code-golf with error handling solution

code.exs

# To-Do app

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" ->
      state.to_dos 
      |> Enum.reverse()
      |> Enum.with_index()
      |> Enum.map_join("\n", fn {%{todo: todo, completed: completed}, idx} -> 
        "#{idx}. #{todo} [#{if(completed, do: "✔", else: " ")}]"
      end) 
      |> IO.puts()
      state
      
    "2" ->
      todo = IO.gets("Insert your new to-do\n>> ") |> String.trim()
      %{state | to_dos: [%{todo: todo, completed: false} | state.to_dos], count: state.count + 1}
    "3" ->
      try do
        {todo_idx, _} = IO.gets("Insert the index for the to-do to be completed\n>> ") |> Integer.parse()
        
        idx = state.count - todo_idx - 1
        update_in(state, [:to_dos, Access.at(idx)], &%{&1 | completed: true})
      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()
        idx = state.count - todo_idx - 1
        %{state | to_dos: List.delete_at(state.to_dos, idx), 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

run.(run, %{count: 0, to_dos: []})

output.md

Output:

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

0. a [ ]
1. b [ ]
2. c [ ] Choose one of the following options:
3. List TO-DOs
4. Add a new TO-DO
5. Mark TO-DO as completed
6. Delete TO-DO.
7. Exit

3 Insert the index for the to-do to be completed 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

0. a [ ]
1. b [ ]
2. c [✔] Choose one of the following options:
3. List TO-DOs
4. Add a new TO-DO
5. Mark TO-DO as completed
6. Delete TO-DO.
7. 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

0. a [ ]
1. b [✔]
2. c [✔] Choose one of the following options:
3. List TO-DOs
4. Add a new TO-DO
5. Mark TO-DO as completed
6. Delete TO-DO.
7. 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

0. a [ ]
1. c [✔] Choose one of the following options:
2. List TO-DOs
3. Add a new TO-DO
4. Mark TO-DO as completed
5. Delete TO-DO.
6. 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

1

0. a [ ]
1. c [✔]
2. d [ ] Choose one of the following options:
3. List TO-DOs
4. Add a new TO-DO
5. Mark TO-DO as completed
6. Delete TO-DO.
7. Exit

5 Exiting :exit