There's no such thing as a "valid" value. Values can only be valid in some context. The empty string is valid only in contexts where… it has meaning. (Quite har

There's no such thing as a "valid" value. Values can only be valid in some context. The empty string is valid only in contexts where… it has meaning. (Quite hard to say this without being obviously circular!) Golang has chosen the point of view that "in most contexts, the zero value is valid"; it is wrong about this. There are certainly some contexts where for some particular type the zero value is valid, but it is rarely true in general. Booleans are harmful for other reasons, sometimes related to "parse, don't validate". Write a discriminated union that makes the true/false distinction meaningful, if you really do have a two-valued data type ("--dry-run" is `| Dry | Wet`, not a bool; this mistake is called "boolean blindness"). Write a type that actually contains the data you want, if the boolean is supposed to indicate the validity of some other data (`option<string>`, not `string * bool` where `something, false` implicitly means the `something` is meaningless).