Yeah, when wrapping `(Int -> Int) -> Any` you would need to package it up with a proof of its type if you want to unwrap it and check. A weaker promise might be

Yeah, when wrapping `(Int -> Int) -> Any` you would need to package it up with a proof of its type if you want to unwrap it and check. A weaker promise might be merely to unpack `Any` into `Dyn -> Dyn` which states only that we have a function and nothing of its domain or range. Those would have to be unwrapped specifically later. A function `Dyn` to `Dyn` probably doesn't evaluate its argument's type anyway so it could fail at runtime regardless. The receiver of its output would then be required to unwrap the `Dyn` and check its type (if needed).