(*
    ||M||  This file is part of HELM, an Hypertextual, Electronic        
    ||A||  Library of Mathematics, developed at the Computer Science     
    ||T||  Department, University of Bologna, Italy.                     
    ||I||                                                                
    ||T||  HELM is free software; you can redistribute it and/or         
    ||A||  modify it under the terms of the GNU General Public License   
    \   /  version 2 or (at your option) any later version.      
     \ /   This software is distributed as is, NO WARRANTY.     
      V_______________________________________________________________ *)

(* $Id: nCic.ml 9058 2008-10-13 17:42:30Z tassi $ *)

val repeat : ('a -> 'a option) -> 'a -> 'a

module type Elem = sig type t val pp : t -> string end ;;

module type ZipTree = sig
  type t
  type tree = Node of (t * tree) list
  type position

  val start : tree -> position

  val up    : position -> position option
  val down  : position -> position option
  val left  : position -> position option
  val right : position -> position option

  val root: position -> tree
  val previsit: ('a -> t -> 'a) -> 'a -> position -> 'a

  val get: position -> t
  val set: t -> position -> position

  val inject: tree -> position -> position
  val eject: position -> tree

end

module Make(T : Elem) : ZipTree with type t = T.t