- Haskell-Cafe - Haskell.org

happstack file serving
by Antoine Latter 01 Nov '11

01 Nov '11

Including list. ---------- Forwarded message ---------- From: Antoine Latter <aslatter(a)gmail.com> Date: Tue, Nov 1, 2011 at 11:33 AM Subject: Re: [Haskell-cafe] happstack file serving To: Gary Klindt <gary.klindt(a)googlemail.com> On Tue, Nov 1, 2011 at 11:24 AM, Gary Klindt <gary.klindt(a)googlemail.com> wrote: > Hey Antoine, > > thank you for answering. Your strategy is quite similar to the one I prefer. > I misunderstood the behaviour of serveDirectory. The problem with external > javascript files is solved. > The other problem I had, was, that the argument 'msum' is a list, which has > elements with the same type, so I needed a conversion from > m [Char] to m Response. > In Happstack.Server.Response there is a function, which actually does that: > flatten: > > module Main where > > import Happstack.Server > import Control.Monad > > main :: IO () > main = simpleHTTP nullConf $ > msum [ flatten $ dir "ok" $ ok "jeahh!" > , serveDirectory DisableBrowsing ["index.html"] "static" ] > I would likely write that particular example: > dir "ok" $ ok $ toResponse "jeahh!" I find it convenient to convert to a 'Response' as close to the 'bottom' of the stack as possible. Antoine

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LDTA 2012: Call for Papers
by Anya Helene Bagge 01 Nov '11

01 Nov '11

LDTA 2012 Call for Papers 12th International Workshop on Language Descriptions, Tools, and Applications www.ldta.info Tallinn, Estonia March 31 & April 1, 2012 an ETAPS workshop LDTA is an application and tool-oriented workshop focused on grammarware - software based on grammars in some form. Grammarware applications are typically language processing applications and traditional examples include parsers, program analyzers, optimizers and translators. A primary focus of LDTA is grammarware that is generated from high-level grammar-centric specifications and thus submissions on parser generation, attribute grammar systems, term/graph rewriting systems, and other grammar-related meta-programming tools, techniques, and formalisms are encouraged. LDTA is also a forum in which theory is put to the test, in many cases on real-world software engineering challenges. Thus, LDTA also solicits papers on the application of grammarware to areas including, but not limited to, the following: - program analysis, transformation, generation, and verification, - implementation of Domain-Specific Languages, - reverse engineering and re-engineering, - refactoring and other source-to-source transformations, - language definition and language prototyping, and - debugging, profiling, IDE support, and testing. Note that LDTA is a well-established workshop similar to other conferences on (programming) language engineering topics such as SLE and GPCE, but is solely focused on grammarware. Paper Submission ---------------- LDTA solicits papers in the following categories. - research papers: original research results within the scope of LDTA with a clear motivation, description, analysis, and evaluation. - short research papers: new innovative ideas that have not been completely fleshed out. As a workshop, LDTA strongly encourages these types of submissions. - experience report papers: description of the use of a grammarware tool or technique to solve a non-trivial applied problem with an emphasis on the advantages and disadvantages of the chosen approach to the problem. - tool demo papers: discussion of a tool or technique that explains the contributions of the tool and what specifically will be demonstrated. Each submission must clearly state in which of these categories it falls, and must not be published or submitted elsewhere. Papers are to use the standard LaTeX article style and the authblk style for affiliations; a sample of which is provided at www.ldta.info. Research and experience papers are limited to 15 pages, tool demonstration papers are limited to 10 pages, and short papers are limited to 6 pages. The final version of the accepted papers will, pending approval, be published in the ACM Digital Library and will also be made available during the workshop. Please submit your abstract and paper using EasyChair at http://www.easychair.org/conferences/?conf=ldta2012. The authors of each submission are required to give a presentation at LDTA 2011 and tool demonstration paper presentations are intended to include a significant live, interactive demonstration. The authors of the best papers will be invited to write a journal version of their paper which will be separately reviewed and, assuming acceptance, be published in journal form. As in past years this will be done in a special issue of the journal Science of Computer Programming (Elsevier Science). Invited Speaker --------------- To be announced Important Dates --------------- Abstract submission: Nov. 28, 2011 Full paper submission: Dec. 5, 2011 Author notification: Jan. 20, 2012 Camera-ready papers: Feb. 05, 2012 LDTA Workshop: Mar. 31 - Apr. 1, 2012 LDTA Tool Challenge ------------------- The 2011 Workshop pioneered the LDTA Tool Challenge where tool developers were invited to develop solutions to a range of language processing tasks over a simple but evolving set of imperative programming languages. We expect a challenge to form part of LDTA every two years. The 2012 workshop will feature presentations devoted to a de-brief of the 2011 challenge, based on the paper currently being prepared by challenge participants. Program Committee ----------------- Suzana Andova, Eindhoven University of Technology, The Netherlands (co-chair) Anya Helene Bagge, University of Bergen, Norway Kyung-Goo Doh, Hanyang University, Ansan, South Korea Jeff Gray, University of Alabama, USA Görel Hedin, Lund Institute of Technology, Sweden Zoltán Horváth, Eötvös Loránd University, Budapest, Hungary Zhenjiang Hu, National Institute of Informatics, Japan Roberto Ierusalimschy, Pontifícia Universidade Católica do Rio de Janeiro, Brazil Ivan Kurtev, University of Twente, The Netherlands Marjan Mernik, University of Maribor, Slovenia Nate Nystrom, University of Lugano, Switzerland João Saraiva, Universidade do Minho, Braga, Portuga Sylvain Schmitz, Ecole Normale Supérieure de Cachan, France Anthony Sloane, Macquarie University, Australia (co-chair) Robert Tairas, Inria, France Laurence Tratt, King's College London, UK Vadim Zaytsev, Centre for Mathematics & Computer Science, The Netherlands Organizing Committee -------------------- Anya Helene Bagge, University of Bergen, Norway Emilie Balland, INRIA, France Steering Committee ------------------ Mark van den Brand, Eindhoven University of Technology, The Netherlands Görel Hedin, Lund University, Sweden Tony Sloane, Macquarie University, Australia Eric Van Wyk, University of Minnesota, United States

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Organizing big repository
by Konstantin Litvinenko 01 Nov '11

01 Nov '11

I am trying to understand how to organize my code and edit-compile-run cycles. I can't figure out how to setup environment in such why that when I build some program using cabal, cabal will rebuild program dependencies if some was changed. I don't want to configure/build/install manually. Having program 'foo' depends on lib 'bar' I want to edit some files in 'bar' than build 'foo' and get 'bar' rebuilt and 'foo' rebuilt/relink. How can I do this?

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lazy A-star search
by Anton Kholomiov 01 Nov '11

01 Nov '11

Recently I was looking for an A-star search algorithm. I've found a package but I couldn't understand the code. Then I saw some blogposts but they were difficult to understand too. I thought about some easier solution that relies on laziness. And I've come to this: Heuristic search is like depth-first search but solutions in sub-trees are concatenated with mergeBy function, that concatenates two list by specific order: module Search where import Control.Applicative import Data.Function(on) import Control.Arrow(second) import Data.Tree -- | Heuristic search. Nodes are visited from smaller to greater. searchBy :: (a -> a -> Ordering) -> Tree a -> [a] searchBy heur (Node v ts) = v : foldr (mergeBy heur) [] (searchBy heur <$> ts) -- | Merge two lists. Elements concatenated in specified order. mergeBy :: (a -> a -> Ordering) -> [a] -> [a] -> [a] mergeBy _ a [] = a mergeBy _ [] b = b mergeBy p (a:as) (b:bs) | a `p` b == LT = a : mergeBy p as (b:bs) | otherwise = b : mergeBy p bs (a:as) Now we can define specific heuristic search in terms of searchBy: -- | Heuristic is distance to goal. bestFirst :: Ord h => (a -> h) -> (a -> [a]) -> a -> [a] bestFirst dist alts = searchBy (compare `on` dist) . unfoldTree (\a -> (a, alts a)) -- | A-star search. -- Heuristic is estimated length of whole path. astar :: (Ord h, Num h) => (a -> h) -> (a -> [(a, h)]) -> a -> [a] astar dist alts s0 = fmap fst $ searchBy (compare `on` astarDist) $ unfoldTree gen (s0, 0) where astarDist (a, d) = dist a + d gen (a, d) = d `seq` ((a, d), second (+d) <$> alts a) I'm wondering is it effective enough? Anton

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ANN: Monad.Reader Issue 19
by Brent Yorgey 31 Oct '11

31 Oct '11

I am pleased to announce that Issue 19 of The Monad.Reader, a special issue on parallelism and concurrency, is now available: http://themonadreader.files.wordpress.com/2011/10/issue19.pdf Issue 19 consists of the following three articles: * Mighttpd – a High Performance Web Server in Haskell by Kazu Yamamoto * High Performance Haskell with MPI by Bernie Pope and Dmitry Astapov * Coroutine Pipelines by Mario Blažević Feel free to browse the source files. You can check out the entire repository using darcs: darcs get http://code.haskell.org/~byorgey/TMR/Issue19 If you’d like to write something for Issue 20, please get in touch. The deadline will likely be in December; more details will be forthcoming.

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Re: [Haskell-cafe] Amazon AWS storage best to use with Haskell?
by dokondr 31 Oct '11

31 Oct '11

On Mon, Oct 31, 2011 at 6:50 PM, John Lenz <lenz(a)math.uic.edu> wrote: > 4) My code processes hundreds of messages. Every message is processed in > >> exactly the same way as the others. So the code can be easily >> parallelized. Any Haskell frameworks that will allow me to run this code >> in a simple concurrency model? >> >> > Yes, there are many options. > > http://www.haskell.org/**haskellwiki/GHC/Concurrency<http://www.haskell.org/haskellwiki/GHC/Concurrency> > > > John, thanks for detailed reply! I am looking at Haskell Concurrency wiki, but can not figure out which framework - STM, sparks, threads, etc. Amazon AWS will be able to scale? As far as I know, to scale CPU and program memory in Amazon, all you can ask from AWS is to start some number of additional extra VMs. Every VM contains a complete image of your OS and executables, all images are exactly the same. That's fine with me as currently all my workflow tasks are performed by separately compiled Haskell executables communicating via regular files. So to reformulate my question: - Does any Haskell framework exist that allow to orchestrate separate processes (NOT threads that share the same process memory)? On the other hand, in case there is a way to make Amazon AWS to scale Haskell STM, sparks, threads, etc. - I would happily rewrite my Haskell code to use these frameworks. So my second question: - Is there a way to make Amazon AWS to scale Haskell STM, sparks, threads or any other Haskell concurrency frameworks?

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Figures 6 and 7 from `Programming with Arrows'?
by Captain Freako 31 Oct '11

31 Oct '11

Does anyone have figures 6 and 7, as well as the intervening unnumbered figure, from `Programming with Arrows'? Thanks, -db

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is Haskell missing a non-instantiating polymorphic case?
by Adam Megacz 31 Oct '11

31 Oct '11

The title might be a bit more provocative than necessary. I'm starting to suspect that there are very useful aspects of the parametricity of System F(C) which can't be taken advantage of by Haskell in its current state. To put it briefly, case-matching on a value of type (forall n . T n) forces one to instantiate the "n", even though the branch taken within the case cannot depend on "n" (parametricity). I came up with the simplest example I could and posted it to StackOverflow, but there haven't been any successes (despite some excellent attempts!): http://stackoverflow.com/questions/7720108/ This might sound like an obscure problem, but it actually starts to get in the way of the very useful Washburn+Weirich "Boxes Go Bananas" and related PHOAS representation. I've written up a short example of the problems that happen here: The link above also includes a very rough sketch of a proposal for a "pcase" construct that doesn't instantiate its argument. Is it possible to do what I'm attempting without adding "pcase" to the language? Would "pcase" break the soundness of the type system (I don't think so) or complicate type inference (probably)? I'd be interested in any comments/thoughts/help people can offer. Thanks! - a PS, I suspect that this is somehow related to the issue that Guillemette and Monnier mention in section 5.1 of their paper on type-preserving closure conversion, although I wasn't able to find the code online in order to be sure.

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Amazon AWS storage best to use with Haskell?
by dokondr 31 Oct '11

31 Oct '11

Hi, Please share your experience / ideas on AWS storage most friendly to Haskell. So far I store my data mostly in Data.Map structures serialized to text files with write / read functions. Now I was requested to move my app and data to Amazon cloud. As far as I know there are two main storage types that Amazon provides: S3 - basic block storage and SimpleDB ( http://docs.amazonwebservices.com/AmazonSimpleDB/latest/GettingStartedGuide/ ) Questions: 1) I would like to continue working with my data using abstractions similar to the ones that Data.Map provides. Any ideas how to iterate and modify SimpleDB records in a similar powerful way as provided by Data.Map? Or maybe S3? 2) It would be great to do development and testing offline without actually connecting to AWS S3 / SimpleDB. Are there any AWS simulators + Haskell libraries that will allow to do such an offline development? 3) Any experience / ideas with Haskell libs for NoSQL, not AWS-native, storages, that will run well both offline and in AWS? 4) My code processes hundreds of messages. Every message is processed in exactly the same way as the others. So the code can be easily parallelized. Any Haskell frameworks that will allow me to run this code in a simple concurrency model? Thanks! Dmitri

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Efficient mutable arrays in STM
by Ben Franksen 31 Oct '11

31 Oct '11

I have an application in mind where concurrent access to large arrays (up to millions of elements) of mostly small elements (Int or Double) is common. Typical access patterns would be chunk-wise, i.e. reads or writes from index n up to index m. Imagine stuff like images, scientific data, etc. All this suggests that Control.Concurrent.STM.TArray, in its current implementation, is not appropriate. Quoting the docs: "It is currently implemented as Array ix (TVar e), but it may be replaced by a more efficient implementation in the future (the interface will remain the same, however)." An array of TVars is certainly *much* too inefficient for what I have in mind w.r.t. both memory and cpu time. In fact I had already decided to use Data.Vector.Unboxed from the vector package. I see that Data.Vector.Unboxed.Mutable provides slice :: Unbox a => Int -> Int -> MVector s a -> MVector s a Yield a part of the mutable vector without copying it. which is almost what I need... Can I use this together with unsafeIOToSTM internally inside a library to provide shared transactional access to an IOArray? The docs warn that using unsafeIOToSTM is (obviously) "highly dangerous", but for what I have in mind the listed problems are not an issue: * running the IO code multiple times is ok * aborting is ok, too * inconsistent views are ok, too The main question is: does the STM transaction actually "see" that I changed part of the underlying array, so that the transaction gets re-tried? Or do I have to implement this manually, and if yes: how? Has anyone done something like that before? (If you tried this and found it doesn't work, please tell me, it would save me a lot of work repeating the effort). Is someone working on providing a more efficient version of TArray? Would it help if I said I'd be a happy user of a better TArray? ;-) If what I sketched above is infeasible (I would not be surprised if it was, I haven't yet spent much effort trying it out), what other options do I have? Is there an internal API for the STM stuff, i.e. a C header file or something which would make it possible to add efficient TArrays? Or should I use a high-level approach, something like a Data.Sequence.Seq of medium sized chunks (TVar (IOVector e))? Any comments are highly appreciated! Cheers Ben

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MonadPlus versus Alternative
by Gregory Crosswhite 31 Oct '11

31 Oct '11

Hey everyone, What is the difference between MonadPlus and Alternative? In my mind, it would make sense for the difference to be that the former provides "and" semantics (i.e., x `mplus` y means do both x and y) whereas the latter provides "or" semantics (i.e., x <|> y means do x or y but not both). However, when I look at the instances defined for List I see that it is exactly the same as MonadPlus. So is there any difference between the interpretation of MonadPlus and Alternative, or is the only difference between them that the former applies to Monad whereas the latter applies to Applicative? Also, along similar lines, why does MonadPlus exist when it is essentially just a special case of Monoid? (That is, any MonadPlus instance could be equivalently cast as a Monoid instance.) Thanks! Greg

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control-c only caught once -- bug?
by Brian Johnson 30 Oct '11

30 Oct '11

Hi, The second time I press control-c, it isn't caught -- the program exits instead. Why? (The context is, I'm writing an interactive program where calculations may take a long time. Control-c during a calculation should return the user to a prompt. As things stand, this can only be done once -- the second calculation so interrupted causes the whole program to exit.) $ ./ctrlctest ^Cuser interrupt ^C -- program exits! $ cat ctrlctest.hs module Main where import Control.Concurrent (threadDelay) import qualified Control.Exception as C main :: IO () main = do (threadDelay 1000000 >> return ()) `C.catch` (\e -> print (e::C.AsyncException)) main $ ghc --version The Glorious Glasgow Haskell Compilation System, version 7.0.3 $ uname -mrsv Darwin 11.2.0 Darwin Kernel Version 11.2.0: Tue Aug 9 20:54:00 PDT 2011; root:xnu-1699.24.8~1/RELEASE_X86_64 x86_64 $ file ctrlctest ctrlctest: Mach-O executable i386

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ANN: Haskell OpenGL package updates
by Jason Dagit 30 Oct '11

30 Oct '11

Several months ago I announced my intent to take over maintainership of the Haskell OpenGL bindings and associated packages. Today I have pushed new minor revisions to hackage. I have updated the following packages: * OpenGL * OpenGLRaw * GLURaw * GLUT The change log is very minor for each of these. For my first release as the new maintainer I opted to be very conservative about changes. Consider this a bug fix release with updated metadata. Please report bugs to either the Haskell OpenGL mailing list or the appropriate issue tracker on the github page: http://www.haskell.org/mailman/listinfo/hopengl https://github.com/haskell-opengl I would like to give a big thank you to the following individuals: Sven Panne Lars Corbjin Dylan Simon Alexey Karakulov Balazs Komuves If you contributed to this release by giving advice, filing a bug report, sending a patch, or in some other way, and I've not listed your name then I apologize for the omission. Going forward I could use help with testing, development, and documentation so if you're interested in OpenGL and Haskell let me know and also keep your eyes out for calls for volunteers. Thank you! Jason

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Package documentation complaints -- and a suggestion
by Max Rabkin 30 Oct '11

30 Oct '11

Hi all Following a link from the Yesod book, I arrived at [1], curious to find out what groundhog was. Once there, I learned... nothing: "This library provides just the general interface and helper functions. You must use a specific backend in order to make this useful." [1] http://hackage.haskell.org/package/groundhog Hoping to find more, I clicked on the top-level module. Once again, the text here was uninformative, though from the example it seems to be something to do with databases (and it is to be applauded for including an example in the docs). So, package authors: PLEASE, tell me what your package does in the description. Tell me *again* in the top-level haddocks (I may have come directly there by a link). And then, tell me where to look for more information. Instead of "This module defines the functions and datatypes used throughout the framework. Most of them are for internal use", tell me which are *not* for internal use. Write documentation for people who don't know how to use your package. Some people prefer to have this outside of the haddocks (I don't like this because papers and blogs are less likely to stay up to date than what is embedded in the file, but for tutorials etc. a website might be more appropriate) but if so link to it from both the Haddocks and the package description. But I also have a concrete suggestion for Hackage: include the package synopsis on the package's page. The distinction between synopsis and description can be confusing, and sometimes it seems to violate DRY to have the same info in both. To the author of groundhog: I hope you are not offended by my picking on your package. It's not the only culprit -- just the one that pushed me over the edge. Of course, I would be pleased if this email encouraged you to fix it, but I am addressing this rant to the Haskell community because the problem is a cultural one. --Max

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What library package fulfills these requirements?
by Joosten, Han 29 Oct '11

29 Oct '11

I am planning to give a workshop on FP using Haskell. The audience will be programmers with quite a bit of experience with conventional languages like Java and .net . I want to give them some feeling about FP. And hopefully, they will become interested so they want more... A couple of years ago, Simon Peyton Jones gave a splendid presentation<http://www.bestechvideos.com/2007/08/09/oscon-2007-simon-peyton-jones-a-tas…> with a comparable goal. He used Xmonad as an example to show some 'real code'. I like this idea, because Xmonad contains some code that is suitable to explain (not too hard to understand), and still gives a feeling about the power of Haskell. However, Xmonad needs X11 to run. Me and most people in the audience are stuck to windows (no flames please ;-s ) , and don't want to fiddle around with cygwin or the likes) I am wondering what package is suitable to be used as an example too? It needs to fulfill at least the following requirements: + I have to be able to explain the purpose of the software in no more than 1 or 2 minutes + There should be parts of the code that can be easily linked to the purpose /use of the package + These code parts must show the 'prettiness' of Haskell + It would be nice if there is something GUI-like to demo, which runs under windows. + I prefer not to use some kind of a compiler as an example. Now the question is: What package would you suggest, and of course, why? Thanks! Han Joosten. Dit bericht is vertrouwelijk en kan geheime informatie bevatten enkel bestemd voor de geadresseerde. Indien dit bericht niet voor u is bestemd, verzoeken wij u dit onmiddellijk aan ons te melden en het bericht te vernietigen. Aangezien de integriteit van het bericht niet veilig gesteld is middels verzending via internet, kan Atos Nederland B.V. niet aansprakelijk worden gehouden voor de inhoud daarvan. Hoewel wij ons inspannen een virusvrij netwerk te hanteren, geven wij geen enkele garantie dat dit bericht virusvrij is, noch aanvaarden wij enige aansprakelijkheid voor de mogelijke aanwezigheid van een virus in dit bericht. Op al onze rechtsverhoudingen, aanbiedingen en overeenkomsten waaronder Atos Nederland B.V. goederen en/of diensten levert zijn met uitsluiting van alle andere voorwaarden de Leveringsvoorwaarden van Atos Nederland B.V. van toepassing. Deze worden u op aanvraag direct kosteloos toegezonden. This e-mail and the documents attached are confidential and intended solely for the addressee; it may also be privileged. If you receive this e-mail in error, please notify the sender immediately and destroy it. As its integrity cannot be secured on the Internet, the Atos Nederland B.V. group liability cannot be triggered for the message content. Although the sender endeavours to maintain a computer virus-free network, the sender does not warrant that this transmission is virus-free and will not be liable for any damages resulting from any virus transmitted. On all offers and agreements under which Atos Nederland B.V. supplies goods and/or services of whatever nature, the Terms of Delivery from Atos Nederland B.V. exclusively apply. The Terms of Delivery shall be promptly submitted to you on your request. Atos Nederland B.V. / Utrecht KvK Utrecht 30132762

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Libraries to compare trees?
by dokondr 29 Oct '11

29 Oct '11

Please advise on Haskell libraries to compare trees in textual representation. I need to compare both structure and node contents of two trees, find similar sub-trees, and need some metric to measure distance between two trees. Also need advice on simple parser to convert textual tree representation into a data type convenient for tree manipulation (comparison, matching, etc.) What data type to use for trees with arbitrary structure? Example trees: *** Tree 1: (ROOT (S (NP (DT The) (NN voice) (NN quality)) (VP (VBD was) (ADJP (JJ clear) (RB too))) (. .))) *** Tree 2: (ROOT (S (SBAR (IN Although) (S (NP (DT the) (NN battery) (NN life)) (VP (VBD was) (RB not) (ADJP (JJ long))))) (, ,) (NP (DT that)) (VP (VBZ is) (VP (VBN ok) (PP (IN for) (NP (PRP me))))) (. .))) Thanks! Dmitri

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What is the status of GPU-accelerated Haskell?
by Rafael Gustavo da Cunha Pereira Pinto 29 Oct '11

29 Oct '11

Hi folks, I just bought a NVidia Fermi-based card and remembered reading a few months (years?) ago about some effort to accelerate array processing in Haskell using GPUs. How is this going on? Any progresses? Do we have GPU based DPH already? (the last one is a joke...) I keep thinking on the advantages of such GPU data processing on the signal processing field. Best regards, Rafael Gustavo da Cunha Pereira Pinto

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A catch-all MonadIO instance
by Bas van Dijk 28 Oct '11

28 Oct '11

Hello, Is it unsafe to add the following catch-all MonadIO instance to transformers' Control.Monad.IO.Class module? {-# LANGUAGE FlexibleInstances, FlexibleContexts, UndecidableInstances #-} instance (MonadTrans t, Monad (t m), MonadIO m) => MonadIO (t m) where liftIO = lift . liftIO It could get rid of all the similarly looking instances: instance (MonadIO m) => MonadIO (ReaderT r m) where liftIO = lift . liftIO instance (MonadIO m) => MonadIO (StateT s m) where liftIO = lift . liftIO instance (Monoid w, MonadIO m) => MonadIO (WriterT w m) where liftIO = lift . liftIO ... The reason I ask is that I want to do something similar for monad-control's MonadControlIO type class. But I'm not sure if I don't introduce any undecidability in the type-checker. Regards, Bas

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Reminder Munich Haskell
by Heinrich Hördegen 28 Oct '11

28 Oct '11

Hi all, this evening, Haskeller meet at Cafe Puck at 19h30: www.haskell-munich.de See you, Heinrich -- -- hoerdegen(a)funktional.info www.funktional.info --

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When does the UNPACK pragma work?
by Eugene Kirpichov 28 Oct '11

28 Oct '11

Hi, I'm trying to speed up Data.Time (the time package) 'cause my program is spending a very substantial fraction of time manipulating dates. I decided to start with strictifying and unpacking the date/time types, as there's no point in having them be lazy and I indeed had a lot of allocation in date/time arithmetic in my performance profile. data UTCTime = UTCTime { utctDay :: {-# UNPACK #-} !Day, utctDayTime :: {-# UNPACK #-} !DiffTime } (unpacks and strictness mine) newtype Day = ModifiedJulianDay {toModifiedJulianDay :: Integer} newtype DiffTime = MkDiffTime Pico And Pico is also essentially a newtype for Integer. So, I'm getting warnings on this definition of UTCTime. QUESTION: Is it the case that I can only UNPACK primitive fields, and not even their newtypes? Data\Time\Clock\UTC.hs:30:16: Warning: Ignoring unusable UNPACK pragma on the first argument of `UTCTime' In the definition of data constructor `UTCTime' In the data type declaration for `UTCTime' Data\Time\Clock\UTC.hs:30:16: Warning: Ignoring unusable UNPACK pragma on the second argument of `UTCTime' In the definition of data constructor `UTCTime' In the data type declaration for `UTCTime' -- Eugene Kirpichov Principal Engineer, Mirantis Inc. http://www.mirantis.com/ Editor, http://fprog.ru/

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Trouble defining `instance Arrow SF'
by Captain Freako 28 Oct '11

28 Oct '11

In trying to follow along with `Programming with Arrows' by John Hughes, I'm entering the following code: 1 -- Taken from `Programming with Arrows'. 2 3 module SF where 4 5 import Control.Arrow 6 7 newtype SF a b = SF {runSF :: [a] -> [b]} 8 9 instance Arrow SF where 10 arr f = SF (map f) 11 SF f >>> SF g = SF (f >>> g) and getting the following error from GHCI: GHCi, version 7.0.3: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. Prelude> :load SF [1 of 1] Compiling SF ( SF.hs, interpreted ) SF.hs:11:10: `>>>' is not a (visible) method of class `Arrow' Failed, modules loaded: none. Can anyone help? Thanks, -db

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Who is working on high performance threadsafe mutable data structures in Haskell?
by Ryan Newton 28 Oct '11

28 Oct '11

Hello cafe, In the context of the monad-par project we're just getting to the point of trying to replace our work stealing Deque's with something more efficient (in Haskell). Based a quick perusal of Hackage there does not seem to be a lot of work in this area. Of course, for Haskell the importance of this topic may be diminished relative to pure data structures, but for doing systems-level work like monad par good concurrent data structures are also very important. We are about to embark on some work to fix this problem for monad-par & Deques, but if there are others working in this vicinity it would be nice to team up. We are going to try both pure Haskell approaches using the new casMutVar# primop as well as wrapping foreign data structures such as those provided by TBB. There are a whole bunch of issues with the latter -- see Appendix A and help me out if you know how to do this. My first goal is to get a parameterizable deque interface, implementation, and benchmarks that makes it possible to express variations of queues including: - Double, single, and 1.5-ended (e.g. both ends can be RW or only R or W) - Threadsafe or single-threaded on both ends - Bounded or unbounded If you require that at least the "left"-end support Write and the "right" end support Read (excluding, for example stacks), that leaves a configuration space of 32 options. Some of these 32 options have much better algorithms than others, but a general algorithm (such as Michael & Scott queues) could satisfy all of them while leaving "room to improve". The TBB guys have considered making their concurrent_queus configurable to this extent but haven't gotten around to it. Thanks, -Ryan Appendix A: Using foreign data structures with Haskell ---------------------------------------------------------------------------- It's easy to call foreign code in Haskell, but how to use a foreign data structure to store polymorphic Haskell values? For example we would want a TBB concurrent_queue to store words representing pointers into the Haskell heap. We would need, for example: - (1) to pin arbitrary objects by making StablePtrs - (2) to communicate those to a foreign enqueue operation - (3) to unpin objects when the pointer is removed from a foreign structure (or use a reference count to determine when to unpin/free the StablePtr) I don't have any experience here and would appreciate hearing from anyone who does. Is this a non-starter? Will the overheads introduced by all the StablePtr ops destroy any gains from using an efficient data structure?

2 1

STM program
by Ketil Malde 27 Oct '11

27 Oct '11

Hi, Café, I'm playing with STM a bit, and did a small writeup. As I'm considering to submit it, uh, tomorrow, I was wondering if anybody would care to take a look? I'm especially nervous about the accuracy and clarity of my descriptions of monads and STM, which are terse and written in a hurry. Anyway: I'd be most grateful for any feedback you care to give. http://malde.org/~ketil/stmcluster.pdf -k -- If I haven't seen further, it is by standing in the footprints of giants

1 0

Really impossible to reinstall `base' using cabal?
by Captain Freako 27 Oct '11

27 Oct '11

In response to this: dbanas@dbanas-eeepc:~$ cabal install arrows Resolving dependencies... Configuring lazysmallcheck-0.6... Preprocessing library lazysmallcheck-0.6... Building lazysmallcheck-0.6... [1 of 1] Compiling Test.LazySmallCheck ( Test/LazySmallCheck.hs, dist/build/Test/LazySmallCheck.o ) Implicit import declaration: Could not find module `Prelude': Perhaps you haven't installed the "dyn" libraries for package `base'? Use -v to see a list of the files searched for. cabal: Error: some packages failed to install: Stream-0.4.6 depends on lazysmallcheck-0.6 which failed to install. arrows-0.4.4.0 depends on lazysmallcheck-0.6 which failed to install. lazysmallcheck-0.6 failed during the building phase. The exception was: ExitFailure 1 I did this: dbanas@dbanas-eeepc:~$ cabal install base and got this: Resolving dependencies... cabal: internal error: impossible Is it really impossible to use cabal to reinstall `base'? Thanks, -db

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Haskell Weekly News: Issue 205
by Daniel Santa Cruz 27 Oct '11

27 Oct '11

Welcome to issue 205 of the HWN, a newsletter covering developments in the Haskell community. This release covers the week of October 16 to 22, 2011. You can find an HTML version of this issue at: http://contemplatecode.blogspot.com/2011/10/haskell-weekly-news-issue-205.h… Announcements Ian Lynah sent out a call for nominations for the haskell.org committee. See the link for details on how to submit a nomination. Nominations close on October 29. [1] http://goo.gl/J9J6H New and Updated Projects * netwire (Ertugrul Soeylemez; 1.2.7) [2] http://goo.gl/ULujm Quotes of the Week * kmc: i just used Hayoo to see if anyone implemented this function and it came back with one of my own libraries * JoeyA: LLVM: The easy-to-use compiler infrastructure nobody knows how to use. * kmc: Haskell isn't really designed by mathematicians. it's designed by people who programmers would consider to be mathematicians and mathematicians would consider to be programmers * Cale: foldr is the real fold; foldl is an imposter * @remember hey daniel kmc wants his uploads featured on HWN [edit note: oops, I guess that was meant for me :) +1 for new and inventive ways to communicate!] Top Reddit Stories * Tech-talk about Haskell at Google: Haskell Amuse-Bouche Domain: youtu.be, Score: 86, Comments: 5 On Reddit: [3] http://goo.gl/Pf0NZ Original: [4] http://goo.gl/NPZ17 * Deprecate Prelude.head and partial functions Domain: chrisdone.com, Score: 58, Comments: 60 On Reddit: [5] http://goo.gl/Yat8J Original: [6] http://goo.gl/NyiRO * What does your company use Haskell for? I'll go first. Domain: self.haskell, Score: 51, Comments: 38 On Reddit: [7] http://goo.gl/VOfrO Original: [8] http://goo.gl/VOfrO * I am working on a functional web-programming language as a senior thesis. What do you think so far? Domain: elm-lang.org, Score: 40, Comments: 58 On Reddit: [9] http://goo.gl/6PrQM Original: [10] http://goo.gl/l3odM * Dear Redditor Emac-loving Haskeller(s): what cool emacs Haskell Mode (or custom) features do you use? Domain: self.haskell, Score: 40, Comments: 7 On Reddit: [11] http://goo.gl/LKW0A Original: [12] http://goo.gl/LKW0A * Macros in Haskell Domain: playingwithpointers.com, Score: 38, Comments: 0 On Reddit: [13] http://goo.gl/pwfjt Original: [14] http://goo.gl/bSYN8 * Type-safe event-based programming Domain: jaspervdj.be, Score: 35, Comments: 0 On Reddit: [15] http://goo.gl/gyj9J Original: [16] http://goo.gl/ZBC55 * Yesod excellent ideas Domain: yannesposito.com, Score: 34, Comments: 5 On Reddit: [17] http://goo.gl/ikFJV Original: [18] http://goo.gl/UgBaC * AI Challenge: Ants. Haskell support is only for GHC 6.12. Shall we lobby for 7.0? Domain: aichallenge.org, Score: 28, Comments: 24 On Reddit: [19] http://goo.gl/ShqaM Original: [20] http://goo.gl/O2YOp * Why not Haskell? Domain: neugierig.org, Score: 27, Comments: 26 On Reddit: [21] http://goo.gl/INmRp Original: [22] http://goo.gl/wK3U3 Top StackOverflow Questions * What are some compelling use cases for dependent method types? votes: 44, answers: 2 Read on SO: [23] http://goo.gl/2Xmgu * Why monads? How does it resolve side-effects? votes: 14, answers: 7 Read on SO: [24] http://goo.gl/UJimh * How does Haskell printf work? votes: 13, answers: 1 Read on SO: [25] http://goo.gl/351dE * Why is my genetic algorithm seemingly behaving randomly? votes: 10, answers: 1 Read on SO: [26] http://goo.gl/a5FtH * What are the benefits of applicative parsing over monadic parsing? votes: 10, answers: 4 Read on SO: [27] http://goo.gl/UEkpx * Fixity of backtick operators? votes: 9, answers: 1 Read on SO: [28] http://goo.gl/nwji2 * Bit Size of GHC's Int Type votes: 8, answers: 2 Read on SO: [29] http://goo.gl/DDtFZ * Simple word count in haskell votes: 8, answers: 4 Read on SO: [30] http://goo.gl/ZAYyT * existential search and query without the fuss votes: 8, answers: 2 Read on SO: [31] http://goo.gl/Fnes6 * How to selectively link certain system libraries statically into Haskell program binary? votes: 8, answers: 2 Read on SO: [32] http://goo.gl/HjPTc Until next time, Daniel Santa Cruz References 1. http://permalink.gmane.org/gmane.comp.lang.haskell.general/18983 2. http://permalink.gmane.org/gmane.comp.lang.haskell.cafe/93163 3. http://youtu.be/b9FagOVqxmI 4. http://www.reddit.com/r/haskell/comments/lkiiw/techtalk_about_haskell_at_go… 5. http://chrisdone.com/posts/2011-10-17-boycott-head.html 6. http://www.reddit.com/r/haskell/comments/lf71l/deprecate_preludehead_and_pa… 7. http://www.reddit.com/r/haskell/comments/lfwlv/what_does_your_company_use_h… 8. http://www.reddit.com/r/haskell/comments/lfwlv/what_does_your_company_use_h… 9. http://elm-lang.org/ 10. http://www.reddit.com/r/haskell/comments/liqb4/i_am_working_on_a_functional… 11. http://www.reddit.com/r/haskell/comments/llt44/dear_redditor_emacloving_has… 12. http://www.reddit.com/r/haskell/comments/llt44/dear_redditor_emacloving_has… 13. http://playingwithpointers.com/archives/615 14. http://www.reddit.com/r/haskell/comments/lgeuk/macros_in_haskell/ 15. http://jaspervdj.be/posts/2011-10-16-type-safe-events.html 16. http://www.reddit.com/r/haskell/comments/le2dk/typesafe_eventbased_programm… 17. http://yannesposito.com/Scratch/en/blog/Yesod-excellent-ideas/ 18. http://www.reddit.com/r/haskell/comments/lj2br/yesod_excellent_ideas/ 19. http://aichallenge.org/starter_packages.php 20. http://www.reddit.com/r/haskell/comments/ljs9z/ai_challenge_ants_haskell_su… 21. http://neugierig.org/software/blog/2011/10/why-not-haskell.html 22. http://www.reddit.com/r/haskell/comments/lfv4b/why_not_haskell/ 23. http://stackoverflow.com/questions/7860163/what-are-some-compelling-use-cas… 24. http://stackoverflow.com/questions/7840126/why-monads-how-does-it-resolve-s… 25. http://stackoverflow.com/questions/7828072/how-does-haskell-printf-work 26. http://stackoverflow.com/questions/7792456/why-is-my-genetic-algorithm-seem… 27. http://stackoverflow.com/questions/7861903/what-are-the-benefits-of-applica… 28. http://stackoverflow.com/questions/7807994/fixity-of-backtick-operators 29. http://stackoverflow.com/questions/7786662/bit-size-of-ghcs-int-type 30. http://stackoverflow.com/questions/7803449/simple-word-count-in-haskell 31. http://stackoverflow.com/questions/7813691/existential-search-and-query-wit… 32. http://stackoverflow.com/questions/7832112/how-to-selectively-link-certain-…

1 0

Operator precedence and associativity with Polyparse
by Tom Hawkins 26 Oct '11

26 Oct '11

Hi, Can someone provide guidance on how handle operator precedence and associativity with Polyparse? Thanks in advance. -Tom

3 4

Re: [Haskell-cafe] Open CV or alternate image processing library for Haskell on windows?
by Ivan Perez 26 Oct '11

26 Oct '11

Hi, Sorry for reopening an old thread (May 2011), but I just want to report that I'm using HOpenCV and cv-combinators under windows and I just wanted to tell you that it works just fine. I downloaded the opencv2 libraries as stated on this thread, and I'm successfully building software that works both on Windows (XP and 7, both x86) and Linux (x86 & amd64). The software will be released in a few days, if everything goes well. You'll be able to find it at keera.es, but I'll let you know when I release it anyway. Cheers, Ivan Perez. PS. I just re-subscribed to this mailing list. I can't reply to the old messages (don't have them), and I can't set the old Message-ID with gmail, so I'm providing a link to the original message. [1] http://www.mail-archive.com/haskell-cafe@haskell.org/msg89834.html

1 0

blanket license for Haskell Platform?
by Eric Y. Kow 26 Oct '11

26 Oct '11

So I'm combining Haskell software with some non-free/closed source work. I was wondering what sort of effort it would take to organise a blanket license for everything in the Haskell Platform, and whether it would be worthwhile to anybody. Here's my use case: - I am combining my Haskell [:-)] program with some non-free/closed source [:-(] software - My user is concerned that a large number of having a large number of individual licenses even though textually identical modulo author, date, etc would mean a big hassle getting their lawyers and their user's lawyers to sign off on each and every license I feel a bit embarrassed asking this as it's already great and also very convenient that I can just grab this closed source stuff, but suppose we were to decide that putting together some sort of blanket license for the Haskell Platform would be a good idea. How would we go about organising such an effort? I wonder if this is a sort of thing we could tie to the IHG... Thanks, -- Eric Kow <http://erickow.com>

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Re: [Haskell-cafe] ANNOUNCE: Hac Boston from January *20-22* at MIT
by Edward Kmett 25 Oct '11

25 Oct '11

Correction: January 20-22nd ;) On Tue, Oct 25, 2011 at 5:45 PM, Edward Kmett <ekmett(a)gmail.com> wrote: > I am very pleased to officially announce Hac Boston, a Haskell hackathon > to be held January 21-23, 2012 at MIT in Cambridge, MA. > > The hackathon will officially kick off at 2:30 Friday afternoon, and go > until 5pm on Sunday with the occasional break for sleep. > > Everyone is welcome -- you do not have to be a Haskell guru to attend! > Helping hack on someone else's project could be a great way to increase > your Haskell skills. > > If you plan on coming, please officially register<http://haskell.org/haskellwiki/Hac_Boston/Register>, > even if you already put your name on the wiki. Registration, travel, some > information about lodging and many other details can now be found on the Hac > Boston wiki <http://haskell.org/haskellwiki/Hac_Boston>. > > We have confirmed space for about 30 people, so please register early! > Beyond that we'll have to either seek additional space or close > registration. > > We're also looking for a few people interested in giving short (15-20 min.) > talks, probably on Saturday afternoon. Anything of interest to the > Haskell community is fair game---a project you've been working on, a > paper, a quick tutorial. If you'd like to give a talk, add it on <http://goog_145539007>the > wiki <http://haskell.org/haskellwiki/Hac_Boston/Talks>. > > We look forward to seeing you at MIT! > > -Edward Kmett >

1 0

ANNOUNCE: Hac Boston from January 21-23rd at MIT
by Edward Kmett 25 Oct '11

25 Oct '11

I am very pleased to officially announce Hac Boston, a Haskell hackathon to be held January 21-23, 2012 at MIT in Cambridge, MA. The hackathon will officially kick off at 2:30 Friday afternoon, and go until 5pm on Sunday with the occasional break for sleep. Everyone is welcome -- you do not have to be a Haskell guru to attend! Helping hack on someone else's project could be a great way to increase your Haskell skills. If you plan on coming, please officially register<http://haskell.org/haskellwiki/Hac_Boston/Register>, even if you already put your name on the wiki. Registration, travel, some information about lodging and many other details can now be found on the Hac Boston wiki <http://haskell.org/haskellwiki/Hac_Boston>. We have confirmed space for about 30 people, so please register early! Beyond that we'll have to either seek additional space or close registration. We're also looking for a few people interested in giving short (15-20 min.) talks, probably on Saturday afternoon. Anything of interest to the Haskell community is fair game---a project you've been working on, a paper, a quick tutorial. If you'd like to give a talk, add it on <goog_145539007>the wiki<http://haskell.org/haskellwiki/Hac_Boston/Talks> . We look forward to seeing you at MIT! -Edward Kmett

1 0

List archives searchable?
by Captain Freako 25 Oct '11

25 Oct '11

Are the archives of this list searchable?

3 2

ANN: diagrams 0.4
by Brent Yorgey 25 Oct '11

25 Oct '11

I am pleased to announce the release of version 0.4 of diagrams, a full-featured framework and embedded domain-specific language for declarative drawing. The last announcement was of the 0.1 release; there have been quite a few changes and improvements since then, including: - A new website including a gallery of examples: http://projects.haskell.org/diagrams/gallery.html - A new comprehensive user manual with lots of illustrative examples: http://projects.haskell.org/manual/diagrams-manual.html - New primitive shapes: rounded rectangles, wedges, and a new flexible API for generating polygons - Cubic splines - Basic text support - Support for external image primitives - Lots more convenient combinators, bug fixes, and improvements Cool, how can I try it out? --------------------------- For the truly impatient: cabal install gtk2hs-buildtools cabal install diagrams For the slightly less impatient, read the quick tutorial, which has detailed information about how to install the necessary packages and will introduce you to the fundamentals of the framework: http://projects.haskell.org/diagrams/tutorial/DiagramsTutorial.html For those who are even less impatient but want to really dig in and use the power features, read the user manual: http://projects.haskell.org/manual/diagrams-manual.html Cool, how can I contribute? --------------------------- There are lots of ways you can contribute! First, you may want to subscribe to the project mailing list (http://groups.google.com/group/diagrams-discuss) and/or come hang out in the #diagrams IRC channel on freenode.org. - There are lots of easy bug fixes, improvements, and feature requests just waiting for people wanting to get involved: see the bug tracker for a list of open tickets: http://code.google.com/p/diagrams/issues/list - The source repositories are mirrored using both darcs (on patch-tag.com) and git (on github.com) and patches are accepted in either place, thanks to Owen Stephen's great work on darcs-bridge [1]. - Create a higher-level module built on top of the diagrams framework (e.g. tree or graph layout, generating Turing machine configuration diagrams, Penrose tilings ... your imagination is the only limit!) and submit it for inclusion in a special diagrams-contrib package which will be created for such higher-level user-contributed modules. - Use diagrams to create some cool graphics and submit them for inclusion in the gallery. - Start your own project built on top of diagrams and let us know how it goes! - Last but certainly not least, just try it out for your pet graphics generation needs and contribute your bug reports and feature requests. Happy diagramming! Brought to you by the diagrams team: - Brent Yorgey - Ryan Yates with contributions from: - Sam Griffin - Claude Heiland-Allen - John Lato - Vilhelm Sjöberg - Luite Stegeman - Kanchalai Suveepattananont - Scott Walck [1] http://wiki.darcs.net/DarcsBridgeUsage

8 19

Two new lectureships (assistant professorships) in Nottingham
by Graham Hutton 25 Oct '11

25 Oct '11

Dear all, We are currently seeking two new Lecturers (Assistant Professors) in Computer Science at the University of Nottingham, UK. These posts are available from 1st January 2012 on a fixed-term basis for three years. Applications from within the area of functional programming would be most welcome. For further details, see: http://www.nottingham.ac.uk/jobs/currentvacancies/ref/CE05936S The deadline for applications is 9th November 2011. Best wishes, Graham Hutton -- Prof Graham Hutton Functional Programming Lab School of Computer Science University of Nottingham, UK http://www.cs.nott.ac.uk/~gmh This message and any attachment are intended solely for the addressee and may contain confidential information. If you have received this message in error, please send it back to me, and immediately delete it. Please do not use, copy or disclose the information contained in this message or in any attachment. Any views or opinions expressed by the author of this email do not necessarily reflect the views of the University of Nottingham. This message has been checked for viruses but the contents of an attachment may still contain software viruses which could damage your computer system: you are advised to perform your own checks. Email communications with the University of Nottingham may be monitored as permitted by UK legislation.

1 0

New rss maintainer
by Bas van Dijk 25 Oct '11

25 Oct '11

Hello, I've a small patch[1] that updates the rss package to the latest versions of its dependencies. (I'm trying to get the new hackage-server to build on ghc-7.2.1) However Bjorn Bringert told me he's no longer maintaining the package. He asked me to ask you if there's already a new maintainer. If not, does any one want to take over the package? Jeremy, maybe you? Otherwise I could take it over. I probably won't make lots of changes since I'm a bit swamped at the moment. Just updating it to the latest versions. Regards, Bas [1] http://code.haskell.org/~basvandijk/update_rss.dpatch

4 5

Error when installing RSA (for yesod) with GHC 7.2.1
by Yves Parès 25 Oct '11

25 Oct '11

I'm using GHC 7.2.1 and cabal-install 0.8 (Cabal 1.8.0.2), and when "cabal install rsa" I got the error $ cabal install rsa Resolving dependencies... Configuring RSA-1.0.6.2... Preprocessing library RSA-1.0.6.2... Preprocessing executables for RSA-1.0.6.2... Building RSA-1.0.6.2... [1 of 1] Compiling Codec.Crypto.RSA ( Codec/Crypto/RSA.hs, dist/build/Codec/Crypto/RSA.o ) Codec/Crypto/RSA.hs:580:10: Duplicate instance declarations: instance Random Word8 -- Defined at Codec/Crypto/RSA.hs:580:10-21 instance Random Word8 -- Defined in System.Random cabal: Error: some packages failed to install: RSA-1.0.6.2 failed during the building phase. The exception was: ExitFailure 1 Apparently it's an instance being declared twice. However RSA hackage page states that it compiles under GHC 7.2: http://hackage.haskell.org/package/RSA

3 4

lost in generics
by Rustom Mody 24 Oct '11

24 Oct '11

I need some help finding my way around the various generics libraries. My usage scenario is -- at least to start with -- the ASTs of programming languages. It appears to me that there are two generations of generics -- earlier there was generic haskell and strafunski Now there is uniplate and kure (and syb? -- not sure of its generation...) I get this impression because I saw a comment somewhat along these lines. And also the very first reference link on the strafunski webpage: http://www.haskell.org/haskellwiki/Applications_and_libraries/Generic_progr… viz http://www.cs.vu.nl/Strafunski/ seems to be dead. So I am wondering whether strafunski is still under development or is it defunct? The following paras from http://www.cs.uu.nl/research/techreps/repo/CS-2008/2008-010.pdf The current status of generic programming in Haskell is comparable > to the lazy Tower of Babel preceding the birth of Haskell > in the eighties [Hudak et al., 2007]. We have many single-site languages > or libraries, each individually lacking critical mass in terms > of language/library-design effort, implementations, and users. > Although generic programming has been used in several applications, > it has few users for real-life projects. This is understandable. > Developing a large application takes a couple of years, and > choosing a particular approach to generic programming for such a > project involves a risk. Few approaches that have been developed > over the last decade are still supported, and there is a high risk that > the chosen approach will not be supported anymore, or that it will > change in a backwards-incompatible way in a couple of years time. > sound omninous :-) In general my question is: What is alive/active and what is alive/active and what is -- um -- moved-on-from. And of course which are easier and which more difficult to dig into. Thanks Rusi

5 4

Re: [Haskell-cafe] thespian thoughts
by Simon Michael 24 Oct '11

24 Oct '11

Hi Alex. I'm testing thespian in rss2irc, FYI: http://joyful.com/darcsden/simon/rss2irc/browse/rss2irc.hs#L-114 . Maybe there's a better way to use it, but for now it brings me one extra thread and higher memory usage/leakage - an instance grew to 350M overnight where I'd normally see 50-100M. The leak may be in my code, but I haven't found it yet. Did you notice high memory usage when using thespian ? Whether or not I end up keeping it, it has influenced the ordinary thread-based manager for the better, eg see forkMonitoredIO which is like a poor man's monitor using exceptions rather than actor messages. Best, - Simon On Oct 12, 2011, at 8:44 AM, Simon Michael wrote: > Hi Alex, thanks for the reply (it didn't seem to reach haskell-cafe, if that matters) and the update on status. I passed over CloudHaskell as it seemed (a) over-complex for my needs and (b) not ready, eg not on hackage. I need something that will still permit cabal install rss2irc. But perhaps that's not far off. I'll look again more closely, at both. > > Best - Simon > > > On Oct 11, 2011, at 10:48 PM, Alex Constandache wrote: > >> Hi Simon, >> >> Sorry for the late reply. I no longer work on thespian, as there is >> another project, called Cloud Haskell which provides much more >> functionality than thespian (including Erlang style distributed >> computing). It is not available on Hackage, but it lives on Github at >> >> https://github.com/jepst/CloudHaskell >> >> Simon Peyton-Johnes himself seems to be associated with the project, >> so you should have a look at it. If it does not match your needs, feel >> free to hack thespian and send me a pull request on bitbucket. You are >> the second person who emailed about thespian in the last month, so >> maybe I should reconsider the decision to abandon it (which was >> motivated by my desire to avoid contributing to the insane >> fragmentation that plagues Hackage). >> >> --Alex >> >> On Sun, Oct 9, 2011 at 12:45 PM, Simon Michael <simon(a)joyful.com> wrote: >>> Hi Alexander, >>> I went looking for something to clean up rss2irc's thread management, and >>> your recently released thespian package looks like the simplest, most >>> practical actors/erlang/OTP-ish lib for haskell so far. Thanks! >>> I need to restart threads (actors) in a controlled way when they die or >>> hang. I think some of all of that is also part of Erlang/OTP, and maybe it's >>> already on your todo list. Here are some notes I made, for your interest and >>> in case you have any further thoughts. >>> I thought of adding some actor-transforming combinators like these: >>> -- | Spawn the specified action and restart it whenever it dies, unless >>> -- the restart frequency exceeds any of the given maximum frequencies in >>> -- which case throw an exception. >>> restart :: [Frequency] -> IO a -> IO Address >>> restart fs action = spawn $ do >>> setFlag TrapRemoteExceptions >>> let start times = [] >>> forever >>> t <- getCurrentTime >>> update start times >>> when (any fs exceeded by start times) throw error >>> worker <- spawn action >>> monitor worker >>> receive worker [Case _ -> return ()] >>> -- | Convert hangs to exceptions using a watchdog timer: spawn the >>> -- specified action under the control of a watcher which monitors it and >>> -- also kills it and throws an exception if the worker ever fails to >>> -- send (something) to the watcher within the specified interval. >>> watchdog :: Seconds -> (Address -> IO a) -> IO Address >>> watchdog t action = spawn $ do >>> watcher <- self >>> worker <- spawn $ action watcher >>> monitor worker >>> forever >>> receiveTimeout t [Case _ -> return () >>> Default -> throw error >>> ] >>> which I would use something like: >>> main = do >>> (feed, bot) <- ... >>> spawn $ do >>> reader <- restart [MaxPerHour 2] $ watchdog 60 $ feedReader feed bot >>> announcer <- restart [MaxPerHour 2] $ watchdog 60 $ ircAnnouncer bot >>> responder <- restart [MaxPerHour 2] $ watchdog 60 $ ircResponder bot >>> monitor reader >>> monitor announcer >>> monitor responder >>> setFlag TrapRemoteExceptions >>> receive [Case e :: RemoteException -> exitFailure (show e) -- one of the >>> above died or hung too frequently >>> ] >>> but the types aren't right. I'm not sure if these combinators are possible >>> with the current thespian api. Also they would complicate things, eg what is >>> the address of a restarted actor ? >>> On second thoughts it might be better if these features were built in to the >>> library. I imagine something like: >>> main = do ... >>> reader <- spawnWith [RestartSpec [MinInterval (minutes 5), MaxPerHour >>> 3, MaxPerWeek 6], Watchdog (seconds 60)] $ feedReader feed bot >>> feedReader = do >>> forever >>> poll feed, do stuff >>> resetWatchdog >>> What do you think ? >>> Best - Simon >> >> >> >> -- >> AC >> I used to have a signature, but now I don't. >> >> -----BEGIN PGP PUBLIC KEY BLOCK----- >> Version: BCPG v1.45 >> >> mQINBE2kb5sBEADO/4u9AVkyz+jEnhgYzfdJ2tIIxOfAL4rqx2jXbxeFVq7vyBRS >> vM+K8u2Xw2TBC0dXzNy9GiBf9qjZS1EGPPiIvTLsp5aIoQLsO7E6H6g7Z5eqijMC >> c4qhrnmWsxcOZv8s0iil6H6OXa/EQzP2M1DRmyU8W49Cvo+Jg9hHZGbvdqpNrmYZ >> ZV5cA9hTneAFe7wixfQ7GDu80dCELmwwWX2adVpeW5dyX0u42Bp7e263GU1wPWTY >> t5CTkrgvHkFu7Hu3SGt66Q95xvCkK/RFLJbKJyeuHOY3uIa6YWKtMCNPcFz9C520 >> D+MQElWU9xFssxXj626v/GhTGoOPKu948rRgZl5OrBJjzOqaGtrDxuT45qjBfYV2 >> pkVzkTD2/3WNQNZapdrwNjf/fgomUVBTbeow1zPEypg1LHdX2Y58M54l6hCxbcgy >> JHALDCnROoEPeupJfncIYkp54hL3MJCspPHJoBMHpwfXZgmTNNfEQE2LX4recZ/7 >> PRIAntZ6/MZjBH/1vGc+BcIT5S5Z2J1INeZkEscz3pSl5iR8wYE1VyBRreaQptmq >> DtIIc2qyRN+BwbF7T0zCdYB2MHW1PA0pS3r4k//K8bmEf1ThH7u9jYuKKANDCltI >> ariGvz5/CxmW1+JnkSZtwb8w+3qcaMgOGYJhyD6K6RlYqq2htkjteWSdOwARAQAB >> tDpBbGV4IENvbnN0YW5kYWNoZSAoYWxleCkgPGFsZXhhbmRlci50aGUuYXZlcmFn >> ZUBnbWFpbC5jb20+iQIcBBMBAgAGBQJNpHAsAAoJEHNeWOpiNrFPBbUP/RCJC7C/ >> 78g0lQ1mvOzmfWoZ/tc0RceZqnfYYhm8VbZ6oNT3G4s2b7T5NdGCWqL1hGYVHupM >> 6TB4KA2eW8/3xh+oxbdC70i1WQYyfE81oKTSfW2+kBqtPIXueTs9AJ5rRX4cpPBr >> 8cDTx6tjCe+Vew59hUQ8JxAzs32Ol5mGOf4wpHhS4Un1mJwO+as0kHJnsA15dXoI >> Moo15NiJL9y77+8u1T6tHbGLYT9J/paoWOglA02FQIdlOAmQdCNhjZ4HKCKmMKsn >> WwlctvORzH+VtIpF9oxBtu0n3pPAE3wU4GyyVtg27wa+LNg7CEVHhJ/m6QSoPRFa >> TLYhK7OP4bOPdWZZUM1En4mWQFnb2fyKDPUIjqtbMBP6dcZin0nwRxZzngdLcdpm >> Prz14F5aS1+NvZOXhkPevBC6xXOnLwEr+egyM0jMGPdE3YnqMKOVR3e6bGE/wvPy >> OKtebMhFqLy1Yg87p3IU3Tv0Y1WV8GVEZr5lYHkbgM3yIY/WlH+MO5I4j7YXUdXf >> gvMjOMOxZ4wG8QEfkpdpaBm6JcRAkf9gb7IgBiOmdtC/N8s02NWyjRchvb/kOz5C >> eSCm6WV07Yhzxm+XTn+L8VxSN5YwCsF7gwD+Mtmone5TdmHS+7JJtjiq8WIbQrv3 >> /cwj2+7pnh7F032s2TpoJw0Og5HqjakiIkzYiQI2BBMBAgAgBQJNpHAsApsPBosJ >> CAcDAgSVAggDBJYCAwEFiQM9P4AACgkQc15Y6mI2sU8rfRAAtBCtd+XVjuqR/Of4 >> vy8Ev6N1/naqg7zOOQzQXT5UNpuoHO+y4oIYDvjkhGlxK4fVeIUHTQvhXS/INqyX >> 3oCKXYrzrsAgrq5FVdkRPwUV6H52ik/ani+IoGP2u85Y10DTnPGQnMzVwtN9Z6/T >> m486XA460J4jCIrRMpm+OJDHN6xUkgZFXaMW+scQK4At2wwcNvuOp9I9T4HP3viy >> b4g5IVgTsSZZoCIlSEvch2jGbM4hXDnLPFfIdSDxxn91sRgcmkNxCtGvKMVTDGYK >> JBvJYKki+X/CXfKlPwxTqHHjEbm8+uLyLDL32d7XTiS+0q31XthrVnVummiyIVtp >> tVhaBeY0JjX6Umi8DeaUWmT1xOckMIXMoAZBGux94hyaeKNEsSYXKQeM7nAvbEf9 >> EYPwoG82qRj/NyxqVH/Cx2IM24OYfoW2HwtU9l3QCHkCK1txCd3PvcWIFoSbwvX5 >> 1wB8/TgdhY4VM5BEJTBHTd8YZ6qi2pHeu+RdZoSCCHqeZA2WmGFpNsxRvHqw0sow >> YyadDulJu8AWT1+K0DTIxa3YWYIjMV9a/1LV5+/b4xx6KLvIbgS5aWsMMqmdhxMR >> w1cQ8JtkUSBgx8XzZIXqbMZEIhUmGeTGFBm+dKv91vTvxcM0vrrKPzAgiobRL2EE >> 43JwGJtFoGAc4zoRBUcXoRzodkc= >> =9igb >> -----END PGP PUBLIC KEY BLOCK----- >

1 0

Haskell in Munich 2
by Dr. Heinrich Hördegen 24 Oct '11

24 Oct '11

Dear all, last month's meeting of Haskellers in Munich was a success. Let's repeat it! We will meet on Wednesday, 26 Oct, at Cafe Puck at Cafe Puck (www.cafepuck.de) Everybody interested in Haskell or functional programming is cordially invited. If you can't make it this time, check out this site for other dates: http://www.haskell-munich.de See you on Wednesday, Heinrich Hördegen P.S.: Some hours ago, I send this message with a wrong date. The correct date is Wednesday, 26 Oct, 19h30. Sorry.

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hello Haskell
by R J 24 Oct '11

24 Oct '11

hey Haskell this is nuts http://www.business10i.com

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haskell-janitors (was Re: New rss maintainer)
by Conrad Parker 24 Oct '11

24 Oct '11

On 22 October 2011 22:52, Bas van Dijk <v.dijk.bas(a)gmail.com> wrote: > I released a new rss: > > http://hackage.haskell.org//package/rss-3000.2.0 > > It no longer requires old-time and is tested with the latest versions > of its dependencies. > > On 21 October 2011 17:34, Vincent Hanquez <tab(a)snarc.org> wrote: >> Perhaps, unless someone step up, it would be nice to move packages that have >> no maintainer anymore into a github organisation (haskell-janitors ?), > > Nice idea! However I think we should always strive for having a single > or a limited number of maintainers. Finally when nobody wants to take > over a package we can hand it over to haskell-janitors. I like the janitors idea because it is practical, and I also like the ideal world where every package has an active maintainer. How about we set up the haskell-janitors github group as Vincent suggests, with some basic rules like: * when you upload a package you put your name and email address in the maintainer field, with a comment saying that you are maintaining this package through the haskell-janitors group * anyone in the haskell-janitors group can upload a new version of a package which is maintained through the haskell-janitors group. When you do so you set (or prepend?) your name as maintainer. * if anyone anywhere ever gets keen to take exclusive maintenance of a project, to redesign it or whatever, they're welcome to take it out of haskell-janitors. Goals would be: * timely uploads (anyone can upload) * accountability (you put your name on it) * packages still have someone who can accept patches, answer questions etc. (you put your name on it) Conrad.

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Will changing associativity of enumerator's ($=) affect anyone? (also: enumerator mailing list)
by John Millikin 24 Oct '11

24 Oct '11

A user recently suggested changing the associativity of ($=) from [[ infixr 0 ]] to [[ infixl 1 ]]. This allows the following expressions to be equivalent: run $ enumerator $$ enumeratee =$ enumeratee =$ iteratee run $ enumerator $= enumeratee $$ enumeratee =$ iteratee run $ enumerator $= enumeratee $= enumeratee $$ iteratee Although this is technically a backward-incompatible change, I feel it's small enough that it could go in a minor release *if nobody depends on the current behavior*. So, if anybody using 'enumerator' will have code broken by this change, please speak up. If I don't hear anything in a week or so, I'll assume it's all clear and will cut the new release. ------------------------- Second, I was asked whether there's a mailing list for enumerator stuff. To my knowledge there isn't, so I started one on librelist. To subscribe and/or post, send an email to haskell.enumerator(a)librelist.com . Archives are available at http://librelist.com/browser/haskell.enumerator/ . I plan to make release announcements there (for releases not important enough for haskell-cafe), and it might be useful for general discussion.

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SpecConstr message while compiling
by Daniel Díaz Casanueva 24 Oct '11

24 Oct '11

Hi, cafe! I wrote a program and had the following message while compiling (with -O2): SpecConstr Function `addOc{v s6RL} [lid]' has four call patterns, but the limit is 3 Use -fspec-constr-count=n to set the bound Use -dppr-debug to see specialisations What it means? Is it bad? It only happens when compiling with -O2. addOc is a local function (defined in a where clause). If it helps, here is the definition: addOc x [] = [(x,1)] addOc x ((y,n):ys) = if x == y then (y,n+1) : ys else (y,n) : addOc x ys I want to know if there is something wrong or a I don't need to take care about this. Thanks in advance, Daniel Díaz.

2 2

Problem installing svgcairo
by Roly Perera 23 Oct '11

23 Oct '11

Hi, I'm having a problem installing svgcairo with Cabal, which I need for something else. I don't know what's going on, but something (maybe a C preprocessor, judging by Google search results) barfs with the complaint: ./Graphics/Rendering/Cairo/SVG.chs:209:28: error: missing binary operator before token "(" I can't find the file SVG.chs on my system to inspect this line, but perhaps I'm looking in the wrong place. Has anyone encountered this? Am I perhaps using the wrong version of Cairo or Gtk? Any suggestions welcome. thanks Roly ====== $ cabal install svgcairo Resolving dependencies... [1 of 2] Compiling SetupWrapper ( /tmp/svgcairo-0.12.125554/svgcairo-0.12.1/SetupWrapper.hs, /tmp/svgcairo-0.12.125554/svgcairo-0.12.1/dist/setup/SetupWrapper.o ) [2 of 2] Compiling Main ( /tmp/svgcairo-0.12.125554/svgcairo-0.12.1/Setup.hs, /tmp/svgcairo-0.12.125554/svgcairo-0.12.1/dist/setup/Main.o ) Linking /tmp/svgcairo-0.12.125554/svgcairo-0.12.1/dist/setup/setup ... [1 of 2] Compiling Gtk2HsSetup ( Gtk2HsSetup.hs, dist/setup-wrapper/Gtk2HsSetup.o ) [2 of 2] Compiling Main ( SetupMain.hs, dist/setup-wrapper/Main.o ) Linking dist/setup-wrapper/setup ... Configuring svgcairo-0.12.1... Preprocessing library svgcairo-0.12.1... ./Graphics/Rendering/Cairo/SVG.chs:209:28: error: missing binary operator before token "(" gtk2hsC2hs: Error during preprocessing chs file cabal: Error: some packages failed to install: svgcairo-0.12.1 failed during the building phase. The exception was: ExitFailure 1

1 0

Web API attempt: Thrift + Evernote API -- apparent brick wall: HTTPS support
by Ryan Newton 23 Oct '11

23 Oct '11

Hi all, An old fogey here -- new to this world of web APIs / rpc over HTTP. I was thinking that since Thrift supports Haskell that it wouldn't be to hard to plug my Haskell program into the Thrift-based Evernote API to upload notes to the cloud. The first step to do that would be to authenticate: http://www.evernote.com/about/developer/api/evernote-api.htm#_Toc297053064 Uh, oh! Trouble already. You must use THttpClient to connect using HTTPS! It looks like the Thrift library for Haskell doesn't offer that option (plain HttpClient only). Presumably because the package HTTP doesn't support https? http://stackoverflow.com/questions/3988115/haskell-network-browser-https-co… Is there a way that libcurl could be used to provide THttpClient? I don't know enough to say... More generally, my problem is that it hard to figure out how to use Thrift from Haskell. Simple examples like this are helpful: http://mortenib.wordpress.com/2009/10/29/thrift-and-haskell/ But the Thrift library itself lacks full Haddock documentation: http://hackage.haskell.org/package/Thrift-0.6.0 And the generated Thrift code doesn't restrict its export lists to give you a hint as to what the "entry points" are. This is not to blame the thrift authors. They have N languages to support! But for someone with some extra time from the Haskell community, it seems like there would be some good return-on-investment for effort spent cleaning up the Haskell Thrift support. Maybe this is what Christian Lavoie is already doing? (http://hackage.haskell.org/package/thrift) Cheers, -Ryan P.S. One final note in the language-interop department. Since OCaml is supported by SWIG, Haskell should be too! Manuel's caveats notwithstanding: http://www.haskell.org/pipermail/c2hs/2003-May/000016.html

1 0

Data.Vector.Mutable.mapM
by Joachim Breitner 23 Oct '11

23 Oct '11

Hi, I’m consdering to change some performance critical code from Vector to MVector, hopefully avoiding a lot of copying and garbage collecting. But it seems that the Data.Vector.Mutable interface at http://hackage.haskell.org/packages/archive/vector/0.9/doc/html/Data-Vector… is quite limited; e.g. I am missing simple functions having type modifyM :: PrimMonad m => (a -> m a) -> MVector (PrimState m) a -> m () that would do something with each element in the vector. Is this an indication that such use is actually not desired, or is it just the case that nobody has developed that yet? Thanks, Joachim -- Joachim "nomeata" Breitner mail(a)joachim-breitner.de | nomeata(a)debian.org | GPG: 0x4743206C xmpp: nomeata(a)joachim-breitner.de | http://www.joachim-breitner.de/

3 3

hackage and cabal test support: why does it claim I have no type field when I do?
by Doug Burke 23 Oct '11

23 Oct '11

I've just been updating my code to take advantage of the test support in Cabal. I have it so that cabal configure --enable-tests cabal build cabal test works. However, when I try to upload to hackage, I get cabal upload -c dist/swish-0.6.2.0.tar.gz Checking dist/swish-0.6.2.0.tar.gz... Error: dist/swish-0.6.2.0.tar.gz: 400 Error in upload 400 Error in upload line 271: The 'type' field is required for test suites. The available test types are: exitcode-stdio-1.0 and here are the relevant lines from the cabal file: 267 if flag(developer) 268 ghc-options: -Werror 269 ghc-prof-options: -auto-all 270 271 Test-Suite test-builtinmap 272 type: exitcode-stdio-1.0 273 Hs-Source-Dirs: tests/ src/ 274 Main-Is: BuiltInMapTest.hs 275 Other-Modules: TestHelpers 276 As you can see, there's a type field for the Test-Suite and I don't see any obvious discrepancy with the information from the user's guide (http://www.haskell.org/cabal/users-guide/#test-suites) I also have Cabal-Version: >= 1.9.2 in the file; the full version can be found at https://bitbucket.org/doug_burke/swish/src/4545220d88e2/swish.cabal#cl-271 What am I doing wrong? Thanks in advance, Doug

2 3

runStateT execution times measurement baffling
by thomas burt 22 Oct '11

22 Oct '11

Hello - I've been trying to measure execution time for some code I'm running with the StateT monad transformer. I have a function f :: StateT MyState IO a Now, I measure the time it takes to run an invocation of this function from beginning to end, i.e. f = do t0 <- getCurrentTime stuffToDo t1 <- getCurrentTime liftIO $ putStrLn (show $ diffUTCTime t1 t0) And also measure like this: g :: IO g = do t0 <- getCurrentTime (val,newState) <- runStateT f initialState t1 <- getCurrentTime putStrLn $ "outside: " ++ (show $ diffUTCTime t1 t0) Curiously, the times reported for "outside" are about 5-8 times as long. I should probably note that stuffToDo calls itself a few hundred times (and uses liftIO once per loop). Anyone with ideas on why runStateT apparently has so much overhead? By the way I'm using ghc-6.10.4 and Control.Monad.Trans.State.Strict. Thanks for any suggestions or advice. Thomas

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Haddock fails on ConfigFile, but why?
by Magnus Therning 22 Oct '11

22 Oct '11

Would love to get some help on making Haddock accept ConfigFile[1]. The error message is about as far from helpful as you can get ;) dist/build/tmp-15743/src/Data/ConfigFile/Monadic.hs:34:1: parse error on input `import' The author is informed but is as confused as me, it seems[2]. /M [1] http://hackage.haskell.org/package/ConfigFile [2] https://github.com/jgoerzen/configfile/issues/4 -- Magnus Therning OpenPGP: 0xAB4DFBA4 email: magnus(a)therning.org jabber: magnus(a)therning.org twitter: magthe http://therning.org/magnus Most software today is very much like an Egyptian pyramid with millions of bricks piled on top of each other, with no structural integrity, but just done by brute force and thousands of slaves. -- Alan Kay

3 4

What is the etiquette for posting to multiple forums?
by Michael Litchard 21 Oct '11

21 Oct '11

I know it's bad form to post the same question to multiple mailing lists. But what about say, the beginner's mailing list and stackoverflow.com?

2 1

ANN: OpenCL 1.0.1.3 package
by Luis Cabellos 21 Oct '11

21 Oct '11

Hello, all. I want to show you the OpenCL package. I have done this using Jeff Heard OpenCLRaw package, but I create a new one due the lack of updates of the former. # Where to get it * Hackage page (http://hackage.haskell.org/package/OpenCL) * Repository (https://github.com/zhensydow/opencl) * Bugs (https://github.com/zhensydow/opencl/issues) * Examples (https://github.com/zhensydow/opencl/tree/master/examples) # Things: * I write it's high-level binding to OpenCL libraries, but only because I added more types to hide most of the alloc/free of the API, and hide the enums using c2hs enums. * The worst problem of the OpenCLRaw is the bad types it use, I learn to fix 32/64 bits issues with c2hs, and test it on linux machines. * Tested on Linux + NVidia only. * Jason Dagit is helping with Windows, OSX testing in own fork, also the call-conv fork in github has changes to work on Windows Please, Consider it's on experimental status but it works, I need lots of feedbacks for detect posible errors, Thanks,

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