content: {-# LANGUAGE GADTs #-}
  {-# LANGUAGE TypeOperators #-}
  {-# LANGUAGE KindSignatures #-}
  {-# LANGUAGE RankNTypes #-}
  {-# LANGUAGE PatternSynonyms #-}
  module PM where
  
  import Data.Type.Equality ( type (:~:)(..) )
  import qualified Data.Kind
  
  data Type :: Data.Kind.Type -> Data.Kind.Type where
    SRecNil :: Type ()
    SRecCons :: String -> Type a -> Type b -> Type (a, b)
    SIntTy  :: Type Int
  
  pattern RecCons1 a <- (SRecCons _ _ a)
  
  eqType :: Type ty1 -> Type ty2 -> Maybe (ty1 :~: ty2)
  eqType SRecNil SRecNil = Just Refl
  eqType (SRecCons l1 s1 t1) (SRecCons l2 s2 t2)
    | Just Refl <- s1 `eqType` s2
    , Just Refl <- t1 `eqType` t2
    , l1 == l2
    = Just Refl
  eqType SIntTy  SIntTy  = Just Refl
  eqType _ _ = Nothing
  
  massive :: Int -> Type ty -> Type recty -> (forall ty'. Type ty' -> m r) -> m r
  massive fieldN sFieldTy sRecTy k =
    case (fieldN, sFieldTy, sRecTy) of
      (0, t, SRecCons _ t' _)
          |  Just Refl <- t `eqType` t' -> k sFieldTy
      (1, t, RecCons1 (SRecCons _ t' _))
          |  Just Refl <- t `eqType` t' -> k sFieldTy
      (2, t, RecCons1 (RecCons1 (SRecCons _ t' _)))
          |  Just Refl <- t `eqType` t' -> k sFieldTy
      (3, t, RecCons1 (RecCons1 (RecCons1 (SRecCons _ t' _))))
          |  Just Refl <- t `eqType` t' -> k sFieldTy
      (4, t, RecCons1 (RecCons1 (RecCons1 (RecCons1 (SRecCons _ t' _)))))
          |  Just Refl <- t `eqType` t' -> k sFieldTy
      (5, t, RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (SRecCons _ t' _))))))
          |  Just Refl <- t `eqType` t' -> k sFieldTy
      (6, t, RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (SRecCons _ t' _)))))))
          |  Just Refl <- t `eqType` t' -> k sFieldTy
      (7, t, RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (SRecCons _ t' _))))))))
          |  Just Refl <- t `eqType` t' -> k sFieldTy
      (8, t, RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (SRecCons _ t' _)))))))))
          |  Just Refl <- t `eqType` t' -> k sFieldTy
      (9, t, RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (SRecCons _ t' _))))))))))
          |  Just Refl <- t `eqType` t' -> k sFieldTy
      (10, t, RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (SRecCons _ t' _)))))))))))
          |  Just Refl <- t `eqType` t' -> k sFieldTy
      (11, t, RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (SRecCons _ t' _))))))))))))
          |  Just Refl <- t `eqType` t' -> k sFieldTy
      (12, t, RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (SRecCons _ t' _)))))))))))))
          |  Just Refl <- t `eqType` t' -> k sFieldTy
      (13, t, RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (SRecCons _ t' _))))))))))))))
          |  Just Refl <- t `eqType` t' -> k sFieldTy
      (14, t, RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (SRecCons _ t' _)))))))))))))))
          |  Just Refl <- t `eqType` t' -> k sFieldTy
      (15, t, RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (SRecCons _ t' _))))))))))))))))
          |  Just Refl <- t `eqType` t' -> k sFieldTy
      (16, t, RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (SRecCons _ t' _)))))))))))))))))
          |  Just Refl <- t `eqType` t' -> k sFieldTy
      (17, t, RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (SRecCons _ t' _))))))))))))))))))
          |  Just Refl <- t `eqType` t' -> k sFieldTy
      (18, t, RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (SRecCons _ t' _)))))))))))))))))))
          |  Just Refl <- t `eqType` t' -> k sFieldTy
      (19, t, RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (SRecCons _ t' _))))))))))))))))))))
          |  Just Refl <- t `eqType` t' -> k sFieldTy
      (20, t, RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (SRecCons _ t' _)))))))))))))))))))))
          |  Just Refl <- t `eqType` t' -> k sFieldTy
      (21, t, RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (SRecCons _ t' _))))))))))))))))))))))
          |  Just Refl <- t `eqType` t' -> k sFieldTy
      (22, t, RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (SRecCons _ t' _)))))))))))))))))))))))
          |  Just Refl <- t `eqType` t' -> k sFieldTy
      (23, t, RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (SRecCons _ t' _))))))))))))))))))))))))
          |  Just Refl <- t `eqType` t' -> k sFieldTy
      (24, t, RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (SRecCons _ t' _)))))))))))))))))))))))))
          |  Just Refl <- t `eqType` t' -> k sFieldTy
      (25, t, RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (SRecCons _ t' _))))))))))))))))))))))))))
          |  Just Refl <- t `eqType` t' -> k sFieldTy
      (26, t, RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (SRecCons _ t' _)))))))))))))))))))))))))))
          |  Just Refl <- t `eqType` t' -> k sFieldTy
      (27, t, RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (SRecCons _ t' _))))))))))))))))))))))))))))
          |  Just Refl <- t `eqType` t' -> k sFieldTy
      (28, t, RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (SRecCons _ t' _)))))))))))))))))))))))))))))
          |  Just Refl <- t `eqType` t' -> k sFieldTy
      (29, t, RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (SRecCons _ t' _))))))))))))))))))))))))))))))
          |  Just Refl <- t `eqType` t' -> k sFieldTy
      (30, t, RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (SRecCons _ t' _)))))))))))))))))))))))))))))))
          |  Just Refl <- t `eqType` t' -> k sFieldTy
      (31, t, RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (SRecCons _ t' _))))))))))))))))))))))))))))))))
          |  Just Refl <- t `eqType` t' -> k sFieldTy
      (32, t, RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (RecCons1 (SRecCons _ t' _)))))))))))))))))))))))))))))))))
          |  Just Refl <- t `eqType` t' -> k sFieldTy
      _ -> error "TODO support records >32"
  