I can't type anything in terminal when I run my app with "iex -S mix"

Questions / Help
,
1

Hi guys!

I’m a beginner user in Elixir. I wrote a small program using Mix project. It’s work fine when I run my app with “mix run”, but when I use “iex -S mix” (for debug) I can’t type anything in terminal and I need to use ctrl+C for exit.

2

No idea what is going on there. Are you calling iex -S mix from within the root directory of your project? Are you able to just run iex normally?

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3

Yes, iex console it’s working.
I run in terminal inside vscode, mix run works fine, but iex -S mix not. I tested in terminal outside vscode and the same error happens too.

4

Hey @alrigotto welcome! This usually means that one of your supervisor’s children has hung and so the app is unable to boot. If you do iex -S mix run --no-start do you get a REPL? Can you show your application.ex file?

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5

Hi benwilson!

I did iex -S mix run --no-start and get normaly REPL.

I guess this problem started when I was made several debug testing for learning.

I wonder if this changed some file inside mix folder project, because new projects are working fine.

My app.ex:

It’s a simple guess number game tutorial.

defmodule GuessGame do
  use Application


  def start(_,_) do
    run()
    {:ok, self()}
    |> IO.inspect(label: "run after2")
  end

  def run() do

    IO.puts("Let's pĺay Guess the Number")
    IO.gets("Choose a dificult level (1, 2 or 3):")
    # the "|>" (pipe) operator in Elixir put the output from the previous line to the first function's argument in the next line
    |> parse_input()
    |> pickup_number()
    |> IO.inspect(label: "Before play()")
    |> play()
    |> IO.inspect(label: "After play()")
    # require IEx; IEx.pry
  end

  def pickup_number(level) do
    level
    |> IO.inspect()
    |> get_range()
    |> IO.inspect()
    |> Enum.random()
  end

  def play(picked_num) do
    IO.gets("I have my number. What is your guess?")
    |> parse_input()
    |> guess(picked_num, 1)
  end

  # In the function 'guess()' is being used 'Guards' technique in Elixir
  def guess(usr_guess, picked_num, count) when usr_guess > picked_num do
    IO.gets("Your number is too high. Guess again: ")
    |> parse_input()
    |> guess(picked_num, count + 1)
  end

  def guess(usr_guess, picked_num, count) when usr_guess < picked_num  do
    IO.gets("Your number is too low. Guess again: ")
    |> parse_input()
    |> guess(picked_num, count + 1)
  end

  # the last option for 'guess()' (guards)
  def guess(_usr_guess, _picked_num, count) do # '_' underscore makes the arguments to be ignored
  IO.puts("You got it #{count} guess. ")
  show_score(count)
  end

  def show_score(guesses) when guesses > 6 do
    IO.puts("Better luck next time!")
  end

  def show_score(guesses) do
    {_, msg} = %{1..1 => "You're a mind rider!",
      2..4 => "Most impressive!",
      3..6 => "You can do better than that!"}
    |> Enum.find(fn {range, _} -> Enum.member?(range, guesses) end)
    IO.puts(msg)
  end

  # The function "parse-input" is defined twice (it could be more) because Elixir has this feature where is possible...
  #...to choose what the functions will be used based on its argument.

  # if the player set a non number a ":error" will come up, so the game will ru again after a message error.
  def parse_input(:error) do
    IO.inspect(label: ":erro")
    IO.puts("Invalid level!!!")
    run()
  end

  # if the player set a number, this number will be returned.
  def parse_input({num, _}), do: num #one line def function

  def parse_input(data) do
    data
    |> Integer.parse()
    |> IO.inspect()
    |> parse_input()
    |> IO.inspect()
  end

  def get_range(level) do
    case level do
      1 -> 1..10 # define a range in Elixir
      2 -> 1..100
      3 -> 1..1000
      # in case the player set a number higher than 3 (max level)
      _ -> IO.puts("Invalid level--------!!!")
      run()
    end
  end

  def teste() do
    IO.getn("dsdsd: ")
    |> IO.puts()
  end
end

Thank you for your support!

6

Looks like you use this code at application start.

That’s good for normal app start or script, but when your are using iex then IO.gets/1 is blocking shell. Running the game in supervised task also does not solves the problem.

The only way to “play” a game in iex (using IO.gets/1) is to call the code directly from shell instead of adding it to application supervisor tree. However in that case when starting app normally the game would not run.

Therefore I would suggest to check some args/environment variables, so for some runs simply start the game automatically and when using iex shell start the game manually, for example:

defmodule GuessGame do
  use Application

  def start(_,_) do
    if some_check_here do
      run()
    end

    {:ok, self()}
  end

  # …
end

iex> GuessGame.run()
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7

I could be wrong but I’m pretty sure that returning {:ok, self()} from start is also a problem. The application root needs to be an actual supervisor, not whatever pid is booting the app.

1 Like
8

Thank you guys for your helps.

I’ll try to use your tips.
As a beginner this problem is a bit complex than I expected, I thought that was only a beginner’s mistake.

I have a lot of basic things to learn in Elixir, mainly in Mix projects.

Thank you again!! :smiley:

9

Also, might I suggest using the 1.14 version of elixir and the new dbg features?

The IEX+dbg and pipeline debugging will make your live much better, and remove the need for the many inspects.
The videos on that link give a view of how it can help you.

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