The question of the kid was legit, but the "a free theorem is when you can say something that is always true about a function machine if you only know its type, but you don’t know anything about what it does on the inside" is likely not what he asked for.
The author acknowledged that was a bit much and pivoted it to a game that his son loves, who put you in charge of taking that away from him?
> This seemed a bit beyond him [...] But the whole conversation had given me a different idea. "Hey, I have a good idea for a game," I said. [...] He immediately liked this game and it has been a huge hit; he wants to play it all the time.
It's probably made even better by being 'the game that daddy reads about/does at work'.
Fair, tbh it may not have been needed, but I also struggle with letting go the original question asked even though the child may have moved on! Still, this example is hardly robbing anyone of their childhood.
