2 files changed, 16 insertions, 0 deletions
diff --git a/lib/option.ml b/lib/option.ml
index fbb883d30a..f3047a3ca7 100644
--- a/lib/option.ml
+++ b/lib/option.ml
@@ -188,4 +188,14 @@ module List =
 	 |None -> find f t
 	 |x -> x
 
+  let map f l =
+    let rec aux f l = match l with
+    | [] -> []
+    | x :: l ->
+      match f x with
+      | None -> raise Exit
+      | Some y -> y :: aux f l
+    in
+    try Some (aux f l) with Exit -> None
+
 end
diff --git a/lib/option.mli b/lib/option.mli
index 5e085620e7..a336c895cc 100644
--- a/lib/option.mli
+++ b/lib/option.mli
@@ -123,4 +123,10 @@ module List : sig
   val flatten : 'a option list -> 'a list
 
   val find : ('a -> 'b option) -> 'a list -> 'b option
+
+  (** [List.map f [a1;...;an]] is the list [Some [b1;...;bn]] if
+      for all i, there is a [bi] such that [f ai] is [Some bi]; it is
+      [None] if, for at least one i, [f ai] is [None]. *)
+  val map : ('a -> 'b option) -> 'a list -> 'b list option
+
 end