add Sequence.append_l

src/Sequence.ml

@@ -150,6 +150,8 @@ let filter p seq k = seq (fun x -> if p x then k x)
 
 let append s1 s2 k = s1 k; s2 k
 
+let append_l l k = List.iter (fun sub -> sub k) l
+
 let concat s k = s (fun s' -> s' k)
 
 (*$R

src/Sequence.mli

@@ -184,6 +184,11 @@ val append : 'a t -> 'a t -> 'a t
 (** Append two sequences. Iterating on the result is like iterating
     on the first, then on the second. *)
 
+val append_l : 'a t list -> 'a t
+(** Append sequences. Iterating on the result is like iterating
+    on the each sequence of the list in order.
+    @since NEXT_RELEASE *)
+
 val concat : 'a t t -> 'a t
 (** Concatenate a sequence of sequences into one sequence. *)