- Haskell-Cafe - Haskell.org

Histogram creation
by Alexey Khudyakov 11 Nov '08

11 Nov '08

Hello! I'm tryig to write efficient code for creating histograms. I have following requirements for it: 1. O(1) element insertion 2. No reallocations. Thus in place updates are needed. accumArray won't go because I need to fill a lot of histograms (hundrends) from vely long list of data (possibly millions of elements) and it will traverse input data for each histogram. It seems that I need to use mutable array and/or ST monad or something else. Sadly both of them are tricky and difficult to understand. So good examples or any other ideas greatly appreciated. -- Alexey Khudyakov

5 5

Closed type classes [was: Exporting a Type Class for Type Signatures]
by oleg＠okmij.org 11 Nov '08

11 Nov '08

Dominic Steinitz wrote: > In the crypto package, I have two functions > > encrypt :: AESKey a => a -> Word128 -> Word128 > > decrypt :: AESKey a => a -> Word128 -> Word128 but the class AESKey is not exported, to prevent the user from adding more instances to it. Since AESKey is not exported, the users cannot write signatures that mention that class constraint. The question is, how to export a _closed_ class -- a class the user cannot extend. Chung-chieh Shan and I had a similar problem in our TFP2007 paper: the classes that implement type-level arithmetic must be closed, to prevent the user from declaring that 1+1=1. It seems the best method is to use class aliases: In the implementation of AES, introduce class AESKey a => AESKeyExport a instance AESKey a => AESKeyExport a -- the only instance and now export AESKeyExport (but leave AESKey hidden). If the user needs to write the signature for their function: foo :: AESKeyExport a => a -> Word128 -> Word128 foo x y = encrypt x y they should use the constraint AESKeyExport a. That constraint entails AESKey a, which they cannot mention. The users can try to extend the class ESKeyExport a, but that would do them no good: the library uses the instances of AESKey rather than AESKeyExport. The TFP2007 paper explains that in a bit more detail: http://okmij.org/ftp/Computation/resource-aware-prog/tfp.pdf (Section 2.1). It also mentions a different method, relying on partial type signatures.

1 0

A video of Frag
by Korcan Hussein 11 Nov '08

11 Nov '08

I don't understand why there is no video of Frag online so I made one here: http://uk.youtube.com/watch?v=0jYdu2u8gAU _________________________________________________________________ BigSnapSearch.com - 24 prizes a day, every day - Search Now! http://clk.atdmt.com/UKM/go/117442309/direct/01/

4 4

Haskell Weekly News: Issue 92 - November 8, 2008
by Brent Yorgey 11 Nov '08

11 Nov '08

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20081108 Issue 92 - November 08, 2008 --------------------------------------------------------------------------- Welcome to issue 92 of HWN, a newsletter covering developments in the [1]Haskell community. GHC 6.10 is released!! Go forth and drool over its new features. Be sure to have the editline libraries (libedit-dev on Debian/Ubuntu, for example) installed before you try building it. Announcements GHC version 6.10.1. Ian Lynagh [2]announced the release of [3]GHC version 6.10.1! This new major release features a number of significant changes, including wild-card patterns, punning, and field disambiguation in record syntax; generalised quasi-quotes; generalised SQL-like list comprehensions; view patterns; a complete reimplementation of type families; parallel garbage collection; a new extensible exception framework; a more user-friendly API; included Data Parallel Haskell (DPH); and more! See [4]the full release notes for more information. new community.haskell.org features: webspace, mailing lists. Ian Lynagh [5]announced that the community server, http://community.haskell.org/, has two new features for hosted projects: project webspace, and project mailing lists. GHC blog. Simon Marlow [6]has set up a [7]GHC blog. This is for all things related to GHC, particularly people working on GHC to blog about what they're up to. If you want a write-bit, sign up for a [8]wordpress account, let Simon know your account name, and blog away! The GHC blog should be syndicated on [9]Planet Haskell soon. Haddock 2.4.0. David Waern [10]announced a [11]new release of [12]Haddock, the Haskell documentation tool. This is a later version than the one shipped with GHC 6.10.1, which is version 2.3.0. That version will not be released on Hackage since it only builds with GHC 6.10.1 (by accident, actually). Besides adding back support for earlier GHC versions, this release contains some more fixes and support for HTML frames. htags-1.0. David Sankel [13]announced the [14]htags package, a tag file generator to enable extra functionality in editors like vim. It expands upon hasktags by using a full Haskell 98 parser and options for recursion. Haskell Quick Reference (1-page PDF). Malcolm Wallace [15]sent a 1-page Haskell quick reference prepared for a recent Haskell tutorial. Permission is granted for anyone to distribute it more widely as they wish, in the hope that it might be useful. Editable sources can be passed along if anyone would like to extend it. Proposal for associated type synonyms in Template Haskell. Thomas van Noort [16]submitted a proposal for adding associated type synonyms to Template Haskell. Comments are welcomed. announce [("InfixApplicative", 1.0), ("OpenGLCheck", 1.0), ("obj", 0.1)]. Thomas Davie [17]announced the upload of a few packages to Hackage which he has produced while working at Anygma. [18]obj-0.1 is a library for loading and writing obj 3D models; [19]OpenGLCheck-1.0 is a micro-package containing instances of Arbitrary for the data structures provided in Graphics.Rendering.OpenGL; and [20]InfixApplicative-1.0 is a second micro-package containing a pair of functions (<^) and (^>) which can be used to provide an infix version of liftA2 applied to an operator. Graphalyze-0.5 and SourceGraph-0.3. Ivan Lazar Miljenovic [21]announced the latest versions of [22]Graphalyze and [23]SourceGraph, which fix a couple of bugs in the previous versions. zlib and bzlib 0.5 releases. Duncan Coutts [24]announced updates to the [25]zlib and [26]bzlib packages, featuring a slightly nicer extended API. The simple API that most packages use is unchanged. There is also a new parameter to control the size of the first output buffer; this lets applications save memory when they happen to have a good estimate of the output size. Discussion Efficient parallel regular expressions. Martijn van Steenbergen [27]asked about efficiently running multiple regular expressions in parallel, leading to an interesting discussion of regular expressions and various parsing methods and libraries. Problems with strictness analysis?. Patai Gergely started an informative [28]discussion about strictness, laziness, strictness analysis, and compiler optimization. If you don't know a lot about these topics but would like to learn, this thread is a good starting point! Jobs 1-year postdoc position in Chalmers Functional Programming group. John Hughes [29]announced a position for a post-doctoral researcher with the Chalmers Functional Programming Group, with a one-year tax-free stipend funded by Intel. The funded project will develop a Domain Specific Language (DSL) for high level modelling, design and analysis of hardware and microarchitectures. Blog noise [30]Haskell news from the [31]blogosphere. * Edward Kmett: [32]Still Alive. Edward is still alive but sadly lost a few recursion scheme posts. =( * >>> Max Rabkin: [33]Beautiful folding. A very cool post about composable folds! * Eric Kow (kowey): [34]timesheet helper. * Philip Wadler: [35]A bizarre function over streams. * David Sankel: [36]Introducing Reactive: Events. A very readable introduction to the Reactive library. I look forward to reading more! * "FP Lunch": [37]Numbers vs Sets. * Mark Jason Dominus: [38]Addenda to recent articles 200810. * Darcs: [39]darcs weekly news #11. * >>> Ken G.: [40]Haskell?. Ken shares some thoughts on Real World Haskell. * Real-World Haskell: [41]Some early reviews. * David Sankel: [42]freeglut + Windows + HOpenGL + HGLUT. * GHC mutterings: [43]GHC 6.10.1 is out!. * Chung-chieh Shan: [44]Cognitive jobs. * London Haskell Users Group: [45]Duncan Coutts: The Haskell Platform. The abstract for Duncan's talk at the London HUG. * Well-Typed.Com: [46]GHC 6.10.1 released!. * Well-Typed.Com: [47]Haskell Platform talk at the London Haskell Users Group. * Mark Wassell: [48]GIS with Haskell 1. * >>> phoenix: [49]Haskell Tricks: Indexing a List. Getting the index of an element satisfying a predicate by zipping. * JP Moresmau: [50]Haskell for counting votes!. JP illustrates five different voting methods with some Haskell implementations. * Ivan Lazar Miljenovic: [51]Graph Theoretic Analysis of Relationships within Discrete Data. * Braden Shepherdson: [52]Pimp Your XMonad #1: Status bars. The first in a planned series of articles on not-so-well-known ways to extend your xmonad configuration. * >>> Cory: [53]Euler and Haskell. Cory just started learning Haskell (a "fun, slightly ridiculous language") via Project Euler. * >>> Sadek Drobi: [54]Code Safety and Correctness is a matter of Mindset Cultured by the Language. * Well-Typed.Com: [55]zlib and bzlib package updates. * >>> Bryan St. Amour: [56]Haskell Solution To The Farmer Problem. * >>> Nathan Hartman: [57]Haskell, Lambert, and the Clarke Ellipsoid. Nathan has started porting a map projection library to Haskell. * David Sankel: [58]Analysis of lazy-stream programs.. Quotes of the Week * Cory: Any language which makes frequent use of monads, functors and has a wikibook describing its relation to category theory is the result of an evil genius (or several, to be precise). * mmorrow: in langs with dependent types, you can just map numbers directly to types instead of having to ride a unicycle along a tightrope while battling an unruly gang of monkeys with knives. * conal: -fsemantics-shemantics * roconnor: all sorts of wonderful things could be done if we are less anal about bottoms. No pun intended. About the Haskell Weekly News New editions are posted to [59]the Haskell mailing list as well as to [60]the Haskell Sequence and [61]Planet Haskell. [62]RSS is also available, and headlines appear on [63]haskell.org. To help create new editions of this newsletter, please see the information on [64]how to contribute. Send stories to byorgey at cis dot upenn dot edu. The darcs repository is available at darcs get [65]http://code.haskell.org/~byorgey/code/hwn/ . References 1. http://haskell.org/ 2. http://article.gmane.org/gmane.comp.lang.haskell.glasgow.user/15591 3. http://www.haskell.org/ghc/ 4. http://haskell.org/ghc/docs/6.10.1/html/users_guide/release-6-10-1.html 5. http://article.gmane.org/gmane.comp.lang.haskell.general/16600 6. http://article.gmane.org/gmane.comp.lang.haskell.glasgow.user/15603 7. http://ghcmutterings.wordpress.com/ 8. http://wordpress.com/ 9. http://planet.haskell.org/ 10. http://www.haskell.org//pipermail/haskell-cafe/2008-November/050271.html 11. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/haddock-2.4.0 12. http://www.haskell.org/haddock 13. http://article.gmane.org/gmane.comp.lang.haskell.general/16582 14. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/htags 15. http://article.gmane.org/gmane.comp.lang.haskell.cafe/47344 16. http://article.gmane.org/gmane.comp.lang.haskell.cafe/47301 17. http://article.gmane.org/gmane.comp.lang.haskell.cafe/47241 18. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/obj 19. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/OpenGLCheck 20. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/InfixApplicative 21. http://article.gmane.org/gmane.comp.lang.haskell.cafe/47171 22. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Graphalyze 23. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/SourceGraph 24. http://article.gmane.org/gmane.comp.lang.haskell.cafe/47144 25. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/zlib 26. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/bzlib 27. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/47242 28. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/47183 29. http://article.gmane.org/gmane.comp.lang.haskell.general/16596 30. http://planet.haskell.org/ 31. http://haskell.org/haskellwiki/Blog_articles 32. http://comonad.com/reader/2008/still-alive/ 33. http://squing.blogspot.com/2008/11/beautiful-folding.html 34. http://koweycode.blogspot.com/2008/11/timesheet-wishlist.html 35. http://wadler.blogspot.com/2008/11/bizarre-function-over-streams.html 36. http://netsuperbrain.com/blog/posts/introducing-reactive-events/ 37. http://sneezy.cs.nott.ac.uk/fplunch/weblog/?p=114 38. http://blog.plover.com/addenda/200810.html 39. http://blog.darcs.net/2008/11/darcs-weekly-news-11.html 40. http://monolith149daily.blogspot.com/2008/11/haskell.html 41. http://www.realworldhaskell.org/blog/2008/11/06/some-early-reviews/ 42. http://netsuperbrain.com/blog/posts/freeglut-windows-hopengl-hglut/ 43. http://ghcmutterings.wordpress.com/2008/11/05/ghc-6101-is-out/ 44. http://conway.rutgers.edu/~ccshan/wiki/blog/posts/Cognitive_jobs/ 45. http://www.londonhug.net/2008/11/04/duncan-coutts-the-haskell-platform/ 46. http://blog.well-typed.com/2008/11/ghc-6101-released/ 47. http://blog.well-typed.com/2008/11/haskell-platform-talk-at-the-london-hask… 48. http://pound-stone.blogspot.com/2008/11/gis-with-haskell-1.html 49. http://phoenixblitz.blogspot.com/2008/11/haskell-tricks-indexing-list.html 50. http://jpmoresmau.blogspot.com/2008/11/haskell-for-counting-votes.html 51. http://ivanmiljenovic.wordpress.com/2008/11/03/graph-theoretic-analysis-of-… 52. http://braincrater.wordpress.com/2008/11/02/pimp-your-xmonad-1-status-bars/ 53. http://onag.blogspot.com/2008/11/euler-and-haskell.html 54. http://sadekdrobi.com/2008/11/02/code-safety-and-correctness-is-a-matter-of… 55. http://blog.well-typed.com/2008/11/zlib-and-bzlib-package-updates/ 56. http://bryanstamour.com/?p=49 57. http://parsemymonad.blogspot.com/2008/10/haskell-lambert-and-clarke-ellipso… 58. http://netsuperbrain.com/blog/posts/analysis-of-lazy-stream-programs/ 59. http://www.haskell.org/mailman/listinfo/haskell 60. http://sequence.complete.org/ 61. http://planet.haskell.org/ 62. http://sequence.complete.org/node/feed 63. http://haskell.org/ 64. http://haskell.org/haskellwiki/HWN 65. http://code.haskell.org/~byorgey/code/hwn/

3 2

Haskell source packages in Hackage
by Hugo Pacheco 11 Nov '08

11 Nov '08

Hi guys, I am having an hard time installing the haskell-src and haskell-src-exts packages, since both seem to have problems with happy. I have installed happy 1.18.2 successfully, but it does not seem to be visible (although the happy executable is in my path). I get the errors: $ cabal install haskell-src Resolving dependencies... 'haskell-src-1.0.1.3' is cached. Configuring haskell-src-1.0.1.3... Preprocessing library haskell-src-1.0.1.3... cabal: The program happy is required but it could not be found cabal: Error: some packages failed to install: haskell-src-1.0.1.3 failed during the building phase. The exception was: exit: ExitFailure 1 $ cabal install haskell-src-exts Resolving dependencies... 'haskell-src-exts-0.3.9' is cached. Configuring haskell-src-exts-0.3.9... cabal: happy version >=1.17 is required but it could not be found. cabal: Error: some packages failed to install: haskell-src-exts-0.3.9 failed during the configure step. The exception was: exit: ExitFailure 1 Is this some kind of bug in cabal, or in the packages themselves? Thanks, hugo -- www.di.uminho.pt/~hpacheco

1 0

generalized list comprehensions
by Johannes Waldmann 11 Nov '08

11 Nov '08

Looking at this funny new feature http://haskell.org/ghc/docs/6.10.1/html/users_guide/syntax-extns.html#gener… I have just one question - why doesn't this work with the do-notation? I avoid list comprehensions because I feel that "return" belongs at the end, not in front. If I recall correctly, "putting the SQL-select where it belongs" is a slogan used by Hijlsberg to justify the LINQ syntax for C#, and of course he is right. Now ghc copies LINQ (syntactically), but stops halfway? Just wondering - J.W.

9 22

Are arbitrary rank types and existentials equivalent?
by Loup Vaillant 11 Nov '08

11 Nov '08

Maybe one subsumes the other? What I want to know is if there is an easy way to emulate one with the other, and how much convenience is lost in doing so. For instance, is it possible to implement stream fusion with rank2 types, or the ST monad with existantials? Is there any paper discussing this kind of things? Thanks, Loup

5 5

ANN (sorta): OpenGL with extra type safety
by Neal Alexander 11 Nov '08

11 Nov '08

I recently modified the hOpenGL (and GLFW) source tree to force extra type checking on its various IO actions using the -XGeneralizedNewtypeDeriving extension (see http://hackage.haskell.org/trac/ghc/ticket/736) The main motivation was for writing concurrent OpenGL applications. Here its important to know what functions contain OpenGL commands so they can be directed to the proper threads (ones with active rendering contexts). Plus it aids in partitioning work that can be offloaded or done asynchronously. The second motivation was to enforce static type checking on commands that can only be executed in certain OpenGL contexts (sending vertex data for example). As it is now, there are 3 new monads (their names will probably change): OpenGLM: the basic opengl command PrimitiveM: commands that can only be issued between begin/end() class MonadGL: commands that can be issued in any GL context Now for the big question: Does anyone care? If so, should i make it a new hackageDB package, or try to merge it into the official GL package. Ideally, it'd be nice to get some more input on the API changes, since they're more or less a rough draft as is. Also, the GLU modules were all placed in the OpenGLM monad, which is probably wrong, assuming some commands can be called between begin/end. I'll post the code later if anyone is interested. ---------------- class MonadIO m => MonadGL m instance MonadGL OpenGLM instance MonadGL PrimitiveM newtype OpenGLM a = OpenGLM (IO a) deriving (Functor, Monad, MonadIO) newtype PrimitiveM a = PrimitiveM (IO a) deriving (Functor, Monad, MonadIO)

2 1

Announce: FieldTrip library (functional 3D) and mailing list
by Conal Elliott 11 Nov '08

11 Nov '08

FieldTrip [1] is a library for functional 3D graphics. It is intended for building static, animated, and interactive 3D geometry, efficient enough for real-time synthesis and display. Since FieldTrip is functional, one describes what models are, not how to render them (being rather than doing). Surfaces are described as functions from 2D space to 3D space. As such, they are intrinsically curved rather than faceted. Surface rendering tessellates adaptively, caching tessellations in an efficient, infinite data structure (from the MemoTrie library) for reuse. Surface normals are computed automatically and exactly, using the derivative tools in the vector-space library. For animation or interaction, FieldTrip can be used with the Reactive [2] library for functional reactive programming (and possibly other animation frameworks). By design, FieldTrip is completely orthogonal to any formulation or implementation of FRP. The reactive-fieldtrip [3] library links Reactive and FieldTrip. FieldTrip now has a mailing list [4] and a feature/bug tracker [5]. [1] http://haskell.org/haskellwiki/FieldTrip [2] http://haskell.org/haskellwiki/reactive [3] http://haskell.org/haskellwiki/reactive-fieldtrip [4] http://www.haskell.org/mailman/listinfo/FieldTrip [5] http://trac.haskell.org/FieldTrip

2 4

FFI documentation?
by Nun Aurbiz 11 Nov '08

11 Nov '08

Where do I find the documentation for the FFI for GHC? I've read the FFI report, the GHC user guide and scoured haskell.org but they all gloss over what commands you actually need to give GHC and how to give them. "foreign import blah blah" just gives me undefined references.

4 3

Re: [Haskell-cafe] A video of Frag
by Hugo Pacheco 10 Nov '08

10 Nov '08

Yes, I installed it via cabal-install.I am using GHC 6.10.1 now, but it had > the same results in 6.6 (if I remember well) before. It may be a Mac issue. > > On Mon, Nov 10, 2008 at 1:39 PM, Korcan Hussein <korcan_h(a)hotmail.com>wrote: > >> Sorry I have no idea, which version of GHC are you using? did you try >> using cabal-install? ( >> http://hackage.haskell.org/trac/hackage/wiki/CabalInstall) >> >> ------------------------------ >> Date: Mon, 10 Nov 2008 10:46:45 +0000 >> >> From: hpacheco(a)gmail.com >> To: korcan_h(a)hotmail.com >> Subject: Re: [Haskell-cafe] A video of Frag >> >> Oh, sorry I haven't noticed.Trying to compile in my OS X machine, all >> compiles ok via cabal, but then I get >> >> $ ./frag ../share/frag-1.1.2/leveleg >> Bus error >> >> I remember compiling frag 1/2 years ago and getting the same result. >> It is not windows, but do you have any hint? >> >> On Mon, Nov 10, 2008 at 10:12 AM, Korcan Hussein <korcan_h(a)hotmail.com>wrote: >> >> Actually such a package already exists, it's quite a simple procedure as >> long as you have the right tools and and setup but for windows platform >> this information is a bit scattered/dispersed and there is no central >> information about getting such a thing up and running from complete scratch. >> This is what i'm referring to in my comment. >> >> ------------------------------ >> Date: Mon, 10 Nov 2008 09:15:14 +0000 >> From: hpacheco(a)gmail.com >> To: korcan_h(a)hotmail.com >> Subject: Re: [Haskell-cafe] A video of Frag >> CC: haskell-cafe(a)haskell.org >> >> >> I read on your youtube post that you are planning to write a >> build-it-yourself tutorial. Perhaps this effort could be targeted at >> creating a cabal package in Hackage (I do not know the implications of that, >> just speaking out loud). >> >> Cheers, >> hugo >> >> 2008/11/10 Korcan Hussein <korcan_h(a)hotmail.com> >> >> I don't understand why there is no video of Frag online so I made one >> here: http://uk.youtube.com/watch?v=0jYdu2u8gAU >> >> ------------------------------ >> Click here for FREE customisable desktop wallpapers. Get them Now!<http://wallpapers.msn.com/?ocid=%5BB001MSN42A0716B%5D> >> >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> >> >> >> >> -- >> www.di.uminho.pt/~hpacheco <http://www.di.uminho.pt/%7Ehpacheco> >> >> ------------------------------ >> Click here for FREE customisable desktop wallpapers. Get them Now!<http://wallpapers.msn.com/?ocid=%5BB001MSN42A0716B%5D> >> >> >> >> >> -- >> www.di.uminho.pt/~hpacheco <http://www.di.uminho.pt/%7Ehpacheco> >> >> ------------------------------ >> Get the best wallpapers on the Web - FREE. Click here!<http://wallpapers.msn.com/?ocid=[B001MSN42A0716B]> >> > > > > -- > www.di.uminho.pt/~hpacheco >

1 0

announcing darcs 2.1.1rc2
by Eric Kow 10 Nov '08

10 Nov '08

Hi everybody, The release candidate for darcs 2.1.1 is now available at http://darcs.net/darcs-2.1.1rc2.tar.gz This release is very much intended to be darcs 2.1.0 plus GHC 6.10.1 support. We have also thrown in some simplifications to the regression testing suite and a Windows bugfix (which we pulled in because of a dependency and retained because it was a small and useful). Please give this a try, especially those of you on GHC 6.10 or Windows, and let us know how things work out. Because we have only selected a very small subset of changes to include (using darcs's cherry-picking abilities, of course!), I am confident that we can get by on a reduced release cycle. If all goes well, the official release date for darcs 2.1.1 will be 2008-11-17. Thanks! Eric darcs (2.1.1rc2) * Portability: Removed accidental QuickCheck 2.1 configure check. Note that it may be required in a future version of darcs. -- Eric Kow <kowey(a)darcs.net> Mon, 10 Nov 2008 11:17:00 GMT darcs (2.1.1rc1) * Portability: GHC 6.10.1 support (Petr Ročkai, Eric Kow) * Bug Fix: Fix file handle leak and check for exceptions on process running on Windows (issue784, Salvatore Insalaco) * Quality Assurance: Consolidated regression test suites using shell scripts only (Eric Kow, Tommy Petterson, Matthias Kilian) -- Eric Kow <kowey(a)darcs.net> Mon, 10 Nov 2008 09:49:00 GMT -- Eric Kow <http://www.nltg.brighton.ac.uk/home/Eric.Kow> PGP Key ID: 08AC04F9

1 0

How to getCh on MS Windows command line?
by Ahn, Ki Yung 10 Nov '08

10 Nov '08

What I mean by getCh is the non-buffered non-echoed version of getChar, which Hugs used to provided as an extension but not any more. Is there any way to have a non-buffered non-echoed single character input function on MS Windows command line using only the libraries in the MS Windows distribution packages of either GHC or Hugs? The reason to why this is important for me is because I am translating Graham Hutton's "Programming in Haskell" into Korean (soon to be published), which illustrates interactive programming with the example of a calculator that responds instantly for every keystroke of numbers and arithmetic operations running on text mode. It is very important to consider the readers who only have access to MS Windows systems, because Korean OS market share is completely skewed towards MS Windows for very embarrassing reasons that I do not even want to mention. And, isn't GHC developed in MSR anyway? :-) I remember that this is an old problem for both of the two most widely used Haskell implementation, Hugs and GHC. In ghc 6.8 getChar had a bit strange behavior. As far as I remember it always worked as if it were NoBuffering. Fortunately, in the recently released ghc 6.10, this has been fixed. We now actually have to set the buffering mode to NoBuffering with hSetBufferring to get the non-buffered behavior of getChar. But, it still isn't working on MS Windows. In Hugs, hSetBuffering neither works on Unix terminal nor on MS Windows command line. Surprisingly, it works in WinHugs. However, I cannot use WinHugs for my purpose because the interactive calculator example in the book also uses beep characters and ANSI codes which do not work in WinHugs. Thanks for any hacks or suggestions, -- Ahn, Ki Yung

2 1

foldl vs foldl'
by Daryoush Mehrtash 10 Nov '08

10 Nov '08

Are there cases (function or list) where the result of foldl (or foldr)would be different that foldl' (or foldr')? thanks, daryoush

8 11

Announce: Reactive library (FRP) and mailing list
by Conal Elliott 10 Nov '08

10 Nov '08

Reactive [1] is a library for functional reactive programming (FRP), similar to the original Fran [2] but with a more modern interface (using standard type classes) and a hybrid push/pull implementation. It is designed to be used in a variety of contexts, such as interactive 2D and 3D graphics, graphical user interfaces, web services, and automatic recompilation/re-execution. It has a simple and precise semantics based on continuous time and is built on a notion of functional future values. The semantics and implementation are described in the paper "Simply efficient functional reactivity" [3]. Reactive now has a mailing list [4] and a feature/bug tracker [5]. [1] http://haskell.org/haskellwiki/Reactive [2] http://conal.net/Fran [3] http://conal.net/papers/simply-reactive [4] http://www.haskell.org/mailman/listinfo/reactive [5] http://trac.haskell.org/reactive

2 1

Physics engines purely in Haskell?
by Mark Wassell 10 Nov '08

10 Nov '08

Has anyone thought about or embarked on the task of developing a 2D or 3D physics engine purely in Haskell? There is Hipmunk but I'm wondering about a purely Haskell implementation; possibly a port of Chipmunk to Haskell. Mark

3 2

Is there a plan for HappS and ghc-6.10.1?
by Hugo Pacheco 10 Nov '08

10 Nov '08

Hi all, The HappS version on Hackage does not yet support ghc 6.10, since GADT pattern matching and the Exception API have changed. One sample error is: src/HAppS/Data/Xml/Base.hs:281:23: GADT pattern match with non-rigid result type `t1' Solution: add a type signature ... Adding a type signature via an auxiliary function instead of a case expression, the problem goes away. readElementRigidity :: (Monad m,Xml t) => Rigidity m -> m ([Element],t) -> Maybe t readElementRigidity Rigid m = ... readElementRigidity Flexible m = ... Is there a plan to update the version on Hackage to support ghc 6.10.1? I don't know either if it may break backwards compatibility. Cheers, hugo -- www.di.uminho.pt/~hpacheco

2 2

Convolution
by Andrew Coppin 09 Nov '08

09 Nov '08

A simple and straight-forward way to define the DSP operations of correlation and convolution is as follows: correlate1 :: [Double] -> [Double] -> Double correlate1 ks = sum . zipWith (*) ks correlate :: [Double] -> [Double] -> [Double] correlate ks [] = [] correlate ks xs = correlate1 ks xs : correlate ks (tail xs) convolute :: [Double] -> [Double] -> [Double] convolute ks = correlate (reverse ks) This very simple code work - and actually works quite well. It has the nice property of generating output from input lazily, as it is demanded. If the correlate function could be altered to use Prelude list functions only, I would think the above code works quite well with stream fusion too. (Presumably you could do this using "inits" or something?) Assuming DPH ever becomes a reality, how would you implement the above with it? (My intuition tells me that unless you have a really *big* filter kernel, breaking correlate1 into parallel chunks is too granular. However, each call to correlate1 could be run independently, presumably confering a more or less linear speedup. Unless having two cores writing to the same memory page is going to upset the cache system...) Presumably if you want to use parallel arrays, then the data must all exist in memory at once, and any chunking must be implemented manually and tediously?

2 3

Dealing with CStringLen
by Maurício 09 Nov '08

09 Nov '08

Hi, How is CStringLen supposed to be used? The only usual C string I'm familiar with is the null terminated sequence of chars. I remember some Pascal version where the first 2 bytes were used as an integer counting the following characters. What is the convention used in Foreign.C.String? I have a C function signature like this: void function (int,const void*,int,const void*) where each (int,const void*) pair is a string. Can (should) I use CStringLen here? How? Thanks, Maurício

2 1

view patterns
by Cetin Sert 09 Nov '08

09 Nov '08

let has [] = False; has _ = True -- this one is ok let empty list = case has list of True -> False; False -> True -- the following is problematic let emp (has -> True) = False; emp (has -> False) = True <interactive>:1:4: Warning: Pattern match(es) are overlapped In the definition of `emp': emp ((has -> True)) = ... emp ((has -> False)) = ... Why do I get this error in ghc or when I try to compile a file with view patterns? (using -fglasgow-exts and -XViewPatterns, ghc 6.10.1)

4 3

Haskell Quick Reference (1-page PDF)
by Malcolm Wallace 09 Nov '08

09 Nov '08

Some time ago, there was a thread about a "CheatSheet" for Haskell beginners. As I recall, the CheatSheet was more than 12 pages long. For a Haskell tutorial I was running at a conference recently, I needed a "Quick Reference Guide" that would fit onto a single side of A4. So I knocked one together quickly, and it is attached as a PDF. I send it to this list, with permission for anyone to distribute it more widely as they wish, in the hope that it might be useful. Doubtless it is incomplete, and I have no particular desire to fix errors or maintain this document, so if anyone is interested and would like to adopt it, I can pass on the editable sources. It was originally created as an Apple Numbers spreadsheet (simply for speed of creation) but could be converted to Excel or CSV, for import into other tools. Regards, Malcolm

4 3

Bit Field Marshalling
by Michael D. Adams 08 Nov '08

08 Nov '08

I'm writing a Storable instance for a data type that marshals to a C structure that contains bit fields such as the following: struct Foo { short x; short y; unsigned int a : 1; unsigned int b : 1; unsigned int c : 1; unsigned int d : 1; unsigned int reserved : 12; } For the "x" and "y" fields I've been using hsc2hs and something like #{peek Foo, x} to extract the fields. However, bit fields such as "a" have me stumped. But as far as I can tell, hsc2hs doesn't support bit fields. On top of that I'm not sure I can make any safe assumptions about what order the bit fields are packed (LSB or MSB first). Have others run into this problem before? What options are there for working around it? Michael D. Adams mdmkolbe(a)gmail.com

5 5

performance difference for binary-0.4.3.1 with ghc-6.8.3 and ghc-6.10
by John Lato 08 Nov '08

08 Nov '08

Hello, I was experimenting with using ghc-6.10.0.20081007 on a project, and it seems that binary-0.4.3.1 has markedly worse performance in certain cases. With the following simple test: > import qualified Data.ByteString.Lazy as L > import Data.Binary > import Data.Binary.Get > import Control.Monad > > main :: IO () > main = do > b <- L.readFile "some_binary_file" > putStrLn $ show $ runGet getter b > getter :: Get [Word16] > getter = replicateM 1000000 getWord16le running this program compiled with ghc-6.10 takes about 4 times as long (and consumes much more memory) as when compiled with ghc-6.8.3. The extra time appears to be proportional to the number of elements processed in the Get. Running the programs with -hT shows a clear memory difference, which I think is the source of the problem. I've placed pdfs of that output at https://webspace.utexas.edu/latojw/data/ The difference seems to manifest itself only when the elements are actually processed; changing "show $ runGet " to "show $ length $ runGet " is slightly faster in 6.10. I was working on an Intel Mac with OS 10.4, binary-0.4.3.1, and bytestring-0.9.1.4. Can anyone confirm this, or suggest what might be the difference? Thank you, John Lato

6 9

Monad.Reader with updates
by Mauricio 08 Nov '08

08 Nov '08

Hi, Is there some abstraction in current ghc library that implements something like Reader, but where the value of the environment is updated at every "step"? I imagine something that instead of running like this: runReader ( do ... ) environment I would run like: runReader ( do ... ) environment update_function So, when I write a monad like: do a <- asks f b <- asks f2 c <- asks f3 f, f2 and f3 would be called with parameters environment, (update_function environment), (update_function . updatefunction $ environment) etc. Does that make sense? Is it easy to adapt something already existing to do that? Thanks, Maurício

7 12

Problems with strictness analysis?
by Patai Gergely 07 Nov '08

07 Nov '08

Hi everyone, I was experimenting with simple accumulator functions, and found that an apparently tail recursive function can easily fill the stack. Playing around with ghc and jhc gave consistently unpleasant results. Look at this program: %%%%%%%%%%% -- ghc: no, ghc -O3: yes, jhc: no isum 0 s = s isum n s = isum (n-1) (s+n) -- ghc: no, ghc -O3: no, jhc: yes (because gcc -O3 is clever) rsum 0 = 0 rsum n = n + rsum (n-1) main = case isum 10000000 0 {- rsum 10000000 -} of 0 -> print 0 x -> print x %%%%%%%%%%% I would expect the analysis to find out that the result of the function is needed in every case (since we are matching a pattern to it), yet I need to add a $! to the recursive call of isum to get a truly iterative function. It's interesting how ghc and jhc seem to diverge, one favouring the "iterative" version, the other the "recursive" one (although it only works because gcc figures out that the function can be expressed in an iterative way). Of course this is a real problem when I'm trying to write an actual program, since it means I can be bitten by the laziness bug any time... Is there any solution besides adding strictness annotations? Can I expect the compiler to handle this situation better in the foreseeable future? Gergely -- http://www.fastmail.fm - IMAP accessible web-mail

17 35

Anyone know why this always returns invalid texture objects?
by Jefferson Heard 07 Nov '08

07 Nov '08

import Graphics.UI.Gtk import Graphics.UI.Gtk.Glade import Graphics.UI.Gtk.OpenGL import qualified Graphics.Rendering.OpenGL as GL import Graphics.Rendering.OpenGL (($=)) main = do initGUI initGL GL.shadeModel $= GL.Flat GL.depthFunc $= Just GL.Less (window1,gui,dlgs) <- constructGUIObject (sX, sY) <- liftM (mapPair fromIntegral) . widgetGetSize . drawing_canvas $ gui -- get the canvas size for determining the part of the widget to repaint pb <- pixbufNew ColorspaceRgb False 8 (round pbWidth) (round pbHeight) pixbufFill pb 0 0 0 255 pxbufs <- initSubpixbufs pb texRows texCols textures <- GL.genObjectNames (texRows*texCols) print textures -- I try to take things like a crow; war and chaos don't always ruin a picnic, they just mean you have to be careful what you swallow. -- Jessica Edwards

2 2

Problem compiling hdbc with GHC 6.10.1 in windows
by PJ Durai 07 Nov '08

07 Nov '08

Greetings I would like to report that I am not able to compile hdbc 1.1.5.0. $ runghc.exe Setup.lhs build Preprocessing library HDBC-1.1.5... Building HDBC-1.1.5... [1 of 6] Compiling Database.HDBC.ColTypes ( Database\HDBC\ColTypes.hs, dist\build\Database\HDBC\ColTypes.o ) [2 of 6] Compiling Database.HDBC.Statement ( Database\HDBC\Statement.hs, dist\build\Database\HDBC\Statement.o ) [3 of 6] Compiling Database.HDBC.Types ( Database\HDBC\Types.hs, dist\build\Database\HDBC\Types.o ) [4 of 6] Compiling Database.HDBC.DriverUtils ( Database\HDBC\DriverUtils.hs, dist\build\Database\HDBC\DriverUtils.o ) [5 of 6] Compiling Database.HDBC.Utils ( Database\HDBC\Utils.hs, dist\build\Database\HDBC\Utils.o ) Database\HDBC\Utils.hs:51:11: Not in scope: `catchDyn' Database\HDBC\Utils.hs:55:16: Not in scope: `catchDyn' Database\HDBC\Utils.hs:60:18: Not in scope: `dynExceptions' Environment: Windows XP SP2 GHC 6.10.1 thanks pj I had no problems compiling this with GHC 6.8.

3 3

Re: [Haskell] ANNOUNCE: Haddock version 2.4.0
by Thomas Schilling 07 Nov '08

07 Nov '08

[Redirecting to cafe@ since haskell@ is not meant for discussions] Sure, they are bad for one reason: you cannot link to a frame configuration directly. However, for this particular use case they are quite handy. There are some features missing (like hoogle integration) and some annoyances (if javascript is enabled, we show both a mini-synopsis, but this interacts badly with the back-button.) You can simulate this if you add a lot more javascript, have some kind of server, generate many more static pages, or use some CSS magic. But the implemented solution works and is reasonably useful. If someone wants to improve this I certainly don't mind. 2008/11/6 Wolfgang Jeltsch <g9ks157k(a)acme.softbase.org>: > Am Donnerstag, 6. November 2008 00:21 schrieb David Waern: >> * Add framed view of the HTML documentation > > After many years with many people telling us that frames are bad, you add > frame support to Haddock? Hmm. > > Best wishes, > Wolfgang > _______________________________________________ > Haskell mailing list > Haskell(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell >

1 0

Writing an IRC bot, problems with plugins
by Alexander Foremny 07 Nov '08

07 Nov '08

Hello, Community. I already bothered #haskell a few times with the very same problem and always got interesting responses. But I seem to have always simplified my problem too much ending up with an helpful answer to my (simplified) problem, but not with a real solution. Thus I'm giving the mailing list a try where I don't feel like having to wrap up my concerns in as few lines as possible. I am writing an single server, multi channel IRC bot with the support of plugins and limited plugin communication. With the plugin system I am facing problems I cannot really solve myself. My general idea is to have the main application listening to the network socket and then calling all the plugins on each incoming message. Therefore I maintain a list of plugin states in the main application's state and on each incoming message I call a function which modifies the plugin's state. There's a PluginClass class which contains definitions of functions for each plugin which they all share. Simplyfied it's like this: type PL = StateT PluginConfig class PluginClass a where identifier :: a -> String rawMessage :: (MonadIO m) => a -> Message -> PL m () So plugins can be identified uniquely using the identifier function and they can respond to messages using the rawMessage function. This function is executed in the PL monad, which is essentially a StateT monad for updating the plugin's state trough put and maybe accessing a few data fields from the underlying Bot monad in which the main application is operating. Then again I want to be able to query a plugin's state from a different plugin. For instance I'll have a plugin which keeps track of the channels the bot has joined collecting user information, the topic, etc. Another plugin could then query the "chan info" plugin and get all the users in a certain channel through a queryPlugin function which takes a plugin and looks that plugin up in the main application's plugin state list for the right state and then calls a function on it. The plugin and the corresponding functions would be exported by the plugin's module. queryPlugin :: (PluginClass a) => a -> (a -> b) -> PL m b queryPlugin pl f = do plugins <- getGlobalPlugins -- ideally (PluginClass a) => [a] let pluginNames = map identifier plugins targetName = identifier pl [(_, target)] = filter ((==) targetName . fst) (zip pluginNames plugin) return (f target) But here I am facing either one or the other problem, depending on the "solution." 1) I somehow have to store all the plugin states in the main application. Since plugins are essentially their states, they are quite arbitrary. I either cannot use a list for that or I have to use existential types which would make that possible. 2) Using an existential plugin type would restrict the functions I am able to call on the plugin to those which are supported by the PluginClass. This would render queryPlugin unusable since the functions a plugin exports for query the state are arbitrary. 3) I could use Dynamics to store the plugin in a list *and* call arbitrary functions, but then again how would I run a plugin? All the main application know about the plugin state is that all the functions defined by PluginClass are callable on the state. But the type (PluginClass a) => a isn't enough to unwrap the Dynamic, apply the function and wrap it again. Another suggestion was to not use a class but make each plugin a record, exporting the functions itself. Though I haven't given that a serious thought, it seems not ideal to me. Using a class a plugin can define the functions it actually uses. In my real code, they're about 12 functions the class exports and there could be more. Using a record I would have to implement all possible functions even though they're not changing the plugin's state nor causing side effects. The most obvious solution would be to use an algebraic data type with a constructor for each plugin. But I'd like to develop the plugins independent from the core and I'd like to make them more dynamic than that, maybe implementing dynamic loading of plugins at some time. Then there are two other potential solutions, but I haven't looked into them seriously since they seemed a little hackish to me at first glance. One would be using Hlist (which seems to be over-sized for my problem as well) and another would be to store a tupel of (Dynamic, (PluginClass a) => (Dynamic -> a)) as plugin state list where the first element would be the plugin's state wrapped in a dynamic and the second a unwrap function exported by the plugin's module. I *might* get around the problem of being to unspecific about the type when unwrapping, but this idea came only at the point of writing this email and I would expect running into the same problems I have: It can be achieved by either being too general or being to specific. Hopefully I've explained everything well enough while not being too long with all this. Thanks in advance for your help!

3 2

pure programs
by Jason Dusek 07 Nov '08

07 Nov '08

Informally, a "pure program" an executable such that the stream of bytes entering it totally determines the stream of bytes leaving it. Many useful programs that I would like to write in Haskell don't fall into this category -- for example, network servers -- but a lot of their components do. Can these components can be Haskell functions without IO in their signatures? Though that seems reasonable, it is not, in general, true. For example, System.Info.os is generally treated as pure, though it is not. It's not clear to me how to disambiguate these "born again" values from really pure values. -- _jsn

9 10

ghc-6.11 + OpenGL/GLUT crashes on WinXP
by Conal Elliott 07 Nov '08

07 Nov '08

I'm getting crashes from ghc-6.10.0.20081007 and ghc-6.11.20081024 when doing a very simple GLUT program (below) with OpenGL-2.2.1.1 and GLUT-2.1.1.2 (the latest from Hackage), running on WinXP. It works fine on ghc-6.9.20080622 . I'd appreciate hearing about other attempts with these versions on Windows systems. Thanks, - Conal import Graphics.UI.GLUT main :: IO () main = do putStrLn "Initializing" getArgsAndInitialize return ()

6 9

[Haskell-cafe] http://www.haskell.org/ghc/docs/latest/html/libraries/Cabal/Distribution-Simple.html
by Mauricio 07 Nov '08

07 Nov '08

Hi, According to this page: http://www.haskell.org/ghc/docs/latest/html/libraries/Cabal/Distribution-Si… there's an available toplevel declaration named: autoconfUserHooks in Distribution.Simple. However: ghci --version The Glorious Glasgow Haskell Compilation System, version 6.8.2 ghci Prelude> :m +Distribution.Simple Prelude Distribution.Simple> :t autoconfUserHooks <interactive>:1:0: Not in scope: `autoconfUserHooks' What would the experienced Haskell programmer do in such situation? Is there some way to ask ghci (or ghc) to list all available declarations, in a way that I could '| grep' it or save it to a file? Can I ask ghci to look for a declaration inside all available modules in all available packages? Thanks, Maurício

4 3

ANNOUNCE: Haddock version 2.4.0
by David Waern 06 Nov '08

06 Nov '08

-------------------------------------------- -- Haddock 2.4.0 -------------------------------------------- A new version of Haddock, the Haskell documentation tool, is out. This is a later version than the one shipped with GHC 6.10.1, which is version 2.3.0. That version will not be released on Hackage since it only builds with GHC 6.10.1 (by accident, actually). Besides adding back support for earlier GHC versions, this release contains some more fixes and support for HTML frames. Please use the bug tracker to submit bug reports or feature requests. -------------------------------------------- -- Changes in version 2.4.0 -------------------------------------------- * Add framed view of the HTML documentation * Build with GHC 6.8.2 and 6.8.3 again * Support images in documentation comments again * Small improvements to the Hoogle output * A few bugs has been fixed -------------------------------------------- -- Changes in version 2.3.0 -------------------------------------------- * Support for GHC 6.10.1 * Slightly improved space usage * Fix a bug that made hidden modules show up in the contents & index pages * Fix a bug that made Haddock load modules twice * Improvements to the Hoogle output -------------------------------------------- -- Links -------------------------------------------- Homepage: http://www.haskell.org/haddock Hackage page: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/haddock-2.4.0 Bugtracker and wiki: http://trac.haskell.org/haddock Mailing list: haskelldoc(a)haskell.org Code repository: http://code.haskell.org/haddock -------------------------------------------- -- Contributors -------------------------------------------- The persons who contributed to the 2.3.0 and 2.4.0 releases are: Clemens Fruhwirth Peter Gavin Ian Lynagh Neil Mitchell Luke Plant Thomas Schilling David Waern -------------------------------------------- -- Get Involved -------------------------------------------- We welcome new contributors. To get involved, start by grabbing the code: http://code.haskell.org/haddock Then take a look at the bug and feature tracker for things to work on: http://trac.haskell.org/haddock

2 2

Undefined symbols base_DataziTuple_ZxxxT_con_info
by dmitry shkurko 06 Nov '08

06 Nov '08

Hello everyone, I am trying to compile my program, but during the linking phase I see errors like: (.text+0x66dd7):fake: undefined reference to `base_DataziTuple_Z110T_con_info Library libHSbase.a contains symbols base_DataziTuple_ZxxxT_con_info for xxx <=62. It look like I hit some compiler limit (I used GHC 6.8.3 for compilation). Any thoughts are appreciated. Thank you, Dmitry

2 2

Efficient parallel regular expressions
by Martijn van Steenbergen 06 Nov '08

06 Nov '08

Hello all, For my mud client Yogurt (see hackage) I'm currently working on improving the efficiency of the hooks. Right now several hooks, each consisting of a regex and an action can be active at the same time. Every time a line of input is available (usually several times a second) I run the line through all the available regexes and execute the first matching action. I figured this is not the cleverest approach and it'd be better if I |'ed all regexes into one big DFA. However, how do I then find out which of the original hooks matched and so which action to execute? As far as I know there's no way to do that with Text.Regex. Alex looks promising but is really only an executable and doesn't offer an API. I've also found mr. João Saraiva's HaLex but I don't know if that was meant to be used seriously. Does anyone have any experience with this? What's the best way to achieve this? Thanks much, Martijn.

18 23

Strictness problems with Control.Event?
by Brian Troutwine 06 Nov '08

06 Nov '08

I'm attempting to use Control.Event to limit HTTP requests made by a dippy little scraper I'm constructing to once per second but I think, maybe, that the Events are not being evaluated. First, some imports. > import qualified Data.ByteString as B > import qualified Data.ByteString.Char8 as C > import Network.Curl.Download > import Network.Curl.Opts > import System.Exit > import System.Environment > import System.Time > import Control.Event > import Control.Monad > import Data.Char The Event function of this program is append. It takes a local path and a URL, retrieves the contents pointed to by the URL and appends them to the local path. The function download, below, performs the retrieval. > append :: FilePath -> C.ByteString -> IO () > append f u = > B.appendFile f . addNew . C.filter (not . isAscii) =<< download u > where addNew = C.append (C.pack "\n") > download :: B.ByteString -> IO B.ByteString > download url = do > res <- openURIWithOpts [CurlEncoding "gzip", CurlUserAgent "aule-0.0.2"] $ C.unpack url > case res of > Left _ -> exitFailure > Right cont -> B.putStrLn cont >> return cont The function sched adds a list of Events to the evtSys system, a fixed time delay between each. > sched :: EventSystem -> ClockTime -> Integer -> Integer -> (t -> IO ()) -> [t] -> IO () > sched _ _ _ _ _ [] = return () > sched evtSys (TOD sec _) delay mul action (x:xs) = do > addEvent evtSys (TOD (sec + (delay*mul)) 0) (action x) > sched evtSys (TOD sec 0) delay (mul + 1) action xs main is, as usual, pretty boring. The program compiles and runs, but no output file is made. This being one of my first appreciable Haskell programs, I rather imagine I've run into a strictness problem, maybe. Would someone be so kind as to steer me in the right direction? > main :: IO () > main = do > [i, o] <- getArgs > eS <- initEventSystem > t <- getClockTime > inp <- B.readFile i > sched eS t 1 1 (append o) (C.lines inp) Thanks, Brian

1 0

two problems with Data.Binary and Data.ByteString
by Tim Newsham 06 Nov '08

06 Nov '08

I have a program that read in and populated a large data structure and then saved it out with Data.Binary and Data.ByteString.Lazy.Char8: saveState db = B.writeFile stateFile =<< encode <$> atomically (readTVar db) when I go to read this in later I get a stack overflow: loadState db = do d <- decode <$> B.readFile stateFile atomically $ writeTVar db d Stack space overflow: current size 8388608 bytes. Use `+RTS -Ksize' to increase it. or from ghci: d <- liftM decode (Data.ByteString.Lazy.Char8.readFile "savedState.bin") :: IO InstrsDb fromList *** Exception: stack overflow The data type I'm storing is a Map (of maps): type DailyDb = M.Map Date Daily type InstrsDb = M.Map String DailyDb What's going on here? Why is the system capable of building and saving the data but not in reading and umarhsalling it? What is the proper way to track down where the exception is happening? Any debugging tips? I also noticed another issue while testing. If my program loads the data at startup by calling loadState then all later calls to saveState give an error: Log: savedState.bin: openFile: resource busy (file is locked) this does not occur if the program wasnt loaded. My best guess here is that B.readFile isnt completing and closing the file for some reason. Is there a good way to force this? Tim Newsham http://www.thenewsh.com/~newsham/

10 49

HOpenGL wiki link to documentation is broken
by Jefferson Heard 06 Nov '08

06 Nov '08

I suspect this has to do with the latest GHC not including it by default, but the HOpenGL wiki's documentation links are broken. -- Jeff

1 0

Re: [Haskell-cafe] Efficient parallel regular expressions
by roger peppe 05 Nov '08

05 Nov '08

On Tue, Nov 4, 2008 at 6:44 PM, i wrote: > i'm sorry if this is obviously wrong (i haven't used Text.Regex), but > can't you do this with submatches? rights or wrongs of regexps aside, i just checked that the above approach *is* feasible with Text.Regex here's some code: >module Multimatch(multimatch) where > import Text.Regex > import qualified Data.List as DL > import qualified Data.Maybe as DM > > brcount :: String -> Int > brcount ('\\' : _ : s) = > brcount s > brcount ('(' : s) = > 1 + brcount s > brcount (_ : s) = > brcount s > brcount [] = > 0 > > -- given a list of strings representing regular expressions, > -- each associated with a tag, match against a string > -- and return the match, along with the associated tag, > -- or Nothing if there's no match. > multimatch :: [(tag, String)] -> (String -> Maybe (tag, String)) > multimatch rs = > let re = mkRegex $ DL.intercalate "|" $ map ((\s -> "(x(" ++ s ++ "))") . snd) rs in > let tags = submatches rs in > (\ s -> > do > ms <- matchRegex re ("x" ++ s) > (tag, m) <- DL.find (\(_, m) -> not (null m)) (zip tags ms) > return (DM.fromJust tag, tail m)) > submatches [] = > [] > submatches ((tag, r) : rs) = > (Just tag : take (brcount r + 1) (repeat Nothing)) ++ submatches rs i'm sure there's a more compact implementation in there somewhere: i'm just a haskell newbie. cheers, rog.

1 0

Re: [Haskell-cafe] Memory efficiency questions for real-time graphics
by T Willingham 05 Nov '08

05 Nov '08

On Sat, Nov 1, 2008 at 2:11 PM, Sebastian Sylvan <sebastian.sylvan(a)gmail.com> wrote: > On Sat, Nov 1, 2008 at 6:57 PM, T Willingham <t.r.willingham(a)gmail.com> >> >> The per-vertex computation is a quite complex time-dependent function >> applied to the given domain on each update. Yet even if it were >> simple, I would still first implement the formulas in Haskell and >> leave the optimization for later, if at all. > > I'd be very surprised to see a vertex transform that would be faster to > implement on the CPU than the GPU. It appears you misunderstood "complex time-dependent function". This is quite a bit of Haskell code involving a significant amount of octonion algebra. It could, in principle, be put on the GPU, however that should be the very last step after everything else works. > There are various ways of writing out your vertex data too, so if it doesn't > change too often you can still do the transformation on the GPU, As I previously stated, it changes every frame. Take a highly complicated function and apply it to N vertices. Now increase N until the framerate is affected. That is where I am. It is obvious that any N-sized allocations will cause the framerate to stutter. This is not just theoretical: I *see* it as I increase N while it's running. This is the point of my initial email, the subject of which is memory efficiency.

5 6

Making 'community' server our social network
by Maurício 05 Nov '08

05 Nov '08

Hi, I've beeing doing something with darcs that is so great that, although I'm sure a lot of people are already doing the same, I think it would be nice to share with you. I did 'cd ~' and then: darcs initialize darcs add .emacs darcs add .xmonad/xmonad.hs darcs add .inputrc ... etc. So I'm using darcs to keep track of all my configuration files, and now I don't need to care about reinstalling the OS, changing machines from office to home, changing configurations and then realizing it was a mistake etc. Then I thought community.haskell.org could offer a default darcs repositories for all users named after their owners. For instance, if you want to check my personal files you would do: darcs get http://code.haskell.org/MauricioAntunes That would allow us not only to share our configuration, but also share all those small files that are not "professional" enough to became projects for their own, but that are nevertheless interesting since we put our good ideas there: scripts to start our favorite software or do system maintenance; small Haskell utilities to do some cool math or science trick, stress some language feature or download our standard music collection from the web; a list of favorite sites and a related completion script so we can list then in 'dmenu' completion; etc. etc. etc. The next bonus step would be to get a list at all users default repository main page of all other users they have granted write access to some of their projects. Then we would be able to navigate throw linked lists of people with related interests and needs. I think we need no more to get what will be MySpace, Facebook or something else for text-driven people. And then, of course, world domination. Although I don't really imagine any business model around that :) Best, Maurício

6 5

Re: [Haskell-cafe] HXT/Practical/Weather.hs difficulties
by Brian Troutwine 05 Nov '08

05 Nov '08

Oh my, how silly of me. The page has moved to http://www.weather.gov/xml/current_obs/KAGC.xml ! Firefox simply follows the redirect. Thanks for the putStrLn suggestion, George. On Tue, Nov 4, 2008 at 5:28 PM, George Pollard <porges(a)porg.es> wrote: > On Tue, 2008-11-04 at 17:04 -0800, Brian Troutwine wrote: >> > blt@doritos:~ >> > $ ./weather >> > >> > error: ""<!DOCTYPE HTML PUBLIC \"-//IETF//DTD HTML 2.0/..."" (line 1, column 16): >> > unexpected "P" >> > expecting white space, "[" or ">" >> > >> > Unable to parse weather data. >> >> Woops. Would someone be so kind as to explain why this is failing? I'm >> at rather a loss. > > The HXT parser is stopping because it's expecting XML not HTML, which is > what you're receiving for some reason. > > I just loaded up the weather URL in Firefox > [http://www.weather.gov/xml/current_obs/KAGC.xml] and it is XML... Is it > possible that you are behind a proxy that is blocking the page? (I can't > run the code at the moment; cleaning out Haskell packages to upgrade to > 6.10.) > > You could try printing out the contents of the page as well (putStrLn > doc) so you can see the rest of the HTML that `weather` is receiving. > -- Brian

1 0

HXT/Practical/Weather.hs difficulties
by Brian Troutwine 05 Nov '08

05 Nov '08

Hello all, I'm working through the practical HXT examples and have gotten stumped with the weather example[1]. I'm using GHC 6.8.3 and HXT 8.1.0. I compile the example like so... > blt@doritos:~ > $ ghc --make weather.hs > [1 of 1] Compiling Main ( weather.hs, weather.o ) > Linking weather ... And execute it... > blt@doritos:~ > $ ./weather > > error: ""<!DOCTYPE HTML PUBLIC \"-//IETF//DTD HTML 2.0/..."" (line 1, column 16): > unexpected "P" > expecting white space, "[" or ">" > > Unable to parse weather data. Woops. Would someone be so kind as to explain why this is failing? I'm at rather a loss. [1] http://www.haskell.org/haskellwiki/HXT/Practical/Weather1 --Brian P.S. Is this question better suited to the haskell-beginner list?

1 0

announce [("InfixApplicative", 1.0), ("OpenGLCheck", 1.0), ("obj", 0.1)]
by Thomas Davie 05 Nov '08

05 Nov '08

Dear Haskellers, I've just uploaded a few packages to Hackage which I have produced while working at Anygma. I thought that people might be interested in knowing about these: obj-0.1: A library for loading and writing obj 3D models. This is still an early version and rather limited, but it's a starting point. Features: • Load models, complete with normals, texture coordinates and materials • Compute normals where smoothing groups are specified • An example program to load an obj model and render it spinning on the screen. • Faster loading that Maya itself! Bugs: • Memory usage is rather large • The exposed API is rather limited To Dos: • Add support for loading groups • Support for smooth surfaces OpenGLCheck-1.0: A micro-package containing instances of Arbitrary for the data structures provided in Graphics.Rendering.OpenGL. InfixApplicative-1.0: A second micro-package containing a pair of functions -- (<^) and (^>) which can be used to provide an infix liftA2 thus: Suppose we wanted to calculate liftA2 (+) [1,2] [2,3], but are unhappy with the fact that (+) is no longer infix, we may now use [1,2] <^(+)^> [2,3] Thanks -- any comments are greatly appreciated! Tom Davie

1 0

Syntax question regarding 'import'
by Maurício 05 Nov '08

05 Nov '08

Hi, About this teste code: module Main (main) where { import Foreign hiding (unsafePerformIO,Foreign.Ptr,Data.Bits,) ; blo = xor 10 10 :: Int ; main = return () } Data.Bits is in the 'hiding' list. According to the syntax reference, this seems not to be allowed. GHC allows it, but do allow following code to use 'xor' from Data.Bits. I think this is correct, since 'xor' was exported by Foreign unqualified, but does 'Data.Bits' in that list mean something or it's just ignored? Haskell syntax allows a comma at the end of names to be imported or exported, like in the second line. What does that mean? Thanks, Maurício

3 3

Re: [Haskell-cafe] code generation
by Martin Hofmann 04 Nov '08

04 Nov '08

Sorry for referring to a post, a bit ago. > http://www-users.cs.york.ac.uk/~ndm/derive/ (Deriving Generic Functions > by Example). > Thanks for the pointer, it was already on my to-read-pile :-) > I think using Template Haskell for your work would fit very nicely, so > is a good choice to learn :-) > I already got used to TH a bit, but I am not sure if it is appropriate for my purpose, or at least not completely. I want to load Haskell code into my program at runtime in an abstract representation (as TH), modify it and then type-check it or coerce it into a value (or execute it). For me it looks like I need a combination of Hint and TH. However, Hint can only interpret strings and to get a string from a QExp I have to enter the IO Monad using runQ. So, wouldn't it deteriorate my performance to do it all in the IO? Is there another way? Thanks, Martin

2 1

Network.FastCGI does not emit stderr outputs to lighttpd's error.log?
by Agent Zhang 04 Nov '08

04 Nov '08

Hi, I'm trying Network.FastCGI + lighttpd 1.4.9 to develop a RESTful service platform. I've found that stderr (especially those from Debug.Trace) get lost in the error.log file. But plain CGI mode with Network.CGI works perfectly (all stderr outputs appear in error.log). Besides, my Perl fastcgi script also logs stderr with the same lighttpd. So it does seem that my lighttpd's mod_fastcgi module is OK. Is this a known issue in the Haskell fastcgi library? Is there a workaround or a fix? Thanks in advance :) Cheers, -agentzh

3 4

a minimal Windows program in Haskell?
by Nun Aurbiz 04 Nov '08

04 Nov '08

How do I make a minimal Windows application in Haskell? I know there are Win API bindings in the libraries, and of course the ffi lets you call into and out of C, but I have no sense of how to bring it all together. I can't find any samples either. Is the Haskell code the "main" application and you just ffi into the Win API? Or does it ffi into a win_main.c that I write? Or is the win_main.c the "main" application and it calls into Haskell? Here is what I am talking about by a "minimal Windows application" (written in psuedo C code). #define WIN32_LEAN_AND_MEAN #include <windows.h> LRESULT CALLBACK windowsProcedure(..) { switch(message) { case WM_CLOSE: PostQuitMessage(0); return 0; } return DefWindowProc(..); } int APIENTRY WinMain(..){ WNDCLASS window_class; RegisterClass(&window_class) window = CreateWindow(..); ShowWindow(..); while(true) { /* do whatever */ while(PeekMessage(..)) if(msg.message == WM_QUIT) return msg.wParam; else DispatchMessage(&msg); } return 0; }

2 3

ANNOUNCE: Graphalyze-0.5 and SourceGraph-0.3
by Ivan Lazar Miljenovic 04 Nov '08

04 Nov '08

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 I've just submitted my thesis this morning (w00t!!!) and as such I'm announcing the latest versions of Graphalyze [1,2] and SourceGraph [3,4], which fix a couple of bugs in the previous versions (these bugs were fixed whilst waiting for my supervisor to finish reading through my draft, and as such I had to re-write bits of my thesis that talked about the limitations of the software :s ). [1] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Graphalyze [2] http://code.haskell.org/Graphalyze [3] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/SourceGraph [4] http://code.haskell.org/SourceGraph Briefly, SourceGraph is a utility that uses the Graphalyze library to analyse Cabalized Haskell software. Its input/output is rather restrictive at the moment: it takes a single argument, which is the path to a .cabal file, and then produces an HTML report in: <project directory>/SourceGraph/<project name>.html This report contains visualisation of the code for each module, for the imports (similar to what graphmod [5] does) as well as the entire code base. Furthermore, the entire code base is also visualised with functions grouped by the modules they're defined in, as well some simple analyses (such as comparing the export list to what functions are actually roots, similar to the output for top-level functions returned by GHC when using -fwarn-unused-binds). Main changes in Graphalyze since version 0.4: * When writing my thesis, I found some obvious silly mistakes (such as copying the rootsOf function definition to leavesOf, but not changing the function definition). * Images in the document representation are now inline elements. * When using Pandoc [6] for document generation, the size of generated graphs is now customisable on a per-format basis; furthermore, for web pages graph visualisations link to larger versions. Also, graph visualisations can now be created in a sub-directory. Main changes in SourceGraph since version 0.2: * Now uses Cabal 1.6 * Improve visual layout of generated HTML report (still no CSS though). * "Smarter" analysis: don't show trivial analysis results, and when analysing the entire code base don't return cliques, etc. that contain functions all in the same module (as they would have been reported in the per-module section). Note, however, that the parsing limitations for version 0.2 still apply: cpp is still as-yet unsupported (as I'm not sure what I'll do about choosing cpp flags); Template Haskell, HaRP and HXML are still ignored and functions in class declarations/records are still ignored (the former because it's ambiguous which actual function you want, the latter because they're boring :p ). Also, SourceGraph is _still_ not a refactoring tool ;-) If anyone's interested, I'll soon be uploading the final version of my thesis to my blog. Also, if anyone is interested in hacking on any of this, feel free! I'll probably leave it for a while (I'm going to be doing Java coding over summer, blech :s ), but I intend to come back to it later on. - -- Ivan Lazar Miljenovic Ivan.Miljenovic(a)gmail.com IvanMiljenovic.wordpress.com -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.9 (GNU/Linux) iEYEARECAAYFAkkOcaAACgkQfEfFJ9JhvyjhIwCeM9VXsJeSVK2CdWURJDer6zoA A5YAoIfayHtjpw0qt/gyPZhhhypOwzSh =x+/X -----END PGP SIGNATURE-----

3 4

Typeable and Dynamic
by minh thu 04 Nov '08

04 Nov '08

Hi, Given a TypeRep and a Dynamic value with type corresponding to the TypeRep, I'd like to be able to use fromDyn *without* specifying a type (given as an additional 'default' argument) (since it is somewhat known from the TypeRep). That is, I'd like an undefinedOf that can be used in extract :: Typeable a => TypeRep -> Dynamic -> a extract typerep dyn = fromDyn (undefinedOf typerep) dyn For instance, if TypeRep is Int, extract Int dyn = fromDyn (undefined::Int) dyn Is it possible to write "extract" ? Thanks, Thu

3 3