adding opt_map to simplify result function application over optionals (…

…#397)

adding `Result.opt_map` to simplify result function application over optionals

src/core/CCResult.ml

@@ -68,6 +68,14 @@ let of_exn_trace e =
   in
   Error res
 
+let opt_map f e = match e with 
+  | None -> Ok None 
+  | Some x ->
+    begin match f x with 
+      | Ok x -> Ok (Some x)
+      | Error e -> Error e
+    end
+
 let map f e = match e with
   | Ok x -> Ok (f x)
   | Error s -> Error s

src/core/CCResult.mli

@@ -63,6 +63,10 @@ val add_ctxf : ('a, Format.formatter, unit, ('b, string) t -> ('b, string) t) fo
     ]}
     @since 1.2 *)
 
+val opt_map : ('a -> ('b, 'c) t) -> 'a option -> ('b option, 'c) t
+(** Map a fallible operation through an option.
+    @since NEXT_RELEASE *)
+
 val map : ('a -> 'b) -> ('a, 'err) t -> ('b, 'err) t
 (** Map on success. *)