add CCOpt.choice_seq

src/core/CCOpt.ml

@@ -153,6 +153,25 @@ type 'a random_gen = Random.State.t -> 'a
 let random g st =
   if Random.State.bool st then Some (g st) else None
 
+exception ExitChoice
+
+let choice_seq s =
+  let r = ref None in
+  begin try
+    s (function
+    | None -> ()
+    | (Some _) as o -> r := o; raise ExitChoice
+    )
+  with ExitChoice -> ()
+  end;
+  !r
+
+(*$T
+  choice_seq (Sequence.of_list [None; Some 1; Some 2]) = Some 1
+  choice_seq Sequence.empty = None
+  choice_seq (Sequence.repeat None |> Sequence.take 100) = None
+*)
+
 let to_gen o =
   match o with
   | None -> (fun () -> None)

src/core/CCOpt.mli

@@ -126,6 +126,11 @@ type 'a random_gen = Random.State.t -> 'a
 
 val random : 'a random_gen -> 'a t random_gen
 
+val choice_seq : 'a t sequence -> 'a t
+(** [choice_seq s] is similar to {!choice}, but works on sequences.
+    It returns the first [Some x] occurring in [s], or [None] otherwise.
+    @since NEXT_RELEASE *)
+
 val to_gen : 'a t -> 'a gen
 val to_seq : 'a t -> 'a sequence