Nx (?!) solution for to-do app

code.exs

# To-Do app
Mix.install [:exla, {:nx, github: "elixir-nx/nx", sparse: "nx", override: true}]

max_todo_length = 5
max_todos = 10

run = fn run_fn, state ->
  case IO.gets("Choose one of the following options:\n1. List TO-DOs\n2. Add a new TO-DO\n3. Mark TO-DO as completed\n4. Delete TO-DO.\n5. Exit\n>> ") |> String.trim() do
    "1" ->
      todos = if state.count > 0, do: Nx.to_list(state.to_dos[0..(state.count - 1)]), else: []
      IO.puts("To-Dos: ")
      todos
      |> Enum.with_index(fn row, index ->
        {contents, [completed]} = Enum.split(row, -1)
        {String.trim_trailing(List.to_string(contents), "\0"), if(completed == 1, do: "✔", else: " "), index}
      end)
      |> Enum.map_join("\n", fn {todo, completed, idx} ->
        "#{idx}. #{todo} [#{completed}]"
      end)
      |> IO.puts()
      state

    "2" ->
      todo = IO.gets("Insert your new to-do\n>> ") |> String.trim()
      todo = String.slice(todo, 0, min(byte_size(todo), max_todo_length)) |> String.pad_trailing(max_todo_length, "\0")
      todo_tensor = Nx.from_binary(todo <> <<0>>, :u8) |> Nx.reshape({1, max_todo_length + 1})
      %{state | to_dos: Nx.put_slice(state.to_dos, [state.count, 0], todo_tensor), count: state.count + 1}
    "3" ->
      try do
        {todo_idx, _} = IO.gets("Insert the index for the to-do to be completed\n>> ") |> Integer.parse()
        %{state | to_dos: Nx.indexed_put(state.to_dos, Nx.tensor([todo_idx, max_todo_length]), Nx.u8(1))}
      rescue
        _ ->
          IO.warn("Failed to complete to-do.")
          state
      end
    "4" ->
      try do
        {todo_idx, _} = IO.gets("Insert the index for the to-do to be deleted\n>> ") |> Integer.parse()
        to_dos =
          if todo_idx == state.count do
            state.to_dos
          else
            Nx.put_slice(state.to_dos, [todo_idx, 0], state.to_dos[[(todo_idx + 1)..-1//1, 0..-1//1]])
          end
        %{state | to_dos: to_dos, count: state.count - 1}
      rescue
        _ ->
          IO.warn("Failed to delete to-do.")
          state
      end
    "5" ->
      IO.puts("Exiting")
      :exit

    cmd ->
      IO.warn("Invalid command #{inspect(cmd)}")
      state
  end
  |> then(fn
    :exit ->
      :exit

    state ->
      run_fn.(run_fn, state)
  end)
end

Nx.default_backend(EXLA.Backend)
run.(run, %{count: 0, to_dos: Nx.broadcast(Nx.u8(0), {max_todos, max_todo_length + 1})})

output

05:56:47.344 [info] TfrtCpuClient created.
Choose one of the following options:
1. List TO-DOs
2. Add a new TO-DO
3. Mark TO-DO as completed
4. Delete TO-DO.
5. Exit
>> 2
Insert your new to-do
>> a
Choose one of the following options:
1. List TO-DOs
2. Add a new TO-DO
3. Mark TO-DO as completed
4. Delete TO-DO.
5. Exit
>> 2
Insert your new to-do
>> b
Choose one of the following options:
1. List TO-DOs
2. Add a new TO-DO
3. Mark TO-DO as completed
4. Delete TO-DO.
5. Exit
>> 2
Insert your new to-do
>> c
Choose one of the following options:
1. List TO-DOs
2. Add a new TO-DO
3. Mark TO-DO as completed
4. Delete TO-DO.
5. Exit
>> 1
To-Dos: 
0. a [ ]
1. b [ ]
2. c [ ]
Choose one of the following options:
1. List TO-DOs
2. Add a new TO-DO
3. Mark TO-DO as completed
4. Delete TO-DO.
5. Exit
>> 3
Insert the index for the to-do to be completed
>> 1
Choose one of the following options:
1. List TO-DOs
2. Add a new TO-DO
3. Mark TO-DO as completed
4. Delete TO-DO.
5. Exit
>> 1
To-Dos: 
0. a [ ]
1. b [✔]
2. c [ ]
Choose one of the following options:
1. List TO-DOs
2. Add a new TO-DO
3. Mark TO-DO as completed
4. Delete TO-DO.
5. Exit
>> 4
Insert the index for the to-do to be deleted
>> 2
Choose one of the following options:
1. List TO-DOs
2. Add a new TO-DO
3. Mark TO-DO as completed
4. Delete TO-DO.
5. Exit
>> 1
To-Dos: 
0. a [ ]
1. b [✔]
Choose one of the following options:
1. List TO-DOs
2. Add a new TO-DO
3. Mark TO-DO as completed
4. Delete TO-DO.
5. Exit
>> 2
Insert your new to-do
>> d
Choose one of the following options:
1. List TO-DOs
2. Add a new TO-DO
3. Mark TO-DO as completed
4. Delete TO-DO.
5. Exit
>> 2
Insert your new to-do
>> e
Choose one of the following options:
1. List TO-DOs
2. Add a new TO-DO
3. Mark TO-DO as completed
4. Delete TO-DO.
5. Exit
>> 1
To-Dos: 
0. a [ ]
1. b [✔]
2. d [ ]
3. e [ ]
Choose one of the following options:
1. List TO-DOs
2. Add a new TO-DO
3. Mark TO-DO as completed
4. Delete TO-DO.
5. Exit
>> 4
Insert the index for the to-do to be deleted
>> 0
Choose one of the following options:
1. List TO-DOs
2. Add a new TO-DO
3. Mark TO-DO as completed
4. Delete TO-DO.
5. Exit
>> 1
To-Dos: 
0. b [✔]
1. d [ ]
2. e [ ]
Choose one of the following options:
1. List TO-DOs
2. Add a new TO-DO
3. Mark TO-DO as completed
4. Delete TO-DO.
5. Exit
>> 4
Insert the index for the to-do to be deleted
>> 1
Choose one of the following options:
1. List TO-DOs
2. Add a new TO-DO
3. Mark TO-DO as completed
4. Delete TO-DO.
5. Exit
>> 1
To-Dos: 
0. b [✔]
1. e [ ]
Choose one of the following options:
1. List TO-DOs
2. Add a new TO-DO
3. Mark TO-DO as completed
4. Delete TO-DO.
5. Exit
>> 5
Exiting