This would be absolutely amazing actually.
Both purescript and agda have this
IMHO a Rust-style type `Option<HashMap<String, Vec<u32>>>` is a little noiser than the Haskell-style type `Maybe (Map String [Int])`, but not fatally so. Maybe there are much worse cases though?
I am not a fan of C#'s `Func<a,b>` at all.