I am sure I am missing something, but this thread of comments really got me thinking. I started thinking this was a use case for existential types, but I’m not

I am sure I am missing something, but this thread of comments really got me thinking. I started thinking this was a use case for existential types, but I’m not sure it’s immediately applicable. Then went down a research paper rabbit hole and google binge looking at various ideas. Now I’m sitting here thinking (and I doubt this scotch is making it clearer) that this is sort of like Haskell’s type classes being seen as the ‘Data Type’ level and regular type constructors being seen as the ‘Data Structure’ level. Obviously a language would need to incorporate the class syntax as a less separate construct than it is in Haskell, but I can’t shake the feeling this almost captures the thrust of the concept.