Ajout list_fold_right_and_left

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/coq/trunk@535 85f007b7-540e-0410-9357-904b9bb8a0f7

2 files changed, 19 insertions, 0 deletions

diff --git a/lib/util.ml b/lib/util.ml
index e17e586c20..c733ed3335 100644
--- a/lib/util.ml
+++ b/lib/util.ml
@@ -141,6 +141,24 @@ let list_fold_left_i f =
   in 
   it_list_f 
 
+(* [list_fold_right_and_left f [a1;...;an] hd =
+   f (f (... (f (f hd
+                   an
+                   [an-1;...;a1])
+              an-1
+              [an-2;...;a1])
+         ...)
+        a2
+        [a1])
+     a1
+     []] *)
+
+let rec list_fold_right_and_left f l hd =
+  let rec aux tl = function
+    | [] -> hd
+    | a::l -> let hd = aux (a::tl) l in f hd a tl
+   in aux [] l
+
 let list_iter_i f l = list_fold_left_i (fun i _ x -> f i x) 0 () l
 
 let list_for_all_i p = 
diff --git a/lib/util.mli b/lib/util.mli
index 35d181098d..22953788af 100644
--- a/lib/util.mli
+++ b/lib/util.mli
@@ -58,6 +58,7 @@ val list_map2_i :
 val list_index : 'a -> 'a list -> int
 val list_iter_i :  (int -> 'a -> unit) -> 'a list -> unit
 val list_fold_left_i :  (int -> 'a -> 'b -> 'a) -> int -> 'a -> 'b list -> 'a
+val list_fold_left_right : ('a -> 'b -> 'b list -> 'a) -> 'b list -> 'a -> 'a
 val list_for_all_i : (int -> 'a -> bool) -> int -> 'a list -> bool
 val list_except : 'a -> 'a list -> 'a list
 val list_for_all2eq : ('a -> 'b -> bool) -> 'a list -> 'b list -> bool