- Haskell-Cafe - Haskell.org

Re: [Haskell-cafe] ANNOUNCE: fad 1.0 -- Forward Automatic Differentiation library
by Kalman Noel 26 Apr '09

26 Apr '09

Henning Thielemann schrieb: > with advanced type classes: > http://hackage.haskell.org/packages/archive/numeric-prelude/0.0.5/doc/html/… I'll take this as another opportunity to point out that the Haddock docs of the Numeric Prelude are highly unreadable, due to all qualified class and type names appearing as just C or T. I'm wondering, too, if the Numeric Prelude could be organized more cleanly if we had a fancier module system - does someone have sufficient experience with, say, ML-style module systems to tell? Kalman

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Haskell Weekly News: Issue 115 - April 25, 2009
by Brent Yorgey 25 Apr '09

25 Apr '09

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20090425 Issue 115 - April 25, 2009 --------------------------------------------------------------------------- Welcome to issue 115 of HWN, a newsletter covering developments in the [1]Haskell community. By all reports, the [2]5th Haskell Hackathon was a resounding success, with over 50 hackers present and many interesting Haskell projects worked on! Announcements darcs hacking sprint 2 and hac5 report. Eric Kow [3]sent out a link to a [4]report on the second darcs hacking sprint, held as part of the Haskell Hackathon. HPong-0.1.2: A simple OpenGL Pong game based on GLFW. R.A. Niemeijer [5]announced the release of [6]HPong, a simple Pong game implemented using OpenGL and GLFW. Hac5 roundup. Martijn van Steenbergen [7]reported on the 5th Haskell Hackathon. See the [8]wiki page for details, pictures, and links to blog posts. HTTP-4000.0.6. Sigbjorn Finne [9]announced a new release of the [10]HTTP package, which adds more robust handling of ill-formed cookies, and fixes a bug in normalization of certain proxy-bound requests. dataenc 0.12.1.0. Magnus Therning [11]announced version 0.12.1.0 of the [12]dataenc package. This version adds a bunch of new encodings, including xxencode, hexadecimal, quoted-printable, python escaping, and url encoding; and also fixed some bugs. list-tries-0.0 - first release. Matti Niemenmaa [13]announced the first public release of [14]list-tries, a library providing implementations of finite sets and maps for list keys using tries, both simple and of the Patricia kind. The data types are parametrized over the map type they use internally to store the child nodes: this allows extending them to support different kinds of key types or increasing efficiency. curl-1.3.5. Sigbjorn Finne [15]announced a new release of the [16]curl package, which provides Haskell bindings to libcurl. It works with ghc 6.10.2, taking into account the updated story on how to register Haskell-based finalizers. Runge-Kutta library -- solve ODEs. Uwe Hollerbach [17]announced a [18]Runge-Kutta library for numerically solving ordinary differential equations. funsat-0.6. Denis Bueno [19]announced version 0.6 of [20]funsat, a modern, DPLL-style SAT solver written in Haskell. Funsat solves formulas in conjunctive normal form and produces a total variable assignment for satisfiable problems. Version 0.6 adds a representation for logical circuits (and, or, not, onlyif, iff, if-then-else) supporting efficient conversion to CNF, and now uses the BSD3 license. control-monad-exception-0.1: Explicitly typed exceptions. Pepe Iborra [21]announced the [22]control-monad-exception package, which provides explicitly typed exceptions for Haskell. The type of a computation in the EM monad carries a list of the exceptions that the computation may throw. A exception is raised with 'throw', which in addition adds it to the type, and captured with 'catch', which correspondingly removes it from the type. Only safe computations (all exceptions handled) can escape from the monad. Haskell Implementers' Workshop 2009 (co-located with ICFP). Simon Marlow [23]issued a call for talks to be given at the ACM SIGPLAN [24]Haskell Implementers' Workshop, to be held on September 3 in Edinburgh, Scotland, in conjunction with [25]ICFP 2009. The proposal deadline in 15 June. The Haskell Implementers Workshop is a new workshop to be held alongside ICFP 2009 this year in Edinburgh, Scotland. There will be no proceedings; it is an informal gathering of people involved in the design and development of Haskell implementations, tools, libraries, and supporting infrastructure. persistent-map-0.0.0. Peter Robinson [26]announced the [27]persistent-map package, which provides a thread-safe (STM) frontend for finite map types together with a backend interface for persistent storage. A pragmatic Haskell .NET interop layer, 0.4.0. Sigbjorn Finne [28]announced a new release of [29]hs-dotnet, a Haskell .NET interop layer. It lets you access .NET functionality from Haskell and vice versa. The new version includes development done since the start of the year. Apart from rewriting the internals completely to put it all on a sounder footing, this release includes proper support for .NET generic types (classes and interfaces), mapping them naturally on to Haskell parameterized types. Utrecht Haskell Compiler (UHC) -- first release. atze [30]announced the first public release of the [31]Utrecht Haskell Compiler (UHC). UHC supports almost all Haskell98 features plus many experimental extensions. The compiler runs on MacOSX, Windows (cygwin), and various Unix flavors. Features include multiple backends, including a bytecode interpreter backend and a GRIN based, full program analysing backend; experimental language extensions, some of which have not been implemented before; implementation via attribute grammars and other high-level tools; and ease of experimentation with language variants, thanks to an aspect-oriented internal organisation. 6.10.3 plans. Ian Lynagh [32]announced plans for a 6.10.3 release of GHC, in order to fix the handling of ^C in ghci. 6.10.3 will also use haskeline instead of editline. A HERE Document syntax. Jason Dusek [33]proposed a lightweight syntax for HERE documents in Haskell. Discussion Functor and Haskell. Daryoush Mehrtash [34]asked about the link between functors in category theory and Haskell's Functor class; the resulting thread is a good introduction to the connections between Haskell and category theory for those just learning the latter. breaking too long lines. Christian Maeder [35]asked how to break long lines in Haskell source, leading to an interesting discussion of coding style. Jobs Haskell consultant wanted to develop small, Mac-based utility in Haskell or AppleScript. R J [36]announced an opportunity to develop a short program to annotate lists of words with their definitions. Blog noise [37]Haskell news from the [38]blogosphere. * Twan van Laarhoven: [39]Where do I get my non-regular types?. * Sebastian Fischer: [40]Reinventing Haskell Backtracking. * Darcs: [41]darcs hacking sprint #2 report. * Well-Typed.Com: [42]Platform progress and the Hackathon. * Roman Cheplyaka: [43]Hac5: the rest of the story (almost). * Twan van Laarhoven: [44]A non-regular data type challenge. * Magnus Therning: [45]dataenc 0.12.1.0 released. * Galois, Inc: [46]Portland Next Week: ICFP PC Functional Programming Workshop. * Christophe Poucet (vincenz): [47]Flattening Data.Map. * Roman Cheplyaka: [48]Hac5: second day. * Xmonad: [49]contribs review. * GHC / OpenSPARC Project: [50]Loose ends and register pairing. * Sean Leather: [51]Latest on the incremental fold and attributes. * >>> Matthew Podwysocki: [52]Functional Solution for the Shortest Path Problem . * Chris Smith: [53]Code for Manipulating Graphs in Haskell. * Austin Seipp: [54]A little fun with Haskabelle. Proving things about *existing* Haskell code in Isabelle. * Tupil: [55]Running Happstack applications with FastCGI. * Martijn van Steenbergen: [56]Hac5-Saturday. * beelsebob: [57]Bottoms. * Antoine Latter: [58]Using Haskeline. * Darcs: [59]darcs weekly news #26. * Martijn van Steenbergen: [60]Hacking GHC-What I've learned. * >>> Brandon Simmons: [61]Initial tests of Tries: Follow Up. * >>> Lab 49: [62]The Algebra of Data, and the Calculus of Mutation. * Martijn van Steenbergen: [63]Hac5-Friday. Pictures from the Hackathon. * >>> Matthew Podwysocki: [64]Haskell and Collective Intelligence . Quotes of the Week * Gracenotes: foldr chosen for its magical evil terminating powers * uninverted: Moving from lisp to haskell with respect to functions is like moving from c to perl with respect to strings. * Berengal: [On infinitely fast computers] The OS probably has a failsafe built in: If a program is running it's in an infinite loop and needs to be killed... * nikki93: After a bit more delving, I've come to see the power of haskell at last. You have to treat functions like crap, forget about the C idea that they're 'big things'. They're not. * Berengal: I was squashing a bug, got frustrated, and typed "fix error" in ghci... About the Haskell Weekly News New editions are posted to [65]the Haskell mailing list as well as to [66]the Haskell Sequence and [67]Planet Haskell. [68]RSS is also available, and headlines appear on [69]haskell.org. To help create new editions of this newsletter, please see the information on [70]how to contribute. Send stories to byorgey at cis dot upenn dot edu. The darcs repository is available at darcs get [71]http://code.haskell.org/~byorgey/code/hwn/ . References 1. http://haskell.org/ 2. http://www.haskell.org/haskellwiki/Hac5 3. http://article.gmane.org/gmane.comp.lang.haskell.cafe/57551 4. http://blog.darcs.net/2009/04/darcs-hacking-sprint-2-report.html 5. http://article.gmane.org/gmane.comp.lang.haskell.cafe/57493 6. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HPong 7. http://article.gmane.org/gmane.comp.lang.haskell.cafe/57470 8. http://www.haskell.org/haskellwiki/Hac5 9. http://article.gmane.org/gmane.comp.lang.haskell.cafe/57336 10. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HTTP 11. http://article.gmane.org/gmane.comp.lang.haskell.libraries/10945 12. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/dataenc 13. http://article.gmane.org/gmane.comp.lang.haskell.cafe/57311 14. http://iki.fi/matti.niemenmaa/list-tries/ 15. http://article.gmane.org/gmane.comp.lang.haskell.cafe/57251 16. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/curl 17. http://article.gmane.org/gmane.comp.lang.haskell.cafe/57160 18. http://www.korgwal.com/software/rk-1.0.0.tar.gz 19. http://article.gmane.org/gmane.comp.lang.haskell.cafe/57101 20. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/funsat 21. http://article.gmane.org/gmane.comp.lang.haskell.general/17120 22. http://article.gmane.org/gmane.comp.lang.haskell.general/17120 23. http://article.gmane.org/gmane.comp.lang.haskell.general/17113 24. http://haskell.org/haskellwiki/HaskellImplementorsWorkshop 25. http://www.cs.nott.ac.uk/~gmh/icfp09.html 26. http://article.gmane.org/gmane.comp.lang.haskell.general/17106 27. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/persistent-map 28. http://article.gmane.org/gmane.comp.lang.haskell.general/17105 29. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hs%2Ddotnet 30. http://article.gmane.org/gmane.comp.lang.haskell.general/17103 31. http://www.cs.uu.nl/wiki/UHC 32. http://article.gmane.org/gmane.comp.lang.haskell.glasgow.user/16792 33. http://article.gmane.org/gmane.comp.lang.haskell.prime/2787 34. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/57324 35. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/57207 36. http://article.gmane.org/gmane.comp.lang.haskell.cafe/57568 37. http://planet.haskell.org/ 38. http://haskell.org/haskellwiki/Blog_articles 39. http://twan.home.fmf.nl/blog/haskell/non-regular2.details 40. http://www-ps.informatik.uni-kiel.de/~sebf/pub/atps09.html 41. http://blog.darcs.net/2009/04/darcs-hacking-sprint-2-report.html 42. http://blog.well-typed.com/2009/04/platform-progress-and-the-hackathon/ 43. http://ro-che.blogspot.com/2009/04/hac5-rest-of-story-almost.html 44. http://twan.home.fmf.nl/blog/haskell/non-regular1.details 45. http://therning.org/magnus/archives/568 46. http://www.galois.com/blog/2009/04/23/portland-next-week-icfp-pc-functional… 47. http://cpoucet.wordpress.com/2009/04/18/flattening-datamap/ 48. http://ro-che.blogspot.com/2009/04/hac5-second-day.html 49. http://xmonad.wordpress.com/2009/04/22/contribs-review/ 50. http://ghcsparc.blogspot.com/2009/04/loose-ends-and-register-pairing.html 51. http://feedproxy.google.com/~r/splonderzoek/~3/KWqNCgsK1ww/latest-on-increm… 52. http://codebetter.com/blogs/matthew.podwysocki/archive/2009/04/21/functiona… 53. http://cdsmith.wordpress.com/2009/04/20/code-for-manipulating-graphs-in-has… 54. http://www.jedi-ninja.net/2009/04/20/A-little-fun.html 55. http://blog.tupil.com/running-happstack-applications-with-fastcgi/ 56. http://martijn.van.steenbergen.nl/journal/2009/04/19/hac5-saturday/ 57. http://noordering.wordpress.com/2009/04/19/bottoms/ 58. http://panicsonic.blogspot.com/2009/04/using-haskeline.html 59. http://blog.darcs.net/2009/04/darcs-weekly-news-26.html 60. http://martijn.van.steenbergen.nl/journal/2009/04/18/hacking-ghc-what-ive-l… 61. http://coder.bsimmons.name/blog/2009/04/initial-tests-of-tries-follow-up/ 62. http://blog.lab49.com/archives/3011 63. http://martijn.van.steenbergen.nl/journal/2009/04/17/hac5-friday/ 64. http://codebetter.com/blogs/matthew.podwysocki/archive/2009/04/17/haskell-a… 65. http://www.haskell.org/mailman/listinfo/haskell 66. http://sequence.complete.org/ 67. http://planet.haskell.org/ 68. http://sequence.complete.org/node/feed 69. http://haskell.org/ 70. http://haskell.org/haskellwiki/HWN 71. http://code.haskell.org/~byorgey/code/hwn/

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Takusen, postgres and boolean fields
by Sasha Shipka 25 Apr '09

25 Apr '09

Let say one has to do something similar to this: execDML $ cmdbind (sql "update some_table set some_boolean_field = ? where ...") [bindP True, ...] When I do it, I have an error: DBError ("42","804") 7 "ERROR: 42804: column \"some_boolean_field\" is of type boolean but expression is of type text ..." I've noticed that when I read boolean fields from postgres it reads them as string "t" or "f". So I also tried bindP "t" and had same error.

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Not in scope
by siso dagbovie 25 Apr '09

25 Apr '09

Hi, I've defined the datatype: data Graph a b = Empty | Context a b :& Graph a b and the function isEmpty :: Graph a b -> Bool isEmpty Empty = True isEmpty _ = False and when I do a test run with the graph, ( [ ],2,'c',[("down",3)]) :& Empty Haskell is bringing the message " Not in scope: data constructor `:&' " Why is that so? Kind regards

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compilation to C, not via-C
by Sam Martin 25 Apr '09

25 Apr '09

Hi Everyone, It appears the GHC compiler (and other) compile Haskell *via-C* but not *to C*. I've never really understood why there isn't a C generation option, or why GDC ships with its own compulsory copy of gcc. I work in Games middleware, and am very interested in looking at how Haskell could help us. We basically sell C++ libraries. I would like to be able to write some areas of our libraries in Haskell, compile the Haskell to C and incorporate that code into a C++ library. As an example, I think Haskell would be great at doing geometry processing. I don't want to write all our geometry processing code in C++. I'd prefer to write a big chunk of it in Haskell and wrap that in C++. The pattern here is using Haskell to generate C code as the end result. It sounds like this end result isn't that far out of reach, so I'm curious as to why it doesn't appear to be possible at present. Have I missed something? Is there some fundamental reason this isn't possible? Has anyone wished for this before? Any thoughts/help much appreciated, Thanks, Sam Martin --- Lead Programmer www.geomerics.com

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parse error on input `&'
by siso dagbovie 25 Apr '09

25 Apr '09

Hi, I've defined the following datatype with haskell data Graph a b = Empty | Context a b & Graph a b But I am having the error message: " parse error on input `&' ". I am wondering what it is wrong with my definition. How can I fix this? Thanks in advance. Kind regards

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Binary I/O options
by David Leimbach 25 Apr '09

25 Apr '09

I see that there are a few approaches to doing Binary I/O with Haskell, and the one I'm currently looking at using is Data.Binary from Hackage. I was just wondering what folks were choosing for building networked applications and doing Binary I/O. The approach I was about to take was to use Data.Binary to create ByteString for Network calls with a standard I/O package. Are there other good options? Dave

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leksah on window - problems with installation.
by Raja Koduru 25 Apr '09

25 Apr '09

Hello, I want to install leksah haskell IDE on my windows(xp) system. I download leksah's source (leksah-0.4.4.1). I also have gtk2hs (0.10.0) in my path. I am having ghc-6.10.2. As suggested on leksah's website.. I used "runhaskell setup configure" command But it is failing with this error "Configuring leksah-0.4.4.1... Setup: At least the following dependencies are missing: glib >=0.10, gtk >=0.10, gtksourceview2 >=0.10.0" I tried to do "cabal install glib" but not able to do so. Can you give me clues on how to go forward. with thanks & regards, raja koduru

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OT: Good Linux distro for netbook + Haskell?
by Magnus Therning 25 Apr '09

25 Apr '09

I've decided to shop around for other options when it comes to a Debian distro to put on my Eee PC 900. Since it has no HDD I want something that isn't too bloated (some is all right) and ideally leaves up to me what to install and what not to. At the same time I'd like to have up-to-date Haskell packages in the native packaging system available (sure, cabal-install is all right for the odd package, but I'd rather use the native packaging system). Debian Sid would be a contender, though (no offence, I know they work hard) it's often slow in providing the latest versions of packages. Arch Linux is very up-to-date, but I'm not convinced it's a distro suitable for an Eee without HDD (I'm prepared to be proven wrong though). Is there something else out there I should be looking at? /M -- Magnus Therning (OpenPGP: 0xAB4DFBA4) magnus＠therning．org Jabber: magnus＠therning．org http://therning.org/magnus identi.ca|twitter: magthe Haskell is an even 'redder' pill than Lisp or Scheme. -- PaulPotts

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ANN: Cute Hack - Hyena handler + Bamboo Blog Engine :)
by Jinjing Wang 25 Apr '09

25 Apr '09

Hia, A few interesting progress on Hack: * many middleware ported from Rack, including a lambda! ( just like a pony for wsgi, and a lobster for rack ) * 2 handlers, one for Kibro on fcgi / lighttpd, one for Hyena web server * apps are portable, Bamboo is a port of Panda that runs on Hack, works fine with both handlers * Hyena handler is still experimental A lambda app looks like this -- Main.hs source module Main where import Hack import Hack.Utils import Hack.Handler.Hyena import Hack.Contrib.Lambda main = run $ lambda dummy_app -- compile ghc --make -O2 Main.hs -- run ./Main now go to http://localhost:3000/lambda Cheers, Links: * [Hack] (http://github.com/nfjinjing/hack/tree/master) * [Bamboo] (http://github.com/nfjinjing/bamboo/tree/master) -- jinjing

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