Hi I'm trying to write a function: reaches :: Type -> Q [Type] The intention is that reaches (Either Bool [Int]) would return [Either Bool [Int], Bool, [Int], Int] - i.e. all types which are contained by the initial type at any level. I took a shot at this: getTypes :: Type -> Q [Type] getTypes t = do let (ConT c, cs) = typeApp t TyConI dat <- reify c return $ concatMap ctorTypes $ dataCtors dat reaches :: Type -> Q [Type] reaches t = f [] [t] where f done [] = return done f done (t:odo) | t `elem` done = f done odo | otherwise = do ts <- getTypes t f (t:done) (odo ++ ts) Where typeApp splits a type to find its constructor, ctorTypes gets the types of the fields, and dataCtors gets the constructors in a data type. Unfortunately reify doesn't seem to work on types. Is it possible to do what I am after? Thanks Neil