How would you type lambda? If something like Symbol -> AST -> Closure is a type you accept for lambda, I guess vau's type would be the same except with two Sym

How would you type lambda? If something like Symbol -> AST -> Closure is a type you accept for lambda, I guess vau's type would be the same except with two Symbols (one for the argument like lambda except it won't be evaluated before being passed to the closure, and one for the dynamic environment which you will need to evaluate the argument).