bot.ex

defmodule Bot do
  use Application
  alias Alchemy.client
  
  @token "token here"
  
  def start(_, _) do
    run = Client.start(@token)
    use Commands
    run
  end

commands.ex

defmodule Commands do
  use Alchemy.Cogs
  
  Cogs.def ping do
    Cogs.say("pong!")
  end
end

mix.exs

def application do
  [mod: {Bot, []}]
end