Optimistically prepare the instance declaration for Pages that should replace get / getAll, not really getting out of the Monad

src/PDF/Pages.hs

@@ -1,4 +1,7 @@
 {-# LANGUAGE NamedFieldPuns #-}
+{-# LANGUAGE TypeSynonymInstances #-}
+{-# LANGUAGE FlexibleInstances #-}
+{-# LANGUAGE MultiParamTypeClasses #-}
 module PDF.Pages (
       Page(..)
     , get
@@ -109,6 +112,11 @@ loadPage source = do
   contents <- extractText =<< objectById source
   return $ Page {contents, source}
 
+data Pages = Pages
+
+instance Box T Pages Layer (Map ObjectId Page)
+instance Box T ObjectId Layer Page
+
 getAll :: Layer -> Either String (Map Int Page)
 getAll content = runError $ fst <$> evalRWST getPages content Map.empty
   where