diff --git a/src/lwt/lwt_pipe.ml b/src/lwt/lwt_pipe.ml
index eb02d9c0..368ef67b 100644
--- a/src/lwt/lwt_pipe.ml
+++ b/src/lwt/lwt_pipe.ml
@@ -53,6 +53,7 @@ module LwtErr = struct
       ) x
 end
 
+let (>>>=) = LwtErr.(>>=)
 let (>>|=) = LwtErr.(>|=)
 
 let ret_end = Lwt.return `End
@@ -341,21 +342,24 @@ let to_list_exn r =
   | `Error msg -> Lwt.fail (Failure msg)
   | `Ok x -> Lwt.return x
 
-let to_buffer buf =
-  let p = create () in
-  keep p (
-    Reader.iter ~f:(fun c -> Buffer.add_char buf c) p >>= fun _ ->
-    Lwt.return_unit
-  );
-  p
+let to_buffer buf r =
+  Reader.iter ~f:(fun c -> Buffer.add_char buf c) r
 
-let to_buffer_str buf =
-  let p = create () in
-  keep p (
-    Reader.iter ~f:(fun s -> Buffer.add_string buf s) p >>= fun _ ->
-    Lwt.return_unit
-  );
-  p
+let to_buffer_str ?(sep="") buf r =
+  let first = ref true in
+  Reader.iter r
+    ~f:(fun s ->
+        if !first then first:= false else Buffer.add_string buf sep;
+        Buffer.add_string buf s
+      )
+
+let to_string r =
+  let buf = Buffer.create 128 in
+  to_buffer buf r >>>= fun () -> LwtErr.return (Buffer.contents buf)
+
+let join_strings ?sep r =
+  let buf = Buffer.create 128 in
+  to_buffer_str ?sep buf r >>>= fun () -> LwtErr.return (Buffer.contents buf)
 
 (** {2 Basic IO wrappers} *)
 
diff --git a/src/lwt/lwt_pipe.mli b/src/lwt/lwt_pipe.mli
index 87ba7ecc..2c9cdcec 100644
--- a/src/lwt/lwt_pipe.mli
+++ b/src/lwt/lwt_pipe.mli
@@ -170,17 +170,21 @@ val of_array : 'a array -> 'a Reader.t
 
 val of_string : string -> char Reader.t
 
-val to_list_rev : 'a Reader.t -> 'a list LwtErr.t
+val to_list_rev : ('a,[>`r]) t -> 'a list LwtErr.t
 
-val to_list : 'a Reader.t -> 'a list LwtErr.t
+val to_list : ('a,[>`r]) t -> 'a list LwtErr.t
 
-val to_list_exn : 'a Reader.t -> 'a list Lwt.t
+val to_list_exn : ('a,[>`r]) t -> 'a list Lwt.t
 (** Same as {!to_list}, but can fail with
     @raise Failure if some error is met *)
 
-val to_buffer : Buffer.t -> char Writer.t
+val to_buffer : Buffer.t -> (char ,[>`r]) t -> unit LwtErr.t
 
-val to_buffer_str : Buffer.t -> string Writer.t
+val to_buffer_str : ?sep:string -> Buffer.t -> (string, [>`r]) t -> unit LwtErr.t
+
+val to_string : (char, [>`r]) t -> string LwtErr.t
+
+val join_strings  : ?sep:string -> (string, [>`r]) t -> string LwtErr.t
 
 (** {2 Basic IO wrappers} *)