diff --git a/src/core/CCResult.mli b/src/core/CCResult.mli
index a5b47bb6..ffd67510 100644
--- a/src/core/CCResult.mli
+++ b/src/core/CCResult.mli
@@ -188,6 +188,9 @@ end
 (** {2 Collections} *)
 
 val map_l : ('a -> ('b, 'err) t) -> 'a list -> ('b list, 'err) t
+(** [map_l f \[a1; ...; an\]] applies function f to a1, ..., an , and, in case of
+    success for every elements, return the list of [Ok]-value.
+    Otherwise, it fails and return the first error encountered. Tail-recursive.*)
 
 val fold_l : ('b -> 'a -> ('b, 'err) t) -> 'b -> 'a list -> ('b, 'err) t