July 2008 - Haskell-Cafe

ANN: RandomDotOrg-0.1
by Austin Seipp 28 Jul '08

28 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 28 Jul '08

28 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 28 Jul '08

28 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 27 Jul '08

27 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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