At the end of the day, if you look at a low enough level in the stack, there are no types. In a very concrete way, types are a high-level idea, and if the high-

At the end of the day, if you look at a low enough level in the stack, there are no types. In a very concrete way, types are a high-level idea, and if the high-level stops matching the low-level, then bugs crop up. See for example Tetris implemented in Pokémon Yellow via runtime code injection: https://www.youtube.com/watch?v=Vjm8P8utT5g https://www.youtube.com/watch?v=Vjm8P8utT5g Their compiler missed that! So I think there's good reason to switch from talking about types as "assumptions", and think of them as compile time "assertions". Something lower-level in the stack could break the high-level code, but that doesn't make the high-level code useless, just imperfect.