- Haskell-Cafe - Haskell.org

Typeclass question
by Andrew Wagner 27 Dec '08

27 Dec '08

I'm sure there's a way to do this, but it's escaping me at present. I want to do something like this: data Foo = Bar a => Foo a Bool ... That is, I want to create a new type, Foo, whose constructor takes both a Boolean and a value of a type of class Bar.

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ANNOUNCE: citeproc-hs-0.2
by Andrea Rossato 27 Dec '08

27 Dec '08

Hello, I'm happy to announce the release of citeproc-hs-0.2. WHAT'S NEW 1. Added support for citation collapsing options. This fills the last major gap to a usable CSL implementation; 2. added a wrapper around hs-bibutils[1] (disabled by default). By installing hs-bibutils and linking citeproc-hs to it with the '-fbibutils' configuration flag, it is possible to read all the bibliographic databases supported by bibutils[2]; 3. added some haddock API documentation: http://code.haskell.org/citeproc-hs/docs/ 4. simplified and started to document the internals of the library. DOWNLOADS citeproc-hs can be downloaded from Hackage: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/citeproc-hs ABOUT citeproc-hs is a Haskell implementation of the Citation Style Language. It adds to pandoc, the famous Haskell text processing tool, a Bibtex like citation and bibliographic formatting and generation facility. The Citation Style Language (CSL) is an XML language for specifying citation and bibliographic formatting, similar in principle to BibTeX .bst files or the binary style files in commercial products like Endnote or Reference Manager. CSL is used by Zotero for bibliographic style formatting, and a huge number of CSL styles have been developed by the Zotero community. More information, with installation instructions, can be found here: http://code.haskell.org/citeproc-hs/ Hope you'll enjoy, Andrea Rossato [1] http://code.haskell.org/hs-bibutils/ [2] http://www.scripps.edu/~cdputnam/software/bibutils/

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ANNOUNCE: hs-bibutils-0.1
by Andrea Rossato 27 Dec '08

27 Dec '08

Hello, I'm happy to announce the first release of hs-bibutils, the Haskell bindings to Chris Putnam's bibutils.[1] Bibutils is a library and a set of bibliographic utilities to interconvert between various bibliography database formats using a common MODS-format XML intermediate. hs-bibutils is meant to provide to citeproc-hs, and indirectly to pandoc, the ability to parse all the bibliographic database formats supported by bibutils. citeproc-hs[2] is a Haskell implementation of the Citation Style Language. It adds to pandoc a Bibtex like citation and bibliographic formatting and generation facility. DOWNLOADS hs-bibutils can be downloaded from Hackage: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hs-bibutils The project home page can be found here: http://code.haskell.org/hs-bibutils/ INSTALLATION AND KNOWN ISSUES bibutils builds, without installing it, a static library to be used to compile the various converting utilities. But in order to use the library with pandoc (or ghci) it is necessary to create and install a shared object before building and installing hs-bibutils. hs-bibutils provides a patch to the bibutils building scripts to enable the shared object creation and installation. Alternatively a patched version of the latest release of bibutils can be downloaded from the project home page, where all the needed information for the installation are provided: http://code.haskell.org/hs-bibutils/#installation I was able to test the patched building scripts only on a Linux machine with a x86 system. Please report me any success or failure on other systems/architectures. BUG REPORTS To submit bug reports you can either contact me directly or use the citeproc-hs bug tracking system available at the following address: http://code.google.com/p/citeproc-hs/issues Hope you'll enjoy, Andrea Rossato [1] http://www.scripps.edu/~cdputnam/software/bibutils/ [2] http://code.haskell.org/citeproc-hs/

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ByteString typechecking issues....
by Galchin, Vasili 27 Dec '08

27 Dec '08

Hello, I have a ByteString -> [ByteString] -> ByteString situation, i.e. concatenation ..... -- marshall into ByteString representation join (encode (buildHeader ss)) -- ByteString (map encode (buildEntries (sequenceListExtract ss))) -- [ByteString] I get the following typecheck error which is vexing me .... Couldn't match expected type `t -> t -> B.ByteString' against inferred type `B.ByteString' ??? Thanks, Vasili

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Type classes
by Oscar Picasso 27 Dec '08

27 Dec '08

>From Real World Haskell: data JValue = JString String | JNumber Double | JBool Bool | JNull | JObject [(String, JValue)] | JArray [JValue] deriving (Eq, Ord, Show) .... type JSONError = String class JSON a where toJValue :: a -> JValue fromJValue :: JValue -> Either JSONError a instance JSON JValue where toJValue = id -- Really ? fromJValue = Right Now, instead of applying a constructor like JNumber to a value to wrap it, > we apply the toJValue function. If we change a value's type, the compiler > will choose a suitable implementation of toJValue to use with it. Actually it does not work. And I don't see how it could with this toJValue implementation. Is it possible to make it work by providing another implementation? Oscar

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Haskell Weekly News: Issue 98 - December 25, 2008
by Brent Yorgey 26 Dec '08

26 Dec '08

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20081225 Issue 98 - December 25, 2008 --------------------------------------------------------------------------- Welcome to issue 98 of HWN, a newsletter covering developments in the [1]Haskell community. Happy holidays! An exciting HWN for you this week, including a number of cool new libraries, the [2]public release of [3]Cryptol, a [4]Haskell logo contest, and the [5]second most awesome GHC bug ever (see augustss's quote at the end of the Quotes section for the most awesome GHC bug ever). Announcements Hieroglyph 0.85. Jeff Heard [6]announced that the Thingie library has been renamed [7]Hieroglyph, and now has support for displaying images on the Cairo canvas. Cryptol now freely available. Don Stewart [8]announced that [9]Cryptol, the language of cryptography, is [10]now available to the public! Cryptol is a domain specific language for the design, implementation and verification of cryptographic algorithms, developed over the past decade by Galois for the United States National Security Agency. It has been used successfully in a number of projects, and is also in use at Rockwell Collins, Inc. Cryptol is implemented in Haskell. Control.Monad.IfElse. Jeff Heard [11]announced the [12]Control.Monad.IfElse module, which provides useful anaphoric and monadic versions of if-else and when. llvm-0.4.0.1. Lennart Augustsson [13]announced version 0.4.0.1 of the [14]release that is quite incompatible with the old 0.0.2 release.) Haskell LLVM bindings. LLVM is a virtual machine and the bindings allow you to generate code for this virtual machine. This code can then be executed by a JIT or written to a file for further processing by the LLVM tools. bytestring-trie 0.1.0. wren ng thornton [15]announced the release of [16]bytestring-trie 0.1.0, an efficient finite map from (byte)strings to values. The implementation is based on big-endian patricia trees, like Data.IntMap. RWH book club. Don Stewart [17]announced that Matt Podwysocki has set up a [18]Real World Haskell book club, a mailing list on google groups with already some 200 members discussing typical new user Haskell questions. Feel free to join if you like talking about Haskell, or teaching new users. Thingie-0.80. Jeff Heard [19]announced the release of [20]Thingie, a library for creating 2D visualizations in a purely functional manner. It supports static visualizations and animation, and like most vis libraries, can probably do games as well as simple viz graphics. typehash version 1.3. Lennart Augustsson [21]announced the release of the [22]typehash library, which allows you to produce a unique identifier (a cryptographic hash) for a type. This is useful if you save values of some type to a file (text, binary, whatever format you wish) and then when you read it back in again you want to verify that the type you want to read is the one you actually wrote. The library also supports type codes, which encode the complete structure of a type and can be used for finer comparison than just equality. uvector-algorithms 0.1. Dan Doel [23]announced the release of [24]uvector-algorithms, a library of algorithms (mostly sorting) for the mutable arrays defined in uvector. It has several varieties of sorting, including introsort (quicksort which falls back on heapsort in bad cases), heapsort, a simple top- down merge sort and a radix sort. Also exposed are the operations that allow you to use the arrays as heaps and a combinator for safely using these mutable array algorithms to sort immutable arrays. All algorithms have been painstakingly profiled and optimized. Data.List.Split. Brent Yorgey [25]announced the release of [26]Data.List.Split, which provides a wide range of strategies and a unified combinator framework for splitting lists with respect to some sort of delimiter. Hoogle with more libraries. Neil Mitchell [27]announced that [28]Hoogle will now search lots of the libraries present on hackage! HLint 1.0. Neil Mitchell [29]announced the re-release of [30]HLint, a tool for making suggestions to improve your Haskell code. Previously this tool was called Dr Haskell and depended on a working installation of Yhc; now it depends on GHC 6.10.1. rangemin-1.0. Louis Wasserman [31]announced the release of [32]rangemin, a library for efficiently preprocessing an array to find minimum elements of subranges of the array in constant time. Discussion length of module name affecting performance??. Daniel Gorin [33]reported a GHC bug where in certain cases, changing the name of a module to something longer results in a 2x-3x performance hit! Strange but true. Time for a new logo?. Don Stewart [34]proposed a competition to produce a new Haskell logo! Submissions should go on the [35]wiki page; the deadline for logo submissions is December 31. Pattern combinators. Andrew Wagner [36]started a thread turning a [37]paper on pattern-matching in Haskell into actual code for hackage. Coroutines. Ryan Ingram [38]posted some interesting code showing how to implement coroutines with session types. Type wildcards. Eyal Lotem [39]proposed a 'type wildcards' extension to the language. Blog noise [40]Haskell news from the [41]blogosphere. * Galois, Inc: [42]Cryptol, the language of cryptography, now available. * Dan Piponi (sigfpe): [43]The Mother of all Monads. * Real-World Haskell: [44]Pat Eyler Interviews the Real World Haskell Team. * Philip Wadler: [45]Unsafe. * Conrad Parker: [46]Release: HOgg 0.4.1. * ezekiel smithburg: [47]fast string appending/concatenation in haskell. * Brent Yorgey: [48]Data.List.Split. * Alson Kemp: [49]Turbinado: Implementing a poor-man's wiki. * Luke Palmer: [50]Reactive spaces. * Conal Elliott: [51]Smarter termination for thread racing. * Real-World Haskell: [52]RWH on Twitter. * >>> Muharem Hrnjadovic: [53]My new favourite book. * Alson Kemp: [54]Turbinado update. * Philip Wadler: [55]Type Safe Pattern Combinators, by Morten Rhiger. * Osfameron: [56]Crossword puzzles in Haskell. * Brent Yorgey: [57]QuickCheck rocks my socks. * >>> Matt Youell: [58]If programming languages were martial arts. * >>> Sebastian Fischer: [59]Haskell idioms I did not understand before hacking them on my own. * Alson Kemp: [60]Thinking about Haskell: You Know Lazy Evaluation; You Just Don't Know It. * >>> Brian McCallister: [61]Real World Haskell, for Jon. * Ivan Lazar Miljenovic: [62]RWH Arrives Down Under!. * >>> Thomas ten Cate: [63]XMonad with Ubuntu, dvorak, Pidgin and Skype. * >>> Jeremy Frens: [64]PE Problem #3 in All Languages. * Jeremy Shaw: [65]Data Migration with HApps-Data. * Chris Done: [66]Haskell Formlets: Composable web form construction and validation. * Real World Haskell: [67]Haskell around the world. * Dougal Stanton: [68]A brief look at fingertrees. Quotes of the Week * luqui: no!!! I was building a joke, but then I sent it before I thought of one. * roconnor: We put up a clothes line and made a turing machine by hand at a party once ... that is the sort of parties I go to. * cjs: In what other language could I have learned so much about Win32 programming (summary: basically, the Windows 3.0 API but with all sorts of hacks to deal with having more than one thread in the system), and come out having *enjoyed* myself? Praise to the Lord! * PaulJohnson: A paradox of the Haskell world is that, while the language is Vulcan, the community around it is dominated by Warm Fuzziness. Clearly the two are not mutually exclusive. * Botje: Caleskell even has unsafeSolveHaltingProblem? * Taejo: * Taejo needs to write Sitar Hero in Yampa * dons: it is safer for incompetent people to be working in Haskell than C++. * mpeter: the quality of my code increased drastically when i realized i should stop telling the computer to do things which were stupid. * byorgey: <Cale> RandomT/Random are effectively state monads. (in fact, they're thin candy shells around StateT/State.) <byorgey> "newtype: melts in the compiler, not in your hands" * quicksilver: [on classes having the same name as constructs in other languages] it's like having a laxative called "after dinner mint", and people being upset when they were looking for something nice to eat after dinner. * quicksilver: #haskell is a loquacracy! * quicksilver: It's also the same thing as the Yoneda lemma. That's the thing about maths. Everything is actually the same. * hugo: i feel like i was drugged with imperative programming, and now im in rehab. * chrisdone: yo dawg we heard you like haskell so we installed a lambdabot in your ghci so you can monad while you monad * augustss: ghc had a bug once where it deleted the source file if it had a type error. Quite sensible, I think. About the Haskell Weekly News New editions are posted to [69]the Haskell mailing list as well as to [70]the Haskell Sequence and [71]Planet Haskell. [72]RSS is also available, and headlines appear on [73]haskell.org. To help create new editions of this newsletter, please see the information on [74]how to contribute. Send stories to byorgey at cis dot upenn dot edu. The darcs repository is available at darcs get [75]http://code.haskell.org/~byorgey/code/hwn/ . References 1. http://haskell.org/ 2. http://www.galois.com/blog/2008/12/24/cryptol-the-language-of-cryptography-… 3. http://www.cryptol.net/ 4. http://haskell.org/haskellwiki/Haskell_logos/New_logo_ideas 5. http://thread.gmane.org/gmane.comp.lang.haskell.glasgow.user/16037 6. http://article.gmane.org/gmane.comp.lang.haskell.cafe/49528 7. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Hieroglyph 8. http://article.gmane.org/gmane.comp.lang.haskell.cafe/49516 9. http://www.cryptol.net/ 10. http://www.galois.com/blog/2008/12/24/cryptol-the-language-of-cryptography-… 11. http://article.gmane.org/gmane.comp.lang.haskell.cafe/49365 12. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/IfElse 13. http://article.gmane.org/gmane.comp.lang.haskell.cafe/49340 14. file://localhost/home/brent/hacking/hwn/(This 15. http://article.gmane.org/gmane.comp.lang.haskell.cafe/49234 16. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/bytestring-trie 17. http://article.gmane.org/gmane.comp.lang.haskell.cafe/49168 18. http://groups.google.com/group/real-world-haskell-book-club 19. http://article.gmane.org/gmane.comp.lang.haskell.cafe/49147 20. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Thingie 21. http://article.gmane.org/gmane.comp.lang.haskell.cafe/48902 22. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/typehash 23. http://article.gmane.org/gmane.comp.lang.haskell.cafe/48889 24. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/uvector%2Dalgori… 25. http://article.gmane.org/gmane.comp.lang.haskell.general/16700 26. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/split 27. http://article.gmane.org/gmane.comp.lang.haskell.general/16698 28. http://haskell.org/hoogle 29. http://article.gmane.org/gmane.comp.lang.haskell.general/16692 30. http://www-users.cs.york.ac.uk/~ndm/hlint/ 31. http://article.gmane.org/gmane.comp.lang.haskell.general/16686 32. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/rangemin 33. http://thread.gmane.org/gmane.comp.lang.haskell.glasgow.user/16037 34. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/48892 35. http://haskell.org/haskellwiki/Haskell_logos/New_logo_ideas 36. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/49267 37. http://www.itu.dk/people/mir/typesafepatterns.pdf 38. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/49108 39. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/48987 40. http://planet.haskell.org/ 41. http://haskell.org/haskellwiki/Blog_articles 42. http://www.galois.com/blog/2008/12/24/cryptol-the-language-of-cryptography-… 43. http://sigfpe.blogspot.com/2008/12/mother-of-all-monads.html 44. http://www.realworldhaskell.org/blog/2008/12/24/pat-eyler-interviews-the-re… 45. http://wadler.blogspot.com/2008/12/unsafe.html 46. http://blog.kfish.org/2008/12/release-hogg-041.html 47. http://tehgeekmeister.wordpress.com/2008/12/22/fast-string-appendingconcate… 48. http://byorgey.wordpress.com/2008/12/21/datalistsplit/ 49. http://www.alsonkemp.com/haskell/turbinado-implementing-a-poor-mans-wiki/ 50. file://localhost/home/brent/hacking/hwn/20081225.html 51. http://conal.net/blog/posts/smarter-termination-for-thread-racing/ 52. http://www.realworldhaskell.org/blog/2008/12/18/rwh-on-twitter/ 53. http://muharem.wordpress.com/2008/12/18/my-favourite-book/ 54. http://www.alsonkemp.com/haskell/turbinado-update/ 55. http://wadler.blogspot.com/2008/12/type-safe-pattern-combinators.html 56. http://greenokapi.net/blog/2008/12/18/crossword-puzzles-in-haskell/ 57. http://byorgey.wordpress.com/2008/12/16/quickcheck-rocks-my-socks/ 58. http://www.youell.com/matt/writing/?p=46 59. http://www-ps.informatik.uni-kiel.de/~sebf/projects/haskell-idioms-i-did-no… 60. http://www.alsonkemp.com/?p=110 61. http://kasparov.skife.org/blog/src/haskell/real-world-haskell-for-jon.html 62. http://ivanmiljenovic.wordpress.com/?p=30 63. http://typethinker.blogspot.com/2008/12/xmonad-with-ubuntu-dvorak-pidgin-an… 64. http://jdfrens.blogspot.com/2008/12/pe-problem-3-in-all-languages.html 65. http://nhlab.blogspot.com/2008/12/data-migration-with-happs-data.html 66. http://chrisdone.com/blog/2008/12/14/Haskell-Formlets:-Composable-web-form-… 67. http://www.realworldhaskell.org/blog/?p=154 68. http://www.dougalstanton.net/blog/index.php/2008/12/12/a-brief-look-at-fing… 69. http://www.haskell.org/mailman/listinfo/haskell 70. http://sequence.complete.org/ 71. http://planet.haskell.org/ 72. http://sequence.complete.org/node/feed 73. http://haskell.org/ 74. http://haskell.org/haskellwiki/HWN 75. http://code.haskell.org/~byorgey/code/hwn/

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How does one use Text.Regex.Base.RegexLike?
by Lyle Kopnicky 26 Dec '08

26 Dec '08

I'm trying to migrate code from using the old Text.Regex to the new Text.Regex.Base. But, I'm getting type errors. I can't even create a regex. Looking at the docs, it seems like this should print "bcd": import Data.Array import Text.Regex.Base import Text.Regex.Posix rx = makeRegex "a(.*)A" Just (_, mt, _) = matchOnceText rx "abcdA" main = putStrLn (fst (mt ! 0)) But I get an error: src\regex.hs:5:5: No instance for (RegexMaker regex compOpt execOpt [Char]) arising from a use of `makeRegex' at src\regex.hs:5:5-22 Possible fix: add an instance declaration for (RegexMaker regex compOpt execOpt [Char]) In the expression: makeRegex "a(.*)A" In the definition of `rx': rx = makeRegex "a(.*)A" src\regex.hs:7:18: No instance for (RegexLike regex [Char]) arising from a use of `matchOnceText' at src\regex.hs:7:18-41 Possible fix: add an instance declaration for (RegexLike regex [Char]) In the expression: matchOnceText rx "abcdA" In a pattern binding: Just (_, mt, _) = matchOnceText rx "abcdA" Why does it say there is no instance? Isn't the instance imported by Text.Regex.Posix? Why in the world is it so complicated just to get a matched substring out of the text? Is there an easier way? Thanks, Lyle

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forkIO on multicore
by Paul Keir 25 Dec '08

25 Dec '08

Hi all, I'm seeing no performance increase with a simple coarse-grained 2-thread code using Control.Concurrent. I compile with: > hc conc.hs -o conc --make -threaded and I run with > time ./conc +RTS -N2 But using either "-N1" or "-N2", the program runs in about 1.8secs. (I'd prefer a longer running thread task, but my fib function currently runs out of memory). Anyway, my program is below, and I'm using GHC version 6.8.2 on a 2-core Pentium D. Can anyone help? module Main where import Control.Concurrent fibs = 0 : 1 : zipWith (+) fibs (tail fibs) heavytask m = putMVar m (fibs !! 100000) main = do ms <- sequence $ replicate 2 newEmptyMVar mapM_ (forkIO . heavytask) $ tail ms heavytask $ head ms ms' <- mapM takeMVar ms mapM_ print ms' Regards, Paul

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Hackage packages for indexing by Google
by Henning Thielemann 25 Dec '08

25 Dec '08

When testing the ShowMeta parallel web: http://hackage.haskell.org.showmeta.parallelnetz.de/packages/archive/pkg-li… I found, that all HackageDB pages forbid crawling and indexing. Actually, the content of this page is dynamic - but it changes only incrementally. It would be very worth when I search for "markov chain haskell" with Google, that I will be directed to the according package page of HackageDB.

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ANN: Hieroglyph 0.85
by Jeff Heard 25 Dec '08

25 Dec '08

I have changed the name of Thingie to Hieroglyph and added support for displaying images on the Cairo canvas. I'm still working on using template haskell to derive the basic UIState class, but I don't understand template haskell all that well, so it's taking some time. Hopefully I can get some examples of the library up over the christmas holiday. -- Jeff

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