Programming Elixir 1.6: Enumerable.count return value erratum (page 337)

On page 337, in the description of the count/1 function of the Enumerable protocol, the return value in the uncountable case is incorrect. If the collection isn’t countable, the return value should be {:error, __MODULE__}, rather than {:ok, __MODULE__}. See the documentation of the Enumerable protocol.