Is such a function familia to the Haskell users? foldlWhile :: (a -> b -> a) -> (a -> Bool) -> a -> [b] -> a foldlWhile f p a bs = case (bs, p a) of ([], _ ) -> a (_, False) -> a (b:bs', _ ) -> foldlWhile f p (f a b) bs' foldl does not seem to cover this. Example. Sum the list while the sum is less than bound: boundSum :: Integer -> [Integer] -> Integer boundSum b = foldlWhile (+) (< b) 0 Example: boundSum 100 $ map (^2) [1 ..] Is this reasonable? More `generic' variant: foldlWhileJust :: (a -> b -> Maybe a) -> a -> [b] -> a foldlWhileJust f a bs = case bs of [] -> a b:bs' -> case f a b of Just a' -> foldlWhileJust f a' bs' _ -> a Please, copy the replies to mechvel@botik.ru ----------------- Serge Mechveliani mechvel@botik.ru