Normally I'm a core.typed person, but static type constraints don't quite make sense here. We want heterogeneity in some cases (e.g. you want to be able to mix nils and ints), but not in others (e.g. this short and int mixing, which could be intentional, but also, might not be)

I've considered spec as well, but spec has a weird insistence that a keyword has exactly one meaning in a given namespace, which is emphatically not the case in pretty much any code I've tried to verify. Also its errors are... not exactly helpful.