// CommandHandler.cs
private readonly CommandService _service = new CommandService();

// Imagine this being a message callback, whether it'd be from an IRC bot,
// a Discord bot, or any other chat based commands bot.
private async Task MessageReceivedAsync(Message message)
{
    if (!CommandUtilities.HasPrefix(message.Content, '!', out string output))
        return;
        
    IResult result = await _service.ExecuteAsync(output, new CommandContext(message));
    if (!result.IsSuccessful)
        await message.Channel.SendMessageAsync((result as FailedResult).Reason); 
}

// CommandContext.cs
public sealed class CommandContext : ICommandContext
{
    public Message Message { get; }
    
    public Channel Channel => Message.Channel;
  
    public CommandContext(Message message)
      => Message = message;
}

// CommandModule.cs
public sealed class CommandModule : ModuleBase<CommandContext>
{
    public CommandService Service { get; set; }

    // Invoked with:   !help
    // Responds with:  `help` - Lists available commands.
    //                 `sum` - Sums two given numbers.
    //                 `echo` - Echoes given text.
    [Command("help", "commands")]
    [Description("Lists available commands.")]
    public Task HelpAsync()
        => Context.Channel.SendMessageAsync(
            string.Join('\n', Service.GetAllCommands().Select(x => $"`{x.Name}` - {x.Description}")));

    // Invoked with:  !sum 3 5
    // Responds with: 3 + 5 = 8
    [Command("sum")]
    [Description("Sums two given numbers.")]
    public Task SumAsync(int firstNumber, int secondNumber)
      => Context.Channel.SendMessageAsync(
          $"{firstNumber} + {secondNumber} = {firstNumber + secondNumber}");

    // Invoked with:  !echo Hello, world.
    // Responds with: Hello, world.
    [Command("echo")]
    [Description("Echoes given text.")]
    public Task EchoAsync([Remainder] string text)
      => Context.Channel.SendMessageAsync(text);
}