{-# LANGUAGE DataKinds, GADTs #-}
data Typ = TInt | TInteger | TUnk deriving Show
data SType a where
  STInt :: SType 'TInt
  STInteger :: SType 'TInteger
  STUnk :: SType 'TUnk
  
data Some f where
  Some :: f a -> Some d
  
data Expr a 
  = Expr (SType a)

parse :: String -> Maybe (Some Expr)
parse "3" = Just (Some (Expr STInt))
parse "()" = Just (Some (Expr STUnk))
parse _ = Nothing

main = pure ()