Reminds me of something I saw recently, a tri-value boolean, a "trilean" or "tribool".
true, false, unknown
yes, no, maybe
nullable boolean
> The tribool class acts like the built-in bool type, but for 3-state boolean logic
https://www.boost.org/doc/libs/1_48_0/doc/html/tribool/tutor...
Apparently this is also called "three-valued logic".
> In logic, a three-valued logic (also trinary logic, trivalent, ternary, or trilean, sometimes abbreviated 3VL) is any of several many-valued logic systems in which there are three truth values indicating true, false, and some third value.
> the primary motivation for research of three-valued logic is to represent the truth value of a statement that cannot be represented as true or false.
https://en.wikipedia.org/wiki/Three-valued_logic
Personally I think I'd prefer a language to instead support multiple return values, like result and optional error. Or a union of result and error types.
> no reason not to use int8 directly
Hm, so it gets into the territory of flags, bit fields, packed structs.
const BitField = packed struct {
a: u3,
b: u3,
c: u2,
};