stream_test.ex

defmodule StreamTest do
  def shift(stream) do
    case Enumerable.reduce(stream, {:cont, :first}, fn
          val, :first -> {:suspend, val}
          val, _ -> {:cont, val}
        end) do
      {:done, nil} -> nil
      {:done, final} -> nil
      {:halted, final} -> {final, fn _,_ -> {:halt, nil} end}
      {:suspended, val, continuation} -> {val, fn _,_ -> continuation.({:cont, :first}) end}
    end
  end

end
x = [1,2,3]
# x = Stream.iterate(0, &(&1+1))
{_, x} = StreamTest.shift(x)
{_, x} = StreamTest.shift(x)
{_, x} = StreamTest.shift(x)