Either issues

[AHBruns]

Currently, the way Either is implement, there is no way to unwrap it while handling the left value other than a raw case statement. There's no way to fold both the left and right into a single value because the foldable instances are:

definst Witchcraft.Foldable, for: Algae.Either.Left do
  def right_fold(_, seed, _), do: seed
end

definst Witchcraft.Foldable, for: Algae.Either.Right do
  def right_fold(%Right{right: inner}, seed, fun), do: fun.(inner, seed)
end

Ideally we'd implement bifoldable in Witchcraft to allow:

Either.Left.new(1) |> bifold_right(fn err, _ -> {:error, err} end, fn result, _ -> {:ok, result} end)

In the meantime, just making Either a comonad and have it raise when your extract a left will be very helpful.

[github-actions]

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