For 'deriving' bits (e.g. 1.8) - maybe use Kittens?

[hmemcpy]

data Maybe a = Nothing | Just a deriving Functor

I intend to add a "notes" page in the scala edition of the CT book that explains some pre-requisites (e.g. Kind projector). So maybe we can add a Kittens example?

[kailuowang]

Sounds good to me.