October 2008 - Haskell-Cafe

2008-10-13 Hackage status with GHC 6.10 release candidate
by Don Stewart 18 Oct '08

18 Oct '08

Hey all. The GHC 6.10 RCs are out, and we're preparing the release of GHC proper. To help manage the transistion to GHC 6.10 it is now possible to actually build all the 3rd party Haskell packages, and publish their results wrt. the release candidate. For the first time ever, we're able to have all the 3rd party code tested and ready to go *prior* to the release of the new compiler and base libraries. Using GHC 6.10 RC from today, Cabal 1.6 and cabal-install 1.16, of 682 libraries and apps tried in total, 1 UnpackFailed 2 DownloadFailed 2 InstallFailed 16 ConfigureFailed 68 DependencyFailed 122 BuildFailed 469 InstallOk Since yesterday, * dependency failures have reduced by 5 * build failures have reduced by 10 * total successfully installed packages are **up by 14** These new packages now all build ok with the GHC 6.10 release candidate, Graphalyze-0.4 alsa-midi calc glome-hs harpy heap hmp3 ircbouncer mohws panda pandoc roguestar-engine type-level typeof unicode-prelude urlcheck Good work everyone! Some packages are still not ready though, if you maintain one of the following packages, and are able to fix it before GHC 6.10 is released, your users will be happy. The most common issues for these differences are, * Changes to Arrow class definition * Changes to types of Map and Set functions * Cabal changes * Changes to ghc-api * Changes to when 'forall' is parsed (add Rank2Types) * GHC.Prim was moved, * Changes to -fvia-C and headers * GADT changes, * pragma warnings tightened * Integer constructors have moved * New warnings and used -Werror The following packages are still producing different results than with ghc 6.8.2. Package maintainers are invited to look at them. I've marked the easy ones. ArrayRef-0.1.2 Easy: duplicate type signatures CLASE-2008.9.23.2 Hard: GADT changes EdisonCore-1.2.1.2 Easy: Monadic Map HPDF-1.4 Easy: Monadic Map HaLeX-1.1 Easy: Name clash with permutations Hashell-0.15 ? : GHC API Hipmunk-0.2 Easy: Monadic Map MemoTrie-0.0 Easy: 'forall' parsing NewBinary-0.1.1 Easy: Integer constructors moved PArrows-0.1 Easy: GHC.Prim moved (use GHC.Exts) TypeCompose-0.5 Easy: Arrow class changes YamlReference-0.9.2 Hard. Unknown Yampa-0.9.2.2 Arrow class changes arrows-0.4 Arrow class changes bytestring-show-0.2 Easy: Integer constructors moved cabal-setup-1.2.1 Hard: Cabal changes chp-1.1.0 Easy: Arrow class changes cmath-0.3 Hard: -fvia-C changes fixpoint-0.1 Easy: Uses -Werror unnecessarily hasim-0.1 Hard: GADT changes hask-home-2007.12.6 Easy: Cabal changes hetris-0.2 Easy: header macros/-fvia-C hexpat-0.2 Easy: 'forall' parsing in RULES hinstaller-2008.2.16 Easy: Cabal changes hint-0.2.4.1 Hard? GHC API hslackbuilder-0.0.1 Easy: Cabal changes hxt-8.1.0 Easy: Arrow class change iException-0.0.1 ? Exception changes libGenI-0.16.1 Easy: Monadic Map changes mage-1.1.0 Hard: -fvia-C changes numeric-prelude-0.0.4 Easy: Lanuage pragma plugins-1.3 Easy: Cabal changes quantum-arrow-0.0.4 Easy: Arrow class changes regex-tdfa-0.94 Easy: Map changes streamproc-1.1 Easy: Arrow class changes stringtable-atom-0.0.4 Easy: Monadic Map typalyze-0.1.1 ? GHC API xmonad-utils-0.1 ? GHC API yhccore-0.9 ? Pragma parsing Build reports for everything, produced today, are here, http://galois.com/~dons/tmp/build-logs-2008-10-13/ How to address these, as library maintainers, is addressed here, http://haskell.org/haskellwiki/Upgrading_packages If you'd like to try your own build of all of hackage, grab a package list (such as this one), http://www.galois.com/~dons/tmp/pkgs-6.10 Install a GHC 6.10 release candidate, upgrade to Cabal 1.6 (on hackage), and cabal-install 0.6 (on hackage), and then simply, cabal install -v -O0 $(cat pkgs-6.10) --build-reports This will construct a clever plan to install all the packages in the right order, and write logs to ~/.cabal/logs and a full structured build report into ~/.cabal/packages/hackage.*/build-report.log I'll start mailing maintainers personally tomorrow. -- Don

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Re: [Haskell-cafe] ANNOUNCE: Glob 0.1, globbing library
by Krzysztof Skrzętnicki 18 Oct '08

18 Oct '08

On Sat, Oct 18, 2008 at 19:28, Matti Niemenmaa <matti.niemenmaa+news(a)iki.fi> wrote: > Gah, I fail at posting to mailing lists. For posterity, the message I sent to > Krzysztof: > > Krzysztof Skrzętnicki wrote: >> On Fri, Oct 17, 2008 at 22:02, Matti Niemenmaa <matti.niemenmaa+news(a)iki.fi> >> wrote: >>> Web page at: http://iki.fi/matti.niemenmaa/glob/index.html Hackage: >>> http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Glob >> >> I tried out your package, but it doesn't seem to work correctly on Windows. I >> checked the code and it has directory separator hard coded, which seem to be >> the source of problems. > > Interesting, given that I've only tested it on Windows. ;-) Can you give an > example which doesn't work? > Ouch... I feel like I deserve an entry on http://failblog.org/ Somehow I assumed that globDir has type [Pattern] -> FilePath -> IO [FilePath] where in reality it has type [Pattern] -> FilePath -> IO ([[FilePath]], [FilePath]) When I saw lots of files that didn't match my query I thought there is a bug... I'll certainly doublecheck any bug reports before submitting. Sorry for the noise. All best Christopher Skrzętnicki

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ANNOUNCE: Glob 0.1, globbing library
by Matti Niemenmaa 18 Oct '08

18 Oct '08

Greetings to all, I hereby announce the release of Glob 0.1, a small library for glob-matching purposes based on a subset of zsh's syntax. Web page at: http://iki.fi/matti.niemenmaa/glob/index.html Hackage: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Glob Simple example: match (compile "foo*baz") "foobarbaz" == True. It can also group the contents of a directory given a list of patterns to match: globDir [compile "foo*baz"] "<a directory containing foobarbaz and joe>" gives (["dir/foobarbaz"],["dir/joe"]). Comments, complaints, feature requests, bug reports are all welcome. It should work on both GHC 6.8 and 6.10, but I've only tested the latter.

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Haskell Weekly News: Issue 89 - October 18, 2008
by Brent Yorgey 18 Oct '08

18 Oct '08

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20081018 Issue 89 - October 18, 2008 --------------------------------------------------------------------------- Welcome to issue 89 of HWN, a newsletter covering developments in the [1]Haskell community. Announcements New Haskell tutorial. Miran Lipovaca (BONUS) has written a new and most excellent Haskell tutorial, [2]"Learn You a Haskell For Great Good!". Glob 0.1, globbing library. Matti Niemenmaa [3]announced the release of [4]Glob 0.1, a [5]small library for glob-matching purposes based on a subset of zsh's syntax. hledger 0.1, command-line accounting tool. Simon Michael [6]announced the [7]first release of [8]hledger, a command-line accounting tool similar to John Wiegley's c++ ledger. hledger generates simple ledger-compatible transaction and account balance reports from a plain text ledger file. [ANN] Haskell Cheatsheet v1.0. Justin Bailey [9]announced a [10]"cheat sheet" for Haskell, a PDF that tries to summarize Haskell 98's syntax, keywords and other language elements. Salsa: A .NET Bridge for Haskell. Andrew Appleyard [11]announced the [12]first release of [13]Salsa, an experimental Haskell library that allows Haskell programs to access .NET libraries. Salsa operates by loading the .NET runtime into your Haskell process and using the FFI (and run-time code generation) to marshall calls between the .NET and Haskell runtimes. It includes a code generator and a type-level library (which uses type families) to provide type-safe access to .NET libraries in Haskell with C#-style method overload resolution and implicit conversions. maccatcher-1.0.0. Jason Dusek [14]announced the [15]maccatcher package, which obtains a MAC address on *NIX and Windows. Call for Contributions - Haskell Communities and Activities Report, November 2008 edition. Janis Voigtlaender sent out [16]call for contributions to the 15th edition of the [17]Haskell Communities & Activities Report. The submission deadline is 31 October 2008. If you are working on any project that is in some way related to Haskell, please write a short entry and submit it. Even if the project is very small or unfinished or you think it is not important enough -- please reconsider and submit an entry anyway! Data.IVar 0.1. Luke Palmer [18]announced the release of the [19]Data.IVar module, which provides write-once variables that can be blocked on in parallel. Unlike other implementations, Data.IVar does not use thread racing, since empirical tests have shown that the GHC scheduler is not quite good enough to handle thread-racing efficiently. A wiki page for managing the 6.10 handover. Don Stewart [20]announced a [21]wiki page to help with the transition to GHC 6.10. It collects the 7 or so known issues that break code with GHC 6.10. Please feel free to clean up, and especially add techniques for handling each change. GHC 6.10.1 RC 1. Ian Lynagh [22]announced [23]GHC 6.10.0.20081007, the first release candidate for GHC 6.10.1. There is also a [24]status page for GHC 6.10.1. Graphalyze-0.4 and SourceGraph-0.2. Ivan Lazar Miljenovic [25]announced the release of version 0.4 of the [26]Graphalyze library and version 0.2 of the [27]SourceGraph programme. SourceGraph is a programme designed to help you analyse the static complexity of your Haskell code when represented as a graph. These releases fix the bugs reported by Gwern Branwen, Magnus Therning, and Christopher Hinson. ListZipper-1.1.0.0. Ryan Ingram [28]announced the release of a simple list zipper library to Hackage, [29]ListZipper-1.1.0.0. darcs 2.1.0. Eric Kow [30]announced the release of [31]darcs 2.1.0. This version provides over 20 bug fixes and 7 new features since darcs 2.0.2. Most notably, the darcs-2 repository format is now the default, there is better HTTP support, and a longstanding 'pending patch' regression has been fixed. Yi 0.5.0.1. Jean-Phillipe Bernardy [32]announced the [33]0.5 release of Yi, 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. Discussion OT: Haskell desktop wallpaper?. Magnus Therning [34]asked for Haskell-themed desktop wallpapers, and the community responded with quite a few nice images. Abusing quickcheck to check existential properties. Norman Ramsey [35]asked about using QuickCheck to check existential properties; suggestions involved SmallCheck and skolemization. Repair to floating point enumerations?. Malcolm Wallace began a [36]discussion on the merits of changing the (admittedly wonky) H98 [37]semantics for the Enum instances of Float and Double in Haskell Prime. A general question about the use of classes in defining interfaces. S. Doaitse Swierstra [38]asked about the feasibility of including top-level functions implemented using Applicative combinators as class methods with default implementations, to allow for the possibility of giving them more efficient implementations in specific instances. Proposal #2659: Add sortOn and friends to Data.List. Twan van Laarhoven [39]proposed adding sortOn (:: Ord b => (a -> b) -> [40]-> [a) and related functions to Data.List. Blog noise [41]Haskell news from the [42]blogosphere. * Andy Gill: [43]Pretty Printing Code with Markup. writes about a [44]new version of the HughesPJ pretty printing library which allows for pretty-printing with markup. * "FP Lunch": [45]Is purity inefficient?. Are idiomatic pure functional programs less efficient than idiomatic impure ones? * Eric Kow (kowey): [46]darcs weekly news #8. * Conal Elliott: [47]Composing memo tries. * Conal Elliott: [48]Elegant memoization with functional memo tries. * >>> Paolo Capriotti: [49]Monads for Markov chains. * Real-World Haskell: [50]Production status update: we're in QC1. * Joachim Breitner: [51]Infinite loops in Haskell. * Luke Palmer: [52]FRP Rant. * Luke Palmer: [53]data-memocombinators. * Bryan O'Sullivan: [54]Using Bloom filters for large scale gene sequence analysis in Haskell. Bryan and Ketil Malde's paper was accepted to PADL 09! * Arnar Birgisson: [55]Generating legal subsets of a dependency graph. * Creighton Hogg: [56]A silly example and a brief history. * >>> Robert Ottaway: [57]Sorting using Haskell. * Dan Piponi (sigfpe): [58]Untangling with Continued Fractions: part 5. * Holumbus: [59]Source Links Are Back!. * London Haskell Users Group: [60]Getting things going again. * >>> Justin Bailey: [61]The Haskell Cheatsheet. * >>> Nathan Sanders: [62]Type-directed programming. * >>> Micah Cowan: [63]Adventures in Haskell, Part 2: Kewlness. * Manuel M T Chakravarty: [64]GpuGen: Bringing the Power of GPUs to Haskell.. * >>> Binu Raghavan: [65]Haskell.... Binu is trying to learn Haskell. * Bjoern Edstroem: [66]Let's build an MP3-decoder!. Quotes of the Week * mckinna: you don't need to produce elements of an *arbitrary* whatever-it-is when you can produce elements of the *initial* whatever-it-is * tristes_tigres: thinks that programming languages can be divided into two broad classes: functional and dysfunctional * luqui: Down with the IO bourgeoisie! Long live the purely functional proletariat * ystael: it seems like every time i switch channels over to #haskell someone is talking about launching missiles. one might be inclined to draw freudian conclusions. About the Haskell Weekly News New editions are posted to [67]the Haskell mailing list as well as to [68]the Haskell Sequence and [69]Planet Haskell. [70]RSS is also available, and headlines appear on [71]haskell.org. To help create new editions of this newsletter, please see the information on [72]how to contribute. Send stories to byorgey at cis dot upenn dot edu. The darcs repository is available at darcs get [73]http://code.haskell.org/~byorgey/code/hwn/ . References 1. http://haskell.org/ 2. http://learnyouahaskell.com/ 3. http://article.gmane.org/gmane.comp.lang.haskell.cafe/46583 4. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Glob 5. http://iki.fi/matti.niemenmaa/glob/index.html 6. http://article.gmane.org/gmane.comp.lang.haskell.cafe/46461 7. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hledger 8. http://joyful.com/Ledger#hledger 9. http://article.gmane.org/gmane.comp.lang.haskell.cafe/46122 10. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/CheatSheet 11. http://article.gmane.org/gmane.comp.lang.haskell.cafe/46076 12. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Salsa 13. http://haskell.org/haskellwiki/Salsa 14. http://article.gmane.org/gmane.comp.lang.haskell.cafe/46072 15. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/maccatcher 16. http://article.gmane.org/gmane.comp.lang.haskell.cafe/45967 17. http://www.haskell.org/communities/ 18. http://article.gmane.org/gmane.comp.lang.haskell.cafe/45953 19. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/data-ivar 20. http://article.gmane.org/gmane.comp.lang.haskell.glasgow.user/15442 21. http://haskell.org/haskellwiki/Upgrading_packages#Typical_breakages_with_GH… 22. http://article.gmane.org/gmane.comp.lang.haskell.glasgow.user/15376 23. http://www.haskell.org/ghc/dist/stable/dist/6.10.1-rc-1/rc.html 24. http://hackage.haskell.org/trac/ghc/wiki/GHC-6.10.1 25. http://article.gmane.org/gmane.comp.lang.haskell.general/16473 26. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Graphalyze 27. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/SourceGraph 28. http://article.gmane.org/gmane.comp.lang.haskell.general/16468 29. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/ListZipper 30. http://article.gmane.org/gmane.comp.lang.haskell.general/16465 31. http://darcs.net/darcs-2.1.0.tar.gz 32. http://www.haskell.org//pipermail/haskell/2008-October/020648.html 33. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/yi 34. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/45961 35. http://thread.gmane.org/gmane.comp.lang.haskell.general/16477 36. http://thread.gmane.org/gmane.comp.lang.haskell.prime/2678 37. http://haskell.org/onlinereport/basic.html#sect6.3.4 38. http://thread.gmane.org/gmane.comp.lang.haskell.libraries/10206 39. http://thread.gmane.org/gmane.comp.lang.haskell.libraries/10184 40. file://localhost/home/brent/haskell/hwn/a] 41. http://planet.haskell.org/ 42. http://haskell.org/haskellwiki/Blog_articles 43. http://blog.unsafeperformio.com/?p=31 44. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/marked%2Dpretty 45. http://sneezy.cs.nott.ac.uk/fplunch/weblog/?p=113 46. http://koweycode.blogspot.com/2008/10/darcs-weekly-news-8.html 47. http://feeds.feedburner.com/~r/conal/~3/422189172/ 48. http://feeds.feedburner.com/~r/conal/~3/422171822/ 49. http://pcapriotti.wordpress.com/2008/10/16/monads-for-markov-chains/ 50. http://www.realworldhaskell.org/blog/2008/10/15/production-status-update-we… 51. https://www.joachim-breitner.de/blog/archives/308-Infinite-loops-in-Haskell… 52. http://luqui.org/blog/archives/2008/10/15/frp-rant/ 53. http://luqui.org/blog/archives/2008/10/14/data-memocombinators/ 54. http://www.serpentine.com/blog/2008/09/28/using-bloom-filters-for-large-sca… 55. http://www.hvergi.net/2008/10/generating-legal-subsets-of-a-dependency-grap… 56. http://abstractabsurd.blogspot.com/2008/10/silly-example-and-brief-history.… 57. http://tech-nickel.blogspot.com/2008/10/sorting-using-haskell.html 58. http://sigfpe.blogspot.com/2008/10/untangling-with-continued-fractions.html 59. http://holumbus.fh-wedel.de/blog/?p=15 60. http://www.londonhug.net/2008/10/11/getting-things-going-again/ 61. http://blog.codeslower.com/2008/10/The-Haskell-Cheatsheet 62. http://sandersn.com/blog/index.php?title=type_directed_programming 63. http://micah.cowan.name/2008/10/10/computers/software-development/adventure… 64. http://justtesting.org/post/53418059 65. http://variably-volatile.blogspot.com/2008/10/haskell.html 66. http://blog.bjrn.se/2008/10/lets-build-mp3-decoder.html 67. http://www.haskell.org/mailman/listinfo/haskell 68. http://sequence.complete.org/ 69. http://planet.haskell.org/ 70. http://sequence.complete.org/node/feed 71. http://haskell.org/ 72. http://haskell.org/haskellwiki/HWN 73. http://code.haskell.org/~byorgey/code/hwn/

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Implementing pi-calculus using STM
by Edsko de Vries 18 Oct '08

18 Oct '08

Hi, (Note: assumes knowledge of pi-calculus.) I am playing with writing a simple interpreter for the pi-calculus using STM. The implementation of most of the operators of the pi- calculus is straightforward, but I am unsure on how to implement the replication operator. The interpretation of !P should be the interpretation of the infinite number of parallel processes P | P | P ... . I am implementing parallel processes using the fork operation, but spawning an infinite amount of processes -- even if the (infinite) majority of them all immediately lock -- seems like a bad idea. So I would prefer to spawn one P, and as soon as the thread that interprets P makes any progress at all, spawn another, and so on. I'm not too sure however how to achieve this. Any ideas? Edsko

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mysql server on Linux
by Galchin, Vasili 18 Oct '08

18 Oct '08

Hello, I want to use the mysql server (mysqld) on Linux. What Haskell packages must I install in order to write a Haskell mysql package?? Thank you, Vasili

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Fwd: [Haskell-beginners] HaXml.SAX successfully parses a malformed XML document
by David Frey 17 Oct '08

17 Oct '08

I asked this question on the haskell-beginners list, but I didn't get a response, so I am forwarding it on to the cafe list. David --- Original Message --- Date: 10/16/2008 From: "David Frey" <dpfrey(a)shaw.ca> Subject: [Haskell-beginners] HaXml.SAX successfully parses a malformed XML document It seems that saxParse from Text.XML.HaXml.SAX will successfully parse a malformed XML document. Notice that the SubElem opening and closing tag are not matched in the XML document below. --- input.xml --- <RootNode> <ElemOne> <SubElem attr="foo">element data</SubElemBroken> <NoDataElem/> <ElemOne> </RootNode> --- end input.xml --- The Haskell code below runs without error. It prints out the type of elements found during the parse. --- Haskell Code --- module Main where import qualified Text.XML.HaXml.SAX as SAX import Data.Maybe main = let inputFilename = "input.xml" in do content <- readFile inputFilename let (elements, error) = SAX.saxParse inputFilename content if isNothing error then mapM_ putStrLn (summarizeElements elements) else putStrLn $ "ERROR:" ++ (fromJust error) summarizeElements :: [SAX.SaxElement] -> [String] summarizeElements elements = map summarizeElement elements summarizeElement :: SAX.SaxElement -> String summarizeElement element = case element of (SAX.SaxDocTypeDecl d) -> "DocType" (SAX.SaxProcessingInstruction p) -> "Processing Instruction" (SAX.SaxComment s) -> "Comment" (SAX.SaxElementOpen name attrs) -> "Element Open" (SAX.SaxElementClose name) -> "Element Close" (SAX.SaxElementTag name attrs) -> "No Content Element" (SAX.SaxCharData charData) -> "Character Data" (SAX.SaxReference reference) -> "Reference" --- End Haskell Code --- The Python code below throws an exception when parsing the same input document. --- Python Code --- from xml.sax import make_parser from xml.sax.handler import ContentHandler def main(): c = ContentHandler() p = make_parser() p.setContentHandler(c) p.parse(open('input.xml')) if __name__ == '__main__': main() -- End Python Code --- Is this a bug in the HaXml SAX parser? Thanks, David _______________________________________________ Beginners mailing list Beginners(a)haskell.org http://www.haskell.org/mailman/listinfo/beginners

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How to deal with pointers to pointers in the FFI
by Jefferson Heard 17 Oct '08

17 Oct '08

I have the following functions in C: OGRErr OGR_G_CreateFromWkb (unsigned char *, OGRSpatialReferenceH, OGRGeometryH *, int) OGRErr OGR_G_CreateFromWkt (char **, OGRSpatialReferenceH, OGRGeometryH *) void OGR_G_DestroyGeometry (OGRGeometryH) OGRGeometryH OGR_G_CreateGeometry (OGRwkbGeometryType) The normal sequence of calls is OGRGeometryH handle = OGR_G_CreateGeometry(SOME_TYPE); // do stuff OGR_G_DestroyGeometry(handle); OR OGR_G_CreateFromWkb(blob, ref, &handle, 0); // do stuff OGR_G_DestroyGeometry(handle); As you can see, in one case, I have to pass in a pointer to the returned handle, and not just the handle. How can I accomplish this feat using a single type? I had data OGRGeometryH type Geometry = Ptr OGRGeometryH but then can I declare that a function returns a Ptr (Geometry) ? -- I try to take things like a crow; war and chaos don't always ruin a picnic, they just mean you have to be careful what you swallow. -- Jessica Edwards

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Troubles getting isA of ArrowIf from HXT 8.10 to work as expected
by Corey O'Connor 17 Oct '08

17 Oct '08

I'm attempting to use ifA to conditionalize generated XHTML. ifA (arr test_status >>> arr (/= "Running")) (mkelem "a" [attr "href" (arr test_log_URL >>> mkText)] [txt "log"]) (mkelem "a" [attr "href" (arr test_log_URL >>> mkText)] [txt "no log"]) The arrow type at the point of the ifA is (I think) "XmlArrow a => a XmlTree TestRun" where TestRun is defined as: data TestRun = TestRun { test_log_URL :: String, test_status :: String } The issue I'm seeing is that regardless of the predicate arrow the result is always the same: The XmlTree for the True branch is always generated. In other words, I get the same behavior using this code: ifA (arr (const False)) (mkelem "a" [attr "href" (arr test_log_URL >>> mkText)] [txt "log"]) (mkelem "a" [attr "href" (arr test_log_URL >>> mkText)] [txt "no log"]) Which, I thought, the "arr (const False)" would force the ifA to always descend the False path. This is my first attempt at using HXT and Arrows (Which is otherwise going great!) so I figure I'm missing something. Any ideas? Cheers, Corey O'Connor

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Temlpate Haskell: [d| ... |]
by Achim Schneider 17 Oct '08

17 Oct '08

> [d| ... |], where the "..." is a list of top-level declarations; the > quotation has type Q [Dec]. (http://www.haskell.org/ghc/docs/latest/html/users_guide/template-haskell.ht…) Can someone elaborate on what a list means here? Neither declarations = [d| foo = "bar" bar = "foo" |] nor declarations = [d| [ foo = "bar" , bar = "foo" ] |] work. I'm trying to automatically generate a bunch of functions out of an xml file. -- (c) this sig last receiving data processing entity. Inspect headers for copyright history. All rights reserved. Copying, hiring, renting, performance and/or quoting of this signature prohibited.

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