https://old.reddit.com/r/haskell/comments/xuou06/is_there_a_way_to_describe_a_family_of_types/

D.hs

{-# LANGUAGE DataKinds, TypeFamilies, TypeOperators #-}
module D where

import Control.Applicative (liftA2)
import Data.Kind (Type)

data F = VALUE | F :-> F

infixr 1 :->

type family Unquote (t :: F) :: Type where
  Unquote VALUE = Value
  Unquote (t :-> t') = Unquote t -> Unquote t'

data Value

data Expr a = Closed (Unquote a) | Open (Expr (VALUE :-> a))

mapExpr :: (Unquote a -> Unquote b) -> Expr a -> Expr b
mapExpr f (Closed x) = Closed (f x)
mapExpr f (Open y) = Open (mapExpr (fmap f) y)

pureExpr :: Unquote a -> Expr a
pureExpr = Closed

liftA2Expr :: Unquote (a :-> b :-> c) -> Expr a -> Expr b -> Expr c
liftA2Expr f (Closed x) y = mapExpr (f x) y
liftA2Expr f x (Closed y) = mapExpr (flip f y) x
liftA2Expr f (Open x) (Open y) = Open (liftA2Expr (liftA2 f) x y)