Hi all, I observe a strange "deriving Show" behaviour for my data type Foo that has proxies: data Foo :: k -> * where Foo :: Proxy t -> Foo t deriving instance Show (Foo t) This works as expected. But now I add instance {-# OVERLAPPING #-} KnownSymbol s => Show (Proxy (s :: Symbol)) where show = ('#' :) . symbolVal instance {-# OVERLAPPING #-} KnownNat n => Show (Proxy (n :: Nat)) where show = ('#' :) . show . natVal these orphan instances, and "deriving Show" won't pick them up. When I go and specialise deriving instance {-# OVERLAPPING #-} KnownNat t => Show (Foo (t :: Nat)) deriving instance {-# OVERLAPPING #-} KnownSymbol s => Show (Foo (s :: Symbol)) then it seems to work allright. Is polykinded derivation so different from the monokinded one? Or is this simply a bug? (a more elaborate WIP example can be found here: https://code.google.com/p/omega/source/browse/mosaic/CloudAtlas.hs?spec=svn2465&r=2465) Cheers, Gabor