Discrepancy between IEx and Livebook with Machinery

[ndrean]

I have a discrepancy between running a module in IEx and in Livebook. The module below doesn't return the async task in Livebook, but it does in IEx.

I understand this might be related to the package https://github.com/joaomdmoura/machinery, but Livebook should run any Elixir code, shouldn't it? Or raise an issue in the Machinery repo?

Mix.install([{:machinery, "~> 1.0"}])

defmodule FSM do
  use Machinery,
    field: :state,
    states: [1, 2],
    transitions: %{1 => 2}

    defstruct [name: "a"]

    def before_transition(%FSM{} = struct, 2) do
      Task.async(&asyncTask/0)  |> Task.await()
      %FSM{struct | name: "b"}
    end

    def asyncTask do 
      Task.async(fn -> 
        Process.sleep(1000);  IO.puts "async code"
      end)
    end
end

Run it:

Machinery.transition_to(%FSM{}, FSM, 2)

Expected output (ok in IEX):

{:ok, %{__struct__: FSM, name: "b", state: 2}}
...
async_code

[josevalim]

Which output did you get? I got the same in Livebook.

[ndrean]

Just this in Livebook: {:ok, %{struct: FSM, name: "b", state: 2}}, and not "async_code". In a brand new Livebook session.

[josevalim]

Ah, this is because we are only capturing the log messages coming from Livebook itself and not from processes outside of Livebook. It seems Machinery runs on its own supervision tree.

[josevalim]

Please ignore me. That's IO.puts. It should work if you do require Logger; Logger.debug("hello").

[ndrean]

Yes it works with the Logger. Probably Machniery capturing it, but this happens only on Livebook. I will keep the logger. Thks!