- Haskell-Cafe - Haskell.org

ANN: HLint 1.2
by Neil Mitchell 08 Feb '09

08 Feb '09

Hi, I am pleased to announce HLint version 1.2. HLint is a lint-like tool for Haskell that detects and suggests improvements for your code. HLint is compatible with most GHC extensions, and supports a wide variety of suggestions, and can be extended with additional user suggestions. To install: cabal update && cabal install hlint Web page: http://www-users.cs.york.ac.uk/~ndm/hlint/ Biggest new feature: List recursion suggestions. For example, running HLint over the GHC compiler now suggests things such as: Example.hs:3:1: Warning: Use foldr Found: seqList [] b = b seqList (x : xs) b = x `seq` seqList xs b Why not: seqList xs b = foldr seq b xs Example.hs:6:1: Warning: Use foldr Found: seqIds [] = () seqIds (id : ids) = seqId id `seq` seqIds ids Why not: seqIds ids = foldr (seq . seqId) () ids Example.hs:13:1: Warning: Use foldl Found: rev_app [] xs = xs rev_app (y : ys) xs = rev_app ys (y : xs) Why not: rev_app ys xs = foldl (flip (:)) xs ys HLint will automatically detect if you should have used a map, a foldr or a foldl and suggest how to change your code. In the GHC, darcs and Hoogle code bases there are no obvious map-like functions, which is a good sign :-) Changes from last time: * More GHC extensions supported - including record wild cards and fixes to a number of existing extensions. These changes are thanks to Niklas and the haskell-src-exts package. * Many infix operators are now correctly associated with the right priority. * All hints are now ignored, warnings or errors. Hopefully this should make it clearer what hints are most important. As part of this, the format for defining ignore files has changed completely - see the manual for the new format. * Lots of new hints have been added - many from users of HLint. * Many bugs have been fixed. Can any follow-up discussions please be directed to haskell-cafe@. All comments, questions, bug reports are welcome! Neil

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Function const (Binding)
by TKM 08 Feb '09

08 Feb '09

Hello, I've a small question about the function const. I'm a bit of confused about how it binds. Let me take the following expression as example: const id 1 2 If I execute this expression, I will get as answer 2 with Helium. Now is my question, why doesn't it give me 1 as the answer? Because the type of id would be: a -> a. So first it would execute id 1 in my opinion. That gives us 1. And after executing const 1 2 it should give us 1. Can somebody explain to me why it does not bind as I expect? (I know I can do: const (id 1) 2 to get what I want) Thank you for your answers. Greetz TKM

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HSGI: Haskell Server Gateway Interface
by Manlio Perillo 08 Feb '09

08 Feb '09

Lately I have started to think about how I would like to implement a web application framework in Haskell. To keep my thoughts well defined, I have decided to write some documents. My ideas are heavily based on my experience with Python WSGI, and a Python WSGI framework I'm implementing (wsgix). Note that there is already another attempt to define an Haskell Gateway interface, and it may also have the same name! However I'm not trying to write a formal specification. The core of my idea is in the Haskell Web Application Framework, I just need a gateway interface as a building block. I apologize for my not very good experience at writing in english and Haskell. Also note that the document is in a very rough state. I'm announcing it here, to receive feedback, just to make sure that what I would like to do is possible/convenient to do in Haskell. The documents (only the first one - HSGI - available at the moment) are available here: http://mperillo.ath.cx/haskell/ Thanks and regards Manlio Perillo

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morphisms in IO
by Gregg Reynolds 08 Feb '09

08 Feb '09

I'm working on a radically different way of looking at IO. Before I post it and make a fool of myself, I'd appreciate a reality check on the following points: a) Can IO be thought of as a category? I think the answer is yes. b) If it is a category, what are its morphisms? I think the answer is: it has no morphisms. The morphisms available are natural transformations or functors, and thus not /in/ the category. Alternatively: we have no means of directly naming its values, so the only way we can operate on its values is to use morphisms from the outside (operating on construction expressions qua morphisms.) c) All categories with no morphisms ("bereft categories"?) are isomorphic (to each other). I think yes. Thanks, gregg

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Haskell Weekly News: Issue 104 - February 7, 2009
by Brent Yorgey 08 Feb '09

08 Feb '09

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20090207 Issue 104 - February 07, 2009 --------------------------------------------------------------------------- Welcome to issue 104 of HWN, a newsletter covering developments in the [1]Haskell community. Community News Andre Pang (ozone) will be soon [2]moving to San Fransisco to begin work with [3]Pixar! Announcements Mutually recursive modules. Henning Thielemann [4]announced a [5]small writeup explaining how mutually recursive modules are currently supported, and how they can be avoided. Please add information about other compilers and more ideas on breaking cycles. UrlDisp, a friendly URL dispatching library. Artyom Shalkhakov [6]announced the first release of [7]UrlDisp, a small library for URL dispatching (aka routing). Right now it works with CGI, and should be compatible with FastCGI as well (not tested); Happstack compatibility is planned. [8]Documentation and usage examples are available. Purely functional LU decomposition. Rafael Gustavo da Cunha Pereira Pinto [9]released some code to perform purely functional LU decomposition. Ready for testing: Unicode support for Handle I/O. Simon Marlow [10]announced that proper Unicode support in Handle I/O is ready for testing in GHC. Just download the [11]set of patches, compile GHC with them, and test away! Comments and discussion welcome. HaskellWiki Accounts. Ashley Yakeley can [12]create a HaskellWiki account for anyone who wants one (account creation has been disabled as a spam-fighting measure). multiplicity 0.1.0 released. Dino Morelli [13]announced the release of [14]multiplicity 0.1.0, a configuration file driven wrapper around [15]duplicity. It allows you to easily define backup sets as config files and avoid long, repetitive command lines. Happstack 0.1 Released!. Matthew Elder [16]announced the [17]0.1 release of [18]Happstack, the successor for the HAppS project. #haskell-in-depth IRC channel. Philippa Cowderoy [19]announced the creation of a new IRC channel, #haskell-in-depth. The new channel is open to everyone, just like #haskell, but is intended for more in-depth conversations, to allow the #haskell channel to be a more newbie-friendly place. regex-posix-unittest-1.0 AND regex-posix-0.94.1 AND regex-tdfa-0.97.1. ChrisK [20]announced an update to the [21]regex-posix package which provides better semantics for multiple matches; an update to the [22]regex-tdfa package, which provides the same new multiple match semantics and fixes a bug; and finally, a new package, [23]regex-posix-unittest, along with an [24]accompanying wiki page; it runs a suite of unit tests which regex-tdfa passes, but reveals bugs in the standard glibc, OS X, FreeBSD, and NetBSD implementations! Jane Street Summer Project 2009. Yaron Minsky [25]announced the [26]Jane Street Summer Project for 2009, the goal of which is to make functional programming languages into better practical tools for programming in the real world. Students will be funded over the summer to work on open-source projects which aim at improving the practical utility of their favorite functional language. gitit 0.5.1. John MacFarlane [27]announced the release of [28]gitit 0.5.1, a wiki program that uses git or darcs as a filestore and HAppS as a server. Changes include major code reorganization, bug fixes, new debugging features, and more. regex-xmlschema. Uwe Schmidt [29]announced the [30]release of [31]regex-xmlschema, (yet another) package for processing text with regular expressions, containing a complete implementation of the W3C XML Schema specification language for regular expressions. diagrams 0.2. Brent Yorgey [32]announced version 0.2 of the [33]diagrams package, an embedded domain-specific language for creating simple graphics in a compositional style. New features include support for arbitrary paths, text, multiple output formats, and support for the [34]colour library. Discussion Haddock Markup. David Waern began a [35]discussion on Haddock markup syntax: should it support (La)TeX for embedded mathematics? Should it support other stuff? Elegant & powerful replacement for CSS. Conal Elliott began a [36]discussion on an elegant replacement for CSS that is consistent, composable, orthogonal, functional, and based on an elegantly compelling semantic model---what might such a thing look like? type metaphysics. Gregg Reynolds began a long and interesting [37]discussion on the type system, denotational semantics, and related matters. Jobs Postdoc Positions at the CLIP group, Spain. CFP [38]announced the availability of [39]postdoctoral research positions within the [40]CLIP (Computational Logic, Implementation and Parallelism) group in Madrid, Spain. The application deadlines are February 13th and 18th; see the original email for more details. Multiple funded Ph.D. positions available. Martin Erwig [41]announced the availability of multiple funded Ph.D. positions in the [42]school of EECS at Oregon State University, in the areas of programming languages (focusing on DSLs and language design), software engineering, and HCI. If you are interested, email Martin with a resume and contact information by February 15. Blog noise [43]Haskell news from the [44]blogosphere. * Erik de Castro Lopo: [45]libsndfile 1.0.18.. * >>> Gregg Reynolds: [46]Moggi :: CT -> Hask. An interesting perspective on Haskell and category theory. * Osfameron: [47]Functional Pe(a)rls v2 (now with Monads!) at the London Perl Workshop 2008. * ezekiel smithburg: [48]google code project, google group, and darcs repository for WikimediaParser. * ezekiel smithburg: [49]releasing WikimediaParser 0.1. * Andre Pang (ozone): [50]Change. * Lennart Augustsson: [51]Is Haskell fast?. * Lennart Augustsson: [52]Regression. A library for writing embedded BASIC programs in Haskell? What is the world coming to? * Galois, Inc: [53]Equivalence and Safety Checking in Cryptol. * GHC / OpenSPARC Project: [54]Just Testing. * Jeff Heard: [55]Hieroglyph: Interactively graph a spreadsheet in 99 lines of code.. * Jeff Heard: [56]Snippet: sorting the elements of a map. * LHC Team: [57]Grin a little.. * Alex Mason: [58]Other shootout news. * Xmonad: [59]contribs review: SpawnOn. * Jeff Heard: [60]Hieroglyph Haddock docs. * Alex Mason: [61]More n-bodies speedups. * Alex Mason: [62]N-bodies evolution. * Eric Kow (kowey): [63]practical quickcheck (wanted). Eric is seeking practical advice on how to effectively use QuickCheck. * Alex Mason: [64]TextMate haskell bundle improvements. * Haskell application server stack: [65]Happstack 0.1 Released (one day early!). * Haskell application server stack: [66]SOCALFP presentation: patch-tag as a startup using Happstack. * Neil Mitchell: [67]Monomorphism and Defaulting. * Jeff Heard: [68]Hieroglyph Part II, basic mouse/keyboard interactivity. * Jeff Heard: [69]Introducing Hieroglyph. Purely functional 2D visualization on top of Cairo.. The Hieroglyph library looks pretty cool! * Jeff Heard: [70]Hieroglyph HOWTO, part I: Sparklines. * Alex Mason: [71]N-bodies speedup (50%!). * >>> John Lato: [72]Build a better WAVE reader, pt 2. * GHC / OpenSPARC Project: [73]Join Points. * Luke Palmer: [74]Parallel Rewrite System. * >>> John Lato: [75]Build a better WAVE reader, pt 1. Notes on building an 'optimal audio I/O library in Haskell'. * Luke Palmer: [76]Dana update: System U-Box compiler is go. * Luke Palmer: [77]Dana needs a self-embedding of U-Box. * Beelsebob: [78]Simulating n-bodies and functional programming. A beautiful implementation of an n-bodies simulation using reactive. * Xmonad: [79]New layout: GridVariants.SplitGrid. * Lane: [80]Christopher Lane Hinson: MaybeArrow?. An arrow with possible failure, which still allows later effects to happen after failure. * Don Stewart (dons): [81]#haskell is a busy place. Some statistics on the #haskell IRC channel. * Alson Kemp: [82]Cabal-install is awesome. Enough said! * FP-Syd: [83]Sydney FP Group: FP-Syd #11.. * Brent Yorgey: [84]Diagrams 0.2 release. * Dan Piponi (sigfpe): [85]Beyond Regular Expressions: More Incremental String Matching. More incremental brain expansion courtesy of Dan. * Don Stewart (dons): [86]Reviving the Gofer Standard Prelude (circa. 1994). Haskell, retro-style! Quotes of the Week * sigfpe: If I took some Ritalin, maybe I could write an entire book on Haskell and algebra. * cjb: It's all fun and games until somebody loses an IOVar. * Gracenotes: You are likely to be eaten by a poset * Gracenotes: A public service announcement: if you find yourself overusing the Writer monad, tell (Sum 1) * Anonymous: Haskell, the world's leading purely fictional programming language * ehird: 2009: The Year of the Combinatorial Explosion of Haskell Web Frameworks. Also, the Linux Desktop. * ehird: [on the previous quote] Someone re-remember that quote when lambdabot's back so I don't have to and thereby look egotistical, thanks * luqui: Hmph! My program which uses unsafeCoerce everywhere is not working properly! Who'd have thought... About the Haskell Weekly News New editions are posted to [87]the Haskell mailing list as well as to [88]the Haskell Sequence and [89]Planet Haskell. [90]RSS is also available, and headlines appear on [91]haskell.org. To help create new editions of this newsletter, please see the information on [92]how to contribute. Send stories to byorgey at cis dot upenn dot edu. The darcs repository is available at darcs get [93]http://code.haskell.org/~byorgey/code/hwn/ . References 1. http://haskell.org/ 2. http://www.algorithm.com.au/blog/files/change.php#unique-entry-id-605 3. http://www.pixar.com/ 4. http://article.gmane.org/gmane.comp.lang.haskell.cafe/52272 5. http://haskell.org/haskellwiki/Mutually_recursive_modules 6. http://article.gmane.org/gmane.comp.lang.haskell.cafe/52045 7. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/UrlDisp 8. http://www.haskell.org/haskellwiki/UrlDisp 9. http://article.gmane.org/gmane.comp.lang.haskell.cafe/52012 10. http://article.gmane.org/gmane.comp.lang.haskell.cafe/51988 11. http://www.haskell.org/~simonmar/base-unicode.tar.gz 12. http://article.gmane.org/gmane.comp.lang.haskell.general/16846 13. http://article.gmane.org/gmane.comp.lang.haskell.general/16840 14. http://ui3.info/d/proj/multiplicity.html 15. http://duplicity.nongnu.org/index.html 16. http://article.gmane.org/gmane.comp.lang.haskell.general/16838 17. http://blog.happstack.com/2009/02/03/happstack-01-released 18. http://happstack.com/ 19. http://article.gmane.org/gmane.comp.lang.haskell.general/16833 20. http://article.gmane.org/gmane.comp.lang.haskell.general/16829 21. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/regex%2Dposix 22. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/regex%2Dtdfa 23. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/regex%2Dposix%2D… 24. http://www.haskell.org/haskellwiki/Regex_Posix 25. http://article.gmane.org/gmane.comp.lang.haskell.general/16822 26. http://janestreetsummer.com/ 27. http://article.gmane.org/gmane.comp.lang.haskell.cafe/51783 28. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/gitit 29. http://article.gmane.org/gmane.comp.lang.haskell.cafe/51764 30. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/regex-xmlschema 31. http://www.haskell.org/haskellwiki/Regular_expressions_for_XML_Schema 32. http://article.gmane.org/gmane.comp.lang.haskell.cafe/51726 33. http://code.haskell.org/diagrams 34. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/colour 35. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/52219 36. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/51998 37. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/51858 38. http://article.gmane.org/gmane.comp.lang.haskell.general/16837 39. http://clip.dia.fi.upm.es/Job_Openings/RyC2009.html 40. http://clip.dia.fi.upm.es/ 41. http://article.gmane.org/gmane.comp.lang.haskell.general/16841 42. http://eecs.oregonstate.edu/ 43. http://planet.haskell.org/ 44. http://haskell.org/haskellwiki/Blog_articles 45. http://www.mega-nerd.com/erikd/Blog/CodeHacking/libsndfile/rel_18.html 46. http://syntax.wikidot.com/blog:1 47. http://greenokapi.net/blog/2008/12/01/functional-pearls-v2-now-with-monads-… 48. http://tehgeekmeister.wordpress.com/2009/02/06/google-code-project-google-g… 49. http://tehgeekmeister.wordpress.com/2009/02/05/releasing-wikimediaparser-01/ 50. http://www.algorithm.com.au/blog/files/change.php#unique-entry-id-605 51. http://augustss.blogspot.com/2009/02/is-haskell-fast-lets-do-simple.html 52. http://augustss.blogspot.com/2009/02/regression-they-say-that-as-you-get.ht… 53. http://www.galois.com/blog/2009/02/05/equivalence-and-safety-checking-in-cr… 54. http://ghcsparc.blogspot.com/2009/02/just-testing.html 55. http://vis.renci.org/jeff/2009/02/05/heiroglyph-interactively-graph-a-sprea… 56. http://vis.renci.org/jeff/2009/02/05/snippet-sorting-the-elements-of-a-map/ 57. http://lhc-compiler.blogspot.com/2009/02/grin-little.html 58. http://axman6.homeip.net/blog/2009/02/other-shootout-news.html 59. http://xmonad.wordpress.com/2009/02/04/contribs-review-spawnon/ 60. http://vis.renci.org/jeff/2009/02/04/hieroglyph-haddock-docs/ 61. http://axman6.homeip.net/blog/2009/02/more-n-bodies-speedups.html 62. http://axman6.homeip.net/blog/2009/02/n-bodies-evolution.html 63. 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http://haskell.org/haskellwiki/HWN 93. http://code.haskell.org/~byorgey/code/hwn/

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Re: [Haskell-cafe] Re: [Haskell-beginners] Just how unsafe is unsafe
by Kalman Noel 08 Feb '09

08 Feb '09

As I didn't catch the whole thread, I hope I'm not just repeating everyone else: Roel van Dijk wrote: > I guess what unsafe should mean is a matter of taste. Personally I > find correctness more important that pureness. An unsafe function will > crash your program if evaluated when its preconditions do not hold. > Whether that is because of impurity (segmentation fault?), a partial > pattern match or a direct error "bla" is not that important. It might > be important when determining why your program crashed, but the result > is still the same. Maybe for the purposes of naming functions it's sufficient to argument that a crash is a crash whatsoever, but as for terminology in general, I think it's good to distinguish (1) partial functions from (2) functions that break purity, may lead to segmentation faults etc. I suppose (2) is the »traditional« meaning of unsafe. The motivation for this distinction is that you can still reason to some extent about (1) if you consider _|_, and that there are many functions that, although useful and correct, aren't guaranteed to terminate on infinite input, thus are partial. On the other hand, functions from (2) should always be called unsafeFoo, and/or wrapped by safe functions. Kalman

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1,000 packages, so let's build a few!
by Andrew Coppin 07 Feb '09

07 Feb '09

In celebration of Hackage reachin over 1,000 unique packages, I decided that I would re-visit the problem of attempting to build them on Windows. I began by removing all existing Haskellness from my PC. I now have a vanilla Windows XP (32-bit) system with Service Pack 3. So, let's see what we can do here... - Install GHC 6.10.1. As you'd expect, no issues here. - Now, let's install stream-fusion. First let me ch... woah! What the hell? OK, it seems that Google is temporarily "broken". (All websites show up as "this site may damange your computer".) Obviously this has nothing to do with Haskell, but it makes navigating Hackage moderately more tedious. Oh well, anyway, where was I? Ah yes, I already have the tarball for stream-fusion-0.1.1, but I see that the latest release is 0.1.2.1. (Unfortunately, there doesn't appear to be any way to determine what the difference is between the two versions...) - Right, I've got the tarball for stream-fusion. Now let's see if it will install... J:\Haskell\unpack> runhaskell Setup configure J:\Haskell\unpack> runhaskell Setup build J:\Haskell\unpack> runhaskell Setup install J:\Haskell\unpack> ghc-pkg list ...stream-fusion-0.1.2.1... OK, nothing much wrong with that then. :-D - Hmm, doesn't GHC 6.10.1 now come with Haddock included? I wonder if there's a way to ask Cabal to build the docs for me... [Grr! Google is still busted.] Ah, yes there is. OK, let's try this: J:\Haskell\unpack> runhaskell Setup haddock ... Data\Stream.hs:292:33: parse error on input `!' haddock: Failed to check module: Data.Stream Uh... OK. So I guess I *won't* build the docs for that one then. :-/ Oh well, maybe it's a one-off failure? Let's try some more packages... - Next up, let's try the excellent ansi-terminal package. Checking Hackage [again without Google] and I see that the tarball I've got is still the latest version (0.5.0). Let's see what happens now... J:\Haskell\unpack> runhaskell Setup configure J:\Haskell\unpack> runhaskell Setup build J:\Haskell\unpack> runhaskell Setup haddock J:\Haskell\unpack> runhaskell Setup install J:\Haskell\unpack> ghc-pkg list ...ansi-terminal-0.5.0... Well, that installed OK. And look... it's given me a little folder full of Haddock documentation. How nice! Pitty it's burried 5 subfolders deep on the system drive with no hyperrefs to it... but I guess I could just bookmark the root folder or something? That'll work. (I.e., when I add more packages, it'll still be easy to navigate to their documentation this way.) - Now on to the ambiguously-named "binary" package. Again, I have a tarball for 0.4.2 but the latest is 0.4.4. (And, again, no indication of how this is different. But let's hope the difference is that it's fixed to work with GHC 6.10...) Configure, build, Haddock, install... no issues. That's refreshing. - OK, so what have we done? We've done stream-fusion, which is 100% Haskell. We've done ansi-terminal, which only links to standard Win32 headers [which, oddly, seem to come bundled with GHC]. And we've done binary, which (I think!) comes bundled with a few small snippets of C. Now let's try something harder... - Gtk2hs doesn't seem to want to work with GHC 6.10 yet; that's a pitty. It's a nice library. OTOH, how many Windows users have GTK+ installed? It's fairly uncommon. Fortunately you can just bundle the DLLs along with your app; unfortunately there's *a lot* of them, and they're quite large. And, obviously, you get a very non-native look & feel. Still, it *is* a nice library, and I'm sure at some point people will hassle Duncan to the point where an update appears. ;-) - A better choice, theoretically, should be wxHaskell. As I understand it, wxWidgets is supposed to look native. (Do you still have to bundle a DLL? Or is it statically linked in? Or...?) Oh well, I'd like to at least try it out and see how it works... Hmm, looks like you can obtain it via Cabal, or there's a special Windows build where you just run a BAT file and it registers everything for you. Let's try that first... "Click on the newly created wxhaskell-0.11.0\bin\wxhaskell-register.bat program to register the wxHaskell package. To uninstall, you can click on wxhaskell-0.11.0\bin\wxhaskell-unregister.bat and than remove the wxhaskell-0.11.0 directory." That sounds easy. Let's try it... 1 file(s) copied. 1 file(s) copied. 1 file(s) copied. - register packages 'ghc-pkg' is not recognized as an internal or external command, operable program or batch file. 'ghc-pkg' is not recognized as an internal or external command, operable program or batch file. error: Unable to register the package using "ghc-pkg". Maybe you have an incompatible version of ghc installed? Press any key to continue . . . Uh... what? OK, let's see if I can figure out what this batch file is trying to do... Er... wow. o_O Alright, there's no way I'm going to figure this out. I can't even tell where it's trying to install to or anything. Hmm. Well, it looks like it's all compiled and it's just trying to copy a few files and register them with GHC. That's probably a lot simpler than trying to actually compile from source using Cabal. I don't know what's confusing it, but maybe somebody in HCafe will know? I'm going to leave this one for now... - Another exciting package is the Haskell binding for libSDL. I am just *dying* to start doing some sound coding with Haskell, so I'm very interested in getting this one to work. Last time I tried it failed miserably, but let's see what we get this time around... Hmm, OK. Well let me see now... There's a project on Sourceforge called "hSDL" which seems to be dated Apr 2005. Then there's a thing called "hsSDL" on somebody's website dated around Feb 2008. And finally on Hackage itself there's a "SDL-0.5.4" dated Apr 2008. Oh... goodie. Well, let's go with the latest date, shall we? OK, download SDL-0.5.4. Unpack. Let's see if there's any useful documentation in here... Ah, "Win32". What does that contain? Mmm, looks useful. OK, let's follow these instructions and see what I get... Need to grab libSDL... Downloaded SDL-devel-1.2.13-mingw32.tar.gz. Unpacked it to C:\SDL. OK, now what? Ooo, manually edit the Cabal file... goodie! OK, well this shouldn't be too hard... Right, now... configure... That looked OK... build... Preprocessing library SDL-0.5.4... Graphics\UI\SDL\General.hsc:1:17: SDL.h: No such file or directory Graphics\UI\SDL\General.hsc: In function `main': Graphics\UI\SDL\General.hsc:57: error: `SDL_INIT_TIMER' undeclared (first use in this function) Graphics\UI\SDL\General.hsc:57: error: (Each undeclared identifier is reported o nly once Graphics\UI\SDL\General.hsc:57: error: for each function it appears in.) Graphics\UI\SDL\General.hsc:58: error: `SDL_INIT_AUDIO' undeclared (first use in this function) Graphics\UI\SDL\General.hsc:59: error: `SDL_INIT_VIDEO' undeclared (first use in this function) Graphics\UI\SDL\General.hsc:60: error: `SDL_INIT_CDROM' undeclared (first use in ...etc... OK, that's fantastic. Now what? So where *is* SDL.H then? Ah, it's in C:\SDL\include\SDL. Maybe if I adjust the Cabal path... configure... build... OMG! It looks like that might even have worked... Haddock... install... Well, well! That seems to have worked! Right, are there any example programs with this puppy?... No, there aren't. Apparently. Well that keeps things interesting... OK, well it looks like Graphcs.UI.SDL.CPUInfo is trivial, so let's see if I can compile a short program that calls it. Right, well it compiles. Does it run? ...no. It can't find SDL.dll. Presumably if I insert that into my search path somewhere... woo! It works! :-D Right, well. I guess if I can find some nontrivial examples from somewhere, I can try this thing out properly. (Looking at the API documentation, it's not very obvious how to do anything with it...) - OK, well I guess this message is long enough already. I notice there's a brand new version of HDBC out, so tomorrow I'm going to attempt to finally make a Haskell program actually talk to a database. ;-) TO BE CONTINUED...

11 25

Fastest regex package?
by Eugene Kirpichov 07 Feb '09

07 Feb '09

Hello. What is the fastest regex package of the multitude of packages present on Hackage (namely, PCRE, PCRE-light, DFA, TDFA and many more)? My benchmark (parsing a huge logfile with a regex like "GET /foo.xml.*fooid=([0-9]++).*barid=([0-9]++)") shows that plain PCRE is the fastest one (I tried PCRE, PCRE-light and TDFA; DFA can't do capturing groups at all, TDFA was abysmally slow (about 20x slower than PCRE), and it doesn't support ++), but maybe have I missed any blazing-fast package? Even PCRE seems somewhat too slow to me - matching this regex eats 50% of the program time; considering that the only things it does is ungzipping the log and searching for the regex, this seems like far too much, the regex is not that complex to my mind. I tried to replace this regex by Data.ByteString.Search.KnuthMorrisPratt and BoyerMoore from stringsearch, but they work even twice slower. I also noticed that PCRE does about 2x fewer allocations than PCRE-Light, but is not much faster. However, PCRE, strangely, has a non-pure interface, I had to use it with unsafePerformIO. It's a pity I can't put these findings on haskellwiki to http://www.haskell.org/haskellwiki/Regular_expressions since I don't have an account and new accounts can't be created right now. Could anyone put them there? All in all, my question remains: what is the fastest way to do this kind of parsing on a lazy bytestring?

4 5

Haskell tutorial for pseudo users?
by Emil Axelsson 07 Feb '09

07 Feb '09

Hello, Are there any Haskell tutorials suitable for people who don't (and possibly don't want to) know Haskell, but just want to use an embedded language that happens to be in Haskell? Such a tutorial would focus on using libraries rather than defining them. For example, it might explain how to interpret a type signature involving type classes, but not how to write one's own type class. Thanks, / Emil

8 13

about integer and float operations
by Manlio Perillo 07 Feb '09

07 Feb '09

Hi. During some experiments with Python and Haskell I found some important differences about how some integer and float operations are implemented. The first difference is about a `mod` b, when a and b are Float types. Python use the fmod function, and it also implement divmod; Haskell seems to lack support for this operation. The second difference is about the division of two integers. Consider this Python code: >>> from __future__ import division >>> def fac(n): ... return reduce(lambda a, b: a * (b + 1), xrange(n), 1) ... >>> float(fac(777)) Traceback (most recent call last): File "<stdin>", line 1, in <module> OverflowError: long int too large to convert to float >>> fac(777) / fac(777) 1.0 Here CPython does not convert the two integers to float before to divide them, but make use of a special algorithm. GHC, instead, returns NaN I don't know if the implementations of divMod and "true" integer division in CPython are "robust", but there is some important reason why these operations are not supported in Haskell? Thanks Manlio Perillo

9 32

Re: [Haskell-cafe] Re: [Haskell-beginners] Just how unsafe is unsafe
by Roel van Dijk 07 Feb '09

07 Feb '09

On Fri, Feb 6, 2009 at 5:22 PM, Alberto G. Corona <agocorona(a)gmail.com> wrote: > then Data.List.head Data.Maybe.fromMaybe etc are also unsafe?. Yes, I consider them unsafe. Whenever I see those functions I know that I have to look elsewhere to see if their preconditions hold. I would have preferred that listToMaybe was called head and the existing head called unsafeHead, partialHead or something else of that nature. > unsafe does > not mean "with possible errors". unsafeXXX convert something in the IO monad > into something that is not. So it can potentially contaminate your pure > code. > But Data.List.head applied to a empty list will interrupt the computation > abruptly, so your code using head will either run side effect free or not > run at all. I guess what unsafe should mean is a matter of taste. Personally I find correctness more important that pureness. An unsafe function will crash your program if evaluated when its preconditions do not hold. Whether that is because of impurity (segmentation fault?), a partial pattern match or a direct error "bla" is not that important. It might be important when determining why your program crashed, but the result is still the same. The ByteString library has a module called Data.ByteString.Unsafe with plenty of unsafeXXX functions. The comment for unsafeHead for example states: "A variety of head for non-empty ByteStrings. unsafeHead omits the check for the empty case, so there is an obligation on the programmer to provide a proof that the ByteString is non-empty." That perfectly reflects my own philosophy on this issue.

2 1

Are you using Haskell on the job?
by Kirk Martinez 07 Feb '09

07 Feb '09

Hello, fellow Haskell hackers! I am writing a term paper on Haskell in Business, and while I have gathered a lot of good information on the Internet, I would really like direct feedback from software professionals who have used Haskell in a business setting. I would really appreciate a few minutes of your time to provide insights gained from applying Haskell in the real world. Who knows, this could lead to a greater adoption of Haskell in the business community! Rather than a list of Haskell's technical strengths (purity, laziness, composition, etc.), I want to get a sense of the process leading up to the decision to use Haskell for a given project and the insights gained during and after completion. I am particularly interested in questions related to *business value*: - What were the pros and cons you considered when choosing a language? Why FP? Why Haskell? - What aspects of your problem domain were most critical to making that choice? - How has using Haskell given you a competitive advantage? - How is the software development lifecycle positively/negatively affected by using Haskell as opposed to a different language? - How did you convince management to go with a functional approach? - Was the relative scarcity of Haskell programmers a problem? If so, how was it managed? - Would you choose to use Haskell again for a similar project given what you know now? The best responses will not simply list answers, but also provide background and a bit of narrative on the project and insights gained. Feel free to reply to the list, or just to me personally if you prefer. My email is below. Thank you, Kirk Martinez (Kirk dot Martinez at gmail dot com)

3 2

ANN: diagrams 0.2
by Brent Yorgey 07 Feb '09

07 Feb '09

I am very pleased to announce the 0.2 release of the diagrams package, an embedded domain-specific language for creating simple graphics in a compositional style. This release includes a number of significant new features, including: * support for arbitrary straight and curved paths * more shape primitives, including polygons and rounded rectangles * support for rendering text * PNG, PDF, PS, and SVG output * built-in color support replaced with external dependence on the feature-rich colour library and many more! More information, examples, and installation instructions can be found at http://code.haskell.org/diagrams. More features are planned for future releases, so contributions and suggestions are welcome. (Please note: since diagrams depends on the Cairo library, which has unfortunately not been Cabalized, you cannot install the diagrams library with cabal-install, unless you already have the cairo package installed. See the above website for instructions.) A special thanks to Dougal Stanton for his contributions to the library and help in preparing this release. -Brent

6 9

HGL window update problem
by Rodrigo Queiro 07 Feb '09

07 Feb '09

In this program, the HGL window only updates when I mouseover it. Can someone tell me why this is / how I should avoid it? Thanks! Rodrigo module Main where import Graphics.HGL import Control.Concurrent import Control.Concurrent.MVar import Control.Monad main = do stringMVar <- newEmptyMVar forkIO . runGraphics $ do w <- openWindowEx "HGLTest" Nothing (300, 100) DoubleBuffered Nothing forever $ do string <- takeMVar stringMVar setGraphic w $ text (0, 0) string forever $ do string <- getLine putMVar stringMVar string

1 0

Happstack 0.1 Released!
by Matthew Elder 07 Feb '09

07 Feb '09

Hello Haskell Cafe, I just wanted to inform you that the Happstack project has shipped it's 0.1 release. For those of you who don't know, Happstack is the successor for the HAppS project. More details on the release can be found at http://blog.happstack.com/2009/02/03/happstack-01-released . Thanks for your time, Matthew Elder -- Need somewhere to put your code? http://patch-tag.com Want to build a webapp? http://happstack.com

8 7

Re: [Haskell-cafe] Happstack 0.1 Released!
by Henning Thielemann 07 Feb '09

07 Feb '09

1 0

Re: [Haskell-cafe] about integer and float operations
by Henning Thielemann 07 Feb '09

07 Feb '09

1 0

Re: OpenAL
by Paul Langevin 06 Feb '09

06 Feb '09

> AL lib: alSource.c:2291: alcDestroyContext(): 1 Source(s) NOT deleted Brian, have you tried currentContext $= Nothing before closing the device ? It works for me now : no message from ALSA (and still the sounds) _________________________________________________________________ Téléphonez gratuitement à tous vos proches avec Windows Live Messenger ! Téléchargez-le maintenant ! http://www.windowslive.fr/messenger/1.asp

1 0

Re: Haddock
by David Waern 06 Feb '09

06 Feb '09

Hi everyone, I received this question from Lennart Augustsson (via Simon M) and thought I'd send out an inquiry to the Haskell community in general (Lennart, I hope you don't mind): Lennart writes: > We have some local patches for haddock that extends the <<blah>> > syntax so you can put TeX formulae in the documentation. > It looks like, <<! LaTeX stuff here !>>, but I'd like to extend it so > you can process the string with any command. > > Are you interested in folding this into the main branch? So the question is about extending the Haddock markup language. When modifying the language we should think about the tension between familiarity, presentation features (pictures, math, whatever) and visual portability across different mediums (HTML, ghci, IDE tooltips, etc). And here I should say that Haddock already supports pictures using the << url >> syntax. IMHO, adding <<! LaTeX !>> for TeX math is fine, because: - math in documentation is often useful - if you're going to write math, you need a format, even when the medium is plain text as in ghci. - TeX formulae seem to be relatively widely used and understood. As for running arbitrary commands, I think we are opening up to a lot of unfamiliar syntax. I'd like to hear what everyone thinks about that. There was also a thread about Haddock markup on haskell-cafe@ about a year ago, which originated with the interesting idea of using Markdown (or a Pandoc-extended version of it) instead of the current language: http://www.mail-archive.com/haskell-cafe@haskell.org/msg38054.html I think the original idea there is pretty nice, but let's first focus on the current markup language in order to answer Lennart's question. That thread contains some useful opinions on this matter, also. So, any comments? :) David

3 3

Mutually recursive modules
by Henning Thielemann 06 Feb '09

06 Feb '09

I have written a small overview, how mutually recursive modules are currently supported and how they can be avoided: http://haskell.org/haskellwiki/Mutually_recursive_modules Please add information about other compilers and more ideas on breaking cycles.

1 0

How to properly design a Haskell TK
by Achim Schneider 06 Feb '09

06 Feb '09

I've been thinking a bit, and come to the conclusion that we should just do it as others did it before: Start off with application-specific tk's, figure out what's cool and what's compatible and then put them into libraries. In short: Stop building cathedrals. -- (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.

5 4

Re : OpenAL
by Paul Langevin 06 Feb '09

06 Feb '09

For those who follow, I finally find the way to mix (simpler than I thought) import Sound.ALUT playSound :: IO () playSound = withProgNameAndArgs runALUT $ \ _ _ -> do ↠ buffer1 <- createBuffer $ Sine 440 0 1 ↠ buffer2 <- createBuffer $ HelloWorld ↠ [source1,source2] <- genObjectNames 2 ↠ buffer source1 $= Just buffer1 ↠ buffer source2 $= Just buffer2 ↠ play [source1,source2] ↠ sleep 2 ↠ return () main = playSound (sorry if unicode if ugly, I don't know what to do with spaces) _________________________________________________________________ Téléphonez gratuitement à tous vos proches avec Windows Live Messenger ! Téléchargez-le maintenant ! http://www.windowslive.fr/messenger/1.asp

1 0

Re : OpenAL
by Paul Langevin 06 Feb '09

06 Feb '09

by the way, a mean to get it done without error is to not use runALUTUsingCurrentContext : import Sound.ALUT playSound :: IO () playSound = withProgNameAndArgs runALUT $ \ _ _ -> do buffer1 <- createBuffer $ Sine 440 0 1 buffer2 <- createBuffer HelloWorld [source] <- genOjectNames 1 queueBuffers source [buffer1,buffer2] play [source] sleep 2 return () main = playSound I'm not sure if haskell-cafe will take spaces into account. If not, only 7 lines should be tabulated after do. Does anyone know how to mix buffers ? _________________________________________________________________ Vous voulez savoir ce que vous pouvez faire avec le nouveau Windows Live ? Lancez-vous ! http://www.microsoft.com/windows/windowslive/default.aspx

1 0

Automation and COM
by Günther Schmidt 06 Feb '09

06 Feb '09

Hi, has anyone yet been using Sigbjorns COM package? Sigbjorn hasn't had the time yet to gather some docs on how to use it, so I wonder if someone else could post some examples on how to use it. I'm asking because I need to do some COM stuff with excel, which I know how to do in another language, but can't seem to get it even started with haskell. Any help appreciated. Günther

2 1

Purely funcional LU decomposition
by Rafael Gustavo da Cunha Pereira Pinto 06 Feb '09

06 Feb '09

Hello folks After a discussion on whether is possible to compile hmatrix in Windows, I decided to go crazy and do a LU decomposition entirely in Haskell... At first I thought it would be necessary to use a mutable or monadic version of Array, but then I figured out it is a purely interactive process. I am releasing this code fragment as LGPL. {- This program is free software: you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <http://www.gnu.org/licenses/>. -} import Data.Array.IArray type Dim=(Int,Int) lu::Array Dim Double -> (Array Dim Double,Array Dim Double) lu a = (aa l,aa u) where (l,u)=lu' a [] [] aa = accumArray (+) 0 (bounds a) lu'::(Floating e) => Array Dim e -> [(Dim,e)] -> [(Dim,e)] -> ([(Dim,e)],[(Dim,e)]) lu' a l u=if (ui==li) then ( ((ui,uj),1.0):l,((ui,uj),a!(ui,uj)):u) else (lu' an (l++ln) (u++un)) where k=li ((li,lj),(ui,uj))=bounds a lik i=(a!(i,k)/a!(k,k)) un=[((k,j),a!(k,j)) | j<-[lj..uj]] ln=((lj,lj),1.0):[((i,k),lik i) | i<-[li+1..ui]] an=array ((li+1,lj+1),(ui,uj)) [((i,j),e_an i j) | i<-[li+1..ui],j<-[lj+1..uj]] e_an i j=a!(i,j)-(lik i)*a!(k,j) Still needed: 1) Partial pivoting 2) Profiling... Lots! 3) Parallelize -- Rafael Gustavo da Cunha Pereira Pinto Electronic Engineer, MSc.

7 12

Signatures in defining functions
by TKM 06 Feb '09

06 Feb '09

Hello, I'm kind of new with Haskell and I would like to know about the following: [some function]:: Int -> Int -> Int Now is my question, how should I interpret "Int -> Int -> Int"? Meaning what does "Int -> Int -> Int" mean? Thank you for answering my question. Kind Regards, JTKM

4 3

Re: OpenAL
by Paul Langevin 06 Feb '09

06 Feb '09

>Does the example code at >http://articles.bluishcoder.co.nz/Haskell/OpenAL work for anyone? sorry for the delay, Brian : I can hear the two sounds one after the other (I wish I knew how to hear them at the same time). However, I've got a strange error message from ALSA : " alsa_blitbuffer: Could not write audio data to sound device: File descriptor in bad state mixer: pcm.c:2644: snd_pcm_areas_copy: Assertion 'dst_areas' failed. " (mixer is the name of the executable (because I thought...)) OpenAL version : 1.3 ALC version : 1.0 AL version : 1.1 Ghc version : 6.6 _________________________________________________________________ Téléphonez gratuitement à tous vos proches avec Windows Live Messenger ! Téléchargez-le maintenant ! http://www.windowslive.fr/messenger/1.asp

1 0

Success (was: cURL under Windows again)
by Iliya Kuznetsov 06 Feb '09

06 Feb '09

The problem has solved. Solution, given by http://awson.livejournal.com/, is: 1. Copy libcurl-4.dll to libcurl.dll beause of namescheme 2. Before building haskell curl-1.3.4 _under windows_ you have to change #define CURL_EXTERN __declspec(dllimport) to #define CURL_EXTERN. After that, curl-7.19.3 and curl-1.3.4 work fine. ---------- Forwarded message ---------- From: Iliya Kuznetsov <iliya.kuznetsov(a)gmail.com> Date: 2009/2/2 Subject: cURL under Windows again To: haskell-cafe(a)haskell.org Hello cafe-subscribers, I saw some issues about installing haskell bindings for cURL under Windows, and now I'm trapped too. So, here is actions' log for everything (very detail; you can PgDn to the end with questions): 1. Windows Vista without UAC 2. ghc-6.10.1-i386-windows.exe is installed to C:\Program Files\Haskell "C:\Program Files\Haskell\package.conf" wasn't touched after installation (Cabal nor manually) 3. MinGW-5.1.4 installed to C:\temp\MinGW 4. MSys-1.0 installed to C:\temp\msys\1.0\ 5. curl-7.19.3.tar.bz2 had taken from http://curl.haxx.se/download/curl-7.19.3.tar.bz2 6. Under msys, curl-7.19.3.tar.bz2 is untared into /home/Kuznetsov/curl-7.19.3 7. cURL is made as: cd curl-7.19.3 $ ./configure configure: Configured to build curl/libcurl: ... curl version: 7.19.3 Host setup: i686-pc-mingw32 Install prefix: /usr/local Compiler: gcc SSL support: no (--with-ssl / --with-gnutls) SSH support: no (--with-libssh2) zlib support: no (--with-zlib) krb4 support: no (--with-krb4*) GSSAPI support: no (--with-gssapi) SPNEGO support: no (--with-spnego) c-ares support: no (--enable-ares) ipv6 support: no (--enable-ipv6) IDN support: no (--with-libidn) Build libcurl: Shared=yes, Static=yes Built-in manual: no (--enable-manual) Verbose errors: enabled (--disable-verbose) SSPI support: no (--enable-sspi) ca cert bundle: no ca cert path: no LDAP support: enabled (winldap) LDAPS support: no (--enable-ldaps) $ make ... make[2]: Leaving directory `/home/Kuznetsov/curl-7.19.3/src' make[1]: Leaving directory `/home/Kuznetsov/curl-7.19.3/src' make[1]: Entering directory `/home/Kuznetsov/curl-7.19.3' make[1]: Nothing to be done for `all-am'. make[1]: Leaving directory `/home/Kuznetsov/curl-7.19.3' $ make install ... libtool: install: /bin/install -c .libs/libcurl.dll.a /usr/local/lib/libcurl.dll.a libtool: install: base_file=`basename libcurl.la` libtool: install: dlpath=`/bin/sh 2>&1 -c '. .libs/'libcurl.la'i; echo libcurl-4.dll'` libtool: install: dldir=/usr/local/lib/`dirname ../bin/libcurl-4.dll` libtool: install: test -d /usr/local/lib/../bin || mkdir -p /usr/local/lib/../bin libtool: install: /bin/install -c .libs/libcurl-4.dll /usr/local/lib/../bin/libcurl-4.dll libtool: install: chmod a+x /usr/local/lib/../bin/libcurl-4.dll libtool: install: if test -n '' && test -n 'strip --strip-unneeded'; then eval 'strip --strip-unneeded /usr/local/lib/../bin/libcurl-4.dll' || exit 0; fi libtool: install: /bin/install -c .libs/libcurl.lai /usr/local/lib/ libcurl.la libtool: install: /bin/install -c .libs/libcurl.a /usr/local/lib/libcurl.a libtool: install: chmod 644 /usr/local/lib/libcurl.a libtool: install: ranlib /usr/local/lib/libcurl.a ---------------------------------------------------------------------- Libraries have been installed in: /usr/local/lib If you ever happen to want to link against installed libraries in a given directory, LIBDIR, you must either use libtool, and specify the full pathname of the library, or use the `-LLIBDIR' flag during linking and do at least one of the following: - add LIBDIR to the `PATH' environment variable during execution - add LIBDIR to the `LD_RUN_PATH' environment variable during linking - use the `-LLIBDIR' linker flag ... /bin/install -c -m 644 'curl.h' '/usr/local/include/curl/curl.h' /bin/install -c -m 644 'curlver.h' '/usr/local/include/curl/curlver.h' /bin/install -c -m 644 'easy.h' '/usr/local/include/curl/easy.h' /bin/install -c -m 644 'mprintf.h' '/usr/local/include/curl/mprintf.h' /bin/install -c -m 644 'stdcheaders.h' '/usr/local/include/curl/stdcheaders.h' /bin/install -c -m 644 'types.h' '/usr/local/include/curl/types.h' /bin/install -c -m 644 'multi.h' '/usr/local/include/curl/multi.h' /bin/install -c -m 644 'typecheck-gcc.h' '/usr/local/include/curl/typecheck-gcc.h' /bin/install -c -m 644 'curlbuild.h' '/usr/local/include/curl/curlbuild.h' /bin/install -c -m 644 'curlrules.h' '/usr/local/include/curl/curlrules.h' ... 8. $ which curl && curl /usr/local/bin/curl curl: try 'curl --help' for more information I have following files in C:\temp\msys\1.0\local\bin\ (/usr/local/bin in Unix-scheme): 02.02.2009 15:10 4 029 curl-config 02.02.2009 15:10 98 591 curl.exe 02.02.2009 15:09 262 934 libcurl-4.dll In /usr/local/include/curl ten includes: 02.02.2009 15:10 67 183 curl.h 02.02.2009 15:10 5 865 curlbuild.h 02.02.2009 15:10 7 478 curlrules.h 02.02.2009 15:10 2 799 curlver.h 02.02.2009 15:10 3 526 easy.h 02.02.2009 15:10 2 850 mprintf.h 02.02.2009 15:10 13 039 multi.h 02.02.2009 15:10 1 383 stdcheaders.h 02.02.2009 15:10 33 337 typecheck-gcc.h 02.02.2009 15:10 15 types.h ---- Sorry for many details, but now I can show the wrong behaviour of the haskell bindings for cURL under windows: 9. curl-1.3.4 is taken from hackage and unzipped to /home/Kuznetsov $ cd ~/curl-1.3.4 $ runhaskell Setup.hs configure --extra-include-dirs=/usr/local/include --extra-lib-dirs=/usr/local/lib Configuring curl-1.3.4... $ runhaskell Setup.hs build Preprocessing library curl-1.3.4... Building curl-1.3.4... [1 of 8] Compiling Network.Curl.Debug ( Network\Curl\Debug.hs, dist\build\Network\Curl\Debug.o ) [2 of 8] Compiling Network.Curl.Types ( Network\Curl\Types.hs, dist\build\Network\Curl\Types.o ) [3 of 8] Compiling Network.Curl.Post ( Network\Curl\Post.hs, dist\build\Network\Curl\Post.o ) [4 of 8] Compiling Network.Curl.Opts ( Network\Curl\Opts.hs, dist\build\Network\Curl\Opts.o ) [5 of 8] Compiling Network.Curl.Code ( Network\Curl\Code.hs, dist\build\Network\Curl\Code.o ) [6 of 8] Compiling Network.Curl.Info <http://network.curl.info/> ( Network\Curl\Info.hs, dist\build\Network\Curl\Info.o ) Network\Curl\Info.hs:80:0: Warning: Defined but not used: `stringTag' Network\Curl\Info.hs:83:0: Warning: Defined but not used: `longTag' Network\Curl\Info.hs:86:0: Warning: Defined but not used: `doubleTag' Network\Curl\Info.hs:89:0: Warning: Defined but not used: `slistTag' [7 of 8] Compiling Network.Curl.Easy ( Network\Curl\Easy.hs, dist\build\Network\Curl\Easy.o ) [8 of 8] Compiling Network.Curl ( Network\Curl.hs, dist\build\Network\Curl.o ) C:\Program Files\Haskell\bin\ar.exe: creating dist\build\libHScurl-1.3.4.a $ runhaskell Setup.hs install Installing library in C:\Program Files\Haskell\curl-1.3.4\ghc-6.10.1 Registering curl-1.3.4... Reading package info from "dist\\installed-pkg-config" ... done. Writing new package config file... done. 10. In package.conf I have seen: InstalledPackageInfo {package = PackageIdentifier {pkgName = PackageName "curl", pkgVersion = Version {versionBranch = [1,3,4], versionTags = []}}, license = BSD3, copyright = "", maintainer = "Sigbjorn Finne < sigbjorn.finne(a)gmail.com>", author = "Sigbjorn Finne", stability = "", homepage = "", pkgUrl = "", description = "libcurl is a client-side URL transfer library, supporting FTP, FTPS, HTTP,\nHTTPS, SCP, SFTP, TFTP, TELNET, DICT, LDAP, LDAPS and FILE.\nlibcurl supports SSL certificates, HTTP POST, HTTP PUT, FTP uploading,\nHTTP form based upload, proxies, cookies, user+password authentication\n(Basic, Digest, NTLM, Negotiate, Kerberos4), file transfer resume,\nhttp proxy tunneling and more!\n\nThis package provides a Haskell binding to libcurl.", category = "Network", exposed = True, exposedModules = ["Network.Curl","Network.Curl.Code"," Network.Curl.Info <http://network.curl.info/>","Network.Curl.Opts","Network.Curl.Post","Network.Curl.Types","Network.Curl.Easy","Network.Curl.Debug"], hiddenModules = [], importDirs = ["C:\\Program Files\\Haskell\\curl-1.3.4\\ghc-6.10.1"], libraryDirs = ["C:\\Program Files\\Haskell\\curl-1.3.4\\ghc-6.10.1","C:/temp/msys/1.0/local/lib"], hsLibraries = ["HScurl-1.3.4"], extraLibraries = ["curl"], extraGHCiLibraries = [], includeDirs = ["C:/temp/msys/1.0/local/include"], includes = [], depends = [PackageIdentifier {pkgName = PackageName "base", pkgVersion = Version {versionBranch = [3,0,3,0], versionTags = []}},PackageIdentifier {pkgName = PackageName "bytestring", pkgVersion = Version {versionBranch = [0,9,1,4], versionTags = []}},PackageIdentifier {pkgName = PackageName "containers", pkgVersion = Version {versionBranch = [0,2,0,0], versionTags = []}}], hugsOptions = [], ccOptions = [], ldOptions = [], frameworkDirs = [], frameworks = [], haddockInterfaces = ["C:\\Program Files\\Haskell\\doc\\curl-1.3.4\\html\\curl.haddock"], haddockHTMLs = ["C:\\Program Files\\Haskell\\doc\\curl-1.3.4\\html"]} In "C:\Program Files\Haskell\curl-1.3.4\ghc-6.10.1\" I have seen HScurl-1.3.4.o , libHScurl-1.3.4.a and other Curl files. 11. Final tests: under msys: $ ghci Prelude> :m Network.Curl module `Network.Curl' is not loaded Bad, but not a disaster. under windows: C:\> ghci GHCi, version 6.10.1: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer ... linking ... done. Loading package base ... linking ... done. Prelude> :m Network.Curl Prelude Network.Curl> let a = curlGet Loading package syb ... linking ... done. Loading package base-3.0.3.0 ... linking ... done. Loading package array-0.2.0.0 ... linking ... done. Loading package containers-0.2.0.0 ... linking ... done. Loading package bytestring-0.9.1.4 ... linking ... done. Loading package curl-1.3.4 ... <interactive>: curl: Не найден указанный модуль. (text in russian here because of localized Vista. The message is near "Can't load specified module") can't load .so/.DLL for: curl (addDLL: could not load DLL) Prelude Network.Curl> So, the question is why curl doesn't work? I tried to use Cabal but it failed with building too. How can I test the fact that C:\temp\msys\1.0\local\bin\libcurl-4.dll is used in curl-1.3.4 ? -- Iliya Kuznetsov +7-916-878-75-70 -- Iliya Kuznetsov +7-916-878-75-70

1 0

build problems on Hackage
by Wolfgang Jeltsch 06 Feb '09

06 Feb '09

Hello all, alas, I couldn’t found any information about who is responsible for the build system on Hackage. So I address this issue to all of you. type-level built fine with GHC 6.8 but failed to build with GHC 6.10. The last line of the build log is this: > haddock: internal Haddock or GHC error: Maybe.fromJust: Nothing The complete log is at <http://tinyurl.com/as67x5>. This problem has the unfortunate consequence that type-equality-check cannot be built since it depends on type-level and nowadays only GHC 6.10 seems to be used for building packages on Hackage. This, in turn, will make almost all Grapefruit packages unbuildable when they are released (which is expected to happen soon). This, in turn, means almost no Grapefruit documentation on Hackage which, I think, would be very bad. So could someone please take the time and fix this problem soon? Thank you in advance. Best wishes, Wolfgang

3 8

RE: Define variable types
by Tsunkiet Man 06 Feb '09

06 Feb '09

Hello, thank you guys for your responds. I got it working now =). Thanks a lot! Greetx JTKM

1 0

Re: [Haskell-cafe] Purely funcional LU decomposition
by Henning Thielemann 05 Feb '09

05 Feb '09

2 1

Re: [Haskell-cafe] Purely funcional LU decomposition
by Henning Thielemann 05 Feb '09

05 Feb '09

1 0

Re: [Haskell-cafe] Bytestrings vs String? parameters within package names?
by Henning Thielemann 05 Feb '09

05 Feb '09

1 0

Define variable types
by Tsunkiet Man 05 Feb '09

05 Feb '09

Hello, I'm new to Haskell and it seems like a very nice language to learn. However I'm not really familiar with the errormessages it produces. I am using a Helium interpreter. I've created the following module (however it is just a small sketch). I've written the following code: fac :: Int -> Int fac n = product[1..n] boven :: Int -> Int -> Int boven n k = (fac n) `div` fac k * fac (n-k) bin :: Int -> Int -> Int -> Int bin n k p |(n-k)>0 && k>0 = (boven n k) * (p^k) * (1-p)^(n-k) |(n-k)<0 && k>0 = (boven n k) * (p^k) * (1/((1-p)^(-(n-k)))) |(n-k)<0 && k<0 = (boven n k) * (1/(p^(-k))) * (1/((1-p)^(-(n-k)))) When I load this into my interpreter it says: Compiling ./Test.hs (11,55): Type error in infix application expression : 1 / ((1 - p) ^ (-(n - k))) operator : / type : Float -> Float -> Float does not match : Int -> Int -> Int (12,47): Type error in infix application expression : 1 / (p ^ (-k)) operator : / type : Float -> Float -> Float does not match : Int -> Int -> a (12,62): Type error in infix application expression : 1 / ((1 - p) ^ (-(n - k))) operator : / type : Float -> Float -> Float does not match : Int -> Int -> a Compilation failed with 3 errors Some details that might be usefull: Line 11 is |(n-k)<0 && k>0 = (boven n k) * (p^k) * (1/((1-p)^(-(n-k)))) Line 12 is |(n-k)<0 && k<0 = (boven n k) * (1/(p^(-k))) * (1/((1-p)^(-(n-k)))) So my question is: how can I fix these errors? (I used these lines of codes because it is not possible to use a negative exponent in the Helium interpreter.) Thank you for answering my question! Greetings JTKM

6 5

Crash using GHCi and GHC API under Windows
by Peter Verswyvelen 05 Feb '09

05 Feb '09

We have a program that uses the GHC API to dynamically compile and run new code. We're using GHC 6.10.1 Under GHCi it works fine under OSX, but when running it on Windows, I get Loading package ghc-prim ... GHCi runtime linker: fatal error: I found a duplicate definition for symbol _hs_gtWord64 whilst processing object file C:\app\ghc-6.10.1\ghc-prim-0.1.0.0\HSghc-prim-0.1.0.0.o This could be caused by: * Loading two different object files which export the same symbol * Specifying the same object file twice on the GHCi command line * An incorrect `package.conf' entry, causing some object to be loaded twice. GHCi cannot safely continue in this situation. Exiting now. Sorry. When compiling the program using GHC --make, it runs fine Is this a know issue? Other people encountered this? Thanks, Peter

1 0

darcs send errors that I don't understand ....
by Galchin, Vasili 05 Feb '09

05 Feb '09

Shall I send this patch? (1/1) [ynWvpxqadjk], or ? for help: y Error in execvp: No such file or directory darcs: timer_settime: Invalid argument Failed to execute external command: /usr/sbin/sendmail -i -t Lowlevel error: execvp: Illegal seek Redirects: (File "/home/vigalchin/FTP/Ketil/biolib/darcsOuDSC9",Null,AsIs) Can anybody help me on the errors above? (The /usr/sbin/sendmail I think I understand ... probably haven't set up sendmail yet). Kind regards, Vasili

2 1

pure crisis :)
by Bulat Ziganshin 05 Feb '09

05 Feb '09

Hello haskell-cafe, pure functional denotation for crisis: (_|_) -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com

6 5

Open unqualified imports
by eyal.lotem＠gmail.com 05 Feb '09

05 Feb '09

Hi, I would like to suggest a change to Haskell prime's handling of imports. First, let me define a few terms: Qualified import: import qualified Data.Map [as Map] Closed-unqualified import: import Data.Map(Map, lookup) Open-unqualified import: import Data.Map I believe that the last type, open-unqualified is a really bad idea, and should be discouraged or even disallowed. It should definitely not be the default, like it is today. These are my reasons: A) Most importantly, reading code that has even a few open unqualified imports makes deciphering where names are coming from really difficult. The other two forms make it really easy. Code is read more often than it is written -- lets optimize for the reading case. B) Code that has open unqualified imports may break when new symbols are added to the libraries its importing. This means that libraries cannot even be considered backwards compatible if they retain semantics, but add new exported names. C) In my experience, Haskell modules can map their semantics to standard type-classes such as Monoid, Functor, Applicative, etc. This means that many Haskell modules can do without exporting many names. Sometimes, they can export no names at all (Only instances). This means that closed-unqualified imports often do just fine. When there are many exported names, qualified imports are good. ----------------- I think currently many modules are designed to be imported unqualified, and this is unfortunate. Haskell' libraries can fix this. For example, the various Monadic counterparts such as mapM, replicateM, etc could do without the "M" in their names, and one could use: import qualified Control.Monad as M M.for M.map and so on. Additionally, I think there are some strong sentiments against the choice of the function-composition dot as the qualified module name lookup symbol. It discourages people from using qualified imports. Some other symbol ought to be used, but its not clear which symbol is free. Perhaps if unicode operators are allowed, then function composition can move to the "right" symbol. I believe qualified imports should probably have this syntax: import Control.Monad as M Closed-qualified imports can remain in the same syntax. Open-qualified imports should probably be discouraged with a syntax like: import unqualified Control.Monad And symbol clashes with these should probably just always choose the overriding name. Additionally, it would be nice if open unqualified imported were considered quick&dirty enough for -Wall to warn that they generate name clashes or are more difficult to read, to further discourage them. Eyal

8 9

Temporarily overriding Data.Generics
by Deniz Dogan 05 Feb '09

05 Feb '09

Hi I'm currently working on "hacking" Data.Generics for my master thesis. I'm basically trying to find out whether it can be made a bit faster using e.g. rewrite rules. The problem I'm having is that I need an easy way to import my own modified version of Data.Generics (currently located in the same directory as my testing program) without unregistering or hiding syb-0.1.0.0 as base seems to depend on it. I've read the GHC user manual trying to find nice ways to do this using a bunch of different parameters to ghc, but I can't figure it out. Does anyone here know? Any help appreciated, Deniz

2 1

Elegant & powerful replacement for CSS
by Conal Elliott 05 Feb '09

05 Feb '09

[Spin-off from the haskell-cafe discussion on functional/denotational GUI toolkits] I've been wondering for a while now what a well-designed alternative to CSS could be, where well-designed would mean consistent, composable, orthogonal, functional, based on an elegantly compelling semantic model (denotational). - Conal

11 15

Data Parallel Haskell Question
by James Swaine 05 Feb '09

05 Feb '09

I am somewhat of a beginner with DPH and wanted to ask a few (maybe elementary) questions. There appear to be two main libraries - regular and unlifted. I was a little unclear on the difference between the two and was hoping to get some clarification. If you use the 'regular' api, it seems that you can use the sort of 'syntactic sugar' language extensions (e.g. [: blah blah :]), but you are restricted to the somewhat limited Prelude explicitly written for use with code that is to be vectorised. If you use the 'unlifted' libraries, are you able to use functions/types from the standard Prelude? My problem is that I want to write a recursively-subdividing radix sort (for integer keys), where on each iteration I partition my keys into separate sets based on whether a certain bit is set or not. So I start with the most significant digit bit (say 31), and then work down to the least significant digit. I can write this in DPH just fine, but I'm getting 'panic' errors when I attempt to compile, and I wonder if it has something to do with the fact that I'm using the standard Data.Bits to inspect bits of each key. {-# LANGUAGE PArr, ParallelListComp #-} {-# OPTIONS -fvectorise #-} module RankPar(radix_sort) where import qualified Prelude import Data.Array.Parallel.PArray (fromList) import Data.Array.Parallel.Prelude ((+:+), fromPArrayP, not) import Data.Array.Parallel.Prelude.Int import Data.Bits {-# NOINLINE radix_sort #-} radix_sort :: Int -> [:Int:] -> [:Int:] radix_sort (-1) keys = keys radix_sort bit [:k:] = [:k:] radix_sort bit [: :] = [: :] radix_sort bit keys = (radix_sort (bit - 1) left) +:+ (radix_sort (bit - 1) right) where right = [: x | x <- keys, (testBit x bit) :] left = [: y | y <- keys, (not (testBit y bit)) :] Syntactically, this looks correct to me, but won't compile. Any ideas? Thanks all! -James

1 0

ANN: UrlDisp, a friendly URL dispatching library
by Artyom Shalkhakov 04 Feb '09

04 Feb '09

Hello, I would like to announce the first release of UrlDisp. <http://hackage.haskell.org/cgi-bin/hackage-scripts/package/UrlDisp> It's a small library for URL dispatching (aka routing). Right now it works with CGI, and should be compatible with FastCGI as well (not tested). Happstack compatibility is planned. Documentation and usage examples are available at HaskellWiki: <http://www.haskell.org/haskellwiki/UrlDisp> Thanks to Sterling Clover for his HVAC; this is where inspiration came from. Cheers, Artyom Shalkhakov.

1 0

ANN: #haskell-in-depth IRC channel
by Philippa Cowderoy 04 Feb '09

04 Feb '09

Hi folks. As I've been daft enough to get a few things rolling, it looks like it's fallen on me to announce the new IRC channel, #haskell-in-depth. #haskell has been a roaring success over the last few years, as Don has repeatedly pointed out. Unfortunately that roar is starting to make it hard for some to participate - there's so much traffic that it can be difficult to fit an additional conversation in. We're starting to hit the limits as to how far one channel can take us, and that means we need to explore ways to divide up traffic. Actually, this isn't entirely new - a number of years ago now, #haskell-blah was formed as a space for off-topic (and sometimes less-than-worksafe) conversation among #haskell regulars. We also created #haskell-overflow, but it doesn't see much use except among some of the cabal implementors because it's hard to know when to take the conversation you're currently in to -overflow. We need channels that people start their conversations in, not ones to send people to! So we're trying a space for in-depth discussion. The new channel is open to everyone, just like #haskell. But just as we're hoping for certain kinds of discussion, there're others we want to avoid. If you need to know how to use monads so you can do IO, #haskell-in-depth isn't the place. On the other hand, if you want to discuss how Haskell's monads compare to the category theory or what the category theory can tell us about how individual monads relate to the language as a whole, -in-depth is a good place! In particular, we're hoping that the kind of category theory discussions that give the mistaken impression you actually need to know CT will increasingly live in #haskell-in-depth. We're not after a theory channel though - architectural discussion, compiler implementation, possible type system extensions, library design, all are good subjects. Anyway, I shouldn't ramble on for too long here - #haskell-in-depth is open for business and we look forward to seeing you there! -- Philippa Cowderoy <flippa(a)flippac.org>

6 6

circular dependencies in cabal
by Valentyn Kamyshenko 04 Feb '09

04 Feb '09

Hello all, when I tried to install plugins package with cabal, I've got the following error: # sudo cabal install plugins --global Resolving dependencies... cabal: dependencies conflict: ghc-6.10.1 requires process ==1.0.1.1 however process-1.0.1.1 was excluded because ghc-6.10.1 requires process ==1.0.1.0 It looks like both versions of process package are currently required: # ghc-pkg unregister process-1.0.1.0 ghc-pkg: unregistering process-1.0.1.0 would break the following packages: haddock-2.3.0 ghc-6.10.1 Cabal-1.6.0.1 gnuplot-0.2 pandoc-1.0.0.1 Graphalyze-0.5 haddock-2.4.1 kibro-0.4.2 panda-2008.11.7 (use --force to override) # ghc-pkg unregister process-1.0.1.1 ghc-pkg: unregistering process-1.0.1.1 would break the following packages: haddock-2.3.0 ghc-6.10.1 haskell-src-1.0.1.3 polyparse-1.1 Graphalyze-0.5 cpphs-1.6 hscolour-1.10.1 haddock-2.4.1 HaXml-1.19.4 hcheat-2008.11.6 rss-3000.1.0 kibro-0.4.2 panda-2008.11.7 haskell98-1.0.1.0 hxt-8.2.0 hcheat-2008.11.14 hxt-filter-8.2.0 xml- parsec-1.0.3 graphviz-2008.9.20 readline-1.0.1.0 uulib-0.9.5 derive-0.1.4 hslogger-1.0.6 MissingH-1.0.2.1 HStringTemplateHelpers-0.0.3 HSHHelpers-0.17 haskell-src-exts-0.4.4 haskell-src-exts-0.4.4.1 haskell-src-exts-0.4.5 ConfigFile-1.0.4 HStringTemplateHelpers-0.0.4 haskell-src-exts-0.4.6 kibro-0.4.3 panda-2008.12.16 HStringTemplateHelpers-0.0.6 SybWidget-0.4.0 wxcore-0.10.5 wx-0.10.5 xtc-1.0 HStringTemplateHelpers-0.0.8 wxcore-0.10.7 wx-0.10.6 HNM-0.1 HNM-0.1.1 wxcore-0.10.12 wxcore-0.11.0 wx-0.11.0 HSHHelpers-0.18 haskell-src-exts-0.4.8 darcs-2.2.0 hslogger-1.0.7 MissingH-1.0.3 HSH-1.2.6 HStringTemplateHelpers-0.0.10 HSHHelpers-0.19 hscolour-1.11 HNM-0.1.2 pandoc-1.1 mps-2008.11.6 hcheat-2008.11.25 panda-2009.1.20 testpack-1.0.0 convertible-1.0.1 gnuplot-0.3 HDBC-2.0.0 HDBC-2.0.1 HDBC-sqlite3-2.0.0.0 HDBC- postgresql-2.0.0.0 (use --force to override) Any suggestions? -- Valentyn

5 11

type metaphysics
by Gregg Reynolds 04 Feb '09

04 Feb '09

Hi, The concept of "type" seems to be a little like porno: I know it when I see it, but I can't define it (apologies to Justice Stewart). I've picked through lots of documents that discuss types in various ways, but I have yet to find one that actually says what a type "really" is. For example, definitions of the typed lambda calculus usually define some type symbols and rules like "a : T means a is of type T", and then reasoning ensues without discussion of what "type" means. The only discussion I've found that addresses this is at the Stanford Encyclopedia of Philosophy, article "Types and Tokens" [1]. It's all very philosophical, but there is one point there that I think has relevance to Haskell. It's in section 4.1, discussing the distinction between types and sets: "Another closely related problem also stems from the fact that sets, or classes, are defined extensionally, in terms of their members. The set of natural numbers without the number 17 is a distinct set from the set of natural numbers. One way to put this is that classes have their members essentially. Not so the species homo sapiens, the word 'the', nor Beethoven's Symphony No. 9. The set of specimens of homo sapiens without George W. Bush is a different set from the set of specimens of homo sapiens with him, but the species would be the same even if George W. Bush did not exist. That is, it is false that had George W. Bush never existed, the species homo sapiens would not have existed. The same species might have had different members; it does not depend for its existence on the existence of all its members as sets do." So it appears that one can think of a type as a predicate; any token (value?) that satisfies the predicate is a token (member?) of that type. This gives a very interesting way of looking at Haskell type constructors: a value of (say) Tcon Int is anything that satisfies "isA Tcon Int". The tokens/values of Tcon Int may or may not constitute a set, but even if they, we have no way of describing the set's extension. My hunch is that it /cannot/ be a set, although I'm not mathematician enough to prove it. My reasoning is that we can define an infinite number of data constructors for it, including at least all possible polynomials (by which I mean data constructors of any arity taking args of any type). To my naive mind this sounds suspiciously like the set of all sets, so it's too big to be a set. In any case, Tcon Int does not depend on any particular constructor, just as homo sapiens does not depend on any particular man. So it can't be a set because it doesn't have its members essentially. (I suspect this leads to DeepThink about classical v. constructivist mathematics, but that's a subject for a different discussion.) I'm not sure that works technically, but it seems kinda cool. My question for the list: is the collection of e.g. Tcon Int values a set, or not? If it is, how big is it? Thanks, gregg [1] http://plato.stanford.edu/entries/types-tokens/

21 43

Converting Lists to Sets
by rodrigo.bonifacio 04 Feb '09

04 Feb '09

Hi all, I'm trying to use the Funsat library. One of its data types is CNF: data CNF = CNF { numVars :: Int numClauses :: Int clauses :: Set Clause } I have a list of clauses, but I'm getting an error when converting such a list to a Set. Using the fromList function, the ghc compiler reports that the fromList function is not applicable to literals. type Clause = [Lit] newtype Lit = L { unLit :: Int } So, my question is: How can I solve this problem? Thanks in advance, Rodrigo.

4 3

Re: [Haskell-cafe] Elegant & powerful replacement for CSS
by Patai Gergely 04 Feb '09

04 Feb '09

> I've been wondering for a while now what a well-designed alternative > to CSS could be, where well-designed would mean consistent, composable, > orthogonal, functional, based on an elegantly compelling semantic model > (denotational). Well, if you think about CSS as in webpage styling, it's simply a way to override some attributes in the DOM tree. If you will, you can easily relate CSS selectors to your semantic editor combinators, since a concrete stylesheet makes explicit references to the structure of the document/interface it is associated with. One important difference is that in the case of CSS you don't need to mention all the intermediate nodes explicitly, which can make selectors shorter as well as "non-deterministic", i.e. they can match different structural patterns at the same time. Also, you can perform a kind of pattern matching (filtering by class/id names) besides just blindly walking down the tree along the type structure. I'd say these two features make it a direct generalisation of the SEC concept. Gergely -- http://www.fastmail.fm - The way an email service should be

2 1

Bytestrings vs String?
by Marc Weber 04 Feb '09

04 Feb '09

A lot of people are suggesting using Bytestrings for performance, strictness whatsoever reasons. However how well do they talk to other libraries? One I've in mind is hslogger right now. Should hslogger be implemented using Strings or Bytestrings ? Should there be two versions? hslogger-bytestring and hslogger-string? Or would it be better to implement one String class which can cope with everthing (performance will drop, won't it?) I feel it would make sense to talk about how to provide this? In the future I'd like to explore using haskell for web developement. So speed does matter. And I don't want my server to convert from Bytestrings to Strings and back multiple times.. So is the best we could do compile the same library twice using different flags ? One providing a Bytestring API, the other using Strings? Cluttering up code by from to Bytestring conversions doesn't look compelling to me. Thoughts? Marc Weber

4 6

Why binding to existing widget toolkits doesn't make any sense
by Achim Schneider 04 Feb '09

04 Feb '09

Hacking away on bindings to (http://libagar.org) specifically (http://libagar.org/mdoc.cgi?man=AG_Object.3) I was suddenly swept away by a general crisis of purpose: I was spending time on figuring out how to create agar objects, implemented in Haskell, on the fly, to enable me to write a high-level interface, instead of spending time on designing The FRUI API To Obsolete Them All. The reason for this are means of composability: What use is a nice interface to a button and an isomorphic interface to a textbox, if I can't compose them properly? Users might want to use standard widgets in indefinitely many combinations of type, with an equal amount of distinct wirings and external interfaces. As some of you might have noticed [1][2], constructing foreign objects is painful, specifying custom classes even more so... in case it's not infeasible hard to support in the first place. In agar's case it's certainly possible, by the virtue of being implemented in plain C. So we _could_ expose the whole generality of a TK's means of composing to the user. Which is most likely not what he wants, he wants to use the whole generality of Haskell to compose UI's. In Agar's case, the user won't care much about generating N checkboxes for a bitfield integer, he'd rather use [Event Bool]. Summing up, there's a lot of plumbing to be done, in the end still amounting to a lot of dead, unused code in the TK, BECAUSE TOOLKITS ARE DESIGNED TO BE USED IN THE LANGUAGE THEY WERE BLEEDING WRITTEN IN AND PROVIDE CUSTOM ABSTRACTIONS TAILORED TO THAT LANGUAGE. This is basically the Saphir-Worph hypothesis adapted to programs. So what's left of those TK's if we don't use their abstractions and replace them with Haskell? Drawing and layouting, that's what's left[3]. Both, IMNSHO, do not justify carrying around bloaty external dependencies, they're too trivial. They certainly don't justify using unsafePerformIO to hide foreign side effects and the headaches associated with it. So, if you don't mind, I'm going to stop trying to fit cubes into round holes and gonna use reactive and fieldtrip[4] to do things. [1]http://softbase.org/hqk/qoo/qoo.pdf [2]http://haskell.org/gtk2hs/docs/devel/System-Glib-GObject.html#v%3AmakeNew… [3]Somewhat disregarding using OS widgets, but that's unimportant since native look+feel is vastly overrated. I've got enough asbestos to defend that against alt.politics. [4]Gotta get rid of glut, though. -- (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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Re: Why binding to existing widget toolkits doesn't make any sense
by John A. De Goes 04 Feb '09

04 Feb '09

CSS is purely declarative in nature and entirely deterministic. Moreover, it's expressive power is such that you can completely and radically alter the look of a website with modifications to CSS alone (see Zen Garden). The grammar and semantics are relatively simple and can be interpreted and generated by tools, which means that a designer can work with CSS files without knowing anything about CSS. Is it perfect? No. But it's a lot better than trying to encode everything in a single language that only a software developer can safely work with. Regards, John A. De Goes N-BRAIN, Inc. The Evolution of Collaboration http://www.n-brain.net | 877-376-2724 x 101 On Feb 3, 2009, at 10:09 AM, Peter Verswyvelen wrote: > On Tue, Feb 3, 2009 at 5:49 PM, John A. De Goes <john(a)n-brain.net> > wrote: > I never said, "CSS", I said "like CSS". > > Oh, I missed the "like" word! What do you mean with that? What > aspects of CSS do you prefer to? In WPF a "style" is basically just > a bunch of attribute key/value pairs. > > > Layout combinators in the spirit of TeX or Lout are more > flexible while being simpler. In any case, a simple primitive > > grid :: [[Rect a]] -> Rect a > > that arranges widgets in a rectangular grid should be enough for GUIs. > > > Spoken like a true programmer who knows nothing about usability. :-) > > Yes, layout must be very versatile and user definable. > > > > Regards, > > John A. De Goes > N-BRAIN, Inc. > The Evolution of Collaboration > > http://www.n-brain.net | 877-376-2724 x 101 > > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe >

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