TIL I can do
defmodule :foo do
# ....
end
And it should work. 
Fl4m3Ph03n1x
sodapopcan
This is technically what you are doing when you do defmodule Foo do. Foo is like an “auto alias” as it expands to :"Elixir.Foo" so you’re really doing:
iex(1)> defmodule :"Elixir.Foo", do: (def hi, do: "hi")
{:module, Foo,
<<70, 79, 82, 49, 0, 0, 5, 68, 66, 69, 65, 77, 65, 116, 85, 56, 0, 0, 0, 164,
0, 0, 0, 17, 10, 69, 108, 105, 120, 105, 114, 46, 70, 111, 111, 8, 95, 95,
105, 110, 102, 111, 95, 95, 10, 97, 116, ...>>, {:hi, 0}}
iex(2)> Foo.hi()
"hi"
Even though it’s pretty simple, I still get confused and I find it much easier to make the distinction when talking about them. And sometimes the difference is meaningful when a macro expects an (unexpanded) alias, like Phoenix.Router.scope.
3
gregvaughn
Hehe. I once tweeted some “evil” Elixir in which I did defmodule :false do. Alas, someone reported it as a bug and it got fixed 
edit: actually, I don’t think I needed the colon, but … details
4
sodapopcan
This has some Scooby Doo villain vibes to it
On another note, I realized that a fun example of where alias vs atom matters is the alias macro! (Or is it a special form? I’m too lazy to check). It can only infer a value if given an alias, ie alias Foo.Bar. If given an atom, the :as option is required! alias :foo, as: Foo. This is the very type of thing I’m talking about that is both quite logical while being a little bit dizzying 
3