Does this type definition handle empty lists?
haskell, list
Solution
The datatype `NestedList a` contains either elements of type `Elem a`, or elements of type `List [NestedList a]`.
The first of these, you already seem to understand. The second one, though, has as its argument a list (the normal sort) of `NestedList a`'s. This can be any list, including `[]`. Thus, `List []` is a valid `NestedList`, as would be `List[Elem 5]`, or `List [Elem 5, List [Elem 3, Elem 2] ]`.
Problem
I am answering question seven of Haskell's 99 questions. However, I have come to the point where they define the type ``` data NestedList a = Elem a | List [NestedList a] ``` and it, from my understanding, will not handle empty lists (ie. `[]`). But in their example tests they show ``` *Main> flatten (List []) [] ``` Does this type cover empty lists? If so, why? If it does not, and is a mistake of the websites, how would one write a nested list type that handles empty lists?