Hi, I'm wondering about a syntactic sugar for comonads. These are still very new to me, but it seems like their usage will become much more common once manipulations are more convenient (I believe this was the case with monads and arrows, correct?). Here's an example for motivation. Consider the data type data Stream a = a :< Stream a and suppose we want to write a function movingWindow :: Stream a -> Stream [a] so that, for example, movingWindow 3 (1 :< 2 :< 3 :< ...) evaluates to [1,2,3] :< [2,3,4] :< [3,4,5] :< ... Recognizing Stream as a comonad, this is pretty easy: movingWindow n s = s =>> (take n . toList) toList :: Stream a -> [a] toList (x :< xs) = x : toList xs If the second argument of (=>>) is written in lambda form, this comes out as movingWindow n s = s =>> \x -> take n $ toList x This looks analogous to the way do is translated for monads, so a sugary alternative could be movingWindow n s = do x -< s take n $ toList x Note that the presence of "-<" tells us we're in a comonad, rather than a monad. I'm not at all stuck on this, but I think it would be good to get the ball rolling. What do you think? Chad Scherrer Computational Mathematics Group Pacific Northwest National Laboratory "Time flies like an arrow; fruit flies like a banana." -- Groucho Marx