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+(************************************************************************)
+(*  v      *   The Coq Proof Assistant  /  The Coq Development Team     *)
+(* <O___,, * CNRS-Ecole Polytechnique-INRIA Futurs-Universite Paris Sud *)
+(*   \VV/  **************************************************************)
+(*    //   *      This file is distributed under the terms of the       *)
+(*         *       GNU Lesser General Public License Version 2.1        *)
+(************************************************************************)
+
+(* $Id$ *)
+
+(** Module implementing basic combinators for OCaml option type.
+   It tries follow closely the style of OCaml standard library.
+
+   Actually, some operations have the same name as [List] ones:
+   they actually are similar considering ['a option] as a type
+   of lists with at most one element. *)
+
+(** [has_some x] is [true] if [x] is of the form [Some y] and [false]
+    otherwise.  *)
+let has_some = function
+  | None -> false
+  | _ -> true
+  
+exception IsNone
+
+(** [get x] returns [y] where [x] is [Some y]. It raises IsNone
+    if [x] equals [None]. *)
+let get = function
+  | Some y -> y
+  | _ -> raise IsNone
+
+
+(** [flatten x] is [Some y] if [x] is [Some (Some y)] and [None] otherwise. *)
+let flatten = function
+  | Some (Some y) -> Some y
+  | _ -> None
+
+
+(** {6 "Iterators"} ***)
+
+(** [iter f x] executes [f y] if [x] equals [Some y]. It does nothing 
+    otherwise. *)
+let iter f = function
+  | Some y -> f y
+  | _ -> ()
+
+
+exception Heterogeneous
+
+(** [iter2 f x y] executes [f z w] if [x] equals [Some z] and [y] equals
+    [Some w]. It does nothing if both [x] and [y] are [None]. And raises
+    [Heterogeneous] otherwise. *)
+let iter2 f x y = 
+  match x,y with
+  | Some z, Some w -> f z w
+  | None,None -> ()
+  | _,_ -> raise Heterogeneous
+
+(** [map f x] is [None] if [x] is [None] and [Some (f y)] if [x] is [Some y]. *)
+let map f = function
+  | Some y -> Some (f y)
+  | _ -> None
+
+(** [smartmap f x] does the same as [map f x] except that it tries to share
+    some memory. *)
+let smartmap f = function
+  | Some y as x -> let y' = f y in if y' == y then x else Some y'
+  | _ -> None
+
+(** [fold_left f a x] is [f a y] if [x] is [Some y], and [a] otherwise. *)
+let fold_left f a = function
+  | Some y -> f a y
+  | _ -> a
+
+(** [fold_right f x a] is [f y a] if [x] is [Some y], and [a] otherwise. *)
+let fold_right f x a = 
+  match x with
+  | Some y -> f y a
+  | _ -> a
+
+
+(** {6 More Specific operations} ***)
+
+(** [default f x a] is [f y] if [x] is [Some y] and [a] otherwise. *)
+let default f x a = 
+  match x with
+  | Some y -> f y
+  | _ -> a
+
+(** [lift f x] is the same as [map f x]. *)
+let lift = map
+
+(** [lift_right f a x] is [Some (f a y)] if [x] is [Some y], and 
+    [None] otherwise. *)
+let lift_right f a = function
+  | Some y -> Some (f a y)
+  | _ -> None
+
+(** [lift_left f x a] is [Some (f y a)] if [x] is [Some y], and 
+    [None] otherwise. *)
+let lift_left f x a =
+  match x with
+  | Some y -> Some (f y a)
+  | _ -> None
+
+(** [lift2 f x y] is [Some (f z w)] if [x] equals [Some z] and [y] equals 
+    [Some w]. It is [None] otherwise. *)
+let lift2 f x y =
+  match x,y with
+  | Some z, Some w -> Some (f z w)
+  | _,_ -> None