I love this idea. My knowledge of lisp is very basic but I wonder if optional declarations could be added to functions: e.g. f(Number) -> (Number,Number) (sort

I love this idea. My knowledge of lisp is very basic but I wonder if optional declarations could be added to functions: e.g. f(Number) -> (Number,Number) (sort of similar to haskell) and then these could be used in the pretty printing / presentation layer. This would help lisp from missing those implicit clues that are present in other languages without compromising its flexibility.