- Haskell-Cafe - Haskell.org

helping you contribute to darcs (poll results so far)
by Eric Y. Kow 07 Aug '08

07 Aug '08

Dear Haskellers, Last Friday, I had posted a message asking how the darcs community could a better job recruiting developers to hack on darcs. Thanks for all the great responses! I am gratified by the suggestions you have offered, as well as the recent uptick in community involvement. The responses so far fall along three themes: offering new features, improving code accessibility and shaking up the community: Features - GUI (david48, Bit Conner) - splitting/merging (Luke Palmer, Ben Franksen) - binary file handling (Jason Dusek) - ... already does what I want (Allan Clark, Andrew Coppin) Code accessibility - split into libs (Neil Mitchell) - unit tests! (Ashley Moran) - code documentation (Lele Gaifax) - patch theory docs (Apfelmus, Ferenc Wagner) - inherent simplicity of model, cf git (Austin Seipp) Community - release announcements (Brandon Allbery, Neil Mitchell, Don Stewart) - showing ways to help (Wren Ng Thorton, Ferenc Wagner) - announcing our need for help (Wren Ng Thorton) - easier entry point to darcs code, à la xmonad (Petr Rockai) - more active leadership (Don Stewart, Lele Gaifax) One thing which is clear is that the darcs team have failed to communicate effectively: the code is not as well-documented as it should be, patch theory is still not defined clearly or rigorously enough for Haskellers, the recent release announcements gave people the impression that darcs was being abandoned, and we haven't made it clear that we needed your help. We need your help ----------------- Hopefully one thing is clearer after this discussion. We definitely need your help! What we need most of all are some Haskell optimisation gurus to join the project, even in a minor way. Darcs 2 offers some huge improvements in safety and core efficiency. Unfortunately, these improvements are overshadowed by poor performance. Paradoxically speaking, darcs 2 just isn't fast enough for people to notice how much faster it has gotten! We need somebody to comb through our code and spot the silly things which are making performance suffer. Is there something too strict? Too lazy? Are going about IO completely the wrong way? There is no patch theory needed for this! Anybody with an eye for performance should be able to rip into this code and find something to fix. If you are not an optimisation guru, there are still loads of ways to help. For starters, you could help us to improve our support for Windows, or maybe some of the ProbablyEasy bugs: http://bugs.darcs.net/issue?@columns=title,id,activity,status,assignedto&@f… We will communicate better -------------------------- The darcs 2 release announcement was very frank, but it also painted an inaccurate picture of the situation. Here is a clearer picture: we are all still very interested in darcs and want to keep using it! If you have a large repository and you cannot wait for us to fix performance bugs, we wish you the best with git (etc). But if darcs can handle your repository, we hope you stick around. It is true that David is taking a lower profile, but this just means that he is not following every discussion on the mailing list or every new bug and feature request. David is still receiving patches and reviewing them on a daily basis, providing the usual technical insight. So keep sending those patches! That's all for now ------------------ I am going to leave things here for now, despite all the interesting points we could still address and see where else the discussion leads. In my next reply, I hope to address some of the more of suggestions you have offered. Thanks again! -- Eric Kow <http://www.nltg.brighton.ac.uk/home/Eric.Kow> PGP Key ID: 08AC04F9

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Looking for a more functional way to do this
by Jefferson Heard 07 Aug '08

07 Aug '08

Working with HOpenGL and GLUT, I find myself approaching a common problem with a common solution that I don't really like all that much, as it reeks of procedural programming. Basically the problem is that of complex program state, such that when the user provides input to the program in the form of a mouse click or a typed string or character, the program updates its internal state to reflect this, whether that's changing the rotation, scale, or position of a screen element, or deciding what data to have loaded from disc. What I often do is something that looks like this: data ProgramState = ProgramState { some_associative_data :: Map String String , position :: GL.Vector3 Float , look_at :: GL Vector3 Float , selectables :: Map GLuint NamedObject } render :: IORef ProgramState -> IO () render state = do st <- readIORef state ... handleMouseClicks :: IORef ProgramState -> GLUT.KeyboardMouseHandler handleMouseClicks state ... = do st <- readIORef state ... main = do ... let st = ProgramState { Map.empty ... } render' = render st mouse' = handleMouseClicks st GLUT.renderCallback $= render GLUT.keyboardMouseCallback $= Just mouse' and so on and so forth. Generally there are not fewer than 5 and not more than about 32 variables that I have to track between mouse clicks, and there's all this boilerplate code as well. I'm searching for a better way to do this, and I feel sure there is one. I'm considering using Template Haskell or possibly SYB to generate this code, but it also seems like I also ought to be able to declare some kind of state monad or continuation monad that can encapsulate ProgramState without having to declare an explicit structure for it everytime. For one thing, I'd like to genericize this code and write something akin to Processing for Haskell (http://www.processing.org)

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Haskell Weekly News: Issue 80 - August 6, 2008
by Brent Yorgey 06 Aug '08

06 Aug '08

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20080806 Issue 80 - August 6, 2008 --------------------------------------------------------------------------- Welcome to issue 80 of HWN, a newsletter covering developments in the [1]Haskell community. Community News Brent Yorgey (byorgey, your friendly neighborhood HWN editor) has completed a move to Philadelphia and looks forward to starting a PhD in the programming languages group at U Penn next month. Roman Cheplyaka (Feuerbach) won second prize at the 2008 [2]International Mathematics Competition! Announcements prof2dot, version 0.4.1. Gregory Wright [3]announced the release of prof2dot, a graphical profiling tool for use with GHC. prof2dot is a filter that takes the profiling output generated by running a GHC-compiled program with the "+RTS -pix -RTS", option and turns it into a graphviz dot file. GHC switching to git. Simon Marlow [4]announced that the GHC team has made the decision to switch the version control system hosting the GHC repository from darcs to git. Haddock 2.2.1. David Waern [5]announced the release of version 2.2.1 of Haddock, the Haskell documentation tool. Haskore tutorial. jinjing is creating [6]a Haskore tutorial while learning it. Suggestions and corrections are welcome. Hoogle 4 beta. Neil Mitchell [7]announced the availability of beta versions of Hoogle 4, both a [8]web client and [9]command-line version. Testing and [10]feedback welcome! Design your own xmonad shirt. David Lazar has prepared a design on [11]spreadshirt under Designs > Computer > Programming. Choose the color and other formatting and get your very own custom xmonad shirt! Google Summer of Code Progress updates from participants in the 2008 [12]Google Summer of Code. Generic tries. Jamie Brandon is working on a library for efficient maps using generalized tries. This week, he has worked on implementing AVL trees and has created several [13]more [14]benchmarks. Hoogle 4. Neil Mitchell (ndm) is working on [15]Hoogle 4. [16]This week, he finished up type search, which now gives much better results than Hoogle 3. He also [17]released a [18]public beta version of the command-line interface. [19]Bug reports or feature requests are welcome. DPH physics engine. Roman Cheplyaka (Feuerbach) is working on a [20]physics engine using [21]Data Parallel Haskell. [22]Last week, he won second prize at the 2008 International Mathematics Competition; while he was away he also found time to read several papers on broad phase collision detection and to begin thinking about [23]general convex polyhedra. GHC plugins. Max Bolingbroke is working on dynamically loaded plugins for GHC. Cabal dependency framework. Andrea Vezzosi (Saizan) is working on a [24]make-like dependency analysis framework for Cabal. Language.C. Benedikt Huber (visq) is [25]working on Language.C, a standalone parser/pretty printer library for C99. GHC API. Thomas Schilling (nominolo) is working on [26]improvements to the GHC API. Discussion poll: how can we help you contribute to darcs?. Eric Kow (kowey) [27]asked how the darcs team could better encourage more people to contribute, precipitating a long and productive discussion with many good suggestions. Jobs Lectureship in Functional Programming, Nottingham. Graham Hutton [28]announced an opening for a Lecturer (Assistant Professor) in the Functional Programming Lab in Nottingham, a recently formed research group that comprises Thorsten Altenkirch, Graham Hutton, Henrik Nilsson, four research fellows, and eleven PhD students. Applications from the Haskell community are encouraged! The closing date for applications is Friday, 15th August 2008. Blog noise [29]Haskell news from the [30]blogosphere. * Roman Cheplyaka: [31]Physics and polyhedra. * Chris Done: [32]Kibro: Haskell, lighttpd and fastcgi. * Neil Mitchell: [33]Hoogle 4.0 web client preview. * >>> Sven Heyll: [34]Lazy Evaluation (there be dragons and basement cats). * Clifford Beshers: [35]Two-dimensional zip. * Brent Yorgey: [36]Philadelphia!. * Luke Plant: [37]Haskell API docs suck. A lot.. * Neil Mitchell: [38]Hoogle 4.0 release (beta, command line). * Mikael Johansson (Syzygy-): [39]The end of the line. * Jamie Brandon: [40]Yet more mini benchmarks. * Douglas M. Auclair (geophf): [41]Combinators in Haskell. * Holumbus: [42]Search Packages. * Douglas M. Auclair (geophf): [43]How do I get better?. * Neil Mitchell: [44]GSoC Hoogle: Week 10. * Dan Piponi (sigfpe): [45]Hopf Algebra = Group + Monad. * >>> Ayumilove: [46]Haskell Programming Tutorial Part 4. * Douglas M. Auclair (geophf): [47]Trivial Monad solutions. * Douglas M. Auclair (geophf): [48]Trivial Monad solutions (cont.). * Douglas M. Auclair (geophf): [49]Orators' exercise. * Roman Cheplyaka: [50]Status report: week 9-10. * Matthew Sackman: [51]Reflections on the ICFP Programming Contest 2008. * Jamie Brandon: [52]More benchmarks. * Chris Done: [53]GHCi on Acid (GOA). * Audrey Tang: [54]Pugs now builds again from SVN.. * "FP Lunch": [55]An ad-hoc approach to productive definitions. * Ketil Malde: [56]A plan for Bloom filters. * Audrey Tang: [57]Pugs.hs is back.. * Holumbus: [58]OpenSearch Available Again. Quotes of the Week * shepheb: don't forget YMCArray * matthew-_: you know I increasingly think I'm a very bad haskell programmer - I spend all my time programming at the type level, which is basically untyped. So I just write untyped programs, that happen to run at compile time. * SyntaxNinja: just picture monads as tiny, silly, luminous, and devious sprites who fly around your haskell code carrying state from one piece of code to another. I don't think that'll help, but it can't hurt. * poetix: Avoiding lambdas is pointless <-- *groan* * kzm: My program contains a bug. How ungrateful, after all I've done for it. * sw17ch: FunPtrs do not live up to their name About the Haskell Weekly News New editions are posted to [59]the Haskell mailing list as well as to [60]the Haskell Sequence and [61]Planet Haskell. [62]RSS is also available, and headlines appear on [63]haskell.org. Headlines are available as [64]PDF. To help create new editions of this newsletter, please see the information on [65]how to contribute. Send stories to byorgey at cis dot upenn dot edu. The darcs repository is available at darcs get [66]http://code.haskell.org/~byorgey/code/hwn/ . References 1. http://haskell.org/ 2. http://imc-math.org/ 3. http://article.gmane.org/gmane.comp.lang.haskell.glasgow.user/14821 4. http://article.gmane.org/gmane.comp.lang.haskell.glasgow.user/14819 5. http://www.haskell.org//pipermail/haskell-cafe/2008-August/045791.html 6. http://article.gmane.org/gmane.comp.lang.haskell.cafe/42861 7. http://neilmitchell.blogspot.com/2008/08/hoogle-40-web-client-preview.html 8. http://haskell.org/hoogle/beta/ 9. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hoogle 10. http://code.google.com/p/ndmitchell/issues/list 11. http://spreadshirt.com/ 12. http://hackage.haskell.org/trac/summer-of-code/wiki/SoC2008 13. http://jamiiecb.blogspot.com/2008/08/more-benchmarks.html 14. http://jamiiecb.blogspot.com/2008/08/yet-more-mini-benchmarks.html 15. http://code.haskell.org/hoogle/ 16. http://neilmitchell.blogspot.com/2008/08/gsoc-hoogle-week-10.html 17. http://neilmitchell.blogspot.com/2008/08/hoogle-40-release-beta-command-lin… 18. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hoogle 19. http://code.google.com/p/ndmitchell/issues/list 20. http://haskell.org/haskellwiki/Hpysics 21. http://www.haskell.org/haskellwiki/GHC/Data_Parallel_Haskell 22. http://physics-dph.blogspot.com/2008/08/status-report-week-9-10.html 23. http://physics-dph.blogspot.com/2008/08/physics-and-polyhedra.html 24. http://code.haskell.org/~Saizan/cabal 25. http://www.sivity.net/projects/language.c/wiki/ 26. http://hackage.haskell.org/trac/ghc/wiki/GhcApiStatus 27. http://www.haskell.org//pipermail/haskell-cafe/2008-August/045701.html 28. http://article.gmane.org/gmane.comp.lang.haskell.general/16365 29. http://planet.haskell.org/ 30. http://haskell.org/haskellwiki/Blog_articles 31. http://physics-dph.blogspot.com/2008/08/physics-and-polyhedra.html 32. http://chrisdone.com/blog/2008/08/06/kibro-haskell-lighttpd-and-fastcgi/ 33. http://neilmitchell.blogspot.com/2008/08/hoogle-40-web-client-preview.html 34. http://sheyll.blogspot.com/2008/08/lazy-evaluation-there-be-dragons-and.html 35. http://cliffordbeshers.blogspot.com/2008/08/two-dimensional-zip.html 36. http://byorgey.wordpress.com/2008/08/04/philadelphia/ 37. http://lukeplant.me.uk/blog.php?id=1107301692 38. http://neilmitchell.blogspot.com/2008/08/hoogle-40-release-beta-command-lin… 39. http://blog.mikael.johanssons.org/archive/2008/08/the-end-of-the-line/ 40. http://jamiiecb.blogspot.com/2008/08/yet-more-mini-benchmarks.html 41. http://logicaltypes.blogspot.com/2008/08/combinators-in-haskell.html 42. http://holumbus.fh-wedel.de/blog/?p=14 43. http://logicaltypes.blogspot.com/2008/08/how-do-i-get-better.html 44. http://neilmitchell.blogspot.com/2008/08/gsoc-hoogle-week-10.html 45. http://sigfpe.blogspot.com/2008/08/hopf-algebra-group-monad.html 46. http://www.5min.com/Video/Ayumilove-Haskell-Programming-Tutorial-Part-4-328… 47. http://logicaltypes.blogspot.com/2008/05/trivial-monad-solutions.html 48. http://logicaltypes.blogspot.com/2008/05/trivial-monad-solutions-cont.html 49. http://logicaltypes.blogspot.com/2008/05/orators-exercise.html 50. http://physics-dph.blogspot.com/2008/08/status-report-week-9-10.html 51. http://www.wellquite.org/icfp_contest_2008_reflections.html 52. http://jamiiecb.blogspot.com/2008/08/more-benchmarks.html 53. http://chrisdone.com/blog/2008/08/01/ghci-on-acid-goa/ 54. http://pugs.blogs.com/pugs/2008/08/pugs-now-builds.html 55. http://sneezy.cs.nott.ac.uk/fplunch/weblog/?p=109 56. http://blog.malde.org/index.php/2008/07/31/a-plan-for-bloom-filters/ 57. http://pugs.blogs.com/pugs/2008/07/pugshs-is-back.html 58. http://holumbus.fh-wedel.de/blog/?p=13 59. http://www.haskell.org/mailman/listinfo/haskell 60. http://sequence.complete.org/ 61. http://planet.haskell.org/ 62. http://sequence.complete.org/node/feed 63. http://haskell.org/ 64. http://code.haskell.org/~byorgey/code/hwn/archives/20080806.pdf 65. http://haskell.org/haskellwiki/HWN 66. http://code.haskell.org/~byorgey/code/hwn/

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GHC Feature or Bug: f x = (`head` x, ())
by Jeremy Shaw 06 Aug '08

06 Aug '08

Hello, GHC is happy to compile this code: > f x = (`head` x, ()) but Hugs does not like it, and Section 3.5 of the Haskell Report does not give any obvious indications that it is valid. Numerous people have suggested that some additional parens are required: > f x = ((`head` x), ()) Is this GHC behavior intentional? If not, is it perhaps a happy accident? Or is it ambigious in some way with out the additional parenthesis ? I am curious because trhsx (the preprocessor for HSP/HSX) currently does not accept this construct. If it is a bug in GHC (that will eventually be fixed), then we can leave trhsx alone. If it is a feature, then a precise definition of the adjusted syntax would be helpful. (Or, if this construct is valid H98, an explaination of how to read the report correctly). Thanks! j.

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Re: [haskell-art] Haskore Tutorial
by Vikrant 06 Aug '08

06 Aug '08

Hi, I get this error. I think have zlib installed! what package should I install to compile cabal on my machine (ubuntu - 8.04) Configuring cabal-install-0.5.2... Setup: At least the following dependencies are missing: zlib >=0.4 status of zlib on my machine is as following bahs$ aptitude search zlib p gambas2-gb-compress-bzlib2 - The Gambas bzlib2 component p gambas2-gb-compress-zlib - The Gambas zlib compression component p libcompress-raw-zlib-perl - low-level interface to zlib compression l p libcompress-zlib-perl - Perl module for creation and manipulation p libio-compress-zlib-perl - Perl interface to zlib p libio-zlib-perl - IO:: style interface to Compress::Zlib p libjzlib-java - Reimplementation of zlib in pure java i libzlib-ruby - transitional dummy package v libzlib-ruby1.8 - i zlib-bin - compression library - sample programs i zlib1g - compression library - runtime p zlib1g-dbg - compression library - development i A zlib1g-dev - compression library - development i zlibc - Uncompressing C Library Regards, Vikrant 2008/8/5 jinjing <nfjinjing(a)gmail.com> > What I did was to compile from source: > > http://hackage.haskell.org/trac/hackage/wiki/CabalInstall > > notice the darcs repo? > > http://darcs.haskell.org/cabal-install/ > > I used > > runghc Setup configure --user --prefix=$HOME > > to keep packages in user space, i.e. inside ~/.cabal folder. > > > On Wed, Aug 6, 2008 at 1:00 AM, Sebastian Menge > <sebastian.menge(a)uni-dortmund.de> wrote: > > Am Tue, 5 Aug 2008 22:10:16 +0530 > > schrieb Vikrant <vikrant.patil(a)gmail.com>: > > > >> well, How do I get cabal! on my ubuntu installation it gives me error > >> saying libghc6-cabal-dev depends ghc < 6.6.1 but 6.8.2 installed! > > > > Thats a known bug, but I cant remeber my workaround. Anyways I have > > installed > > > > libhugs-cabal-bundled > > > > IIRC from a gutsy-repository > > > > HTH, Sebastian. > > _______________________________________________ > > haskell-art mailing list > > haskell-art(a)lurk.org > > http://lists.lurk.org/mailman/listinfo/haskell-art > > > _______________________________________________ > haskell-art mailing list > haskell-art(a)lurk.org > http://lists.lurk.org/mailman/listinfo/haskell-art >

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Haskell garbage collector notes?
by Galchin, Vasili 06 Aug '08

06 Aug '08

hello, Is http://hackage.haskell.org/trac/ghc/wiki/GarbageCollectorNotes a reliable source of info on the ghc garbage collector? thx, vasili

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more adjunction questions -- where to send them?
by Jason Dusek 06 Aug '08

06 Aug '08

I've gotten most of my category theory help through the Haskell community one way or another, but I hesitate to ask more questions on this list if there is a better forum. Googling turned up an old, closed list. Is there somewhere else I should be asking my questions -- for example, I am now working on the adjunction of "right product" and "exponentiation" -- or is the Haskell Cafe list a good place? -- _jsn

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code review? store server, 220loc.
by Tim Newsham 06 Aug '08

06 Aug '08

Anyone interested in critiquing some code? I'm looking for ideas for making it faster and/or simpler: http://www.thenewsh.com/%7Enewsham/store/Server5.hs This is an exercise to see how well a server in Haskell would perform. My goals are roughly: - retargetability to other server types (ie. easy to replace request and response structures and business logic). - readability. - performance. My measurements show that a simple dummy server (accept, forkio, recv byte) handles roughly 7500 requests/connects per second, the server/client that do real messages do about 4500 req and connections per second. If all requests are on the same connection one after another it does about 13500 requests/second. For comparisons, a C ping-pong server does about 3600/second if it has to fork for each new connection/request, and about 35000/sec if its all on the same connection. So it seems at least competitive with a forking C server. I havent tested threaded C servers. Tim Newsham http://www.thenewsh.com/~newsham/

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Stripping text of xml tags and special symbols
by Pieter Laeremans 06 Aug '08

06 Aug '08

Hi, I 've got a lot of files which I need to proces in order to make them indexable by sphinx. The files contain the data of a website with a custom perl based cms. Unfortunatly they sometimes contain xml/html tags like <i> And since most of the texts are in dutch and some are in French they also contain a lot of special characters like ë é, ... I'm trying to replace the custom based perl based cms by a haskell one. And I would like to add search capability. Since someone wrote sphinx bindings a few weeks ago I thought I try that. But transforming the files in something that sphinx seems a challenge. Most special character problems seem to go aways when I use encodeString (Codec.Binary.UTF8.String) on the indexable data. But the sphinx indexer complains that the xml isn't valid. When I look at the errors this seems due to some documents containing not well formed html. I would like to use a programmatic solution to this problem. And is there some haskell function which converts special tokens lik & -> & and é -> &egu; ? thanks in advance, Pieter -- Pieter Laeremans <pieter(a)laeremans.org> "The future is here. It's just not evenly distributed yet." W. Gibson

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Brainstorming on how to parse IMAP
by John Goerzen 06 Aug '08

06 Aug '08

Hi folks, I'm interested in writing a library to work with IMAP servers. I'm interested in thoughts people have on parsing libraries and methods. I'm a huge fan of Parsec overall -- it lets me have a single-stage parser, for instance. But it isn't sufficiently lazy for this task, and I probably will need to deal with ByteStrings instead of Strings, since some IMAP messages may be 30MB or more. So to give a very, very brief rundown of RFC3501, there are lots of ways that an IMAP server can encode things. For instance, we could see this: A283 SEARCH "TEXT" "string not in mailbox" which is the same as: A283 SEARCH TEXT "string not in mailbox" and the same as: A283 SEARCH {4} "string not in mailbox" TEXT The braces mean that the given number of octets follows after the CRLF at the end of the given line. We could even see: A283 SEARCH {4} {21} TEXTstring not in mailbox Note that when downloading messages, I would fully expect to see things like * FETCH {10485760} representing a 10MB message. Also, quoted strings have escaping rules. [ please note that the above is paraphrased and isn't really true RFC3501 for simplicity sake ] Now then... some goals. 1) Ideally I could parse stuff lazily. I have tried this with FTP and it is more complex than it seems at first, due to making sure you never, never, never consume too much data. But being able to parse lazily would make it so incredibly easy to issue a command saying "download all new mail", and things get written to disk as they come in, with no buffer at all. 2) Avoiding Strings wherever possible. 3) Avoiding complex buffering schemes where I have to manually buffer data packets. Thoughts and ideas? BTW, if any of you have heard of OfflineIMAP, yes I am considering rewriting OfflineIMAP in Haskell. -- John

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Capitalization and associated type families
by Brian Hulley 06 Aug '08

06 Aug '08

Hi, I'm familiar with the capitalization rules for identifiers in Haskell and know that they are very useful and practical e.g. by allowing variables to be distinguished from "constants" in patterns etc. However I'm trying to understand on a much deeper level whether or not they can really be justified and indeed if there is a danger that they can lead to inconsistency in the light of future extensions to the language. For example, why is there any distinction between a type "variable" and a type "constant"? To make this clearer consider the type of (map): (a -> b) -> List a -> List b (ignoring the special [] syntax for list types which would just confuse the issue here). With explicit quantifiers, we'd write: forall a b. (a -> b) -> List a -> List b Now this begs the question: why does "List" need to start with a capital? (supposing that quantifiers were always written explicitly) The same distinction between "constants" and "variables" is also used in predicate logic e.g. On(x, Table) & Colour(x, Red) but similarly the above could surely be written just as easily by: exists x. on(x, table) & colour(x, red) where (on), (table), (colour), and (red) are just considered to be variables that have already been introduced (by some enclosing scope) instead of having to think of them as "constants" and make a distinction between "constant" and "variable". Anyway to get to the point of this post what I'm really trying to find is some explanation of why there is the concept of "constant" as opposed to "variable" or whether this concept is now redundant in the light of lexical scoping/ explicit quantification? Somewhat related to this issue is the syntax of associated type families. For example in section 5.2.2 of http://www.haskell.org/haskellwiki/GHC/Indexed_types there is the example: class C a b where data T a which raises in my mind several questions: 1) Why is (T) given a parameter? I.e. why does an associated type declared inside a class decl not automatically get all the parameters of the class passed to it so that one would just write: class C a b where data T f :: T -> T === data family T a b class C a b where ... f :: T a b -> T a b 2) Compare: class C a b t | a b -> t with class C a b where data T In other words, why is (T) a "constant" when it is declared inside the class but a "variable" when passed as a parameter? Is the fact that (T) needs to be given a parameter even when it is declared inside the "scope" of the class type parameters the result of needing to fulfill the idea of "constant" vs "variable"? 3) In the syntax: class C a b data T a it seems rather odd that the "a" in "T a" should be related to the "a" in "C a b" since one might expect that the name chosen for a parameter should be local to the data decl. Apologies for such a rambling post. I've spent literally at least 6 months scouring the internet trying to find a real discussion about capitalization rules because I'm trying to answer the following question: if I make use of a similar capitalization rule in my own language, can I guarantee that this rule will not lead to an inconsistency at some future point? Ie is there a real rock solid theoretical basis for making a distinction between "constants" and "variables" that holds even in the presence of lexical scoping? Thanks, Brian.

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Re: [Haskell-cafe] Brainstorming on how to parse IMAP
by Donn Cave 06 Aug '08

06 Aug '08

Quoth John Goerzen <jgoerzen(a)complete.org>: | Donn Cave wrote: ... |> So I would let the application come up with the data. In general, | | Well, your response here begs the question of how much you want to | automate from the application. Yes, there are multiple ways of | communicating with IMAP servers, but you have the same synchronization | issues with all of them. Yes, I plan to let the application supply | functions to read data. But in the end, that is pointless if those | functions can't be written in Haskell! Sorry, I didn't entirely understand that, but the way I see it, you might or might not be able to map the set of issues with one transport vs. another onto some common abstraction. And anyway it's much easier and cleaner for you to implement the protocol parser as a pure function of bytestring -> response, than tangle it up with I/O. OK, here's a trivial example of what I see as the virtues of this approach. I don't think I actually return any size information along with my `incomplete' failure response, but it occurs to me that I should. Then a graphic application can use that to start a progress indicator for large transfers. It will be easy for my application to update that progress indicator, because it got the expected size and is getting the data. Harder to make that work through generic I/O functions invoked inside the parser, I think. | > I don't think there's any way to specify how much to read - I mean, | > the counted literal certainly provides that information, but that's the | > exception - so I would assume the application will need some kind of | > recv(2)-like function that reads data as available. | | Exactly. But there is no recv()-like function, except the one that | returns IO String. There is no recv()-like function that returns IO | ByteString. Well, right, that's needed. I just hacked out my own FFI. (Likewise for SSL.) In a platform context where you're forced to use buffered input semantics, you might use hGetLine and then read fixed amounts as required for counted literals (so the parser would need to return a bytes-needed-to-complete value to support that.) Donn

1 0

Re: [Haskell-cafe] Brainstorming on how to parse IMAP
by Donn Cave 06 Aug '08

06 Aug '08

Quoth John Goerzen <jgoerzen(a)complete.org>: ... | One problem with that is that if I use specific parsing library foo, | then only others that are familiar with specific parsing library foo can | hack on it. Well, you asked. For me, the parsing is a relatively minor part of the problem and maybe not one that benefits greatly from external support. MIME might be a different story. | 2) A lot of RFC protocols -- and IMAP in particular -- can involve | complex responses from the server with hierarchical data, and the parse | of, say, line 1 and of each successive line can indicate whether or not | to read more data from the server. Parsing of these lines is a stateful | activity. I mentioned that my parser may return an incomplete status. In principle, something like parseResponse :: ByteString -> Maybe (IMAPResponse, ByteString) That means the parse needs to be repeated each time until enough input data has accumulated. I worried a little about how to represent a useful incomplete parse state, but decided that it isn't worth the trouble - the amount of parsing in an ordinary response is too trivial. | 3) The linkage between Parsec and IO is weak. I cannot write an | "IMAPResponse" parser. I would have a write a set of parsers to parse | individual components of the IMAP response as part of the IO monad code | that reads the IMAP response, since the result of one dictates how much | network data I attempt to read. The parser should just parse data, and not read it. You don't need to worry about whether you can get recv(2) semantics on a socket with bytestrings, and you don't need to saddle users of this parser with whatever choice you might make there. You don't need to supply an SSL input function with the same semantics, or account for the possibility that data might actually not be coming from a socket at all (UNIX pipes are not unheard of.) You don't need to lock users into whatever execution dispatching might be supported by that I/O, potentially ruling out graphics libraries etc. that might not be compatible. So I would let the application come up with the data. In general, I don't think there's any way to specify how much to read - I mean, the counted literal certainly provides that information, but that's the exception - so I would assume the application will need some kind of recv(2)-like function that reads data as available. By the way, if you haven't already run across this, you may be interested to read about the IMAP "IDLE" command, cf. RFC2177. I think the value of this feature can be overstated, but it depends on the server, and some IMAP client implementators are very fond of it. At this point, the reason it might be interesting is that it moves away from the call & response pattern. Donn

2 1

ActiveX and COM
by Günther Schmidt 05 Aug '08

05 Aug '08

Hi, what is currently the recommend way to interface with COM from haskell? I need to create an Excel Sheet and thus need to use Excel via COM. Günther

4 4

Re: [Haskell-cafe] array fusion interface
by Henning Thielemann 05 Aug '08

05 Aug '08

On Sat, 2 Aug 2008, Evan Laforge wrote: > >> I have streams of samples with irregular sampling rates, so they look > >> like [(Time, SampleVal)]. In practice, this means [(Double, Double)]. > > > > Maybe I have already mentioned my eventlist package on Hackage which > > supports such resampling operations - but is based on lists. > > http://hackage.haskell.org/cgi-bin/hackage-scripts/package/event-list > > Ah, I had seen event-list and even downloaded and read parts of it, > but it was hard for me to figure out what was going on and how to > actually use it based on the scattered comments in the source. I commented only non-trivial parts, because I thought it is clear, that 'mapTime' is a 'map' on the time stamps and so on. > Apparently there are absolute and relative time variants, but within > that there are further "body" and "time" variants, and they're built > on a similarly sparsely documented alternating list library. Are > there some simple examples of its use out there? There are all four variants of whether a list starts and ends with a time or a data body. The 'midi' package uses 'event-list'. > Unfortunately, storable vector, unlike ByteString, doesn't export > 'create' and whatnot so I have to keep a locally patched version of > it. Well, it does export 'create': http://hackage.haskell.org/packages/archive/storablevector/0.1.2.2/doc/html… However in my applications I could use the safe 'unfoldrN' in most cases.

1 0

timing question
by Arie Groeneveld 05 Aug '08

05 Aug '08

Suppose I've: f = map g I want to know how much time it takes (interpreted mode) to fully process list xs (at least 1e6 elements) with function g. Is it sufficient to execute: *Main> last . f $ xs <result> (x.xx secs, yyyyyyyyyyy bytes) Are there any hidden difficulties involved? Reason is: comparing timings Haskell vs an interpreted language without laziness. thanks =@@i

5 7

ICFP08 Call for Participation
by Matthew Fluet (ICFP Publicity Chair) 05 Aug '08

05 Aug '08

===================================================================== Call for Participation The 13th ACM SIGPLAN International Conference on Functional Programming (ICFP 2008) http://www.icfpconference.org/icfp2008 Victoria, BC, Canada, 22-24 September 2008 ===================================================================== ICFP 2008 provides a forum for researchers and developers to hear about the latest work on the design, implementations, principles, and uses of functional programming. The conference covers the entire spectrum of work, from practice to theory, including its peripheries. Preliminary program: * http://www.icfpconference.org/icfp2008/schedule.html * Invited speakers: + Butler Lampson, Microsoft Research; Lazy and Speculative Execution in Computer Systems + Olivier Danvy, University of Aarhus; Defunctionalized Interpreters for Higher-Order Languages + Mark Jones, Portland State University; Polymorphism and Page Tables -- Systems Programming From a Functional Programmer's Perspective Schedule including related workshops: * Sep 20: ACM SIGPLAN Workshop on Generic Programming * Sep 20: ACM SIGPLAN Workshop on Mechanizing Metatheory * Sep 20: ACM SIGPLAN Workshop on Scheme and Functional Programming * Sep 21: ACM SIGPLAN Workshop on ML * Sep 21: ACM SIGPLAN Functional and Declarative Programming in Education * Sep 22-24: ICFP08 * Sep 25: ACM SIGPLAN Haskell Symposium * Sep 25: Functional Programming Developer Tracks * Sep 26: Commercial Users of Functional Programming * Sep 27: ACM SIGPLAN Erlang Workshop * Sep 27: Functional Programming Developer Tracks Registration information: * http://www.regmaster.com/conf/icfp2008.html * Early registration deadline: August 20, 2008 Conference hotel accommodation information: * http://www.deltahotels.com/groups/online/VIC/acm.php * Conference rate deadline: August 18, 2008 * Wiki page to coordinate room-sharing: http://www.icfpconference.org/pmwiki/pmwiki.php?n=Main.ICFP08RoomShare Conference organizers: * General Chair: James Hook (Portland State University) * Program Chair: Peter Thiemann (Universität Freiburg) * Local Arrangements Chair: George Tzanetakis (University of Victoria) * Workshop Co-Chairs: Michael Sperber (DeinProgramm) and Graham Hutton (University of Nottingham) * Programming Contest Co-Chairs: John Reppy (University of Chicago) and Tim Sheard (Portland State University) * Publicity Chair: Matthew Fluet (Toyota Technological Institute at Chicago)

1 0

HDBC-ODBC linking problems in windows.
by PJ Durai 05 Aug '08

05 Aug '08

Greetings everyone, I am having issues getting hdbc/odbc working on windows. When using GHC, I am not able to compile a simple program. It ends up with linker errors like C:\Program Files\Haskell\HDBC-odbc-1.1.4.3\ghc-6.8.3/libHSHDBC-odbc-1.1.4.3.a(Connection.o)(.text+0x52c):fake: undefined reference to `SQLAllocHandle' C:\Program Files\Haskell\HDBC-odbc-1.1.4.3\ghc-6.8.3/libHSHDBC-odbc-1.1.4.3.a(Connection.o)(.text+0x5b8):fake: undefined reference to `SQLSetEnvAttr' C:\Program Files\Haskell\HDBC-odbc-1.1.4.3\ghc-6.8.3/libHSHDBC-odbc-1.1.4.3.a(Connection.o)(.text+0x62c):fake: undefined reference to `SQLDriverConnect' C:\Program Files\Haskell\HDBC-odbc-1.1.4.3\ghc-6.8.3/libHSHDBC-odbc-1.1.4.3.a(Connection.o)(.text+0x700):fake: undefined reference to `SQLEndTran' C:\Program Files\Haskell\HDBC-odbc-1.1.4.3\ghc-6.8.3/libHSHDBC-odbc-1.1.4.3.a(Connection.o)(.text+0x770):fake: undefined reference to `SQLGetInfo' C:\Program Files\Haskell\HDBC-odbc-1 When I use ghci, it exits silently. It looks like calling convension mix-up in FFI declarations to me. I ran 'dumpbin' on odbc32.lib and all the exported function names are decorated like they are PASCAL calls, not ccall's. But GHC in this case is looking for undecorated names. I assume it works as is on Unix (unixODBC) ? Is there an easy workaround for this? Or am I doing something wrong? MySetup ======= Windows XP SP2 ghc 6.8.3 hdbc 1.1.5.0 hdbc-odbc 1.1.4.3.0 appreciate your time. Thanks pj

3 3

your RSA code
by Galchin, Vasili 04 Aug '08

04 Aug '08

Hi John, I am reading your RSA code as suggested. 1) Do you have an example code that uses your RSA API? 2) a ForeignPtr is created in function createPkey and "returned" to the caller. I am trying to follow which function(s) GC the associated heap. ?? 3) My assertion: It seems in my Posix asynch IO case ... that functions like aioRead, aioWrite, lioListIO would create ForeignPtrs that would "carried around in the AIO application and the associated heap would only be GC'd (garbage collected) when aioReturn or aio_Cancel get called. True? Kind regards, Vasili

1 0

Re: [Haskell-cafe] question about "faulting in" Haskell packages ...
by david48 04 Aug '08

04 Aug '08

You need to get cabal-install. Here's how I got it working on kubuntu : 1) install GHC 6.8.3 from haskell.org's binaries (kubuntu hardy isn't at 6.8.3 yet....) 2) download from hackage : * cabal-install-0.5.1.tar.gz from hackage * HTTP-3001.0.4.tar.gz * zlib-0.4.0.4.tar.gz * Cabal-1.4.0.1.tar.gz 3) build and install http, zlib, Cabal and then cabal-install for each package you have to type (*) : runhaskell Setup.hs configure runhaskell Setup.hs build sudo runhaskell Setup.hs install (*) sometimes it'll be Setup.lhs, I'm annoyed that it's not always the same name, can't rely on shell history :( 4) once cabal-install is installed you can do cabal update sudo cabal upgrade --global that'll upgrade all your ghc's packages. 5) from now if you want to install package a just type cabal install a --global cabal should download packages b,c,d for you if required. P.S. Sorry for the previous email, it got sent before I finished it :)

4 3

Memory problems reading a IntMap from a binary file
by Ludger Steens 04 Aug '08

04 Aug '08

Hi, I have IntMap String with about 40,000 entries. After saving it to disk (via Data.Binary) the file is 3.5 Mb small. However if I load it and save it back again my program needs 180 MB memory. Is there anything I do wrong or does the map really need that much memory? The (simple) program I wrote: main = do mp <- decodeFile "i.bin" :: IO ( IntMap String ) encodeFile "i2.bin" mp exitWith ExitSuccess Thanks, Ludger

2 1

adjoint of coproduct & diagonal
by Jason Dusek 04 Aug '08

04 Aug '08

I'm trying to figure out the adjunction diagrams for the adjunction where the diagonal functor is right adjoint to the coproduct functor. I'm |almost done|, but the co-unit has me stumped, because I can't figure out how the arrow at the top can be unique -- it seems it could be either one of: i_1 . [f,g] i_2 . [f,g] i_1, i_2 : C -> C+C f : A -> C g : B -> C The net effect of [id,id] on the right is to blur out the distinction. On #haskell, someone suggested there is a constraint I am missing; I've poked around for a day and still can't figure it out. -- _jsn |almost done| http://hpaste.org/9303

3 13

Kleisli composition operator
by Roly Perera 04 Aug '08

04 Aug '08

Hi, I'm obviously missing something basic here but I don't seem to be able to use the >=> operator which is apparently defined in the Prelude and also in Control.Monad. My imports are: import Prelude hiding (abs, lookup, init) import Data.Maybe import Data.List as List hiding (lookup, insert, delete, union, init) import Data.Map as Map hiding (update, delete, union, null, findIndex) import qualified Data.Tree as Tree import Control.Monad import Control.Monad.State Any suggestions anyone? thanks, Roly Perera

3 5

Re: [darcs-users] [Haskell-cafe] Re: poll: how can we help you contribute to darcs?
by Ashley Moran 03 Aug '08

03 Aug '08

On Aug 03, 2008, at 12:53 pm, Lele Gaifax wrote: > I fail to see what's so cool with GitHub: a quick overview didn't > reveal anything that couldn't be done with, say, Trac+Darcs. Can you > elaborate on that? Hi Lele It probably doesn't do anything you couldn't in Trac+darcs. But that's not the point - it's easy to jump on there, and fork a repo, track the changes in both directions. The barrier to working on a project on there is virtually nil (there is, of course, the issue of figuring out git when you've got the source on your machine, but that's a separate issue). What GitHub does really well is build a community around the repos. They could have used Hg or bzr or pretty much and DVCS and been as successful, but they (unfortunately) chose git. > IMHO, the biggest problem with darcs is with its underdocumented (from > the technical point of view) code base, that only an handful of people > understand. As already stated, I doubt Haskell is the real culprit > here: the algorithms are effectively difficult to explain in any > language, English to starts with. I wish David used a less succint > coding style, and could spend some time to enlight and mentor new > developers, but that's the way it is. My issue with the code base is the lack of unit tests. Coming from a Ruby background, I'm used to very short methods with very specific tests, often for things that to new programmers look trivial. To RSpec users, these unit tests *are* the documentation. By comparison, darcs only has functional tests, and it's hard to see how you can tell what code is covered by them. This would make me very wary about hacking at the code, not knowing if I could inadvertently break something. It also means you have to understand much bigger chunks of code to know how to fix something. I've very often fixed a bug in Ruby code because there's a one-line spec that describes exactly the behaviour that is at fault (or a missing one for the case I want). I don't know what the standard for Haskell testing is, and how FP testing compares to OOP testing. As a very trivial example the function "showPatchInfo :: PatchInfo -> Doc" could do with a test to show it produces output of the format "Initial import Ashley Moran <ashley.moran(a)patchspace.co.uk>**20080630153800]" (and if it *doesn't*, that is the point I'm making!) I think having the patch algorithms broken down and tested in this way would be the best form of documentation, although a plain-English specification would probably also be necessary. Simpler stuff (like showPatchInfo) just needs something to demonstrate what it does. Just my (naive) opinion coming from a OOP, test-obsessed background. Ashley -- http://www.patchspace.co.uk/ http://aviewfromafar.net/

1 0

Web processing
by Rafael C. de Almeida 03 Aug '08

03 Aug '08

Hello, I understand that nowadays there are several frameworks and wrapper libraries for making some sense of the XHTML documents you find over the web. That is, making the life of those who want to process the semi-structured data you find on the sites. I don't have much experience on that field myself, but I want to learn a little more about how I can, for instance, associate information from one site with information in another site. Even though it is structured differently in both places. Does anyone know about libraries that would help me out with that sort of work? Hope I'm being clear. []'s Rafael

3 2

Cabal + yi + alex problem.
by Yann Golanski 03 Aug '08

03 Aug '08

I cannot seem to be able to install yi via cabal install. The error I get is as follows. I suspect alex is not installed in the correct place. ; sudo cabal install yi Resolving dependencies... Downloading yi-0.4.3... Configuring yi-0.4.3... cabal: alex version >=2.0.1 && <3 is required but it could not be found. cabal: Error: some packages failed to install: yi-0.4.3 failed during the configure step. The exception was: exit: ExitFailure 1 ; sudo cabal install alex Resolving dependencies... Downloading alex-2.2... [1 of 1] Compiling Main ( Setup.lhs, dist/setup/Main.o ) Linking dist/setup/setup ... Warning: defaultUserHooks in Setup script is deprecated. Configuring alex-2.2... Warning: No 'build-type' specified. If you do not need a custom Setup.hs or ./configure script then use 'build-type: Simple'. Preprocessing executables for alex-2.2... Building alex-2.2... [...] Linking dist/build/alex/alex ... Installing: /home/yann/.cabal/bin ; sudo cabal install yi Resolving dependencies... 'yi-0.4.3' is cached. Configuring yi-0.4.3... cabal: alex version >=2.0.1 && <3 is required but it could not be found. cabal: Error: some packages failed to install: yi-0.4.3 failed during the configure step. The exception was: exit: ExitFailure 1 -- yann(a)kierun.org -= H+ =- www.kierun.org PGP: 009D 7287 C4A7 FD4F 1680 06E4 F751 7006 9DE2 6318

6 9

How can I get the mutable array out of an IOUArray for FFI use?
by Ryan Ingram 02 Aug '08

02 Aug '08

I wrote some fast bit-twiddling functions in C because my Haskell performance wasn't good enough. Now I'm trying to recompile with GHC6.8.3 and failing. This code worked on GHC6.6.1. I get the following error: > ghc --make main.hs Bitmap.hs:11:7: Could not find module `Data.Array.IO.Internals': it is hidden (in package array-0.1.0.0) I suppose I can declare a copy of the internal type and use unsafeCoerce#, but that seems like a terrible idea if there is a better way. What's the right way to make this work? Can I force that module to be unhidden? Should I file a GHC bug? -- ryan {-# OPTIONS_GHC -fffi -fglasgow-exts #-} {-# INCLUDE "bitmap_operations.h" #-} module Bitmap ( clearBitmap, ) where import Foreign.Ptr import Data.Array.Base import Data.Array.IO.Internals import GHC.Exts import Data.Word foreign import ccall unsafe clear_bitmap :: MutableByteArray# RealWorld -> Word32 -> Word32 -> IO () {-# INLINE unsafeGetMutableArray# #-} unsafeGetMutableArray# :: IOUArray Int Word32 -> MutableByteArray# RealWorld unsafeGetMutableArray# (IOUArray (STUArray _ _ array#)) = array# clearBitmap :: IOUArray Int Word32 -> Word32 -> Word32 -> IO () clearBitmap a1 color size = clear_bitmap (unsafeGetMutableArray# a1) color size

2 1

Using fundeps to resolve polymorphic types to concrete types
by Bryan Donlan 02 Aug '08

02 Aug '08

Hi, Is there any theoretical reason that functional dependencies can't be used to resolve a polymorphic type to a concrete type? For example: > -- compile with -fglasgow-exts > > class DeriveType a b | a -> b > > data A = A > data B = B > > instance DeriveType A B > > simpleNarrow :: DeriveType A b => b -> B > simpleNarrow = id Since 'b' is uniquely determined by the fundep in DeriveType, it seems that this ought to work; ie, since the only type equation satisfying DeriveType A b is B -> B, it should reduce to that before trying to fit its type against its body. The motivation is this case: > data ComplexType a where > SomeConstructor :: DeriveType a b => a -> b -> ComplexType a > > specialCaseFunc :: ComplexType A -> B > specialCaseFunc (SomeConstructor _ b) = b Essentially, if I have a data structure with two types used as fields, and one uniquely determines the other, I'd like to use these instances to avoid re-stating the implied one in the type equations, if possible. Is there some theoretical reason for this not to work, or is it just a limitation of GHC's current implementation? (Note, I'm testing with GHC 6.8.2, so it's possible this might be fixed in trunk already...) Thanks, Bryan Donlan

5 9

question about "faulting in" Haskell packages ...
by Galchin, Vasili 02 Aug '08

02 Aug '08

Hello, Sorry I asked this question before .. say I want to install package A that depends on package B, C, D but maybe B and D are not installed on my machine. Basically I want to "fault in" (i.e. install automatically) in B and D with "no fuss no muss". ??? In reality I would like to get my laptop which is running Ubuntu totally "faulted up" with all Haskell packages ... ;^) Regards, Vasili

1 0

Cabal files on Windows
by John Lato 02 Aug '08

02 Aug '08

Hello, Can anyone point me to a method for including path names with spaces in a cabal file? I would like to add a line similar to the following: include-dirs: C:\Program Files\program\include and of course a corresponding library as well. I've tried various methods of escaping the space and quoting, and nothing seems to work. Is this possible at all? I'm using Cabal-1.2.4.0 on Windows. I've tried running with a Windows shell and MSYS bash, with the same results. Thanks, John Lato

4 8

Analysing Haskell Program
by Roberto D'Aprile 02 Aug '08

02 Aug '08

Hello to everybody I'm using haskell for some research work and now i need to evaluate the performance of some simple haskell programs in particular information on the like, CPU cycles, bus usage, memory access and so on; so i wish to know if there is a way to compile haskell programms so they can be used with simplescalar or if there is another tool which i can use. Thank you

3 2

category theory tutorial pdfs .....
by Galchin, Vasili 01 Aug '08

01 Aug '08

Hello, Prof. Harold Simmons' tutorial IMO are like a Russian matroshka doll ... first layer is for newbie ... inner layers require more sophistication. IMO a very subtle writer ... I have every book imaginable on cat theory and topos theory so I think can compare a little. 1) http://www.cs.man.ac.uk/~hsimmons/BOOKS/books.html ... an earlier version ... "An Intro to Category Theory in Four Easy Movements" ... this version delves a little into Topos Theory ... pretty subtle .. cool 2) http://www.cs.man.ac.uk/~hsimmons/MAGIC-CATS/magic-cats.html ... newer version which also has its cool merits IMO! Regards, Vasili

2 1

a really dumb posting question ;^(
by Galchin, Vasili 01 Aug '08

01 Aug '08

Hello, What do I do to do a followup haskell cafe posting? E.g. I want to put a posting on the category theory thread! Kind regards, Vasili

3 2

an array of pointers in FFI?
by Galchin, Vasili 01 Aug '08

01 Aug '08

Hello, Is a (Ptr (Ptr a)) a polymorphic representation of an array of pointers of type "a"? I want to pass an array of pointers to a C function. Kind regards, Vasili

3 3

Point-free style in guards
by L29Ah 01 Aug '08

01 Aug '08

outStanza | (isMessage) = outMessage | (isPresence) = outPresence | (isIQ) = outIQ Why such a style doesn't work, so I must write ugly code like that: outStanza a | (isMessage a) = outMessage a | (isPresence a) = outPresence a | (isIQ a) = outIQ a so, guards can't be useful in point-free function definitions in any way

8 7

array fusion interface
by Evan Laforge 01 Aug '08

01 Aug '08

With all the noise lately about high performance array libraries with list-like interfaces, such as bytestring, storablevector, uvector, and vector, I thought I would try to make use of one in a project of mine, and I'm either bumping up against the limits of its expressiveness, or am missing out on how to express my problem. I have streams of samples with irregular sampling rates, so they look like [(Time, SampleVal)]. In practice, this means [(Double, Double)]. I can do this with storablevector by either storing two Vector Double, or by making a (Double, Double) Storable instance (more natural but requires -XFleixbleInstances). Now most functions that operate over a sample stream actually want a pair of samples so they can get an exact time with linear interpolation. Combining two streams requires them to both be resampled so their points line up, e.g. with a list implementation (ignoring the edges): resample as@((ax0, ay0) : (ax1, ay1) : _) bs@((bx0, by0) : (bx1, by1) : _) | ax1 == bx1 = (ax1, (ay1, by1)) : resample (tail as) (tail bs) | ax1 < bx1 = (ax1, (ay1, y_at (bx0, by0) (bx1, by1) ax1)) : resample (tail as) bs | otherwise = (bx1, (y_at (ax0, ay0) (ax1, ay1) bx1, by1)) : resample as (tail bs) y_at (x0, y0) (x1, y1) x = (y1 - y0) / (x1 - x0) * (x - x0) + y0 So there are a number of things here that don't seem to work so well with a vector interface. The first is that this returns [(Val, (Val, Val))]. I could either write an instance of Storable for (Double, (Double, Double)), or I could pass a function (Val, Val) -> Val. It looks like uvector handles zips more nicely though. The second is that this, like most such functions, wants a pair of samples to do linear interpolation. With lists I can do pattern matching as above or 'zip xs (drop 1 xs)', and with vectors the slightly less natural mapAccumL. Ok, then the third problem is that this progresses at a variable rate down two vectors, and I don't know any way to express that. Also, as a fourth problem, many functions taking samples will wind up generating more samples, which requires a concatMap kind of thing, which uvector doesn't seem to have, but in storablevector and lazy bytestring involves converting the whole thing to a list and back. What I'd ideally like is a lazy stream of unpacked chunks ala ByteString.Lazy. It seems like it might be possible to do something with ST and mutable arrays, and somehow come up with an abstraction that hides the packing and chunks and freezing but is still flexible enough to write something like 'resample', but I haven't thought about what that would look like. And it would be much nicer to try to fit something into the array fusion kind of interface. Is it possible? Is concatMap and "complicated zip" incompatible with the listlike array interface and fusion? Is there a better way to express this that avoids the problems? Initially this seemed like the perfect application for storablevector or uvector, but maybe it's not actually.

2 1

message-passing IPC for Haskell?
by Galchin, Vasili 01 Aug '08

01 Aug '08

Hello, I have seen postings about work on message-passing IPCs for Haskell. I like STM but want to keep an open mind ... I can't find those postings. Can something remind of this work and where/how I can read about? Very kind regards, Vasili

2 1

Haskell Weekly News: Issue 79 - July 31, 2008
by Brent Yorgey 01 Aug '08

01 Aug '08

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20080731 Issue 79 - July 31, 2008 --------------------------------------------------------------------------- Welcome to issue 79 of HWN, a newsletter covering developments in the [1]Haskell community. Apologies for the slightly late issue this week, attributable to a combination of having to transfer all my files onto a different computer (my former employer had the audacity to request the return of their laptop, now that I no longer work for them) and packing up to move to Philadelphia on Saturday. At any rate, some exciting news this week, including #haskell passing the 500 mark and a new release of Yi -- enjoy! Community News Correction from last week's issue: congratulations were bestowed upon a certain "Dr. Johansson" who does not, in fact, exist, having been replaced almost a year ago by the happily married but otherwise identical Dr. Mikael Vejdemo-Johansson. Announcements A fancier Get monad or two (a la binary and binary-strict). Chris Kuklewicz [2]announced two new Get-like monads for binary data, with a number of additional features. #haskell irc channel reaches 500 users. Don Stewart [3]announced that 6 1/2 years after its inception, under the guiding hand of Shae Erisson (aka shapr), the [4]#haskell IRC channel on freenode has finally reached 500 users! This puts the channel at around the 12th largest (and mostest friendliest) community of the 7000 freenode channels. RandomDotOrg-0.1. Austin Seipp [5]announced the release of the [6]RandomDotOrg package, an interface to the [7]random.org random number generator. Mueval 0.3.1, 0.4, 0.4.5, 0.4.6, 0.5. Gwern Branwen [8]announced a number of releases of [9]Mueval, a package allowing dynamic runtime evaluation of Haskell expressions. As far as anyone knows, all possible security holes have been plugged, and it's missing only a few features before it can replace hs-plugins as lambdabot's evaluation mechanism. Need functional programmers for debugging study. Chris Bogart [10]asked for functional programmers currently developing or maintaining a medium to large-sized program, willing to let him look over their shoulder while they do debugging or coding on the project. Yi 0.4.1. Jean-Philippe Bernardy [11]announced the 0.4.1 release of the Yi editor, a text editor written and extensible in Haskell. The long-term goal of the Yi project is to provide the editor of choice for Haskell programmers. Hipmunk 0.1 and HipmunkPlayground 0.1. Felipe Lessa [12]announced the availability of [13]Hipmunk, containing bindings for the [14]Chipmunk 2D physics engine, and [15]Hipmunk Playground, where you may see some of Hipmunk's features in action. The bindings are low-level but try to hide most of the nasty details of the C code. faster BLAS bindings. Patrick Perry [16]announced that he has [17]largely closed the C performance gap with his recent [18]Haskell BLAS bindings. Expect a new release shortly. FPers in Northwest Arkansas?. Nathan Bloomfield [19]is wondering if there are any Haskellers in the NW Arkansas region to start a functional programming interest group in the area. Italian Haskellers Summer Meeting. Pasqualino 'Titto' Assini [20]announced something about a summer meeting for Italian Haskellers. If you would like to know precisely what it was that was announced, I suggest you learn Italian. InterleavableIO. Marco Tulio Gontijo e Silva [21]announced a package, [22]interleavableIO, based on Jules Bean (quicksilver)'s [23]monadic tunneling code. Google Summer of Code Progress updates from participants in the 2008 [24]Google Summer of Code. Hoogle 4. Neil Mitchell (ndm) is working on [25]Hoogle 4. [26]This week, he rewrote type search: after three days of coding, it required only a few minor debugging tweaks to get it to work. Haskell FTW! Expect a public beta of the command line interface next week. Generic tries. Jamie Brandon is working on a library for efficient maps using generalized tries. [27]This week, he has finally got everything up and running bug free on the new API, except the internals are still using association lists instead of AVL trees. He also exhibits a promising benchmark. DPH physics engine. Roman Cheplyaka (Feuerbach) is working on a [28]physics engine using [29]Data Parallel Haskell. GHC plugins. Max Bolingbroke is working on dynamically loaded plugins for GHC. Cabal dependency framework. Andrea Vezzosi (Saizan) is working on a [30]make-like dependency analysis framework for Cabal. Language.C. Benedikt Huber (visq) is [31]working on Language.C, a standalone parser/pretty printer library for C99. GHC API. Thomas Schilling (nominolo) is working on [32]improvements to the GHC API. Discussion Build system woes. Roman Leshchinskiy began a [33]discussion on Cabal and GHC's new build system, with some suggestions for improving the process. Syb Renovations? Issues with Data.Generics. Claus Reinke [34]brought up a number of issues with Data.Generics, with suggestions for improvement. A question about mfix. Wei Hu [35]asked a question about the definition and semantics of mfix, the monadic fix operation. Using fundeps to resolve polymorphic types to concrete types. Bryan Donlan [36]asked a question about the interaction between functional dependencies and type checking, with a rather subtle answer. Best book/tutorial on category theory and its applications. fero [37]asked for recommendations on a book about category theory. Loss of humour. Andrew Coppin [38]laments the loss of some of Haskell's humorous heritage. Blog noise [39]Haskell news from the [40]blogosphere. * Ketil Malde: [41]Updates and other trivialities. * Ulisses Costa: [42]Lex/yacc. A short lex/yacc tutorial. * Luke Plant: [43]Haskell Regex replace. Luke wonders if anyone knows how to do regex replace in Haskell. * Eric Kow (kowey): [44]simple random numbers in Haskell. Eric writes a simple tutorial for the System.Random module. * Jamie Brandon: [45]Week 7 progress (respect my formatting damnit). An update on Jamie's Google Summer of Code project. * Tupil: [46]Formlets in Haskell. * John Goerzen (CosmicRay): [47]Seen in the Haskell wiki. * Ulisses Costa: [48]Type inference. * Dennis Bueno: [49]ICFP Contest 2008 -- The One Liners. Dennis describes his experiences participating in this year's ICFP Programming Contest. * Magnus Therning: [50]More prefixes. * Don Stewart (dons): [51]Haskell: Batteries Included. * >>> Harry Pierson: [52]Monadic Philosophy Part 2 - The LINQ Monad. * >>> Harry Pierson: [53]Monadic Philosophy. Harry begins a series explaining his journey through understanding monads. * Ulisses Costa: [54]Pointfree Calculator. * Eric Kow (kowey): [55]pandoc gets mediawiki support. * Dan Piponi (sigfpe): [56]The Fibonacci Numbers, Coalgebraicaly. * Twan van Laarhoven: [57]Solving nonograms. * >>> Ayumilove: [58]Haskell Programming Tutorial Part 2A. * >>> Ayumilove: [59]Haskell Programming Tutorial Part 2B. * >>> Ayumilove: [60]Haskell Programming Tutorial Part 3. * >>> Darren Moffat: [61]T5120 donated to Haskell Community. Sun's donation inspires Darren to get back into Haskell and maybe contribute some code to GHC again, like he did back when he was a student at Glasgow. * Mikael Vejdemo-Johansson (DrSyzygy): [62]Blackbox computing of A-infinity algebras. The last results from Mikael's thesis have made it into article form, and are [63]available on the arXiv. * John Goerzen (CosmicRay): [64]OSCon Update. * Real-World Haskell: [65]Beta availability hiccups. * John Goerzen (CosmicRay): [66]First 2 Days of OSCon. John reports live from OSCon. * Neil Mitchell: [67]GSoC Hoogle: Week 9. An update on Neil's Google Summer of Code project. * Patrick Perry: [68]Addressing Haskell BLAS Performance Issues. Patrick's Haskell BLAS bindings are now significantly sped up, and he explains what made the difference. * Arnar Birgisson (Arnar): [69]Parsing annotated postfix operators with Haskell. Arnar exhibits a neat pattern for constructing certain types of parsers, which makes essential use of first-class functions. Quotes of the Week * mauke: a hint to beginners: typing 'fix error' in ghci does not have the intended effect. * mauke: Hungarian Notation constructs a type system in the mind of the programmer. * rwbarton: I was hoping for a pile of Functors. * Baughn: [on lambdabot] Yes, PMS is a real issue. Poor memory size, that is. * Cale: There should be a website called "Static Equilibrium or Not" where you rate pictures according to whether you think the depicted objects are in static equilibrium. * sahko: xmonad is an ancient african word for "you dont need to use a mouse fool". * doidydoidy: Category theory is exactly like a comic book alternative universe, except they use the prefix "co-" instead of "bizarro". About the Haskell Weekly News New editions are posted to [70]the Haskell mailing list as well as to [71]the Haskell Sequence and [72]Planet Haskell. [73]RSS is also available, and headlines appear on [74]haskell.org. Headlines are available as [75]PDF. To help create new editions of this newsletter, please see the information on [76]how to contribute. Send stories to byorgey at seas dot upenn dot edu. The darcs repository is available at darcs get [77]http://code.haskell.org/~byorgey/code/hwn/ . References 1. http://haskell.org/ 2. http://article.gmane.org/gmane.comp.lang.haskell.libraries/9691 3. http://article.gmane.org/gmane.comp.lang.haskell.cafe/42671 4. http://haskell.org/haskellwiki/IRC_channel 5. http://article.gmane.org/gmane.comp.lang.haskell.cafe/42643 6. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/RandomDotOrg 7. http://random.org/ 8. http://article.gmane.org/gmane.comp.lang.haskell.cafe/42629 9. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/mueval 10. http://article.gmane.org/gmane.comp.lang.haskell.general/16360 11. http://article.gmane.org/gmane.comp.lang.haskell.cafe/42582 12. http://article.gmane.org/gmane.comp.lang.haskell.general/16355 13. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Hipmunk 14. http://wiki.slembcke.net/main/published/Chipmunk 15. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HipmunkPlayground 16. http://article.gmane.org/gmane.comp.lang.haskell.cafe/42534 17. http://quantile95.com/2008/07/24/addressing-haskell-blas-performance-issues/ 18. http://www-stat.stanford.edu/~patperry/code/blas/ 19. http://article.gmane.org/gmane.comp.lang.haskell.cafe/42548 20. http://article.gmane.org/gmane.comp.lang.haskell.cafe/42545 21. http://article.gmane.org/gmane.comp.lang.haskell.cafe/42502 22. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/interleavableIO 23. http://www.haskell.org/pipermail/haskell-cafe/2007-July/028501.html 24. http://hackage.haskell.org/trac/summer-of-code/wiki/SoC2008 25. http://code.haskell.org/hoogle/ 26. http://neilmitchell.blogspot.com/2008/07/gsoc-hoogle-week-9.html 27. http://jamiiecb.blogspot.com/2008/07/week-7-progress-respect-my-formatting.… 28. http://haskell.org/haskellwiki/Hpysics 29. http://www.haskell.org/haskellwiki/GHC/Data_Parallel_Haskell 30. http://code.haskell.org/~Saizan/cabal 31. http://www.sivity.net/projects/language.c/wiki/ 32. http://hackage.haskell.org/trac/ghc/wiki/GhcApiStatus 33. http://thread.gmane.org/gmane.comp.lang.haskell.glasgow.user/14800 34. http://thread.gmane.org/gmane.comp.lang.haskell.libraries/9672 35. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/42677 36. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/42639 37. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/42616 38. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/42510 39. http://planet.haskell.org/ 40. http://haskell.org/haskellwiki/Blog_articles 41. http://blog.malde.org/index.php/2008/07/31/updates-and-other-trivialities/ 42. http://caos.di.uminho.pt/~ulisses/blog/2008/07/31/lexyacc/ 43. http://lukeplant.me.uk/blog.php?id=1107301690 44. http://koweycode.blogspot.com/2008/07/simple-random-numbers-in-haskell.html 45. http://jamiiecb.blogspot.com/2008/07/week-7-progress-respect-my-formatting.… 46. http://blog.tupil.com/formlets-in-haskell/ 47. http://changelog.complete.org/posts/736-Seen-in-the-Haskell-wiki.html 48. http://caos.di.uminho.pt/~ulisses/blog/2008/07/30/type-inference/ 49. http://obfuscatedcode.wordpress.com/2008/07/30/icfp-contest-2008-the-one-li… 50. http://therning.org/magnus/archives/355 51. http://www.cse.unsw.edu.au/~dons/blog/2008/07/29#batteries 52. http://devhawk.net/2008/07/30/Monadic+Philosophy+Part+2+The+LINQ+Monad.aspx 53. http://devhawk.net/2008/07/30/Monadic+Philosophy.aspx 54. http://caos.di.uminho.pt/~ulisses/blog/2008/07/29/pointfree-calculator/ 55. http://koweycode.blogspot.com/2008/07/pandoc-gets-mediawiki-support.html 56. http://sigfpe.blogspot.com/2008/07/fibonacci-numbers-coalgebraicaly.html 57. http://twan.home.fmf.nl/blog/haskell/Nonograms.details 58. http://www.5min.com/Video/-Ayumilove-Haskell-Programming-Tutorial-Part-2-A-… 59. http://www.5min.com/Video/Ayumilove-Haskell-Programming-Tutorial-Part-2-B-3… 60. http://www.5min.com/Video/Ayumilove-Haskell-Programming-Tutorial-Part-3-318… 61. http://blogs.sun.com/darren/entry/t5120_donated_to_haskell_community 62. http://blog.mikael.johanssons.org/archive/2008/07/blackbox-computing-of-a-i… 63. http://arxiv.org/abs/0807.3869 64. http://changelog.complete.org/posts/733-OSCon-Update.html 65. http://www.realworldhaskell.org/blog/2008/07/16/beta-availability-hiccups/ 66. http://changelog.complete.org/posts/732-First-2-Days-of-OSCon.html 67. http://neilmitchell.blogspot.com/2008/07/gsoc-hoogle-week-9.html 68. http://quantile95.com/2008/07/24/addressing-haskell-blas-performance-issues/ 69. http://www.hvergi.net/2008/07/parsing-annotated-postfix-operators-with-hask… 70. http://www.haskell.org/mailman/listinfo/haskell 71. http://sequence.complete.org/ 72. http://planet.haskell.org/ 73. http://sequence.complete.org/node/feed 74. http://haskell.org/ 75. http://code.haskell.org/~byorgey/code/hwn/archives/20080731.pdf 76. http://haskell.org/haskellwiki/HWN 77. http://code.haskell.org/~byorgey/code/hwn/

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www.haskell.org is currently very slow in responding to HTTP requests
by Benjamin L.Russell 01 Aug '08

01 Aug '08

Currently, www.haskell.org is very slow in responding to HTTP requests, taking over a minute just to display the main home page. This problem is causing difficulties in displaying options for mailing lists or in displaying HaskellWiki pages. Perhaps the server needs to be rebooted? Could somebody responsible for maintaining the server please look into this issue? It seems to have been persisting for at least about half an hour. Thank you.... -- Benjamin L. Russell

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Best book/tutorial on category theory and its applications
by fero 31 Jul '08

31 Jul '08

Hi, I would like to buy some booke on category theory and its applications. Can you recommend me the best? Here is what I like: 1. Easy to understatnd, concise book. I like e.g. "Gentle introduction to Haskell" it was quite good with a little of text. There are bigger tutorials in number of pages but there is much less in them. I downloaded "Categories for Software Engineering". I read 2 first chapters, but there is a lot of text and sometimes I need to look on internet to seach for exact definitions/equations which I can understand better. That's why I don't like books "for Dummies" - lot of text, little of content, very shallow and lot of slang. I like "The Haskell: School of expression" and I am searching for another book to read after I finish this. The style of SOE is suitable for me. It is very clear with good theory and examples. But now I want book mainly about theory and the examples as second. 2. With applications and its examples. I would like to see some examples. I doesn't matter if it will be only in pseudo-language in Haskell or another language. What do you think about "Categories and Computer Science (Cambridge Computer Science Texts)" at http://www.amazon.com/Categories-Computer-Science-Cambridge-Texts/dp/052142… ? Thanks Fero -- View this message in context: http://www.nabble.com/Best-book-tutorial-on-category-theory-and-its-applica… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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haddock build failure
by Jason Dusek 31 Jul '08

31 Jul '08

I am unable to build Haddock 2.1, with the odd error: src/Haddock/GHC/Typecheck.hs:82:4: Constructor `HsModule' should have 7 arguments, but has been given 8 What is the root of it, you think? -- _jsn Configuring haddock-2.1.0... Dependency base-any: using base-3.0.2.0 Dependency haskell98-any: using haskell98-1.0.1.0 Dependency ghc>=6.8.2&&<6.9: using ghc-6.8.3 Dependency filepath-any: using filepath-1.1.0.0 Dependency directory-any: using directory-1.0.0.1 Dependency pretty-any: using pretty-1.0.0.0 Dependency containers-any: using containers-0.1.0.2 Dependency array-any: using array-0.1.0.0 Using compiler: ghc-6.8.3 Using install prefix: /usr/local Binaries installed in: /usr/local/bin Libraries installed in: /usr/local/lib/haddock-2.1.0/ghc-6.8.3 Private binaries installed in: /usr/local/libexec Data files installed in: /usr/local/share/haddock-2.1.0 Documentation installed in: /usr/local/share/doc/haddock-2.1.0 No alex found Using ar found on system at: /usr/bin/ar No c2hs found No cpphs found No ffihugs found Using ghc version 6.8.3 found on system at: /usr/bin/ghc Using ghc-pkg version 6.8.3 found on system at: /usr/bin/ghc-pkg No greencard found No haddock found No happy found No hmake found Using hsc2hs version 0.66-ghc found on system at: /usr/bin/hsc2hs No hscolour found No hugs found No jhc found Using ld found on system at: /usr/bin/ld No nhc98 found No pfesetup found Using pkg-config version 0.23 found on system at: /opt/local/bin/pkg-config Using ranlib found on system at: /usr/bin/ranlib Using tar found on system at: /usr/bin/tar Creating dist/build (and its parents) Creating dist/build/autogen (and its parents) Preprocessing library haddock-2.1.0... Preprocessing executables for haddock-2.1.0... Building haddock-2.1.0... Building library... Creating dist/build (and its parents) Creating dist/build (and its parents) /usr/bin/ghc -package-name haddock-2.1.0 --make -hide-all-packages -i -idist/build/autogen -idist/build -isrc -Idist/build -odir dist/build -hidir dist/build -stubdir dist/build -package base-3.0.2.0 -package haskell98-1.0.1.0 -package ghc-6.8.3 -package filepath-1.1.0.0 -package directory-1.0.0.1 -package pretty-1.0.0.0 -package containers-0.1.0.2 -package array-0.1.0.0 -O -XCPP -XPatternGuards -XDeriveDataTypeable -XPatternSignatures -XMagicHash Distribution.Haddock Haddock.Types Haddock.InterfaceFile Haddock.Exception Linking... /usr/bin/ar q dist/build/libHShaddock-2.1.0.a dist/build/Distribution/Haddock.o dist/build/Haddock/Types.o dist/build/Haddock/InterfaceFile.o dist/build/Haddock/Exception.o ar: creating archive dist/build/libHShaddock-2.1.0.a /usr/bin/ld -x -r -o dist/build/HShaddock-2.1.0.o.tmp dist/build/Distribution/Haddock.o dist/build/Haddock/Types.o dist/build/Haddock/InterfaceFile.o dist/build/Haddock/Exception.o Building executable: haddock... Creating dist/build/haddock (and its parents) Creating dist/build/haddock/haddock-tmp (and its parents) Creating dist/build/haddock/haddock-tmp (and its parents) /usr/bin/ghc -o dist/build/haddock/haddock --make -hide-all-packages -i -idist/build/autogen -idist/build/haddock/haddock-tmp -isrc -Idist/build/haddock/haddock-tmp -odir dist/build/haddock/haddock-tmp -hidir dist/build/haddock/haddock-tmp -stubdir dist/build/haddock/haddock-tmp -package base-3.0.2.0 -package haskell98-1.0.1.0 -package ghc-6.8.3 -package filepath-1.1.0.0 -package directory-1.0.0.1 -package pretty-1.0.0.0 -package containers-0.1.0.2 -package array-0.1.0.0 -O -funbox-strict-fields -O2 -XCPP -XPatternGuards -XDeriveDataTypeable -XPatternSignatures -XMagicHash src/Main.hs [ 8 of 24] Compiling Paths_haddock ( dist/build/autogen/Paths_haddock.hs, dist/build/haddock/haddock-tmp/Paths_haddock.o ) [15 of 24] Compiling Haddock.GHC.Typecheck ( src/Haddock/GHC/Typecheck.hs, dist/build/haddock/haddock-tmp/Haddock/GHC/Typecheck.o ) src/Haddock/GHC/Typecheck.hs:82:4: Constructor `HsModule' should have 7 arguments, but has been given 8 In the pattern: HsModule _ _ _ _ _ mbOpts _ _ In a pattern binding: HsModule _ _ _ _ _ mbOpts _ _ = unLoc parsed In the definition of `mkGhcModule': mkGhcModule (mod, file, checkedMod) dynflags = GhcModule {ghcModule = mod, ghcFilename = file, ghcMbDocOpts = mbOpts, ghcHaddockModInfo = info, ghcMbDoc = mbDoc, ghcGroup = group, ghcMbExports = mbExports, ghcExportedNames = modInfoExports modInfo, ghcNamesInScope = fromJust $ modInfoTopLevelScope modInfo, ghcInstances = modInfoInstances modInfo} where HsModule _ _ _ _ _ mbOpts _ _ = unLoc parsed (group, _, mbExports, mbDoc, info) = renamed (parsed, renamed, _, modInfo) = checkedMod

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Libevent FFI problems
by Levi Greenspan 31 Jul '08

31 Jul '08

Dear list members, This is my first attempt to create a FFI to libevent (http://monkey.org/~provos/libevent/) which is an event notification library. A simple usage example is for instance given here: http://unx.ca/log/libevent_echosrv1c/ . In C one basically creates struct event instances which are initialized with a callback function and the kind of event (e.g. read) one is intested in. Optionally a data argument can be given which will be passed to the callback function when invoked eventually. An event dispatcher loop will invoke the callback when the event occurs. I have attached my first attempt at a FFI to libevent. However it doesn't work correctly. In the client code I want to pass 99 as data to the callback function, but what is printed out is 0. I guess there is an issue with pointer derefencing, but I don't know. Also I am not sure how to handle the FunPtr deallocation. Since the FunPtr is stored in the foreign event structure I don't know when I can free it. I would be grateful for any advices, hints or comments. And I really look forward to the FFI section in the "Real World Haskell" book. Thank you very much. - Levi

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ANN: Yi 0.4.1
by Jean-Philippe Bernardy 31 Jul '08

31 Jul '08

I'm very pleased to announce the 0.4.1 release of the Yi editor. == Yi == Yi is a text editor written and extensible in Haskell. The long-term goal of the Yi project is to provide the editor of choice for Haskell programmers. In the meantime, we have fun by hacking an editor in a decent language :) Yi is not a finished product. This is an alpha-quality release. However, Yi has become a lot more accessible than previously, so if you feel like testing it, now might be a good time to take a look. == Installation == Using cabal install: cabal install yi-0.4.1 If you want gtk support, first install gtk2hs 0.9.13. If you want vty support, pass the -fvty option to cabal install. == Features == * A purely functional editor core; * Key-bindings written as parsers of the input; * Emacs, Vim and (partial) Cua emulations provided by default; * Vty, Gtk2Hs, and (experimental) Cocoa front-ends; * Static configuration (XMonad style) for fast load; * Simple Haskell support: * Syntax highlighting * Auto-indentation * Call cabal-build within the editor == Links == * download: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/yi * FAQ: http://haskell.org/haskellwiki/Yi/FAQ * homepage: http://haskell.org/haskellwiki/Yi * check and report issues: http://code.google.com/p/yi-editor/issues/list * darcs repository: http://code.haskell.org/yi * get involved: mailto:yi-devel@googlegroups.com * release notes: http://code.google.com/p/yi-editor/wiki/ReleaseNotes0o4 == Acks == This release is brought to you by: Allan Clark Andrew Birkett Corey O'Connor Duncan Coutts Evan Martin Fraser Wilson Gustav Munkby Gwern Branwen Jean-Philippe Bernardy Krasimr Angelov Nicolas Pouillard Sean Leather Thomas Schilling and all the contributors to the previous versions.

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[Off-topic] Loss of humour
by Andrew Coppin 30 Jul '08

30 Jul '08

A while back I found a page somewhere containing some rather amusing IRC quotes. Unfortunately it seems to have vanished. I can't remember where on earth I found it, but I've scoured the Internet trying to track it down. (In particular, it contained a quote of somebody impersonating a typical Haskell newbie - lots of enthusiasm and no attention span! Well it amused *me* anyway...) Anybody have any ideas where this has gone? Also... the current Humour page on the Haskell wiki contains a link to Lambdabot's quotes database, but on my system, clicking this link just displays a few hundred pages of gibberish. Is this normal? As I final note... http://www.haskell.org/haskellwiki/Humor/Goldilocks Damn, I wish *I* thought of that! ;-)

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[Haskell Beginner] Compiling wxhaskell fails for me
by Daniel Kahlenberg 30 Jul '08

30 Jul '08

Hi, I try to build the current wxhaskell stuff from the darcs repository on the sh provided by msys with mingw32 (`uname -a' : MINGW32_NT-5.1 ... 1.0.11(0.46/3/2) 2007-01-12 12:05 i686 Msys), but it fails with the message `wx/graphics.h' isn't found, when it comes to build the wxc part. On the wxhaskell site they advice to use the 2.6.x version of the wxWidgets distribution, which I followed so far. The tool call which sets the wxversion variable (`wx-config --version') is executed and returns 2.6.4. The searched hosted graphics.h as I determined seems available as part of the 2.8.x version of wxwidgets at first. Now my question: Why does the build process search for it, especially how do I get it to succeed. Would I have to use the 2.8.x version against the recommendation? Has anyone of you successfully built the recommended version of the bindings, if yes - how? Could you share? Did I forget to build something on the wxwidgets side? Thank you so far Daniel.

3 3

A question about mfix
by Wei Hu 30 Jul '08

30 Jul '08

What's wrong about giving mfix the following general definition? > mfix :: (a -> m a) -> m a > mfix f = (mfix f) >>= f I know it diverges if (>>=) is strict on the first argument. My question is, is this definition correct for all lazy monads? The documentation (http://haskell.org/ghc/docs/latest/html/libraries/base/ Control-Monad-Fix.html#v%3Amfix) says "mfix f executes the action f only once, with the eventual output fed back as the input.". So my definition looks like a valid one, doesn't it? I haven't fully wrapped my head around this monadic fixed-point thing yet. So, if you can give an example showing how my definition differs from a standard monad, that'll be great.

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Fw: patch applied (ghc): Remove the OpenGL family of libraries fromextralibs
by Claus Reinke 30 Jul '08

30 Jul '08

FYI: Haskell's OpenGL binding has just been dropped from GHC's extralibs, which means that it will no longer be kept in sync with GHC development, at least not by GHC HQ. GHC HQ has its hands full and -generally speaking - extralibs are to be replaced by H(L)P, the Haskell (Library) Platform: http://haskell.org/haskellwiki/Haskell_Platform so this part is understandable. But OpenGL has been dropped before H(L)P is ready to take over from extralibs, and at the recent GHC Irc meeting on the topic http://hackage.haskell.org/trac/ghc/attachment/wiki/IRC_Meetings/ghc-2008-0… the mood seemed to favour not including OpenGL&co in the initial versions of H(L)P. Sven put a lot of good work into these libraries, but he is often not around for a long time, and it would be a shame if these gems were orphaned and went out of sync in the meantime. While I haven't used OpenGL in a while, I've always hoped to come back to that, not to mention Sven's spatial audio binding additions. And if I'm not mistaken, there are other community members who are using these libs right now for research, possibly even prototyping in connection with a startup? So, if one of you wanted to step forward and offer to keep these Haskell bindings for OpenGL&co maintained, perhaps steward them into the H(L)P, now would probably be a good time. Just thought I'd forward this, for those not following cvs-ghc, Claus ----- Original Message ----- From: "Ian Lynagh" <igloo(a)earth.li> To: <cvs-ghc(a)haskell.org> Sent: Friday, July 25, 2008 12:11 AM Subject: patch applied (ghc): Remove the OpenGL family of libraries fromextralibs > Thu Jul 24 03:27:36 PDT 2008 Ian Lynagh <igloo(a)earth.li> > * Remove the OpenGL family of libraries from extralibs > > M ./libraries/Makefile -4 > M ./libraries/extra-packages -4 > > View patch online: > http://darcs.haskell.org/ghc/_darcs/patches/20080724102736-3fd76-f5601cb7a2… > > _______________________________________________ > Cvs-ghc mailing list > Cvs-ghc(a)haskell.org > http://www.haskell.org/mailman/listinfo/cvs-ghc

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Problem compiling a CGI script that needs to write to file during its execution
by Jefferson Heard 30 Jul '08

30 Jul '08

Please ignore the obvious security holes, as this is not a script meant for public consumption, but some internal testing and prototyping. I would like to write the result of my computation out to a file inside of cgiMain, but the type of the monad inside cgiMain is this odd CGIT IO CGIResult. I tried using liftM on writeFile, but it then complained that "newanns" was a string instead of a list of strings, which I don't understand at all. Here's the code: DeleteAnnotation.hs: -------------------------------------------------------------------------------- import Network.CGI import Annotations import Graphics.Rendering.OpenGL.GL (GLfloat) import Control.Monad (liftM) import Data.List (filter) getInput' v = do x <- getInput v case x of Nothing -> fail "essential variable not found" Just y -> return y cgiMain :: String -> CGI CGIResult cgiMain anns_dot_txt = do ordnl <- (liftM read) $ getInput' "ordinal" let anns = (filter (notequal ordnl) . read $ anns_dot_txt) :: [Annotation] newanns = show anns output $ newanns writeFile "Annotations.txt" $ newanns notequal :: String -> Annotation -> Bool notequal ordnl ann = ordnl == ordinal ann main :: IO () main = do f <- readFile "Annotations.txt" runCGI (handleErrors (cgiMain f)) -------------------------------------------------------------------------------- $ ghc --make DeleteAnnotation DeleteAnnotation.hs:19:2: Couldn't match expected type `CGIT IO CGIResult' against inferred type `IO ()' In the expression: writeFile "Annotations.txt" $ newanns In the expression: do ordnl <- (liftM read) $ getInput' "ordinal" let anns = ... newanns = show anns output $ newanns writeFile "Annotations.txt" $ newanns In the definition of `cgiMain': cgiMain anns_dot_txt = do ordnl <- (liftM read) $ getInput' "ordinal" let anns = ... .... output $ newanns .... If I change writeFile "Annotations.txt" to (liftM (writeFile "Annotations.txt")): $ ghc --make DeleteAnnotation DeleteAnnotation.hs:19:42: Couldn't match expected type `String' against inferred type `Char' Expected type: [String] Inferred type: String In the second argument of `($)', namely `newanns' In the expression: (liftM (writeFile "Annotations.txt")) $ newanns

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#haskell irc channel reaches 500 users
by Don Stewart 30 Jul '08

30 Jul '08

A small announcement :) 6 1/2 years after its inception, under the guiding hand of Shae Erisson (aka shapr), the #haskell IRC channel[1] on freenode has finally reached 500 users! To chart the growth, we can note that the channel was founded in late 2001, and had slow growth till 2006, reaching 200 users in January of that year. Since then growth in the user base has been far more rapid, reaching 300 users in Dec 2006, 400 users in August 2007, and 500 users by July 2008. This puts the channel at around the 12th largest community of the 7000 freenode channels. For comparision, a sample of the state of the other language communities, with comments comapred to their status a year ago: #php 720 #python 640 -- up from 5th place #perl 620 ##c++ 585 ##c 530 > #haskell 502 #rubyonrails 428 #ruby-lang 350 -- down from 420 max. ##javascript 308 #lisp 295 #erlang 178 #perl6 129 -- unchanged #scheme 148 -- unchanged #lua 120 #ocaml 70 -- unchanged You can see the growth of the channel over here: http://www.cse.unsw.edu.au/~dons/irc If you've not dropped by the channel yet, feel free to come and chat, and toss around some lambdas! :) Cheers, Don

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ANN: Hayoo! beta 0.2
by Timo B. Hübel 30 Jul '08

30 Jul '08

Hello, we are pleased to announce the second beta release of Hayoo!, a Haskell API search engine providing advanced features like suggestions, find-as-you-type, fuzzy queries and much more. Visit Hayoo! here: http://holumbus.fh-wedel.de/hayoo The major change is the inclusion of all packages available on Hackage, i.e. the documentation of the latest versions of all packages is included in the index. Unfortunately we had to drop the direct links to the source code, as the documentation on Hackage is currently generated without source code. But as soon as this changes, we will include these links again. Additionally, we added some tweaks to the interface which make the browser history/the back button work (at least in Firefox). Please bear in mind that this is still a beta release and we are continuously working on further improvements. Any suggestions and feedback is highly welcomed. Cheers, Timo & Sebastian

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