Write a function `ListAt` that takes a pointer to the head of the list `l` and an `int pos` as parameters. This function should return the `NodeL` in the position `pos` of the linked list `l`.
Write a function `ListAt` that takes a pointer to the head of the list `l` and an `int pos` as parameters. This function should return the pointer to the `NodeL` in the position `pos` of the linked list `l`.
- In case of error the function should return `nil`.