I'm just finishing lesson 2 of unit 1 and I have a minor comment which is that it seems to be inconsistent where the writer is informed of what to write, which confused me initially. If there is an error, the reader tells itself via a message and it handles the message by telling the writer. However, if the input is valid, then the writer is told directly in the validation code. To me it feels a little inconsistent. Maybe this gets picked up down the line as I can imagine that I'll be drowning in messages in a larger project and knowing where and when one actor talks to another could make things easier. Anyway, just a thought.