[Haskell-beginners] Is it possible to implement groupBy using folds?

Hi, The source code of groupBy shows that groupBy does not go through every element. Is it really possible to implement it using folds? Thanks. -- | The 'groupBy' function is the non-overloaded version of 'group'. groupBy :: (a -> a -> Bool) -> [a] -> [[a]] groupBy _ [] = [] groupBy eq (x:xs) = (x:ys) : groupBy eq zs where (ys,zs) = span (eq x) xs Best regards, Zhi-Qiang Lei zhiqiang.lei@gmail.com