I totally missed the homework part for day 2 as I only watched the stream and didn't check github. Going back there now, I'm curious if the homework was intended as a "look ahead" or a "review", as from the description it appears to be a parser, which he hadn't yet covered at that point. Perhaps it's based on the readings? Are people starting on the homework from the ion code, or from scratch?
I think it's up to you how you want to do it. I did it as a look ahead because i wanted to get familiar with the problem. Per didn't make the s-expression implementation on stream so you could still watch day 3 and use what you learn to finish the homework.