2 files changed, 9 insertions, 0 deletions
diff --git a/lib/util.ml b/lib/util.ml
index 57fea38084..a7d2099f1f 100644
--- a/lib/util.ml
+++ b/lib/util.ml
@@ -687,6 +687,13 @@ let list_map_i f =
   in 
   map_i_rec
 
+let list_filter_i p =
+  let rec filter_i_rec i = function
+    | [] -> []
+    | x::l -> let l' = filter_i_rec (succ i) l in if p i x then x::l' else l'
+  in
+  filter_i_rec 0
+
 let rec list_sep_last = function
   | [] -> failwith "sep_last"
   | hd::[] -> (hd,[])
diff --git a/lib/util.mli b/lib/util.mli
index 1be7f807a2..34e91215ad 100644
--- a/lib/util.mli
+++ b/lib/util.mli
@@ -124,6 +124,8 @@ val list_map3 :
   ('a -> 'b -> 'c -> 'd) -> 'a list -> 'b list -> 'c list -> 'd list
 val list_map4 :
   ('a -> 'b -> 'c -> 'd -> 'e) -> 'a list -> 'b list -> 'c list -> 'd list -> 'e list
+val list_filter_i :
+  (int -> 'a -> bool) -> 'a list -> 'a list
 (* [list_index] returns the 1st index of an element in a list (counting from 1) *)
 val list_index : 'a -> 'a list -> int
 (* [list_unique_index x l] returns [Not_found] if [x] doesn't occur exactly once *)