[Haskell-cafe] Is there a name for this algebraic structure?

[Albert Y. C. Lai]

On 2015-04-21 05:18 AM, Gleb Peregud wrote:
> I think I need to think a bit more about this to find a proper 
> definitions and laws.

Remember to specify accessors, not just constructors.

Last time, there was no accessor, so S = () would fit the bill.