Re: [Haskell-cafe] Finding the average in constant space

There are a few blog posts by Conal Elliott and Max Rabkin (I think) reifying folds as a data type to get more "composition" and thus fold different functions at the same time. Search for "beautiful folding" with the above authors names. Personally I didn't find the examples significantly more "beautiful" that using regular composition in a normal fold - only that that the helper functions to manage pairs aren't in the standard library.