Start working on the (versioned) OPDS catalog

src/Data/Versioned.hs

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+{-# Language KindSignatures #-}
+{-# Language DataKinds #-}
+{-# Language DefaultSignatures #-}
+{-# Language MultiParamTypeClasses #-}
+{-# Language FunctionalDependencies #-}
+module Data.Versioned where
+
+import GHC.TypeLits
+import ClassyPrelude
+import Data.Generics.Product
+
+newtype Versioned (v :: Nat) a = Versioned a deriving (Show)
+
+instance Functor (Versioned v) where
+  fmap f (Versioned a) = Versioned (f a)
+
+instance Applicative (Versioned v) where
+  pure = Versioned
+  (Versioned f) <*> (Versioned a) = Versioned (f a)
+
+class Migrate a b | b -> a where
+  migrate :: a -> b
+  default migrate :: (Subtype b a) => a -> b
+  migrate = upcast