I spent a few days this week at POPL (one day too short due to a massive blizzard currently pounding Philadelphia). As always at conferences, I had a great time and left full of new ideas. This time, I sat in on a series of talks on gradual typing. Forgive me as I’m nowhere near an expert on gradual typing, but I took away this gist: with a gradual typing system, a type-checker does the best it ca