2008/2/2, Rodrigo Queiro
Sorry, I was lazy. New maximum': maximum' = foldl1' max
Sorry but none of those propositions change the heart of the problem : the list of elements is totally produced before she can be consumed due to the strict monadic (IO or ST) nature of getElems. Thus you get an extraordinary waste of memory as well as resources... To address this I propose this function : foldl1MArray' :: (MArray a e m, Ix i) => (e -> e -> e) -> a i e -> m e foldl1MArray' f a = do (l,u) <- getBounds a firstElem <- readArray a l foldM (\a mb -> a `seq` mb >>= return . f a) firstElem (map (readArray a) (range (l,u))) With this, we can rewrite the original program using the excellent modifyArray from Rodrigo : normalizeArray :: (MArray a e m, Ix i, Fractional e, Ord e) => a i e -> m () normalizeArray arr = do max_elem <- foldl1MArray' max arr modifyArray (* (1/max_elem)) arr -- Jedaï