> > The type system is not rich enough to distinguish between 0-lists'  
> > and 1-list's. It is just a list.
>
> So what is the gain ?

I'm not sure about the actual implementation, but in theory a list is something like:

type 'a list = Nil | Cons of 'a * 'a list

[] and [a]  and h :: t are just syntactic sugar.

So lists don't even know their own length internally, unlike an array.