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how to calculate the sum of list of lists?
by Miranda Kajtazi 05 Feb '07

05 Feb '07

Help, How to calculate the sum of list of lists in Haskell? Please help me, Miranda

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mixing wxhaskell state and file io
by Martin DeMello 05 Feb '07

05 Feb '07

I'm having a lot of trouble mixing file io and wxhaskell's varCreate/Get/Set functions. I have functions readWords :: String -> IO WordMap wordGrid :: WordMap -> Layout And within my GUI code, the following compiles (ignores the variable, basically): words <- varCreate (do {w <- readWords "words"; return w}) wGrid <- do w <- readWords "words" return $ wordGrid w but I can't get the following (noncompiling code, but it shows what I'm trying to do) working: wGrid <- do w <- varGet words return $ wordGrid w Could someone give me a minimal example of reading in a list of words from a file, binding a wxHaskell variable to the list, and then mapping some GUI code over it? (Also, I'm making the base assumption that varSet and varGet are wxHaskell's analogue of the State monad - should I be looking at using StateT instead?) martin

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Connected!
by Bulat Ziganshin 05 Feb '07

05 Feb '07

Hello haskell-cafe, i've just got ADSL connection here! it's slow (64k) and not cheap, but at least it is completely different from dial-up i've used before -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com

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Win32 help please
by John Ky 05 Feb '07

05 Feb '07

Hi, I'm interested in writing accessing some Win32 functions not available from GHC. I wrote this short little file and tried to compile: mywin32.hsc > module MyWin32 where > > #include <windows.h> Then tried to compile it like this: # hsc2hs mywin32.hsc # ghc -fffi mywin32.hs C:/system/ghc/ghc-6.6/libHSrts.a(Main.o):Main.c:(.text+0x1b): undefined reference to `__stginit_ZCMain' C:/system/ghc/ghc-6.6/libHSrts.a(Main.o):Main.c:(.text+0x3f): undefined reference to `ZCMain_main_closure' collect2: ld returned 1 exit status What am I missing? Thanks -John

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Strange behaviour with writeFile
by C.M.Brown 04 Feb '07

04 Feb '07

Hi, I am observing some rather strange behaviour with writeFile. Say I have the following code: answer <- AbstractIO.readFile "filename" let (answer2, remainder) = parseAnswer answer if remainder == "" && answer2 == "" then do AbstractIO.putStrLn $ "completed" else do AbstractIO.putStrLn answer2 AbstractIO.writeFile "filename" remainder With the above I get an error saying the resources to "filename" are locked. If I add the line "AbstractIO.putStrLn $ show (answer2, remainder) before I call writeFile it suddenly magically works! Has anyone seen strange behaviour like this before? Regards, Chris.

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(no subject)
by C Rodrigues 04 Feb '07

04 Feb '07

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Another Space Leak
by Dominic Steinitz 04 Feb '07

04 Feb '07

Many thanks for the help on the original space leak which is now fixed -see the function pad below and test runs in small constant space. However, that has merely revealed the next space leak. The problem appears to be blockWord8sIn512 :: [Word8] -> [[Word8]] blockWord8sIn512 = unfoldr g where g [] = Nothing g xs = Just (splitAt 64 xs) or its alternative bws :: [Word8] -> [[Word8]] bws [] = [] bws xs = ys:(bws zs) where (ys,zs) = splitAt 64 xs But I can't see why a big expression is being built up. Shouldn't these produce elements of the list when they are required and they are then consumed by foldl'? Dominic. module Main(main) where import Data.Word import Data.Bits import Data.List ss = [0x67452301, 0xefcdab89, 0x98badcfe, 0x10325476, 0xc3d2e1f0] pad = pad' 0 where pad' l [] = [0x80] ++ ps where pl = (64-(l+9)) `mod` 64 ps = replicate pl 0x00 pad' l (x:xs) = x : (pad' $! l+1) xs -- otherwise (l+1) it will be deferred until replicate blockWord8sIn512 :: [Word8] -> [[Word8]] blockWord8sIn512 = unfoldr g where g [] = Nothing g xs = Just (splitAt 64 xs) bws :: [Word8] -> [[Word8]] bws [] = [] bws xs = ys:(bws zs) where (ys,zs) = splitAt 64 xs test :: Int -> Word8 test n = foldl' xor 0x55 (pad (replicate n 0x55)) test1 :: Int -> [Word8] test1 n = foldl' (zipWith xor) [0x01..0x40] (blockWord8sIn512 (pad (replicate n 0x55))) test2 :: Int -> [Word8] test2 n = foldl' (zipWith xor) [0x01..0x40] (bws (pad (replicate n 0x55))) main = do putStrLn (show (test 1000000)) putStrLn (show (test1 1000000)) putStrLn (show (test2 1000000))

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Suggestions for a hReadUntilStr implementation
by Matt Revelle 04 Feb '07

04 Feb '07

Hey there, A few weeks back I was thinking of writing a Haskell program that automated a telnet session. One function that could be useful is a hReadUntilStr - that is, a function that takes a Handle as an input source, a String to match, and a "Num a" as the number of seconds to wait before returning a (String, Bool) where the String is all the text read from the Handle until either matching or timing out and the Bool is true if the input String was matched. Something like: hReadUntilStr :: (Num a) => Handle -> String -> a -> IO (String, Bool) Is this the wrong way to think about the problem? If so, how should it be handled? If not, any ideas on the implementation? Any advice is appreciated. Cheers, Matt

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Space Leak Help
by Dominic Steinitz 04 Feb '07

04 Feb '07

I have re-written SHA1 so that is more idiomatically haskell and it is easy to see how it implements the specification. The only problem is I now have a space leak. I can see where the leak is but I'm less sure what to do about getting rid of it. Here's the offending function: pad :: [Word8] -> [Word8] pad xs = xs ++ [0x80] ++ ps ++ lb where l = length xs pl = (64-(l+9)) `mod` 64 ps = replicate pl 0x00 lb = i2osp 8 (8*l) I've thought about zipping the xs with [1..] which will give me a length as I go. Is this the right way to go are there better techniques for dealing with this? I've attached the full source below. Dominic. module Main(main) where import Data.Char import Data.Bits import Data.List import Data.Word import System import Codec.Utils type Rotation = Int rotL :: Rotation -> Word32 -> Word32 rotL s a = shiftL a s .|. shiftL a (s-32) instance Num [Word32] where a + b = zipWith (+) a b f n x y z | (0 <= n) && (n <= 19) = (x .&. y) .|. ((complement x) .&. z) | (20 <= n) && (n <= 39) = x `xor` y `xor` z | (40 <= n) && (n <= 59) = (x .&. y) .|. (x .&. z) .|. (y .&. z) | (60 <= n) && (n <= 79) = x `xor` y `xor` z | otherwise = error "invalid index for f" k n | (0 <= n) && (n <= 19) = 0x5a827999 | (20 <= n) && (n <= 39) = 0x6ed9eba1 | (40 <= n) && (n <= 59) = 0x8f1bbcdc | (60 <= n) && (n <= 79) = 0xca62c1d6 | otherwise = error "invalid index for k" -- Word120 -> Word512 -> Word120 oneBlock ss xs = (as!!80):(bs!!80):(cs!!80):(ds!!80):(es!!80):[] where ws = xs ++ map (rotL 1) (zipWith4 xxxor wm3s wm8s wm14s wm16s) where xxxor a b c d = a `xor` b `xor` c `xor` d wm3s = drop (16-3) ws wm8s = drop (16-8) ws wm14s = drop (16-14) ws wm16s = drop (16-16) ws as = (ss!!0):ts bs = (ss!!1):as cs = (ss!!2):(map (rotL 30) bs) ds = (ss!!3):cs es = (ss!!4):ds ts = (map (rotL 5) as) + (zipWith4 f [0..] bs cs ds) + es + (map k [0..]) + ws ss :: [Word32] ss = [0x67452301, 0xefcdab89, 0x98badcfe, 0x10325476, 0xc3d2e1f0] pad :: [Word8] -> [Word8] pad xs = xs ++ [0x80] ++ ps ++ lb where l = length xs pl = (64-(l+9)) `mod` 64 ps = replicate pl 0x00 lb = i2osp 8 (8*l) blockWord8sIn512 :: [Word8] -> [[Word8]] blockWord8sIn512 = unfoldr g where g [] = Nothing g xs = Just (splitAt 64 xs) getWord32s :: [Word8] -> [Word32] getWord32s s = map f [0..15] where f i = foldl (+) 0 $ map (\n -> toEnum (fromEnum (s!!(i*4+n))) `shiftL` (fromIntegral (8 * (3-n)))) [0..3] blockWord32sIn512 :: [Word8] -> [[Word32]] blockWord32sIn512 = (map getWord32s) . blockWord8sIn512 . pad -- Word120 -> Word512 -> Word120 hashOnce ss a = ss + oneBlock ss a hash = foldl' hashOnce ss . blockWord32sIn512 convert :: String -> [Word8] convert = map (fromIntegral . ord) short :: [Word8] short = convert "abc" message :: [Word8] message = convert "abcdbcdecdefdefgefghfghighijhijkijkljklmklmnlmnomnopnopq" performance n = (convert . take n . repeat) 'a' test n = mapM_ (putStrLn . show . hash) [short, message, performance n] main = do progName <- getProgName args <- getArgs if length args /= 1 then putStrLn ("Usage: " ++ progName ++ " <testSize>") else test (read (args!!0))

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Alternate instance Show (Maybe a)?
by Sergey Zaharchenko 04 Feb '07

04 Feb '07

Hello list, Suppose I want show Nothing to return "", and show (Just foo) return show foo. I don't seem to be able to. Looks like I either have to use some other function name, like `mShow', or have to import Prelude hiding Maybe, reimplement Maybe, write all the other useful instances (Functor, Monad) for it, etc. Not particularly hard, but looks ugly. Isn't there a better solution? I recall some discussion about this, but can't find it in the archives... TIA, -- DoubleF No virus detected in this message. Ehrm, wait a minute... /kernel: pid 56921 (antivirus), uid 32000: exited on signal 9 Oh yes, no virus:)

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