[brundolf]

They don't, though.

For example: a technique I've used to work with arbitrary, unknown JSON values, is to type them as a union of primitives + arrays of json values + objects of json values. And then I can pick these values apart in a way that's totally safe while making no dangerous assumptions about their contents.

Of course this opens the door for lots of potential mistakes (though runtime errors at least are impossible), but it's 100% compatible with any statically-typed language that has unions.