[Haskell-cafe] know a workaround for greedy context reduction?

With these three declarations {-# LANGUAGE FlexibleInstances #-} {-# LANGUAGE UndecidableInstances #-} class C a where c :: a class C a => D a where d :: a instance C a => D a where d = c ghci exhibits this behavior: *> :t d d :: (C a) => a Where I would prefer "d :: (D a) => a". In my actual examples, the context is much larger and I can't involve overlapping instances. Is there a known workaround? I didn't find a related bug on the GHC trac, and I don't know if other compilers behave in the same way.