TioComodo

TioComodo provides a simple, embeddable Read-Eval-Print Loop (REPL) for your Elixir applications. It allows you to define a custom set of commands and run them in an interactive terminal session, for a simple terminal I/O application. TioComodo avoids native dependencies for ease of use. For a more advanced TUI, look at other packages like Ratatouille.

Installation

To use TioComodo in your project, add it to your list of dependencies in mix.exs.

def deps do
  [
    {:tio_comodo, "~> 0.1.2"}
  ]
end

Integration Guide

Follow these steps to integrate the TioComodo REPL into your Elixir application.

1. Create Commands Using the Simple Provider (Recommended)

The easiest way to add commands to your REPL is to use the built-in default provider TioComodo.Repl.Provider and supply a simple command map via :simple_provider.

Create a module that exposes commands/0 returning a map of command names to {module, function, []}:

# lib/my_app/repl/commands.ex

defmodule MyApp.Repl.Commands do
  @moduledoc "Commands for the REPL"

  def commands do
    %{
      "hello" => {__MODULE__, :hello, []},
      "time" => {__MODULE__, :time, []},
      "quit" => {__MODULE__, :quit, []}
    }
  end

  def hello(args), do: {:ok, "Hello, #{Enum.join(args, " ")}!"}
  def time(_args), do: {:ok, "Current time is: #{DateTime.utc_now() |> DateTime.to_string()}"}
  def quit(_args), do: {:stop, :normal, "Goodbye!"}
end

2. Configure the Simple Provider

Tell TioComodo to use your simple command map. In your config/config.exs, add the following:

# config/config.exs

import Config

config :tio_comodo,
  simple_provider: {MyApp.Repl.Commands, :commands}

With this setup, you do not need to implement the full provider behaviour; the default provider will dispatch commands based on your commands/0 map and also supply tab-completions from the command names.

3. Configure Colorscheme (Optional)

TioComodo includes a beautiful default colorscheme inspired by Gruvbox, but you can customize the colors to match your preferences. In your config/config.exs, add a colorscheme configuration:

# config/config.exs

import Config

config :tio_comodo,
  simple_provider: {MyApp.Repl.Commands, :commands},
  colorscheme: [
    user: :green,        # Color for user input
    background: :black,  # Background color
    prompt: :blue,       # Prompt color
    error: :red,         # Error message color
    success: :green,     # Success message color
    warning: :yellow,    # Warning message color
    info: :blue,         # Info message color
    completion: :cyan    # Tab completion color
  ]

Available colors include standard terminal colors like :red, :green, :blue, :yellow, :cyan, :magenta, :white, and :black. You can also use lighter versions like :light_red, :light_green, etc. Note that colors must be specified as atoms (with colons), not as strings.

Optional: Add a Catchall Handler

You can optionally configure a catchall handler that will receive any input that doesn't match a defined command:

# lib/my_app/repl/commands.ex

defmodule MyApp.Repl.Commands do
  @moduledoc "Commands for the REPL"

  def commands do
    %{
      "hello" => {__MODULE__, :hello, []},
      "time" => {__MODULE__, :time, []},
      "quit" => {__MODULE__, :quit, []},
      "catchall_handler" =>, {__MODULE__, :handle_unknown, []}
    }
  end

  def hello(args), do: {:ok, "Hello, #{Enum.join(args, " ")}!"}
  def time(_args), do: {:ok, "Current time is: #{DateTime.utc_now() |> DateTime.to_string()}"}
  def quit(_args), do: {:stop, :normal, "Goodbye!"}

  # Catchall handler receives the full input string
  def handle_unknown(input) do
    {:ok, "I don't understand: #{input}. Try 'hello', 'time', or 'quit'."}
  end
end

The catchall handler will not appear in tab-completion suggestions.

4. Alternative: Create a Custom Command Provider

If you need more control over command parsing and dispatch, you can implement a full command provider module.

Create a new file, for example, at lib/my_app/repl/custom_commands.ex:

# lib/my_app/repl/custom_commands.ex

defmodule MyApp.Repl.CustomCommands do
  @moduledoc "Provides commands for the interactive REPL."

  @doc "Handles command dispatch."
  def dispatch(command_line) do
    # Simple parsing: command is the first word, args are the rest.
    [command | args] = String.split(command_line)

    case command do
      "hello" -> hello(args)
      "time" -> time(args)
      "quit" -> quit(args)
      _ -> {:error, "Unknown command: #{command}"}
    end
  end

  # Command Implementations

  defp hello([]), do: {:ok, "Hello, World!"}
  defp hello(args), do: {:ok, "Hello, #{Enum.join(args, " ")}!"}

  defp time(_args) do
    {:ok, "Current time is: #{DateTime.utc_now() |> DateTime.to_string()}"}
  end

  defp quit(_args) do
    # This special tuple signals the REPL server to stop.
    {:stop, :normal, "Goodbye!"}
  end
end

Then configure TioComodo to use your custom command provider:

# config/config.exs

import Config

config :tio_comodo,
  provider: MyApp.Repl.CustomCommands

5. Update Your Application Supervisor

To run the REPL when your application starts, you need to add the TioComodo.Repl.Server to your application's supervision tree. You also need a lightweight process to listen for the REPL's termination signal to ensure a clean shutdown of the entire application.

Modify your lib/my_app/application.ex file:

# lib/my_app/application.ex

defmodule MyApp.Application do
  @moduledoc false
  use Application

  @impl true
  def start(_type, _args) do
    # This process waits for the REPL to terminate, then stops the entire VM.
    parent = spawn_link(fn ->
      receive do
        :repl_terminated -> :init.stop()
      end
    end)

    children = [
      # Start the TioComodo REPL server, passing it the parent PID.
      # The server will send :repl_terminated to the parent when it exits.
      {TioComodo.Repl.Server, prompt: "my_app> ", name: MyApp.Repl, parent: parent}
    ]

    opts = [strategy: :one_for_one, name: MyApp.Supervisor]
    Supervisor.start_link(children, opts)
  end
end

Explanation:

6. Run Your Application

Now you are ready to run your application's REPL. Use the following command, and the interactive prompt will appear.

$ mix run --no-halt
my_app>

You can now use the hello, time, and quit commands.