diff --git a/core/CCArray.ml b/core/CCArray.ml
index 69d6f445..4f7ad5c6 100644
--- a/core/CCArray.ml
+++ b/core/CCArray.ml
@@ -162,3 +162,10 @@ let pp_i ?(sep=", ") pp_item buf a =
     (if i > 0 then Buffer.add_string buf sep);
     pp_item buf i a.(i)
   done
+
+let print ?(sep=", ") pp_item fmt a =
+  Array.iteri
+    (fun i x ->
+      if i > 0 then Format.pp_print_string fmt sep;
+      pp_item fmt x
+    ) a
diff --git a/core/CCArray.mli b/core/CCArray.mli
index 047ef761..555a77c8 100644
--- a/core/CCArray.mli
+++ b/core/CCArray.mli
@@ -68,9 +68,13 @@ val shuffle : 'a t -> unit
 (** shuffle randomly the array, in place *)
 
 val pp: ?sep:string -> (Buffer.t -> 'a -> unit)
-          -> Buffer.t -> 'a array -> 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 array -> 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
+(** print an array of items with printing function *)
diff --git a/core/CCVector.ml b/core/CCVector.ml
index 0ea564e7..cf5de68a 100644
--- a/core/CCVector.ml
+++ b/core/CCVector.ml
@@ -25,30 +25,76 @@ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 (** {1 Growable, mutable vector} *)
 
+type 'a sequence = ('a -> unit) -> unit
+type 'a klist = unit -> [`Nil | `Cons of 'a * 'a klist]
+type 'a gen = unit -> 'a option
+type 'a equal = 'a -> 'a -> bool
+type 'a ord = 'a -> 'a -> int
+type 'a printer = Buffer.t -> 'a -> unit
+type 'a formatter = Format.formatter -> 'a -> unit
+
 (** a vector of 'a. *)
 type 'a t = {
   mutable size : int;
   mutable vec : 'a array;
 }
 
-let create i =
-  let i = max i 3 in
-  { size = 0;
-    vec = Array.create i (Obj.magic None);
-  }
+let create () = {
+  size = 0;
+  vec = [| |];
+}
 
-let resize v newcapacity =
+let create_with ?(capacity=128) x = {
+  size = 0;
+  vec = Array.make capacity x;
+}
+
+(*$T
+  (create_with ~capacity:200 1 |> capacity) >= 200
+*)
+
+let make n x = {
+  size=n;
+  vec=Array.make n x;
+}
+
+let init n f = {
+  size=n;
+  vec=Array.init n f;
+}
+
+(* is the underlying empty? *)
+let _empty_array v =
+  Array.length v.vec = 0
+
+(* assuming the underlying array isn't empty, resize it *)
+let _resize v newcapacity =
   assert (newcapacity >= v.size);
-  let new_vec = Array.create newcapacity (Obj.magic None) in
+  assert (not (_empty_array v));
+  let new_vec = Array.create newcapacity v.vec.(0) in
   Array.blit v.vec 0 new_vec 0 v.size;
   v.vec <- new_vec;
   ()
 
+(*$T
+  (let v = create_with ~capacity:10 1 in ensure v 200; capacity v >= 200)
+*)
+
+(* grow the array, using [x] as a filler if required *)
+let _grow v x =
+  if _empty_array v
+    then v.vec <- Array.make 32 x
+    else
+      let size = min (2 * Array.length v.vec + 10) Sys.max_array_length in
+      _resize v size
+
 let ensure v size =
-  if v.size < size
+  if Array.length v.vec = 0
+    then ()
+  else if v.size < size
     then
-      let size' = min (2 * v.size) Sys.max_array_length in
-      resize v size'
+      let size' = min size Sys.max_array_length in
+      _resize v size'
 
 let clear v =
   v.size <- 0
@@ -56,59 +102,92 @@ let clear v =
 let is_empty v = v.size = 0
 
 let push v x =
-  (if v.size = Array.length v.vec then resize v (2 * v.size));
+  if v.size = Array.length v.vec
+    then _grow v x;
   Array.unsafe_set v.vec v.size x;
   v.size <- v.size + 1
 
 (** add all elements of b to a *)
 let append a b =
-  (if Array.length a.vec < a.size + b.size
-    then resize a (2 * (a.size + b.size)));
-  Array.blit b.vec 0 a.vec a.size b.size;
-  a.size <- a.size + b.size
+  if _empty_array a
+  then if _empty_array b
+    then ()
+    else (
+      a.vec <- Array.copy b.vec;
+      a.size <- b.size
+    )
+  else (
+    ensure a (a.size + b.size);
+    assert (Array.length a.vec >= a.size + b.size);
+    Array.blit b.vec 0 a.vec a.size b.size;
+    a.size <- a.size + b.size
+  )
 
-let append_array a b =
-  (if Array.length a.vec < a.size + Array.length b
-    then resize a (2 * (a.size + Array.length b)));
-  Array.blit b 0 a.vec a.size (Array.length b);
-  a.size <- a.size + Array.length b
+let get v i =
+  if i < 0 || i >= v.size then failwith "Vector.get";
+  Array.unsafe_get v.vec i
+
+let set v i x =
+  if i < 0 || i >= v.size then failwith "Vector.set";
+  Array.unsafe_set v.vec i x
 
 let append_seq a seq =
   seq (fun x -> push a x)
 
-let pop v =
-  (if v.size = 0 then failwith "Vector.pop on empty vector");
+let append_array a b =
+  Array.iter (push a) b
+
+let equal eq v1 v2 =
+  let n = min v1.size v2.size in
+  let rec check i =
+    if i = n
+      then v1.size = v2.size
+      else eq (get v1 i) (get v2 i) && check (i+1)
+  in check 0
+
+let compare cmp v1 v2 =
+  let n = min v1.size v2.size in
+  let rec check i =
+    if i = n
+      then Pervasives.compare v1.size v2.size
+      else
+        let c = cmp (get v1 i) (get v2 i) in
+        if c = 0 then check (i+1) else c
+  in check 0
+
+let pop_exn v =
+  if v.size = 0
+    then failwith "Vector.pop on empty vector";
   v.size <- v.size - 1;
   let x = v.vec.(v.size) in
   x
 
-let copy v =
-  let v' = create v.size in
-  Array.blit v.vec 0 v'.vec 0 v.size;
-  v'.size <- v.size;
-  v'
+let pop v =
+  try Some (pop_exn v)
+  with Failure _ -> None
+
+let copy v = {
+  size = v.size;
+  vec = Array.sub v.vec 0 v.size;
+}
+
+(*$T
+  (let v = of_list [1;2;3] in let v' = copy v in \
+    to_list v' = [1;2;3])
+  create () |> copy |> is_empty
+*)
 
 let shrink v n =
-  if n > v.size
-    then failwith "cannot shrink to bigger size"
-    else v.size <- n
+  if n < v.size then v.size <- n
 
-let member ?(eq=(=)) v x =
-  let n = v.size in
-  let rec check i =
-    if i = n then false
-    else if eq x v.vec.(i) then true
-    else check (i+1)
-  in check 0
-
-let sort ?(cmp=compare) v =
+let sort cmp v =
   (* copy array (to avoid junk in it), then sort the array *)
   let a = Array.sub v.vec 0 v.size in
   Array.fast_sort cmp a;
   v.vec <- a
 
-let uniq_sort ?(cmp=compare) v =
-  sort ~cmp v;
+let uniq_sort cmp v =
+  sort cmp v;
   let n = v.size in
   (* traverse to remove duplicates. i= current index,
      j=current append index, j<=i. new_size is the size
@@ -116,64 +195,83 @@ let uniq_sort ?(cmp=compare) v =
   let rec traverse prev i j =
     if i >= n then () (* done traversing *)
     else if cmp prev v.vec.(i) = 0
-      then (v.size <- v.size - 1; traverse prev (i+1) j) (* duplicate, remove it *)
-      else (v.vec.(j) <- v.vec.(i); traverse v.vec.(i) (i+1) (j+1)) (* keep it *)
+      then (
+        v.size <- v.size - 1;
+        traverse prev (i+1) j
+      ) (* duplicate, remove it *)
+      else (
+        v.vec.(j) <- v.vec.(i);
+        traverse v.vec.(i) (i+1) (j+1)
+      ) (* keep it *)
   in
   if v.size > 0
-    then traverse v.vec.(0) 1 1 (* start at 1, to get the first element in hand *)
+    then traverse v.vec.(0) 1 1
+    (* start at 1, to get the first element in hand *)
 
-let iter v k =
+let iter k v =
   for i = 0 to v.size -1 do
     k (Array.unsafe_get v.vec i)
   done
 
-let iteri v k =
+let iteri k v =
   for i = 0 to v.size -1 do
     k i (Array.unsafe_get v.vec i)
   done
 
-let map v f =
-  let v' = create v.size in
-  for i = 0 to v.size - 1 do
-    let x = f (Array.unsafe_get v.vec i) in
-    Array.unsafe_set v'.vec i x
-  done;
-  v'.size <- v.size;
-  v'
+let map f v =
+  if _empty_array v
+  then create ()
+  else {
+    size=v.size;
+    vec=Array.map f v.vec
+  }
 
-let filter v f =
-  let v' = create v.size in
-  for i = 0 to v.size - 1 do
-    let x = Array.unsafe_get v.vec i in
-    if f x then push v' x;
-  done;
-  v'
+let filter p v =
+  if _empty_array v
+  then create ()
+  else (
+    let v' = create_with ~capacity:v.size v.vec.(0) in
+    Array.iter
+      (fun x -> if p x then push v' x)
+      v.vec;
+    v'
+  )
 
-let fold v acc f =
-  let acc = ref acc in
-  for i = 0 to v.size - 1 do
-    let x = Array.unsafe_get v.vec i in
-    acc := f !acc x;
-  done;
-  !acc
+(*$T
+  filter (fun x-> x mod 2=0) (of_list [1;2;3;4;5]) |> to_list = [2;4]
+*)
 
-let exists v p =
+let fold f acc v =
+  let rec fold acc i =
+    if i = v.size then acc
+    else
+      let x = Array.unsafe_get v.vec i in
+      fold (f acc x) (i+1)
+  in fold acc 0
+
+(*$T
+  fold (+) 0 (of_list [1;2;3;4;5]) = 15
+  fold (+) 0 (create ()) = 0
+*)
+
+let exists p v =
   let n = v.size in
   let rec check i =
     if i = n then false
-    else if p v.vec.(i) then true
-    else check (i+1)
+    else p v.vec.(i) || check (i+1)
   in check 0
 
-let for_all v p =
+let for_all p v =
   let n = v.size in
   let rec check i =
     if i = n then true
-    else if not (p v.vec.(i)) then false
-    else check (i+1)
+    else p v.vec.(i) && check (i+1)
   in check 0
 
-let find v p =
+let member ?(eq=(=)) x v =
+  exists (eq x) v
+
+let find_exn p v =
   let n = v.size in
   let rec check i =
     if i = n then raise Not_found
@@ -181,65 +279,166 @@ let find v p =
     else check (i+1)
   in check 0
 
-let get v i =
-  (if i < 0 || i >= v.size then failwith "Vector.get");
-  Array.unsafe_get v.vec i
+let find p v =
+  try Some (find_exn p v)
+  with Not_found -> None
 
-let set v i x =
-  (if i < 0 || i >= v.size then failwith "Vector.set");
-  Array.unsafe_set v.vec i x
+let filter_map f v =
+  let v' = create () in
+  iter
+    (fun x -> match f x with
+      | None -> ()
+      | Some y -> push v' y
+    ) v;
+  v'
+
+let flat_map f v =
+  let v' = create () in
+  iter (fun x -> iter (push v') (f x)) v;
+  v'
+
+let flat_map' f v =
+  let v' = create () in
+  iter
+    (fun x ->
+      let seq = f x in
+      seq (fun y -> push v' y)
+    ) v;
+  v'
+
+let (>>=) x f = flat_map f x
+
+let (>|=) x f = map f x
+
+let rev' v =
+  if v.size > 0
+  then (
+    let n = v.size in
+    let vec = v.vec in
+    for i = 0 to (n-1)/2 do
+      let x = Array.unsafe_get vec i in
+      let y = Array.unsafe_get vec (n-i-1) in
+      Array.unsafe_set vec i y;
+      Array.unsafe_set vec (n-i-1) x;
+    done
+  )
 
 let rev v =
-  let n = v.size in
-  let vec = v.vec in
-  for i = 0 to (n-1)/2 do
-    let x = Array.unsafe_get vec i in
-    let y = Array.unsafe_get vec (n-i-1) in
-    Array.unsafe_set vec i y;
-    Array.unsafe_set vec (n-i-1) x;
-  done
+  let v' = copy v in
+  rev' v';
+  v'
+
+(*$T
+  rev (of_list [1;2;3;4]) |> to_list = [4;3;2;1]
+  rev (of_list [1;2;3;4;5]) |> to_list = [5;4;3;2;1]
+  rev (create ()) |> to_list = []
+*)
 
 let size v = v.size
 
 let length v = v.size
 
+let capacity v = Array.length v.vec
+
 let unsafe_get_array v = v.vec
 
-type 'a sequence = ('a -> unit) -> unit
-
-let of_seq ?(init=create 10) seq =
+let of_seq ?(init=create ()) seq =
   append_seq init seq;
   init
 
-let to_seq = iter
+(*$T
+  of_seq CCSequence.(1 -- 10) |> to_list = CCList.(1 -- 10)
+*)
+
+let to_seq v k = iter k v
 
 let slice v start len =
   assert (start >= 0 && len >= 0);
   fun k ->
     assert (start+len < v.size);
-    for i = start to start+len do
+    for i = start to start+len-1 do
       let x = Array.unsafe_get v.vec i in
       k x
     done
 
-let from_array a =
-  let c = Array.length a in
-  let v = create c in
-  Array.blit a 0 v.vec 0 c;
-  v.size <- c;
-  v
+(*$T
+  slice (of_list [0;1;2;3;4]) 1 3 |> CCList.of_seq = [1;2;3]
+*)
 
-let from_list l =
-  let v = create 10 in
-  List.iter (push v) l;
-  v
+let (--) i j =
+  if i>j
+    then init (i-j+1) (fun k -> i-k)
+    else init (j-i+1) (fun k -> i+k)
+
+(*$T
+  (1 -- 4) |> to_list = [1;2;3;4]
+  (4 -- 1) |> to_list = [4;3;2;1]
+  (0 -- 0) |> to_list = [0]
+*)
+
+let of_array a =
+  if Array.length a = 0
+  then create ()
+  else {
+    size=Array.length a;
+    vec=Array.copy a;
+  }
+
+let of_list l = match l with
+  | [] -> create()
+  | x::l' ->
+      let v = create_with ~capacity:(List.length l + 5) x in
+      List.iter (push v) l;
+      v
 
 let to_array v =
   Array.sub v.vec 0 v.size
 
 let to_list v =
-  let l = ref [] in
-  for i = 0 to v.size - 1 do
-    l := get v i :: !l;
-  done;
-  List.rev !l
+  List.rev (fold (fun acc x -> x::acc) [] v)
+
+let of_gen ?(init=create ()) g =
+  let rec aux g = match g() with
+    | None -> init
+    | Some x -> push init x; aux g
+  in aux g
+
+let to_gen v =
+  let i = ref 0 in
+  fun () ->
+    if !i < v.size
+      then (
+        let x = v.vec.( !i ) in
+        incr i;
+        Some x
+      ) else None
+
+let of_klist ?(init=create ()) l =
+  let rec aux l = match l() with
+    | `Nil -> init
+    | `Cons (x,l') -> push init x; aux l'
+  in aux l
+
+let to_klist v =
+  let rec aux i () =
+    if i=v.size then `Nil
+    else `Cons (v.vec.(i), aux (i+1))
+  in aux 0
+
+let pp ?(start="[") ?(stop="]") ?(sep=", ") pp_item buf v =
+  Buffer.add_string buf start;
+  iteri
+    (fun i x ->
+      if i > 0 then Buffer.add_string buf sep;
+      pp_item buf x
+    ) v;
+  Buffer.add_string buf stop
+
+let print ?(start="[") ?(stop="]") ?(sep=", ") pp_item fmt v =
+  Format.fprintf fmt "@[%s" start;
+  iteri
+    (fun i x ->
+      if i > 0 then Format.pp_print_string fmt sep;
+      pp_item fmt x
+    ) v;
+  Format.fprintf fmt "%s@]" stop
diff --git a/core/CCVector.mli b/core/CCVector.mli
index 697c601e..6981935c 100644
--- a/core/CCVector.mli
+++ b/core/CCVector.mli
@@ -29,16 +29,33 @@ type 'a t
 (** the type of a vector of 'a *)
 
 type 'a sequence = ('a -> unit) -> unit
+type 'a klist = unit -> [`Nil | `Cons of 'a * 'a klist]
+type 'a gen = unit -> 'a option
+type 'a equal = 'a -> 'a -> bool
+type 'a ord = 'a -> 'a -> int
+type 'a printer = Buffer.t -> 'a -> unit
+type 'a formatter = Format.formatter -> 'a -> unit
 
-val create : int -> 'a t
-(** create a vector of given initial capacity *)
+val create : unit -> 'a t
+(** Create a new, empty vector *)
+
+val create_with : ?capacity:int -> 'a -> 'a t
+(** Create a new vector, using the given value as a filler.
+    @param capacity the size of the underlying array
+    {b caution}: the value will likely not be GC'd before the vector is. *)
+
+val make : int -> 'a -> 'a t
+(** [make n x] makes a vector of size [n], filled with [x] *)
+
+val init : int -> (int -> 'a) -> 'a t
+(** Init the vector with the given function and size *)
 
 val clear : 'a t -> unit
 (** clear the content of the vector *)
 
 val ensure : 'a t -> int -> unit
-(** Ensure that the vector can contain that much elements, resizing it
-    if required *)
+(** Hint to the vector that it should have at least the given capacity.
+    Just a hint, will not be enforced if the vector is empty. *)
 
 val is_empty : 'a t -> bool
 (** is the vector empty? *)
@@ -55,56 +72,88 @@ val append_array : 'a t -> 'a array -> unit
 val append_seq : 'a t -> 'a sequence -> unit
 (** Append content of sequence *)
 
-val pop : 'a t -> 'a
-(** remove last element, or raise a Failure if empty *)
+val equal : 'a equal -> 'a t equal
+
+val compare : 'a ord -> 'a t ord
+(** Lexicographic comparison *)
+
+val pop : 'a t -> 'a option
+(** Remove last element, or [None] *)
+
+val pop_exn : 'a t -> 'a
+(** remove last element, or raise a Failure if empty
+    @raise Failure on an empty vector *)
 
 val copy : 'a t -> 'a t
 (** shallow copy *)
 
 val shrink : 'a t -> int -> unit
-(** shrink to the given size (remove elements above this size) *)
+(** shrink to the given size (remove elements above this size).
+    Does nothing if the parameter is bigger than the current size. *)
 
-val member : ?eq:('a -> 'a -> bool) -> 'a t -> 'a -> bool
+val member : ?eq:('a -> 'a -> bool) -> 'a -> 'a t -> bool
 (** is the element a member of the vector? *)
 
-val sort : ?cmp:('a -> 'a -> int) -> 'a t -> unit
+val sort : ('a -> 'a -> int) -> 'a t -> unit
 (** sort the array in place*)
 
-val uniq_sort : ?cmp:('a -> 'a -> int) -> 'a t -> unit
+val uniq_sort : ('a -> 'a -> int) -> 'a t -> unit
 (** sort the array and remove duplicates in place*)
 
-val iter : 'a t -> ('a -> unit) -> unit
+val iter : ('a -> unit) -> 'a t -> unit
 (** iterate on the vector *)
 
-val iteri : 'a t -> (int -> 'a -> unit) -> unit
+val iteri : (int -> 'a -> unit) -> 'a t -> unit
 (** iterate on the vector with indexes *)
 
-val map : 'a t -> ('a -> 'b) -> 'b t
+val map : ('a -> 'b) -> 'a t -> 'b t
 (** map elements of the vector *)
 
-val filter : 'a t -> ('a -> bool) -> 'a t
+val filter : ('a -> bool) -> 'a t -> 'a t
 (** filter elements from vector *)
 
-val fold : 'a t -> 'b -> ('b -> 'a -> 'b) -> 'b
+val fold : ('b -> 'a -> 'b) -> 'b -> 'a t -> 'b
 (** fold on elements of the vector *)
 
-val exists : 'a t -> ('a -> bool) -> bool
+val exists : ('a -> bool) -> 'a t -> bool
 (** existential test *)
 
-val for_all : 'a t -> ('a -> bool) -> bool
+val for_all : ('a -> bool) -> 'a t -> bool
 (** universal test *)
 
-val find : 'a t -> ('a -> bool) -> 'a
-(** find an element that satisfies the predicate, or Not_found *)
+val find : ('a -> bool) -> 'a t -> 'a option
+(** Find an element that satisfies the predicate *)
+
+val find_exn  : ('a -> bool) -> 'a t -> 'a
+(** find an element that satisfies the predicate, or
+    @raise Not_found if no element does *)
+
+val filter_map : ('a -> 'b option) -> 'a t -> 'b t
+(** Map elements with a function, possibly filtering some of them out *)
+
+val flat_map : ('a -> 'b t) -> 'a t -> 'b t
+(** Map each element to a sub-vector *)
+
+val flat_map' : ('a -> 'b sequence) -> 'a t -> 'b t
+(** Like {!flat_map}, but using {!sequence} for intermediate collections *)
+
+val (>>=) : 'a t -> ('a -> 'b t) -> 'b t
+
+val (>|=) : 'a t -> ('a -> 'b) -> 'b t
 
 val get : 'a t -> int -> 'a
-(** access element, or Failure if bad index *)
+(** access element, or
+    @raise Failure if bad index *)
 
 val set : 'a t -> int -> 'a -> unit
-(** access element, or Failure if bad index *)
+(** access element, or
+    @raise Failure if bad index *)
 
-val rev : 'a t -> unit
-(** Reverse array in place *)
+val rev : 'a t -> 'a t
+(** Reverse the vector *)
+
+val rev' : 'a t -> unit
+(** Reverse the vector in place *)
 
 val size : 'a t -> int
 (** number of elements in vector *)
@@ -112,21 +161,37 @@ val size : 'a t -> int
 val length : _ t -> int
 (** Synonym for {! size} *)
 
+val capacity : _ t -> int
+(** Number of elements the vector can contain without being resized *)
+
 val unsafe_get_array : 'a t -> 'a array
-(** Access the underlying *shared* array (do not modify!).
+(** Access the underlying {b shared} array (do not modify!).
     [unsafe_get_array v] is longer than [size v], but elements at higher
     index than [size v] are undefined (do not access!). *)
 
+val (--) : int -> int -> int t
+(** Range of integers (both included) *)
+
+val of_array : 'a array -> 'a t
+val of_list : 'a list -> 'a t
+val to_array : 'a t -> 'a array
+val to_list : 'a t -> 'a list
+
 val of_seq : ?init:'a t -> 'a sequence -> 'a t
 
 val to_seq : 'a t -> 'a sequence
 
 val slice : 'a t -> int -> int -> 'a sequence
 (** [slice v start len] is the sequence of elements from [v.(start)]
-    to [v.(start+len)] included. *)
+    to [v.(start+len-1)]. *)
 
-val from_array : 'a array -> 'a t
-val from_list : 'a list -> 'a t
-val to_array : 'a t -> 'a array
-val to_list : 'a t -> 'a list
+val of_klist : ?init:'a t -> 'a klist -> 'a t
+val to_klist : 'a t -> 'a klist
+val of_gen : ?init:'a t -> 'a gen -> 'a t
+val to_gen : 'a t -> 'a gen
 
+val pp : ?start:string -> ?stop:string -> ?sep:string ->
+         'a printer -> 'a t printer
+
+val print : ?start:string -> ?stop:string -> ?sep:string ->
+            'a formatter -> 'a t formatter