An updated HKT encoding

hkt-via-ai-take-2.rs

trait StarToStar<Input> {
    type Output;
}
type Apply<Name, Elt> where Name: StarToStar<Elt> = Name::Output;

struct Vec_;
struct DList_;

impl<T> StarToStar<T> for Vec_ {
    type Output = Vec<T>;
}

impl<T> StarToStar<T> for DList_ {
    type Output = DList<T>;
}

trait Mappable
{
    type E;
    type HKT where Apply<HKT, E> = Self;

    fn map<F>(self, f: E -> F) -> Apply<HKT, F>;
}