{-# LANGUAGE GHC2024 #-}
{-# LANGUAGE AllowAmbiguousTypes #-}
{-# LANGUAGE PatternSynonyms #-}
-- base
import GHC.TypeLits (SNat, KnownNat (natSing), natVal, withSomeSNat, fromSNat)

class KnownNat n => ValidUINTn n

data UINTn where
  UINTn :: ValidUINTn n  => SNat n -> UINTn

instance ValidUINTn 1
instance ValidUINTn 2
instance ValidUINTn 3
instance ValidUINTn 4

instance Show UINTn where
  show (UINTn sn) = "UINT" <> show (natVal sn * 8)

getValidUINTn :: Integer -> Maybe UINTn
getValidUINTn x = withSomeSNat x $ \maybeSn -> maybeSn >>=
  \sn -> let n = fromSNat sn in
    if n == 1 then Just (UINTn (natSing @1))
    else if n == 2 then Just (UINTn (natSing @2))
    else if n == 2 then Just (UINTn (natSing @3))
    else if n == 4 then Just (UINTn (natSing @4))
    else Nothing

main = do
  print $ UINTn (natSing @2)
  print $ getValidUINTn 4
  print $ getValidUINTn 5