diff --git a/.ocamlinit b/.ocamlinit
index f477d71c..7711334d 100644
--- a/.ocamlinit
+++ b/.ocamlinit
@@ -9,7 +9,7 @@
 #load "containers_misc.cma";;
 #require "threads";;
 #load "containers_thread.cma";;
-open Containers;;
+open Containers_misc;;
 #install_printer Bencode.pretty;;
 #install_printer HGraph.Default.fmt;;
 #require "CamlGI";;
diff --git a/_oasis b/_oasis
index da7316d4..ff9b3700 100644
--- a/_oasis
+++ b/_oasis
@@ -59,7 +59,7 @@ Library "containers_misc"
                     PHashtbl, SkipList, SplayTree, SplayMap, Univ,
                     Bij, PiCalculus, Bencode, Sexp, RAL,
                     UnionFind, SmallSet, AbsSet, CSM,
-                    ActionMan, BencodeOnDisk, TTree,
+                    ActionMan, BencodeOnDisk, TTree, PrintBox,
                     HGraph, Automaton, Conv, Bidir, Iteratee,
                     Ty, Tell, BencodeStream, RatTerm, Cause, AVL, ParseReact
   BuildDepends:     unix,containers
diff --git a/misc/printBox.ml b/misc/printBox.ml
new file mode 100644
index 00000000..4d8f5eca
--- /dev/null
+++ b/misc/printBox.ml
@@ -0,0 +1,329 @@
+
+(*
+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 Pretty-Printing of Boxes} *)
+
+type position = { x:int ; y: int }
+
+let origin = {x=0; y=0;}
+
+let _move pos x y = {x=pos.x + x; y=pos.y + y}
+let _add pos1 pos2 = _move pos1 pos2.x pos2.y
+let _move_x pos x = _move pos x 0
+let _move_y pos y = _move pos 0 y
+
+(** {2 Output: where to print to} *)
+
+module Output = struct
+  type t = {
+    put_char : position -> char -> unit;
+    put_string : position -> string -> unit;
+    put_sub_string : position -> string -> int -> int -> unit;
+    flush : unit -> unit;
+  }
+
+  let put_char out pos c = out.put_char pos c
+  let put_string out pos s = out.put_string pos s
+  let put_sub_string out pos s s_i s_len = out.put_sub_string pos s s_i s_len
+
+  (** An internal buffer, suitable for writing efficiently, then
+      convertable into a list of lines *)
+  type buffer = {
+    mutable buf_lines : buf_line array;
+    mutable buf_len : int;
+  }
+  and buf_line = {
+    mutable bl_str : string;
+    mutable bl_len : int;
+  }
+
+  let _make_line _ = {bl_str=""; bl_len=0}
+
+  let _ensure_lines buf i =
+    if i >= Array.length buf.buf_lines
+    then (
+      let lines' = Array.init (2 * i + 5) _make_line in
+      Array.blit buf.buf_lines 0 lines' 0 buf.buf_len;
+      buf.buf_lines <- lines';
+    )
+
+  let _ensure_line line i =
+    if i >= String.length line.bl_str
+    then (
+      let str' = String.make (2 * i + 5) ' ' in
+      String.blit line.bl_str 0 str' 0 line.bl_len;
+      line.bl_str <- str';
+    )
+
+  let _buf_put_char buf pos c =
+    _ensure_lines buf pos.y;
+    _ensure_line buf.buf_lines.(pos.y) pos.x;
+    buf.buf_len <- max buf.buf_len (pos.y+1);
+    let line = buf.buf_lines.(pos.y) in
+    line.bl_str.[pos.x] <- c;
+    line.bl_len <- max line.bl_len (pos.x+1)
+
+  let _buf_put_sub_string buf pos s s_i s_len =
+    _ensure_lines buf pos.y;
+    _ensure_line buf.buf_lines.(pos.y) (pos.x + s_len);
+    buf.buf_len <- max buf.buf_len (pos.y+1);
+    let line = buf.buf_lines.(pos.y) in
+    String.blit s s_i line.bl_str pos.x s_len;
+    line.bl_len <- max line.bl_len (pos.x+s_len)
+
+  let _buf_put_string buf pos s =
+    _buf_put_sub_string buf pos s 0 (String.length s)
+
+  (* create a new buffer *)
+  let make_buffer () =
+    let buf = {
+      buf_lines = Array.init 16 _make_line;
+      buf_len = 0;
+    } in
+    let buf_out = {
+      put_char = _buf_put_char buf;
+      put_sub_string = _buf_put_sub_string buf;
+      put_string = _buf_put_string buf;
+      flush = (fun () -> ());
+    } in
+    buf, buf_out
+
+  let buf_to_lines ?(indent=0) buf =
+    let buffer = Buffer.create (5 + buf.buf_len * 32) in
+    for i = 0 to buf.buf_len - 1 do
+      for k = 1 to indent do Buffer.add_char buffer ' ' done;
+      let line = buf.buf_lines.(i) in
+      Buffer.add_substring buffer line.bl_str 0 line.bl_len;
+      Buffer.add_char buffer '\n';
+    done;
+    Buffer.contents buffer
+
+  let buf_output ?(indent=0) oc buf =
+    for i = 0 to buf.buf_len - 1 do
+      for k = 1 to indent do output_char oc ' '; done;
+      let line = buf.buf_lines.(i) in
+      output oc line.bl_str 0 line.bl_len;
+      output_char oc '\n';
+    done
+end
+
+(* find [c] in [s], starting at offset [i] *)
+let rec _find s c i =
+  if i >= String.length s then None
+  else if s.[i] = c then Some i
+  else _find s c (i+1)
+
+let rec _lines s i k = match _find s '\n' i with
+  | None -> ()
+  | Some j ->
+      let s' = String.sub s i (j-i) in
+      k s';
+      _lines s (j+1) k
+
+module Box = struct
+  type grid_shape =
+    | GridBase
+    | GridFramed
+
+  type 'a shape =
+    | Line of string
+    | Text of string list  (* in a box *)
+    | Frame of 'a
+    | Grid of grid_shape * 'a array array
+
+  type t = {
+    shape : t shape;
+    size : position lazy_t;
+  }
+
+  let size box = Lazy.force box.size
+
+  let shape b = b.shape
+
+  let _array_foldi f acc a =
+    let acc = ref acc in
+    Array.iteri (fun i x -> acc := f !acc i x) a;
+    !acc
+
+  let _dim_matrix m =
+    if Array.length m = 0 then {x=0;y=0}
+    else {y=Array.length m; x=Array.length m.(0); }
+
+  (* height of a line composed of boxes *)
+  let _height_line a =
+    _array_foldi
+      (fun h i box ->
+        let s = size box in
+        max h s.y
+      ) 0 a
+
+  (* how large is the [i]-th column of [m]? *)
+  let _width_column m i =
+    let acc = ref 0 in
+    for j = 0 to Array.length m - 1 do
+      acc := max !acc (size m.(j).(i)).x
+    done;
+    !acc
+
+  (* from a matrix [m] (line,column), return two arrays [lines] and [columns],
+    with [col.(i)] being the start offset of column [i] and
+    [lines.(j)] being the start offset of line [j].
+    Those arrays have one more slot to indicate the end position. *)
+  let _size_matrix m =
+    let dim = _dim_matrix m in
+    (* columns *)
+    let columns = Array.make (dim.x + 1) 0 in
+    for i = 0 to dim.x - 1 do
+      (* +1 is for keeping room for the vertical/horizontal line/column *)
+      columns.(i+1) <- columns.(i) + 1 + (_width_column m i)
+    done;
+    (* lines *)
+    let lines = Array.make (dim.y + 1) 0 in
+    for j = 1 to dim.y do
+      lines.(j) <- lines.(j-1) + 1 + (_height_line m.(j-1))
+    done;
+    (* no trailing bars, adjust *)
+    columns.(dim.x) <- columns.(dim.x) - 1;
+    lines.(dim.y) <- lines.(dim.y) - 1;
+    lines, columns
+
+  let _size = function
+    | Line s -> { x=String.length s; y=1 }
+    | Text l ->
+        let width = List.fold_left
+          (fun acc line -> max acc (String.length line)) 0 l
+        in
+        { x=width; y=List.length l; }
+    | Frame t ->
+        let {x;y} = size t in
+        { x=x+2; y=y+2; }
+    | Grid (_,m) ->
+        let dim = _dim_matrix m in
+        let lines, columns = _size_matrix m in
+        { y=lines.(dim.y); x=columns.(dim.x)}
+
+  let _make shape =
+    { shape; size=(lazy (_size shape)); }
+
+  let line s =
+    assert (_find s '\n' 0 = None);
+    _make (Line s)
+
+  let text s =
+    let acc = ref [] in
+    _lines s 0 (fun x -> acc := x :: !acc);
+    _make (Text (List.rev !acc))
+
+  let lines l =
+    assert (List.for_all (fun s -> _find s '\n' 0 = None) l);
+    _make (Text l)
+
+  let frame b = _make (Frame b)
+
+  let grid ?(framed=true) m =
+    _make (Grid ((if framed then GridFramed else GridBase), m))
+
+  let init_grid ?framed ~line ~col f =
+    let m = Array.init line (fun j-> Array.init col (fun i -> f ~line:j ~col:i)) in
+    grid ?framed m
+
+  let vlist ?framed l =
+    let a = Array.of_list l in
+    grid ?framed (Array.map (fun line -> [| line |]) a)
+
+  let hlist ?framed l =
+    grid ?framed [| Array.of_list l |]
+end
+
+let _write_vline ~out pos n =
+  for j=0 to n-1 do
+    Output.put_char out (_move_y pos j) '|'
+  done
+
+let _write_hline ~out pos n =
+  for i=0 to n-1 do
+    Output.put_char out (_move_x pos i) '-'
+  done
+
+(* render given box on the output, starting with upper left corner
+    at the given position. *)
+let rec _render ~out b pos =
+  match Box.shape b with
+    | Box.Line s -> Output.put_string out pos s
+    | Box.Text l ->
+        List.iteri
+          (fun i line ->
+            Output.put_string out (_move_y pos i) line
+          ) l
+    | Box.Frame b' ->
+        let {x;y} = Box.size b' in
+        Output.put_char out pos '+';
+        Output.put_char out (_move pos (x+1) (y+1)) '+';
+        Output.put_char out (_move pos 0 (y+1)) '+';
+        Output.put_char out (_move pos (x+1) 0) '+';
+        _write_hline out (_move_x pos 1) x;
+        _write_hline out (_move pos 1 (y+1)) x;
+        _write_vline out (_move_y pos 1) y;
+        _write_vline out (_move pos (x+1) 1) y;
+        _render ~out b' (_move pos 1 1)
+    | Box.Grid (grid_shape,m) ->
+        let dim = Box._dim_matrix m in
+        let lines, columns = Box._size_matrix m in
+
+        (* write boxes *)
+        for j = 0 to dim.y - 1 do
+          for i = 0 to dim.x - 1 do
+            let pos' = _move pos (columns.(i)) (lines.(j)) in
+            _render ~out m.(j).(i) pos'
+          done;
+        done;
+
+        (* write frame if needed *)
+        begin match grid_shape with
+        | Box.GridBase -> ()
+        | Box.GridFramed ->
+          let size = Box.size b in
+          for j=1 to dim.y - 1 do
+            _write_hline ~out {pos with y=lines.(j)} size.x
+          done;
+          for i=1 to dim.x - 1 do
+            _write_vline ~out {pos with x=columns.(i)} size.y
+          done;
+        end
+
+let render out b =
+  _render ~out b origin
+
+let to_string b =
+  let buf, out = Output.make_buffer () in
+  render out b;
+  Output.buf_to_lines buf
+
+let output ?(indent=0) oc b =
+  let buf, out = Output.make_buffer () in
+  render out b;
+  Output.buf_output ~indent oc buf;
+  flush oc
diff --git a/misc/printBox.mli b/misc/printBox.mli
new file mode 100644
index 00000000..25c34474
--- /dev/null
+++ b/misc/printBox.mli
@@ -0,0 +1,100 @@
+
+(*
+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 Pretty-Printing of Boxes} *)
+
+type position = { x:int ; y: int }
+(** Positions are relative to the upper-left corner, that is,
+when [x] increases we go toward the right, and when [y] increases
+we go toward the bottom (same order as a printer) *)
+
+val origin : position
+(** Initial position *)
+
+module Output : sig
+  type t = {
+    put_char : position -> char -> unit;
+    put_string : position -> string -> unit;
+    put_sub_string : position -> string -> int -> int -> unit;
+    flush : unit -> unit;
+  }
+
+  (** {6 Default Instance: a buffer} *)
+
+  type buffer
+
+  val make_buffer : unit -> buffer * t
+  (** New buffer, and the corresponding output (buffers are mutable) *)
+
+  val buf_to_lines : ?indent:int -> buffer -> string
+  (** Print the content of the buffer into a string.
+      @param indent number of spaces to insert in front of the lines *)
+
+  val buf_output : ?indent:int -> out_channel -> buffer -> unit
+  (** Print the buffer on the given channel *)
+end
+
+module Box : sig
+  type t
+
+  val size : t -> position
+  (** Size needed to print the box *)
+
+  val line : string -> t
+  (** Make a single-line box.
+      @raise Invalid_argument if the string contains ['\n'] *)
+
+  val text : string -> t
+  (** Any text, possibly with several lines *)
+
+  val lines : string list -> t
+  (** Shortcut for {!text}, with a list of lines *)
+
+  val frame : t -> t
+  (** Put a single frame around the box *)
+
+  val grid : ?framed:bool -> t array array -> t
+  (** Grid of boxes (no frame between boxes). The matrix is indexed
+      with lines first, then columns.
+      @param framed if [true], each item of the grid will be framed.
+        default value is [true] *)
+
+  val init_grid : ?framed:bool ->
+                  line:int -> col:int -> (line:int -> col:int -> t) -> t
+  (** Same as {!grid} but takes the matrix as a function *)
+
+  val vlist : ?framed:bool -> t list -> t
+  (** Vertical list of boxes *)
+
+  val hlist : ?framed:bool -> t list -> t
+  (** Horizontal list of boxes *)
+end
+
+val render : Output.t -> Box.t -> unit
+
+val to_string : Box.t -> string
+
+val output : ?indent:int -> out_channel -> Box.t -> unit