problems implementing protocol (errors not helpful)

[Jordi Polo]

I'm writing to the core list because it seems to me a problem with the language.

To teach myself, I've done this silly thing, mostly following the official documentation:

defmodule NewTable do
  defstruct data: []
  @type t :: %__MODULE__{
    data: nonempty_list(any)
  }
end

defimpl Enumerable, for: NewTable do
  def reduce(t, acc, fun) do
    Enum.reduce(t.data, acc, fun)
  end
  def count(t) do
    {:ok, length(t.data)}
  end
  def member?(t, x) do
    {:ok, Enum.member?(t.data, x)}
  end
end

I know there is no point of implementing Enumerable for a list but this is just a learning exercise.
count and member work.
The above reduce method does not work. Trying to use Enum.at, Enum.max, etc on that struct will give back several errors about anonymous functions which are not clear at all.
I've tried with current master also, I get a different set of errors and even something I really do not know how to interpret:

Enum.max(%NewTable{ data: [1,2]})
{:cont, {:cont, #Reference<0.0.4.735>}}

I've tried to use  :lists.foldl(fun, acc, t.data) instead of Enum.reduce(t.data, acc, fun) but gets the same kind of error.

I'm thinking this may be a language issue because if the above code is totally broken, it seems to me, reading the docs that it should work, so maybe the docs are misleading? Or maybe I'm just too new and I'm using some old way of thinking?
And in any case the errors provided does not give a hint about the problem

[José Valim]

The docs are definitely wrong. It should be Enumerable.reduce (or Enumerable.List.reduce) instead of Enum.reduce. Enumerable.reduce is expected to receive and return tagged tuples, opposite to Enum.reduce. Could you please send a pull request or open up an issue with a link to exactly where in the documentation it is wrong.

Thank you for reporting, it is very appreciated!

José Valim

www.plataformatec.com.br

Skype: jv.ptec

Founder and Director of R&D

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