Hello GHC 6.12 introduced type level splices. They are great for instances generation. They allow for much clearer and easier to understand code. However I run into problem with them. It's possible to create instance for type class which doesn't have superclass. If it does have one compiler complains that it could not deduce context. All my attempts to provide context fail. Is that accidental limitation or because of Some Good Reason? Or just due to lack of understanding on my side? Below is simplest example.

{-# LANGUAGE FlexibleInstances #-} {-# LANGUAGE TemplateHaskell #-} import Language.Haskell.TH

-- OK but require FlexibleInstances makeEq :: Name -> Q [Dec] makeEq name = [d| instance Eq $(conT name) where (==) = undefined |]

-- Could not deduce Eq context makeOrd :: Name -> Q [Dec] makeOrd name = [d| instance Ord $(conT name) where compare = undefined |]

And GHC output: test.hs:14:17: Could not deduce (Eq t) from the context () arising from the superclasses of an instance declaration at test.hs:14:17-32 Possible fix: add (Eq t) to the context of the instance declaration In the instance declaration for `Ord t_aS5' In the Template Haskell quotation [d| instance Ord $(conT name) where { compare = undefined } |] In the expression: [d| instance Ord $(conT name) where { compare = undefined } |] -- Khudyakov Alexey