title: Adding item to list
body: <p>I don't get it. I want to add an item to a list. But it is not working. Here my code:</p>
  
  <pre><code>  def put_viewed(items, user_id) do
    lll = []
    Enum.each items, fn item -&gt;
      viewed = check_viewed(item.id, user_id)
      new_item = Map.put(item, :viewed, viewed)
      Enum.concat(lll, [new_item])
    end
    IO.inspect lll
  end
  </code></pre>
  
  <p>I always get [] as result. Same with <code>lll ++ [new_item]</code></p>