I have returned from a bike ride and am back at my keyboard, so I can share the third post about Candid:
https://www.joachim-breitner.de/blog/784-A_Candid_explainer__Opt_is_special
Here I explain the problem with extending records in argument position, and how we came up with some special rules around the opt type that solves that problem.
This solution was the conclusion after a two year saga where we considered and dismissed a dozen different solutions (all summarized here, if you like reading up on old discussions). It’s not perfect, but it’s the best one we found so far.