- Haskell-Cafe - Haskell.org

matrix manipulations and calculations
by Thomas Friedrich 10 Sep '11

10 Sep '11

Hi everyone, I need to do a lot of matrix manipulation and it needs to be fast. There seems to be a whole bunch of packages dealing with matrix calculations on HackageDB. I am wondering, what is the current state-of-the-art? I started of using hmatrix [1] now. However, I eventually would like to use some functions from the statisics-package [2]. They both use different types for their vector representations. In hmatrix a vector is of type Data.Packed.Vector. In the statistics package, vectors are based on [3]. I found this: http://www.haskell.org/haskellwiki/Linear_algebra but the last post is from 2005. That is 6 years ago. What is the state now? What would you recommend me to use? I don't want to code and then realise in a few month, I made the wrong decision. So, help is greatly appreciated. Thanks, Thomas -- [1] http://hackage.haskell.org/package/hmatrix-0.12.0.0 [2] http://hackage.haskell.org/package/statistics-0.9.0.0 [3] http://hackage.haskell.org/package/vector-0.9

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First CfP: International Conference on Test and Proofs (TAP 2012), Next Deadline: 2011-12-14
by Achim D. Brucker 10 Sep '11

10 Sep '11

(Apologies for duplicates) CALL FOR PAPERS Full and short Research Paper, Industrial Expierence Papers, Tool Papers Abstract submission: Dec 14, 2011, Paper submission Dec 21, 2012 6th INTERNATIONAL CONFERENCE ON TEST AND PROOFS (TAP 2012) http://lifc.univ-fcomte.fr/tap2012/ May 31 - June 1, 2012, Prague, Czech Republic Part of the TOOLS Federated Conferences 2012 http://tools2012.fit.cvut.cz/ The TAP conference is devoted to the convergence of proofs and tests, to the application of techniques from both sides and their combination for the advancement of software quality. Test and Proof seem to be contradictory techniques: if you have proved your program to be correct, it is fruitless to comb it for bugs; and if you are testing it, that is surely a sign that you have given up on any hope to prove its correctness. Accordingly, proofs and tests have, since the onset of software engineering research, been pursued by distinct communities. However, the development of both approaches lead to the discovery of common issues and to the realization that each may need the other. The emergence of model checking has been one of the first signs that contradiction may yield to complementarity. Further evidence give test data generation techniques from models or programs which boil down to constraint resolution techniques for relatively large formula; the advent of powerful SMT solvers have therefore powered new testing techniques. Finally, since formal, proof-based verification is costly, testing invariants and background theories can be helpful to detect errors early and to improve cost effectivity. Summing up, in the past few years an increasing number of research efforts have encountered the need for combining proofs and tests, dropping earlier dogmatic views of incompatibility and taking instead the best of what each of these software engineering domains has to offer. The TAP conference aims to bring together researchers and practitioners working in the converging fields of testing and proving, and will offer a generous allocation of papers, panels and informal discussions. Topics of interest cover theory definitions, tool constructions and experimentations and include (other topics related to TAP are welcome): - Transfer of concepts from testing to proving (e.g., coverage criteria) and from proving to testing - Program proving with the aid of testing techniques - New problematics in automated reasoning emerging from specificities of test generation - Verification and testing techniques combining proofs and tests - Generation of test data, oracles, or preambles by deductive techniques such as: theorem proving, model checking, symbolic execution, constraint logic programming - Model-based testing and verification - Generation of specifications by deduction - Automatic bug finding - Debugging of programs combining static and dynamic analysis - Formal frameworks - Tool descriptions and experience reports - Case studies combining tests and proofs - Applying combination of test and proof techniques to new application domains such as validating security procotols or vulnerability detection of programs Important Dates: ================ Abstract submission: December 14, 2011 Paper submission: December 21, 2011 Notification: March 2, 2012 Camera ready version: March 19, 2012 TAP conference: May 31 - June 1, 2012 (to be confirmed) TOOLS conferences (TOOLS, ICMT, SC, TAP): May 29 - June 01, 2012 Conference Chairs: Bertrand Meyer Program Chairs: Achim D. Brucker and Jacques Julliand Program Committee (to be extended): =================================== Nazareno Aguirre, Bernhard K. Aichernig, Paul Ammann, Dirk Beyer, Nikolaj Bjorner, Robert Clarisó, Marco Comini, Catherine Dubois, Gordon Fraser, Angelo Gargantini, Patrice Godefroid, Martin Gogolla, Arnaud Gotlieb, Reiner Hähnle, Bart Jacobs, Thierry Jéron, Gregory Kapfhammer, Nikolai Kosmatov, Victor Kuliamin, Karl Meinke, Holger Schlingloff, T.H. Tse, Margus Veanes, Luca Viganò, Burkhart Wolff, Fatiha Zaidi Submission: =========== Please submit your papers via http://lifc.univ-fcomte.fr/tap2012/. TAP 2012 will accept two types of papers: - Research papers: full papers with at most 16 pages in LNCS format (pdf), which have to be original, unpublished and not submitted elsewhere. - Short contributions: work in progress, (industrial) experience reports or tool demonstrations, position statements; an extended abstract with at most 6 pages in LNCS format (pdf) is expected. Accepted papers will be published in the Springer LNCS series and will be available at the conference. The contents of previous TAP proceedings is available at: http://www.informatik.uni-trier.de/~ley/db/conf/tap/ -- Dr. Achim D. Brucker, SAP Research, Vincenz-Priessnitz-Str. 1, D-76131 Karlsruhe Phone: +49 6227 7-52595, Fax: +49-6227 78-50502, http://www.brucker.ch

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Leipzig (Germany) Haskell Workshop 7 October - Program and Registration
by Johannes Waldmann 09 Sep '11

09 Sep '11

Dear all, the 6th Haskell in Leipzig workshop, on October 7, will present an absolutely thrilling mixture of tutorials and talks, with special emphasis on parallel programming. for details and registration, http://portal.imn.htwk-leipzig.de/events/hal6-haskell-workshop See you - Johannes Waldmann.

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Converting wiki pages into pdf
by mukesh tiwari 09 Sep '11

09 Sep '11

Hello all I am trying to write a Haskell program which download html pages from wikipedia including images and convert them into pdf . I wrote a small script import Network.HTTP import Data.Maybe import Data.List main = do x <- getLine htmlpage <- getResponseBody =<< simpleHTTP ( getRequest x ) -- open url --print.words $ htmlpage let ind_1 = fromJust . ( \n -> findIndex ( n `isPrefixOf`) . tails $ htmlpage ) $ "" ind_2 = fromJust . ( \n -> findIndex ( n `isPrefixOf`) . tails $ htmlpage ) $ "" tmphtml = drop ind_1 $ take ind_2 htmlpage writeFile "down.html" tmphtml and its working fine except some symbols are not rendering as it should be. Could some one please suggest me how to accomplish this task. Thank you Mukesh Tiwari

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mapM is supralinear?
by Travis Erdman 09 Sep '11

09 Sep '11

The performance of mapM appears to be supralinear in the length of the list it is mapping on. Does it need to be this way? As a comparison, both mapM_ and map are linear in the length of the list. To wit: travis@PW:~/Documents/insurer$ ghci GHCi, version 7.0.3: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. Loading package ffi-1.0 ... linking ... done. Prelude> :set +s Prelude> :set +t Prelude> :m Data.List Data.Maybe Prelude Data.List Data.Maybe> foldl' (+) 0 $ fromJust $ mapM (\x -> Just x) [1..500000] 125000250000 it :: Integer (2.23 secs, 112875864 bytes) Prelude Data.List Data.Maybe> foldl' (+) 0 $ fromJust $ mapM (\x -> Just x) [1..1000000] 500000500000 it :: Integer (6.86 secs, 214002204 bytes) Prelude Data.List Data.Maybe> foldl' (+) 0 $ fromJust $ mapM (\x -> Just x) [1..2000000] 2000001000000 it :: Integer (24.39 secs, 429299748 bytes) Prelude Data.List Data.Maybe> foldl' (+) 0 $ map (\x -> x - 1) [1..1000000] 499999500000 it :: Integer (0.77 secs, 171213436 bytes) Prelude Data.List Data.Maybe> foldl' (+) 0 $ map (\x -> x - 1) [1..10000000] 49999995000000 it :: Integer (7.42 secs, 1723399472 bytes) Prelude Data.List Data.Maybe> foldl' (+) 0 $ map (\x -> x - 1) [1..40000000] 799999980000000 it :: Integer (30.46 secs, 6894835952 bytes) Prelude Data.List Data.Maybe> mapM_ (\x -> Just x) [1..1000000] Just () it :: Maybe () (0.42 secs, 82761248 bytes) Prelude Data.List Data.Maybe> mapM_ (\x -> Just x) [1..10000000] Just () it :: Maybe () (3.87 secs, 808012660 bytes) Prelude Data.List Data.Maybe> mapM_ (\x -> Just x) [1..100000000] Just () it :: Maybe () (38.40 secs, 8054769564 bytes) Prelude Data.List Data.Maybe>

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Next European Hackathon
by Christopher Done 08 Sep '11

08 Sep '11

‘Ello! Any plans for the next European hackathon location that will presumably be in 6~ months? I need time to reap potential participants. Wonder if we could arrange an Italian hackathon? Verohac? Hm. :-) Maybe Utrecht? Hac6? Ciao!

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Solving the configuration problem with parametrized modules
by Joachim Breitner 08 Sep '11

08 Sep '11

Hi Cafe, this is an idea that has been floating in my head for a while, and I’m wondering about its feasibility and, if feasible, complexity (in the range from „trivial“ over “blog post” over “paper” to “thesis”). Application authors in Haskell often face the problem of run-time constants, e.g. values that are expected to be determined once during program start and then stay fixed for the remainder of the run. Good examples are user configuration values (--verbose, certain paths, debugging level, etc.). Usually in Haskell, you’d determine them in the main function and then pass them in an argument to all functions needing them, or you wrap that in a monad. This works and has the advantage of being explicit. One can locally change the value when passing it to another function – this can be a good thing (more powerful) or a bad thing (if the programmer had runtime-constant behavior in mind, an invariant not enforced by the type system or the compiler). The big downside is the verbosity of the approach: A lot of parameters need to be passed, and if one such value is suddenly required in a function where it was not before, this function’s signature and all functions using it have to be modified. Also, I expect that the explicit passing causes a small performance penalty. A less idiomatic approach would be something like this: ====== module M confRef = unsafePerformIO $ newIORef (error "not set yet") conf = unsafePerformIO $ readIORef confRef f = ... conf ... ====== import M main = do ... writeIORef confRef theValue ... f ... ====== This has the nice effect that the programmer can use "conf" as if it is a proper constant value. It could also be quicker, as nothing needs to be passed on the stack. But besides the subtle issues about inlining, this has the big issue of glaring unsafeness: There is no guarantee that confRef is actually set before conf is evaluated, and any code can easily change the confRef anywhere during the runtime. I’d like to propose (on the theoretical level for now, don’t worry) an extension to the language to support _parametrized modules_, which work internally similar to the example above, but with the compiler statically ensuring correctness, where correctness means * The parameter is not evaluated before it is set. * It is set at most once. Rouch syntax sketch: ====== module M parameters (conf1, conf2) f = ... conf ... ====== import M main = do ... M.setParameters someVal1 someVal2 ... f ... ====== where setParameters is a symbol generated by the compiler. The tricky part is, of course, ensuring the correctness. For example while > main = do > M.setParameters 1 2 > ...f... should be easy to check, how about > main = do > id $ M.setParameters 1 2 > ...f... or even > main = do > bool <- someIOAction > guard bool $ M.setParameters 1 2 > ...f... ? I envision a ghc extensions that would allow to one to hook into the type checker and attach bits of information (here: „uses conf“ and „initizalizes M“) to the types, and also check certain conditions (e.g. a >>= b is invalid if a and b both have „initializes M“ attached). If this extension was loaded when id was compiled, it should probably accept the second case, but when no such information is available, or in the third case, reject the code. A framework for such attached bits would surely enable more extensions that statically check some condition that is hard or unwieldy to express in the type system. I have more ideas in that direction, but before I start brabbling, maybe I should first wait for your reactions. Do you think this could be useful (from a user point of view)? Has this idea maybe already been proposed? Thanks, Joachim -- Joachim "nomeata" Breitner mail(a)joachim-breitner.de | nomeata(a)debian.org | GPG: 0x4743206C xmpp: nomeata(a)joachim-breitner.de | http://www.joachim-breitner.de/

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Haskell Weekly News: Issue 198
by Daniel Santa Cruz 08 Sep '11

08 Sep '11

Welcome to issue 198 the HWN, a newsletter covering developments in the Haskell community. This release covers the week of August 28 to September 3, 2011. Announcements Eric Y. Know released the 5th edition of the Parallel Haskell Digest. [1] http://goo.gl/Jqx01 New and Updated Projects * swapper (New - Roman Smrz) Provides a wrapper for functors, which allows their data to be automatically and transparently swapped to disk and loaded back when necessary. [2] http://goo.gl/CwojE * GA (New - Kenneth Hoste) Provides support for working with genetic algorithms in Haskell. [3] http://goo.gl/XjvFA * hledger[-web] (Update - Simon Michael) Bugfix update. [4] http://goo.gl/98ApM * bindings-DSL (Update - Mauricio CA) Provides a language to describe foreign interfaces on top of hsc2hs. [5] http://goo.gl/fFL4Y * hspec (Update - Trystan Spangler) This latest release includes a command line runner that can search through directory trees for specs and support for nested specs. [6] http://goo.gl/rVbF0 * EclipseFP (Update - JP Moresmau) New features and bugfixes. [7] http://goo.gl/dXS6t Quotes of the Week * dankna: I do [gui on osx] by writing a polyglot ObjC/Haskell program * maurer: I'd do it kmc style * hpc: your next challenge: write a definition of fix in java that fits in a twitter post * kmc: i leave for 3 seconds and you're all metaprogramming and shit * acowley: Haskellers are so abstract they can't even spell primitive * edwardk: i was happy that i had the 4th entry on google for a topic... but then i realized it was only for me, not for everyone that searches for it * kmc: oh, my suggestion was to hand off the fd's directly through a UNIX socket ... but that's probably silly ... i just like the fact that fd's can be passed through a unix socket * monochrom: "linear types change the world!" says Wadler. "Record updates change the type!" says Haskell. :) * gosu: Type parameters are covariant. This is not sound, and that does not matter. * Yitzchak Gale: I certainly wouldn't dream of dragging in type-level olegery, unsafe coercion, implicit parameters and other experimental extensions. Simplicity just works. Top Reddit Stories * 8 ways to report errors in Haskell revisited : Inside 233 Domain: blog.ezyang.com, Score: 51, Comments: 33 On Reddit: [8] http://goo.gl/RBcIL Original: [9] http://goo.gl/A2m2Z * Yesod 0.9 Released! A Massive Changelog explained. Domain: yesodweb.com, Score: 43, Comments: 6 On Reddit: [10] http://goo.gl/go7Zo Original: [11] http://goo.gl/dGoMa * EclipseFP 2.1.0 released, with Hoogle and HLint integration, and much more! Domain: jpmoresmau.blogspot.com, Score: 40, Comments: 42 On Reddit: [12] http://goo.gl/6E1QV Original: [13] http://goo.gl/mkx7g * And they say complexity has no philosophical implications Domain: scottaaronson.com, Score: 36, Comments: 9 On Reddit: [14] http://goo.gl/g97k3 Original: [15] http://goo.gl/9OGU7 * data Maybe -- harmful? Domain: blog.dbpatterson.com, Score: 29, Comments: 26 On Reddit: [16] http://goo.gl/fd2QC Original: [17] http://goo.gl/x4ibO * haskell-TLS framework progress report Domain: tab.snarc.org, Score: 29, Comments: 14 On Reddit: [18] http://goo.gl/Mdc8x Original: [19] http://goo.gl/UpyZ6 * I made a simple image upload site using haskell, sqlite3 and lighttpd. Check it out. Domain: self.haskell, Score: 27, Comments: 15 On Reddit: [20] http://goo.gl/vuF8E Original: [21] http://goo.gl/vuF8E * Manuel Chakravarty on Data Parallel Haskell Domain: vimeo.com, Score: 26, Comments: 2 On Reddit: [22] http://goo.gl/CLXJU Original: [23] http://goo.gl/jCf9w * Functional Programming Day : Oct 14th, Cambridge, UK SPJ & D Syme - early book. bef. Aug 31st Domain: fpday.net, Score: 18, Comments: 11 On Reddit: [24] http://goo.gl/wbIWr Original: [25] http://goo.gl/8OPgK * How does AwesomePrelude transform non-strict code to efficient strict code? Domain: self.haskell, Score: 18, Comments: 12 On Reddit: [26] http://goo.gl/VgIQt Original: [27] http://goo.gl/VgIQt * Composable MVCs (or UIs), a google talk by Conal Elliot Domain: youtube.com, Score: 18, Comments: 14 On Reddit: [28] http://goo.gl/9ekmO Original: [29] http://goo.gl/GDEkN Top StackOverflow Questions * Good examples of Not a Functor/Functor/Applicative/Monad? votes: 17, answers: 3 Read on SO: [30] http://goo.gl/F2q5y * Haskell: What monad did I just reinvent? votes: 17, answers: 4 Read on SO: [31] http://goo.gl/HCko4 * Why is Scalas type inference not as powerful as Haskells? votes: 17, answers: 4 Read on SO: [32] http://goo.gl/gvCF1 * Hard to understand Haskell memory allocation behaviour votes: 11, answers: 1 Read on SO: [33] http://goo.gl/X7HtB * Haskell on JVM? votes: 11, answers: 1 Read on SO: [34] http://goo.gl/Ra4kA * Implementations of spatial indexes in Haskell? votes: 11, answers: 1 Read on SO: [35] http://goo.gl/ThqRA * Does Haskell have variadic functions/tuples? votes: 9, answers: 3 Read on SO: [36] http://goo.gl/NLYCE * couldn't match expected type (Int -> Int -> Int) with actual type `(t0, t1, t2)' votes: 9, answers: 2 Read on SO: [37] http://goo.gl/5EmAS * What is the advantage of using a parser generator like happy as opposed to using parser combinators? votes: 9, answers: 3 Read on SO: [38] http://goo.gl/04s9n * manually defining boolean conjunction votes: 8, answers: 1 Read on SO: [39] http://goo.gl/FGbAj About the Haskell Weekly News To help create new editions of this newsletter, please send stories to dstcruz(a)gmail.com. Until next time, Daniel Santa Cruz References 1. http://permalink.gmane.org/gmane.comp.lang.haskell.cafe/92123 2. http://permalink.gmane.org/gmane.comp.lang.haskell.general/18903 3. http://permalink.gmane.org/gmane.comp.lang.haskell.general/18908 4. http://permalink.gmane.org/gmane.comp.finance.ledger.hledger/479 5. http://permalink.gmane.org/gmane.comp.lang.haskell.general/18909 6. http://permalink.gmane.org/gmane.comp.lang.haskell.general/18912 7. http://permalink.gmane.org/gmane.comp.lang.haskell.cafe/92150 8. http://blog.ezyang.com/2011/08/8-ways-to-report-errors-in-haskell-revisited/ 9. http://www.reddit.com/r/haskell/comments/jy34j/8_ways_to_report_errors_in_h… 10. http://www.yesodweb.com/blog/2011/08/announcing-yesod-0.9 11. http://www.reddit.com/r/haskell/comments/jy42c/yesod_09_released_a_massive_… 12. http://jpmoresmau.blogspot.com/2011/09/eclipsefp-210-released.html 13. http://www.reddit.com/r/haskell/comments/k2idm/eclipsefp_210_released_with_… 14. http://www.scottaaronson.com/blog/?p=103 15. http://www.reddit.com/r/haskell/comments/k2kuu/and_they_say_complexity_has_… 16. http://blog.dbpatterson.com/post/9528836599 17. http://www.reddit.com/r/haskell/comments/jxj8i/data_maybe_harmful/ 18. http://tab.snarc.org/post/2011/8/31/tls_progress/ 19. http://www.reddit.com/r/haskell/comments/k12g7/haskelltls_framework_progres… 20. http://www.reddit.com/r/haskell/comments/k2b10/i_made_a_simple_image_upload… 21. http://www.reddit.com/r/haskell/comments/k2b10/i_made_a_simple_image_upload… 22. http://vimeo.com/28477220 23. http://www.reddit.com/r/haskell/comments/k3x2l/manuel_chakravarty_on_data_p… 24. http://www.fpday.net/fpday2011/index.php 25. http://www.reddit.com/r/haskell/comments/jz592/functional_programming_day_o… 26. http://www.reddit.com/r/haskell/comments/k05fo/how_does_awesomeprelude_tran… 27. http://www.reddit.com/r/haskell/comments/k05fo/how_does_awesomeprelude_tran… 28. http://www.youtube.com/watch?v=faJ8N0giqzw 29. http://www.reddit.com/r/haskell/comments/k14k7/composable_mvcs_or_uis_a_goo… 30. http://stackoverflow.com/questions/7220436/good-examples-of-not-a-functor-f… 31. http://stackoverflow.com/questions/7223901/haskell-what-monad-did-i-just-re… 32. http://stackoverflow.com/questions/7234095/why-is-scalas-type-inference-not… 33. http://stackoverflow.com/questions/7247058/hard-to-understand-haskell-memor… 34. http://stackoverflow.com/questions/7261039/haskell-on-jvm 35. http://stackoverflow.com/questions/7270796/implementations-of-spatial-index… 36. http://stackoverflow.com/questions/7220953/does-haskell-have-variadic-funct… 37. http://stackoverflow.com/questions/7232375/couldnt-match-expected-type-int-… 38. http://stackoverflow.com/questions/7269025/what-is-the-advantage-of-using-a… 39. http://stackoverflow.com/questions/7220297/manually-defining-boolean-conjun…

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Fwd: Is there any way to parametrize a value update using record syntax?
by David Barbour 08 Sep '11

08 Sep '11

forgot to CC list. ---------- Forwarded message ---------- From: David Barbour <dmbarbour(a)gmail.com> Date: 2011/9/6 Subject: Re: [Haskell-cafe] Is there any way to parametrize a value update using record syntax? To: Poprádi Árpád <popradi_arpad(a)freemail.hu> 2011/9/6 Poprádi Árpád <popradi_arpad(a)freemail.hu> > But it's ugly. Always the same, only the record selector has another > name. Is it possible to generalize it? > You can generalize using template haskell. I believe Oleg's HList already provides such mechanisms, so you don't need to do this yourself. If you're doing this a lot, try the HList package. (If not, just do the Also, I would say you've too tightly coupled your BigData to the MonadicEnv. I suggest you reduce it instead to: setX :: X -> BigData -> BigData setX x' bd = bd { dataX = x' } updX :: (X -> X) -> BigData -> BigData updX fx bd = bd { dataX = fx (dataX bd) } Then in your state monad you can use: modify (setX x') gets dataX And use of 'updX' is much more composable. That aside, from personal experience, I'm usually okay just using: modify (\ s -> s { dataX = x' }) in the few places I need it.

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ghc-mtl and ghc-7.2.1
by José Romildo Malaquias 08 Sep '11

08 Sep '11

Hello. In order to compile ghc-mtl-1.0.1.0 (the latest released version) with ghc-7.2.1, I would apply the attached patch, which removes any references to WarnLogMonad. ghc-7.2.1 does not have the monad WarnLogMonad anymore. As I do not know the details of the GHC api, I am not sure if this is enough to use ghc-mtl with ghc-7.2.1. I want ghc-mtl in order do build lambdabot. Any thoughts? Romildo

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