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This is still the case in the published book.

I'm very disappointed - usually Manning publications are high quality.
Edit: Dupe.
Cool. Thank you for replying.

Look forward to the next MEAP.
From the book:

defmodule ListHelper do
  def smallest(list) when length(list) > 0 do
  def smallest(_), do: {:error, :invalid_argument}

You might think that calling ListHelper.smallest/1 with anything other than list will raise an error. This however will not happen. If an error is raised from inside the guard, it will not be propagated, and the guard expression will return false. The corresponding clause will not match, but some other might.
So in the example above, if we call ListHelper.smallest(123), we will get the result :something_else, which demonstrates that an error in the guard expression is internally handled.

However my output from iex...

Interactive Elixir (1.0.2) - press Ctrl+C to exit (type h() ENTER for help)
iex(1)> ListHelper.smallest(123)
{:error, :invalid_argument}

Did I just misunderstand the passage or was some other error supposed to be returned...?