[Haskell-cafe] Need ideas how to model the lack of something

[Tillmann Rendel]

Hi,

martin wrote:
> I started like this
>
> data C a = C {
>              insert :: a -> Maybe (C a),
>              remove :: Maybe (a, C a)
>          }
>
> but I could not implement anything sensible on top of this.

Looks reasonable to me. What do you want to implement on top of it?

For starters, here are three values of this type:

stack ::