April 2009 - Haskell-Cafe

Re: [Haskell] Marketing Haskell
by Maarten Hazewinkel 01 Apr '09

01 Apr '09

That's not you usual Koala face. Must be a special Simon^H^H^H^H^HHaskell-Koala species. On 1 Apr 2009, at 10:07, Simon Peyton-Jones wrote: > > Dear Haskell enthusiasts, > > Now that the logo issue finally has been settled, it is time to select > the proper Haskell mascot. As you are no doubt aware, Microsoft's > involvement in Haskell means that we have moved from avoiding success > at all cost to actively marketing the language, and any language > striving for success is entirely dependent on a cute and distinctive > mascot. Where would Perl be today without its camel? > > Since the recent logo discussion has demonstrated once and for all the > futility of attempting a democratic process in the Haskell community - > to be quite honest, the elected logo looks like an error message > from an IBM > mainframe - I have decided to decide on a mascot myself. > > So I hereby declare the official Haskell mascot to be the koala, in > the form of the image attached below. Please ensure that this image > accompanies any material published on the web or on paper. > > Simon > > <haskell-mascot.jpg>_______________________________________________ > Haskell mailing list > Haskell(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell Maarten Hazewinkel maarten.hazewinkel(a)gmail.com Tel: 06-53 692 432 (+31-653 692 432 from outside the Netherlands)

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DEFUN09: Call for Talks & Tutorials (co-located w/ ICFP09)
by Matthew Fluet (ICFP Publicity Chair) 01 Apr '09

01 Apr '09

Call for Talks and Tutorials ACM SIGPLAN 2009 Developer Tracks on Functional Programming http://www.defun2009.info/ Edinburgh, Scotland, September 3 and 5, 2009 The workshop will be held in conjunction with ICFP 2009 http://www.cs.nott.ac.uk/~gmh/icfp09.html Important dates Proposal Deadline: June 5, 2009, 0:00 UTC Notification: June 19, 2009 DEFUN 2009 invites functional programmers and researchers who know how to solve problems with functional progamming to give talks and lead tutorials at the The ICFP Developer Tracks. We want to know about your favorite programming techniques, powerful libraries, and engineering approaches you've used that the world should know about and apply to other projects. We want to know how to be productive using functional programming, write better code, and avoid common pitfalls. We invite proposals for presentations in the following categories. Lightning talks 5- to 10-minute talks that introduce exciting and promising research or techniques that may be in progress or not yet ready for widespread use, but that offer a glimpse into the near future of real world functional programming. Examples: * Clustered high performance computing in a functional language * Making advanced type systems more accessible to working programmers * How and why we're infiltrating category theory info industry How-to talks 45-minute "how-to" talks that provide specific information on how to solve specific problems using functional programming. These talks focus on concrete examples, but provide useful information for developers working on different projects or in different contexts. Examples: * "How I use Haskell for oilfield simulations." * "How I replaced /sbin/init by a Scheme program." * "How I hooked up my home appliances to an Erlang control system." * "How I got an SML program to drive my BMW." General language tutorials Half-day general language tutorials for specific functional languages, given by recognized experts for the respective languages. Technology tutorials Half-day tutorials on techniques, technologies, or solving specific problems in functional programming. Examples: * How to make the best use of specific FP programming techniques * How to inject FP into a development team used to more conventional technologies * How to connect FP to existing libraries / frameworks / platforms * How to deliver high-performance systems with FP * How to deliver high-reliability systems with FP Remember that your audience will include computing professionals who are not academics and who may not already be experts on functional programming. Presenters of tutorials will receive free registration to CUFP 2009. Submission guidelines Submit a proposal of 150 words or less for either a 45-minute talk with a short Q&A session at the end, or a 300-word-or-less proposal for a 3-hour tutorial, where you present your material, but also give participants a chance to practice it on their own laptops. Some advice: * Give it a simple and straightforward title or name; avoid fancy titles or puns that would make it harder for attendees to figure out what you'll be talking about. * Clearly identify the level of the talk: What knowledge should people have when they come to the presentation or tutorial? * Explain why people will want to attend: o Is the language or library useful for a wide range of attendees? o Is the pitfall you're identifying common enough that a wide range of attendees is likely to encounter it? * Explain what benefits attendees are expected to take home to their own projects. * For a tutorial, explain how you want to structure the time, and what you expect to have attendees to do on their laptops. List what software you'll expect attendees to have installed prior to coming. Submit your proposal in plain text electronically to defun-2009-submissions(a)serpentine.com by the beginning of Friday, June 5 2009, Universal Coordinated Time. Organizers * Yaron Minsky (Jane Street Capital) * Ulf Wiger (Erlang Training and Consulting) * Mike Sperber - co-chair (DeinProgramm) * Bryan O'Sullivan - co-chair (Linden Lab)

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Call for Contributions - Haskell Communities and Activities Report, May 2009 edition
by Janis Voigtlaender 01 Apr '09

01 Apr '09

Dear Haskellers, so much has happened in the Haskell world in the past months. Therefore, I would very much like to collect contributions for the 16th edition of the ================================================================ Haskell Communities & Activities Report http://www.haskell.org/communities/ Submission deadline: 1 May 2009 (please send your contributions to hcar at haskell.org, in plain text or LaTeX format) ================================================================ This is the short story: * 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! * If you are interested in any project related to Haskell that has not previously been mentioned in the HC&A Report, please tell me, so that I can contact the project leaders and ask them to submit an entry. * Feel free to pass on this call for contributions to others that might be interested. More detailed information: The Haskell Communities & Activities Report is a bi-annual overview of the state of Haskell as well as Haskell-related projects over the last, and possibly the upcoming six months. If you have only recently been exposed to Haskell, it might be a good idea to browse the November 2008 edition -- you will find interesting topics described as well as several starting points and links that may provide answers to many questions. Contributions will be collected until the submission deadline. They will then be compiled into a coherent report that is published online as soon as it is ready. As always, this is a great opportunity to update your webpages, make new releases, announce or even start new projects, or to talk about developments you want every Haskeller to know about! Looking forward to your contributions, Janis (current editor) FAQ: Q: What format should I write in? A: The required format is a LaTeX source file, adhering to the template that is available at: http://haskell.org/communities/05-2009/template.tex There is also a LaTeX style file at http://haskell.org/communities/05-2009/hcar.sty that you can use to preview your entry. If you do not know LaTeX, then use plain text. If you modify an old entry that you have written for an earlier edition of the report, you should receive your old entry as a template soon (provided I have your valid email address). Please modify that template, rather than using your own version of the old entry as a template. Q: Can I include images? A: Yes, you are even encouraged to do so. Please use .jpg format, then. Q: How much should I write? A: Authors are asked to limit entries to about one column of text. This corresponds to approximately one page, or 40 lines of text, with the above style and template. A general introduction is helpful. Apart from that, you should focus on recent or upcoming developments. Pointers to online content can be given for more comprehensive or ``historic'' overviews of a project. Images do not count towards the length limit, so you may want to use this opportunity to pep entries up. There is no minimum length of an entry! The report aims at being as complete as possible, so please consider writing an entry, even if it is only a few lines long. Q: Which topics are relevant? A: All topics which are related to Haskell in some way are relevant. We usually had reports from users of Haskell (private, academic, or commercial), from authors or contributors to projects related to Haskell, from people working on the Haskell language, libraries, on language extensions or variants. We also like reports over distributions of Haskell software, Haskell infrastructure, books and tutorials on Haskell. Reports on past and upcoming events related to Haskell are also relevant. Finally, there might be new topics we do not even think about. As a rule of thumb: if in doubt, then it probably is relevant and has a place in the HCAR. You can also ask the editor. Q: Is unfinished work relevant? Are ideas for projects relevant? A: Yes! You can use the HCAR to talk about projects you are currently working on. You can use it to look for other developers that might help you. You can use it to write ``wishlist'' items for libraries and language features you would like to see implemented. Q: If I do not update my entry, but want to keep it in the report, what should I do? A: Tell the editor that there are no changes. The old entry will be reused in this case, but it might be dropped if it is older than a year, to give more room and more attention to projects that change a lot. Do not resend complete entries if you have not changed them. -- Dr. Janis Voigtlaender http://wwwtcs.inf.tu-dresden.de/~voigt/ mailto:voigt@tcs.inf.tu-dresden.de

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[ANN] salvia-0.1, salvia-extras-0.1
by Sebastiaan Visser 01 Apr '09

01 Apr '09

Hi all, I am pleased to announce a new version of Salvia, the lightweight Haskell Web Server Framework with modular support for serving static files, directories indices, default error responses, connection counting and logging, HEAD and PUT requests, keep-alives, custom banner printing, default handler environments for parsing request and printing responses, dispatching based on request methods, URI, paths and filename extension, URI rewriting and redirection, virtual hosting, cookie, session and user management and more... Changes since previous version: - Some more advanced, non-fundamental handlers have been moved to their own package salvia-extras. This helps pruning the dependencies a bit. - The package now has some default handler environments that simplify setting up a server application. - The server now has support for keep-alive, significantly increasing the performance. - The library functions are now almost fully documented instead of no- documentation-at-all in the previous versions. - Salvia now also works on windows (I heard). - Lots of code cleanups throughout the code. - Lots of minor bug fixes. To install: use cabal. Thanks to the people that helped me with suggestions and bug-reports! -- Sebastiaan.

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Is there a way to see the equation reduction?
by Daryoush Mehrtash 01 Apr '09

01 Apr '09

I am trying to write out the execution of the recursive calls in mkDList example<http:/http://www.haskell.org/haskellwiki/Tying_the_Knot/www.haskell.org/haskellwiki/Tying_the_Knot>for different size lists. Is there a way in ghc, or ghci where for a given list I can see the intermediate recursive and evaluation steps? thanks, Daryoush

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Building/Prerequisites->Linux->glibc-devel libedit-devel ?
by Windoze 01 Apr '09

01 Apr '09

Greetings, am considering learning how to do a build for my slackware-based distro. The doc sited below say's it requires: glibc-devel libedit-devel ncurses-devel gmp-devel .etc. Must I used the dev versions, or will it work with the lastest, stable release versions of same? thanks much for the assistance http://hackage.haskell.org/trac/ghc/wiki/Building/Prerequisites http://hackage.haskell.org/trac/ghc/wiki/Building/Prerequisites -- View this message in context: http://www.nabble.com/Building-Prerequisites-%3ELinux-%3Eglibc-devel--libed… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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QuesoGLC / cabal extra-libraries not used?
by Peter Verswyvelen 01 Apr '09

01 Apr '09

I'm busy writing my first library for Hackage - a wrapper for QuesoGLC, yet another OpenGL font renderer using Freetype2. So if someone else is already doing this, stop doing so :-) I've succesfully build the libquesoglc.a library from C source, and can build my Haskell tutorial file using ghc --make -lquesoglc Tutorial1.hs But I can't drop the -lquesoglc, then I get linker errors. However I did specify extra-libraries: quesoglc in the cabal file, and the package file got configured, build and installed So I must be doing something wrong, but can't figure out what. Thanks a lot, Peter PS: I'm on Windows

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Re: [Haskell-cafe] about the Godel Numbering for untyped lambda calculus
by John Tromp 01 Apr '09

01 Apr '09

> I am reading the book "The lambda calculus: Its syntax and Semantics" in the > chapter about Godel Numbering but I am confused in some points. > > We know for Church Numerals, we have Cn = \fx.f^n(x) for some n>=0, > i.e. C0= \fx.x and C > 1 = \fx.fx. > > >From the above definition, I could guess the purpose of this kind of > encoding is trying to encode numeral via terms. > > How about the Godel Numbering? From definition we know people say #M is the > godel number of M and we also have [M] = C#M to enjoy the second fixed point > theorem : for all F there exists X s.t. F[X] = X. > > What the mapping function # is standing for? How could I use it? What the #M > will be? How to make use of the Godel Numbering? > > Thank you very much! My Wikipedia page on Binary Lambda Calculus. http://en.wikipedia.org/wiki/Binary_lambda_calculus shows a simple encoding of lc terms as bitstrings, which in turn are in 1-1 correspondence with the natural numbers. It also shows how to represent bitstrings as lambda terms, and gives an interpreter that extracts any closed term M from its encoding #M. It also give several examples of how all that is applicable to program size complexity. regards, -John

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uvector package appendU: memory leak?
by Manlio Perillo 31 Mar '09

31 Mar '09

Hi. As with a previous post, I think I have found a possible memory problem with the uvector package. I have this data structure (for, again, my Netflix Prize project): IntMap (UArr (Word16 :*: Word8)) I was adding elements to the map using something like: v = map singletonU (a :*: b) insertWith appendU k v m However doing this eats a *lot* of memory. Today I have rewritten my program to use `alter` and `snocU`: append Nothing = Just $ singletonU (a :*: b) append (Just u) = Just $ snocU u (a :*: b) alter append k m This, finally, works. Unfortunately I'm still not able to load the entire Netflix Prize training data set, grouping ratings by customers, because my PC has only 2 GB of RAM. The required memory is about 2 GB, but when the system start to swap, I have to kill the program. So the question is: why appending an array of only one element to an existing array causes memory problems? This should be pratically the same as adding an element. Thanks Manlio

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TMVar's are great but fail under ghc 6.10.1 windows
by Alberto G. Corona 31 Mar '09

31 Mar '09

Control.Concurrent.STM.TMVar's combine the best of MVars and TVars: -Unlike TVars, they permit blocking/early retry when the TMVar is being used by other process, so that complete processes are not retried at the end when happens that the TVars have been modified in the meantime. - Unlike MVars, they have no deadlocks, specially when a process is trying to adquire exclusive access to more than one TMVar. however, It happens that fails in my windows box with ghc 6.10.1 , single core here is the code and the results: -----------begin code: module Main where import Control.Concurrent.STM import Control.Concurrent import System.IO.Unsafe import GHC.Conc mtxs= unsafePerformIO $ mapM newTMVarIO $ take 5 $ repeat 0 proc i= atomically $ do unsafeIOToSTM $ putStr $ "init of process "++ show i++"\n" xs<- mapM takeTMVar mtxs mapM (\(mtx,x) ->putTMVar mtx (x+1)) $ zip mtxs xs xs' <- mapM readTMVar mtxs unsafeIOToSTM $ putStr $ "End of processs "++show i ++ " result= "++ show xs'++"\n" main=do mapM (forkIO . proc) [1..5] threadDelay 100000000 -------------end code the rigth result must be (occasionally with some "init of process x" repeated) init of process 1 init of process 2 End of processs 1 result= [1,1,1,1,1] init of process 2 -- retried End of processs 2 result= [2,2,2,2,2] init of process 3 End of processs 3 result= [3,3,3,3,3] init of process 4 End of processs 4 result= [4,4,4,4,4] init of process 5 End of processs 5 result= [5,5,5,5,5] under windows the program produces strange results for example init of process 1 init of process 2 init of process 3 init of process 4 init of process 5 End of processs 1 result= [1,1,1,1,1] End of processs 2 result= [1,1,1,1,1] (deadlock) or this other: init of process 1 init of process 2 init of process 3 init of process 4 init of process 5 End of processs 1 result= [1,1,1,1,1] End of processs 2 result= [1,1,1,1,1] init of process 3 init of process 4 init of process 5 init of process 2 End of processs 4 result= [2,2,2,2,2] End of processs 3 result= [2,2,2,2,2] End of processs 5 result= [2,2,2,2,2] End of processs 2 result= [2,2,2,2,2] init of process 3 init of process 5 init of process 2 End of processs 3 result= [3,3,3,3,3] End of processs 5 result= [3,3,3,3,3]

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