Would love a complete Person example :)

[silky]

Hello; thanks for this lovely library!

I'm trying to wrap my mind around it.

In the README, you start with a Person example; but then quickly jump into ASTs.

My usage isn't actually an AST; it's much more like the Person example. I'm here because I couldn't quite get barbies to work ( see jcpetruzza/barbies#47 ).

In my own hacking, I'm trying something like

data Person h = Person
    { height :: h :# Const Double
    , weight :: h :# Const Double
    , name   :: h :# Const Text
    }

person :: Pure # Person
person = Pure $ Person
  { height = Pure $ Const 5.0
  , weight = Pure $ Const 1.0
  , name   = Pure $ Const "name"
  }

maybePerson :: Maybe # Person
maybePerson = undefined

what's not clear to me is how to define the maybePerson type. As-is, it doesn't compile. I think I need to somehow adapt the Maybe type to be a kind of Hyper type; but I'm missing exactly how.

I'd love to know how to do this; and then do barbie-style things such as a bmap which takes, say, an Identity # Person and converts it to a Maybe # Person via runIdentity.

Thanks!

[silky]

Hmm; maybe the answer is this:

data HMaybe a
    = HNothing
    | HJust    (a :# HMaybe)

maybePerson :: HMaybe # Person
maybePerson = HJust $ Person
  { height = HNothing
  , weight = HNothing
  , name   = HJust $ Const "Name"
  }

?

[silky]

I guess I was hoping there was a way to re-use existing types instead of defining my own? But I can live with the fact that there isn't; but I'm sure there's a way to make it work ...

[silky]

I'm fairly sure there has to be a way to define a kind of ToHyper type that would take a Maybe type as an argument; but I'm struggling to make that work ...

[silky]

I feel like I'm missing access to a crucial type variable.

I want to write:

data ToHyper :: (Type -> Type) -> AHyperType -> Type where
  ToHyper :: f :# ToHyper f -> ToHyper f h

but I somehow need to get out the variable of AHyperType and apply f to it; but I'm not sure how.