add slice implementation that only does delegation

Author: princemaple

lib/impls/enumerable.ex

@@ -1,13 +1,13 @@
 defimpl Enumerable, for: Qex do
-  def count(%Qex{data: q}) do
-    {:ok, :queue.len(q)}
-  end
+  def count(%Qex{data: q}), do: {:ok, :queue.len(q)}
 
   def member?(%Qex{data: q}, item) do
     {:ok, :queue.member(item, q)}
   end
 
   def reduce(%Qex{data: q}, acc, fun) do
-    Enumerable.reduce(:queue.to_list(q), acc, fun)
+    Enumerable.List.reduce(:queue.to_list(q), acc, fun)
   end
+  
+  def slice(%Qex{data: q}), do: {:error, __MODULE__}
 end