How to compose effect handlers with Eio

Learning
10

Let me provide you with a simpler example.

module Echo = struct
  type _ Effect.t += Echo : string -> unit Effect.t

  let run f =
    Effect.Deep.try_with f ()
      {
        effc =
          (fun (type b) (eff : b Effect.t) ->
            match eff with
            | Echo string ->
                Some
                  (fun (k : (b, unit) Effect.Deep.continuation) ->
                    print_endline string;
                    Effect.Deep.continue k ())
            | _ -> None);
      }
end

let main () =
  Echo.run (fun () ->
      Eio_main.run (fun _ ->
          Eio.Fiber.both
            (fun () ->
              Eio.Fiber.yield ();
              Effect.perform (Echo.Echo "world"))
            (fun () ->
              Effect.perform (Echo.Echo "hello"))));

That program crashes as well. This is what I mean about composition wrt large.

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