Alpha/Endorser: use filter rather than filter_map

src/lib_error_monad/error_monad.ml

@@ -438,6 +438,28 @@ module Make(Prefix : sig val id : string end) = struct
             tt >>=? fun rt ->
             return (rh :: rt)
 
+  let rec filter_s f l =
+    match l with
+    | [] -> return []
+    | h :: t ->
+        f h >>=? function
+        | false -> filter_s f t
+        | true ->
+            filter_s f t >>=? fun t ->
+            return (h :: t)
+
+  let rec filter_p f l =
+    match l with
+    | [] -> return []
+    | h :: t ->
+        let jh = f h
+        and t = filter_p f t in
+        jh >>=? function
+        | false -> t
+        | true ->
+            t >>=? fun t ->
+            return (h :: t)
+
   let rec iter_s f l =
     match l with
     | [] -> return ()

src/lib_error_monad/error_monad_sig.ml

@@ -151,6 +151,12 @@ module type S = sig
   val filter_map_p :
     ('a -> 'b option tzresult Lwt.t) -> 'a list -> 'b list tzresult Lwt.t
 
+  (** A {!List.filter} in the monad *)
+  val filter_s :
+    ('a -> bool tzresult Lwt.t) -> 'a list -> 'a list tzresult Lwt.t
+  val filter_p :
+    ('a -> bool tzresult Lwt.t) -> 'a list -> 'a list tzresult Lwt.t
+
   (** A {!List.fold_left} in the monad *)
   val fold_left_s :
     ('a -> 'b -> 'a tzresult Lwt.t) -> 'a -> 'b list -> 'a tzresult Lwt.t

src/proto_alpha/lib_delegate/client_baking_endorsement.ml

@@ -144,12 +144,7 @@ let prepare_endorsement (cctxt : #Proto_alpha.full) ~(max_past:int64) state bi =
     let time = Time.(add (now ()) state.delay) in
     let timeout = Lwt_unix.sleep (Int64.to_float state.delay) in
     tzforce state.delegates >>=? fun delegates ->
-    filter_map_p
-      (fun delegate ->
-         allowed_to_endorse cctxt bi delegate >>=? function
-         | true -> return (Some delegate)
-         | false -> return None)
-      delegates >>=? fun delegates ->
+    filter_p (allowed_to_endorse cctxt bi) delegates >>=? fun delegates ->
     state.pending <- Some {
         time ;
         timeout ;