- Haskell-Cafe - Haskell.org

Questions about slow GC with STArray
by FFT 06 Apr '09

06 Apr '09

I've been following with interest the recent discussions on reddit about the extremely slow hash tables in Haskell compared to F# and OCaml, and as I understood it, this performance problem is caused by GC not liking mutable arrays http://hackage.haskell.org/trac/ghc/ticket/650 It appears from the discussion there that this is more than a simple bug, but a fundamental difficulty (slow writes vs slow GC trade-off). What I'm wondering though is how can this be unique to GHC: all arrays in OCaml and probably F# are mutable (and usually unboxed). How is this problem addressed there? Why is this supposed to be specific to boxed arrays only: wouldn't GC have to scan the whole mutable array whether it's boxed or unboxed?

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EclipseFP proposal for Google Summer of Code
by Thomas ten Cate 06 Apr '09

06 Apr '09

To everyone involved in the Google Summer of Code program, I have submitted a GSoC proposal to work on EclipseFP, the Haskell plugin for Eclipse. The proposal is crossposted to both haskell.org and the Eclipse Foundation, each in their respective templates. This is also stated at the top of the proposal. I send this e-mail because of possible scheduling issues: I will be away starting on April 15. So, if you want to ask me things, have suggestions for improvement, or want to do an interview or something, this can only be done *before* that date. This is also stated in the proposal, but since I have no idea how the proposals are processed by the mentoring organizations, I figured that an explicit notification would be a good idea. For your convenience, here are links to the proposal. haskell.org version: http://socghop.appspot.com/student_proposal/show/google/gsoc2009/thomastc/t… and also on http://docs.google.com/Doc?id=dfmvb7sr_13fzdg5qhr Eclipse Foundation version: http://socghop.appspot.com/student_proposal/show/google/gsoc2009/thomastc/t… and also on http://docs.google.com/Doc?id=dfmvb7sr_15gb9258fg If my schedule causes any problems, please let me know. Also, comments on the proposal in general would be much appreciated. Thanks, Thomas P.S. I hope it's okay that I post this to the haskell-cafe list as well; since haskell.org has no GSoC-specific mailing list, it seems to be the most appropriate place that I could find.

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high probability of installation problems and quality of the glorious implementation
by FFT 06 Apr '09

06 Apr '09

I'm still learning Haskell and also evaluating whether I want to use the language in my work. It seems like a fascinating language so far (although I don't know if laziness will be a detriment later for me eventually), but I'm a bit worried about the overall quality of its GHC implementation. For example, I tried installing GHC-6.10.2 on my Ubuntu 8.04 machine (probably the most mainstream Linux these days). 1st attempt: binary => failed "the impossible happened, report bug" (I think it's already in bugzilla for an even earlier version) 2nd attempt: source and docs => followed README, but "make" failed while building docs 3rd attempt: source only, no docs => make install succeeded, but ghci now seems to have its "readline" screwed up (no editing, can't quit even with Ctrl-C or Ctrl-D), while Ubuntu-bundled 6.8.* ghci works fine in this regard. If these kinds of issues are common only during installation, I can live with that, but if GHC is flaky overall, having to deal with this may cancel out whatever productivity advantages Haskell provides. If the quality of the installation procedures is different from the compiler itself, can you explain why?

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minor typo in "The Haskell 98 Report"
by Benjamin L.Russell 06 Apr '09

06 Apr '09

Today, as I was reading through "The Haskell 98 Report" (see http://www.haskell.org/onlinereport/) I came across a minor typo, but it seems that the only way to fix such typos is to report them on one of the Haskell mailing lists; viz.: >The original committees ceased to exist when the original Haskell 98 Reports were published, so every change was instead proposed to the entire Haskell mailing list. Therefore, please allow me to report this typo, though minor, here, as follows: The Haskell 98 Report - Preface (see http://www.haskell.org/onlinereport/preface-jfp.html) under the heading "Haskell 98: language and libraries," fourth paragraph, second line: >If these program were to be portable, a set of libraries would have to be standardised too. should be as follows: >If these programs were to be portable, a set of libraries would have to be standardised too. (I.e., the word "program" should be plural.) Is this the proper place to report any forthcoming similar typos? -- Benjamin L. Russell -- Benjamin L. Russell / DekuDekuplex at Yahoo dot com http://dekudekuplex.wordpress.com/ Translator/Interpreter / Mobile: +011 81 80-3603-6725 "Furuike ya, kawazu tobikomu mizu no oto." -- Matsuo Basho^

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Re: [Haskell] [OT] Plural forms of the word "octopus" [Was: Re: Marketing Haskell]
by ajb＠spamcop.net 06 Apr '09

06 Apr '09

[Shifted to haskell-cafe.] G'day all. Quoting "Benjamin L.Russell" <DekuDekuplex(a)Yahoo.com>: > According to the Merriam-Webster Online Dictionary, it is "topoi" (see > http://www.merriam-webster.com/dictionary/topos) Topoi form a certain class of category. You can study topous, you can prove theorems about topois and you can discover properties of topon. (That last one is an omega, so it's pronounced more like "top-own".) > Where did you find "octoposi?" In my ancient copy of Liddell and Scott. Here's the online entry: http://tinyurl.com/ck8gst Cheers, Andrew Bromage

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Linking hmatrix without LAPACK
by Duane Johnson 06 Apr '09

06 Apr '09

I'm curious if there is a quick fix to this. I installed GLS and hmatrix, and it runs wonderfully together in ghci. When I run ghc -- make, however, I run into the following link dependency: Linking SilkwormGame ... Undefined symbols: "_dgemm_", referenced from: _multiplyR in libHShmatrix-0.5.0.1.a(lapack-aux.o) "_dgesv_", referenced from: _linearSolveR_l in libHShmatrix-0.5.0.1.a(lapack-aux.o) ... etc Is there a way to tell ghc to not link these? Or am I making a poor assumption that if my code runs in ghci, it does not need LAPACK? Thanks, Duane Johnson

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cabal build on mac os 10.5.6 , can't find gmp
by brian 06 Apr '09

06 Apr '09

Hi, Cabal won't build zlib because it can't find libgmp. It's there, in /sw/lib (fink installation). I've modified the bootstrap script and added -L/sw/lib to the ghc options. This is a mystery in itself because ghc is itself a fink package and should know where gmp is, so that's already a bad sign. I can get to the build step with the additional -L option but then ./ Setup fails again because it can't find gmp. Help .... ? Thanks, Brian

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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 06 Apr '09

06 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 06 Apr '09

06 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 05 Apr '09

05 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/> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

3 2

Announcement: Beta of Leksah IDE available
by Jürgen Nicklisch-Franken 05 Apr '09

05 Apr '09

I'm proud to announce release 0.4.4 of Leksah, the Haskell IDE written in Haskell. Leksahs current features include: * On the fly error reporting with location of compilation errors * Completion * Import helper for constructing the import statements * Module browser with navigation to definition * Search for identifiers with information about types and comments * Project management support based on Cabal with a visual editor * Haskell customised editor with "source candy" * Configuration with session support, keymaps and flexible panes For further information: leksah.org Please don't compare what we have reached to IDE's like VisualStudio, Eclipse or NetBeans. I started Leksah June 1997 and work on it in my spare time for fun. I started the project for various reasons. One was to contribute to make Haskell successful in industry, because I suffer from the use of inappropriate programming languages like C, C++, C# or Java in my daily job. Another was to contribute to open source, which I'm using privately almost exclusively. The first alpha version of Leksah was published February 2008. Since the beginning of this year Hamish Mackenzie joined the project and merged his Funa project with Leksah, which gave a real boost. I thank the people who have encouraged and helped me with their comments, enthusiasm and support. I learned as well that the IDE issue is a controversial theme in the community. I learned that "IDEs are big evil nasty things", that "if you need an IDE, something is wrong with your language", that it is scientifically proved, that "real cool hackers will always use Emacs or vi". Most stupid I found the recurring comment: "Every few years there is someone who starts a Haskell IDE project and then gives up after a few years.". That will be true for Leksah as well, if it will not be accepted and supported by the community. The current state of Leksah is a proof of concept, that an IDE for Haskell is not a difficult thing to do if the community supports it and that it will in my view be of great help and will contribute tremendously to spread Haskell. So I please the members of the community to pause for a moment and try out Leksah with a benevolent attitude. Jürgen Nicklisch-Franken

11 19

.editrc
by brad clawsie 05 Apr '09

05 Apr '09

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 does anyone have a .editrc they can provide that allows ghci to be used on freebsd? i'm not looking for anything fancy, just backspace not being broken etc thanks brad -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.10 (Darwin) iEYEARECAAYFAknVGdQACgkQxRg3RkRK91NZ4gCgm8Oktcs3sCYl6YoY6X4igZAR IDIAn2cpF7QnI4zz4LFN1cVlzG7qSHHk =CJXp -----END PGP SIGNATURE-----

2 1

First time I've gotten gtk2hs to install from ports on Mac OS X from scratch
by Jeff Heard 05 Apr '09

05 Apr '09

The instructions in the leksah manuals seem to work for doing a straight-up ports install of gtk2hs. I've never managed to get it to install without compiling manually, but this worked $ sudo port install gtk2 cairo librsvg libglade2 gtksourceview2 gtkglext gtk-chtheme gtk2-clearlooks $ sudo port -k install ghc gtk2hs hs-cabal Unfortunately leksah itself won't link...

2 2

Leksah+Gtk2Hs link error on Mac OS X Leopard
by Jeff Heard 05 Apr '09

05 Apr '09

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

1 0

about Haskell code written to be "too smart"
by Manlio Perillo 05 Apr '09

05 Apr '09

Hi. In these days I'm discussing with some friends, that mainly use Python as programming language, but know well other languages like Scheme, Prolog, C, and so. These friends are very interested in Haskell, but it seems that the main reason why they don't start to seriously learning it, is that when they start reading some code, they feel the "Perl syndrome". That is, code written to be "too smart", and that end up being totally illegible by Haskell novice. I too have this feeling, from time to time. Since someone is starting to write the Haskell coding style, I really suggest him to take this "problem" into strong consideration. Manlio

40 124

happstack example code wanted
by Johannes Waldmann 05 Apr '09

05 Apr '09

Hi, I'm thinking of using happstack for a simple online registration system. [ Customer gives Name and Address and registers for certain workshops. Then the app server should just produce a bill. (Payment is handled through a different channel.) The "store owner" needs to get some overview of registrations. ] According to happs(tack) marketing department, this should be an easy exercise? Any code that I could use as a starting point? ( Or, if you do the coding, I can link to you from the workshop site. But I don't have a serious budget :-) Thanks - J.W.

3 2

ANN: logfloat 0.12.0.1
by wren ng thornton 05 Apr '09

05 Apr '09

-------------------------------------------- -- logfloat 0.12.0.1 -------------------------------------------- This package provides a type for storing numbers in the log-domain, primarily useful for preventing underflow when multiplying many probabilities as in HMMs and other probabilistic models. The package also provides modules for dealing with floating numbers correctly. -------------------------------------------- -- Now using FFI -------------------------------------------- We now use the FFI to gain access to C's accurate log1p (and expm1) functions. This greatly increases the range of resolution, especially for very small LogFloat values. These are currently exposed from Data.Number.LogFloat, though they may move to a different module in future versions. On GHC 6.10 the use of -fvia-C had to be disabled because it conflicts with the FFI (version 0.12.0.0 still used it, which is fine on GHC 6.8). I'm still investigating the use of -fasm and getting proper benchmarking numbers. Contact me if you notice significant performance degradation. Using the FFI complicates the build process for Hugs; details are noted in the INSTALL file. It may also complicate building on Windows (due to ccall vs stdcall), though I'm not familiar with Windows FFI and don't have a machine to test on. The calling convention is "unsafe" in order to avoid overhead. However, in the past this has been noted to cause issues with multithreaded applications since it locks all RTS threads instead of just the calling thread. If you're using logfloat in a multithreaded application and notice a slowdown, or if you're more familiar with these details than I, tell me so I can fix things. If you have any difficulties with the FFI, let me know. As an interim solution the FFI can be disabled by turning off the useFFI Cabal flag during configure, which will compile the package to use the naive log1p implementation from earlier versions. -------------------------------------------- -- Other changes since 0.11.0 -------------------------------------------- * (0.11.1) Felipe Lessa added an instance for IArray UArray LogFloat. On GHC we use newtype deriving; On Hugs we fall back to unsafeCoerce to distribute the newtype over IArray UArray Double. * (0.11.2 Darcs) Moved the log/exp fusion rules from Data.Number.LogFloat into Data.Number.Transfinite where our log function is defined. * Added a Storable LogFloat instance for GHC. No implementation is available yet for Hugs. * Removed orphaned toRational/fromRational fusion rules, which were obviated by the introduction of the Data.Number.RealToFrac module in 0.11.0. * Changed the Real LogFloat instance to throw errors when trying to convert transfinite values into Rational. -------------------------------------------- -- Compatibility / Portability -------------------------------------------- The package is compatible with Hugs (September 2006) and GHC (6.8, 6.10). For anyone still using GHC 6.6, the code may still work if you replace LANGUAGE pragma by equivalent OPTIONS_GHC pragma. The package is not compatible with nhc98 and Yhc because Data.Number.RealToFrac uses MPTCs. The other modules should be compatible. -------------------------------------------- -- Links -------------------------------------------- Homepage: http://code.haskell.org/~wren/ Hackage: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/logfloat Darcs: http://code.haskell.org/~wren/logfloat/ Haddock (Darcs version): http://code.haskell.org/~wren/logfloat/dist/doc/html/logfloat/ -- Live well, ~wren

4 5

about import alias
by Manlio Perillo 05 Apr '09

05 Apr '09

Hi. Haskell 98 allows import alias: import qualified VeryLongModuleName as C however it does not allow aliasing for imported names import NormalModule (veryLongFunctionName as C) what is the rational? IMHO this can be very useful in some cases. Thanks Manlio

4 3

Re: [Haskell-cafe] How to get glyph outline from ttf font.
by Tillmann Vogt 04 Apr '09

04 Apr '09

Dmitry V'yal schrieb: > Greetings. I'm trying to render some glyphs from ttf font to svg > image using gtk2hs cairo binding. Since I can find nothing appropriate > in gtk2hs API, I decided to draw outlines with bezier curves myself. > But how to get them out of font? As far as I know, freetype library is > capable of extracting outlines, but is there any haskell binding for it > which supports this functionality? > > Here [1] one such lib was mentioned, but it wasn't availible online > that time. Have situation changed today? > > Thanks in advance > > [1] > http://www.nabble.com/Re%3A-Rendering-TTF-fonts-in-Haskell-and-OpenGL-p1563… > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe Hi Dmitry, I cannot help you directly with freetype. But I have developped a library that parses the svg-font format (this is not svg). Since svg-font is XML it is much easier to parse than ttf. There is also a program called fontforge that can be used to convert nearly every format into svg-font. The only problem is that currently triangulation has some bugs and is only O(n^2), the algorithm for deleting holes is not finished, and memoization isn't implemented. Should I upload the work although it is not finished?

1 0

g++ std:map vs GHC IntMap
by Manlio Perillo 04 Apr '09

04 Apr '09

Hi. I have tried to compare performance of the g++ std::map versus the GHC IntMap. The test consists in adding 10000000 elements to an empty map. Haskell code is here: http://hpaste.org/fastcgi/hpaste.fcgi/view?id=2899 C++ code is here: http://hpaste.org/fastcgi/hpaste.fcgi/view?id=2900 The execution time and CPU usage is almost the same. However the C++ version requires 305 MB, the GHC version 617 MB. gcc 4.3.2 ghc 6.8.2 on Debian Linux Lenny, i386. Isn't really possible to optimize memory usage in cases like this? I also tried with Data.HashTable: http://hpaste.org/fastcgi/hpaste.fcgi/view?id=2902 but memory usage is 703 MB, and execution time is about 4.5 times slower! Thanks Manlio Perillo

6 11

Optional EOF in Parsec.
by Kannan Goundan 04 Apr '09

04 Apr '09

I'm writing a parser with Parsec. In the input language, elements of a sequence are separated by commas: [1, 2, 3] However, instead of a comma, you can also use an EOL: [1, 2 3] Anywhere else, EOL is considered ignorable whitespace. So it's not as simple as just making EOL a token and looking for (comma | eol). I've implemented this functionality in a hand-written parser (basically a hack that keeps track of whether the last read token was preceded by an EOL, without making EOL itself a token). Does anybody have ideas about how to do this with Parsec?

4 3

Monad transformer, liftIO
by Michael Roth 04 Apr '09

04 Apr '09

Hello list, maybe I'm just stupid, I'm trying to do something like this: import Control.Monad import Control.Monad.Trans import Control.Monad.List foobar = do a <- [1,2,3] b <- [4,5,6] liftIO $ putStrLn $ (show a) ++ " " ++ (show b) return (a+b) main = do sums <- foobar print sums But this apparently doesn't work... I'm total clueless how to achieve the correct solution. Maybe my mental image on the monad transformer thing is totally wrong? Michael

4 4

Generating functions for games
by gwern0＠gmail.com 04 Apr '09

04 Apr '09

So some time ago I saw mentioned the game of Zendo https://secure.wikimedia.org/wikipedia/en/wiki/Zendo_(game) as a good game for programmers to play (and not just by Okasaki). The basic idea of Zendo is that another player is creating arrangements of little colored plastic shapes and you have to guess what rule they satisfy. I thought it'd be fun to play, but not knowing anyone who has it, I figured a Haskell version would be best. 3D graphics and that sort of geometry is a bit complex, though. Better to start with a simplified version to get the fundamentals right. Why not sequences of numbers? For example: [2, 4, 6] could satisfy quite a few rules - the rule could be all evens, or it could be ascending evens, or it could be incrementing by 2, or it could just be ascending period. Now, being in the position of the player who created the rule is no good. A good guesser is basically AI, which is a bit far afield. But it seems reasonable to have the program create a rule and provide examples. Have a few basic rules, some ways to combine them (perhaps a QuickCheck generator), and bob's your uncle. So I set off creating a dataype. The user could type in their guessed rules and then read could be used to compare. I got up to something like 'data Function = Not | Add' and began writing a 'translate' function, along the lines of 'translate Not = not\ntranslate Add = (+)', at which point I realized that translate was returning different types and this is a Bad Thing in Haskell. After trying out a few approaches, I decided the basic idea was flawed and sought help. Someone in #haskell suggested GADTs, which I've never used. Before I plunge into the abyss, I was wondering: does anyone know of any existing examples of this sort of thing or alternative approachs? I'd much rather crib than create. :) -- gwern

2 1

Possible floating point bug in GHC?
by Peter Verswyvelen 04 Apr '09

04 Apr '09

For days I'm fighting against a weird bug. My Haskell code calls into a C function residing in a DLL (I'm on Windows, the DLL is generated using Visual Studio). This C function computes a floating point expression. However, the floating point result is incorrect. I think I found the source of the problem: the C code expects that all the Intel's x86's floating point register tag bits are set to 1, but it seems the Haskell code does not preserve that. Since the x86 has all kinds of floating point weirdness<http://www.informit.com/articles/article.aspx?p=770362> - it is both a stack based and register based system - so it is crucially important that generated code plays nice. For example, when using MMX one must always emit an EMMS instruction<http://msdn.microsoft.com/en-us/library/590b9ks9(VS.80).aspx>to clear these tag bits. If I manually clear these tags bits, my code works fine. Is this something other people encountered as well? I'm trying to make a very simple test case to reproduce the behavior... I'm not sure if this is a visual C compiler bug, GHC bug, or something I'm doing wrong... Is it possible to annotate a foreign imported C function to tell the Haskell code generator the functioin is using floating point registers somehow?

4 7

Problem with prepose.lhs and ghc6.10.1
by Henry Laxen 04 Apr '09

04 Apr '09

Dear Group, I'm trying to read the paper: "Functional Pearl: Implicit Configurations" at http://www.cs.rutgers.edu/~ccshan/prepose/ and when running the code in prepose.lhs I get: ../haskell/prepose.lhs:707:0: Parse error in pattern which is pointing at: normalize a :: M s a = M (mod a (modulus (undefined :: s))) The paper says it uses lexically scoped type variables. I tried reading about them at: http://www.haskell.org/ghc/docs/latest/html/users_guide/other-type-extensio… so I added -XScopedTypeVariables to my OPTIONS but I still get the same error message. I would really like to play with the code in the paper, but I'm stuck at this point. Any pointers would be appreciated. Best wishes, Henry Laxen

3 2

A fair number of updates to Buster since the other day - 0.99.5
by Jeff Heard 04 Apr '09

04 Apr '09

http://vis.renci.org/jeff/2009/04/03/major-updates-to-buster/ Added several new widgets and several new behaviours related to file reading and writing, exceptions, and the system/program environment. -- Jeff

1 0

ANNOUNCE hgettext-0.1.5 - GetText based internationalization of Haskell programs
by Vasyl Pasternak 04 Apr '09

04 Apr '09

Hello, I have extended my previous version of the library to support distribution and installation of PO files. Source tarball - http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hgettext Also I described how to use this feature to distribute haskell packages in my blog entry http://progandprog.blogspot.com/2009/04/configure-and-install-international… Same description was added to the Haskell Wiki - http://www.haskell.org/haskellwiki/Internationalization_of_Haskell_programs Complete example, which uses internationalization capabilities is here: http://hgettext.googlecode.com/files/hello-0.1.3.tar.gz --- Best regards, Vasyl Pasternak

1 0

Re: [Haskell-cafe] ANNOUNCE: fad 1.0 -- Forward Automatic Differentiation library
by Edward Kmett 03 Apr '09

03 Apr '09

A somewhat tricky concern is that that the extra functionality in question depends on a bunch of primitive definitions that lie below this in the package and the AD engine is used by a layer on top. So moving it out would introduce a circular dependency back into the package or require me to stratify into two packages. When I looked into partitioning the package for another reason I found that I couldn't do so without introducing some orphan instances, so it'll probably be a tricky bit of surgery to split out. That said, it's probably still worth doing. I also agree that I should be somewhat more pedantic about the name. =) -Edward Kmett On Fri, Apr 3, 2009 at 10:49 AM, Barak A. Pearlmutter <barak(a)cs.nuim.ie>wrote: > I feel silly, did not even notice that! Thanks for the pointer. > > Would be sensible to merge the functionalities; will try to import > functionality in Data.Ring.Module.AutomaticDifferentiation currently > missing from Numeric.FAD. > > (One pedantic note: should really be named > Data.Ring.Module.AutomaticDifferentiation.Forward, since it is doing > forward-mode accumulation automatic differentiation; reverse is > an adjoint kettle of fish.) > -- > Barak A. Pearlmutter > Hamilton Institute & Dept Comp Sci, NUI Maynooth, Co. Kildare, Ireland > http://www.bcl.hamilton.ie/~barak/ >

1 0

List and description of language extensions
by Michael Snoyman 03 Apr '09

03 Apr '09

It's been multiple times now that I've been confounded by something in Haskell which was then solved by a language extension (first FunctionalDependencies, most recently ScopedTypeVariables). I'm wondering if there is a list anywhere of all the language extensions supported by GHC and a brief description of them. I looked around, but couldn't find one. If there isn't one, would others be willing to fill one in on the Haskell wiki? I'll do what I can, but I obviously have a very limited knowledge of the extensions available. Thanks, Michael

3 3

Program using 500MB RAM to process 5MB file
by lucas＠die.net.au 03 Apr '09

03 Apr '09

I'm relatively new to haskell so as one does, I am rewriting an existing program in haskell to help learn the language. However, it eats up all my RAM whenever I run the program. http://hpaste.org/fastcgi/hpaste.fcgi/view?id=3175#a3175 Obviously I'm doing something wrong, but without my magical FP pants I don't know what that might be. -- Lucas Hazel <lucas(a)die.net.au>

7 9

Wishful thinking: a text editor that expands function applications into function definitions
by Duane Johnson 03 Apr '09

03 Apr '09

So I was thinking about a "killer feature" for a text editor. Wouldn't it be neat if you could expand function calls into their definitions, in-place? For example, suppose we have "minus" defined like so, somewhere in another file: > minus (a, b, c) (x, y, z) = (a - x, b - y, c - z) Later, we make use of the function in our current context: > let p1 = (1, 2, 3) > p2 = (4, 5, 6) > in p1 `minus` p2 By telling the editor to "expand" the minus, we get a temporary replacing of the above with: > (1 - 4, 2 - 5, 3 - 6) Another example: > parse s = map readLine ls And supposing that readLine is defined somewhere else, moving the cursor to readLine in the line above and "expanding" becomes: > parse s = map (\line -> words $ dropWhile (== ' ') line) This is all pretty standard for the kinds of things we do in Haskell to work it out by hand, but is there any reason the parser couldn't do this? I think it would be even harder to do automatically in any other language. Maybe it's already been attempted or done? Curious, Duane Johnson

5 8

Problem with prepose.lhs and ghc6.10.1
by oleg＠okmij.org 03 Apr '09

03 Apr '09

> ../haskell/prepose.lhs:707:0: Parse error in pattern > which is pointing at: > normalize a :: M s a = M (mod a (modulus (undefined :: s))) The code indeed used lexically scoped type variables -- which GHC at that time implemented differently. Incidentally, on the above line, M s a is the type annotation on the result of (normalize a) rather than on the argument 'a'. Therefore, putting a parentheses like (a :: M s a) is wrong. Since the implementation of local type variables in GHC changed over the years, it's best to get rid of them. Here is the same line in the Hugs version of the code > normalize :: (Modular s a, Integral a) => a -> M s a > normalize a = r a __ > where > r :: (Modular s a, Integral a) => a -> s -> M s a > r a s = M (mod a (modulus s)) Of course the signature for normalize can be omitted. Hugs did not support lexically scoped type variables then (and probably doesn't support now). Today I would have written this definition simpler: > normalize :: (Modular s a, Integral a) => a -> M s a > normalize a = r > where r = M (mod a (modulus (tcar2 r))) > > tcar2:: f s x -> s > tcar2 = undefined (the function tcar2 is used in a few other places in the Hugs code, for a similar purpose).

2 1

ANN: hledger 0.4 released
by Simon Michael 03 Apr '09

03 Apr '09

Dear all, I have released hledger 0.4 on hackage. There is also a new website at http://hledger.org , with screenshots (textual!), a demo (will it survive!?), and docs (not too many!) Release notes are at http://hledger.org/NEWS , and bravely pasted below. In case you forgot: hledger is a text-mode double-entry accounting tool. It reads a plain text journal file describing your transactions and generates precise activity and balance reports. I use it every day to track money and time, and as the basis for client invoices and tax returns. hledger is a partial clone, in haskell, of John Wiegley's excellent ledger. I wrote it because I did not want to hack on c++ and because haskell seemed a good fit. Please cabal update and cabal install hledger and give it a whirl. Install with the "-f happs" flag to enable the new happstack-based web interface. I am sm on the #ledger channel on freenode, and I welcome your feedback, especially if you notice a problem. Best - Simon ------------------------------------------------- 2009/04/03 hledger 0.4 released Changes: * new "web" command serves reports in a web browser (install with -f happs to build this) * make the vty-based curses ui a cabal build option, which will be ignored on MS windows * drop the --options-anywhere flag, that is now the default * patterns now use not: and desc: prefixes instead of ^ and ^^ * patterns are now case-insensitive, like ledger * !include directives are now relative to the including file (Tim Docker) * "Y2009" default year directives are now supported, allowing m/d dates in ledger * individual transactions now have a cleared status * unbalanced entries now cause a proper warning * balance report now passes all ledger compatibility tests * balance report now shows subtotals by default, like ledger 3 * balance report shows the final zero total when -E is used * balance report hides the final total when --no-total is used * --depth affects print and register reports (aggregating with a reporting interval, filtering otherwise) * register report sorts transactions by date * register report shows zero-amount transactions when -E is used * provide more convenient timelog querying when invoked as "hours" * multi-day timelog sessions are split at midnight * unterminated timelog sessions are now counted. Accurate time reports at last! * the test command gives better --verbose output * --version gives more detailed version numbers including patchlevel for dev builds * new make targets include: ghci, haddocktest, doctest, unittest, view-api-docs * a doctest-style framework for functional/shell tests has been added * performance has decreased slightly: || hledger-0.3 | hledger-0.4 | ledger-0.3 ==============================++========== -f sample.ledger balance || 0.02 | 0.01 | 0.07 -f sample1000.ledger balance || 1.02 | 1.39 | 0.53 -f sample10000.ledger balance || 12.72 | 14.97 | 4.63 Contributors: * Simon Michael * Tim Docker * HAppS, happstack and testpack developers Stats: * Known errors: 0 * Commits: 132 * Committers: 2 * Tests: 56 * Non-test code lines: 2600 * Days since release: 75

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Wrappers, API's for Web Apps - Google Summer of Code
by Hrushikesh Tilak 03 Apr '09

03 Apr '09

Hi, I am interested in participating in this year's Google Summer of Code. One of my proposals is going to be to write and extend existing Haskell wrappers and API's for web services. Some of the popular web services that I use are Google Maps, Flickr, digg, reddit, Facebook and twitter, Quick google searches reveal that great haskell tools already exist for twitter, while there is an ongoing project for a Facebook API by Jeremy Shaw. I couldn't find any haskell projects for the other tools. I find this project interesting primarily because I use these tools and would like to have haskell interfaces to them. Along with tools like Happstack, these interfaces would extend the power of haskell for developing Web 2.0 apps and mashups. I would like to enquire about the community's opinions and interests in such a project. I would also appreciate any suggestions either pertaining to any other web services. I have created a ticket at http://hackage.haskell.org/trac/summer-of-code/ticket/1578 Thanks, Hrushikesh Tilak

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Loading C object files into ghci
by Murray 03 Apr '09

03 Apr '09

Hi Cafe, A quick question: Is there a way to load a C object file associated with FFI imports into ghci after invocation (or in a .ghci file)? I've checked the docs as carefully as I can and can't find anything. Naming the file on the command line works of course but I was hoping for something I could keep in a per-directory .ghci file so that emacs and yi interactive modes work properly. I know I can (setq haskell-program-name "ghci /long/path/to/my/project/build/dist/.../blah.o") for emacs but I think it's hard-coded in yi. Sorry if this is obvious, or a FAQ. Murray. <murray(a)sonology.net>

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Missing dependency?
by Lyle Kopnicky 03 Apr '09

03 Apr '09

Hi folks, Since the time package is not included in ghc-6.10.2, I installed it via cabal. Then I tried to configure my project, and it says that the dependency is missing. Mysterious. Can anyone explain? lwk@lwk-desktop:~/devel/vintage-basic$ ghc-pkg list /usr/local/lib/ghc-6.10.2/./package.conf: Cabal-1.6.0.3, HUnit-1.2.0.3, QuickCheck-1.2.0.0, array-0.2.0.0, base-3.0.3.1, base-4.1.0.0, bytestring-0.9.1.4, containers-0.2.0.1, directory-1.0.0.3, (dph-base-0.3), (dph-par-0.3), (dph-prim-interface-0.3), (dph-prim-par-0.3), (dph-prim-seq-0.3), (dph-seq-0.3), editline-0.2.1.0, filepath-1.1.0.2, (ghc-6.10.2), ghc-prim-0.1.0.0, haddock-2.4.2, haskell-src-1.0.1.3, haskell98-1.0.1.0, hpc-0.5.0.3, html-1.0.1.2, integer-0.1.0.1, mtl-1.1.0.2, network-2.2.1, old-locale-1.0.0.1, old-time-1.0.0.2, packedstring-0.1.0.1, parallel-1.1.0.1, parsec-2.1.0.1, pretty-1.0.1.0, process-1.0.1.1, random-1.0.0.1, regex-base-0.72.0.2, regex-compat-0.71.0.1, regex-posix-0.72.0.3, rts-1.0, stm-2.1.1.2, syb-0.1.0.1, template-haskell-2.3.0.1, unix-2.3.2.0, xhtml-3000.2.0.1 /home/lwk/.ghc/i386-linux-6.10.2/package.conf: HTTP-4000.0.4, time-1.1.2.3, zlib-0.5.0.0 lwk@lwk-desktop:~/devel/vintage-basic$ runhaskell Setup.hs configure Configuring vintage-basic-1.0.1... Setup.hs: At least the following dependencies are missing: time >=1.1 lwk@lwk-desktop:~/devel/vintage-basic$ Thanks, Lyle

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Type families and kind signatures
by Louis Wasserman 03 Apr '09

03 Apr '09

The following module does not compile, and I can't figure out why: {-# LANGUAGE TypeFamilies #-} {-# LANGUAGE KindSignatures #-} module Foo where import Control.Monad import Data.Maybe class Key k where type Map k :: * -> * empty :: Map k v look :: k -> Map k v -> Maybe v update :: k -> (Maybe v -> Maybe v) -> Map k v -> Map k v instance (Key k1, Key k2) => Key (k1, k2) where type Map (k1, k2) v = Map k1 (Map k2 v) empty = empty update (k1, k2) f = update k1 (update k2 f . fromMaybe empty) look (k1, k2) = look k1 >=> look k2 The compile fails with Foo.hs:16:1: Number of parameters must match family declaration; expected 1 In the type synonym instance declaration for `Map' In the instance declaration for `Key (k1, k2)' Is this a bug with type synonym families? Is there something silly I'm missing? Louis Wasserman wasserman.louis(a)gmail.com

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Issue with IsFunction/Vspace in GHC 6.10.1
by Jacques Carette 03 Apr '09

03 Apr '09

I was playing with some of Oleg's code (at end for convenience). After minor adjustments for ghc 6.10.1, it still didn't work. The error message is quite puzzling too, as it suggests adding exactly the constraint which is present... Any ideas? Jacques -- Oleg's definition of a vector space class, based on IsFunction and -- TypeCast. See http://okmij.org/ftp/Haskell/isFunction.lhs -- for the January 2003 message, which works in GHC 6.2.1 and 6.4 -- code below *works* in 6.8.1 AFAIK {-# LANGUAGE EmptyDataDecls, MultiParamTypeClasses, FunctionalDependencies #-} {-# LANGUAGE FlexibleInstances #-} {-# LANGUAGE UndecidableInstances #-} {-# LANGUAGE OverlappingInstances #-} module Q where class Vspace a v | v -> a where (<+>) :: v -> v -> v (*>) :: a -> v -> v instance (IsFunction v f, Vspace' f a v) => Vspace a v where (<+>) = doplus (undefined::f) (*>) = dostar (undefined::f) class Vspace' f a v | f v -> a where doplus :: f -> v -> v -> v dostar :: f -> a -> v -> v instance Num a => Vspace' HFalse a a where doplus _ = (+) dostar _ = (*) -- etc. No problem. instance (IsFunction v f, Vspace' f a v, Vspace a v) => Vspace' HTrue a (c->v) where doplus _ f g = \x -> f x <+> g x dostar _ a f x = a *> (f x) test1 = (1::Int) <+> 2 test2 = ((\x -> x <+> (10::Int)) <+> (\x -> x <+> (10::Int))) 1 test3 = ((\x y -> x <+> y) <+> (\x y -> (x <+> y) <+> x)) (1::Int) (2::Int) test4 = ((\x y -> x <+> y) <+> (\x y -> ((2 *> x) <+> (3 *> y)))) (1::Int) (2::Int) data HTrue data HFalse class IsFunction a b | a -> b instance TypeCast f HTrue => IsFunction (x->y) f instance TypeCast f HFalse => IsFunction a f -- literally lifted from the HList library class TypeCast a b | a -> b, b->a where typeCast :: a -> b class TypeCast' t a b | t a -> b, t b -> a where typeCast' :: t->a->b class TypeCast'' t a b | t a -> b, t b -> a where typeCast'' :: t->a->b instance TypeCast' () a b => TypeCast a b where typeCast x = typeCast' () x instance TypeCast'' t a b => TypeCast' t a b where typeCast' = typeCast'' instance TypeCast'' () a a where typeCast'' _ x = x

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Retargeting the ghc code generator
by Vasili I. Galchin 03 Apr '09

03 Apr '09

Hello, Is there any project to retarget the GHC code generator to generate Common Intermediate Language(CLI) in order to run on Mono or .NET? I assume that Mondrian did precisely that. Thanks, Vasili

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Looking for practical examples of Zippers
by Gü?nther Schmidt 03 Apr '09

03 Apr '09

Hi, my quest for data structures continues. Lately I came across "Zippers". Can anybody point be to some useful examples? Günther

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Re: HXT: desperatedly trying to "concat"
by Steffen Schuldenzucker 03 Apr '09

03 Apr '09

Hello again. I finally got it myself. It was just a matter of parentheses: See http://hpaste.org/fastcgi/hpaste.fcgi/view?id=3229 for the corrected version. Looks like what I was trying to do is not expressable via just an arrow, one needs a function mapping the input arrow to a new one. I'm gonna make a big "WATCH YOUR PARENTHESES!" poster... Yeah, with some arrows on it... Thanks for reading, anyway. Steffen ________________________________________________________________________ Neu bei WEB.DE: Kostenlose maxdome Movie-FLAT! https://register.maxdome.de/xml/order/LpWebDe?ac=OM.MD.MD008K15726T7073a

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Funny type signature question
by Michael Snoyman 03 Apr '09

03 Apr '09

I've butted into this problem multiple times, so I thought it's finally time to get a good solution. I don't even have the terminology to describe the issue, so I'll just post the code I'm annoyed with and hope someone understands what I mean. import Control.Monad.Random import System.Random data Marital = Single | Married | Divorced deriving (Enum, Bounded, Show) randomEnum :: (Enum a, Bounded a, RandomGen g) => Rand g a randomEnum = do let minb = minBound maxb = maxBound randVal <- getRandomR (fromEnum minb, fromEnum maxb) return $ head [toEnum randVal, minb, maxb] -- if I do the obvious thing (return $ toEnum randVal) I get funny errors main = do stdGen <- newStdGen let marital = evalRand randomEnum stdGen :: Marital putStrLn $ "Random marital status: " ++ show marital Any help is appreciated. Thanks! Michael

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ANN: Buster 0.99.1, a library for application orchestration that is not FRP
by Jeff Heard 03 Apr '09

03 Apr '09

Read more about it on its webpage: http://vs.renci.org/jeff/buster Yes, it’s to solve a particular problem. And yes, this is a rough draft of an explanation of how it works. I’ve not even really solidified the vocabulary yet, but I have this module which couches a large, abstract, interactive (both with the user and the system), multicomponent application in terms of a bus, inputs, behaviours, and events. * Time is continuous and infinite. * An event is a static, discrete item associated with a particular time. * The bus is the discrete view of event in time at an instant. * A widget is an IO action that assigns events to a particular time based only upon sampling the outside world (other events and behaviours are irrelevant to it). e.g. a Gtk Button is a widget, a readable network socket is an widget, the mouse is an widget, the keyboard is an widget, a multitouch gesture engine is a widget. * A behaviour is a continuous item — it exists for the entire program and for all times — which maps events on the bus to other events on the bus. It is an IO action as well — where widgets only sample the outside world and are in a sense read only, behaviours encapsulate reading and writing.

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