February 2007 - Haskell-Cafe

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 05 Feb '07

05 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 05 Feb '07

05 Feb '07

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Another Space Leak
by Dominic Steinitz 05 Feb '07

05 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 05 Feb '07

05 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 05 Feb '07

05 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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The usage of runghc ?
by keepbal 04 Feb '07

04 Feb '07

I tried to install haskell-fastcgi ( http://www.cs.chalmers.se/~bringert/darcs/haskell-fastcgi/ ). >runghc Setup.hs configure --prefix=$HOME/extra >runghc -I$HOME/extra/include Setup.hs build Preprocessing library fastcgi-2006.10.9... FastCGI.hsc:50:21: error: fcgiapp.h: No such file or directory compiling Network/FastCGI_hsc_make.c failed command was: ghc -c Network/FastCGI_hsc_make.c -o Network/FastCGI_hsc_make.o Setup.hs: got error code while preprocessing: Network.FastCGI >runghc --help runghc: syntax: runghc [-f GHCPATH] [GHC-ARGS] FILE ARG... ?

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Proposal for allowing more use of layout to avoid parentheses and commas
by Brian Hulley 04 Feb '07

04 Feb '07

Hi, Following a recent thread on the Haskell' mailing list about the nusiance of having to deal with commas in tuples (when cutting and pasting things to re-order the elements there's always a pesky comma left over in the wrong place), I've written up a proposal for a very simple syntax tweak that would allow you to use the layout rule for function arguments, tuple/list/record contents etc for some future version of Haskell at http://www.haskell.org/haskellwiki/Accessible_layout_proposal This post is not intended to spark a lot of discussion just to point out the existence of the page for anyone interested. I've also added a link to all the new proposals from http://www.haskell.org/haskellwiki/Future . (If I don't reply to any follow up posts to this thread it's not because I'm ignoring them. It will just be because I have to try to get down to actually writing more of my program in the next few weeks, and I find thinking up ideas and reading posts, books, cooking, shopping, watching dvds etc, is infinitely more diverting than the painstakingly hard work of actual coding (though of course it's great in the rare occasions when things fall into place) ... ;-)) Brian. -- http://www.metamilk.com

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(a -> [b]) vs. [a -> b]
by Chad Scherrer 03 Feb '07

03 Feb '07

Are (a -> [b]) and [a -> b] isomorphic? I'm trying to construct a function f :: (a -> [b]) -> [a -> b] that is the (at least one-sided) inverse of f' :: [a -> b] -> a -> [b] f' gs x = map ($ x) gs It seems like it should be obvious, but I haven't had any luck with it yet. Any help is greatly appreciated. Thanks, Chad

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