alt Hacker News> The compiler can still enforce checks, such as with nil checks for pointers.
Only sometimes, when the compiler happens to be able to understand the code fully enough. With sum types it can be enforced all the time, and bypassed when the programmer explicitly wants it to be.
There's nothing preventing this for floats and ints in principle. e.g. the machine representation could be float, but the type in the eyes of the compiler could be `float | nan` until you check it for nan (at which point it becomes `float`). Then any operation which can return nan would return `float | nan` instead.
tbh this system (assuming it works that way) would be more strict at compile-time than the vast majority of languages.