I’ve made the following changes in 0.2.0:

1. now you define message/1 instead of splode_message/1
2. use Splode.ErrorClass can be used now, which adds the errors field and a default message/1 implementation.

As for the other things discussed:

1. deriving error class from namespaces: I’d personally rather not do this. It takes something explicit and makes it implicit. I imagine users that want to do this can create a custom module to use and make it work that way for them.

2. adding a default message/1 for any given error. I’m open to this, I just didn’t get around to it. It wouldn’t be a breaking change, so PRs welcome on that front

If you were to switch from splode_message to using message, I think you’d need to use @before_compile and defoverridable message: 1. A basic sketch:

defmodule Splode.Error do
  defmacro __using__(opts) do
    quote do
      @before_compile unquote(__MODULE__)
      # mostly everything as before, except don't def message here
    end
  end

  defmacro __before_compile__(env) do
    ensure_def_message =
      if Module.defines?(env, {:message, 1}, :def) do
        quote(do: defoverridable message: 1)
      else
        quote do
          # default impl
        end
      end

    quote do
      unquote(ensure_def_message)

      # the existing def message implementation, except use super instead of calling splode_message
      def message(%{vars: vars} = exception) do
        string = super(exception)
        ...
      end
    end
  end
end

I’d like to contribute, but won’t likely have time until mid next week at the earliest. If you want to get to it before then, that’s perfectly fine by me! How about this: I’ll open issues for these suggestions, and whichever of us gets started first can reply to those so that we’re not duplicating effort.