Hello With the resent discussion on comonads on #haskell (mostly due to Uustalo's excellent paper) I am wondering is it possible to model failure with comonads? It seems to me that Reader,Writer and State can be implemented with both monads and comonads. IO can be implemented as a monad but OI wants linear types. Streams make fine comonads. Is there anything corresponding to Maybe or List? - Einar Karttunen