Shell: add Error_monad.{iter2_p,iteri2_p}

src/utils/error_monad.ml

@@ -312,6 +312,37 @@ module Make() = struct
         | Ok (), Error exn
         | Error exn, Ok () -> Lwt.return (Error exn)
 
+  let rec iter2_p f l1 l2 =
+    match l1, l2 with
+    | [], [] -> return ()
+    | [], _ | _, [] -> invalid_arg "Error_monad.iter2_p"
+    | x1 :: l1 , x2 :: l2 ->
+        let tx = f x1 x2 and tl = iter2_p f l1 l2 in
+        tx >>= fun tx_res ->
+        tl >>= fun tl_res ->
+        match tx_res, tl_res with
+        | Ok (), Ok () -> Lwt.return (Ok ())
+        | Error exn1, Error exn2 -> Lwt.return (Error (exn1 @ exn2))
+        | Ok (), Error exn
+        | Error exn, Ok () -> Lwt.return (Error exn)
+
+  let iteri2_p f l1 l2 =
+    let rec iteri2_p i f l1 l2 =
+      match l1, l2 with
+      | [], [] -> return ()
+      | [], _ | _, [] -> invalid_arg "Error_monad.iteri2_p"
+      | x1 :: l1 , x2 :: l2 ->
+          let tx = f i x1 x2 and tl = iteri2_p (i+1) f l1 l2 in
+          tx >>= fun tx_res ->
+          tl >>= fun tl_res ->
+          match tx_res, tl_res with
+          | Ok (), Ok () -> Lwt.return (Ok ())
+          | Error exn1, Error exn2 -> Lwt.return (Error (exn1 @ exn2))
+          | Ok (), Error exn
+          | Error exn, Ok () -> Lwt.return (Error exn)
+    in
+    iteri2_p 0 f l1 l2
+
   let rec fold_left_s f init l =
     match l with
     | [] -> return init

src/utils/error_monad_sig.ml

@@ -118,6 +118,8 @@ module type S = sig
   (** A {!List.iter} in the monad *)
   val iter_s : ('a -> unit tzresult Lwt.t) -> 'a list -> unit tzresult Lwt.t
   val iter_p : ('a -> unit tzresult Lwt.t) -> 'a list -> unit tzresult Lwt.t
+  val iter2_p : ('a -> 'b -> unit tzresult Lwt.t) -> 'a list -> 'b list -> unit tzresult Lwt.t
+  val iteri2_p : (int -> 'a -> 'b -> unit tzresult Lwt.t) -> 'a list -> 'b list -> unit tzresult Lwt.t
 
   (** A {!List.map} in the monad *)
   val map_s : ('a -> 'b tzresult Lwt.t) -> 'a list -> 'b list tzresult Lwt.t