March 2008 - Haskell-Cafe

[GSoC] Parallel Benchmarking and Profiling
by Etienne Laurin 28 Mar '08

28 Mar '08

Hello, I am putting together a student proposal to participate in Google's Summer of Code with one of the following project ideas. Parallel programming benchmarking and benchmark suite - http://hackage.haskell.org/trac/summer-of-code/ticket/1544 Are there open source projects and real world applications that rely on GHC's parrallel programming primitives and libraries? I have found many references to LOLITA, but it seems to be old and not available online. The idea page suggests porting existing benchmark suites such as PARSEC, but PARSEC is 5G of C code. Most of it seems to come from existing applications already written in C. It might also be interesting to automate the discovery of optimal strategies through empirical data, and to modify the thresholds dynamically. Parallel profiling tools for GHC - http://hackage.haskell.org/trac/summer-of-code/ticket/1559 Simon Marlow wrote on the idea page that Gransim was ported to a more up-to-date GHC. The documentation available on the web seems to be for GHC 0.29 but it describes many options for logging and visualising the activity of threads and processors over time. Getting GHC to display that information on the frontpanel would make a nice project. Do you have any comments or suggestions? Thank you, Etienne Laurin

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Re: [Haskell-cafe] Web server libraries
by Sterling Clover 28 Mar '08

28 Mar '08

Yipe. It's just been pointed out to me that the hvac repo was missing a key file. I just committed it and tried a fresh pull and build, and it seems to work properly now. Apologies to all who couldn't get it working. Regards, Sterl. On Fri, 28 Mar 2008, Sterling Clover wrote: > While hvac, which I announced here recently, is not yet ready for > primetime, so to speak, you may want to take a look at it -- with a > few tweaks it should match your specs. (darcs get http:// > community.haskell.org/~sclv/hvac/<http://community.haskell.org/%7Esclv/hvac/> ) > [...]

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MonadMemory class
by Ariel J. Birnbaum 28 Mar '08

28 Mar '08

Two questions came to mind while thinking of memory references in Haskell: 1. Is there a "standard" equivalent of the following: class (Monad m) => MonadMemory m r | m -> r where new :: a -> m (r a) read :: r a -> m a write :: r a -> a -> m () What kind of axioms should an instance of this class satisfy? 2. How would a "pure" instance of this class look like (obvious unsafePerformIO-based solutions aside)? Is it even possible in pure Haskell? Thanks much! -- Ariel J. Birnbaum

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Recursion problem in infinite list model
by Hans Aberg 28 Mar '08

28 Mar '08

When experimenting with list index sets (i.e. lists more general than provided by Haskell), I arrived at the problem that in the example code below for example h(list 6) does not (in Hugs) write out the beginning of the list lazily. It does work for list 6 first (list 6) rest (list 6) 10 -+ (list 3) and so on. So it seems to be a problem with h, also suggested by heap profiling, perhaps similar to that of "foldl". So is it possible to fix it? The function h x is derived by unwinding the monadic construct corresponding to (for lists) do {i <- [x..]; return i} So there are not many possibilities of change. Below, (-+) corresponds, for lists, to ":", "first" to "head", and "rest" to "tail". Hans Aberg -------- data List a = List(Integer->a) instance Show a => Show (List a) where show (List f) = "[" ++ show (f(0)) ++ concat ["," ++ show (f(toInteger i))| i<-[1..]] ++ "]" list :: Integer -> List Integer list x = List(\z -> x+z) (-+) :: a -> List a -> List a x -+ (List y) = List(f) where f 0 = x f k = y(k-1) first :: List a -> a first (List f) = f 0 rest :: List a -> List a rest (List y) = List(f) where f k = y(k+1) h :: List a -> List a h x = (-+) (first x) (h (rest x)) --------

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Running classical logic
by Jim Apple 28 Mar '08

28 Mar '08

We can't safely extract a t out of IO t, but we can run an IO t, interact with the environment, and then see the t. Griffin ( http://citeseer.ist.psu.edu/griffin90formulaeastypes.html ) explained that we can do the same thing with (t -> r) -> r by interacting with the context. That is, he defined a function c :: ((t -> r) -> r) -> t buy interaction with the reduction context of calls to c. I don't expect such a function to be definable in Haskell without some magic, but even with magic, I'm not sure how to write such a function. On #haskell a couple of days ago, we came up with data Empty deriving Typeable toEmpty :: a -> Empty toEmpty = unsafeCoerce fromEmpty :: Empty -> a fromEmpty = unsafeCoerce type Bot = forall x . x griffinC :: Cont Bot a -> IO a griffinC (Cont f) = do key <- newUnique catch (evaluate $ f $ \v -> throwDyn (hashUnique key,toEmpty v)) (\x -> case x of DynException d -> case fromDynamic d of Just (u,y) -> if u == hashUnique key then return $ fromEmpty y else throwIO x Nothing -> throwIO x _ -> throwIO x) The Unique is used to keep the later griffinC calls from being cast to the wrong types. The more I look at this, the less I understand it. Any clues? Jim P.S. Thanks to #haskell, and especially roconnor for the fine help

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Web server libraries
by John Goerzen 28 Mar '08

28 Mar '08

Hi again, I'm currently working on a project that has a Web interface to data stored in a SQL database. I wrote this thing in WASH a few years back. Overall, this has been acceptable, but the non-Haskell-adepts around here run away screaming from the code. Not only that, but we don't get control over the names of the form elements, which can make interacting with other software that sometimes plonks users down halfway through the process -- well, interesting. Also, WASH supports nothing better than CGI, which is a big minus when talking to SQL databases. What I really want is some sort of simple tool that supports FastCGI or some such, has basic support for form data input validation and marshalling to/from Haskell types, and basic control flow. I don't need, or really particularly want, something that uses hs-plugins to compile pages on demand (I'm using Haskell for it's static safety, after all). Nor do I need fancy templating systems or session support (we use HTTP auth and are fine with it for now.) So I've looked around a bit at the landscape. Any recommendations? I've found these: HSP: big on "dynamic pages". I don't want to make my webserver able to compile Haskell code. Develop code, compile, test, make sure it's right, then push to production every 6 months around here. WASH: Pretty much the right niche, but the event model is hard to use. HAppS: Frankly it is a big collection of confusing packages to me. What documentation exists doesn't seem to be relevant anymore, and it seems to be designed to not use a SQL database. FastCGI: Relies upon CGI for a good part of processing. Does not seem to have any form data validation support built in. Thanks again, -- John

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reactive programming, what's hot?
by Greg Fitzgerald 27 Mar '08

27 Mar '08

A new version of yampa<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Yampa-0.9.2>was uploaded to hackage today, but it's website <http://www.haskell.org/yampa/> hasn't been updated since 2004. SpaceInvaders<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/SpaceInvaders-0.…>depends on HGL and Yampa. There's been more noise around Phooey<http://haskell.org/haskellwiki/Phooey>and TV <http://haskell.org/haskellwiki/TV> in recent months, but afaik, hasn't been used for any applications yet. There was also ParseP <http://twan.home.fmf.nl/parsep/> which seems to tackle a similar problem, but from the perspective of a more general parsing library. Are there other purely functional reactive libraries in active development? Why might one choose one over another? Thanks, Greg

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GSoC Project Proposal: Parallel Profiling Tools for GHC.
by Donnie Jones 27 Mar '08

27 Mar '08

Hello Everyone,GSoC Project: Parallel Profiling Tools for GHC. Student: Donnie Jones Mentor: Simon Marlow Project based upon suggestion by Simon Marlow: http://hackage.haskell.org/trac/summer-of-code/ticket/1559 Overview: For Haskell there are currently no tools to investigate the performance of parallel programs. This project would extend the Haskell compiler GHC to support profiling of parallel programs. Parallel programs are inherently difficult to analyze and the prevalence of multi-core processors has increased the need for tools to facilitate gaining performance from parallelism. The ability to profile parallel programs in GHC could lead to improvements in GHC's RTS, and insights into writing parallel Haskell code. Goals: * Investigate the use of the GranSim framework for parallel profiling in GHC i. Decide what is needed to commit the GranSim port to the GHC tree i. Build additional profiling tools upon the GranSim framework * Testing of performance hit accrued from parallel profiling i. Investigate improving performance, possible modifications to GranSim port * Construct tests to measure the performance improvements of parallel programs i. Building benchmarks for parallel programs, related to ticket: http://hackage.haskell.org/trac/summer-of-code/ticket/1544 * Improve upon GranSim visualization of profiles to clarify parallel profiling i. Possibly add new visualization profiles, if time allows I am sure that further details will need to be developed with the help of Simon Marlow; however, I am unsure if some of these details can be defined without first investigating the potential use of GranSim. I look forward to your feedback. Thank you. __ Donnie Jones

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Terminating GLUT/GLFW programs
by hjgtuyl＠chello.nl 27 Mar '08

27 Mar '08

L.S., I am trying GLUT and GLFW (on Windows XP, with GHC 6.8.2); the sample programs do not terminate when I close the window by clicking on the cross in the upper right corner of the window. The sample program for GLUT is at http://blog.mikael.johanssons.org/archive/2006/09/opengl-programming-in-has… the GLFW program: http://haskell.org/haskellwiki/GLFW I tried in the GLUT program: close = exitWith ExitSuccess closeCallback $= Just close -- => User error (unknown GLUT call getCloseFunc, check for freeglut) this needs freeglut (not documented); I downloaded freeglut.dll and placed it in the windows\system32 directory. The error message remained. What is needed to let these programs terminate properly? -- Met vriendelijke groet, Henk-Jan van Tuyl -- http://functor.bamikanarie.com http://Van.Tuyl.eu/ --

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Libraries need a new owner
by Adrian Hey 27 Mar '08

27 Mar '08

Hello Folks, As some of you will be aware, I have been working on various Map implementations that currently live here.. http://code.haskell.org/collections/collections-ghc6.8 The libs in question being Data.Tree.AVL, Data.Trie.General and a few other bits like Data.COrdering and the AVL based Data.Map/Set clones. Well, I have decided to stop work on these. So they need a new owner if they're going to go anywhere. If anyone is interested in the job then I suggest they contact myself or Jean-Philippe Bernardy. Of course I will be happy to provide any help or advise anyone who takes over these libs may feel they need from me. I might even contribute a few patches from time to time myself :-) Thanks -- Adrian Hey

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