Quote function name in Elixir

Question

I'm learning Elixir now and I'm really confused with quote and unquote. Here is how we create a function with a dynamic name using a macro:

defmacro create_fun(n) do
  quote do: def unquote(:"times_#{n}")(a), do: a * 4
end

It creates function times_6, for example, if I pass 6 as a macro parameter.

Now what I don't understand: Here we unquote the atom :"times_#{n}". Elixir docs say that when you quote an atom it returns an atom. So when I unquote an atom, I should get this atom back too. And this is true:

iex(15)> Macro.to_string quote do: unquote(:"times_6")
":times_6"

But using () right after the quote gives this:

iex(14)> Macro.to_string quote do: unquote(:"times_6")()
"times_6()"

An atom with parentheses suddenly becomes not an atom. And if I substitute unquote(:"times_6") with :"times_6" it doesn't work:

iex(4)> Macro.to_string quote do: :"times_6"()
** (SyntaxError) iex:4: syntax error before: '('

Please, what is going on, I don't get it

Answer 1

That's how quote & unquote are implemented in Elixir

From the Elixir Metaprogramming Guide:

The building block of an Elixir program is a tuple with three elements. For example, the function call sum(1, 2, 3) is represented internally as:

iex> quote do: sum(1, 2, 3)
{:sum, [], [1, 2, 3]}

The first element is the function name, the second is a keyword list containing metadata and the third is the arguments list.

---

Module and Method names are internally represented as atoms in elixir. Looking directly at the underlying elixir data generated when calling unquote(:"hello") and unquote(:"hello")() might help clear this up:

iex(27)> quote do: unquote(:"hello")   
:hello

iex(28)> quote do: unquote(:"hello")() 
{:hello, [], []}

The first one simply returns an atom while the second one returns an Elixir Data Structure (a tuple composed of 3 elements) which represents a function call to the hello method with 0 arguments. The unquote(:"hello")() is transformed into hello() which is then used as a method.