February 2009 - Haskell

Announcing Djinn, version 2004-12-11, a coding wizard
by Lennart Augustsson 07 Apr '11

07 Apr '11

Howdy, y'all! I've written a small program that takes a (Haskell) type and gives you back a function of that type if one exists. It's kind of fun, so I thought I'd share it. It's probably best explained with a sample session. calvin% djinn Welcome to Djinn version 2005-12-11. Type :h to get help. # Djinn is interactive if not given any arguments. # Let's see if it can find the identity function. Djinn> f ? a->a f :: a -> a f x1 = x1 # Yes, that was easy. Let's try some tuple munging. Djinn> sel ? ((a,b),(c,d)) -> (b,c) sel :: ((a, b), (c, d)) -> (b, c) sel ((_, v5), (v6, _)) = (v5, v6) # We can ask for the impossible, but then we get what we # deserve. Djinn> cast ? a->b -- cast cannot be realized. # OK, let's be bold and try some functions that are tricky to write: # return, bind, and callCC in the continuation monad Djinn> type C a = (a -> r) -> r Djinn> returnC ? a -> C a returnC :: a -> C a returnC x1 x2 = x2 x1 Djinn> bindC ? C a -> (a -> C b) -> C b bindC :: C a -> (a -> C b) -> C b bindC x1 x2 x3 = x1 (\ c15 -> x2 c15 (\ c17 -> x3 c17)) Djinn> callCC ? ((a -> C b) -> C a) -> C a callCC :: ((a -> C b) -> C a) -> C a callCC x1 x2 = x1 (\ c15 _ -> x2 c15) (\ c11 -> x2 c11) # Well, poor Djinn has a sweaty brow after deducing the code # for callCC so we had better quit. Djinn> :q Bye. To play with Djinn do a darcs get http://darcs.augustsson.net/Darcs/Djinn or get http://darcs.augustsson.net/Darcs/Djinn/Djinn.tar.gz Then just type make. (You need a Haskell 98 implementation and some libraries.) And then start djinn. For the curious, Djinn uses a decision procedure for intuitionistic propositional calculus due to Roy Dyckhoff. It's a variation of Gentzen's LJ system. This means that (in theory) Djinn will always find a function if one exists, and if one doesn't exist Djinn will terminate telling you so. This is the very first version, so expect bugs. :) Share and enjoy. -- Lennart

8 13

ANNOUNCE: ChristmasTree 0.1 (excuses for second attempt)
by S.Doaitse Swierstra 07 Jul '09

07 Jul '09

We are pleased to announce the availability of the package "ChristmasTree", which contains the code associated with our paper at the last Haskell symposium: @inproceedings{1411296, author = {Marcos Viera and S. Doaitse Swierstra and Eelco Lempsink}, title = {Haskell, do you read me?: constructing and composing efficient top-down parsers at runtime}, booktitle = {Haskell '08: Proceedings of the first ACM SIGPLAN symposium on Haskell}, year = {2008}, isbn = {978-1-60558-064-7}, pages = {63--74}, location = {Victoria, BC, Canada}, doi = {http://doi.acm.org/10.1145/1411286.1411296}, publisher = {ACM}, address = {New York, NY, USA}, } The name of the package stands for: "Changing Haskell's Read Implementation Such That by Manipulating Abstract Syntax Trees it Reads Expressions Efficiently" which, given the time of year, seems appropriate. Feel free to download and unpack this "present" at what for the Dutch is called "Sinterklaasavond" (http://en.wikipedia.org/wiki/Sinterklaas) Arthur Baars Marcos Viera Eelco Lempsink Doaitse Swierstra PS: the package uses our library supporting transformation of typed abstract syntax, which we placed in a separate package TTTAS

2 1

Google Summer of Code 2009
by Malcolm Wallace 10 Mar '09

10 Mar '09

Gentle Haskellers, The Google Summer of Code will be running again this year. Once again, haskell.org has the opportunity to bid to become a mentoring organisation. (Although, as always, there is no guarantee of acceptance.) If you have ideas for student projects that you think would benefit the Haskell community, now is the time to start discussing them on mailing lists of your choice. We especially encourage students to communicate with the wider community: if you keep your ideas private, you have a much worse chance of acceptance than if you develop ideas in collaboration with those who will be your "customers", end-users, or fellow-developers. This is the open-source world! The timeline is that Haskell.org will apply for GSoC membership between 9-13 March, and if we are successful, students can submit applications between 23 March - 3 April. If you wish to help publicise GSoC amongst students, there are official posters/fliers available (not specific to haskell.org) http://code.google.com/p/google-summer-of-code/wiki/GsocFlyers Regards, Malcolm

3 3

Take a break: write an essay for Onward! Essays
by Simon Peyton-Jones 02 Mar '09

02 Mar '09

Friends Writing papers is fun, we mostly only get to write one *kind* of paper. Here is an opportunity to write something in a totally different style: Submit an essay to Onward! Essays Deadline: 20 April 2009 http://onward-conference.org/calls/foressays An Onward! essay is a thoughtful reflection upon software-related technology. Its goal is to help the reader to share a new insight, engage with an argument, or wrestle with a dilemma. A successful essay is a clear and compelling piece of writing that explores a topic important to the software community. The subject area should be interpreted broadly, including the relationship of software to human endeavours, or its philosophical, sociological, psychological, historical, or anthropological underpinnings. An essay can be an exploration of its topic, its impact, or the circumstances of its creation; it can present a personal view of what is, explore a terrain, or lead the reader in an act of discovery; it can be a philosophical digression or a deep analysis. It can describe a personal journey, perhaps that by which the author reached an understanding of such a topic. I'm the program chair, and I'd love to get submissions from the POPL/ICFP/types community. Reflections on programming languages, types, testing, verification, software engineering, compilers, society, ... you name it. Anything to do with software. NB: Onward! is co-located with OOPSLA, but they are otherwise unrelated. OO is fine, but not required. Don't forget: 20th April. Simon PS: To get your imagination going, here are a couple of (strongly-contrasting) past essays: * Dan Grossman "The transactional memory / garbage collection analogy" http://www.cs.washington.edu/homes/djg/papers/analogy_oopsla07.pdf * Dick Gabriel "Designed as designer" http://dreamsongs.org/DesignedAsDesigner.html

2 1

Haskell Weekly News: Issue 107 - February 28, 2009
by Brent Yorgey 28 Feb '09

28 Feb '09

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20090228 Issue 107 - February 28, 2009 --------------------------------------------------------------------------- Welcome to issue 107 of HWN, a newsletter covering developments in the [1]Haskell community. Announcements Google Summer of Code 2009 - mentors wanted!. Eric Kow [2]reminded everyone that darcs will be applying to be a mentoring organisation for the Google Summer of Code project 2009, and is seeking people to serve as mentors. You need not be a darcs expert to serve as a mentor! c2hs 0.16.0. Duncan Coutts [3]announced the release of [4]c2hs version 0.16.0, a tool which assists in the development of Haskell bindings to C libraries by extracts interface information from C header files and generating Haskell code with foreign imports and marshaling. The major change in this release is that it now uses the [5]Language.C library. X Haskell Bindings 0.2. Antoine Latter [6]announced the 0.2.* series release of the [7]X Haskell Bindings, mostly aimed at making the API prettier. The goal of XHB is to provide a Haskell implementation of the X11 wire protocol, similar in spirit to the [8]X protocol C-language Binding (XCB). text and text-icu, fast and comprehensive Unicode support using stream fusion. Bryan O'Sullivan , on behalf of the Data.Text team, [9]announced the release of preview versions of two new packages: [10]text 0.1, providing fast, packed Unicode text support with modern stream fusion, and [11]text-icu 0.1, which augments text with comprehensive character set conversion support and normalization (and soon more), via bindings to the ICU library. Boston Area Haskell User's Group, first meeting on Saturday February 28th. Shae Matijs Erisson [12]announced the first meeting of the [13]Boston Area Haskell User's Group this Saturday, February 28, at 2pm. Directions are on the web page; you can also check out the [14]mailing list. New version of Hieroglyph released: Hieroglyph 1.1 is on hackage. Jeff Heard [15]announced the release of a new version of [16]Hieroglyph; the biggest change is that it now uses Russell O'Connor's excellent [17]Data.Colour library. bug fix for regex-tdfa, version 0.97.4 (and "regex-ast"). ChrisK [18]announced another bug fix release for the [19]regex-tdfa package, which fixes another tricksy bug. This is now the only known regex library that passes the entire test suite. Hac5: April 17-19, Utrecht -- Book Now!. Sean Leather [20]announced some updated information regarding the [21]5th Haskell Hackathon. The executive summary: hotel or hostel accommodation may be hard to come by, so book your room now, and check out the website for lots of useful information. pkgenv - disposable, isolated pkg environments. Paolo Losi [22]announced a tool, [23]pkgenv, which facilitates setting up isolated, disposable package environments. Blog noise [24]Haskell news from the [25]blogosphere. * JP Moresmau: [26]A high-level GUI library for Haskell. * Magnus Therning: [27]More fun with Cabal, visualising dependencies. Giant graphs are fun! * Magnus Therning: [28]A no-no in my book (found in Cabal). * Bryan O'Sullivan: [29]Finally! Fast Unicode support for Haskell. Data.Text is here! * happstack.com: [30]Happstack now outputs Apache Combined Logs. * GHC / OpenSPARC Project: [31]Benchmarking. * Christophe Poucet (vincenz): [32]Fibonacci in the Type System. * Eric Kow (kowey): [33]inkscape layers. * Magnus Therning: [34]Another reason to create distro-specific packages for Haskell modules. * boegel: [35]Using Haskell to win the Netflix Prize. * Magnus Therning: [36]Simple Cabal parsing. * GHC / OpenSPARC Project: [37]Bugfixes and pretty graphs. * Jeff Heard: [38]New version of Hieroglyph released.. * Chris Done: [39]Vgrabbj hacking. * Conal Elliott: [40]Paper: Beautiful differentiation. Another draft paper from Conal. * happstack.com: [41]Momentum builds as we approach Happstack 0.2. * Luke Palmer: [42]RTS Research. * GHC / OpenSPARC Project: [43]Sanity. * Darcs: [44]darcs weekly news #18. * Don Stewart (dons): [45]Can Haskell give me a pony?. The answer is: Yes! Haskell can do that. * Neil Mitchell: [46]Hoogle package search. * Alex Mason: [47]AVar changes. * Xmonad: [48]Using gimp under xmonad. It can actually be quite nice, despite what you might think. * FP-Syd: [49]Sydney FP Group: FP-Syd #12.. * Eric Kow (kowey): [50]implementing join in terms of (>>=). * GHC / OpenSPARC Project: [51]Triage. * Benjamin L. Russell: [52]Learning Haskell through Category Theory, and Adventuring in Category Land: Like Flatterland, Only About Categories. Quotes of the Week * lilac: haskell's learning curve is like this: | * cowardlydragon: [from a reddit comment thread] Don't get me started on monad. What is that, a man with a single testicle? About the Haskell Weekly News New editions are posted to [53]the Haskell mailing list as well as to [54]the Haskell Sequence and [55]Planet Haskell. [56]RSS is also available, and headlines appear on [57]haskell.org. To help create new editions of this newsletter, please see the information on [58]how to contribute. Send stories to byorgey at cis dot upenn dot edu. The darcs repository is available at darcs get [59]http://code.haskell.org/~byorgey/code/hwn/ . References 1. http://haskell.org/ 2. http://www.haskell.org//pipermail/haskell-cafe/2009-February/056798.html 3. http://www.haskell.org//pipermail/haskell/2009-February/021052.html 4. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/c2hs 5. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/language%2Dc 6. http://article.gmane.org/gmane.comp.lang.haskell.general/16888 7. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/xhb 8. http://xcb.freedesktop.org/ 9. http://article.gmane.org/gmane.comp.lang.haskell.cafe/53780 10. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/text 11. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/text-icu 12. http://article.gmane.org/gmane.comp.lang.haskell.cafe/53761 13. http://www.haskell.org/haskellwiki/Boston_Area_Haskell_Users%27_Group 14. http://groups.google.com/group/bostonhaskell 15. http://article.gmane.org/gmane.comp.lang.haskell.cafe/53549 16. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Hieroglyph 17. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/colour 18. http://article.gmane.org/gmane.comp.lang.haskell.cafe/53525 19. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/regex%2Dtdfa 20. http://article.gmane.org/gmane.comp.lang.haskell.cafe/53510 21. http://haskell.org/haskellwiki/Hac5 22. http://article.gmane.org/gmane.comp.lang.haskell.cafe/53448 23. http://bitbucket.org/pao/pkgenv/raw/488bfe8e58dd/pkgenv 24. http://planet.haskell.org/ 25. http://haskell.org/haskellwiki/Blog_articles 26. http://jpmoresmau.blogspot.com/2009/02/high-level-gui-library-for-haskell.h… 27. http://therning.org/magnus/archives/534 28. http://therning.org/magnus/archives/523 29. http://www.serpentine.com/blog/2009/02/27/finally-fast-unicode-support-for-… 30. http://blog.happstack.com/2009/02/26/happstack-now-outputs-apache-combined-… 31. http://ghcsparc.blogspot.com/2009/02/benchmarking.html 32. http://cpoucet.wordpress.com/2009/02/26/fibonacci-in-the-type-system/ 33. http://koweycode.blogspot.com/2009/02/inkscape-layers.html 34. http://therning.org/magnus/archives/522 35. http://boegel.kejo.be/?q=node%2F8 36. http://therning.org/magnus/archives/514 37. http://ghcsparc.blogspot.com/2009/02/bugfixes-and-pretty-graphs.html 38. http://vis.renci.org/jeff/2009/02/24/new-version-of-hieroglyph-released/ 39. http://chrisdone.com/blog/html/2009-02-25-vgrabbj.html 40. http://conal.net/blog/posts/paper-beautiful-differentiation/ 41. http://blog.happstack.com/2009/02/23/momentum-builds-as-we-approach-happsta… 42. http://lukepalmer.wordpress.com/2009/02/24/rts-research/ 43. http://ghcsparc.blogspot.com/2009/02/sanity.html 44. http://blog.darcs.net/2009/02/darcs-weekly-news-18.html 45. http://donsbot.wordpress.com/2009/02/22/can-haskell-give-me-a-pony/ 46. http://neilmitchell.blogspot.com/2009/02/hoogle-package-search.html 47. http://axman6.homeip.net/blog/2009/02/avar-changes.html 48. http://xmonad.wordpress.com/2009/02/21/using-gimp-under-xmonad/ 49. http://www.mega-nerd.com/erikd/Blog/FP-Syd/fp-syd-12.html 50. http://koweycode.blogspot.com/2009/02/implementing-join-in-terms-of.html 51. http://ghcsparc.blogspot.com/2009/02/triage.html 52. http://dekudekuplex.wordpress.com/2009/01/16/learning-haskell-through-categ… 53. http://www.haskell.org/mailman/listinfo/haskell 54. http://sequence.complete.org/ 55. http://planet.haskell.org/ 56. http://sequence.complete.org/node/feed 57. http://haskell.org/ 58. http://haskell.org/haskellwiki/HWN 59. http://code.haskell.org/~byorgey/code/hwn/

1 0

ANNOUNCE: c2hs 0.16.0
by Duncan Coutts 28 Feb '09

28 Feb '09

All, c2hs version 0.16.0 is out and is available from hackage http://hackage.haskell.org/cgi-bin/hackage-scripts/package/c2hs What is c2hs ============ The c2hs tool assists in the development of Haskell bindings to C libraries. It extracts interface information from C header files and generates Haskell code with foreign imports and marshaling. The major advantages of using c2hs compared to writing foreign imports by hand (or using hsc2hs) are: * Cross-language type safety: C functions are imported with the correct Haskell types. * Saves time: boilerplate marshaling code is generated. Changes in this release ======================= The major change in this release is that it now uses the Language.C library. This brings the code full circle. Benedikt Huber split out and developed the Language.C library from the C parser I originally wrote for c2hs some years ago. Other changes since 0.15.x: * Works better on OSX, it now uses gcc -E to do the pre-processing of C header files. Previously it used cpp, however on OSX the cpp program appears to operate in an antiquated compatibility mode. * "enum hooks" are now implemented but not yet documented * A couple fixes in the default mapping of C names to Haskell names. * A number of other bugs fixes. Credits ======= Benedikt Huber gets the credit for majority of the work in this release. Thanks also to John Lato for numerous cleanup patches. Links ===== Home page: http://www.cse.unsw.edu.au/~chak/haskell/c2hs/ Bug tracker: http://hackage.haskell.org/trac/c2hs/ Duncan

1 0

ANN: gitit 0.5.1
by John MacFarlane 26 Feb '09

26 Feb '09

I've just uploaded gitit 0.5.1 to HackageDb. Gitit is a wiki program that uses git or darcs as a filestore and HAppS as a server. Changes: * Major code reorganization, making gitit more modular. * Gitit can now optionally be built using Happstack instead of HAppS (just use -fhappstack when cabal installing). * Fixed bug with directories that had the same names as pages. * Added code from HAppS-Extra to fix cookie parsing problems. * New command-line options for --port, --debug. * New debug feature prints the date, the raw request, and the processed request data to standard output on each request. * Files with ".page" extension can no longer be uploaded. * Apostrophes and quotation marks now allowed in page names.

2 1

ANN: bug fix for regex-tdfa, version 0.97.4 (and "regex-ast")
by ChrisK 24 Feb '09

24 Feb '09

Hello, The regex-tdfa package has had a series of bug fix releases (0.97.1 and 2 and 3 and now 4). This 0.97.4 releases finishes fixing the bug that was only mostly fixed in the 0.97.1 release. An example of the fixed bug: Apply the regex pattern (BB(B?))+(B?) to the text BBBB. The "BB" in the pattern should be used twice and both "B?" should match nothing. My code grouped the "+" wrong and matched the "BB" once and then both the "B?" matched a "B". The case fixed here was not initially caught because of how I search for unknown bugs. I use "Arbitrary" from QuickCheck to generate random patterns and strings to search, and compare regex-tdfa to another POSIX engine. Because I am on OS X, I am limited by the the native POSIX libraries bugs: this bug in regex-tdfa was triggered only when the native POSIX was also buggy. But the source of most of my unit tests is AT&T research [1], and they have a "libast" with a POSIX implementation. I have adapted my regex-* wrapper packages to make a "regex-ast" Haskell interface, but the difficulties with the AT&T headers prevent me from releasing this on hackage. This "regex-ast" has given me access to a less buggy POSIX back-end, and randomized testing has led to catching the bug fixed here (as well as a few bug reports back to AT&T). So while regex-tdfa will not win many speed contests, it is the only POSIX regular expression library I have running that passes all the unit tests. [1] http://www.research.att.com/sw/download/ http://www.research.att.com/~gsf/testregex/ http://www.research.att.com/~gsf/testregex/re-interpretation.html

1 0

Hac5: April 17-19, Utrecht -- Book Now!
by Sean Leather 24 Feb '09

24 Feb '09

Twelve days ago, we emailed you about a particular event... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The 5th Haskell Hackathon April 17 - 19, 2009 Utrecht, The Netherlands ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We have some updated information for you. If you don't want to read the details, then the important points are: * Hotel or hostel accommodation may be hard to come by, so book your room now! * Check out the website for lots of useful information. As I mentioned before, you can find out more about the Hackathon here: http://haskell.org/haskellwiki/Hac5 The site is a wealth of useful information gratefully provided by the Utrecht organizing team. If you haven't seen it recently, check again. In particular, however, we'd like to inform you of some newly obtained information. We unknowingly scheduled the Hackathon on the same weekend as a popular record and CD fair. http://www.recordplanet.nl/ So, not only do you get the chance to hack on projects involving your favorite purely functional programming language, you also have the opportunity to visit "the most impressive record fair of the world." However, this does have some drawbacks... Rooms in hotels and hostels in Utrecht are often notoriously difficult to come by. It's already a crowded city sometimes with too few places to stay (esp. if you want cheap). Therefore, if you've decided to join us or have already registered, we highly recommend booking a room at your earliest convenience. (If you haven't decided to visit Utrecht, then you should hurry up and agree to it already!) For this purpose, we have updated the main Hac5 page with information about accommodations. http://haskell.org/haskellwiki/Hac5#Accommodation We also have a Google map with information about places to stay and transportation. http://haskell.org/haskellwiki/Hac5#Map And finally, don't forget that you can use either the Attendees page, the Hackathon mailing list, or the IRC channel to communicate with other (potential) attendees or the organizers about sharing rooms, finding a place, or anything else. http://haskell.org/haskellwiki/Hac5/Attendees http://haskell.org/mailman/listinfo/hackathon #haskell-hac5 (on freenode) Good luck and happy hacking! == Organizers == Andres Löh, Utrecht University (UU) José Pedro Magalhães, UU Sean Leather, UU Eelco Lempsink, UU + Tupil Chris Eidhof, UU + Tupil ... and more ...

1 0

ANNOUNCE: X Haskell Bindings 0.2
by Antoine Latter 22 Feb '09

22 Feb '09

I'd like to announce the 0.2.* series release of the X Haskell Bindings. This release, like the prior 0.1.* series focuses on making the API prettier. This does mean that there's a good chance this is a breaking release. Also, 0.2.* is based on the just-released version 1.4 of the XML descriptions of the X protocol. The goal of XHB is to provide a Haskell implementation of the X11 wire protocol, similar in spirit to the X protocol C-language Binding (XCB). On Hackage: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/xhb New this release: In the core protocol, a lot of the fields which previously were of type 'Word8' or 'Word16' now have appropriate higher-level types. For example, in the type GetWindowAttributesReply, the 'class' field was previously of type 'Word16', and is now of type 'WindowClass,' and the 'all_event_masks' field was of type 'Word32' and is now of type '[EventMask]'. These improvements haven't made their way out to the extensions yet, but the code-generation machinery is now in place for this to happen as the information makes its way into the XML protocol description. Related projects: X C Bindings: http://xcb.freedesktop.org/ -Antoine

2 1