- Haskell-Cafe - Haskell.org

Computing a sorted list of products lazily
by Jason Dagit 18 Apr '09

18 Apr '09

Hello, A colleague of mine recently asked if I knew of a lazy way to solve the following problem: Given two sets of sorted floating point numbers, can we lazily generate a sorted list of the products from their Cartesian product? The algorithm should return the same result as: sortProduct a b = sort [ x * y | x <- a, y <- b ] But, my friend is not satisfied with the strictness of sort. In particular, he doesn't want to have to hold the whole list in memory to sort it. He would like to compute the results one product at a time and in the correct order. Is there an existing algorithm for this problem? We searched but we don't seem to know the right search terms. Additionally, my friend is not writing this in Haskell, but a Haskell solution is fine because we should be able to transform it into a Java solution by hand. We think we know an algorithm that will produce the right result but it's a bit messy and we doubt we're the first to tackle this problem. Any help would be greatly appreciated. Thanks in advance! Jason

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Synchronising cabal package version with self-reported version
by Denis Bueno 18 Apr '09

18 Apr '09

Hi all, In a command-line app of mine I want to have a --version flag, like many GNU apps do to report their version. The only way I know to provide the version number is to hardcode it in the source code somewhere. That means I have the version number in two places: the .cabal file and the source code. I just know that one day they'll get unsynchronised, and --version will be wrong. Is there any way to put the version number in _one_ place, and have both the .cabal and source refer to it? Or even any easier way to synchronise both version numbers? Thanks, Denis

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Debugging a RecSel Error
by Gü?nther Schmidt 18 Apr '09

18 Apr '09

Hi all, I'm trying to find the spot in my source code that triggered a RecSel Exception ("No match in record selector

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Parsec question
by Michael P Mossey 18 Apr '09

18 Apr '09

I want to write a parser that can read a file with this format: the file has sections which are demarcated by keywords. Keywords always begin with two forward slashes and consist of letters, digits, and underscore. The text can be anything, including special characters. For instance: //keyword some text and more text //another_keyword and) some { more text //ya_keyword $$ -- text I'm not sure how to write a parser that considers anything but a double slash to be a valid part of the text. Thanks, Mike

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Announce: funsat-0.6
by Denis Bueno 18 Apr '09

18 Apr '09

Hello haskell-cafe, funsat is 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. Funsat is intended to be reasonably efficient for practical problems and convenient to use as a constraint-solving backend in other software. Version 0.6 is available from Hackage: * http://hackage.haskell.org/cgi-bin/hackage-scripts/package/funsat New in 0.6: * A representation for logical circuits (and, or, not, onlyif, iff, if-then-else) supporting efficient conversion to CNF (for solving) has been added. * Now uses the BSD3 license. Please report any bugs to the github page linked from hackage. Denis

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Haskell Weekly News: Issue 114 - April 17, 2009
by Brent Yorgey 17 Apr '09

17 Apr '09

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20090417 Issue 114 - April 17, 2009 --------------------------------------------------------------------------- Welcome to issue 114 of HWN, a newsletter covering developments in the [1]Haskell community. The [2]5th Haskell Hackathon is underway in Utrecht! Happy Haskell hacking! An early HWN this week since I will be traveling this weekend (but not, unfortunately, to the Hackathon). Announcements Reminder: Haskell Communities and Activities Report. Janis Voigtlaender [3]reminded everyone that the deadline for the [4]May 2009 edition of the Haskell Communities and Activities Report is only two weeks away. If you haven't already, please write an entry for your new project, or update your old entry. primes. Sebastian Fischer [5]announced the release of the [6]primes package, which implements lazy wheel sieves for efficient, purely functional generation of prime numbers in Haskell. level-monad-0.3. Sebastian Fischer [7]announced version 0.3 of the package [8]level-monad, which implements breadth-first search directly as an instance of MonadPlus (without using an intermediate tree representation). Version 0.3 adds a MonadPlus instance for iterative deepening inspired by Michael Spivey's paper on [9]Algebras for combinatorial search. hgettext 0.1.10. Vasyl Pasternak [10]announced a new release of the [11]hgettext package, which now has bindings to all gettext functions. Haskell logo in TeX. Philip Hölzenspies [12]announced a version of the new [13]Haskell logo design prepared using TikZ, for inclusion in LaTeX documents. The Monad.Reader (14) - Call for copy. Wouter Swierstra [14]issued a call for copy for Issue 14 of [15]The Monad.Reader. The deadline for submissions is May 15, 2009. Let Wouter know if you intend to submit something -- the sooner, the better. time 1.1.2.4. Ashley Yakeley [16]announced the release of [17]time 1.1.2.4, which should now compile on Windows. Discussion Code Golf. Sebastian Fischer [18]started a lively round of code golf with his code for list diagonalization. Converting IO [XmlTree] to [XmlTree]. rodrigo.bonifacio [19]asked how to convert an IO [XmlTree] into an [XmlTree], leading to a discussion of Haskell pedagogy. Blog noise [21]Haskell news from the [22]blogosphere. * Roman Cheplyaka: [23]Fun in Utrecht. * Roman Cheplyaka: [24]Utrecht: first impressions. * >>> Daniel van den Eijkel: [25]Hommage: Haskell Offline Music Manipulation And Generation EDSL. * >>> Brandon Simmons: [26]Some initial tests of Tries. * Christopher Lane Hinson: [27]Trends in Profiling Haskell. * >>> Larry O'Brien: [28]Windows & .NET Watch: Haskell: It's like Klingon, but with math!. * Sean Escriva: [29]Why Haskell is a joy to learn. * GHC / OpenSPARC Project: [30]Instruction counts on x86 vs SPARC. * Sebastian Fischer: [31]Barefaced pilferage of monadic bind. * Benjamin L. Russell: [32]Climbing the Towers of Hanoi with Haskell-style Curry from a Monadic Container (While Sparing the Sugar!). Quotes of the Week * Gracenotes: And then the type system goes all crazy and demands that x and 1 are both Word32s! * mauke: data What a = No; instance Monad What where { return _ = No; No >>= _ = No } * pumpkin: makes the next internet hit video, 2 natural transformations, 1 functor * mmorrow: a functor is like an analogy between two analogies * FliPPeh: @faq Can Conficker be rewritten in Haskell? <lambdabot> <no location info>: parse error on input `:' * HairyDude: The Haskell Type System is a Harsh Mistress.. there ain't no such thing as a free theorem. * LeCamarade: Now, let's say the set is {Haskell, SML, Ruby, Tomatoes, Human, Cabbage, Noise, IRC}. * pjdelport: YO DAWG I HERD YOU LIKE CARS SO WE PUT A PAIR IN YO CAR SO YOU CAN CAR WHILE YOU CAR * Babelfish: And there you travel: a beam tracer! Naturally, there are many things that ought to be amend. About the Haskell Weekly News New editions are posted to [33]the Haskell mailing list as well as to [34]the Haskell Sequence and [35]Planet Haskell. [36]RSS is also available, and headlines appear on [37]haskell.org. To help create new editions of this newsletter, please see the information on [38]how to contribute. Send stories to byorgey at cis dot upenn dot edu. The darcs repository is available at darcs get [39]http://code.haskell.org/~byorgey/code/hwn/ . References 1. http://haskell.org/ 2. http://haskell.org/haskellwiki/Hac5 3. http://article.gmane.org/gmane.comp.lang.haskell.cafe/57075 4. http://www.haskell.org/pipermail/haskell/2009-April/021180.html 5. http://article.gmane.org/gmane.comp.lang.haskell.cafe/57042 6. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/primes 7. http://article.gmane.org/gmane.comp.lang.haskell.cafe/56981 8. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/level-monad 9. http://spivey.oriel.ox.ac.uk/mike/search-jfp.pdf 10. http://article.gmane.org/gmane.comp.lang.haskell.cafe/56940 11. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hgettext 12. http://article.gmane.org/gmane.comp.lang.haskell.general/17094 13. http://www.cs.utwente.nl/~holzensp/haskelllogo.sty 14. http://article.gmane.org/gmane.comp.lang.haskell.general/17090 15. http://haskell.org/haskellwiki/The_Monad.Reader 16. http://article.gmane.org/gmane.comp.lang.haskell.libraries/10921 17. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/time 18. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/56957 19. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/56898 21. http://planet.haskell.org/ 22. http://haskell.org/haskellwiki/Blog_articles 23. http://ro-che.blogspot.com/2009/04/fun-in-utrecht.html 24. http://ro-che.blogspot.com/2009/04/utrecht-first-impressions.html 25. http://substitut-fuer-feinmotorik.net/projects/haskellommage/introduction 26. http://coder.bsimmons.name/blog/2009/04/some-initial-tests-of-tries/ 27. http://blog.downstairspeople.org/2009/04/16/trends-in-profiling-haskell/ 28. http://www.sdtimes.com/content/article.aspx?ArticleID=33399 29. http://www.webframp.com/2009/04/15/why-haskell-is-a-joy-to-learn/ 30. http://ghcsparc.blogspot.com/2009/04/instruction-counts-on-x86-vs-sparc.html 31. http://www-ps.informatik.uni-kiel.de/~sebf/haskell/stealing-bind.html 32. http://dekudekuplex.wordpress.com/2009/04/13/climbing-the-towers-of-hanoi-w… 33. http://www.haskell.org/mailman/listinfo/haskell 34. http://sequence.complete.org/ 35. http://planet.haskell.org/ 36. http://sequence.complete.org/node/feed 37. http://haskell.org/ 38. http://haskell.org/haskellwiki/HWN 39. http://code.haskell.org/~byorgey/code/hwn/

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Re: [Haskell-cafe] RE: [Announce] primes
by michael rice 17 Apr '09

17 Apr '09

You're right. Since I'm not familiar with Cabal, I didn't use it. Is there a good tutorial? Docs? Also, I'm running a 32-bit Linux OS. Does one get a significant speed increase by switching to a 64-bit OS? Thanks for the feedback. Michael --- On Fri, 4/17/09, Sebastian Fischer <sebf(a)informatik.uni-kiel.de> wrote: From: Sebastian Fischer <sebf(a)informatik.uni-kiel.de> Subject: Re: [Haskell-cafe] RE: [Announce] primes To: "Haskell Cafe mailing list" <haskell-cafe(a)haskell.org> Date: Friday, April 17, 2009, 4:03 AM Oh, I just remembered, I'm using ghci. I'll bet that's why I'm so slow. I also did, but after installing the package using cabal. IIRC, cabal compiles with -O2 by default. But if you downloaded the tarball and then loaded the module in ghci without installing it, this is probably the reason for the slow response. Cheers,Sebastian -----Inline Attachment Follows----- _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

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types and braces
by Conor McBride 17 Apr '09

17 Apr '09

Hi folks In search of displacement activity, I'm trying to tweak Language.Haskell.Exts to support a few more perfidious Exts I have in mind -- they only need a preprocessor, but I do need to work on parsed programs, ideally. I was hoping to add a production to the grammar of types to admit expressions, delimited by braces: { exp } The idea is that instead of writing, (er, hi Claus), data True data False one just re-uses yer actual Bool (which becomes kind {Bool}) and writes {True} or {False}. The trouble is, the production I've added causes a reduce/reduce conflict in the grammar, but I don't get any more precise complaint than that. I guess what I'd like to know is whether I just need to debug my grammar extension, or whether the notation I'm proposing actually introduces a serious ambiguity that I'm too dim to notice. I'm mostly sending this in the hope that I have one of those "d'oh" moments you sometimes get when you articulate a stupid question in public. Put me out of my misery, please... Cheers Conor

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glut installation using cabal failed
by Raja Koduru 17 Apr '09

17 Apr '09

hi, I am a beginner to haskell. I am trying to install glut using "cabal install glut" Pasting here a tail of the output --------------------------------------------------------------------- checking for unistd.h... yes checking windows.h usability... yes checking windows.h presence... yes checking for windows.h... yes checking GL/glut.h usability... no checking GL/glut.h presence... no checking for GL/glut.h... no checking for GLUT library... no checking for GL/glut.h... (cached) no checking GLUT/glut.h usability... no checking GLUT/glut.h presence... no checking for GLUT/glut.h... no configure: error: no GLUT header found, so this package cannot be built See `config.log' for more details. cabal: Error: some packages failed to install: GLUT-2.1.1.2 failed during the configure step. The exception was: exit: ExitFailure 1 --------------------------------------------------------------------------------- But I do have "glut.h" in my "D:\ghc\ghc-6.10.2\include\mingw\GL". Here is my `ghc-pkg list` -------------------------------------------------------------------------------- D:\ghc\ghc-6.10.2>ghc-pkg list d:/ghc/ghc-6.10.2\package.conf: Cabal-1.6.0.3, GLFW-0.3, HUnit-1.2.0.3, OpenGL-2.2.1.1, QuickCheck-1.2.0.0, Win32-2.2.0.0, 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), filepath-1.1.0.2, (ghc-6.10.2), ghc-paths-0.1.0.5, 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, xhtml-3000.2.0.1 -------------------------------------------------------------------------------- I am on windows XP using ghc-6.10.2 Please advice, regards, raja

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wxHaskell not in scope
by Tsunkiet Man 17 Apr '09

17 Apr '09

Hello, I'm trying to create a GUI by using wxHaskell. However I get the weird error message of "Not in scope "dt"", well so I sorted them so that my so called "dt" was in scope, however it failed. Can someone please tell me how I can solve this error? ... A lot of code that is not relevant in my opinion, if I'm wrong please correct me and I will post my full code --Debug text -- dt <- staticText f [text := "Hello world!"] imagePanel <- panel f [position := Point 2 2, clientSize := Size 100 100, tooltip := "This is a drawPanel", bgcolor := rgb 255 255 255] set f [ clientSize := Size 700 500, menuBar := [mFile, mHelp], visible := True, on (menu exit) := close f, on (menu open) := onOpen f vFile ] return () where onOpen :: Frame a -> Var b -> IO () onOpen frame var = do file <- fileOpenDialog frame False True "Open File" [("PGM bestanden (*.pgm)",["*.pgm"]),("Alle bestanden (*.*)",["*.*"])] "" "" case file of Nothing -> return () Just file -> set dt [text := "HELLO"] return () Thank you for your help, I really owe haskell-cafe. Greetings Tsunkiet Man

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