2 files changed, 13 insertions, 0 deletions
diff --git a/lib/util.ml b/lib/util.ml
index fb271ea421..a8e716e0f3 100644
--- a/lib/util.ml
+++ b/lib/util.ml
@@ -488,6 +488,15 @@ let list_map4 f l1 l2 l3 l4 =
   in
   map (l1,l2,l3,l4)
 
+let rec list_smartfilter f l = match l with
+    [] -> l
+  | h::tl ->
+      let tl' = list_smartfilter f tl in
+	if f h then
+	  if tl' == tl then l
+	  else h :: tl'
+	else tl'
+	  
 let list_index x =
   let rec index_x n = function
     | y::l -> if x = y then n else index_x (succ n) l
diff --git a/lib/util.mli b/lib/util.mli
index 13be5521d6..5248d0e6b1 100644
--- a/lib/util.mli
+++ b/lib/util.mli
@@ -149,6 +149,10 @@ val list_map4 :
 val list_filter_i :
   (int -> 'a -> bool) -> 'a list -> 'a list
 
+(** [list_smartfilter f [a1...an] = List.filter f [a1...an]] but if for all i
+   [f ai = true], then [list_smartfilter f l==l] *)
+val list_smartfilter : ('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