Yes, you would know what it is at that moment. You would not however know if what it is at that moment in time is actually correct, or what the expected shape is, without deconstructing the entire function that is the receiver of the data. That's where static types are useful - I can just hover my mouse over a function and it will show me what is the expected input, and expected output, and I do not need to read and understand the contents of the function to know if the data is correct, because it would throw an exception if it is not, like if a string suddenly becomes a number or is missing a piece of information, etc.
Theoretically, yes. And trust me, I loved static types. I use Rust for almost everything. However, the programming loop or the iteration loop that you get into with Lisp, especially with things like Common Lisp, it's not that much of a concern. But I agree with any other language which is not a Lisp, a static type system is far superior.
