How exclamation marks are supposed to be used in Elixir

scream.ex

defmodule Scream do
  defmacro scream!(ast) do
    {exclams, res} = count_exclams(ast, 0)
    case exclams do
      _ when exclams < 5 ->
        quote do "You say: #{inspect(unquote(res))}." end
      _ when exclams < 10 ->
        quote do "You yell: #{inspect(unquote(res))}!" end
      _ when exclams < 15 ->
        quote do "You scream: #{inspect(unquote(res))}!!" end
      _ ->
        quote do "YOU SCREAM FROM THE BOTTOM OF YOUR LUNGS: #{inspect(unquote(res))}!!!" end
    end
  end


  defp count_exclams({:!, _, [inner]}, accum) do
    count_exclams(inner, accum + 1)
  end
  defp count_exclams(other, accum) do
    {accum, other}
  end
end

Usage instructions:

# Usage: 
import Scream

scream!! 42
scream!!!!!!!!!!!!!! 'I like trains and I cannot lie'