- Haskell-Cafe - Haskell.org

ANNOUNCE: feldspar-language-0.2, feldspar-compiler-0.2
by Emil Axelsson 16 Mar '10

16 Mar '10

We are happy to announce the new release of Feldspar and its compiler! http://feldspar.sourceforge.net/ Feldspar is an embedded domain-specific language for digital signal processing. It is developed as a joint project with Ericsson, ELTE university and Chalmers university. This is an intermediate release to make some of our ongoing work available. The most user-visible change from the previous version is that the vector types have got much simpler, leading to much simpler programs. There have also been some substantial changes under the hood: Most notably, the compiler has a completely new structure which allows defining various optimizations as plugins. The examples available are still very limited. We hope to make a new release quite soon with a reworked tutorial and many more examples. / Emil

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how to listen on a specific IP using the network library
by Jeremy Shaw 16 Mar '10

16 Mar '10

Hello, I would really like to modify happstack so that you can specific what IP address to listen on. So I think I want a function like: listenOnAddr :: SockAddr -> IO Socket The problem is that the user might want to specify IPv4 or IPv6 address. But support for IPv6 is only conditionally compiled into the network library. I can not figure out how to write my code so that it will compile regardless of whether network was compiled with ipv6 enabled. I got this far: -------------------------------- import qualified Control.Exception as Exception import Network.BSD (getProtocolNumber) import Network.Socket listenOnAddr :: Family -> SocketType -> SockAddr -> IO Socket listenOnAddr fam typ sockAddr = do proto <- getProtocolNumber "tcp" Exception.bracketOnError (socket fam typ proto) (sClose) (\sock -> do setSocketOption sock ReuseAddr 1 bindSocket sock sockAddr listen sock maxListenQueue return sock ) --------------------------------------- But I am not sure how to modify it to calculate 'fam' and 'typ' from 'sockAddr' with out making my code depend on IPv6 being enabled. If I was adding this function directly to the network package, there would be no problem. I could just use: #if defined(IPV6_SOCKET_SUPPORT) #endif But in a 3rd party library IPV6_SOCKET_SUPPORT is not defined. I could copy the autoconf code into my library -- but there is no guarantee that my library and the network library were compiled with the same value for IPV6_SOCKET_SUPPORT. In happstack we use a really horrible trick involving template haskell where we see if the SockAddrInet6 constructor exists at compile time and conditionally compile different versions of the code that way. But it is really ugly. We defined supportsIPv6 here: http://patch-tag.com/r/mae/happstack/snapshot/current/content/pretty/happst… And then use it in acceptLite here: http://patch-tag.com/r/mae/happstack/snapshot/current/content/pretty/happst… It wouldn't be that bad if we could actually use the [| |] mechanism. But we can't because it won't compile when ipv6 support is not enabled due to '(S.SockAddrInet6 _ _ ha _) -> showHostAddress6 ha'. Any suggestions? At this point I am thinking that the best solution is to add a new function to network, since it is not trivial to do it anywhere else in a portable way, and it seems like a fairly useful and common operation? - jeremy

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Can't cabal install darcs because hashed-storage needs 'System'
by Daniel McAllansmith 16 Mar '10

16 Mar '10

Hello. Short story: $ cabal install --global --constraint="old-time>=1.0.0.3.1" --reinstall -v darcs /tmp/hashed-storage-0.4.71127/hashed-storage-0.4.7/Setup.hs:13:7: Could not find module `System': Use -v to see a list of the files searched for. This is using GHC 6.12.1, cabal-install 0.8.0 and Cabal 1.8.0.2 How do I get darcs installed? Longer story: I've been trying to install darcs 2.4 built against a patched version of old- time, 1.0.0.3.1 is effectively 1.0.0.4 just that it's patched locally because 1.0.0.4 hasn't been released to hackage yet. I ran into various problems with global vs. user packages, no version of base being valid and a few other bits and pieces. So I am trying a global install and have had to reinstall Cabal (and various other packages), presumably because it was built against old-time 1.0.0.3. Looking at the hashed-storage code it imports System (system, exitWith). Is that old base-3 code? The debug messages show: selecting base-3.0.3.2 (installed) and 4.2.0.0 (installed) and /usr/local/bin/ghc --make /tmp/hashed-storage-0.4.71127/hashed- storage-0.4.7/Setup.hs -o /tmp/hashed-storage-0.4.71127/hashed- storage-0.4.7/dist/setup/setup -odir /tmp/hashed-storage-0.4.71127/hashed- storage-0.4.7/dist/setup -hidir /tmp/hashed-storage-0.4.71127/hashed- storage-0.4.7/dist/setup -i -i/tmp/hashed-storage-0.4.71127/hashed- storage-0.4.7 -package Cabal-1.8.0.2 so I'm not really sure what version of base it's actually trying to compile hashed-storage against. Any further information I can provide? Thanks Dan

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ANNOUNCE: tupleinstances-0.0.1
by Diego Echeverri 16 Mar '10

16 Mar '10

Hello. TupleInstances It's a really small library that provides instances for Functor, Applicative, Foldable and Traversable for tuples of the form (a,a...a). It uses newtypes to wrap the tuples and Template Haskell to generate the code. Here's an example of these instances in action: example6 :: (Int, Int) -> [(Int, Int)] example6 p = map unT $ liftA2 (+) (T2 p) <$> moves where moves = tail $ traverse (\x -> [0,x+1,x-1]) (pure 0 :: T2 Int) -- > Result with (1,1): [(1,2),(1,0),(2,1),(2,2),(2,0),(0,1),(0,2),(0,0)] More examples here: http://github.com/diegoeche/tupleinstances/raw/master/README PS: This is also my first package uploaded to Hackage. I would appreciate any feedback. Best Regards, Diego Echeverri

1 0

definition of sum
by TeXitoi 16 Mar '10

16 Mar '10

After programming as an exercice the sum function, my version is faster than the Data.List's version. Looking at the source code, Data.List uses a foldl and not a foldl'. foldl' seems faster and allows to use very big lists. So, why is foldl used by Data.List for sum? -- Guillaume Pinot http://www.irccyn.ec-nantes.fr/~pinot/ « Les grandes personnes ne comprennent jamais rien toutes seules, et c'est fatigant, pour les enfants, de toujours leur donner des explications... » -- Antoine de Saint-Exupéry, Le Petit Prince () ASCII ribbon campaign -- Against HTML e-mail /\ http://www.asciiribbon.org -- Against proprietary attachments

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HTTP package freezes on Windows 7
by Phil 15 Mar '10

15 Mar '10

Hi, I'm using GHC 6.12.1 on Windows 7. I've built the latest Network package using Haskell's MinGW and installed HTTP package on top of this. The code below builds fine, but on execution it just sits there grabbing ever increasing amounts of memory. It's a simplified call that I've got working fine in Linux. Is this a known issue? Anyone else had success using HTTP from Windows? Thanks, Phil. import qualified Network.HTTP as HTTP main :: IO () main = do x <- HTTP.simpleHTTP(HTTP.getRequest "http://maps.google.com/maps/api/geocode/json?address=London&sensor=false") print x

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How to do the "permutation and combination" thing?
by Magicloud Magiclouds 15 Mar '10

15 Mar '10

Hi, For example, I have this: list1 = [a, b, c] list2 = [d, e, f] list3 = [g, h, i] Now I want: [ [(a, d, g), (b, e, h), (c, f, i)] , ... ] -- a list that contains all the combinations. How to do it pretty? Thanks. -- 竹密岂妨流水过山高哪阻野云飞

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How to define instance for type synonym with parameter.
by Vasyl Pasternak 15 Mar '10

15 Mar '10

Hello, I am start with example. Suppose I have the following type synonym: type SomeMonad a = ErrorT String (ReaderT String IO) a this is monad, and I want to make it instance of Applicative, so, the obvious way is to write the following: instance Applicative SomeMonad where pure = return (<*>) = ap GHCi warns me, that I have to use -XTypeSynonymInstances option to allow this construction, but than I have following error: Type synonym `SomeMonad' should have 1 argument, but has been given 0 In the instance declaration for `Applicative SomeMonad' Neither `instance Applicative (SomeMonad a)` nor `instance Applicative SomeMonad a` help. But works the following: instance Applicative (ErrorT String (ReaderT String IO)) where pure = return (<*>) = ap Which is the same (from my point of view). Could anyone tell me what is going on, and how to declare SomeMonad as instance of Applicative ? Thanks, Vasyl

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Space leak
by Arnoldo Muller 15 Mar '10

15 Mar '10

Hello, I am learning haskell and I found a space leak that I find difficult to solve. I've been asking at #haskell but we could not solve the issue. I want to lazily read a set of 22 files of about 200MB each, filter them and then I want to output the result into a unique file. If I modify the main function to work only with one input file, the program runs without issues. I will call this version A. Version B uses a mapM_ to iterate over a list of filenames and uses appendFile to output the result of filtering each file. In this case the memory usage grows sharply and quickly (profiles show constant memory growth). In less than a minute, memory occupation will make my system hang with swapping. This is version B: ------------------------------- Program B -------------------------------------------------------------------------------------------------------------------- import Data.List import System.Environment import System.Directory import Control.Monad -- different types of chromosomes data Chromosome = C1 | C2 | C3 | C4 | C5 | C6 | C7 | C8 | C9 | C10 | C11 | C12 | C13 | C14 | C15 | C16 | C17 | C18 | C19 | CX | CY | CMT deriving (Show) -- define a window type Sequence = [Char] -- Window data data Window = Window { sequen :: Sequence, chrom :: Chromosome, pos :: Int } -- print a window instance Show Window where show w = (sequen w) ++ "\t" ++ show (chrom w) ++ "\t" ++ show (pos w) -- Reading fasta files with haskell -- Initialize the main = do -- get the arguments (intput is [input, output, windowSize] <- getArgs -- get directory contents (only names) names <- getDirectoryContents input -- prepend directory let fullNames = filter isFastaFile $ map (\x -> input ++ "/" ++ x) names let wSize = (read windowSize)::Int -- process the directories mapM (genomeExecute output wSize filterWindow) fullNames -- read the files one by one and write them to the output file genomeExecute :: String -> Int -> (Window -> Bool) -> String -> IO () genomeExecute outputFile windowSize f inputFile = do fileData <- readFile inputFile appendFile outputFile $ fastaExtractor fileData windowSize f -- isFastaFile :: String -> Bool isFastaFile fileName = isSuffixOf ".fa" fileName -- fasta extractor (receives a Fasta String and returns a windowed string ready to be sorted) -- an example on how to compose several functions to parse a fasta file fastaExtractor :: String -> Int -> (Window -> Bool) -> String fastaExtractor input wSize f = printWindowList $ filter f $ readFasta wSize input -- MAIN FILTER that removes N elements from the strings! filterWindow :: Window -> Bool filterWindow w = not (elem 'N' (sequen w)) -- print a window list (the printing makes it ready for output as raw data) printWindowList :: [Window] -> String printWindowList l = unlines $ map show l -- read fasta, remove stuff that is not useful from it -- removes the readFasta :: Int -> [Char] -> [Window] readFasta windowSize sequence = -- get the header let (header:rest) = lines sequence chr = parseChromosome header in -- We now do the following: -- take window create counter remove newlines map (\(i, w) -> Window w chr i) $ zip [0..] $ slideWindow windowSize $ filter ( '\n' /= ) $ unlines rest slideWindow :: Int -> [Char] -> [[Char]] slideWindow _ [] = [] slideWindow windowSize l@(_:xs) = take windowSize l : slideWindow windowSize xs -- Parse the chromosome from a fasta comment -- produce a more compact chromosome representation parseChromosome :: [Char] -> Chromosome parseChromosome line | isInfixOf "chromosome 1," line = C1 | isInfixOf "chromosome 2," line = C2 | isInfixOf "chromosome 3," line = C3 | isInfixOf "chromosome 4," line = C4 | isInfixOf "chromosome 5," line = C5 | isInfixOf "chromosome 6," line = C6 | isInfixOf "chromosome 7," line = C7 | isInfixOf "chromosome 8," line = C9 | isInfixOf "chromosome 10," line = C10 | isInfixOf "chromosome 11," line = C11 | isInfixOf "chromosome 12," line = C12 | isInfixOf "chromosome 13," line = C13 | isInfixOf "chromosome 14," line = C14 | isInfixOf "chromosome 15," line = C15 | isInfixOf "chromosome 16," line = C16 | isInfixOf "chromosome 17" line = C17 | isInfixOf "chromosome 18" line = C18 | isInfixOf "chromosome 19" line = C19 | isInfixOf "chromosome X" line = CX | isInfixOf "chromosome Y" line = CY | isInfixOf "mitochondrion" line = CMT | otherwise = error "BAD header" -------------------------------- End of program B ------------------------------------------------------------------------------------------------ -------------------------------- Program A --------------------------------------------------------------------------------------------------------- If instead of the main function given above I use the following main function to process only one input file, things work OK for even the largest files. Memory usage remains constant in this case. main = do -- get the arguments [input, output, windowSize] <- getArgs -- keep the input stream inpStr <- readFile input let wSize = (read windowSize)::Int writeFile output $ fastaExtractor inpStr wSize filterWindow It is not easy for me to see why is Haskell keeping data in memory. Do you have any idea why program B is not working? Thank you for your help! Arnoldo Muller

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Happstack basic question
by Dmitry V'yal 15 Mar '10

15 Mar '10

Hello haskellers, I want to host a simple happstack application behind a reverse proxy. So ideally would be to bind it to localhost only. According to http://hackage.haskell.org/packages/archive/happstack-server/0.4.1/doc/html… Conf datatyle has only Port field. Does it mean, there is currently no way to prevent binding happstack to all available interfaces? Regards, Dmitry

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darcs hacking sprint (ZuriHac) info!
by Eric Kow 15 Mar '10

15 Mar '10

Hi everybody, Just some quick information for those of you who are interested in working on Darcs at ZuriHac Pre-sprint meeting - Fri 12:00; pizzeria ----------------------------------------- We'll be meeting for lunch at Friday noon at the Pizzeria Santa Lucia Niederdorf (Marktgasse 21), near the City Backpacker hostel. Details on http://wiki.darcs.net/Sprints/2010-03 This will be a great chance for introductions (especially for new or potential Darcs hackers). On the agenda: - prioritising ProbablyEasy bugs for new Darcs hackers - plans for the sprint (news, other meetings, discussions, etc) Get your laptops ready! ----------------------- You'll have more fun if you can hit the ground running, so please make sure you can do all of these things: 1. darcs get --lazy http://darcs.net 2. cabal configure; cabal build 3. darcs send (your patch should wind up on the tracker) #3 is especially important. Here's the quick start 3a. create a test patch (see http://darcs.net/report.html ) 3b. see http://wiki.darcs.net/Msmtp 3c. darcs send 3d. wait 10 minutes 3e. check the patch tracker http://bugs.darcs.net (Patches > Show Open) Travel reimbursements possible ------------------------------ Thanks to a successful fundraising effort, we will be able to reimburse travel costs for folks working on Darcs. Do let me know if you're interested, and please save your receipts! If you have electronic tickets, I think that's fine (perhaps even better); please email them to me. More information on the wiki --------------------------- Information about the sprint, including meetings and maps will be on http://wiki.darcs.net/Sprints/2010-03 It may be a good idea to darcs get --lazy http://wiki.darcs.net before you leave so that you have an up to date version of the wiki :-) Thanks to our donors for making this sprint possible and to Johan and the Zurich/Google crew for setting up this massive hackathon. Whee! -- Eric Kow <http://www.nltg.brighton.ac.uk/home/Eric.Kow> PGP Key ID: 08AC04F9

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ANN: CPSA - Cryptographic Protocol Shapes Analyzer
by John D. Ramsdell 15 Mar '10

15 Mar '10

The Cryptographic Protocol Shapes Analyzer (CPSA) has been released on Hackage at <http://hackage.haskell.org/package/cpsa>. CPSA attempts to enumerate all essentially different executions possible for a cryptographic protocol. We call them the shapes of the protocol. Naturally occurring protocols have only finitely many, indeed very few shapes. Authentication and secrecy properties are easy to determine from them, as are attacks and anomalies. For each input problem, the CPSA program is given some initial behavior, and it descovers what shapes are compatible with it. Normally, the initial behavior is from the point of view of one participant. The analysis reveals what the other participants must have done, given the participant's view. We are working towards a version of CPSA with the property that whenever it successfully terminates, every possible execution is described by its output. However, the current implementation occasionally fails to find some executions. The package contains a set of programs used to perform and display the analysis. Program documentation is in the doc directory in the source distribution, and installed in the package's data directory. You can locate the package's data directory by searching for the file cpsauser.html. New users should study the documentation and the sample inputs in the data directory. The theory and algorithm used by CPSA was developed with the help of Joshua D. Guttman, John D. Ramsdell, Jon C. Herzog, Shaddin F. Doghmi, F. Javier Thayer, and Paul D. Rowe. John D. Ramsdell implemented the algorithm in Haskell.

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Using regexps to filter data
by michael rice 15 Mar '10

15 Mar '10

Not sure I'm even in the right neighborhood with this. Need to screen for integer data. Am I going about this correctly? Michael ====== [michael@localhost ~]$ ghci GHCi, version 6.10.4: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer ... linking ... done. Loading package base ... linking ... done. Prelude> :m + Text.Regex.Base.RegexLike Prelude Text.Regex.Base.RegexLike> let r = makeRegex "[+-]?[0-9]+" <interactive>:1:8: No instance for (RegexMaker regex compOpt execOpt [Char]) arising from a use of `makeRegex' at <interactive>:1:8-30 Possible fix: add an instance declaration for (RegexMaker regex compOpt execOpt [Char]) In the expression: makeRegex "[+-]?[0-9]+" In the definition of `r': r = makeRegex "[+-]?[0-9]+" Prelude Text.Regex.Base.RegexLike>

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Binaries using shared libraries with cabal-install
by Mathijs Kwik 15 Mar '10

15 Mar '10

Hi all, I'm using cabal-install 0.8.0 on ghc 6.12.1 on linux I switched on shared library support on cabal. Does this enable -dynamic and -fPIC during compilation and -dynamic -shared during linking? Or does it work a little differently? I noticed everything works for libraries. .so files get created, and using ldd on them shows they depend on other haskell shared libraries. But for binaries, it seems it still compiles them with everything included. ldd'ing them shows no haskell-library dependencies and their size is quite big as well. Is it possible to tell cabal-install I want binaries to use shared libs instead? And is there a way to specify which RTS to link binaries with? (debug, threaded, normal) Or a way to defer linking to an RTS so I can do this on execution using LD_PRELOAD ? Thanks for any help Mathijs

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#haskell-web, anyone ?
by Simon Michael 15 Mar '10

15 Mar '10

We just had a big old web dev discussion in #darcs, which made me want to hang out in #haskell-web and hear more of the same. I think it existed briefly and died, but maybe it's time to try again ? Normally I don't like removing interesting chat from the main channel, but #haskell is often pretty noisy/theoretical/general/random and I think there might be enough folks interested in having this more practical, topical channel. If you are one, put #haskell-web on auto-join in your irc client and let's see how it goes. The topic currently reads "friendly, practical discussion of haskell web app/framework/server development".

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how to user mergeIO
by Brock Peabody 15 Mar '10

15 Mar '10

Hi, I've been trying to use Control.Concurrent.mergeIO to parallelize computation, and can't make it work. In the sample program below, I expect the function 'parallelTest' to be almost twice as fast as 'sequentialTest', and to compute its results in two threads, as implied by the documentation for mergeIO. This is not what happens. If I link my program with the option '-threaded', the running process does have three threads. If I run with the option "+RTS -N2", the process will have 5 threads. In no case does the process appear to be using more than one CPU, and in fact it is slower with the threading options turned on. I'm sure I am doing something obviously (to someone else) wrong. Any ideas? I am running the latest version of Mac OSX on a core2 duo machine with 2 cores, using ghc version 6.10.4. Cheers, Brock My test program follows: {-# OPTIONS_GHC -fglasgow-exts #-} module Main where import Control.Concurrent import Random doSum :: RandomGen g => g -> Int -> Integer doSum g count = let runner curG sum numDone | numDone == count = sum | otherwise = let (newNum :: Integer, newG) = random curG newSum = sum + newNum newNumDone = numDone + 1 in ((runner $! newG) $! newSum) $! newNumDone in runner g 0 0 sequentialTest = do let gen = mkStdGen 0 (g0,g1) = split gen count = 10000000 sum0 = doSum g0 count sum1 = doSum g1 count total = sum0 + sum1 putStrLn $ "total: " ++ show total parallelTest = do let gen = mkStdGen 0 (g0,g1) = split gen count = 10000000 sum0 = doSum g0 count sum1 = doSum g1 count [res0, res1] <- mergeIO [sum0] [sum1] let total = res0 + res1 putStrLn $ "total: " ++ show total main = parallelTest

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Splitting list with predicate
by michael rice 14 Mar '10

14 Mar '10

Is there a library function that will create two lists from one based on a predicate, one list for all elements that satisfy the predicate and one for all that do not? Don't want to reinvent the wheel. Michael

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difficulty getting cabal and macports to play nice
by Carter Schonwald 14 Mar '10

14 Mar '10

Hello, I'm not sure if theres a more specialized list for which this might be appropriate, but cabal (up to date) on snow leopard can't seem to find libraries installed by macports even if i show it where they are (which i have in fact installed the most up to date version of with the macports +universal variant) the version info thats relevant is cabal-install version 0.6.4 using version 1.6.0.3 of the Cabal library here is an example transcript sudo cabal install --extra-lib-dirs=/opt/local/lib --extra-include-dirs=/opt/local/include hieroglyph chart Resolving dependencies... cabal: cannot configure Hieroglyph-3.89. It requires cairo -any, glib -any, gtk >=0.10.0 and gtkglext -any There is no available version of cairo that satisfies -any There is no available version of glib that satisfies -any There is no available version of gtk that satisfies >=0.10.0 There is no available version of gtkglext that satisfies -any is there something obvious that i'm overlooking or is this a funny unfixed corner of cabal?

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First time haskell - parse error!
by boblettoj 14 Mar '10

14 Mar '10

Hi, i am getting an error when trying to compile this part of my program, its my first time using haskell and as lovely as it is it didn't give me very much to go on in the error message! <code>score :: String -> String -> String score [s] [] = false score [s] [g] = if valid 4 g then (s1 ++ s2 ++ s3 ++ s4) where s1 = "Golds " s2 = show (gold s g) s3 = ", Silvers " s4 = show (silver s g) else "Bad Guess"</code> when i try to compile it says: test.hs 63:29: parse error on input 'where' (its the line beginning with 'then') Anybody got any ideas whats going on? thanks! -- View this message in context: http://old.nabble.com/First-time-haskell---parse-error%21-tp27839657p278396… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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ANNOUNCE: Haddock 2.7.0
by David Waern 14 Mar '10

14 Mar '10

-------------------------------------------- -- Haddock 2.7.0 -------------------------------------------- A new version of Haddock, the Haskell documentation tool, is out! -------------------------------------------- -- Changes in version 2.7.0 -------------------------------------------- * Instances can be commented * The Haddock API now exposes more of the internals of Haddock * Bug fixes (most importantly #128) -------------------------------------------- -- Links -------------------------------------------- Homepage: http://www.haskell.org/haddock Hackage page: http://hackage.haskell.org/package/haddock-2.7.0 Bugtracker and wiki: http://trac.haskell.org/haddock Mailing list: haddock(a)projects.haskell.org Code repository: http://code.haskell.org/haddock -------------------------------------------- -- Contributors -------------------------------------------- The following people contributed patches to this release: Isaac Dupree Yitzchak Gale David Waern -------------------------------------------- -- Get Involved -------------------------------------------- We would be very happy to get more contributors. To get involved, start by grabbing the code: http://code.haskell.org/haddock Then take a look at the bug and feature tracker for things to work on: http://trac.haskell.org/haddock

2 1

gtk2hs gtkbuilder
by Andrew U. Frank 14 Mar '10

14 Mar '10

i currently use gtk2hs with libglade (and glade). i understand that the gtkbuilder allows more constructs than libglade. how to use gtkbuilder in gtk2hs? i see that John Millikin has posted a patch for gtk2hs - but i cannot find it and no documentation for its use? can anyone point me to a patched version of gtk2hs and some examples? thank you! andrew

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[Haskell.org Google Summer of Code] trac signup issues
by Marc D. Migge 14 Mar '10

14 Mar '10

Hello, my name is Marc Migge. I would like to sign up as a student for this year's summer of code. Could you please add me to the Trac page using the email address marcmigge(a)gmx.net? Thank you. Best regards, Marc Migge

1 0

Data.Binary.GetT or ... ?
by Juraj Hercek 14 Mar '10

14 Mar '10

Hello, I'm thinking about using Data.Binary to parse binary stream of data. Binary data stream consists of messages which can have one or more (sometimes couple of hundreds) sub-messages. The stream is spitting out data slowly. I would like to parse this data with Data.Binary.Get monad, but I would like to send sub-messages to a STM channel while parsing, so "observers" could handle them during parsing process. I believe I could achieve this with a Data.Binary.GetT transformer, but I'm not aware it exists. Implementing GetT would take me a huge amount of time (I'm not that good haskeller). Splitting processing to message level and sub-message level and handling them by two separate "get"s in IO monad is a possibility, but not really appealing one (at least to me). Is there another (preferably cheap) way of doing what I want? Thanks, Juraj

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[Haskell.org Google Summer of Code] trac signup issues
by Edward Kmett 14 Mar '10

14 Mar '10

It has come to my attention that there is an issue with creating accounts on the summer-of-code trac at the moment. We're diligently working on getting the right people involved to get this fixed. In the meantime, if you want to sign up as a student or mentor for this year's summer of code, please email me with your name and desired contact email address, and I'll make sure your name winds up on the list. I apologize for the inconvenience. -Edward Kmett

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Can't get Regions to show up in HGL
by Brandon Simmons 14 Mar '10

14 Mar '10

I'm having trouble finding example code that uses Regions in the Haskell Graphics Library. But the following gives me a black window when I think it should give me a black window with a square in it: ------------------ START CODE ------------------------------------------ import Graphics.HGL main = runGraphics test test = do w <- openWindow "Test" (100,100) drawInWindow w $ withRGB (RGB 255 255 255) testRegion getLBP w closeWindow w testRegion = regionToGraphic $ rectangleRegion (5,5) (30,30) ------------------ END CODE ------------------------------------------ Am I using it correctly? If I am, then any other help is greatly appreciated. I am on Debian Squeeze using GHC 6.12.1 (thanks debian maintainers!), and using HGL-3.2.0.2 Thanks, Brandon Simmons http://coder.bsimmons.name

1 0

When is a bug GHC's fault/strange STM behaviour
by Michael Lesniak 13 Mar '10

13 Mar '10

Hello, In one of my example programs I have a strange behaviour: it is a very simple taskpool using STM; in pseudocode it's 1. generate data structures 2. initialize data structures 3. fork threads 4. wait (using STM) until the pool is empty and all threads are finished 5. print a final message In very few cases, which depend on the number of threads spawned, the program hangs *after* the final message of step 5 has been printed. "Few cases" means, for example, 50.000 good, terminating runs before it hangs. If you increment the number of spawned threads (to a few hundred or thousands), it hangs much faster. Since forked threads terminate after the main thread terminates (which it should after printing the message), this behaviour is quite unexpected. Since I've experienced strange behaviour in the past which was the fault of my system configuration[1], I am a bit cautious before reporting a bug on GHC's bugtracker, especially since its reproduction is so difficult and random. So my question is how much circumspection is expected/needed before one should enter a bug in the bug tracker? I've tested the attached code on three different systems (with different linux systems, but always GHC 6.12.1 (since it's a bit costly to install the older versions)) and observed the mentioned behaviour. Is this enough to justify a bug report? Or, on the other hand, could someone spot the error in the attached code. Given my history with strange parallel behaviour, I am much more sure that it's the fault of my code, but I can't spot the error and the described behaviour (halting *after* the final message) is really strange. Cheers, Michael [1] http://www.haskell.org/pipermail/haskell-cafe/2010-March/073938.html

3 4

Upgrading to Haskell Platform
by David Place 13 Mar '10

13 Mar '10

Hi: I am running GHC 6.10.4 on Mac OSX 10.6.2. Somehow, I have a broken version of Cabal (1.6.0.3) installed. In order to fix it, I thought I should just upgrade to the Haskell Platform. Is it necessary to uninstall my current GHC first? If, so, how? Thanks you. Cheers, David

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Re: [Haskell-cafe] Space leak
by Arnoldo Muller 13 Mar '10

13 Mar '10

Hello Justin, I tried and what I saw was a constant increase in memory usage. Any particular profiling option that you would use? I do remember that there was a particular option in which the leak would dissapear (for the same amount of work) and that is why I stopped using the profiler. Thanks, Arnoldo On Wed, Mar 10, 2010 at 10:20 PM, Justin Bailey <jgbailey(a)gmail.com> wrote: > Have you use the profiling tools available with GHC? > > http://haskell.org/ghc/docs/latest/html/users_guide/profiling.html > > > On Wed, Mar 10, 2010 at 12:45 PM, Arnoldo Muller > <arnoldomuller(a)gmail.com> wrote: > > Hello, > > > > I am learning haskell and I found a space leak that I find difficult to > > solve. I've been asking at #haskell but we could not solve > > the issue. > > > > I want to lazily read a set of 22 files of about 200MB each, filter them > and > > then I want to output the result into a unique file. > > If I modify the main function to work only with one input file, the > program > > runs without issues. I will call this version A. > > Version B uses a mapM_ to iterate over a list of filenames and uses > > appendFile to output the result of filtering each file. > > In this case the memory usage grows sharply and quickly (profiles show > > constant memory growth). In less than a minute, memory > > occupation will make my system hang with swapping. > > > > This is version B: > > > > ------------------------------- Program B > > > -------------------------------------------------------------------------------------------------------------------- > > import Data.List > > import System.Environment > > import System.Directory > > import Control.Monad > > > > > > -- different types of chromosomes > > data Chromosome = C1 > > | C2 > > | C3 > > | C4 > > | C5 > > | C6 > > | C7 > > | C8 > > | C9 > > | C10 > > | C11 > > | C12 > > | C13 > > | C14 > > | C15 > > | C16 > > | C17 > > | C18 > > | C19 > > | CX > > | CY > > | CMT > > deriving (Show) > > -- define a window > > type Sequence = [Char] > > -- Window data > > data Window = Window { sequen :: Sequence, > > chrom :: Chromosome, > > pos :: Int > > } > > -- print a window > > instance Show Window where > > show w = (sequen w) ++ "\t" ++ show (chrom w) ++ "\t" ++ show (pos > w) > > > > -- Reading fasta files with haskell > > > > -- Initialize the > > main = do > > -- get the arguments (intput is > > [input, output, windowSize] <- getArgs > > -- get directory contents (only names) > > names <- getDirectoryContents input > > -- prepend directory > > let fullNames = filter isFastaFile $ map (\x -> input ++ "/" ++ x) > > names > > let wSize = (read windowSize)::Int > > -- process the directories > > mapM (genomeExecute output wSize filterWindow) fullNames > > > > > > -- read the files one by one and write them to the output file > > genomeExecute :: String -> Int -> (Window -> Bool) -> String -> IO () > > genomeExecute outputFile windowSize f inputFile = do > > fileData <- readFile inputFile > > appendFile outputFile $ fastaExtractor fileData windowSize f > > > > -- > > isFastaFile :: String -> Bool > > isFastaFile fileName = isSuffixOf ".fa" fileName > > > > > > -- fasta extractor (receives a Fasta String and returns a windowed string > > ready to be sorted) > > -- an example on how to compose several functions to parse a fasta file > > fastaExtractor :: String -> Int -> (Window -> Bool) -> String > > fastaExtractor input wSize f = printWindowList $ filter f $ readFasta > wSize > > input > > > > -- MAIN FILTER that removes N elements from the strings! > > filterWindow :: Window -> Bool > > filterWindow w = not (elem 'N' (sequen w)) > > > > -- print a window list (the printing makes it ready for output as raw > data) > > printWindowList :: [Window] -> String > > printWindowList l = unlines $ map show l > > > > -- read fasta, remove stuff that is not useful from it > > -- removes the > > readFasta :: Int -> [Char] -> [Window] > > readFasta windowSize sequence = > > -- get the header > > let (header:rest) = lines sequence > > chr = parseChromosome header > > in > > > > -- We now do the following: > > -- take window create counter > > remove newlines > > map (\(i, w) -> Window w chr i) $ zip [0..] $ slideWindow windowSize > $ > > filter ( '\n' /= ) $ unlines rest > > > > > > slideWindow :: Int -> [Char] -> [[Char]] > > slideWindow _ [] = [] > > slideWindow windowSize l@(_:xs) = take windowSize l : slideWindow > > windowSize xs > > > > > > > > -- Parse the chromosome from a fasta comment > > -- produce a more compact chromosome representation > > parseChromosome :: [Char] -> Chromosome > > parseChromosome line > > | isInfixOf "chromosome 1," line = C1 > > | isInfixOf "chromosome 2," line = C2 > > | isInfixOf "chromosome 3," line = C3 > > | isInfixOf "chromosome 4," line = C4 > > | isInfixOf "chromosome 5," line = C5 > > | isInfixOf "chromosome 6," line = C6 > > | isInfixOf "chromosome 7," line = C7 > > | isInfixOf "chromosome 8," line = C9 > > | isInfixOf "chromosome 10," line = C10 > > | isInfixOf "chromosome 11," line = C11 > > | isInfixOf "chromosome 12," line = C12 > > | isInfixOf "chromosome 13," line = C13 > > | isInfixOf "chromosome 14," line = C14 > > | isInfixOf "chromosome 15," line = C15 > > | isInfixOf "chromosome 16," line = C16 > > | isInfixOf "chromosome 17" line = C17 > > | isInfixOf "chromosome 18" line = C18 > > | isInfixOf "chromosome 19" line = C19 > > | isInfixOf "chromosome X" line = CX > > | isInfixOf "chromosome Y" line = CY > > | isInfixOf "mitochondrion" line = CMT > > | otherwise = error "BAD header" > > > > > > -------------------------------- End of program B > > > ------------------------------------------------------------------------------------------------ > > > > -------------------------------- Program A > > > --------------------------------------------------------------------------------------------------------- > > If instead of the main function given above I use the following main > > function to process only one input file, things work OK for even > > the largest files. Memory usage remains constant in this case. > > > > main = do > > -- get the arguments > > [input, output, windowSize] <- getArgs > > -- keep the input stream > > inpStr <- readFile input > > let wSize = (read windowSize)::Int > > writeFile output $ fastaExtractor inpStr wSize filterWindow > > > > > > It is not easy for me to see why is Haskell keeping data in memory. Do > you > > have any idea why program B is > > not working? > > > > Thank you for your help! > > > > Arnoldo Muller > > > > _______________________________________________ > > Haskell-Cafe mailing list > > Haskell-Cafe(a)haskell.org > > http://www.haskell.org/mailman/listinfo/haskell-cafe > > > > >

2 1

ANNOUNCE: attoparsec-iteratee v0.1
by Gregory Collins 13 Mar '10

13 Mar '10

Hi all, I've just uploaded the first version of the attoparsec-iteratee library to Hackage: http://hackage.haskell.org/package/attoparsec-iteratee It takes applicative parsers written using attoparsec and automagically converts them to iteratees that can parse things from streams in O(1) space. ....and the combination is fast: a prototype HTTP server I'm working on uses this library and can handle as many as 13k reqs/sec on my Macbook. G -- Gregory Collins <greg(a)gregorycollins.net>

2 1

mirroring patch tag
by Thomas Hartman 13 Mar '10

13 Mar '10

http://blog.patch-tag.com/2010/03/13/mirroring-patch-tag/ cheers, thomas.

1 0

generalized newtype deriving allows the definition of otherwise undefinable functions
by Wolfgang Jeltsch 13 Mar '10

13 Mar '10

Hello, some time ago, it was pointed out that generalized newtype deriving could be used to circumvent module borders. Now, I found out that generalized newtype deriving can even be used to define functions that would be impossible to define otherwise. To me, this is surprising since I thought that generalized newtype deriving was only intended to save the programmer from writing boilerplate code, not to extend expressiveness. Have a look at the following code: > {-# LANGUAGE > GeneralizedNewtypeDeriving, > MultiParamTypeClasses, > FlexibleInstances > #-} > > class Iso a b where > > conv :: item a -> item b > > instance Iso a a where > > conv = id > > newtype Wrapped a = Wrap a deriving (Iso a, Show) Now any value whose type contains some type t can be converted into a value of the type that you get if you replace t by Wrap t. Here is some code to demonstrate this for binary operations: > newtype BinOp a = BinOp (a -> a -> a) > > convBinOp :: (a -> a -> a) -> (Wrapped a -> Wrapped a -> Wrapped a) > convBinOp op = let BinOp op' = conv (BinOp op) in op' Now, you can enter convBinOp (*) (Wrap 5) (Wrap 3) into GHCi, and you will get Wrap 15 as the result. The point is, of course, that such conversions are not only possible for binary operations but for arbitrary values and that these conversions are done by a single generic function conv. I don’t think it would be possible to implement conv without generalized newtype deriving. Any thoughts? Best wishes, Wolfgang

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Hackaton: A roof to stay
by Hugo Gomes 12 Mar '10

12 Mar '10

Hello, im planing on going to the hackaton, but the prices in Zurich are unusually high for my tight budget, so i was wondering if there is anyone here that lives there and would allow me to sleep on their couch or on the floor during the hackaton. Is there ? Thanks.

3 2

Google Summer of Code 2010.
by Edward Kmett 12 Mar '10

12 Mar '10

It is that time of year again; the Google Summer of Code is upon us! *Sign Up Information* If you are a student and want to sign up to make $4,500 for hacking on the code you love over the summer or are willing to help out as a mentor, now is the time to act. Please sign up by adding your name to the list at: http://hackage.haskell.org/trac/summer-of-code/wiki/People2010 I have extracted an initial list of interested mentors from Malcolm's earlier inquiry to the cafe and have submitted our initial application to Google. A strong list of potential mentors and students will help bolster our case. Our main wiki entry for the Summer of Code 2010 is now online: http://hackage.haskell.org/trac/summer-of-code/wiki/Soc2010 If you are interested in applying as a student, here are some guidelines: http://hackage.haskell.org/trac/summer-of-code/wiki/StudApply2010 The official deadline for student applications with Google is April 7th, but if you are interested please add your name to the People2010 page above, as soon as possible. *Interested in helping out, but not sure how? * There are a number of ideas that we've been collecting for projects available through the trac http://hackage.haskell.org/trac/summer-of-code/report/1 and which have been collecting over time in a reddit: http://www.reddit.com/r/haskell_proposals/top/ While the reddit is a great place to discuss proposals, we had to choose one mechanism to supply Google with our ideas officially, so please submit proposals <http://hackage.haskell.org/trac/summer-of-code/newticket> to the trac if you can think of something you like to work on, or which would be an appropriately beneficial project for a summer worth of work. *Helping Out Darcs * Haskell.org is going to continue to act as an umbrella organization covering darcs <http://darcs.net/> for the Summer of Code once more. If you are interested in helping them out, they also have a page full of project ideas as well: http://wiki.darcs.net/GoogleSummerOfCode Again, please submit proposals<http://hackage.haskell.org/trac/summer-of-code/newticket>as tickets to the trac if you can think of something you'd like to work on. *More Information* Here are a bunch of relevant links that may be able to answer your questions: Google's Summer of Code Homepage <http://socghop.appspot.com/> Google's Summer of Code 2010 FAQ<http://socghop.appspot.com/document/show/gsoc_program/google/gsoc2010/faqs> Google's Summer of Code 2010 Timeline<http://socghop.appspot.com/document/show/gsoc_program/google/gsoc2010/timel…> Google's Summer of Code Wiki Knowledge Base<http://code.google.com/p/google-summer-of-code/wiki/WikiStart> Of course, you can always feel free to email me <ekmett(a)gmail.com> or inquire on irc.freenode.net #haskell-soc or with the darcs folks over on #darcs for more information. If you don't have an IRC client, you can get there from: http://webchat.freenode.net Thank you all very much and we look forward to another successful Summer of Code! -Edward Kmett

1 0

Cabal and LLVM bindings
by Ville Tirronen 12 Mar '10

12 Mar '10

Hi! I'm trying to get cabal build my toy compiler, which is based on llvm bindings on hackage. Everything is fine with ghc --make, but with cabal install I get: Loading package llvm-0.7.1.1 ... <command line>: can't load .so/.DLL for: LLVMSystem (dlopen(libLLVMSystem.dylib, 9): image not found) cabal: Error: some packages failed to install: QV-0.1 failed during the building phase. The exception was: ExitFailure 1 This is done on os x 10.5.8, if that has any relevance. Anyone got any hints on how to proceed with this? Ville Tirronen

2 2

3rd party widgets with qtHaskell (Marble)
by Philip Beadling 12 Mar '10

12 Mar '10

Hi, I know this isn't a qtHaskell list, but I don't think there is one. Was wondering if anyone has any ideas on the below. Basically I'm trying to control a Marble (Map software) Qt widget from qtHaskell. So I've mocked up a very simple user interface in Qt Designer (1 form, 1 Marble widget). I can load this up and display it fine in Haskell, but as soon as I try to interrogate the widget I get a seg fault (eg qObjectProperty) My guess is that the call to findChild, although it executes OK it is not producing a valid QObject - probably casting to Marble::MarbleWidget* it crux of the problem. I can get this working using standard Qt Widgets (just like the examples show from qtHaskell), so I know the method is sound - although calling 3rd party widgets like this may be ambitious or impossible. I recognise this is a fairly broad query! Has anyone tried anything similar? Is it even possible to do this in qtHaskell as I'm proposing? I'm a Qt novice, so it may well be that I've misunderstood qtHaskell. Cheers, Phil. Using: GHC 6.12.1 / QT4.5 / Marble 0.8 / Ubuntu 9.04 module Main where import Qtc main :: IO () main = do app <- qApplication () rok <- registerResource "marble.rcc" loader <- qUiLoader () uiFile <- qFile ":/marble.ui" open uiFile fReadOnly ui <- load loader uiFile close uiFile () ui_map <- findChild ui ("<Marble::MarbleWidget*>", "MarbleWidget") sc <- qObjectProperty ui_map "showCompass" qshow ui () ok <- qApplicationExec () return ()

2 2

If the local variable can be changed ...
by zaxis 11 Mar '10

11 Mar '10

In FP the variable can not be changed once created. Yes, it has much advantage . However, i feel it is too strict. As we know, the local variable is allocated on stack which is thread safe. So if the local variable can be changed, then we can use loop, etc. same as imperative languages. For example, for (i=0; i<100; i++) where `i` is a local variable in function. Any suggestion is appreciated! ----- fac n = let { f = foldr (*) 1 [1..n] } in f -- View this message in context: http://old.nabble.com/If-the-local-variable-can-be-changed-...-tp27844016p2… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

6 7

Re: Anyone up for Google SoC 2010?
by Yakov Zaytsev 11 Mar '10

11 Mar '10

I've got N900 recently and saw that according to this page http://hackage.haskell.org/trac/ghc/wiki/Platforms it's not possible to run GHC and GHCi easily on ARM. This sucks. I want to propose a project "bring GHC back to life on arm-linux". It is supposed that the outcome will be a package for Maemo 5. Actually, I want to apply for this project as a student. I hope to make NCG for ARM working in some sense. Dear list, what do you think about it? -- Yakov

7 7

ANN: HaskellTorrent v0.1.1
by Jesper Louis Andersen 11 Mar '10

11 Mar '10

Hello Cafe, I am pleased to announce yet another release of the HaskellTorrent project. In this release, focus has been on improving upon the work laid in v0.0. Highlights include: * Certain data structures have changed from Data.List to Data.IntSet, yielding much improved performance. * Addition of a GetOpt option parser. * Use of test-framework to run unit-tests. * Assertion optimization, cutting down CPU usage by quite a margin. * Change SHA1 checksumming to use Peter Simons hopenssl package. This plugged some serious memory leaks. * Support for listen() on port 1579 so incoming connections get handled correctly. * Support for more graceful stopping. The supervisor tree is now terminated in the opposite order of creation. * When closing down, tell the tracker we are stopping. * Add KeepAlive messages on idle socket connections. * Improve the console interface a bit so it is quasi-usable. * Change the logging framework from my own to hslogger by John Goerzen. It is better than my attempts and it shaves 150 lines of code from the project not having to maintain a logging framework. This also makes the client BEP003 compliant, so we can now claim to be a full BitTorrent client. Looking forward, I'd like to get less CPU usage, and support for more BitTorrent extensions. -- There are still bugs in the code, so watch out for spinning processes. Also, performance is still far from optimal. From a profiler run, we get the following: total time = 64.26 secs (3213 ticks @ 20 ms) total alloc = 6,712,153,496 bytes (excludes profiling overheads) COST CENTRE MODULE %time %alloc MAIN MAIN 58.0 3.7 assertPieceDB Process.PieceMgr 13.4 29.6 logP Process 3.7 6.0 syncP Process 2.8 12.1 download Main 2.1 0.0 updateBS Digest 2.1 0.0 recvP Process 2.0 4.3 chooseP Process 1.9 7.0 receiverP Process.Peer 1.8 1.5 peerP Process.Peer 1.2 0.6 grabBlocks' Process.PieceMgr 1.0 3.1 senderP Process.Peer 1.0 1.4 sendP Process 0.9 3.1 checkPiece FS 0.7 6.1 msgPeer Process.ChokeMgr 0.6 2.4 registerL Process.Timer 0.2 1.9 getByteString Data.Serialize.Get 0.2 1.0 newBuffer Data.Serialize.Builder 0.0 10.1 which tells us we are still allocating far too much memory. I wonder what the 58.0% on MAIN means (this is with -prof -auto-all -caf-all). The code is heavily concurrent, using the cml package. My guess is that we have somewhere between 500 and 1000 threads when running. I ponder if that has something to do with it. The price of assertPieceDB can easily be removed by running the assertions at a rarer pace. -- J.

1 0

ANN: powerpc-0.0.1
by Tom Hawkins 11 Mar '10

11 Mar '10

Here is a new library for analyzing PowerPC programs [1]. At this point it does instruction set simulation on machine code -- and not all instructions are implemented yet, BTW. To run a simulation, the user defines an instance of the Memory class [2] to represent both instruction and data memory. The Memory class declares functions for memory loads and stores, instruction fetches, and reading and writing special purpose registers. In our test bench, we set up the 'fetch' method to dump out register values so we can see the state of the processor at every step. A neat feature of the library is the instruction behavior is captured by a little DSL [3]. This makes it easy to add new instructions because the translation from the instruction RTL spec [4] to the DSL is nearly one-to-one. And with instruction behavior captured symbolically, this opens the door to other types of analysis besides just simulation. I hope a few folks find it useful. -Tom [1] http://hackage.haskell.org/package/powerpc [2] http://hackage.haskell.org/packages/archive/powerpc/0.0.1/doc/html/Language… [3] http://hackage.haskell.org/packages/archive/powerpc/0.0.1/doc/html/Language… [4] http://www.ibm.com/developerworks/systems/library/es-archguide-v2.html

4 7

Problem installing wxHaskell on Haskell Platform on OSX.
by David Place 11 Mar '10

11 Mar '10

Hi: I have just installed the Haskell Platform 2009.2.0.2 on Mac OSX 10.6.2. When I try to install wx I get the following error which I do not understand. Can anyone give me a hint? $ cabal install wx Resolving dependencies... cabal: cannot configure containers-0.3.0.0. It requires base >=4.2 && <6 For the dependency on base >=4.2 && <6 there are these packages: base-4.2.0.0. However none of them are available. base-4.2.0.0 was excluded because of the top level dependency base -any Here are my packages: $ ghc-pkg list /Library/Frameworks/GHC.framework/Versions/610/usr/lib/ghc-6.10.4/./package.conf: Cabal-1.6.0.3, GLUT-2.1.1.2, HTTP-4000.0.6, HUnit-1.2.0.3, OpenGL-2.2.1.1, QuickCheck-1.2.0.0, array-0.2.0.0, base-3.0.3.1, base-4.1.0.0, bytestring-0.9.1.4, cgi-3001.1.7.1, containers-0.2.0.1, directory-1.0.0.3, (dph-base-0.3), (dph-par-0.3), (dph-prim-interface-0.3), (dph-prim-par-0.3), (dph-prim-seq-0.3), (dph-seq-0.3), editline-0.2.1.0, extensible-exceptions-0.1.1.0, fgl-5.4.2.2, filepath-1.1.0.2, (ghc-6.10.4), ghc-prim-0.1.0.0, haddock-2.4.2, haskell-src-1.0.1.3, haskell98-1.0.1.0, hpc-0.5.0.3, html-1.0.1.2, integer-0.1.0.1, mtl-1.1.0.2, network-2.2.1.2, network-2.2.1.4, old-locale-1.0.0.1, old-time-1.0.0.2, packedstring-0.1.0.1, parallel-1.1.0.1, parsec-2.1.0.1, pretty-1.0.1.0, process-1.0.1.1, random-1.0.0.1, regex-base-0.72.0.2, regex-compat-0.71.0.1, regex-posix-0.72.0.3, rts-1.0, stm-2.1.1.2, syb-0.1.0.1, template-haskell-2.3.0.1, time-1.1.2.4, time-1.1.4, unix-2.3.2.0, xhtml-3000.2.0.1, zlib-0.5.0.0 /Users/davidplace/.ghc/i386-darwin-6.10.4/package.conf: fingertree-0.0.1.0

3 4

Haskell course, training
by Günther Schmidt 11 Mar '10

11 Mar '10

Hi all, all going well this year I'll be able to invest some money on becoming a better Haskeller. I think I've reached the point where I need some tutoring, so provided I've got money for travel and course fees, and time, where do I get it? I'm not a student so some courses aren't available to me. Günther

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Re: Fast Haskell Parser
by Ben Lippmeier 11 Mar '10

11 Mar '10

Hi John, Doing a Google search for "haskell parser" returns the following link as its first result. That's the parser that GHC uses. http://www.haskell.org/happy/ You could also check out the following: http://www.haskell.org/haskellwiki/Parsec http://hackage.haskell.org/package/attoparsec This would also be a perfect question to ask on the haskell-cafe mailing list... Cheers, Ben. On 11/03/2010, at 10:39 AM, John D. Earle wrote: > I was thinking of ways to create an efficient Haskell parser. My initial thinking was to write a top down parser in Haskell, but if you want speed a table driven approach may make greater sense. > > Due to the existence of build bots there is a certain degree of compliancy concerning build times. I feel that convenience is an important factor. It should be convenient to build the source. Build bots make an assumption, namely the existence of a formal infrastructure. I believe that it should be possible to build something from source casually. > > This is a less demanding goal than high performance incremental builds. It would be nice to out perform make files because if you fail to do this, can it really be said that you are making progress? Correctness appears to be a low priority among computer programmers. That said, it may be worth investing some time in advance to figuring out how to best achieve both objectives, namely correctness and performance. Who knows skills acquired in one project may be useful in another and performance is usually welcome. > > So my question is, What sort of tools and methodologies exist in Haskell to create high performance parsers? My impression is the speed at which the parser performs its task is not the bottle-neck, but the parser might as well be designed to be efficient so as not to be intellectually lazy. It may even turn out that the parser may need to be efficient merely to compensate for the spawn of correctness, namely slow builds. > _______________________________________________ > Cvs-ghc mailing list > Cvs-ghc(a)haskell.org > http://www.haskell.org/mailman/listinfo/cvs-ghc

1 0

vector stream fusion, inlining and compilation time
by stefan kersten 10 Mar '10

10 Mar '10

hi, two questions in one post: i've been hunting down some performance problems in DSP code using vector and the single most important transformation seems to be throwing in INLINE pragmas for any function that uses vector combinators and is to be called from higher-level code. failing to do so seems to prevent vector operations from being fused and results in big performance hits (the good news is that the optimized code is quite competitive). does anybody have some more info about the do's and don'ts when programming with vector? the downside after adding the INLINE pragmas is that now some of my modules take _really_ long to compile (up to a couple of minutes); any ideas where i can start looking to bring the compilation times down again? i'm compiling with -O2 -funbox-strict-fields instead of -Odph (with ghc 6.10.4 on OSX 10.4), because it's faster for some of my code, but -O2 vs. -Odph doesn't make a noticable difference in compilation time. many thanks, <sk>

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ANNOUNCE: yesod 0.0.0 (web framework)
by Michael Snoyman 10 Mar '10

10 Mar '10

Hello all, I'm happy to announce the first release of the Yesod Web Framework[1]. This framework has been in development for over a year and is in production use on a number of websites. The project homepage[2] provides a fairly thorough rundown of features; for here, I will suffice to say that this framework aims at the following goals: * RESTful applications * Deployable anywhere (based on WAI) * Safety While this framework is still in active development and can be expected to mature over time, this release is ready for use. To get started quickly, simply install the yesod package from Hackage and type "yesod init". Michael [1] http://hackage.haskell.org/package/yesod [2] http://www.yesodweb.com/code.html

2 6

Re: [Haskell-cafe] more thoughts on "Finally tagless"
by Tom Schrijvers 10 Mar '10

10 Mar '10

On Tue, Mar 9, 2010 at 2:45 PM, Tillmann Rendel <rendel(a)mathematik.uni-marburg.de> wrote: > Tom Schrijvers wrote: >>> >>> Yeah, subject "Finally Tagless" again, sorry, I'm just not done with it >>> yet. >>> >>> In Olegs haskell implementation he is using classes mainly to model the >>> syntax and instances to use for evaluators / compilers to allow multiple >>> interpretations. >>> >>> I wonder if it'd be possible to do the same without classes using data >>> types >>> instead? >>> >>> Something similar to what Luke Palmer has done here: >>> >>> >>> http://lukepalmer.wordpress.com/2010/01/24/haskell-antipattern-existential-… >> >> You can just use the dictionary translation of type classes to replace >> them with data types: >> >> E.g. >> >> class Eval sem where >> val :: Int -> sem Int >> add :: sem Int -> sem Int -> sem Int >> >>> --> >> >> data EvalDict sem = EvalDict { val :: Int -> sem Int, add :: sem Int >> -> sem Int -> sem Int } > > This is the way to program in the final tagless style without using type > classes, but there is an important difference to what Luke Palmer did in the > blog post cited above. While both approaches allow to encode type classes > using data types, they are technically different, and applicable for > different programs. > > In the dictionary approach, the dictionary contains fields of the same types > as the members of the class. For example, val has the type Int -> sem Int in > both the type class and the data type. > > This is not the case in the pattern described by Luke. There, the w type is > dropped from the types of the methods when converting to a data type. For > example, the type of growHorizontal is w -> Bool in the type class, but > simply Bool in the data type. > > The reason for this difference is that Luke uses the fact that w is going to > be always existentially bound, so it will not be externally usable anyway. > The information contained in the w values can just as well be stored in each > of the fields of the data type. > > The dictionary approach encodes abstract data types: The data type is the > interface, each value of the data type is an implementation, and a function > which takes the dictionary and is parametric in the type parameters of the > dictionary is a program which uses the data type abstractly. > > For example, a program using the Eval abstract data type from above could > look like this: > > -- using the type class > add_two :: Eval sem => sem -> sem > add_two x = add x (val 2) > > -- using the dictionary > add_two :: EvalDict sem -> sem -> sem > add_two dict x = add dict x (val dict 2) > > On the other hand, Luke describes an encoding of objects: The data type > describes the interface of an object, and each value of that data type is an > object, with possibly different implementations of each function in the > interface. A program using these objects can invent arbitrary new objects, > as long as all fields in the interface are defined. > > Since abstract data types and objects are fundamentally different, so are > these two programming patterns. Tillmann, Thanks for your insight of objects vs. abstract data types. William Cook's Onward! essay is relevant here. He characterizes the difference between objects and abstract data types nicely: the latter allow binary methods that pattern match (to exploit the combined knowledge of the internals of two different values) whereas objects only know their own implementation. Dictionaries by themselves are objects in Cook's sense: they are just a record of functions that cannot be inspected. We can have an infinite number of them (while we can only have one type class instance per sem type). However, the (sem a) values are not objects, and varying the dictionaries while keeping the sem type the same does not seem very useful for implementing different semantics. For a type class function like add :: sem Int -> sem Int -> sem Int, binary pattern matching seems essential for meaningful implementations, and hence objects don't make much sense. Would you agree? Cheers, Tom

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Anyone up for Google SoC 2010?
by Malcolm Wallace 10 Mar '10

10 Mar '10

Google has announced that the Summer of Code programme will be running again this year. If haskell.org people would like to take part again this year, then we need volunteers: First, * suggestions for suitable projects (in the past this was organised using a reddit) * an administrator to co-ordinate the application to Google (I have done it for the last three years but am very willing to hand on to someone else) Google will accept applications from organisations in the period 8th - 12th March 2010, approx 1900UTC. If haskell.org is accepted again, students can apply between 29th March - 9th April. More volunteers will be required: * to review student applications and choose which to accept * to supervise the accepted students Both of these roles are called "mentor" in the Google system. Putting together a good team of mentors before applying as an organisation is helpful towards us being accepted into the programme. Regards, Malcolm

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Detecting extensions of the host processor
by Henning Thielemann 10 Mar '10

10 Mar '10

I like to detect at runtime whether the processor my program runs on has certain extensions (SSE2, SSE3 or so) in order to execute optimized code. On Linux I can process the contents of /proc/cpuinfo but this will not work on Windows. Is there a portable way in Haskell?

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Re: If the local variable can be changed ...
by John Lato 10 Mar '10

10 Mar '10

> From: zaxis <z_axis(a)163.com> > > So if the local variable can be changed, then we can use loop, etc. same as > imperative languages. For example, for (i=0; i<100; i++) where `i` is a > local variable in function. > In addition to John Millikin's suggestion, you can also do: map f [0..99] where f :: Int -> a; f = ... or mapM f [0..99] where f :: Int -> m a; f = ... for monadic actions. Here "f" is the body of the loop. The loop bodies must be completely independent, but this is a very useful technique. Cheers, John

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Num instance for Lazy ByteStrings (was: NumLazyByteString Package License)
by Thomas DuBuisson 10 Mar '10

10 Mar '10

Tristan and other interested parties on the Cafe, Answering your question first, Tristan: I was going to use BSD3 (if it isn't already) for the NumLazyByteString. For the cafe too: A while ago I made a Num instance for LPS; it is currently on my code.haskell.org account. Notice this isn't on Hackage yet and the semantics will be different soon. Most notably I want to ensure divide and anything else implemented through 'asInteger' and 'asInteger2' results in a bytestring of length equal to the largest of the operands. If that isn't clear then let me be very explicit. NumLazyByteString intentionally allows overflow! If you want operations (mod 2^40) then you need only work with bytestrings of length 5 bytes and the operations will result in 5 byte ByteString. This is already true for basic operations (bit operations, +, -, *) but is not yet done for quot, rem, quotRem, divMod, mod, /, and other you can see leverage Integer instead of using custom code. Any desire for non-overflowing operations (basically, re-expressing Integer as LazyByteString) would have to be done as an newtype with a Num instance that grows the bytestring to the necessary level, preventing overflow prior to calling NumLazyByteString. Finally, I intend for numerous operations to be lazy. If you add two infinite bytestrings you should be able to get the result of that operation (modulo some finite value) using NumLazyByteString. This is obviously not true for those operations leveraging Integer. Any comments or requests on the future of this Library are welcome - I'll probably get around to finishing it and putting it on Hackage in a couple weeks. Cheers, Thomas On Sun, Mar 7, 2010 at 9:24 PM, Tristan Ravitch <travitch(a)cs.wisc.edu> wrote: > I found myself adding Bits and Num instances for ByteStrings when I > found your implementation (which is much better than mine was shaping > up to be). Do you have any particular license in mind for it? > > I used it in an implementation of the Delta Debugging algorithm > (http://www.st.cs.uni-saarland.de/dd/) which I was thinking I would > like to release, and wanted to make sure the licensing could work out > properly. > > Thanks, > -- > Tristan Ravitch > travitch(a)cs.wisc.edu > http://pages.cs.wisc.edu/~travitch > > -----BEGIN PGP SIGNATURE----- > Version: GnuPG v1.4.10 (GNU/Linux) > > iEYEARECAAYFAkuUiiUACgkQJklRJNuIcWSxmACfVblD+gR/Fv57teNTArSfXhHg > NtsAnRqBvinNesMk3mxMxDERw5MBn9jZ > =Jm4O > -----END PGP SIGNATURE----- > >

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Re: First time haskell - parse error!
by John Lato 10 Mar '10

10 Mar '10

> From: Ketil Malde <ketil(a)malde.org> > > "S. Doaitse Swierstra" <doaitse(a)cs.uu.nl> writes: > >>> then (s1 ++ s2 ++ s3 ++ s4) where >>> s1 = "Golds " >>> s2 = show (gold s g) >>> s3 = ", Silvers " >>> s4 = show (silver s g) > >> If you want to keep the definitions local to the expression you should write > > ..but I think it is better style to avoid this kind of one-off named > values. I much prefer: > > then "Golds "++show (gold s g)++... > > For some reason, this is a style isse that doesn't get much attention, > at least not in the non-functional language tradition, where temporary > variables are scattered all over. So instead of doing: > > let ns y = not (isSpace y) > f x = takeWhile ns x > in map f > > We can use anonymous functions in place of the uninformatively named > ones: > > map (\x -> takeWhile (\y -> not (isSpace y)) x) > > and use partial application toward point-free-ness: > > map (takeWhile (not . isSpace)) I agree, and also tend to this style. Although I sometimes use one-off named values to avoid line wraps. For the particular task of combining strings like this, how about using Text.Printf.printf? then printf "Golds %s, Silvers %s" (show (gold s g)) (show (silver s g)) It can be a little hard to understand the type at first, but IMHO it works as expected. Cheers, John

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