Hello Ross, Friday, November 18, 2005, 2:05:37 PM, you wrote: RP> http://www.soi.city.ac.uk/~ross/traversals/ RP> Comments most welcome. 1) imho, it's better to change "Prelude." to "List." here: instance Foldable [] where foldr = Prelude.foldr foldl = Prelude.foldl foldr1 = Prelude.foldr1 foldl1 = Prelude.foldl1 and in other places where you use list functions listed in Prelude 2) i can try to make Template Haskell machinery to automatically derive instances of Foldable and Traversable, using your examples for Tree as sample 3) -- If @f@ is also a 'Functor', define @('<$>') = 'fmap'@. -- If it is also a 'Monad', define @'pure' = 'return'@ and @('<*>') = 'ap'@. why you don't just define: instance Monad m => Applicative m where pure = return (<*>) = ap RP> They are proposed for the base package, and would replace FunctorM. it is a beatiful contribution. but it doesn't work without definitions for All, Any and so on :) -- Best regards, Bulat mailto:bulatz@HotPOP.com