July 2008 - Haskell-Cafe

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

Point-free style in guards
by L29Ah 31 Jul '08

31 Jul '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 31 Jul '08

31 Jul '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 31 Jul '08

31 Jul '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

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

31 Jul '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 31 Jul '08

31 Jul '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

5 5

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 30 Jul '08

30 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 30 Jul '08

30 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 30 Jul '08

30 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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