[Haskell-cafe] heterogeneous container smart constructor question

[Henning Thielemann]

On Tue, 5 Sep 2023, Zoran Bošnjak wrote:

> Dear haskellers,
> I am trying to add some type safety to the program in the following situation:
>
> There are some distinct 'Item t' types which come in groups. That is: 
> 'EList' container can contain either:

> - items 0,1
> - items 0,1,2,3
> - items 0,1,2,3,4,5,6

What about a solution in Haskell 98:

(T0, T1, Maybe (T2, T3, Maybe (T4, T5, T6)))

or with custom data types:

data ItemsA = ItemsA T0 T1 (Maybe ItemsB)
data ItemsB = ItemsB T2 T3 (Maybe ItemsC)
data ItemsC = ItemsC T4 T5 T6

?