This kind of thing is so frustrating because enormous effort has been put into solving exactly one VARIANT of a pretty general problem. The general case is: at a particular point in the code, is $THIS_DATA usable or not, for some appropriate definition of “usable” in that code?

And if “usable” has any additional meaning besides “is not null”, this entire machinery is useless because one STILL has to figure out the state of the data!

For example, what if you are sanitizing input from a user and there is a “wall” in your code beyond which a string is considered safe (e.g. decoded, evaluated by regex, or whatever is supposed to happen)? Or, what if “usable” means that a server has been connected to, or a database opened, or a calculation completed, or whatever else you want to say? What if it’s a numerical denominator and you want it to be nonzero? The list could go on and on, and none of these architectures deals with ANY of those possibilities.