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Animated line art
by Andrew Coppin 08 Dec '08

08 Dec '08

So, the muse has taken me. I'm going to attempt to produce some animated mathematical drawings involving lines and curves. Gtk2hs has a Cairo binding that should make rendering the stuff fairly straight-forward. So no problems there. Now, what I *could* do is write a new Haskell program for each drawing I want, hard-coding in the necessary imperative loops for updating coordinates, looping over multiple lines, etc. But that wasn't be very Haskell, would it? ;-) It seems that the "correct" course of action is to design a DSL for declaratively describing animated line art. Does anybody have ideas about what such a thing might look like?

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Is unsafePerformIO safe here?
by John Ky 08 Dec '08

08 Dec '08

Hi, Is the following safe? moo :: TVar Int moo = unsafePerformIO $ newTVarIO 1 I'm interested in writing a stateful application, and I wanted to start with writing some IO functions that did stuff on some state and then test them over long periods of time in GHCi. I was worried I might be depending on some guarantees that aren't actually there, like moo being discarded and recreated inbetween invocations of different functions. Thanks, -John

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Haskell haikus
by Gwern Branwen 08 Dec '08

08 Dec '08

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA512 Hi everyone. So today I finally got around to something long on my todo list - a compilation of all the Haskell haikus I've seen around! It is at http://haskell.org/haskellwiki/Haiku But I'm afraid I only have 5, and Google doesn't turn up any more. So: does anybody have a haiku I missed? Or even better, is anyone feeling poetically inspired tonight? :) - -- gwern -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (GNU/Linux) iEYEAREKAAYFAkk5ttoACgkQvpDo5Pfl1oJ+ygCfdSSBmbgyoOwkG53rKahF2Su1 84UAoIOrxGwe3u+WwnKxvKulq1AT4IJS =+2kH -----END PGP SIGNATURE-----

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Could FDs help usurp an ATs syntactic restriction?
by Nicolas Frisby 08 Dec '08

08 Dec '08

>From the error below, I'm inferring that the RHS of the associated type definition can only contain type variables from the instance head, not the instance context. I didn't explicitly see this restriction when reading the GHC/Type_families entry. Could perhaps the "a b -> bn" functional dependency of the TypeEq class lift this restriction for bn? This isn't my ball park, but that idea has my hopes up :). <haskell> {-# LANGUAGE TypeFamilies #-} import TypeEq -- Attempting to encapsulate TypeEq behind an associated type. class EQ a b where type BN a b instance TypeEq a b bn => EQ a b where type BN a b = bn </haskell> results in an error <ghci> /tmp/Test.hs:9:16: Not in scope: type variable `bn' Failed, modules loaded: none. </ghci>

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ANN: permutation-0.2
by Patrick Perry 08 Dec '08

08 Dec '08

Hi Everyone, I've uploaded a new version of the permutation library to hackage. Here is the package description: This library includes data types for storing permutations. It implements pure and impure types, the latter which can be modified in-place. The main utility of the library is converting between the linear representation of a permutation to a sequence of swaps. This allows, for instance, applying a permutation or its inverse to an array with O(1) memory use. . Much of the interface for the library is based on the permutation functions in the GNU Scientific Library (GSL). Here's the url: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/permutation Patrick

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[Announce] TTTAS (with excuse for second attempt to post)
by S. Doaitse Swierstra 07 Dec '08

07 Dec '08

We are pleased to announce the availability of the package "TTTAS", which contains the code associated with our paper at the coming TLDI workshop: \@inproceedings{ BSV09, author = {Arthur Baars and S. Doaitse Swierstra and Marcos Viera}, title = {Typed Transformations of Typed Abstract Syntax}, booktitle = {TLDI '09: fourth ACM SIGPLAN Workshop on Types in Language Design and Implementation}, year = {2009}, location = {Savannah, Georgia, USA}, publisher = {ACM}, address = {New York, NY, USA}, } For more information see: http://www.cs.uu.nl/wiki/bin/view/Center/TTTAS Arthur Baars Marcos Viera Doaitse Swierstra

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Dr Dobbs: Time to get good at functional programming
by Tim Wawrzynczak 07 Dec '08

07 Dec '08

Amen to that. People who haven't really given a fair look at functional langauges (Haskell in particular) seem to have a very poor conception of them. Again, this seems to especially be a problem with Haskell (i.e., the whole "monads are hard" thing)... If this is where people are getting their information from, it would definitely behoove the Haskell community to update its image to further Haskell and FP in general :) On Sun, Dec 7, 2008 at 12:11 PM, Don Stewart <dons(a)galois.com> wrote: > jason.dusek: > > Too bad they didn't pimp Haskell as practical. > > It looked like an archaic view of Haskell based on reading wikipedia, > imo. Perhaps we should take charge of the wikipedia page, if it is that > influential. > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe >

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Data.Map.fromListWith
by Paul Johnson 07 Dec '08

07 Dec '08

I've just been looking at the Data.Map function "fromListWith". According to the docs, it has the type: * fromListWith* :: Ord <http://www.haskell.org/ghc/docs/latest/html/libraries/base/Data-Ord.html#t%…> k => (a -> a -> a) -> [(k, a)] -> Map <http://www.haskell.org/ghc/docs/latest/html/libraries/containers/Data-Map.h…> k a I'd have thought that a better type would be * fromListWith* :: Ord <http://www.haskell.org/ghc/docs/latest/html/libraries/base/Data-Ord.html#t%…> k => (a -> b -> b) -> [(k, a)] -> Map <http://www.haskell.org/ghc/docs/latest/html/libraries/containers/Data-Map.h…> k b This wouldn't break any existing code, but would allow things like "fromListWith (:)" to do the Right Thing. Would this be a sensible change (along with the other "with" functions in the module). Paul.

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SDL program under MinGW
by sam lee 07 Dec '08

07 Dec '08

Hi. I am using Windows Vista. I installed the following: - ghc 6.8.3 (using official Windows binary installer) - MinGW (from http://nuwen.net/mingw.html) - SDL binding (from http://hackage.haskell.org/cgi-bin/hackage-scripts/package/SDL) I am trying to compile the following program: module Main where import qualified Graphics.UI.SDL as SDL main = do SDL.init [SDL.InitEverything] SDL.quit I get the following error: C:\Users\client\code\sandbox>ghc --make Example.hs Linking Example.exe ... C:\MinGW\lib/libSDLmain.a(SDL_win32_main.o)(.text+0x409):SDL_win32_main.c: undefined reference to `SDL_main' According to SDL faq (http://www.libsdl.org/faq.php?action=listentries&category=4#48) I should use "int main(int argc, char *argv[])", not "int main()" nor "WinMain()". Can anyone compile the above snippet on windows machine? I am using SDL library that is shipped with MinGW distribution that I'm using. I also recompiled SDL haskell binding with official SDL windows binary (http://www.libsdl.org/release/SDL-devel-1.2.13-mingw32.tar.gz) But I get the same undefined reference to SDL_main linker error. Do I need to have specific main IO action so that SDL would work in Haskell? Thank you. Sam.

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pbkdf2 on hackage Re: Re[2]: [Haskell-cafe] Password hashing
by Thomas Hartman 07 Dec '08

07 Dec '08

http://hackage.haskell.org/cgi-bin/hackage-scripts/package/PBKDF2 Since no one took up my code review request I just did the best I could and uploaded to hackage. There were indeed some mistakes in my initial post, fixed now. (Code review is still wished, though!) Alas, documentation doesn't build with hackage, altough it does for me locally. (Seems like almost everything I do these days -- what am I doing wrong?!) Also I'm open to folding this into a more established crypto package if there are any takers... psst, dominic. Also, dominic, shouldn't your crypto package be added to category Cryptography (a cabal file change) so it lists aside the other crypto packages? thanks, thomas. 2008/11/26 Thomas Hartman <tphyahoo(a)gmail.com>: > Sorry about the hideous formatting above. Reattached as a text file. > > t. > > 2008/11/26 Thomas Hartman <tphyahoo(a)gmail.com>: >> OK, I went ahead and implemented pbkdf2, following the algorithm >> linked to by bulat and Michael. >> >> If there are any crypto gurus who can code-review this I would be much >> obliged, and when I'm confident enough that this does the right thing >> I'll put it up on hackage. >> >> I don't do much crypto so this *definitely* needs a review before it >> becomes a library? >> >> How's this looks, cafe? >> >> Thanks! >> >> Thomas. >> >> >> {-# LANGUAGE ScopedTypeVariables #-} >> module Crypto.PBKDF2 (pbkdf2, pbkdf2') where >> >> import qualified Data.ByteString.Char8 as B >> import qualified Data.ByteString.Lazy as L >> import GHC.Word >> import Control.Monad (foldM) >> import Random >> import Data.Digest.SHA512 (hash) >> import Data.Word >> import Data.Bits >> import Data.Binary >> >> newtype Password = Password [Word8] >> newtype Salt = Salt [Word8] >> newtype HashedPass = HashedPass [Word8] >> deriving Show >> {- | A reasonable default for rsa pbkdf2? Actually I'm not really >> sure, ask folk with more experience. >> >>> pbkdf2 = pbkdf2' prfSHA512 512 512 512 >> -} >> t = pbkdf2 ( Password . toWord8s $ "meh" ) ( Salt . toWord8s $ "moo" ) >> pbkdf2 :: Password -> Salt -> HashedPass >> pbkdf2 = pbkdf2' prfSHA512 512 512 512 >> >> {- | Password Based Key Derivation Function, from RSA labs. >> >>> pbkdf2' prf hlen cIters dklen (Password pass) (Salt salt) >> -} >> pbkdf2' :: ([Word8] -> [Word8] -> [Word8]) -> Integer -> Integer -> >> Integer -> Password -> Salt -> HashedPass >> pbkdf2' prf hlen cIters dklen (Password pass) (Salt salt) >> | dklen > ( (2^32-1) * hlen) = error $ "pbkdf2, (dklen,hlen) : " ++ >> (show (dklen,hlen)) >> | otherwise = >> let --l,r :: Int >> l = ceiling $ (fromIntegral dklen) / (fromIntegral hlen ) >> r = dklen - ( (l-1) * hlen) >> ustream :: [Word8] -> [Word8] -> [[Word8]] >> ustream p s = let x = prf p s >> in x : ustream p x >> --us :: Integer -> [[Word8]] >> us i = take (fromIntegral cIters) $ ustream pass ( salt `myor` >> ((intToFourWord8s i) )) >> --f :: [Word8] -> [Word8] -> Integer -> Integer -> [Word8] >> f pass salt cIters i = foldr1 myxor $ us i >> ts :: [[Word8]] >> ts = map (f pass salt cIters) ( [1..l] ) >> in HashedPass . take (fromIntegral dklen) . concat $ ts >> >> -- The spec says >> -- Here, INT (i) is a four-octet encoding of the integer i, most >> significant octet first. >> -- I'm reading from the right... is this the right thing? >> toWord8s x = L.unpack . encode $ x >> >> --intToFourWord8s :: Integer -> [Word8] >> intToFourWord8s i = let w8s = toWord8s $ i >> in drop (length w8s -4) w8s >> >> myxor :: [Word8] -> [Word8] -> [Word8] >> myxor = zipWith xor >> >> myor :: [Word8] -> [Word8] -> [Word8] >> myor = zipWith (.|.) >> >> prfSHA512 :: [Word8] -> [Word8] -> [Word8] >> prfSHA512 x y = hash $ x ++ y >> >> >> 2008/11/26 John Meacham <john(a)repetae.net>: >>> What you are using there is not a salt, but rather a secret key. The >>> important thing about a salt is that it is different for _every user_. >>> and you actually store the salt unhashed along with the hash. (it is not >>> secret information). A salt protects against a dictionary attack, for >>> instance, you might have a dictionary of hash's and the common passwords >>> they go to but if you add a 32 bit salt, you would need 2^32 entries for >>> each dictionary word, making such an attack unworkable. You can also >>> trivially tell if two users have the _same_ password just by comparing >>> the hashes without a salt. >>> >>> John >>> >>> -- >>> John Meacham - ⑆repetae.net⑆john⑈ >>> _______________________________________________ >>> Haskell-Cafe mailing list >>> Haskell-Cafe(a)haskell.org >>> http://www.haskell.org/mailman/listinfo/haskell-cafe >>> >> >

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