Maybe having a different example will help?
defmodule Counter do
defstruct current: 0
def new, do: struct!(__MODULE__)
defimpl Enumerable do
def count(_), do: {:error, __MODULE__}
def member?(_, _), do: {:error, __MODULE__}
def slice(_), do: {:error, __MODULE__}
def reduce(_counter, {:halt, acc}, _fun), do: {:halted, acc}
def reduce(counter, {:suspend, acc}, fun), do: {:suspended, acc, &reduce(counter, &1, fun)}
def reduce(counter, {:cont, acc}, fun) do
reduce(update_in(counter.current, &(&1 + 1)), fun.(counter.current, acc), fun)
end
end
end
Counter.new()
|> Enum.take(3)
# [0, 1, 2]
