- Haskell-Cafe - Haskell.org

haskelldb, how to escape table names
by Günther Schmidt 06 Apr '09

06 Apr '09

Hi, how can I "escape" table and column names, from something like: kh-internes-kennz to this: [kh-internes-kennz] ? Günther

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Combining sequences
by michael rice 06 Apr '09

06 Apr '09

Is there a simple way to combine two sequences that are in ascending order into a single sequence that's also in ascending order? An example would be the squares [1,4,9,16,25..] combined with the cubes [1,8,27,64,125..] to form [1,1,4,8,9,16,25,27..]. Michael

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Reverting to any old version using Darcs
by Peter Verswyvelen 06 Apr '09

06 Apr '09

Rumor goes that this is very difficult to do with Darcs. Is this correct?

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Confused about readline/editline
by Martijn van Steenbergen 05 Apr '09

05 Apr '09

Hello café, I'm trying to write an executable that depends on Yogurt-0.3, readline (indirectly) and hint. However, including hint in the build-depends field causes cabal to link the executable against editline instead of readline. Here is a small test case: File: Test.cabal > Name: Test > Version: 0 > > Build-Type: Simple > Cabal-Version: >= 1.2 > > Executable test > Main-Is: Test.hs > Build-Depends: base, Yogurt, hint > GHC-Options: -threaded File: Test.hs > module Main where > > import Network.Yogurt > > main:: IO () > main = do > connect "eclipse.cs.pdx.edu" 7680 (return ()) The example doesn't use any functions from hint, but simply mentioning it in the cabal file causes this behaviour. What's going on? How can I fix or work around this? I am able to reproduce this behaviour in two configurations: * Leopard Intel; cabal-install version 0.6.2, using version 1.6.0.1 of the Cabal library; GHC 6.10.1 * Ubuntu; cabal-install version 0.6.2, using version 1.6.0.3 of the Cabal library; GHC 6.10.2 Thank you very much in advance, Martijn.

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Hackage not updating package list
by Johan Tibell 05 Apr '09

05 Apr '09

Hi, I just uploaded network-2.2.1. It appears on Hackage [1] but a `cabal update` followed by `cabal install network-2.2.1` results in: Resolving dependencies... cabal: There is no available version of network that satisfies ==2.2.1 The upload took a very long time and it seemed to time out at some point. My guess is that Hackage got itself into an inconsistent state. Could someone who has access to the Hackage server check what happened? 1. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/network-2.2.1 Cheers, Johan

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Link errors in Gtk2Hs are more general than I thought.
by Jeff Heard 05 Apr '09

05 Apr '09

I tried to get yi to run on my Mac earlier and I get the following errors: dyld: lazy symbol binding failed: Symbol not found: _cairo_quartz_font_face_create_for_atsu_font_id Referenced from: /opt/local/lib/libpangocairo-1.0.0.dylib Expected in: /opt/local/lib/libcairo.2.dylib dyld: Symbol not found: _cairo_quartz_font_face_create_for_atsu_font_id Referenced from: /opt/local/lib/libpangocairo-1.0.0.dylib Expected in: /opt/local/lib/libcairo.2.dylib Trace/BPT trap The commands I used to install gtk2hs (which gave me no errors were) $ sudo port selfupdate $ sudo port install gtk2 cairo librsvg libglade2 gtksourceview2 gtkglext $ sudo port install gtk-chtheme gtk2-clearlooks && sudo port -k install ghc gtk2hs hs-cabal $ cabal install yi Running OS X 10.5.6 (Leopard) on a MacBook 2.4 gHz Core 2 Duo -- Jeff ---------- Forwarded message ---------- From: Jeff Heard <jefferson.r.heard(a)gmail.com> Date: Sat, Apr 4, 2009 at 2:01 PM Subject: Leksah+Gtk2Hs link error on Mac OS X Leopard To: Haskell Cafe <haskell-cafe(a)haskell.org> I tried installing leskah on OS X using the x11 version of gtk2hs (because I use gtkglext a lot in my work, and need it, therefore the quartz build won't work for me) I get these errors. Is this leksah specific or is this a more general problem with gtk2hs? Linking dist/build/leksah/leksah ... ld warning: atom sorting error for _ghczm6zi10zi1_LibFFI_Czuffizutype_closure_tbl and _ghczm6zi10zi1_LibFFI_Czuffizucif_closure_tbl in /opt/local/lib/ghc-6.10.1/ghc-6.10.1/libHSghc-6.10.1.a(LibFFI.o) ld warning: atom sorting error for _ghczm6zi10zi1_LibFFI_Czuffizutype_closure_tbl and _ghczm6zi10zi1_LibFFI_Czuffizucif_closure_tbl in /opt/local/lib/ghc-6.10.1/ghc-6.10.1/libHSghc-6.10.1.a(LibFFI.o) $ ~/.cabal/bin/leksah dyld: lazy symbol binding failed: Symbol not found: _cairo_quartz_font_face_create_for_atsu_font_id Referenced from: /opt/local/lib/libpangocairo-1.0.0.dylib Expected in: /opt/local/lib/libcairo.2.dylib dyld: Symbol not found: _cairo_quartz_font_face_create_for_atsu_font_id Referenced from: /opt/local/lib/libpangocairo-1.0.0.dylib Expected in: /opt/local/lib/libcairo.2.dylib Trace/BPT trap

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trying to download "leksah" ....
by Vasili I. Galchin 05 Apr '09

05 Apr '09

vigalchin@ubuntu:~/FTP$ darcs get http://code.haskell.org/leksah Invalid repository: http://code.haskell.org/leksah darcs failed: Failed to download URL http://code.haskell.org/leksah/_darcs/inventory : HTTP error (404?) I did a google on "HTTP 404" => not found .... why? Kind regards, Vasili

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Haskell Weekly News: Issue 112 - April 5, 2009
by Brent Yorgey 05 Apr '09

05 Apr '09

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20090405 Issue 112 - April 05, 2009 --------------------------------------------------------------------------- Welcome to issue 112 of HWN, a newsletter covering developments in the [1]Haskell community. Announcements hgettext-0.1.5 - GetText based internationalization of Haskell programs. Vasyl Pasternak [2]announced a new release of the [3]hgettext package for internationalization of Haskell programs, which now supports distribution and installation of PO files. Buster 0.99.1, a library for application orchestration that is not FRP. Jeff Heard [4]announced the release of [5]Buster, an FRP-like framework for constructing reactive programs with a bus model. Call for Contributions - Haskell Communities and Activities Report, May 2009 edition. Janis Voigtlaender [6]issued a call for contributions to the 16th edition of the [7]Haskell Communities & Activities Report. The submission deadline is 1 May 2009. If you are working on any project that is in some way related to Haskell, please write a short entry and submit it. Even if the project is very small or unfinished or you think it is not important enough -- please reconsider and submit an entry anyway! fad 1.0 -- Forward Automatic Differentiation library. Bjorn Buckwalter [8]announced the initial release of the Haskell [9]fad library, developed by Barak A. Pearlmutter and Jeffrey Mark Siskind. Fad provides Forward Automatic Differentiation (AD) for functions polymorphic over instances of 'Num'. hledger 0.4 released. Simon Michael [10]announced the release of [11]hledger 0.4, a text-mode double-entry accounting tool. It reads a plain text journal file describing your transactions and generates precise activity and balance reports. Changes include the ability to serve reports in a web browser, and many other fixes and improvements. GHC version 6.10.2. Ian Lynagh [12]announced a new patchlevel release of [13]GHC. This release contains a number of bugfixes relative to 6.10.1, including some performance fixes; see the [14]release notes. Beta of Leksah IDE available. Jürgen Nicklisch-Franken [15]announced release 0.4.4 of [16]Leksah, the Haskell IDE written in Haskell. Current features include on the fly error reporting with location of compilation errors, completion , import helper for constructing import statements, module browser with navigation to definition, project management support based on Cabal with a visual editor, "source candy", and more. satchmo: monadic SAT encoding library. Johannes Waldmann [17]announced a preliminary version of [18]satchmo, a monadic library for encoding boolean and integral number constraints to CNF-SAT. It uses [19]minisat as a backend solver. vacuum-cairo: a cairo frontend to vacuum for live Haskell data visualization. Don Stewart [20]announced the release of [21]vacuum-cairo, a Haskell library for interactive rendering and display of values on the GHC heap using Matt Morrow's vacuum library. This library takes vacuum's output, generates dot graph format from it, renders it to SVG with graphviz, and displays the resulting structure using the gtk2hs Cairo vector graphics bindings ... all at the GHCi command line. Watch some [22]screencasts! vacuum: extract graph representations of ghc heap values.. Matt Morrow [23]announced the release of [24]vacuum, a library for extracting graph representations of values from the GHC heap, which may then be further processed and/or translated to Graphviz dot format to be visualized. new release of HTTP, version 4000.0.5. Sigbjorn Finne [25]announced a [26]new version of the HTTP package, which includes a bunch of fixes and cleanups along with some API documentation. type-level programming support library. spoon [27]asked for feedback on a [28]support library for type level programming. cmonad 0.1.1. Lennart Augustsson [29]announced the [30]CMonad package, which allows one to write Haskell code in a C style. Marketing Haskell. Ketil "Simon Peyton-Jones" Malde [31]announced the new [32]official Haskell mascot. Haskell Platform: status update and call for volunteers. Duncan Coutts gave an [33]update on the status of the [34]Haskell Platform. There are no more policy questions to resolve for the first release. It is a matter of getting things done. The first platform release will contain ghc-6.10.2, the "extra libs", haddock, happy and alex, and the cabal command line tool and it's dependencies. We are calling for volunteers for an action group. We need volunteers to take charge of various platforms and to manage the overall release. See Duncan's email for a list of what is needed, and volunteer! Blog noise [35]Haskell news from the [36]blogosphere. * Jeff Heard: [37]Major updates to Buster. * Bjorn Buckwalter: [38]ANNOUNCE: fad 1.0---Forward Automatic Differentiation for Haskell. * Roman Cheplyaka: [39]Hpysics + GrapeFruit (and hackathon). * Joachim Breitner: [40]Bejeweled AI in Haskell. * >>> iampalmmute: [41]Vacuum + Ubigraph. Visualizing Haskell values in 3D. * Jeff Heard: [42]ANN: Buster, the not quite entirely unlike FRP library.. * Edward Kmett: [43]Reflecting On Incremental Folds. * beelsebob: [44]How you should(n't) use Monad. * Sean Leather: [45]Incremental attributes. * Jeff Heard: [46]Almost, but not quite entirely unlike FRP.. * >>> Gregory Collins: [47]Building a website with Haskell, part 2. * >>> Rubin Mcgowan: [48]Irradiation Tracing in Haskell. * Conal Elliott: [49]Notions of purity in Haskell. * mightybyte: [50]Finished HAppS Application. * Sean Leather: [51]Experiments with EMGM: Emacs org files. * Yi: [52]Haddock is back. * >>> Lab 49: [53]Does Haskell Support Subtyping? It Depends.. * >>> Tim Lopez: [54]Haskell Performance: Lowercase. * >>> Gregory Collins: [55]Building a website with Haskell, part 1. * happstack.com: [56]Happstack-powered Website launched by Gregory David Collins. * >>> LispCast: [57]Writing map in Haskell. * >>> hellfeuer: [58]Laziness and Dynamic Programming. * >>> Leon Smith: [59]Lloyd Allison's Corecursive Queues. Quotes of the Week * mstr: haskell is like f'gg'fggf'fg'g'fg'foldliftM2 f g ''f' :) * simonmar: Wondering how popular Haskell needs to become for intel to optimize their processors for my runtime, rather than the other way around * quicksilver: [about uninstalling packages installed with cabal-install] packages are for life, not just for christmas. * Ethereal: If this conversation had been had in #python #ruby or #php it would have lots of angry people shouting about how it doesn't matter or isn't true or isn't important and what's the point, and no, you guys are like ahhh but no, your preconceived notions of dimensional space are so passe. * Duqicnk: a monad is like a train that runs backwards in time, which is made of tiny chocolate robots * jfredett: I do all of my version numbers in Roman Numerals... * Cale: But in another sense, functional programmers are applied logicians who spend all their time proving trivial theorems in interesting ways in an inconsistent intuitionist logic. About the Haskell Weekly News New editions are posted to [60]the Haskell mailing list as well as to [61]the Haskell Sequence and [62]Planet Haskell. [63]RSS is also available, and headlines appear on [64]haskell.org. To help create new editions of this newsletter, please see the information on [65]how to contribute. Send stories to byorgey at cis dot upenn dot edu. The darcs repository is available at darcs get [66]http://code.haskell.org/~byorgey/code/hwn/ . References 1. http://haskell.org/ 2. http://article.gmane.org/gmane.comp.lang.haskell.cafe/56301 3. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hgettext 4. http://article.gmane.org/gmane.comp.lang.haskell.cafe/56209 5. http://vis.renci.org/jeff/buster 6. http://article.gmane.org/gmane.comp.lang.haskell.cafe/56148 7. http://www.haskell.org/communities/ 8. http://article.gmane.org/gmane.comp.lang.haskell.cafe/56268 9. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/fad 10. http://article.gmane.org/gmane.comp.lang.haskell.general/17054 11. http://hledger.org/ 12. http://article.gmane.org/gmane.comp.lang.haskell.general/17041 13. http://www.haskell.org/ghc/ 14. http://haskell.org/ghc/docs/6.10.2/html/users_guide/release-6-10-2.html 15. http://article.gmane.org/gmane.comp.lang.haskell.cafe/56116 16. http://www.leksah.org/ 17. http://article.gmane.org/gmane.comp.lang.haskell.cafe/56107 18. http://dfa.imn.htwk-leipzig.de/satchmo/ 19. http://minisat.se/ 20. http://article.gmane.org/gmane.comp.lang.haskell.cafe/56063 21. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/vacuum-cairo 22. http://www.youtube.com/watch?v=oujaqo9GAmA 23. http://article.gmane.org/gmane.comp.lang.haskell.cafe/56062 24. http://moonpatio.com/vacuum/ 25. http://article.gmane.org/gmane.comp.lang.haskell.cafe/56058 26. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HTTP 27. http://article.gmane.org/gmane.comp.lang.haskell.cafe/55983 28. http://www.killersmurf.com/projects/typelib 29. http://article.gmane.org/gmane.comp.lang.haskell.cafe/55936 30. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/cmonad 31. http://article.gmane.org/gmane.comp.lang.haskell.general/17021 32. http://www.haskell.org/pipermail/haskell/attachments/20090401/9fb8fa05/hask… 33. http://article.gmane.org/gmane.comp.lang.haskell.general/17020 34. http://www.haskell.org/haskellwiki/Haskell_Platform 35. http://planet.haskell.org/ 36. http://haskell.org/haskellwiki/Blog_articles 37. http://vis.renci.org/jeff/2009/04/03/major-updates-to-buster/ 38. http://flygdynamikern.blogspot.com/2009/04/announce-fad-10-forward-automati… 39. http://physics-dph.blogspot.com/2009/04/hpysics-grapefruit-and-hackathon.ht… 40. https://www.joachim-breitner.de/blog/archives/324-Bejeweled-AI-in-Haskell.h… 41. http://www.youtube.com/watch?v=3mMH1cHWB6c 42. http://vis.renci.org/jeff/2009/04/01/ann-buster-the-not-quite-entirely-unli… 43. http://comonad.com/reader/2009/incremental-folds/ 44. http://noordering.wordpress.com/2009/03/31/how-you-shouldnt-use-monad/ 45. http://feedproxy.google.com/~r/splonderzoek/~3/4B0bHoeTCeQ/incremental-attr… 46. http://vis.renci.org/jeff/2009/03/31/almost-but-not-quite-entirely-like-frp/ 47. http://gregorycollins.net/posts/2009/03/30/building-a-website-part-2 48. http://rubinmcgowaneh.blogspot.com/2009/03/irradiation-tracing-in-haskell.h… 49. http://conal.net/blog/posts/notions-of-purity-in-haskell/ 50. http://softwaresimply.blogspot.com/2008/02/finished-happs-application.html 51. http://feedproxy.google.com/~r/splonderzoek/~3/6bxI33NIRMc/experiments-with… 52. http://yi-editor.blogspot.com/2009/03/haddock-is-back.html 53. http://blog.lab49.com/archives/2954 54. http://www.brool.com/index.php/haskell-performance-lowercase 55. http://gregorycollins.net/posts/2009/03/28/building-a-website-part-1 56. http://blog.happstack.com/2009/03/28/happstack-powered-website-launched-by-… 57. http://www.lispcast.com/haskell-map.html 58. http://caffeinatedcode.wordpress.com/2009/03/26/laziness-and-dynamic-progra… 59. http://blog.melding-monads.com/2009/03/09/lloyd-allisons-corecursive-queues/ 60. http://www.haskell.org/mailman/listinfo/haskell 61. http://sequence.complete.org/ 62. http://planet.haskell.org/ 63. http://sequence.complete.org/node/feed 64. http://haskell.org/ 65. http://haskell.org/haskellwiki/HWN 66. http://code.haskell.org/~byorgey/code/hwn/

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Re: [Haskell-cafe] Combining sequences
by michael rice 05 Apr '09

05 Apr '09

Thanks, guys! This one works perfectly. I was monkeying with similar logic but wasn't sure about syntax. Michael --- On Sat, 4/4/09, Andrew Wagner <wagner.andrew(a)gmail.com> wrote: From: Andrew Wagner <wagner.andrew(a)gmail.com> Subject: Re: [Haskell-cafe] Combining sequences To: "michael rice" <nowgate(a)yahoo.com> Cc: haskell-cafe(a)haskell.org Date: Saturday, April 4, 2009, 8:56 PM Here's a pretty straightforward approach: combine [] ys = ys combine xs [] = xs combine (x:xs) (y:ys) | x <= y = x : combine xs (y:ys) | otherwise = y : combine (x:xs) ys On Sat, Apr 4, 2009 at 8:40 PM, michael rice <nowgate(a)yahoo.com> wrote: Is there a simple way to combine two sequences that are in ascending order into a single sequence that's also in ascending order? An example would be the squares [1,4,9,16,25..] combined with the cubes [1,8,27,64,125..] to form [1,1,4,8,9,16,25,27..]. Michael _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

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ANNOUNCE: fad 1.0 -- Forward Automatic Differentiation library
by Bjorn Buckwalter 04 Apr '09

04 Apr '09

I'm pleased to announce the initial release of the Haskell fad library, developed by Barak A. Pearlmutter and Jeffrey Mark Siskind. Fad provides Forward Automatic Differentiation (AD) for functions polymorphic over instances of 'Num'. There have been many Haskell implementations of forward AD, with varying levels of completeness, published in papers and blog posts[1], but alarmingly few of these have made it into hackage -- to date Conal Elliot's vector-spaces[2] package is the only one I am aware of. Fad is an attempt to make as comprehensive and usable a forward AD package as is possible in Haskell. However, correctness is given priority over ease of use, and this is in my opinion the defining quality of fad. Specifically, Fad leverages Haskell's expressive type system to tackle the problem of _perturbation confusion_, brought to light in Pearlmutter and Siskind's 2005 paper "Perturbation Confusion and Referential Transparency"[3]. Fad prevents perturbation confusion by employing type-level "branding" as proposed by myself in a 2007 post to haskell-cafe[4]. To the best of our knowledge all other forward AD implementations in Haskell are susceptible to perturbation confusion. As this library has been in the works for quite some time it is worth noting that it hasn't benefited from Conal's ground-breaking work[5] in the area. Once we wrap our heads around his beautiful constructs perhaps we'll be able to borrow some tricks from him. As mentioned already, fad was developed primarily by Barak A. Pearlmutter and Jeffrey Mark Siskind. My own contribution has been providing Haskell infrastructure support and wrapping up loose ends in order to get the library into a releasable state. Many thanks to Barak and Jeffrey for permitting me to release fad under the BSD license. Fad resides on GitHub[6] and hackage[7] and is only a "cabal install fad" away! What follows is Fad's README, refer to the haddocks for detailed documentation. Thanks, Bjorn Buckwalter [1] http://www.haskell.org/haskellwiki/Functional_differentiation [2] http://www.haskell.org/haskellwiki/Vector-space [3]: http://www.bcl.hamilton.ie/~qobi/nesting/papers/ifl2005.pdf [4]: http://thread.gmane.org/gmane.comp.lang.haskell.cafe/22308/ [5]: http://conal.net/papers/beautiful-differentiation/ [6] http://github.com/bjornbm/fad/ [7] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/fad ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Copyright : 2008-2009, Barak A. Pearlmutter and Jeffrey Mark Siskind License : BSD3 Maintainer : bjorn.buckwalter(a)gmail.com Stability : experimental Portability: GHC only? Forward Automatic Differentiation via overloading to perform nonstandard interpretation that replaces original numeric type with corresponding generalized dual number type. Each invocation of the differentiation function introduces a distinct perturbation, which requires a distinct dual number type. In order to prevent these from being confused, tagging, called branding in the Haskell community, is used. This seems to prevent perturbation confusion, although it would be nice to have an actual proof of this. The technique does require adding invocations of lift at appropriate places when nesting is present. For more information on perturbation confusion and the solution employed in this library see: <http://www.bcl.hamilton.ie/~barak/papers/ifl2005.pdf> <http://thread.gmane.org/gmane.comp.lang.haskell.cafe/22308/> Installation ============ To install: cabal install Or: runhaskell Setup.lhs configure runhaskell Setup.lhs build runhaskell Setup.lhs install Examples ======== Define an example function 'f': > import Numeric.FAD > f x = 6 - 5 * x + x ^ 2 -- Our example function Basic usage of the differentiation operator: > y = f 2 -- f(2) = 0 > y' = diff f 2 -- First derivative f'(2) = -1 > y'' = diff (diff f) 2 -- Second derivative f''(2) = 2 List of derivatives: > ys = take 3 $ diffs f 2 -- [0, -1, 2] Example optimization method; find a zero using Newton's method: > y_newton1 = zeroNewton f 0 -- converges to first zero at 2.0. > y_newton2 = zeroNewton f 10 -- converges to second zero at 3.0. Credits ======= Authors: Copyright 2008, Barak A. Pearlmutter <barak(a)cs.nuim.ie> & Jeffrey Mark Siskind <qobi(a)purdue.edu> Work started as stripped-down version of higher-order tower code published by Jerzy Karczmarczuk <jerzy.karczmarczuk(a)info.unicaen.fr> which used a non-standard standard prelude. Initial perturbation-confusing code is a modified version of <http://cdsmith.wordpress.com/2007/11/29/some-playing-with-derivatives/> Tag trick, called "branding" in the Haskell community, from Bjorn Buckwalter <bjorn.buckwalter(a)gmail.com> <http://thread.gmane.org/gmane.comp.lang.haskell.cafe/22308/> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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