig
 end
 
 (** Continuation list *)
-type 'a klist =
+type 'a klist = unit ->
   [
   | `Nil
-  | `Cons of 'a * (unit -> 'a klist)
+  | `Cons of 'a * 'a klist
   ]
 
-let rec klist_to_list = function
+let rec klist_to_list l = match l () with
   | `Nil -> []
-  | `Cons (x,k) -> x :: klist_to_list (k ())
+  | `Cons (x,k) -> x :: klist_to_list k
 
 module type S = sig
   type char_
@@ -568,7 +568,7 @@ module Make(Str : STRING) = struct
       let dfa = of_string ~limit s in
       (* traverse at index i in automaton, with
           [fk] the failure continuation *)
-      let rec traverse node i ~(fk:unit->'a klist) =
+      let rec traverse node i ~(fk:'a klist) () =
         match node with
         | Node (opt, m) ->
             (* all alternatives: continue exploring [m], or call [fk] *)
@@ -577,7 +577,7 @@ module Make(Str : STRING) = struct
                 (fun c node' fk ->
                   try
                     let next = __transition dfa i c in
-                    (fun () -> traverse node' next ~fk)
+                    traverse node' next ~fk
                   with Not_found -> fk)
                 m fk
             in
@@ -617,13 +617,13 @@ module Make(Str : STRING) = struct
       fold (fun acc str v -> (str,v) :: acc) [] idx
 
     let to_klist idx =
-      let rec traverse node trail ~(fk:unit->(string_*'a) klist) =
+      let rec traverse node trail ~(fk:(string_*'a) klist) () =
         match node with
         | Node (opt, m) ->
             (* all alternatives: continue exploring [m], or call [fk] *)
             let fk =
               M.fold
-                (fun c node' fk () -> traverse node' (c::trail) ~fk)
+                (fun c node' fk -> traverse node' (c::trail) ~fk)
                 m fk
             in
             match opt with
@@ -650,6 +650,13 @@ end)
 
 let debug_print = debug_print output_char
 
+(*$T
+  edit_distance "foo" "fo0" = 1
+  edit_distance "foob" "foo" = 1
+  edit_distance "yolo" "yoyo" = 1
+  edit_distance "aaaaaaab" "aaaa" = 4
+*)
+
 (*
 open Batteries;;
 let words = File.with_file_in "/usr/share/dict/cracklib-small"  (fun i -> IO.read_all i |> String.nsplit ~by:"\\n");;
diff --git a/string/levenshtein.mli b/string/levenshtein.mli
index d571415e..9affac48 100644
--- a/string/levenshtein.mli
+++ b/string/levenshtein.mli
@@ -58,13 +58,13 @@ strings, we return a continuation list so that, even if there are many results,
 only those actually asked for are evaluated. *)
 
 type 'a klist =
-  [
+  unit -> [
   | `Nil
-  | `Cons of 'a * (unit -> 'a klist)
+  | `Cons of 'a * 'a klist
   ]
 
 val klist_to_list : 'a klist -> 'a list
-  (** Helper. *)
+  (** Helper for short lists. *)
 
 (** {2 Signature}