[Haskell-cafe] Fold that quits early?

This is almost a fold, but seemingly not quite? I know I've seem some talk of folds that potentially "quit" early. but not sure where I saw that, or if it fits. f xs [] = False f xs (y:ys) | any c ys' = True | otherwise = f (nub (y:xs)) (ys' ++ ys) where ys' = g y xs