How to use Witchcraft and Exceptional in the same module ?

[lkuty]

I use Elixir 1.10.2. My module has:

use Witchcraft, except: [>>>: 2]
use Exceptional

but at compilation time I get:

function >>>/2 imported from both Witchcraft.Chain and Exceptional.Raise, call is ambiguous
    expanding macro: Witchcraft.Monad.monad/2

If I try to do instead:

use Witchcraft, only: [monad: 2]
use Exceptional

Then I get:

:only and :except can only be given together to import when :only is either :functions or :macros

I am trying to add some error processing to my Timex usage which is not safe presently. I have copy pasted the code below to get an idea of my use case. It is used in a Phoenix web application.

    stream = monad Either.new() do
      date1 <- case Map.fetch(params, "date1") do
        {:ok, date1_s} -> case Date.from_iso8601(date1_s) do
          {:ok, date} -> date |> Timex.to_datetime(:local) |> Either.Right.new
          {:error, reason} -> Either.Left.new("error for date1: #{inspect(reason)}")
        end
        :error -> Timex.now(:local) |> Timex.beginning_of_day |> Either.Right.new
      end
      # ...    
      return HydroDB.Database.defaults(site, date1, date2, gens, newdefaults, regex)
    end
    case stream do
      %Either.Right{right: stream_} -> send_stream(conn, stream_, "text/xml")
      %Either.Left{left: error}     -> send_resp(conn, 422, error)
    end