How does that fail at compile time if you try to read a value when there is none?

Some of Dawson Engler’s work helps solve this problem, starting around [1]. In that, he shows us how to write custom compiler rules in a high-level language. These rules are sufficient to enforce that maybe type. In another paper, Engler (or one of his several talented students, can’t remember now) shows us how to automatically infer many of these rules.

[1] https://web.stanford.edu/~engler/mc-osdi.pdf

If you try to use it val directly, it fails. You must unpack it first.

To do something like x.get() in Scala when x is empty is a runtime error, not a compile-time error.