diff --git a/README.md b/README.md
index 43610d5b..377b6852 100644
--- a/README.md
+++ b/README.md
@@ -60,6 +60,7 @@ structures comprise (some modules in `misc/`, some other in `core/`):
 - `CCKTree`, an abstract lazy tree structure (similar to what `CCKlist` is to lists)
 - small modules (basic types, utilities):
   - `CCInt`
+  - `CCString` (basic string operations)
   - `CCPair` (cartesian products)
   - `CCOpt` (options)
   - `CCFun` (function combinators)
@@ -70,6 +71,12 @@ structures comprise (some modules in `misc/`, some other in `core/`):
   - `CCHash` (hashing combinators)
   - `CCError` (monadic error handling)
 
+### String
+
+In the module `Containers_string`:
+- `Levenshtein`: edition distance between two strings
+- `KMP`: Knuth-Morris-Pratt substring algorithm
+
 ### Misc
 
 - `PHashtbl`, a polymorphic hashtable (with open addressing)
diff --git a/_oasis b/_oasis
index d2535038..167123e8 100644
--- a/_oasis
+++ b/_oasis
@@ -47,13 +47,13 @@ Library "containers"
                     CCMultiSet, CCBV, CCPrint, CCPersistentHashtbl, CCError,
                     CCHeap, CCList, CCOpt, CCPair, CCFun, CCHash,
                     CCKList, CCInt, CCBool, CCArray, CCBatch, CCOrd,
-                    CCRandom, CCLinq, CCKTree, CCTrie
+                    CCRandom, CCLinq, CCKTree, CCTrie, CCString
   FindlibName:      containers
 
 Library "containers_string"
   Path:             string
   Pack:             true
-  Modules:          KMP, CCString, Levenshtein
+  Modules:          KMP, Levenshtein
   FindlibName:      string
   FindlibParent:    containers
 
diff --git a/core/CCArray.ml b/core/CCArray.ml
index 49bfdd6c..e3d9c5bb 100644
--- a/core/CCArray.ml
+++ b/core/CCArray.ml
@@ -57,6 +57,10 @@ module type S = sig
 
   val iteri : (int -> 'a -> unit) -> 'a t -> unit
 
+  val blit : 'a t -> int -> 'a t -> int -> int -> unit
+  (** [blit from i into j len] copies [len] elements from the first array
+      to the second. See {!Array.blit}. *)
+
   val reverse_in_place : 'a t -> unit
   (** Reverse the array in place *)
 
@@ -92,16 +96,16 @@ module type S = sig
 
   (** {2 IO} *)
 
-  val pp: ?sep:string -> (Buffer.t -> 'a -> unit)
-            -> Buffer.t -> 'a t -> unit
+  val pp: ?sep:string -> (Buffer.t -> 'a -> unit) ->
+          Buffer.t -> 'a t -> unit
   (** print an array of items with printing function *)
 
-  val pp_i: ?sep:string -> (Buffer.t -> int -> 'a -> unit)
-            -> Buffer.t -> 'a t -> unit
+  val pp_i: ?sep:string -> (Buffer.t -> int -> 'a -> unit) ->
+            Buffer.t -> 'a t -> unit
   (** print an array, giving the printing function both index and item *)
 
-  val print : ?sep:string -> (Format.formatter -> 'a -> unit)
-            -> Format.formatter -> 'a t -> unit
+  val print : ?sep:string -> (Format.formatter -> 'a -> unit) ->
+              Format.formatter -> 'a t -> unit
   (** print an array of items with printing function *)
 end
 
@@ -112,13 +116,13 @@ Most of those functions that a range [(i,j)] with
 let rec _foldi f acc a i j =
   if i = j then acc else _foldi f (f acc i a.(i)) a (i+1) j
 
-let _reverse_in_place a i j =
-  if i=j then ()
+let _reverse_in_place a i ~len =
+  if len=0 then ()
   else
-    for k = i to (j-1)/2 do
-      let t = a.(k) in
-      a.(k) <- a.(j-1-k);
-      a.(j-1-k) <- t;
+    for k = 0 to (len-1)/2 do
+      let t = a.(i+k) in
+      a.(i+k) <- a.(i+len-1-k);
+      a.(i+len-1-k) <- t;
     done
 
 let rec _equal eq a1 i1 j1 a2 i2 j2 =
@@ -135,9 +139,16 @@ let rec _compare cmp a1 i1 j1 a2 i2 j2 =
     else
       let c = cmp a1.(i1) a2.(i2) in
       if c = 0
-        then _compare cmp a1 (i1+1) j1 a2 (i2+2) j2
+        then _compare cmp a1 (i1+1) j1 a2 (i2+1) j2
         else c
 
+(*$T
+  compare CCOrd.compare [| 1; 2; 3 |] [| 1; 2; 3 |] = 0
+  compare CCOrd.compare [| 1; 2; 3 |] [| 2; 2; 3 |] < 0
+  compare CCOrd.compare [| 1; 2; |] [| 1; 2; 3 |] < 0
+  compare CCOrd.compare [| 1; 2; 3 |] [| 1; 2; |] > 0
+*)
+
 let rec _find f a i j =
   if i = j then None
   else match f a.(i) with
@@ -150,11 +161,11 @@ let rec _for_all p a i j =
 let rec _exists p a i j =
   i <> j && (p a.(i) || _exists p a (i+1) j)
 
-let rec _for_all2 p a1 a2 i1 i2 j1 =
-  i1 = j1 || (p a1.(i1) a2.(i2) && _for_all2 p a1 a2 (i1+1) (i2+1) j1)
+let rec _for_all2 p a1 a2 i1 i2 ~len =
+  len=0 || (p a1.(i1) a2.(i2) && _for_all2 p a1 a2 (i1+1) (i2+1) ~len:(len-1))
 
-let rec _exists2 p a1 a2 i1 i2 j1 =
-  i1 <> j1 && (p a1.(i1) a2.(i2) || _exists2 p a1 a2 (i1+1) (i2+1) j1)
+let rec _exists2 p a1 a2 i1 i2 ~len =
+  len>0 && (p a1.(i1) a2.(i2) || _exists2 p a1 a2 (i1+1) (i2+1) ~len:(len-1))
 
 (* shuffle a[i...j[ using the given int random generator
    See http://en.wikipedia.org/wiki/Fisher-Yates_shuffle *)
@@ -228,6 +239,8 @@ let iter = Array.iter
 
 let iteri = Array.iteri
 
+let blit = Array.blit
+
 let reverse_in_place a =
   _reverse_in_place a 0 (Array.length a)
 
@@ -303,12 +316,10 @@ let exists p a = _exists p a 0 (Array.length a)
 let for_all2 p a b =
   Array.length a = Array.length b
   &&
-  _for_all2 p a b 0 0 (Array.length a)
+  _for_all2 p a b 0 0 ~len:(Array.length a)
 
 let exists2 p a b =
-  Array.length a = Array.length b
-  &&
-  _exists2 p a b 0 0 (Array.length a)
+  _exists2 p a b 0 0 ~len:(min (Array.length a) (Array.length b))
 
 let (--) i j =
   if i<=j
@@ -374,11 +385,13 @@ module Sub = struct
   }
 
   let make arr i ~len =
-    if i+len > Array.length arr then invalid_arg "Array.Sub.make";
+    if i<0||i+len > Array.length arr then invalid_arg "Array.Sub.make";
     { arr; i; j=i+len; }
 
   let of_slice (arr,i,len) = make arr i ~len
 
+  let to_slice a = a.arr, a.i, a.j-a.i
+
   let full arr = { arr; i=0; j=Array.length arr; }
 
   let underlying a = a.arr
@@ -419,7 +432,16 @@ module Sub = struct
   let iteri f a =
     for k=0 to length a-1 do f k a.arr.(a.i + k) done
 
-  let reverse_in_place a = _reverse_in_place a.arr a.i a.j
+  let blit a i b j len =
+    if i+len>length a || j+len>length b then invalid_arg "Array.Sub.blit";
+    Array.blit a.arr (a.i+i) b.arr (b.i+j) len
+
+  let reverse_in_place a = _reverse_in_place a.arr a.i ~len:(length a)
+
+  (*$T
+  let a = 1--6 in let s = Sub.make a 2 ~len:3 in \
+    Sub.reverse_in_place s; a = [| 1; 2; 5; 4; 3; 6 |]
+  *)
 
   let find f a = _find f a.arr a.i a.j
 
@@ -428,10 +450,14 @@ module Sub = struct
   let exists p a = _exists p a.arr a.i a.j
 
   let for_all2 p a b =
-    length a = length b && _for_all2 p a.arr b.arr a.i b.i b.j
+    length a = length b && _for_all2 p a.arr b.arr a.i b.i ~len:(length a)
 
   let exists2 p a b =
-    length a = length b && _exists2 p a.arr b.arr a.i b.i a.j
+    _exists2 p a.arr b.arr a.i b.i ~len:(min (length a) (length b))
+
+  (*$T
+  Sub.exists2 (=) (Sub.make [| 1;2;3;4 |] 1 ~len:2) (Sub.make [| 0;1;3;4 |] 1 ~len:3)
+  *)
 
   let shuffle a =
     _shuffle Random.int a.arr a.i a.j
diff --git a/core/CCArray.mli b/core/CCArray.mli
index 41637ed5..49564c40 100644
--- a/core/CCArray.mli
+++ b/core/CCArray.mli
@@ -59,6 +59,10 @@ module type S = sig
 
   val iteri : (int -> 'a -> unit) -> 'a t -> unit
 
+  val blit : 'a t -> int -> 'a t -> int -> int -> unit
+  (** [blit from i into j len] copies [len] elements from the first array
+      to the second. See {!Array.blit}. *)
+
   val reverse_in_place : 'a t -> unit
   (** Reverse the array in place *)
 
@@ -94,16 +98,16 @@ module type S = sig
 
   (** {2 IO} *)
 
-  val pp: ?sep:string -> (Buffer.t -> 'a -> unit)
-            -> Buffer.t -> 'a t -> unit
+  val pp: ?sep:string -> (Buffer.t -> 'a -> unit) ->
+          Buffer.t -> 'a t -> unit
   (** print an array of items with printing function *)
 
-  val pp_i: ?sep:string -> (Buffer.t -> int -> 'a -> unit)
-            -> Buffer.t -> 'a t -> unit
+  val pp_i: ?sep:string -> (Buffer.t -> int -> 'a -> unit) ->
+            Buffer.t -> 'a t -> unit
   (** print an array, giving the printing function both index and item *)
 
-  val print : ?sep:string -> (Format.formatter -> 'a -> unit)
-            -> Format.formatter -> 'a t -> unit
+  val print : ?sep:string -> (Format.formatter -> 'a -> unit) ->
+              Format.formatter -> 'a t -> unit
   (** print an array of items with printing function *)
 end
 
@@ -159,6 +163,10 @@ module Sub : sig
       [i] the offset in [arr], and [len] the number of elements of the slice.
       @raise Invalid_argument if the slice isn't valid (See {!make}) *)
 
+  val to_slice : 'a t -> ('a array * int * int)
+  (** Convert into a triple [(arr, i, len)] where [len] is the length of
+      the subarray of [arr] starting at offset [i] *)
+
   val full : 'a array -> 'a t
   (** Slice that covers the full array *)
 
diff --git a/core/CCPersistentHashtbl.ml b/core/CCPersistentHashtbl.ml
index 2f613783..71c1610c 100644
--- a/core/CCPersistentHashtbl.ml
+++ b/core/CCPersistentHashtbl.ml
@@ -26,6 +26,9 @@ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 (** {1 Persistent hash-table on top of OCaml's hashtables} *)
 
 type 'a sequence = ('a -> unit) -> unit
+type 'a printer = Buffer.t -> 'a -> unit
+type 'a formatter = Format.formatter -> 'a -> unit
+type 'a equal = 'a -> 'a -> bool
 
 module type HashedType = sig
   type t
@@ -40,52 +43,92 @@ module type S = sig
   type 'a t
 
   val empty : unit -> 'a t
-    (** Empty table. The table will be allocated at the first binding *)
+  (** Empty table. The table will be allocated at the first binding *)
 
   val create : int -> 'a t
-    (** Create a new hashtable *)
+  (** Create a new hashtable, with the given initial capacity *)
 
   val is_empty : 'a t -> bool
-    (** Is the table empty? *)
+  (** Is the table empty? *)
 
   val find : 'a t -> key -> 'a
-    (** Find the value for this key, or raise Not_found *)
+  (** Find the value for this key, or fails
+      @raise Not_found if the key is not present in the table *)
+
+  val get_exn : key -> 'a t -> 'a
+  (** Synonym to {!find} with flipped arguments *)
+
+  val get : key -> 'a t -> 'a option
+  (** Safe version of !{get_exn} *)
 
   val mem : 'a t -> key -> bool
-    (** Is the key bound? *)
+  (** Is the key bound? *)
 
-  val length : 'a t -> int
-    (** Number of bindings *)
+  val length : _ t -> int
+  (** Number of bindings *)
 
   val replace : 'a t -> key -> 'a -> 'a t
-    (** Add the binding to the table, returning a new table. This erases
-        the current binding for [key], if any. *)
+  (** Add the binding to the table, returning a new table. This erases
+      the current binding for [key], if any. *)
+
+  val update : 'a t -> key -> ('a option -> 'a option) -> 'a t
+  (** [update tbl key f] calls [f None] if [key] doesn't belong in [tbl],
+      [f (Some v)] if [key -> v] otherwise; If [f] returns [None] then
+      [key] is removed, else it returns [Some v'] and [key -> v'] is added. *)
 
   val remove : 'a t -> key -> 'a t
-    (** Remove the key *)
+  (** Remove the key *)
 
   val copy : 'a t -> 'a t
-    (** Fresh copy of the table; the underlying structure is not shared
-        anymore, so using both tables alternatively will be efficient *)
+  (** Fresh copy of the table; the underlying structure is not shared
+      anymore, so using both tables alternatively will be efficient *)
 
-  val merge : (key -> 'a option -> 'a option -> 'a option) -> 'a t -> 'a t -> 'a t
-    (** Merge two tables together into a new table *)
+  val merge : (key -> 'a option -> 'a option -> 'a option) ->
+              'a t -> 'a t -> 'a t
+  (** Merge two tables together into a new table. The function's argument
+      correspond to values associated with the key (if present); if the
+      function returns [None] the key will not appear in the result. *)
 
   val iter : 'a t -> (key -> 'a -> unit) -> unit
-    (** Iterate over bindings *)
+  (** Iterate over bindings *)
 
   val fold : ('b -> key -> 'a -> 'b) -> 'b -> 'a t -> 'b
-    (** Fold over bindings *)
+  (** Fold over bindings *)
 
-  val of_seq : ?init:'a t -> (key * 'a) sequence -> 'a t
-    (** Add (replace) bindings from the sequence to the table *)
+  val map : (key -> 'a -> 'b) -> 'a t -> 'b t
+  (** Map all values *)
 
-  val of_list : ?init:'a t -> (key * 'a) list -> 'a t
+  val filter : (key -> 'a -> bool) -> 'a t -> 'a t
+
+  val filter_map : (key -> 'a -> 'b option) -> 'a t -> 'b t
+
+  val for_all : (key -> 'a -> bool) -> 'a t -> bool
+
+  val exists : (key -> 'a -> bool) -> 'a t -> bool
+
+  (** {3 Conversions} *)
+
+  val of_seq : (key * 'a) sequence -> 'a t
+  (** Add (replace) bindings from the sequence to the table *)
+
+  val of_list : (key * 'a) list -> 'a t
+
+  val add_seq : 'a t -> (key * 'a) sequence -> 'a t
+
+  val add_list : 'a t -> (key  * 'a) list -> 'a t
 
   val to_seq : 'a t -> (key * 'a) sequence
-    (** Sequence of the bindings of the table *)
+  (** Sequence of the bindings of the table *)
 
   val to_list : 'a t -> (key * 'a) list
+
+  (** {3 Misc} *)
+
+  val equal : 'a equal -> 'a t equal
+
+  val pp : key printer -> 'a printer -> 'a t printer  
+
+  val print : key formatter -> 'a formatter -> 'a t formatter
 end
 
 (** {2 Implementation} *)
@@ -107,64 +150,55 @@ module Make(H : HashedType) : S with type key = H.t = struct
 
   let empty () = create 11
 
-  (** Reroot: modify the zipper so that the current node is a proper
-      hashtable, and return the hashtable *)
-  let reroot t =
-    (* pass continuation to get a tailrec rerooting *)
-    let rec reroot t k = match !t with
-    | Table tbl -> k tbl  (* done *)
-    | Add (key, v, t') ->
-      reroot t'
-        (fun tbl ->
-          t' := Remove (key, t);
-          Table.add tbl key v;
-          t := Table tbl;
-          k tbl)
-    | Replace (key, v, t') ->
-      reroot t'
-        (fun tbl ->
-          let v' = Table.find tbl key in
-          t' := Replace (key, v', t);
-          t := Table tbl;
-          Table.replace tbl key v;
-          k tbl)
-    | Remove (key, t') ->
-      reroot t'
-        (fun tbl ->
-          let v = Table.find tbl key in
-          t' := Add (key, v, t);
-          t := Table tbl;
-          Table.remove tbl key;
-          k tbl)
-    in
-    match !t with
+  (* pass continuation to get a tailrec rerooting *)
+  let rec _reroot t k = match !t with
+  | Table tbl -> k tbl  (* done *)
+  | Add (key, v, t') ->
+    _reroot t'
+      (fun tbl ->
+        t' := Remove (key, t);
+        Table.add tbl key v;
+        t := Table tbl;
+        k tbl)
+  | Replace (key, v, t') ->
+    _reroot t'
+      (fun tbl ->
+        let v' = Table.find tbl key in
+        t' := Replace (key, v', t);
+        t := Table tbl;
+        Table.replace tbl key v;
+        k tbl)
+  | Remove (key, t') ->
+    _reroot t'
+      (fun tbl ->
+        let v = Table.find tbl key in
+        t' := Add (key, v, t);
+        t := Table tbl;
+        Table.remove tbl key;
+        k tbl)
+
+  (* Reroot: modify the zipper so that the current node is a proper
+     hashtable, and return the hashtable *)
+  let reroot t = match !t with
     | Table tbl -> tbl
-    | _ -> reroot t (fun x -> x)
+    | _ -> _reroot t (fun x -> x)
 
-  let is_empty t =
-    match !t with
-    | Table tbl -> Table.length tbl = 0
-    | _ -> Table.length (reroot t) = 0
+  let is_empty t = Table.length (reroot t) = 0
 
-  let find t k =
-    match !t with
-    | Table tbl -> Table.find tbl k
-    | _ -> Table.find (reroot t) k
+  let find t k = Table.find (reroot t) k
 
-  let mem t k =
-    match !t with
-    | Table tbl -> Table.mem tbl k
-    | _ -> Table.mem (reroot t) k
+  let get_exn k t = find t k
 
-  let length t =
-    match !t with
-    | Table tbl -> Table.length tbl
-    | _ -> Table.length (reroot t)
+  let get k t =
+    try Some (find t k)
+    with Not_found -> None
+
+  let mem t k = Table.mem (reroot t) k
+
+  let length t = Table.length (reroot t)
 
   let replace t k v =
-    let tbl = match !t with
-    | Table tbl -> tbl
-    | _ -> reroot t in
+    let tbl = reroot t in
     (* create the new hashtable *)
     let t' = ref (Table tbl) in
     (* update [t] to point to the new hashtable *)
@@ -172,15 +206,14 @@ module Make(H : HashedType) : S with type key = H.t = struct
       let v' = Table.find tbl k in
       t := Replace (k, v', t')
     with Not_found ->
-      t := Remove (k, t'));
+      t := Remove (k, t')
+    );
     (* modify the underlying hashtable *)
     Table.replace tbl k v;
     t'
 
   let remove t k =
-    let tbl = match !t with
-    | Table tbl -> tbl
-    | _ -> reroot t in
+    let tbl = reroot t in
     try
       let v' = Table.find tbl k in
       (* value present, make a new hashtable without this value *)
@@ -192,26 +225,63 @@ module Make(H : HashedType) : S with type key = H.t = struct
       (* not member, nothing to do *)
       t
 
+  let update t k f =
+    let v = get k t in
+    match v, f v with
+    | None, None -> t  (* no change *)
+    | Some _, None -> remove t k
+    | _, Some v' -> replace t k v'
+
   let copy t =
-    let tbl = match !t with
-    | Table tbl -> tbl
-    | _ -> reroot t in
+    let tbl = reroot t in
     (* no one will point to the new [t] *)
     let t = ref (Table (Table.copy tbl)) in
     t
   
   let iter t f =
-    let tbl = match !t with
-    | Table tbl -> tbl
-    | _ -> reroot t in
+    let tbl = reroot t in
     Table.iter f tbl
 
   let fold f acc t =
-    let tbl = match !t with
-    | Table tbl -> tbl
-    | _ -> reroot t in
+    let tbl = reroot t in
     Table.fold (fun k v acc -> f acc k v) tbl acc
 
+  let map f t =
+    let tbl = reroot t in
+    let res = Table.create (Table.length tbl) in
+    Table.iter (fun k v -> Table.replace res k (f k v)) tbl;
+    ref (Table res)
+
+  let filter p t =
+    let tbl = reroot t in
+    let res = Table.create (Table.length tbl) in
+    Table.iter (fun k v -> if p k v then Table.replace res k v) tbl;
+    ref (Table res)
+
+  let filter_map f t =
+    let tbl = reroot t in
+    let res = Table.create (Table.length tbl) in
+    Table.iter
+      (fun k v -> match f k v with
+        | None -> ()
+        | Some v' -> Table.replace res k v'
+      ) tbl;
+    ref (Table res)
+
+  exception ExitPTbl
+
+  let for_all p t =
+    try
+      iter t (fun k v -> if not (p k v) then raise ExitPTbl);
+      true
+    with ExitPTbl -> false
+
+  let exists p t =
+    try
+      iter t (fun k v -> if p k v then raise ExitPTbl);
+      false
+    with ExitPTbl -> true
+
   let merge f t1 t2 =
     let tbl = Table.create (max (length t1) (length t2)) in
     iter t1
@@ -227,15 +297,17 @@ module Make(H : HashedType) : S with type key = H.t = struct
           | Some v' -> Table.replace tbl k v2);
     ref (Table tbl)
 
-  let of_seq ?init seq =
-    let tbl = match init with
-    | None -> Table.create 5
-    | Some t -> Table.copy (reroot t) in
-      seq (fun (k,v) -> Table.replace tbl k v);
-      ref (Table tbl)
+  let add_seq init seq =
+    let tbl = ref init in
+    seq (fun (k,v) -> tbl := replace !tbl k v);
+    !tbl
 
-  let of_list ?init l =
-    of_seq ?init (fun k -> List.iter k l)
+  let of_seq seq = add_seq (empty ()) seq
+
+  let add_list init l =
+    add_seq init (fun k -> List.iter k l)
+
+  let of_list l = add_list (empty ()) l
 
   let to_list t =
     let tbl = reroot t in
@@ -244,10 +316,36 @@ module Make(H : HashedType) : S with type key = H.t = struct
 
   let to_seq t =
     fun k ->
-      let tbl = match !t with
-      | Table tbl -> tbl
-      | _ -> reroot t
-      in
+      let tbl = reroot t in
       Table.iter (fun x y -> k (x,y)) tbl
+
+  let equal eq t1 t2 =
+    length t1 = length t2
+    &&
+    for_all
+      (fun k v -> match get k t2 with
+        | None -> false
+        | Some v' -> eq v v'
+      ) t1
+
+  let pp pp_k pp_v buf t =
+    Buffer.add_string buf "{";
+    let first = ref true in
+    iter t
+      (fun k v ->
+        if !first then first:=false else Buffer.add_string buf ", ";
+        Printf.bprintf buf "%a -> %a" pp_k k pp_v v
+      );
+    Buffer.add_string buf "}"
+ 
+  let print pp_k pp_v fmt t =
+    Format.pp_print_string fmt "{";
+    let first = ref true in
+    iter t
+      (fun k v ->
+        if !first then first:=false else Format.pp_print_string fmt ", ";
+        Format.fprintf fmt "%a -> %a" pp_k k pp_v v
+      );
+    Format.pp_print_string fmt "}"
 end
 
diff --git a/core/CCPersistentHashtbl.mli b/core/CCPersistentHashtbl.mli
index 6de2760b..30b07f4e 100644
--- a/core/CCPersistentHashtbl.mli
+++ b/core/CCPersistentHashtbl.mli
@@ -23,9 +23,19 @@ OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *)
 
-(** {1 Persistent hash-table on top of OCaml's hashtables} *)
+(** {1 Persistent hash-table on top of OCaml's hashtables}
+
+Almost as efficient as the regular Hashtbl type, but with a persistent
+interface (rewinding changes to get back in the past history). This is
+mostly useful for backtracking-like uses, or forward uses (never using
+old values).
+
+This module is not thread-safe. *)
 
 type 'a sequence = ('a -> unit) -> unit
+type 'a printer = Buffer.t -> 'a -> unit
+type 'a formatter = Format.formatter -> 'a -> unit
+type 'a equal = 'a -> 'a -> bool
 
 module type HashedType = sig
   type t
@@ -40,52 +50,92 @@ module type S = sig
   type 'a t
 
   val empty : unit -> 'a t
-    (** Empty table. The table will be allocated at the first binding *)
+  (** Empty table. The table will be allocated at the first binding *)
 
   val create : int -> 'a t
-    (** Create a new hashtable *)
+  (** Create a new hashtable, with the given initial capacity *)
 
   val is_empty : 'a t -> bool
-    (** Is the table empty? *)
+  (** Is the table empty? *)
 
   val find : 'a t -> key -> 'a
-    (** Find the value for this key, or raise Not_found *)
+  (** Find the value for this key, or fails
+      @raise Not_found if the key is not present in the table *)
+
+  val get_exn : key -> 'a t -> 'a
+  (** Synonym to {!find} with flipped arguments *)
+
+  val get : key -> 'a t -> 'a option
+  (** Safe version of !{get_exn} *)
 
   val mem : 'a t -> key -> bool
-    (** Is the key bound? *)
+  (** Is the key bound? *)
 
-  val length : 'a t -> int
-    (** Number of bindings *)
+  val length : _ t -> int
+  (** Number of bindings *)
 
   val replace : 'a t -> key -> 'a -> 'a t
-    (** Add the binding to the table, returning a new table. This erases
-        the current binding for [key], if any. *)
+  (** Add the binding to the table, returning a new table. This erases
+      the current binding for [key], if any. *)
+
+  val update : 'a t -> key -> ('a option -> 'a option) -> 'a t
+  (** [update tbl key f] calls [f None] if [key] doesn't belong in [tbl],
+      [f (Some v)] if [key -> v] otherwise; If [f] returns [None] then
+      [key] is removed, else it returns [Some v'] and [key -> v'] is added. *)
 
   val remove : 'a t -> key -> 'a t
-    (** Remove the key *)
+  (** Remove the key *)
 
   val copy : 'a t -> 'a t
-    (** Fresh copy of the table; the underlying structure is not shared
-        anymore, so using both tables alternatively will be efficient *)
+  (** Fresh copy of the table; the underlying structure is not shared
+      anymore, so using both tables alternatively will be efficient *)
 
-  val merge : (key -> 'a option -> 'a option -> 'a option) -> 'a t -> 'a t -> 'a t
-    (** Merge two tables together into a new table *)
+  val merge : (key -> 'a option -> 'a option -> 'a option) ->
+              'a t -> 'a t -> 'a t
+  (** Merge two tables together into a new table. The function's argument
+      correspond to values associated with the key (if present); if the
+      function returns [None] the key will not appear in the result. *)
 
   val iter : 'a t -> (key -> 'a -> unit) -> unit
-    (** Iterate over bindings *)
+  (** Iterate over bindings *)
 
   val fold : ('b -> key -> 'a -> 'b) -> 'b -> 'a t -> 'b
-    (** Fold over bindings *)
+  (** Fold over bindings *)
 
-  val of_seq : ?init:'a t -> (key * 'a) sequence -> 'a t
-    (** Add (replace) bindings from the sequence to the table *)
+  val map : (key -> 'a -> 'b) -> 'a t -> 'b t
+  (** Map all values *)
 
-  val of_list : ?init:'a t -> (key * 'a) list -> 'a t
+  val filter : (key -> 'a -> bool) -> 'a t -> 'a t
+
+  val filter_map : (key -> 'a -> 'b option) -> 'a t -> 'b t
+
+  val for_all : (key -> 'a -> bool) -> 'a t -> bool
+
+  val exists : (key -> 'a -> bool) -> 'a t -> bool
+
+  (** {3 Conversions} *)
+
+  val of_seq : (key * 'a) sequence -> 'a t
+  (** Add (replace) bindings from the sequence to the table *)
+
+  val of_list : (key * 'a) list -> 'a t
+
+  val add_seq : 'a t -> (key * 'a) sequence -> 'a t
+
+  val add_list : 'a t -> (key  * 'a) list -> 'a t
 
   val to_seq : 'a t -> (key * 'a) sequence
-    (** Sequence of the bindings of the table *)
+  (** Sequence of the bindings of the table *)
 
   val to_list : 'a t -> (key * 'a) list
+
+  (** {3 Misc} *)
+
+  val equal : 'a equal -> 'a t equal
+
+  val pp : key printer -> 'a printer -> 'a t printer  
+
+  val print : key formatter -> 'a formatter -> 'a t formatter
 end
 
 (** {2 Implementation} *)
diff --git a/core/CCString.ml b/core/CCString.ml
new file mode 100644
index 00000000..2f5094f3
--- /dev/null
+++ b/core/CCString.ml
@@ -0,0 +1,260 @@
+
+(*
+copyright (c) 2013-2014, simon cruanes
+all rights reserved.
+
+redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+redistributions of source code must retain the above copyright notice, this
+list of conditions and the following disclaimer.  redistributions in binary
+form must reproduce the above copyright notice, this list of conditions and the
+following disclaimer in the documentation and/or other materials provided with
+the distribution.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+*)
+
+(** {1 Basic String Utils} *)
+
+type 'a gen = unit -> 'a option
+type 'a sequence = ('a -> unit) -> unit
+type 'a klist = unit -> [`Nil | `Cons of 'a * 'a klist]
+
+module type S = sig
+  type t
+
+  val length : t -> int
+
+  val blit : t -> int -> t -> int -> int -> unit
+  (** See {!String.blit} *)
+
+  (** {2 Conversions} *)
+
+  val to_gen : t -> char gen
+
+  val to_seq : t -> char sequence
+
+  val to_klist : t -> char klist
+
+  val pp : Buffer.t -> t -> unit
+end
+
+type t = string
+
+let equal a b = a=b
+
+let compare = String.compare
+
+let hash s = Hashtbl.hash s
+
+let length = String.length
+
+let _is_sub ~sub i s j ~len =
+  let rec check k =
+    if k = len
+      then true
+      else sub.[i + k] = s.[j+k] && check (k+1)
+  in
+  j+len <= String.length s && check 0
+
+let is_sub ~sub i s j ~len =
+  if i+len > String.length sub then invalid_arg "String.is_sub";
+  _is_sub ~sub i s j ~len
+
+
+module Split = struct
+  type split_state =
+    | SplitStop
+    | SplitAt of int (* previous *)
+
+  (* [by_j... prefix of s_i...] ? *)
+  let rec _is_prefix ~by s i j =
+    j = String.length by
+    ||
+    ( i < String.length s &&
+      s.[i] = by.[j] &&
+      _is_prefix ~by s (i+1) (j+1)
+    )
+
+  let rec _split ~by s state = match state with
+    | SplitStop -> None
+    | SplitAt prev -> _split_search ~by s prev prev
+  and _split_search ~by s prev i =
+    if i >= String.length s
+      then Some (SplitStop, prev, String.length s - prev)
+      else if _is_prefix ~by s i 0
+        then Some (SplitAt (i+String.length by), prev, i-prev)
+      else _split_search ~by s prev (i+1)
+
+  let _tuple3 x y z = x,y,z
+
+  let _mkgen ~by s k =
+    let state = ref (SplitAt 0) in
+    fun () ->
+      match _split ~by s !state with
+        | None -> None
+        | Some (state', i, len) ->
+            state := state';
+            Some (k s i len)
+
+  let gen ~by s = _mkgen ~by s _tuple3
+
+  let gen_cpy ~by s = _mkgen ~by s String.sub
+
+  let _mklist ~by s k =
+    let rec build acc state = match _split ~by s state with
+      | None -> List.rev acc
+      | Some (state', i, len) ->
+          build (k s i len ::acc) state'
+    in
+    build [] (SplitAt 0)
+
+  let list_ ~by s = _mklist ~by s _tuple3
+
+  let list_cpy ~by s = _mklist ~by s String.sub
+
+  let _mkklist ~by s k =
+    let rec make state () = match _split ~by s state with
+      | None -> `Nil
+      | Some (state', i, len) ->
+          `Cons (k s i len , make state')
+    in make (SplitAt 0)
+
+  let klist ~by s = _mkklist ~by s _tuple3
+
+  let klist_cpy ~by s = _mkklist ~by s String.sub
+
+  let _mkseq ~by s f k =
+    let rec aux state = match _split ~by s state with
+      | None -> ()
+      | Some (state', i, len) -> k (f s i len); aux state'
+    in aux (SplitAt 0)
+
+  let seq ~by s = _mkseq ~by s _tuple3
+  let seq_cpy ~by s = _mkseq ~by s String.sub
+end
+
+(* note: inefficient *)
+let find ?(start=0) ~sub s =
+  let n = String.length sub in
+  let i = ref start in
+  try
+    while !i + n < String.length s do
+      if _is_sub ~sub 0 s !i ~len:n then raise Exit;
+      incr i
+    done;
+    -1
+  with Exit ->
+    !i
+
+let repeat s n =
+  assert (n>=0);
+  let len = String.length s in
+  assert(len > 0);
+  let buf = String.create (len * n) in
+  for i = 0 to n-1 do
+    String.blit s 0 buf (i * len) len;
+  done;
+  buf
+
+let prefix ~pre s =
+  String.length pre <= String.length s &&
+  (let i = ref 0 in
+    while !i < String.length pre && s.[!i] = pre.[!i] do incr i done;
+    !i = String.length pre)
+
+let blit = String.blit
+
+let _to_gen s i0 len =
+  let i = ref i0 in
+  fun () ->
+    if !i = i0+len then None
+    else (
+      let c = String.unsafe_get s !i in
+      incr i;
+      Some c
+    )
+
+let to_gen s = _to_gen s 0 (String.length s)
+
+let of_gen g =
+  let b = Buffer.create 32 in
+  let rec aux () = match g () with
+    | None -> Buffer.contents b
+    | Some c -> Buffer.add_char b c; aux ()
+  in aux ()
+
+let to_seq s k = String.iter k s
+
+let of_seq seq =
+  let b= Buffer.create 32 in
+  seq (Buffer.add_char b);
+  Buffer.contents b
+
+let rec _to_klist s i len () =
+  if len=0 then `Nil
+  else `Cons (s.[i], _to_klist s (i+1)(len-1))
+
+let of_klist l =
+  let rec aux acc n l = match l() with
+    | `Nil ->
+        let s = String.create n in
+        let acc = ref acc in
+        for i=n-1 downto 0 do
+          s.[i] <- List.hd !acc;
+          acc := List.tl !acc
+        done;
+        s
+    | `Cons (x,l') -> aux (x::acc) (n+1) l'
+  in aux [] 0 l
+
+let to_klist s = _to_klist s 0 (String.length s)
+
+let pp buf s =
+  Buffer.add_char buf '"';
+  Buffer.add_string buf s;
+  Buffer.add_char buf '"'
+
+module Sub = struct
+  type t = string * int * int
+
+  let make s i ~len =
+    if i<0||len<0||i+len > String.length s then invalid_arg "CCString.Sub.make";
+    s,i,len
+
+  let full s = s, 0, String.length s
+
+  let copy (s,i,len) = String.sub s i len
+
+  let underlying (s,_,_) = s
+
+  let sub (s,i,len) i' len' =
+    if i+i' + len' > i+len then invalid_arg "CCString.Sub.sub";
+    (s, i+i',len')
+
+  let length (_,_,l) = l
+
+  let blit (a1,i1,len1) o1 (a2,i2,len2) o2 len =
+    if o1+len>len1 || o2+len>len2 then invalid_arg "CCString.Sub.blit";
+    String.blit a1 (i1+o1) a2 (i2+o2) len
+
+  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_klist (s,i,len) = _to_klist s i len
+
+  let pp buf (s,i,len) =
+    Buffer.add_char buf '"';
+    Buffer.add_substring buf s i len;
+    Buffer.add_char buf '"'
+end
diff --git a/core/CCString.mli b/core/CCString.mli
new file mode 100644
index 00000000..83e72342
--- /dev/null
+++ b/core/CCString.mli
@@ -0,0 +1,147 @@
+
+(*
+copyright (c) 2013-2014, simon cruanes
+all rights reserved.
+
+redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+redistributions of source code must retain the above copyright notice, this
+list of conditions and the following disclaimer.  redistributions in binary
+form must reproduce the above copyright notice, this list of conditions and the
+following disclaimer in the documentation and/or other materials provided with
+the distribution.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+*)
+
+(** {1 Basic String Utils}
+Consider using {!Containers_string.KMP} for pattern search, or Regex
+libraries. *)
+
+type 'a gen = unit -> 'a option
+type 'a sequence = ('a -> unit) -> unit
+type 'a klist = unit -> [`Nil | `Cons of 'a * 'a klist]
+
+(** {2 Common Signature} *)
+
+module type S = sig
+  type t
+
+  val length : t -> int
+
+  val blit : t -> int -> t -> int -> int -> unit
+  (** See {!String.blit} *)
+
+  (** {2 Conversions} *)
+
+  val to_gen : t -> char gen
+
+  val to_seq : t -> char sequence
+
+  val to_klist : t -> char klist
+
+  val pp : Buffer.t -> t -> unit
+end
+
+(** {2 Strings} *)
+
+type t = string
+
+val equal : t -> t -> bool
+
+val compare : t -> t -> int
+
+val hash : t -> int
+
+val of_gen : char gen -> t
+
+val of_seq : char sequence -> t
+
+val of_klist : char klist -> t
+
+val find : ?start:int -> sub:t -> t -> int
+(** Find [sub] in the string, returns its first index or -1.
+    Should only be used with very small [sub] *)
+
+val is_sub : sub:t -> int -> t -> int -> len:int -> bool
+(** [is_sub ~sub i s j ~len] returns [true] iff the substring of
+    [sub] starting at position [i] and of length [len],
+    is a substring of [s] starting at position [j] *)
+
+val repeat : t -> int -> t
+(** The same string, repeated n times *)
+
+val prefix : pre:t -> t -> bool
+(** [str_prefix ~pre s] returns [true] iff [pre] is a prefix of [s] *)
+
+include S with type t := t
+
+(** {2 Splitting} *)
+
+module Split : sig
+  val list_ : by:t -> t -> (t*int*int) list
+  (** split the given string along the given separator [by]. Should only
+      be used with very small separators, otherwise
+      use {!Containers_string.KMP}.
+      @return a list of (index,length) of substrings of [s] that are
+      separated by [by]. {!String.sub} can then be used to actually extract
+      the slice.
+      @raise Failure if [by = ""] *)
+
+  val gen : by:t -> t -> (t*int*int) gen
+
+  val seq : by:t -> t -> (t*int*int) sequence
+
+  val klist : by:t -> t -> (t*int*int) klist
+
+  (** {6 Copying functions}
+
+  Those split functions actually copy the substrings, which can be
+  more convenient but less efficient in general *)
+
+  val list_cpy : by:t -> t -> t list
+
+  (*$T
+    Split.list_cpy ~by:"," "aa,bb,cc" = ["aa"; "bb"; "cc"]
+    Split.list_cpy ~by:"--" "a--b----c--" = ["a"; "b"; ""; "c"; ""]
+    Split.list_cpy ~by:" " "hello  world aie" = ["hello"; ""; "world"; "aie"]
+  *)
+
+  val gen_cpy : by:t -> t -> t gen
+
+  val seq_cpy : by:t -> t -> t sequence
+
+  val klist_cpy : by:t -> t -> t klist
+end
+
+(** {2 Slices} A contiguous part of a string *)
+
+module Sub : sig
+  type t = string * int * int
+  (** A string, an offset, and the length of the slice *)
+
+  val make : string -> int -> len:int -> t
+
+  val full : string -> t
+  (** Full string *)
+
+  val copy : t -> string
+  (** Make a copy of the substring *)
+
+  val underlying : t -> string
+
+  val sub : t -> int -> int -> t
+  (** Sub-slice *)
+
+  include S with type t := t
+end
diff --git a/string/CCString.ml b/string/CCString.ml
deleted file mode 100644
index a34614cf..00000000
--- a/string/CCString.ml
+++ /dev/null
@@ -1,150 +0,0 @@
-
-(*
-copyright (c) 2013-2014, simon cruanes
-all rights reserved.
-
-redistribution and use in source and binary forms, with or without
-modification, are permitted provided that the following conditions are met:
-
-redistributions of source code must retain the above copyright notice, this
-list of conditions and the following disclaimer.  redistributions in binary
-form must reproduce the above copyright notice, this list of conditions and the
-following disclaimer in the documentation and/or other materials provided with
-the distribution.
-
-THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
-ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
-WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
-DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
-FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
-DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
-SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
-CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
-OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
-OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
-*)
-
-(** {1 Basic String Utils} *)
-
-type t = string
-
-let equal a b = a=b
-
-let compare = String.compare
-
-let hash s = Hashtbl.hash s
-
-type 'a gen = unit -> 'a option
-type 'a sequence = ('a -> unit) -> unit
-
-let is_sub ~sub i s j =
-  let rec check k =
-    if i + k = String.length sub
-      then true
-      else sub.[i + k] = s.[j+k] && check (k+1)
-  in
-  check 0
-
-(* note: quite inefficient if [by] is long *)
-let split_gen ~by s =
-  let len_by = String.length by in
-  assert (len_by > 0);
-  let n = String.length s in
-  let prev = ref 0 in
-  let stop = ref false in
-  let rec search i =
-    if !stop then None
-    else if i >= n
-      then (
-        stop := true;
-        Some (String.sub s !prev (n- !prev))  (* done *)
-      )
-    else if is_prefix i 0
-      then (
-        let p = !prev in
-        prev := i+len_by;
-        Some (String.sub s p (i-p))
-      )
-    else search (i+1)
-  and is_prefix i j =
-    if j = len_by
-      then true
-    else if i = n
-      then false
-    else s.[i] = by.[j] && is_prefix (i+1) (j+1)
-  in
-  fun () ->
-    search !prev
-
-let split_seq ~by s k =
-  let rec aux g = match g () with
-    | None -> ()
-    | Some x -> k x; aux g
-  in aux (split_gen ~by s)
-
-let split ~by s =
-  let rec aux g acc = match g () with
-    | None -> List.rev acc
-    | Some x -> aux g (x::acc)
-  in aux (split_gen ~by s) []
-
-(*$T
-  split ~by:"," "aa,bb,cc" = ["aa"; "bb"; "cc"]
-  split ~by:"--" "a--b----c--" = ["a"; "b"; ""; "c"; ""]
-*)
-
-(* note: inefficient *)
-let find ?(start=0) ~sub s =
-  let n = String.length sub in
-  let i = ref start in
-  try
-    while !i + n < String.length s do
-      if is_sub ~sub 0 s !i then raise Exit;
-      incr i
-    done;
-    -1
-  with Exit ->
-    !i
-
-let repeat s n =
-  assert (n>=0);
-  let len = String.length s in
-  assert(len > 0);
-  let buf = String.create (len * n) in
-  for i = 0 to n-1 do
-    String.blit s 0 buf (i * len) len;
-  done;
-  buf
-
-let prefix ~pre s =
-  String.length pre <= String.length s &&
-  (let i = ref 0 in
-    while !i < String.length pre && s.[!i] = pre.[!i] do incr i done;
-    !i = String.length pre)
-
-
-let to_gen s =
-  let i = ref 0 in
-  fun () ->
-    if !i = String.length s then None
-    else (
-      let c = String.unsafe_get s !i in
-      incr i;
-      Some c
-    )
-
-let of_gen g =
-  let b = Buffer.create 32 in
-  let rec aux () = match g () with
-    | None -> Buffer.contents b
-    | Some c -> Buffer.add_char b c; aux ()
-  in aux ()
-
-let to_seq s k = String.iter k s
-
-let of_seq seq =
-  let b= Buffer.create 32 in
-  seq (Buffer.add_char b);
-  Buffer.contents b
-
-let pp = Buffer.add_string
diff --git a/string/CCString.mli b/string/CCString.mli
deleted file mode 100644
index 50ba1bcf..00000000
--- a/string/CCString.mli
+++ /dev/null
@@ -1,70 +0,0 @@
-
-(*
-copyright (c) 2013-2014, simon cruanes
-all rights reserved.
-
-redistribution and use in source and binary forms, with or without
-modification, are permitted provided that the following conditions are met:
-
-redistributions of source code must retain the above copyright notice, this
-list of conditions and the following disclaimer.  redistributions in binary
-form must reproduce the above copyright notice, this list of conditions and the
-following disclaimer in the documentation and/or other materials provided with
-the distribution.
-
-THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
-ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
-WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
-DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
-FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
-DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
-SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
-CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
-OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
-OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
-*)
-
-(** {1 Basic String Utils}
-Consider using KMP instead. *)
-
-type t = string
-
-val equal : t -> t -> bool
-
-val compare : t -> t -> int
-
-val hash : t -> int
-
-type 'a gen = unit -> 'a option
-type 'a sequence = ('a -> unit) -> unit
-
-val is_sub : sub:t -> int -> t -> int -> bool
-(** [is_sub ~sub i s j] returns [true] iff [sub] is a substring of [s] starting
-    at position [j] *)
-
-val split : by:t -> t -> t list
-(** split the given string along the given separator [by]. Should only
-    be used with very small separators, otherwise use {!KMP}.
-    @raise Failure if [by = ""] *)
-
-val split_gen : by:t -> t -> t gen
-
-val split_seq : by:t -> t -> t sequence
-
-val find : ?start:int -> sub:t -> t -> int
-(** Find [sub] in the string, returns its first index or -1.
-    Should only be used with very small [sub] *)
-
-val repeat : t -> int -> t
-(** The same string, repeated n times *)
-
-val prefix : pre:t -> t -> bool
-(** [str_prefix ~pre s] returns [true] iff [pre] is a prefix of [s] *)
-
-val to_gen : t -> char gen
-val of_gen : char gen -> t
-
-val to_seq : t -> char sequence
-val of_seq : char sequence -> t
-
-val pp : Buffer.t -> t -> unit