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Cabal and Strings and CPP
by Philip Weaver 30 Jul '08

30 Jul '08

Hello all, I'm trying to use CPP-defined strings in a Haskell module, like this: main :: IO () main = putStrLn FOO This of course will not work: ghc -DFOO="hello world" --make Main.hs -o test You'll get this error message: ./Main.hs:6:16: Not in scope: `hello' ./Main.hs:6:22: Not in scope: `world' Either of these will do what I want: ghc -DFOO="\"hello world\"" --make Main.hs -o test ghc -DFOO='"hello world"' --make Main.hs -o test # (that's double quotes inside single quotes) However, passing the same CPP definition via cabal does not work. runhaskell Setup.hs build --ghc-options=-DFOO="\"hello world\"" runhaskell Setup.hs build --ghc-options=-DFOO='"hello world"' With either of these commands, I get the same error message as above. This is understandable, since cabal has to evaluate the string before sending it to GHC, so I lose my escaped quotes. Any idea how I could change the Haskell module or the command line argument so that I get what I want? I've tried many combinations of quotes and escaped quotes with no luck. Thanks, - Phil

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carry "state" around ....
by Galchin, Vasili 29 Jul '08

29 Jul '08

hello, Following is more of a criticism of Linux implementation of the Posix real-time extension of asynchronous I/O.... if not interesting please skip. The central data structure for Posix AIO is an aiocb. In any case, the Linux implementors added to the aiocb: /* Asynchronous I/O control block. */ struct aiocb { int aio_fildes; /* File desriptor. */ int aio_lio_opcode; /* Operation to be performed. */ int aio_reqprio; /* Request priority offset. */ volatile void *aio_buf; /* Location of buffer. */ size_t aio_nbytes; /* Length of transfer. */ struct sigevent aio_sigevent; /* Signal number and value. */ /* Internal members. */ <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< struct aiocb *__next_prio; int __abs_prio; int __policy; int __error_code; __ssize_t __return_value; #ifndef __USE_FILE_OFFSET64 __off_t aio_offset; /* File offset. */ char __pad[sizeof (__off64_t) - sizeof (__off_t)]; #else __off64_t aio_offset; /* File offset. */ #endif char __unused[32]; }; My viewpoint is that the above "Internal members" must be "carried" around in a Haskell program. Am I correct?? If I am correct, then the Linux implementation of Posix AIO is not portable to say Solaris? In hindsight, if I am correct, it seems that the Linux implementation of AIO should use the ordered pair (pid, fd) to reference the "internal" members and leave the "aiocb" "clean"? Very kind regards, Vasili

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Data Types a la Carte - automatic injections (help!)
by Kenn Knowles 29 Jul '08

29 Jul '08

I have a question about Data Types a la Carte (http://www.cs.nott.ac.uk/~wss/Publications/DataTypesALaCarte.pdf) and more generally hacking smart coproduct injections into Haskell (all extensions are fair game). > {-# LANGUAGE MultiParamTypeClasses,TypeOperators,UndecidableInstances,IncoherentInstances,FlexibleInstances,FlexibleContexts #-} Here are the definitions from Wouter's paper, which cleverly manage the instances of (:<:) > data (f :+: g) a = Inl (f a) | Inr (g a) > infixr 6 :+: > instance (Functor f, Functor g) => Functor (f :+: g) where > fmap f (Inl x) = Inl (fmap f x) > fmap f (Inr x) = Inr (fmap f x) > class (Functor sub, Functor sup) => sub :<: sup where > inj :: sub a -> sup a > instance Functor f => (:<:) f f where > inj = id > instance (Functor f, Functor g) => (:<:) f (f :+: g) where > inj = Inl > instance (Functor f, Functor g, Functor h, (f :<: g)) => (:<:) f (h :+: g) where > inj = Inr . inj Now in my case, I want to be able to inject an arbitrary coproduct into a larger one, assuming the components are in the same order, so it is a subsequence of the larger sum, for example: > coprodInject1 :: (Functor f, Functor g, Functor h, Functor i) => (f :+: g :+: h) a -> (f :+: g :+: h :+: i) a > coprodInject1 = inj > coprodInject2 :: (Functor f, Functor g, Functor h, Functor i) => (f :+: g :+: i) a -> (f :+: g :+: h :+: i) a > coprodInject2 = inj > instance (Functor f, Functor g, Functor h, (g :<: h)) => (:<:) (f :+: g) (f :+: h) where > inj (Inl x) = Inl x > inj (Inr x) = Inr (inj x) The above works fine, and maybe I could manipulate my code to only have injections of those forms, but I want this next one to work too: > coprodInject3 :: (Functor f, Functor g, Functor h, Functor i) => (f :+: g :+: i :+: j) a -> (f :+: g :+: h :+: i :+: j) a > coprodInject3 = inj It fails because after "passing up" the h in the search, it can either use the reflexivity rule or decompose the sum on (i :+: j). The full error is: Overlapping instances for (i :+: j) :<: (i :+: j) arising from a use of `inj' ... Matching instances: instance [incoherent] (Functor f) => f :<: f -- Defined at ... instance [incoherent] (Functor f, Functor g, Functor h, g :<: h) => (f :+: g) :<: (f :+: h) -- Defined at ... In the expression: inj In the definition of `coprodInject3': coprodInject3 = inj What confuses me is that IncoherentInstances is on, but it is still rejected by GHC 6.8.3 seemingly for being incoherent. I haven't tried it with any other version. Am I missing something? Any suggestions or pointers?

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ANN: RandomDotOrg-0.1
by Austin Seipp 29 Jul '08

29 Jul '08

Hi, I've just uploaded a package to hackage which is an interface to the random.org random number generator. For those who don't know, random.org provides random data through the use of atmospheric noise rather than a PRNG that would typically be invoked if you were to use the System.Random module or somesuch. As of current, it can only generate a list of random numbers. However, random.org also provides an interface to generate random strings, randomize an input list and a random sequence generator (the difference being that the sequence generator will not repeat itself, while the integer one may.) Would anybody find these interfaces useful? I think the random number generator alone is pretty nice, but I'm thinking of expanding it in the future with these other things since they're nice to have if you want randomness anyway. You can get it from [1] or just: $ cabal install RandomDotOrg The development repository is tracked using git; you can get yourself a clone by doing $ git clone git://github.com/thoughtpolice/randomdotorg.git Austin [1] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/RandomDotOrg-0.1

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ANN: Mueval 0.3.1, 0.4, 0.4.5, 0.4.6, 0.5
by Gwern Branwen 29 Jul '08

29 Jul '08

Hi everyone. So there've been a number of releases of Mueval lately. I figured I'd tell you about them. WHERE As always, you can 'cabal install mueval', or get it from Hackage <http://hackage.haskell.org/cgi-bin/hackage-scripts/package/mueval>, or get it from the new Darcs repository <http://code.haskell.org/mubot/>. Usage remains as before, but see below for numerous examples, or the file 'tests.sh'. WHAT'S INTERESTING Mueval is now even more capable. I've fixed the big security hole Spencer identified, so right now I know of no vulnerabilities in Mueval (or even potentially dangerous aspects). More interestingly is how close Mueval is now to Lambdabot's capabilities: we can evaluate all the same expressions, and Mueval now even can do QuickCheck tests. The only missing pieces is that currently there's no interface to Smallcheck yet (but hardly anyone in #haskell seems to use that, so I'm considering not even bothering), and currently there's no way to do @let or qualified imports. I hope to add these two missing pieces for the next release - and then I can finally remove hs-plugins from Lambdabot. CHANGES 0.5 Adds support for Unicode in expressions! bash$ mueval -e 'let (ñ) = (+) in ñ 5 5' 10" Adds support for QuickCheck tests! bash-3.2$ mueval -E -e 'myquickcheck (\x -> x == x)' "\"OK, passed 500 tests.\\n\"" bash-3.2$ mueval -E -e 'myquickcheck (\x -> x+1 == x+2)' "\"Falsifiable, after 0 tests:\\n0\\n\"" --inferred-type prints out even more information! bash-3.2$ mueval --inferred-type --expression 'foldr (\x y -> concat ["(f ",x," ",y,")"]) "z" (map show [1..5])' foldr (\x y -> concat ["(f ",x," ",y,")"]) "z" (map show [1..5]) [Char] "\"(f 1 (f 2 (f 3 (f 4 (f 5 z)))))\"" 0.4.6 A README! --print-type was renamed to --inferred-type so as to avoid short-option ambiguity! Refactoring! Haddocks look somewhat nicer! 0.4.5 Even more refactoring and modularization! Performance improvements! (ie. 'call error sooner so mueval doesn't hang around waiting for the timeout to expire') 0.4 Close major security hole! No more: mueval --expression "Foreign.unsafePerformIO $ readFile \"foo\"" (Since now one must declare module imports, and cannot circumvent them due to a certain bad behaviour of the GHC API.) 0.3.1 Blacklist unsafe keywords! mueval --expression "Foreign.unsafePerformIO $ readFile \"/etc/passwd\"" mueval: Unsafe functions to use mentioned. Looser resource limits (so hopefully more people can run it)! A Darcs repository! darcs get http://code.haskell.org/mubot/ (And of course mixed in throughout these changes are various test additions; it's a respectable little suite now.) -- gwern Propaganda Security rip CIO VIP Pershing O/S MPRI JASON AMEMB

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Literate program implementing text editor
by Eric 29 Jul '08

29 Jul '08

Hi all, I wanted to embark on a Haskell program that implements a simple text editor. Before doing so, however, I thought that I should ask: Does anyone know of a literate Haskell program already in existence that does the job? Eric M.

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Control.Concurrent.forkIO versus Control.Parallel.par
by Mario Blažević 28 Jul '08

28 Jul '08

Hello. I have a question about parallel computation in Haskell. After browsing the GHC library documentation, I was left with impression that there are two separate mechanisms for expressing concurrency: Control.Parallel.par for pure computations and Control.Concurrent.forkIO for computations in IO monad. This dichotomy becomes a problem when one tries to use concurrency from a monad transformer, though I'm sure that's not the only such situation. One cannot assume that the base monad is IO so forkIO cannot be used, while Control.Parallel.par won't run monads. My first solution was to replace the base monad class for the monad transformer by the following ParallelizableMonad class: ---------------------------------------------------------------------------- class Monad m => ParallelizableMonad m where parallelize :: m a -> m b -> m (a, b) parallelize ma mb = do a <- ma b <- mb return (a, b) instance ParallelizableMonad Identity where parallelize (Identity a) (Identity b) = Identity (a `par` (b `pseq` (a, b))) instance ParallelizableMonad IO where parallelize ma mb = do va <- newEmptyMVar vb <- newEmptyMVar forkIO (ma >>= putMVar va) forkIO (mb >>= putMVar vb) a <- takeMVar va b <- takeMVar vb return (a, b) ---------------------------------------------------------------------------- I tested this solution, and it worked for IO computations in the sense that they used both CPUs. The test also ran slower on two CPUs that on one, but that's beside the point. Then I realized that par can, in fact, be used on any monad, it just needs a little nudge: ---------------------------------------------------------------------------- parallelize :: m a -> m b -> m (a, b) parallelize ma mb = let a = ma >>= return b = mb >>= return in a `par` (b `pseq` liftM2 (,) a b) ---------------------------------------------------------------------------- However, in this version the IO monadic computations still appear to use only one CPU. I cannot get par to parallelize monadic computations. I've used the same command-line options in both examples: -O -threaded and +RTS -N2. What am I missing?

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multicore programming ...
by Galchin, Vasili 28 Jul '08

28 Jul '08

Hello, I have written quite a bit of multi-threaded code in ANSI C and C++ using mainly Posix threads and some using Win32 API threads. IMO now seems to be a huge opportunity for FPLs to shine .. In any case, now there seems to be an emerging crisis in the computer industry in multithread scalability over large multicore: http://www.hackinthebox.org/modules.php?op=modload&name=News&file=article&s…. This is kind of a "wrag" quote. Do others have more substantial URLs on programming large multi-cores? Kind regards, Vasili

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library for zip compression?
by John MacFarlane 28 Jul '08

28 Jul '08

Haskellers, Is there a library for compressing and uncompressing zip archives? I see zlib and bzlib on HackageDB, but unless I'm mistaken these won't help with a .zip archive. (See http://zlib.net/zlib_faq.html#faq11.) Any help here would be appreciated. John

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Re: [Haskell] ANN: Hipmunk 0.1 and HipmunkPlayground 0.1
by Antoine Latter 27 Jul '08

27 Jul '08

On Sat, Jul 26, 2008 at 9:50 PM, Felipe Lessa <felipe.lessa(a)gmail.com> wrote: > 6.8.1). > > You may get Cabal packages for both on Hackage at: > - http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Hipmunk > - http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HipmunkPlayground > Felipe, I'm getting the following error trying to cabal-install HipmunkPlayground: +++++ Building HipmunkPlayground-0.1... [1 of 1] Compiling Main ( ./Playground.hs, dist/build/HipmunkPlayground/HipmunkPlayground-tmp/Main.o ) Linking dist/build/HipmunkPlayground/HipmunkPlayground ... ld: duplicate symbol _deRefStablePtr in /Library/Frameworks/GHC.framework/Versions/608/usr/lib/ghc-6.8.2.20080211/libHSrts.a(Stable.o) and /Users/alatter/.cabal/lib/Hipmunk-0.1/ghc-6.8.2.20080211/libHSHipmunk-0.1.a(Space_stub.o) collect2: ld returned 1 exit status cabal: Error: some packages failed to install: HipmunkPlayground-0.1 failed during the building phase. The exception was: exit: ExitFailure 1 +++++ I simply typed "cabal install HipmuckPlayground". Should I need to do anything else? I'm running Mac OS 10.5 on Intel. Does this error look useful to anyone? -Antoine

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ANNOUNCE: Sun Microsystems and Haskell.org joint project on OpenSPARC
by Duncan Coutts 26 Jul '08

26 Jul '08

http://haskell.org/opensparc/ I am very pleased to announce a joint project between Sun Microsystems and the Haskell.org community to exploit the high performance capabilities of Sun's latest multi-core OpenSPARC systems via Haskell! http://opensparc.net/ Sun has donated a powerful 8 core SPARC Enterprise T5120 Server to the Haskell community, and $10,000 to fund a student, to further develop support for high performance Haskell on the SPARC. The aim of the project is to improve the SPARC native code generator in GHC and to demonstrate and improve the results of parallel Haskell benchmarks. The student will work with a mentor from Haskell.org and an adviser from Sun's SPARC compiler team. ** We are now inviting applications from students ** Please forward this announcement to any and all mailing lists where you think interested students might be lurking. Further details for students may be found below, and on the project website. Haskell and Multi-core Systems ------------------------------ The latest generation of multi-core machines pose a number of problems for traditional languages and parallel programming techniques. Haskell, in contrast, supports a wealth of approaches for writing correct parallel programs: traditional explicit threads and locks (forkIO and MVars), pure parallel evaluation strategies (par) and also Software Transactional Memory (STM). GHC has supported lightweight preemptable threads for a long time, and for the last couple of years it has been able to take advantage of machines with multiple CPUs or CPU cores. The GHC runtime has also recently gained a parallel garbage collector. OpenSPARC --------- We think the UltraSPARC T1/T2 architecture is a very interesting platform for Haskell. In particular the way that each core multiplexes many threads as a way of hiding memory latency. Memory latency is a performance bottleneck for Haskell code because the execution model uses a lot of memory indirections. Essentially, when one thread blocks due to a main memory read, the next thread is able to continue. This is in contrast to traditional architectures where the CPU core would stall until the result of the memory read was available. This approach can achieve high utilisation as long as there is enough parallelism available. The Project ----------- GHC is increasingly relying on its native code backend for high performance. Respectable single-threaded performance is a prerequisite for decent parallel performance. The first stage of the project therefore is to implement a new SPARC native code generator, taking advantage of the recent and ongoing infrastructure improvements in the C-- and native layers of the GHC backend. There is some existing support for SPARC in the native code generator but it has not kept up with changes in the GHC backend in the last few years. Once the code generator is working we will want to get a range of single threaded and parallel benchmarks running and look for various opportunities for improvement. There is plenty of ongoing work on the generic parts of the GHC backend and run-time system so the project will focus on SPARC-specific aspects. The UltraSPARC T1/T2 architecture supports very fast thread synchronisation (by taking advantage of the fact that all threads share the same L2 cache). We would like to optimise the synchronisation primitives in the GHC libraries and run-time system to take advantage of this. This should provide the basis for exploring whether the lower synchronisation costs make it advantageous to use more fine-grained parallelism. The Server ---------- The T5120 server has a T2 UltraSPARC processor with 8 cores running at 1.2GHz. Each core multiplexes 8 threads giving 64 hardware threads overall. It comes equipped with 32GB of memory. It also has two 146GB 10k RPM SAS disks. http://www.sun.com/servers/coolthreads/t5120/ http://www.sun.com/processors/UltraSPARC-T2/ This server is a donation to the whole Haskell community. We will make accounts available on the same basis as the existing community server as soon as is practical. Our friends at Chalmers University of Technology are kindly hosting the server on our behalf. We will encourage people to use the server for building, testing and benchmarking their Haskell software on SPARC, under both Solaris and Linux. Student applications -------------------- This is a challenging and exciting project and will need a high calibre student. Familiarity with Haskell is obviously important as is some experience with code generation for RISC instruction sets. The summer is now upon us so we do not expect students to be able to work 3 months all in one go. We are inviting students to suggest their own schedule when they apply. This may involve blocks of time in the next 9 months or so. It should add up to the equivalent of 3 months full time work. The application process is relatively informal. Students should send their application to: opensparc(a)community.haskell.org The deadline for applications in Friday 5th September 2008. If that deadline likely to be a problem for you then do get in touch. The application should detail skills and experience. Applications will be reviewed by a panel including the mentor, the adviser from Sun and a number of other Haskell.org community members who have helped with reviewing student projects in the past. The review will be partly interactive; students can expect to get questions and feedback from the reviewers. Students are welcome to contact myself or anyone else to help improve the quality of their application or if they have any questions. The $10k student funding will be paid in three phases, at the beginning ($3k), an intermediate point ($3k) and at the end ($4k). The exact timing will depend on the agreed schedule. The intermediate and final payments will be subject to positive reviews from the mentor. Duncan (project coordinator)

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Hi Nathan ....
by Galchin, Vasili 26 Jul '08

26 Jul '08

Hi Nathan, I am in Houston and want to start a serious Haskell "dialog/group" in the US Southeast! ... Let's rock because Haskell rocks!!!! Very kind regards, Vasili

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ANN: list-extras 0.2.0
by wren ng thornton 26 Jul '08

26 Jul '08

hello all~ After some talks with Aditya Mahajan I've overhauled the Data.List.Extras.Argmax module so it's not quite so braindead. Since it breaks backwards compatibility so soon after the initial announcement, I figured it was worth a mention. I also changed the case of the module's name, so beware on case-sensitive file systems. As always, the code and latest documentation is available from: http://code.haskell.org/~wren/ -- Live well, ~wren

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FPers in Northwest Arkansas?
by Nathan Bloomfield 25 Jul '08

25 Jul '08

Greetings, Haskell-cafe. I am interested in joining or starting a functional programming interest group in my area. Are there any haskellers in the Northwest Arkansas region? Nathan Bloomfield

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Italian Haskellers Summer Meeting?
by Pasqualino 'Titto' Assini 25 Jul '08

25 Jul '08

As a prerequisite for atttending is proficiency in "la bella lingua del si" (also known as Italian) I think I will just write the rest of this message in it. Ottimi, ma non particolarmente abbondanti, haskeller italiani, abbiamo avuto una piccola discussione su #haskell.it circa la possibilita' di organizzare un incontro estivo. Non credo che ne sia stato mai organizzato uno e quindi vorrei intanto che mi faceste sapere: - se vi interessa - dove siete/sarete d'agosto - che formato debba avere l'incontro Riguardo quest'ultimo punto, direi che ci sono almeno tre possibilita' : a) Ritiro spirituale. Luogo: rifugio di montagna, monastero benedettino. Gli adepti giungono al luogo designato dopo un lungo percorso a piedi attraverso regioni desertiche. Hanno barbe lunghe ed occhi severi ma in cui brilla la luce di una pura fede monoidale. Riunitisi davanti ad un semplice pasto gli adepti spezzano il pane e bevono il vino e si scambiano parabole illuminanti circa la vera natura del Monoide, della Monade e del Funtore Applicativo. Un neofita, che non sa spiegare la differenza fra left e right fold, viene giudicato impuro e ritualmente lapidato. b) Scampagnata fuori porta Luogo: ridente localita' marina od agreste. Gli haskeller arrivano alla spicciolata su una spiaggia animata. Hanno costumi colorati e capelli rasta. Qualcuno ha portato i bambini, tutti hanno portato la paletta ed il secchiello. Si fanno castelli di sabbia, qualcuno passa una canna, si divide una pizza e si chiacchiera' in liberta di haskell, zen e viaggi in motocicletta. L'atmosfera si rabbuia pero' improvvisamente quando viene scoperto un infiltrato provocatore che non sa spiegare la differenza fra left e right fold. Sommariamente giudicato da un tribunale del popolo, l'infelice viene affogato ed abbandonato sulla spiaggia, nell'indifferenza dei bagnanti che continuano a giocare a solitario sui telefonini. c) Seminario accademico Luogo: tetra aula universitaria. Serie presentazioni accademiche si susseguono senza posa. Per ragioni di principio nessuno dei relatori usa power point e riempiono le lavagne nere con suggestivi ma incomprensibili sgorbi. Si suda copiosamente nel caldo estivo e l'olezzo di accademici poco lavati riempie la stanza. Un dottorando dell'universita' di Pisa emoziona l'auditorio, dimostrando in maniera inconfutabile la mirabile corrispondenza fra monoidi destrorsi e logica lineare. Un addottorato del politecnico di Torino, geloso, cerca di staccargli un occhio con un gessetto. Un neofita, che non sa spiegare la differenza fra left e right fold, russa in un angolo. Personalmente, vista la stagione, suggerirei di: - Se c'e' disponibilita' a passare un paio di giorni insieme optare per l'opzione a. Paolino ha proposto a questo proposito di riunirci in un rifugio delle Apuane. - Se invece vogliamo fare una cosa in giornata allora andrei per l'opzione b e suggerirei di vederci sulla spiaggia di Monterosso (5 Terre). Come data, suggerirei l'11 agosto (o 11-12 in caso di opzione a). Per registrarsi, proporre date/luoghi etc, proporrei di utilizzare la pagina wiki dedicata: http://www.haskell.org/haskellwiki/ItaloHaskell/Summer_2008 A presto, titto P.S. Io saro' offline per una settimana a partire da domenica. -------------------------------- Pasqualino "Titto" Assini PhD 25 Heath Road - Wivenhoe CO79PT - Colchester - U.K.

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[Haskell-cafe] Re: blas bindings, why are they so much slower the C?
by Patrick Perry 25 Jul '08

25 Jul '08

Last month Anatoly Yakovenko published some disturbing numbers about the Haskell BLAS bindings I wrote being significantly slower than using plain C. I wanted to let everyone know that I've closed the performance gap, and now for doing ten million dot products, the overhead for using Haskell instead of C is about 0.6 seconds on my machine, regardless of the size of the vectors. The next version will incorporate the changes. If you can't wait for a formal release, the darcs repository is at http://www-stat.stanford.edu/~patperry/code/blas/ Anyone interested in more details can check out my blog: http://quantile95.com/2008/07/24/addressing-haskell-blas-performance-issues/ Thanks everyone for the input on this (especially Anatoly). If any else finds any performance discrepancies, please let me know and I will do whatever I can to fix them. Patrick

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ansi2html - one program, several issues
by Krzysztof Skrzętnicki 25 Jul '08

25 Jul '08

Hi all Recently I wrote a little program that takes text file with ANSI color codes and outputs HTML file. Example input and output files (also attached): http://tener.videomed.com.pl/ansi2html/samo_pk_merusa.log http://tener.videomed.com.pl/ansi2html/samo_pk_merusa.log.html The good thing: it is linear in time. But this is not so much surprising given the problem stated. The bad thing: it is also linear in space and have a feeling that it can run a lot faster. I decided to optimize the code and now I have two things I don't understand and one bug: 1) Profiling shows that very simple functions are source of great memory and time consumption. However, if I turn them off and simply print their input arguments instead, the overall time and memory consumption doesn't change. But now another function is acting badly. My guess: somehow the cost of Parsec code is shifted into whatever function is using it's output. Let's see: doOneFile :: String -> IO () doOneFile fname = do t1 <- getCurrentTime doesFileExist (fname ++ ".html") >>= \b -> if b then hPutStrLn stderr $ printf "File already processed, skipping: %s" fname else do src <- readFile fname out <- openFile (fname ++ ".html") WriteMode let parsed = (parse mainParser fname src) hSetBuffering out (BlockBuffering (Just 64000)) hPutStrLn out "<html>" hPutStrLn out "<body bgcolor=\"black\">" hPutStrLn out "<meta http-equiv=\"Content-Type\" content=\"text/html; charset=UTF-8\">" hPutStrLn out "<span style=\"font-family: monospace; font-size: 13;\" ><span>" execStateT (hPrintHtml (St id)) (out,emptyStyle) -- wypisujemy pierwszy wiersz execStateT (mapM_ *hPrintHtml* (((either (\x -> (trace $ show x) [] ) (id) parsed)) :: [CharOrColor])) (out,emptyStyle) -- *[1]* -- mapM_ (hPutStr out . show) (((either (\x -> (trace $ show x) [] ) (id) ((parse mainParser fname src)))) :: [CharOrColor]) -- *[2]* hPutStrLn out "</span></span>" hPutStrLn out "</body>" hPutStrLn out "</html>" t2 <- getCurrentTime hPutStrLn stderr $ printf "File %s processed. It took %s. File size was %d characters." fname (show $ diffUTCTime t2 t1) (length src) hFlush out hClose out When profiled: beginSpan Main 32.7 39.7 hPrintHtml Main 21.1 18.4 dataParser Main 17.3 18.6 doOneFile Main 10.4 7.4 colorParser Main 8.7 8.8 justColor Main 3.2 2.0 mainParser Main 3.2 1.9 code0' Main 1.1 1.1 Ok, let's exchange [1] for [2]. Now: doOneFile Main 53.4 59.9 dataParser Main 21.6 21.7 colorParser Main 13.6 10.3 justColor Main 3.8 2.3 mainParser Main 3.6 2.2 code0' Main 1.3 1.2 2) I tried to use both of my processor cores. But simply typing spawning a thread for every file quickly lead to swapping. So instead of this I implemented "thread pool" with fixed number of threads. -- begin code -- type Pool = Chan () takeFromPool :: Pool -> IO () takeFromPool p = readChan p >> return () fillPool :: Pool -> IO () fillPool p = writeChan p () makeThreadPool :: Int -> IO Pool makeThreadPool num = do p <- newChan repeatNum num (fillPool p) return p repeatNum :: Int -> IO () -> IO () repeatNum n act | n > 0 = act >> (repeatNum (n-1) act) | otherwise = return () sparkComp :: Pool -> IO () -> IO (MVar ()) sparkComp pool comp = do takeFromPool pool >>= evaluate mvar <- newEmptyMVar >>= evaluate forkIO $ (comp >> fillPool pool >> putMVar mvar ()) >>= evaluate -- core dumps when changed do forkOS return mvar mapMPar :: (a -> IO ()) -> [a] -> Int -> IO () mapMPar comp lst numT = do tPool <- makeThreadPool numT mvars <- mapM (sparkComp tPool) (map comp lst) mapM_ takeMVar (mvars :: [MVar ()]) return () numThreads = 2 -- end code -- Now, when compiled with -threaded and run with -N2 the program is not faster, but this may be result of -threaded switch. The real puzzle for me: without -threaded switch code using mapMPar is 30% faster then using mapM_, even when numThreads = 1. I have no idea why. 3) When I changed my thread pool implementation to use forkOS instead of forkIO it core dumped when run with -N2 and multiple file input. With -N1 it was ok. Unfortunately I was unable to reproduce this bug after I changed something unrelated to above code. I'm working on GHC version 6.9.20080622, Windows XP. Perhaps someone will succeed reproducing it. Do you have any ideas about this program? Best regards Christopher Skrzętnicki

6 14

Profiling nested case
by Mitar 25 Jul '08

25 Jul '08

Hi! I am making a simple raycasting engine and have a function which take a point in space and return a color of an object (if there is any) at this point in space. And because the whole thing is really slow (or was really slow) on simple examples I decided to profile it. It takes around 60 seconds for a 640x480 px image with 400 depth of field. This is at worst 122,880,000 calculations (if the scene is rather empty) of a coordinate of a point in space and then checking for a color. And 60 seconds look really a lot to me for that. So I went profiling and found out that the strange part of code is the main color checking function which has a list of objects (at this time the list is hardcoded). It looks like this: world :: SpacePoint -> VoxelColor world point = case msum . sequence elements $ point of Just v -> v Nothing -> noColor where elements = [redSphere (0,50,0) 50, greenSphere (25,-50,0) 50, blueSphere (-150,0,150) 50] So three spheres in a world and I check if the point is in any of them. Like that: sphere :: SpacePoint -> BasicReal -> VoxelColor -> WorldElement -- center of sphere, it's radius, it's color sphere (x0,y0,z0) r color (x,y,z) | x' * x' + y' * y' + z' * z' <= r * r = Just color | otherwise = Nothing where x' = x - x0 y' = y - y0 z' = z - z0 redSphere :: SpacePoint -> BasicReal -> WorldElement redSphere c r = sphere c r redColor So profiling told me that world function takes 38.4 % of all running time. So I decided to play with it. Maybe a more direct approach would be better: world :: SpacePoint -> VoxelColor world point = findColor [redSphere (0,50,0) 50, greenSphere (25,-50,0) 50, blueSphere (-150,0,150) 50] where findColor [] = noColor findColor (f:fs) = case f point of Just v -> v Nothing -> findColor fs Great, it improved. To 40 s. But still it was too much. I tried this: world :: SpacePoint -> VoxelColor world point = case redSphere (0,50,0) 50 point of Just v -> v Nothing -> case greenSphere (25,-50,0) 50 point of Just v -> v Nothing -> case blueSphere (-150,0,150) 50 point of Just v -> v Nothing -> noColor And it took 15 s. And also the profiling was like I would anticipate. Calculating points coordinates and checking spheres takes almost all time. So any suggestions how could I build a list of objects to check at runtime and still have this third performance? Why this big difference? (I am using GHC 6.8.3 with -O2 compile switch.) (The <* operator is casting a ray, that is multiplying a ray direction vector with a scalar factor.) Mitar

10 17

ghc socket weirdness
by Tim Newsham 24 Jul '08

24 Jul '08

FreeBSD/7.0 amd64: GHCi, version 6.8.2: http://www.haskell.org/ghc/ :? for help Loading package base ... linking ... done. Prelude> :module +Network Prelude Network> listenOn $ PortNumber 8765 Loading package parsec-2.1.0.0 ... linking ... done. Loading package network-2.1.0.0 ... linking ... done. *** Exception: getAddrInfo: does not exist (servname not supported for ai_socktype) (same error when compiled). Anyone seen this before? I have multiple NICs, could that be confusing listenOn (does it not just bind on 0.0.0.0?) Tim Newsham http://www.thenewsh.com/~newsham/

2 1

More fun with micro-benchmarks and optimizations. (GHC vs Perl)
by Corey O'Connor 24 Jul '08

24 Jul '08

I have the need to regularly write tiny programs that analyze output logs. The output logs don't have a consistent formatting so I typically choose Perl for these tasks. The latest instance of having to write such a program was simple enough I figured I'd try my hand at using Haskell instead. The short story is that I could quickly write a Haskell program that achieved the goal. Yay! However, the performance was ~8x slower than a comparable Perl implementation. With a lot of effort I got the Haskell version to only 2x slower. A lot of the optimization was done with guesses that the performance difference was due to how each line was being read from the file. I couldn't determine much using GHC's profiler. I still have two questions after all this: - Can I get a Haskell implementation as fast as the Perl? - What do I need to do to get GHC's profiler to provide me usable information? Telling me that 98% of the time was in "main" is not very enlightening ;-) All the code and data for this little experiment I've placed here: http://tothepowerofdisco.com/repo/sum_optimization/ My first, and shortest, version is SumTiny.hs. The optimized version is SumFast.hs. The long version for the curious: The (cleaned up) data was a 78k line file consisting of lines like the following: framerate (prev == no pts): 15 framerate (delta): 25 framerate (invalid timebase): 12.5 ... and so on. The need was for a program that calculated 1.0 / framerate for each line and produced the sum. Easy no? My straightforward Haskell solution was: ------------------------------------------------------------------- import Text.Regex.Posix main = do f_lines <- readFile "test.out" >>= return . lines let duration = foldl add_line 0.0 f_lines add_line sum line = let [[_,m]] = line =~ "([0-9.]+)" framerate = read m delta = 1.0 / framerate in sum + delta putStrLn $ "Duration (sec): " ++ show duration ------------------------------------------------------------------- Just for fun I decided to compare it to a Perl implementation: ------------------------------------------------------------------- #!/usr/bin/perl my @f_lines = split(/\n/,`cat test.out`); my $sum = 0.0; foreach(@f_lines) { /([0-9.]+)/; my $delta = 1.0 / $1; $sum += $delta; } print("Duration (sec): ", $sum, "\n"); ------------------------------------------------------------------- (I'm sure there are other ways to write this same program in both languages.) I was pretty happy with how the Haskell implementation's code compared to the Perl implementation's just in terms of looks. Though I think the Perl implementation is easier to understand at the part where the regex match is extracted. For fun I compared the performance of the two: (64bit linux running on a 2.4ghz Core2Duo) $ time perl ./Sum.pl Duration (sec): 3155.62666666438 real 0m0.121s user 0m0.103s sys 0m0.016s $ time ./SumTiny Duration (sec): 3155.626666664377 real 0m1.099s user 0m1.073s sys 0m0.009s Youch! ~1s is fast enough that I don't care, but I'm still curious why there is a 8x performance difference. Profiling with manual cost center annotations (See SumTinyProf.hs) indicated the "do" expression main is equal to was responsible 90% of the tiny. Which isn't revealing at all! Some experimenting led me to find a 2x slower implementation (SumFast.hs). Quick notes ont he changes I made: - Used ByteStrings instead of String. - Used hGetLine instead of reading the entire file lazily and splitting on "\n" - Fusing the foldl' with the loop of reading each line from the file. - Using bang patterns to make the fused loop strict on the accumulator argument. I think the largest performance gain was from changing how each line was read from the file. The lazy read and split seemed very slow compared to a loop that used hGetLine. -- -Corey O'Connor

5 8

BLAS Solve Example
by Darrin Thompson 24 Jul '08

24 Jul '08

I'm stuck on something that I thought would be easy. I have a matrix and a vector. > module Main where > import Data.Vector.Dense > import Data.Matrix.Dense > import BLAS.Matrix.Solve > > m = listMatrix (2, 3) ([1, 2, 3, 4, 5, 6]::[Double]) > v = listVector 2 ([1, 2]::[Double]) > > main = do ??? Can I use one of the haskell libraries to solve that system? My goal is to automate some tedium on small exercises from the Linear Algebra text by Jim Heffron. -- Darrin

4 4

Aren't type system extensions fun?
by Andrew Coppin 24 Jul '08

24 Jul '08

Haskell 98 provides a simple and clean type system, which I feel I understand very well. GHC provides a vast zoo of strange and perplexing type system extensions, which I don't understand at all. (Well, some of it is simple enough - e.g., multiparameter type classes. But GADTs? FDs? ATs? Hmm...) Anyway, it seems there is a large set of such type system extensions that involve writing "forall" all over the place. I have by now more or less managed to comprehend the fact that data Thing = forall x. Thing x allows a type variable to appear on the RHS that is *not* present on the LHS, thus "hiding" the type of something inside the structure. And for some reason, they call this "existential quantification" [which I can't spell never mind pronounce]. Today I was reading a potentially interesting paper, and I stumbled across something referred to as a "rank-2 type". Specifically, class Typable x => Term x where gmapT :: (forall y. Term y => y -> y) -> x -> x At this point, I am at a complete loss as to how this is any different from gmapT :: Term y => (y -> y) -> x -> x Can anybody enlighten me? This is probably the first real use I've ever seen of so-called rank-2 types, and I'm curios to know why people think they need to exist. [Obviously when somebody vastly more intelligent than me says something is necessary, they probably know something I don't...] At this point, I don't think I even wanna *know* what the hell a rank-N type is... o_O

23 42

Haskell Weekly News: Issue 78 - July 23, 2008
by Brent Yorgey 24 Jul '08

24 Jul '08

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20080723 Issue 78 - July 23, 2008 --------------------------------------------------------------------------- Welcome to issue 78 of HWN, a newsletter covering developments in the [1]Haskell community. Issue 78: In Which Michi and Neil Become Doctors, Sun Donates Some Sweet Loot, and Jules Is Revealed To Be A Helpful Anthropomorphic Robot Community News Congratulations are in order this week to two members of the community who have completed PhDs. Neil Mitchell (ndm) passed his PhD viva last week, subject to minor corrections. Mikael Johansson (Syzygy-) [2]has also completed his PhD and will soon be starting a postdoc at Stanford with the topology in computer science working group. Congratulations, Drs. Mitchell and Johansson! Announcements rosezipper. Eric Kow (kowey) [3]announced the release of [4]rosezipper, Krasimir Angelov and Iavor S. Diatchki's Data.Tree implementation of zippers. list-extras 0.1.0. wren ng thornton (koninkje) [5]announced the initial release of [6]list-extras, a home for common not-so-common list functions. Sun Microsystems and Haskell.org joint project on OpenSPARC. Duncan Coutts (dcoutts) [7]announced a [8]joint project between Sun Microsystems and the Haskell.org community to exploit the high performance capabilities of Sun's latest multi-core [9]OpenSPARC systems via Haskell! Sun has donated a powerful 8 core SPARC Enterprise T5120 Server to the Haskell community, and $10,000 to fund a student to further develop support for high performance Haskell on the SPARC. The student will work with a mentor from Haskell.org and an adviser from Sun's SPARC compiler team. If you're a student and this sounds interesting to you, send in those applications!! Hayoo! beta 0.2. Timo B. [10]announced the second beta release of [11]Hayoo!, a Haskell API search engine providing advanced features like suggestions, find-as-you-type, fuzzy queries and much more. The major change in this release is the inclusion of all packages available on Hackage in the index. Haskell-beginners mailing list. Benjamin L. Russell [12]announced the creation of the [13]Haskell-Beginners Mailing List, beginners at haskell.org, devoted to discussion of primarily beginner-level topics related to Haskell. It's already off to a great start, so if you're a Haskell beginner, or someone interested in answering beginner questions, please subscribe! Haskeline 0.2. Judah Jacobson [14]announced the initial (alpha-ish) release of [15]Haskeline, a library for line input in command-line programs. It is similar in purpose to editline or readline, but is written in Haskell and thus (hopefully) more easily used in other Haskell programs. Google Summer of Code Progress updates from participants in the 2008 [16]Google Summer of Code. Generic tries. Jamie Brandon is working on a library for efficient maps using generalized tries. [17]This week, he ran QuickCheck on his test suite for the first time, and found a large number of failing tests! He's got his work cut out for him straightening those out over the next few days. DPH physics engine. Roman Cheplyaka (Feuerbach) is working on a [18]physics engine using [19]Data Parallel Haskell. [20]This week, he implemented full handling of rigid body collisions, including angular velocity. Next he plans to explore various ways to make the engine faster, including broad-phase collision detection. GHC plugins. Max Bolingbroke is working on dynamically loaded plugins for GHC. [21]This week, he revealed his "mystery project": an HTML pretty-printer for GHC core! [22]Here is a sample. Now his focus turns to tidying things up and solidifying documentation in preparation for getting his patches merged into GHC HEAD. Hoogle 4. Neil Mitchell (ndm) is working on [23]Hoogle 4. [24]This week, he fleshed out the final part of type search, including support for instances and alpha renaming of variables. Unfortunately, it uses too much memory to be feasibly run on the base libraries! Neil has some ideas on how to fix this, however, which he plans to tackle next week. Language.C. Benedikt Huber (visq) is [25]working on Language.C, a standalone parser/pretty printer library for C99. He has finally completed a working implementation for analysing declarations and definitions, and [26]presents a working example of the library's use. Cabal dependency framework. Andrea Vezzosi (Saizan) is working on a [27]make-like dependency analysis framework for Cabal. GHC API. Thomas Schilling (nominolo) is working on [28]improvements to the GHC API. Libraries Proposals and extensions to the [29]standard libraries. generalize mapAccumL/R. Ross Paterson [30]proposed adding generalized versions of mapAccumL and mapAccumR to Data.Traversable. signal-handling API. Simon Marlow [31]proposed a [32]new signal-handling API. Discussion Point-free style in guards. L29Ah [33]asked a question about using a points-free style in guard expressions, leading to a number of clever suggestions involving custom combinators. Optimizing sequence. Gracjan Polak started a [34]discussion on the strictness properties of the sequence function, and its implications for optimization. It sounds as though adding an alternate strict version of sequence to the libraries could be a good idea. Blog noise [35]Haskell news from the [36]blogosphere. * Eric Kow (kowey): [37]rose zipper on hackage. Eric has uploaded an implementation of a zipper for Data.Tree to hackage. * Jamie Brandon: [38]QuickCheck strikes again. An update on Jamie's Google Summer of Code project. Lots of failing QuickCheck tests mean Jamie has his work cut out for him. * >>> Ayumilove: [39]Haskell Programming Tutorial Part 1. A video introduction to Haskell? * Roman Cheplyaka (Feuerbach): [40]Status report: week 7-8. An update on Roman's Google Summer of Code project. * Conal Elliott (conal): [41]Designing for the future. * Benedikt Huber (visq): [42]Language.C: Analysing Definitions. An update on Benedikt's Google Summer of Code project. * Max Bolingbroke: [43]Compiler Plugins For GHC: Week Six. An update on Max's Google Summer of Code project. * Arnar Birgisson (Arnar): [44]Playing with Haskell's lazy lists. Arnar implements Eric Rowland's [45]simple prime-generating recurrence using lazy lists in Haskell. * Neil Mitchell (ndm): [46]GSoC Hoogle: Week 8. An update on Neil's Google Summer of Code project. * Matthew Sackman: [47]What is the point?. Matthew had his submission rejected from the Haskell Symposium, and isn't happy about it. * Tupil: [48]Stemming with Haskell reloaded. An updated, more functional/Haskellish interface to the stemmer library. * Luke Palmer (luqui): [49]Semantic Design. Luke's reflections on a design approach learned from Conal Elliott. * Muad`Dib (vixey): [50]Rascal - Mini-haskell like language. * Jeremy Shaw: [51]HTML Templating in HAppS using HSP. Jeremy writes a very cool introduction/tutorial to using HSP (Haskell Server Pages) with HAppS. * >>> Duane Johnson: [52]Lazy Evaluation at Work. Duane likes the idea of lazy file I/O. * >>> Duane Johnson: [53]A Glimmer of Monadic Hope. Duane figures out do-notation. * >>> Duane Johnson: [54]Using 'foldr' in Haskell. Duane figures out how to define (++) and concat in terms of foldr. * Mikael Johansson (Syzygy-): [55]Dr rer nat, Magna cum laude. * >>> Holden Karau: [56]Integrating your HUnit (or other) tests into your cabal package. * Real-World Haskell: [57]Beta availability hiccups. * >>> Antoine Hersen: [58]ICFP 2008 Postmortem. * Edward Kmett (edwardk): [59]A Sort of Difference. Edward uses an analysis of quicksort in Haskell as a jumping-off point for an introduction to difference lists. * Ralf Lammel: [60]The Expression Lemma -- Explained. Ralf explains the relationship between OOP and FP. * >>> Greg McClure: [61]Learning languages through problem-solving. Greg extols the virtues of [62]Project Euler for learning new languages, and exhibits a solution to the first problem in Haskell, Erlang, and Python. Quotes of the Week * kryptiskt: my point is that our brain isn't some logic machine, it's a jury-rigged contraption to help us get food, friends and sex. It's the Perl of intelligences. * Fallacy: peyton `simon` jones * Quadrescence: [on #haskell] Well, the nice population here attracts people. Unlike other pla_C_es. How'd those underscores get there? * mauke: hmm, regexes get even more cryptic after z-encoding: ZLz3fUZCZLz3fUzlznzrwZRZLz3fUzezrwZRzbZLz3fUzlzezrwZRZLz3fUznzrwZRZR * BMeph: Haskell: Where even the newest newcomer acts monadically: join :: ask (ask something) -> ask something * Quadrescence: quicksilver: You must be an anthropomorphic robot or something. About the Haskell Weekly News New editions are posted to [63]the Haskell mailing list as well as to [64]the Haskell Sequence and [65]Planet Haskell. [66]RSS is also available, and headlines appear on [67]haskell.org. Headlines are available as [68]PDF. To help create new editions of this newsletter, please see the information on [69]how to contribute. Send stories to byorgey at seas dot upenn dot edu. The darcs repository is available at darcs get [70]http://code.haskell.org/~byorgey/code/hwn/ . References 1. http://haskell.org/ 2. http://blog.mikael.johanssons.org/archive/2008/07/dr-rer-nat-magna-cum-laud… 3. http://koweycode.blogspot.com/2008/07/rose-zipper-on-hackage.html 4. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/rosezipper 5. http://article.gmane.org/gmane.comp.lang.haskell.cafe/42485 6. http://code.haskell.org/~wren/ 7. http://article.gmane.org/gmane.comp.lang.haskell.general/16351 8. http://haskell.org/opensparc/ 9. http://opensparc.net/ 10. http://article.gmane.org/gmane.comp.lang.haskell.general/16349 11. http://holumbus.fh-wedel.de/hayoo 12. http://article.gmane.org/gmane.comp.lang.haskell.general/16345 13. http://www.haskell.org/mailman/listinfo/beginners 14. http://article.gmane.org/gmane.comp.lang.haskell.general/16343 15. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/haskeline 16. http://hackage.haskell.org/trac/summer-of-code/wiki/SoC2008 17. http://jamiiecb.blogspot.com/2008/07/quickcheck-strikes-again.html 18. http://haskell.org/haskellwiki/Hpysics 19. http://www.haskell.org/haskellwiki/GHC/Data_Parallel_Haskell 20. http://physics-dph.blogspot.com/2008/07/status-report-week-7-8.html 21. http://blog.omega-prime.co.uk/2008/07/21/compiler-plugins-for-ghc-week-six/ 22. http://www.omega-prime.co.uk/files/GHC-Core-HTML.html 23. http://code.haskell.org/hoogle/ 24. http://neilmitchell.blogspot.com/2008/07/gsoc-hoogle-week-8.html 25. http://www.sivity.net/projects/language.c/wiki/ 26. http://hsbene.blogspot.com/2008/07/languagec-analysing-definitions.html 27. http://code.haskell.org/~Saizan/cabal 28. http://hackage.haskell.org/trac/ghc/wiki/GhcApiStatus 29. http://haskell.org/haskellwiki/Library_submissions 30. http://article.gmane.org/gmane.comp.lang.haskell.libraries/9649 31. http://article.gmane.org/gmane.comp.lang.haskell.libraries/9599 32. http://hackage.haskell.org/trac/ghc/ticket/2451 33. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/42475 34. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/42453 35. http://planet.haskell.org/ 36. http://haskell.org/haskellwiki/Blog_articles 37. http://koweycode.blogspot.com/2008/07/rose-zipper-on-hackage.html 38. http://jamiiecb.blogspot.com/2008/07/quickcheck-strikes-again.html 39. http://www.5min.com/Video/Ayumilove-Haskell-Programming-Tutorial-Part-1-311… 40. http://physics-dph.blogspot.com/2008/07/status-report-week-7-8.html 41. http://feeds.feedburner.com/~r/conal/~3/342784118/ 42. http://hsbene.blogspot.com/2008/07/languagec-analysing-definitions.html 43. http://blog.omega-prime.co.uk/2008/07/21/compiler-plugins-for-ghc-week-six/ 44. http://www.hvergi.net/2008/07/playing-with-haskells-lazy-lists/ 45. http://recursed.blogspot.com/2008/07/rutgers-graduate-student-finds-new.html 46. http://neilmitchell.blogspot.com/2008/07/gsoc-hoogle-week-8.html 47. http://www.wellquite.org/what_is_the_point.html 48. http://blog.tupil.com/stemming-with-haskell-reloaded/ 49. http://luqui.org/blog/archives/2008/07/18/semantic-design/ 50. http://muaddibspace.blogspot.com/2008/07/rascal-mini-haskell-like-language.… 51. http://nhlab.blogspot.com/2008/07/html-templating-in-happs-using-hsp.html 52. http://blog.inquirylabs.com/2008/07/18/lazy-evaluation-at-work/ 53. http://blog.inquirylabs.com/2008/07/17/a-glimmer-of-monadic-hope/ 54. http://blog.inquirylabs.com/2008/07/17/using-foldr-in-haskell/ 55. http://blog.mikael.johanssons.org/archive/2008/07/dr-rer-nat-magna-cum-laud… 56. http://feeds.feedburner.com/~r/holdenkarau/iYtm/~3/337908379/integrating-yo… 57. http://www.realworldhaskell.org/blog/2008/07/16/beta-availability-hiccups/ 58. http://endymion2021.livejournal.com/17117.html 59. http://comonad.com/reader/2008/a-sort-of-difference/ 60. http://blogs.msdn.com/ralflammel/archive/2008/07/16/the-expression-lemma-ex… 61. http://www.codechops.com/?p=15 62. http://www.projecteuler.net/ 63. http://www.haskell.org/mailman/listinfo/haskell 64. http://sequence.complete.org/ 65. http://planet.haskell.org/ 66. http://sequence.complete.org/node/feed 67. http://haskell.org/ 68. http://code.haskell.org/~byorgey/code/hwn/archives/20080723.pdf 69. http://haskell.org/haskellwiki/HWN 70. http://code.haskell.org/~byorgey/code/hwn/

1 0

Optimizing 'sequence'
by Gracjan Polak 24 Jul '08

24 Jul '08

Hi all, On the other day I noticed that we could optimize 'sequence' more. I needed it for my monadic parser. Below is my small experiment. Sequence from standard library needs 2.3s to finish (and additional stack space), my version uses only 0.65s and default stack. Is my version better or am I missing something obvious? -- standard sequence1 :: Monad m => [m a] -> m [a] sequence1 ms = foldr k (return []) ms where k m m' = do { x <- m; xs <- m'; return (x:xs) } -- accumulator version sequence2 :: Monad m => [m a] -> m [a] sequence2 ms = sequence' [] ms where sequence' vs [] = return (reverse vs) sequence' vs (m:ms) = m >>= (\v -> sequence' (v:vs) ms) main = do let l = map return [1..1000000] w <- sequence1 l print (sum w) return () gracjan@home:~/some_faster> time ./Some1 +RTS -K100M 500000500000 real 0m2.318s user 0m2.284s sys 0m0.032s gracjan@home:~/some_faster> time ./Some2 500000500000 real 0m0.652s user 0m0.592s sys 0m0.052s -- Gracjan

7 11

InterleavableIO
by Marco Túlio Gontijo e Silva 24 Jul '08

24 Jul '08

Hello, I've done a package based on the Jules Bean's e-mail [1] to Haskell-Café, with a more generalized implementation. In the original version, you could use InterleavableIO with StateT Int IO (), but not with StateT Int (ReaderT Char IO) (). In this version, this is possible. The package, interleavableIO, is available at [2]. I've also done an application that generates a version of a module with generalized parameters, called interleavableGen, available at [3]. This is very alpha, and interleavableGen has been tested only with Control.Exception yet. Comments are very welcome. Greetings. [1]: http://www.haskell.org/pipermail/haskell-cafe/2007-July/028501.html [2]: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/interleavableIO-… [3]: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/interleavableGen… -- Marco Túlio Gontijo e Silva Página: http://marcotmarcot.googlepages.com/ Blog: http://marcotmarcot.blogspot.com/ Correio: marcot(a)riseup.net XMPP: marcot(a)jabber.org IRC: marcot(a)irc.freenode.net Telefone: 25151920 Celular: 98116720 Endereço: Rua Turfa, 639/701 Prado 30410-370 Belo Horizonte/MG Brasil

1 0

Newbie: Replacing substring?
by Dmitri O.Kondratiev 23 Jul '08

23 Jul '08

A few simple questions: What standard library function can be used to replace substring in a string (or sub-list in a list) ? I wrote my own version, please criticize: -- replace all occurances of "123" with "58" in a string: test = replStr "abc123def123gh123ikl" "123" "58" {-- In a string replace all occurances of an 'old' substring with a 'new' substring --} replStr str old new = foldr ((\newSub before after -> before ++ newSub ++ after) new) [] chunks where chunks = splitStr str old {-- Split string into a list of chunks. Chunks are substrings located in a string between 'sub' substrings --} splitStr str sub = mkChunkLst str sub [] where -- mkChunkLst 'src string' 'substr-to-extract' 'list of chunks' -- makes list of chunks located between 'substr-to-extract' pieces in src string mkChunkLst [] _ chunkLst = chunkLst mkChunkLst str sub chunkLst = mkChunkLst after sub (chunkLst ++ [chunk]) where (chunk, _, after) = takeOut str sub [] [] {-- Take out substring from a string. String is divided into: "before substr" ++ "match" ++ "after substr" where 'match' is substring to split out --} takeOut after [] before match = (before, match, after) takeOut [] _ before match = (before, match, []) takeOut (x:xs) (y:ys) before match | x == y = takeOut xs ys before (match ++ [x]) | otherwise = takeOut xs (y:ys) (before ++ match ++ [x]) [] -- Dmitri O. Kondratiev dokondr(a)gmail.com http://www.geocities.com/dkondr

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ANN: list-extras 0.1.0
by wren ng thornton 23 Jul '08

23 Jul '08

hello all~ I'm pleased to announce the initial version of list-extras, a home for common not-so-common list functions. There are many simple but non-trivial functions for lists which Data.List lacks. Typically we write a version and include it in a larger project or store it in a local source tree for personal jobs. But neither of these approaches makes it easy to distribute the code and take advantage of open-source development for improving the code. Since I had code from both approaches, I'm taking the first step and putting a package out there. So far it's not too large though I'll be adding things as they come up. If you have functions you think would belong, feel free to contact me. list-extras includes: - Prelude.Listless This module provides the "Prelude" but removing all the list functions. This is helpful for modules that overload those function names to work for other types. - Data.List.Extras.LazyLength This module provides least-strict functions for getting a list's length and doing natural things with it. On GHC this module also uses rewrite rules to convert certain calls to 'length' into our least-strict versions. [We could do this inefficiently by defining a version of 'length' which returns a Peano integer, but this module is more efficient.] - Data.List.Extras.Pair This module provides safe zipping functions which will fail (return 'Nothing') on uneven length lists. [We could do this by getting the lengths first and comparing, but this module is less strict when the lengths are uneven, and we only traverse the lists once.] - Data.List.Extras.ArgMax This module provides variants of the 'maximum' and 'minimum' functions which return the element for which some function is maximized or minimized. [We could do this by a decorate-fold-undecorate pattern, but this version is more space efficient.] Links to the hackage and darcs copies of list-extras can be found at: http://code.haskell.org/~wren/ -- Live well, ~wren

2 1

Linux kernel/library question
by Galchin, Vasili 23 Jul '08

23 Jul '08

Hello, I am working on POSIX stuff. I have used Linux as my POSIX OS and have read source when I could find it. Does anybody in this group of Linux newsgroup where one can ask Linux-related implementation questions? Regards, Vasili

3 3

Re: [Haskell-cafe] BLAS Solve Example
by Patrick Perry 23 Jul '08

23 Jul '08

Sorry Darrin, the BLAS library only includes matrix multiplication and solving triangular systems. To solve a general system, you would need to use LAPACK, but there aren't any bindings for that library yet. I would suggest you take a look at the hmatrix package, which includes a lot more linear algebra than blas does.. Patrick

1 0

Portland & OSCon
by John Goerzen 22 Jul '08

22 Jul '08

Hi, OSCon is happening in Portland, OR starting 2 weeks from today, with probably the largest number of people there on July 23 and 24. I know there are a number of Haskellers that live in the Portland area, and I suspect a few more may be going to OSCon. Anyone interested in a Haskell gathering someplace? -- John

4 4

Building NDP with latest GHC
by Austin Seipp 22 Jul '08

22 Jul '08

Hi, After my last issue with GHC's HEAD, I tried checking it out again and getting the patches for the libraries and lo and behold, it worked. So now I'm up to date with the latest libraries and the compiler, but it appears that building NDP itself is proving to be troublesome. (This is on GHC 6.9.20080720, btw) I've pulled the latest ndp package from http://darcs.haskell.org/packages/ndp into ./libraries. Instructions that are listed in [1]: > % cd libraries > % darcs get http://darcs.haskell.org/packages/ndp/ > % make make.library.ndp > % cd ndp/examples > % make This fails on step 3; the Makefile in the libraries subdirectory doesn't recognize 'make.library.ndp' as a valid target. Instructions in the actual README that comes with package ndp: > cd ndp > make boot > make > cd examples > make This fails on the 'make boot' step, because if you look at the Makefile, it thinks the top of the GHC source tree is at '..', when it's actually '../..' in relation to ./libraries/ndp: > TOP=.. > include $(TOP)/mk/boilerplate.mk > include ndp.mk > ... rest of makefile ... No big deal in this case, just a fix of changing TOP to '../..' Having done that, however, now it fails because it it cannot correctly parse bootstrapping.conf which is located in ./libraries: > $ make boot > ../../mk/target.mk:454: warning: overriding commands for target `libHSndp' > ../../mk/package.mk:249: warning: ignoring old commands for target `libHSndp' > ../../mk/target.mk:454: warning: overriding commands for target `ghc-prim.a' > ../../mk/package.mk:249: warning: ignoring old commands for target `ghc-prim.a' > /Users/austinseipp/src/ghc-head/ghc/stage1-inplace/bin/ghc -M > -optdep-f -optdep.depend -osuf o -package-conf > /Users/austinseipp/src/ghc-head/libraries/bootstrapping.conf -H32m > -O -fasm -Rghc-timing -package-name ndp ghc-prim-0.1 -O -fgenerics > -package base -XGenerics -fglasgow-exts -fbang-patterns -O2 > -funbox-strict-fields -fdicts-cheap -fno-method-sharing > -fno-spec-constr-threshold -fmax-simplifier-iterations20 -threaded > -XTypeFamilies -fcpr-off > > ... lots of files trying to get compiled here ... > > <no location info>: > Warning: -fgenerics is deprecated: Use the Generics language > instead > > <no location info>: > Warning: -fbang-patterns is deprecated: Use the BangPatterns > language instead > ghc: > /Users/austinseipp/src/ghc-head/libraries/bootstrapping.conf:1:62: > parse error on input `"' > <<ghc: 41436660 bytes, 4 GCs, 118784/118784 avg/max bytes residency (1 > samples), 31M in use, 0.00 INIT (0.00 elapsed), 0.08 MUT (0.12 > elapsed), 0.01 GC (0.02 elapsed) :ghc>> > make: *** [depend] Error 1 For the record, the thing it fails on is the *first* occurance of a quotation mark, and that's here in bootstrapping.conf: > [InstalledPackageInfo {package = PackageIdentifier {pkgName = > "filepath", pkgVersion = ... So it's failing when it sees the quote at the start of "filepath" I have also attempted to follow the instructions at the top ./libraries/Makefile, which are: > # To do a fresh build: > # > # make clean > # make boot > # make > # > # To rebuild a particular library <package>: > # > # make clean.library.<package> > # make make.library.<package> > # > # or the following is equivalent: > # > # make remake.library.<package> > # > # To add a new library to the tree, do > # > # darcs get http://darcs.haskell.org/packages/foo > # [ -e foo/configure.ac ] && ( cd foo && autoreconf ) > # make make.library.foo As said above, 'make.library.ndp' does not work, doing a full clean, boot and then make again doesn't pick up NDP either, and in the last case (adding a new library,) it doesn't matter because there is no configure.ac at the top level of ./libraries/ndp I think I might simply have a *lot* of outdated information. For the record, this is what I want to try and compile: > {-# OPTIONS_GHC -fglasgow-exts -fparr -fvectorise #-} > module Main where > import GHC.PArr > > dotp :: Num a => [:a:] -> [:a:] -> a > dotp xs ys = sumP [:x * y | x <- xs, y <- ys :] > > main = print $ dotp [:1..5:] [:6..10:] Naturally when trying, it fails because DPH isn't there: > $ ~/ghc-head/bin/ghc --make dotp.hs > > <no location info>: > Warning: -fparr is deprecated: Use the PArr language instead > [1 of 1] Compiling Main ( dotp.hs, dotp.o ) > GHC error in desugarer lookup in main:Main: > Failed to load interface for `Data.Array.Parallel.Lifted.PArray': > no package matching dph-par was found > ghc: panic! (the 'impossible' happened) > (GHC version 6.9.20080720 for i386-apple-darwin): > initDs user error (IOEnv failure) > > Please report this as a GHC bug: > http://www.haskell.org/ghc/reportabug (This leads me to believe I actually want http://darcs.haskell.org/packages/dph, but it's not mentioned. Anywhere.) If I'm just doing everything wrong, I'd really appreciate knowing and I'd be *more* than happy to update the wiki pages so that more people can try it and have it build successfuly, because as it stands I'm coming to the conclusion that basically all the information in [1] is just old and flat-out wrong, and I'm completely of ideas on how to go about this. Thanks, Austin [1] http://haskell.org/haskellwiki/Data_Parallel_Haskell/PackageNDP

2 1

Trees (Rose Trees?)
by Ryan Bloor 22 Jul '08

22 Jul '08

hi I was curious as to whether my implementation of a Rose Tree and a sumTree function was correct. The aumTree adds up the elements of a tree. data Tree a = Leaf a | Node [Tree a] sumTree :: Tree Int -> Int sumTree (Node []) = 0 sumTree (Node xs) = sum (map sumTree xs) The problem with this is I get a pattern matching error. Am I representing trees right... see below. Also, would an empty tree be represented by ... Node [] with this implementation? How would I represent a tree of the form... Tree (Node 2(Node 6 Empty Empty) Empty) taken from a binary one. Like this? Node [ [Leaf 2], Node [ Leaf 6,Node[],Node[] ], Node[] ] Ryan _________________________________________________________________ Find the best and worst places on the planet http://clk.atdmt.com/UKM/go/101719807/direct/01/

2 1

Re: Extending the GSoC model
by Neil Mitchell 22 Jul '08

22 Jul '08

Hi Suggested by Andrew Wager on libraries@, moving to haskell-cafe@ since its a really interesting idea and libraries is probably not the best place for it. > Not sure if this is the best place to suggest this, but I was > wondering about the possibility of extending the model that we > currently use for Google's Summer of Code. > > The benefits: > 1.) A place to make suggestions for code you would never be able to > write, and somebody else might not think of > 2.) A place to see what's being worked on, but not yet done > 3.) A way for people who are less confident in their haskell-foo to find mentors > 4.) A way for people who are more confident in their haskell-foo to > contribute without spending a ton of time hacking up actual code > 5.) Overall, more (and higher-quality) libraries And my thoughts: 1) I think as long as the suggestions are small improvements to existing projects it could work really well. New projects are probably less likely to work without the original author having the original motivation. I have one of these for some of my projects: http://code.google.com/p/ndmitchell/issues/list - a bug tracker works quite well. 2) Bug trackers do this. 3, 4) Fantastic idea, coordinating via the IRC channel already gives some of this, but it could be made more direct. Also having a specific person to talk to, and to review/commit/integrate the work makes the work more useful. 5) Always a great idea. So I think these things could be achieved by integrating various bug trackers, ensuring lots of projects on hackage have bug trackrs, and some mailing list for people working on this to allow people to ask for mentors and mentors to be available to respond. My guess that if there are the people who want mentors, then mentors could be found - but the other way round won't happen. Thanks Neil

1 0

Trouble with non-exhaustive patterns
by Fernando Rodriguez 22 Jul '08

22 Jul '08

Hi, I defiend the following function to get the last element of a list: final [a] = a final (_:t) = final t and it works as expected. Since I didn't want to have a non exhaustive pattern, I added the following case: final [] = [] - I consider that the end of an empty list is the empty list final [a] = a final (_:t) = final t Suddenly, the function stoped working with a rather cryptic (for a newbie at least) error message: *Temp> final [4,5] <interactive>:1:9: No instance for (Num [a]) arising from the literal `5' at <interactive>:1:9 Possible fix: add an instance declaration for (Num [a]) In the expr*Temp> ession: 5 In the first argument of `final', namely `[4, 5]' In the expression: final [4, 5] What have I done so wrong? Thanks in advance, Fernando

6 5

A good sign: languages used at Google Code Jam
by Don Stewart 22 Jul '08

22 Jul '08

http://www.go-hero.net/jam/lang Haskell as the highest ranked FP language in the Google Code Jam, with more submissions than Lisp, Scheme, SML and OCaml put together :) # C++ (used by 2875 people) # Java (used by 1747 people) # Python (used by 691 people) # C# (used by 609 people) # C (used by 453 people) # Perl (used by 193 people) # Ruby (used by 124 people) # PHP (used by 119 people) # Pascal (used by 90 people) # Haskell (used by 46 people) # Visual Basic (used by 43 people) # Objective-C (used by 24 people) # Lisp (used by 15 people) # Javascript (used by 13 people) # Scheme (used by 11 people) # Lua (used by 10 people) # Objective CAML (used by 10 people) # Basic (used by 9 people) # Bourne Shell (bash) (used by 5 people) # D (used by 4 people) # Groovy (used by 4 people) # J (used by 4 people) # Scala (used by 4 people) # ActionScript (used by 3 people) # Clojure (used by 2 people) # Eiffel (used by 2 people) # Erlang (used by 2 people) # SQL (used by 2 people) # Shell Script (sh) (used by 2 people) # Visual Basic Script (used by 2 people) # AWK (used by 1 people) # Arc (Lisp) (used by 1 people) # AutoIt Ver. 3 Script (used by 1 people) # Brainfuck (used by 1 people) # GNU Data Language (used by 1 people) # Informix 4GL (used by 1 people) # K (used by 1 people) # Maple (used by 1 people) # Standard ML (used by 1 people)

1 0

Keeping a set of ForeignPtr's alive
by Felipe Lessa 22 Jul '08

22 Jul '08

Hi! -- Background: -- I have some foreign objects that are mapped to ForeignPtr's, say newtype Obj = O (ForeignPtr Obj) and a foreign "collection" where those objects are added. The adding is something on the lines of addObj, removeObj :: Collection -> Obj -> IO () id est, the C code of the collection maintains a reference to all objects added. That means I have to keep all the ForeignPtr's added alive and that I must not prevent garbage collection of those removed. Of course the 'Collection' isn't just a simple collection, otherwise I would be using normal Haskell counterparts. -- Question: -- What is the best way to keep the added objects alive? Using a list will keep the addition cheap and a low memory overhead, while a Data.Set will make removeObj work in sublinear time (on the Haskell side). Are there any other options? I'm currently heading towards data Collection = C !(ForeignPtr Collection) !(IORef [Obj]) like ForeignPtr itself (although in the case of ForeignPtr's there is no way to remove finalizers). Thanks! -- Felipe.

1 0

Re: Help using Network.Curl
by Jim Burton 21 Jul '08

21 Jul '08

I tried to translate that using the Network.Curl docs and ended up with the following code, but it's not sending the post data correctly (an ebay api error re an "unsupported verb", which I am told means a malformed request). Any ideas? The code from a perl tutorial (which works for me, making me think that my problem is just about the right way to post xml to a web service) follows the haskell version, which is meant to be a straight translation of that. Thanks, Jim ---------------------- [..skipped definitions of tokens etc..] opts = [CurlEncoding "text/xml" , CurlHttpHeaders ["X-EBAY-API-COMPATIBILITY-LEVEL="++compatLevel , "X-EBAY-API-DEV-NAME="++devName , "X-EBAY-API-APP-NAME="++appName , "X-EBAY-API-CERT-NAME="++certName , "X-EBAY-API-CALL-NAME=GeteBayOfficialTime" , "X-EBAY-API-SITEID=0"]] body = "<?xml version='1.0' encoding='utf-8'?>" ++ "<GeteBayOfficialTimeRequest xmlns=\"urn:ebay:apis:eBLBaseComponents\">" ++ " <RequesterCredentials>" ++ " <eBayAuthToken>"++token++"</eBayAuthToken>" ++ " </RequesterCredentials>" ++ "</GeteBayOfficialTimeRequest>" url = "https://api.sandbox.ebay.com/ws/api.dll" postData = HttpPost {postName = "body" , contentType = Just "text/xml" , content = ContentString body , extraHeaders = [] , showName = Nothing} opts = [] --also tried using curlPost and setopts then perform... main = withCurlDo (do h <- initialize curlMultiPost url opts [postData] ) --------------------------- Original perl: use strict; use LWP::UserAgent; use HTTP::Request; use HTTP::Headers; # define the HTTP header my $objHeader = HTTP::Headers->new; $objHeader->push_header('X-EBAY-API-COMPATIBILITY-LEVEL' => '391'); $objHeader->push_header('X-EBAY-API-DEV-NAME' => 'yourdevname'); $objHeader->push_header('X-EBAY-API-APP-NAME' => 'yourappname'); $objHeader->push_header('X-EBAY-API-CERT-NAME' => 'yourcertname'); $objHeader->push_header('X-EBAY-API-CALL-NAME' => 'GeteBayOfficialTime'); $objHeader->push_header('X-EBAY-API-SITEID' => '0'); $objHeader->push_header('Content-Type' => 'text/xml'); # define the XML request my $request = "<?xml version='1.0' encoding='utf-8'?>" . "<GeteBayOfficialTimeRequest xmlns=\"urn:ebay:apis:eBLBaseComponents\">" . " <RequesterCredentials>" . " <eBayAuthToken>TOKENGoesHERE</eBayAuthToken>" . " </RequesterCredentials>" . "</GeteBayOfficialTimeRequest>"; # make the call my $objRequest = HTTP::Request->new( "POST", "https://api.sandbox.ebay.com/ws/api.dll", $objHeader, $request ); # deal with the response my $objUserAgent = LWP::UserAgent->new; my $objResponse = $objUserAgent->request($objRequest); if (!$objResponse->is_error) { print $objResponse->content; } else { print $objResponse->error_as_HTML; } ------------------------------ This is what I get when running my version: $ ./curlTest * About to connect() to api.sandbox.ebay.com port 443 (#0) * Trying 66.135.197.133... * connected * Connected to api.sandbox.ebay.com (66.135.197.133) port 443 (#0) * successfully set certificate verify locations: * CAfile: /etc/ssl/certs/ca-certificates.crt CApath: none * SSL connection using AES256-SHA * Server certificate: * subject: /C=US/ST=California/L=San Jose/O=eBay Inc./OU=Site Operations/CN=api.sandbox.ebay.com * start date: 2008-01-25 00:00:00 GMT * expire date: 2010-03-15 23:59:59 GMT * common name: api.sandbox.ebay.com (matched) * issuer: /C=US/O=VeriSign, Inc./OU=VeriSign Trust Network/OU=Terms of use at https://www.verisign.com/rpa (c)05/CN=VeriSign Class 3 Secure Server CA * SSL certificate verify ok. > POST /ws/api.dll HTTP/1.1 Host: api.sandbox.ebay.com Accept: */* Accept-Encoding: text/xml Content-Length: 1254 Expect: 100-continue Content-Type: multipart/form-data; boundary=----------------------------7c836e9408cd < HTTP/1.1 100 Continue < HTTP/1.1 200 OK < Date: Sat, 19 Jul 2008 20:04:12 GMT < Server: Microsoft-IIS/5.0 < X-EBAY-API-POOL-NAME: ___cDRidW90YmtiZWx9b2l3aQ== < X-EBAY-API-SERVER-NAME: ___dXUucnVlYnVvNzM3KTYzKzc3LTI0KTQxPD8zPTc= < Content-Type: text/xml < Content-Length: 330 < X-Cache: MISS from sjcsbagpigw02.sjc.ebay.com, MISS from sjcsbagpigw02.sjc.ebay.com < Connection: close < * Closing connection #0 <?xml version="1.0" encoding="UTF-8" ?><eBay><EBayTime>2008-07-19 20:04:55</EBayTime><Errors><Error><Code>2</Code><ErrorClass>RequestError</ErrorClass><SeverityCode>1</SeverityCode><Severity>SeriousError</Severity><Line>0</Line><Column>0</Column><ShortMessage><![CDATA[ Unsupported verb. ]]></ShortMessage></Error></Errors></eBay>

2 2

GHC Error: "FATAL:Symbol _XJv_srt already defined."
by Ron Alford 21 Jul '08

21 Jul '08

Anyone know what this is about? Removing parts makes problem go away, but it's not clear what parts to remove! (that, and I wrote those parts for a reason!). bash-3.2$ ghc --version The Glorious Glasgow Haskell Compilation System, version 6.8.3 bash-3.2$ uname -a Darwin silverback-wired.home 9.4.0 Darwin Kernel Version 9.4.0: Mon Jun 9 19:30:53 PDT 2008; root:xnu-1228.5.20~1/RELEASE_I386 i386 $ rm -f DerivingError.o DerivingError.hi; ghc --make DerivingError.hs [1 of 1] Compiling DerivingError ( DerivingError.hs, DerivingError.o ) /var/folders/C0/C0SledGV2RaxbU+8ZLDnVU+++TI/-Tmp-//ghc27223_0/ghc27223_0.s:6080:0: FATAL:Symbol _XxG_srt already defined. -Ron Alford

2 2

Haskell code contributions
by Galchin, Vasili 21 Jul '08

21 Jul '08

Hello, I have a password to upload Haskell code contributions but I can't find the email with the password and I have forgotten who is the "gatekeeper". ?? Regards, Vasili

2 1

Data.Complex.magnitude slow?
by stefan kersten 21 Jul '08

21 Jul '08

hi, i've attached an example program which seems to indicate that the magnitude function from Data.Complex is very slow compared to a more naive implementation (for Complex Float). on my machine (intel core2 duo, osx 10.4) the CPU time using the library function is about 6-7 times as much as when using the other function. any ideas what might be going on? any flaws in my measurement code? thanks, <sk>

7 17

Help with optimization
by Mitar 21 Jul '08

21 Jul '08

Hi! Profiling says that my program spends 18.4 % of time (that is around three seconds) and 18.3 % of allocations in this function which is saving the rendered image to a PPM file: saveImageList :: String -> Int -> Int -> [ViewportDotColor] -> IO () saveImageList filename width height image = do B.writeFile filename file where file = B.append header bytes header = C.pack $ "P6\n" ++ show width ++ " " ++ show height ++ "\n255\n" bytes = B.pack $ concatMap (color . dealpha . (\(ViewportDotColor _ c) -> c)) image where color (VoxelColor red green blue _) = [floor $ red * 255, floor $ green * 255, floor $ blue * 255] dealpha c = addColor c (VoxelColor 1.0 1.0 1.0 1.0) -- white background For a 921615 bytes large file to save this is too much in my opinion. And I think that it consumes to much allocations. Probably it should not store intermediate lists? Any suggestions? Best regards Mitar

3 3

ghc 6.8.3 build error with __DISCARD__ linking problem, please help!
by Yu Di 20 Jul '08

20 Jul '08

Hi, I am trying to build ghc 6.8.3 from source release, my currently installed version is ghc 6.4.2 (x86 linux binary release version), and I got: /usr/local/ghc/bin/ghc -o ghc-pkg.bin -H16m -O -cpp -Wall -fno-warn-name-shadowing -fno-warn-unused-matches -DUSING_COMPAT -i../../compat -ignore-package Cabal -Rghc-timing -package unix -L../../compat -lghccompat Main.o Version.o CRT_noglob.o Main.o: In function `__stginit_ZCMain': ghc13533.hc:(.text+0x4): undefined reference to `__DISCARD__' ghc13533.hc:(.text+0x9): undefined reference to `__DISCARD__' Main.o: In function `__stginit_Main': ghc13533.hc:(.text+0x18): undefined reference to `__DISCARD__' ghc13533.hc:(.text+0x1d): undefined reference to `__DISCARD__' Main.o: In function `__stginit_Main_': ghc13533.hc:(.text+0x2c): undefined reference to `__DISCARD__' Main.o:ghc13533.hc:(.text+0x3d): more undefined references to `__DISCARD__' follow collect2: ld returned 1 exit status <<ghc: 13726704 bytes, 3 GCs, 105428/105428 avg/max bytes residency (1 samples), 15M in use, 0.00 INIT (0.00 elapsed), 0.01 MUT (1.98 elapsed), 0.01 GC (0.03 elapsed) :ghc>> Do you know how I can fix this problem? My ghc and gcc versions are: The Glorious Glasgow Haskell Compilation System, version 6.4.2 gcc (GCC) 4.1.1 20060724 (prerelease) (4.1.1-4pclos2007) Thanks! Di, Yu 7.19

1 0

Trying to install cabal
by Eric 19 Jul '08

19 Jul '08

Dear all, I have downloaded cabal and am trying to install it but have gotten the following error message: C:\cabal\cabal-install-0.5.1>runghc Setup configure Configuring cabal-install-0.5.1... Setup: At least the following dependencies are missing Cabal >=1.4&&<1.5, HTTP >=3000&&<3002, zlib >=0.4 I'm not sure from this message what packages I need to install to get cabal up and running. Can anyone help? Eric M.

8 8

FFI C Structs
by Aleš Bizjak 19 Jul '08

19 Jul '08

Hello, Suppose I have a C struct like typedef { int a; int *b; } Foo; typedef Foo *fooptr; and all worker functions which are all basically int foofun (fooptr , fooptr, fooptr) where the first one is a out argument and the other two are in arguments and the return value is (almost) irrelevant. Now before I can pass arguments I have to initialize them and this is done with void init(fooptr ) function and all values have to be cleared which is done with void clear(fooptr ). I tried to import this to haskell like this. data Foo = Foo type FFptr = ForeignPtr Foo and because I would like to have a nice interface without manually worrying about allocation and freeing up I tried something like this: foreign import ccall "&clear" clear :: FunPtr (Ptr Foo -> IO ()) foreign import ccall "init" init :: Ptr Foo -> IO () foreign import ccall "foofun" foofun_ :: Ptr Foo -> Ptr Foo -> Ptr Foo -> IO Int foofun :: FFptr -> FFptr -> FFptr foofun f1 f2 = unsafePerformIO f where f = withForeignPtr f1 (p1 -> withForeignPtr f2 (p2 -> do p3 <- malloc init p3 r <- foofun_ p3 p1 p2 newForeignPtr clear p3 Now should that work or do I have to do some more reading on ffi and if so, would anyone recommend some material because this is all I could come up with. PS: An example of a haskell binding like this would be even more useful, if anyone knows of such.

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NW Functional Programming Interest Group
by Greg Meredith 19 Jul '08

19 Jul '08

All, Apologies for multiple listings. A small cadre of us are organizing a Northwest Functional Programming Interest Group (hey... NWFPIG, that's kinda funny). Our first official meeting is at the The Seattle Public Library 1000 - 4th Ave. Seattle, WA 98104 from 17:00 - 18:00 on February 20th. On the first meeting's agenda we'll be - giving people who are interested in or actively using FP for work or play a chance to meet - seeking to build up a pipeline of presentations and guest speakers - trying to keep organizational mishigosh to a minimum Hope to see you there. Monadically yours, --greg -- L.G. Meredith Managing Partner Biosimilarity LLC 806 55th St NE Seattle, WA 98105 +1 206.650.3740 http://biosimilarity.blogspot.com

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Help using Network.Curl
by Jim Burton 19 Jul '08

19 Jul '08

I want to convert this code (a Hello World with the ebay API) to the curl binding in the hope that it will handle SSL and redirections etc better. Can someone give me some pointers please, or a link to an example? I haven't used libcurl or Network.Curl and can't find anything helpful...Thanks! ----------------- import Network.URI import Network.HTTP import Network.Browser import Data.Maybe (fromJust) mkRequest :: Request mkRequest = Request { rqURI = fromJust (parseURI "https://api.sandbox.ebay.com/ws/api.dll") , rqMethod = POST , rqBody = body , rqHeaders = headers } headers :: [Header] headers = [Header HdrContentType "text/xml" , Header (HdrCustom "X-EBAY-API-COMPATIBILITY-LEVEL") "391" , Header (HdrCustom "X-EBAY-API-DEV-NAME") "DevName" , Header (HdrCustom "X-EBAY-API-APP-NAME") "AppName" , Header (HdrCustom "X-EBAY-API-CERT-NAME") "CertName" , Header (HdrCustom "X-EBAY-API-CALL-NAME") "GeteBayOfficialTime" , Header (HdrCustom "X-EBAY-API-SITEID") "0" ] body = "<?xml version='1.0' encoding='utf-8'?>" ++ "<GeteBayOfficialTimeRequest xmlns=\"urn:ebay:apis:eBLBaseComponents\">" ++ " <RequesterCredentials>" ++ " <eBayAuthToken>"++"MyToken"++"</eBayAuthToken>" ++ " </RequesterCredentials>" ++ "</GeteBayOfficialTimeRequest>" main = do (_, resp) <- browse (request mkRequest) print resp

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syntactic anti-unification of TH terms --- best practise?
by Martin Hofmann 18 Jul '08

18 Jul '08

I am implementing syntactic anti-unification for TH terms (Exp, Pat, Clause, ...). For example anti-unifying the clauses tail (1:xs) = xs tail (1:2:xs) = (2:xs) would yield tail (1:x1) = x1 whereas the anti-instance of last (1:[]) = 1 last (1:xs) = last xs is last (1:x1) = x2 So different subterms are always replaced with the same variable if anti-unified twice. So far, so good, there is nothing complicated. I am using a State Monad to keep track of my variables and defined a type class for anti-unification and implemented instances for Exp, Pat, ... type AU a = State (Data.Map [a] a) a class Antiunifieable t where antiunify :: (Ord t) => [t] -> t antiunify = (\t -> evalState (aunify t) M.empty) aunify :: (Ord t) => [t] -> AU t Problems arise when I come to clauses, defined in TH as Clause [Pat] Body [Dec] where Body is for example NormalB Exp Since a term can occur both as a pattern on the left-hand side of the equation and also as expression on the right-hand side, I need to keep track of this, too. So in fact, I have to anti-unify the patterns, 'translate' the resulting state (Data.Map [Pat] Pat) to (Data.Map [Body] Body) and pass it to the state transformer for anti-unifying the bodies. Similarly, from Body to Exp. This seems a bit ugly to me, but I have no idea how to solve it more elegantly. I thought about introducing some kind of wrapper type like data Term = TC Clause | TB Body | TP Pat | TE Exp and implement an instance for Eq and Antiunifieable for it. But again, this is not better either and I run into a lot of bookkeeping when processing it. Is there some kind of best practise dealing with such a problem? I am not sure if MonadTransformers would help here, because it is always the same monad but with different parameter. Thanks a lot, Martin

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Space leaks
by Peter Gavin 18 Jul '08

18 Jul '08

Hello everyone, I have this piece of code I've been working on, and I've been stuck on tracking down a space leak in it for some time now. The code is essentially a tight loop that updates a rather largish data structure with embedded functions that are called by the driver loop. The code doesn't accumulate any data as the loop runs (at least deliberately), so I would expect the memory profile to be flat. Unfortunately, the profile is a wedge :) I've added bangs and `seq` literally everywhere, and it looks (to me at least) like there's nothing left to be lazily evaluated anywhere. I've used retainer profiling, and the functions that are leaking space according to the profiler output are strict throughout. I'm really pulling my hair out over this, but I'm reluctant to publish the code just yet because I'm planning on using it (eventually) for my thesis. It seems like I've just about run out of options, though. Does anyone have any advice on tracking down space leaks? I don't want to accuse GHC of having a bug just yet, but has GHC had space leak bugs in the past? Thanks in advance, Peter Gavin <gavin(a)cs.fsu.edu>

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FFI and struct arguments
by Felipe Lessa 18 Jul '08

18 Jul '08

Hi, I tried googling and searching the haskellwiki about this but wasn't lucky enough. My question is: is there a way to send struct arguments to C functions via the FFI or do I need to create a C wrapper? I guess there isn't, and while I can live without it, I'd like to leave no doubt. Details: I have something like ==================== typedef struct vect { float x,y; } vect; void func(vect v); ===================== on the C side and ==================== -- Please disregard float /= Float, just an example :) data Vector = Vector Float Float instance Storable Vector where ... ==================== on the Haskell side, and I want to call func with Vector as argument. Now, Vector isn't a basic FFI type, although it implements Storable. So does that mean that I need to create something like ==================== void funcWrapper(vect *v) { func(*v); } ==================== and then allocate some temporary memory on the Haskell side to use func? Cheers! -- Felipe.

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uvector and the stream interface
by stefan kersten 18 Jul '08

18 Jul '08

currently i'm working on stuff that looks something like this: 1 read soundfile from disk in blocks of N samples (IOCArray, hsndfile package) 2 convert to CArray with unsafeFreeze (simple O(1) cast, carray package) 3 perform FFT (CArray, fftw package) 4 convert to UArr (uvector package) 5 do some stuff with vectors i'd like to minimize copying, and since the FFT returns a new array anyway, the only copying conversion is the one between CArray and UArr in step 4. the approach i've been following is defining a `stream' conversion for CArray, hoping that subsequent carray accesses will be fused with uvector operations without the need for allocating a vector in between. does that make sense? could this be a general strategy for avoiding copying at the boundary between the various array libraries? thanks, <sk>

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