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ghc-HEAD: build succeeds, but install fails with linker errors?
by Reid Barton 26 Jun '08

26 Jun '08

I'm trying to install GHC from the darcs repository for the first time, so I'm hoping someone here can tell me if I'm doing something wrong before I bother cvs-ghc. I'm currently running ghc 6.8.2 on Debian x86 Linux. Following the instructions on the wiki, I put the following in a file and ran it: #!/bin/bash darcs get --partial http://darcs.haskell.org/ghc cd ghc chmod +x darcs-all ./darcs-all get sh boot ./configure --prefix=$HOME/ghc-HEAD make make install but during the "make install" step I get the error ../../compiler/stage1/ghc-inplace -no-user-package-conf -o ghc-pkg.bin -H32m -O -cpp -Wall -fno-warn-name-shadowing -fno-warn-unused-matches -package Cabal -Rghc-timing -package unix -package containers Main.o Version.o CRT_noglob.o Main.o: In function `s7AP_info': (.text+0x1d): undefined reference to `prettyzm1zi0zi0zi0_TextziPrettyPrintziHughesPJ_Str_con_info' {- hundreds of similar errors (not all from the pretty package, some from base and others as well) -} collect2: ld returned 1 exit status <<ghc: 50428432 bytes, 6 GCs, 131072/131072 avg/max bytes residency (1 samples), 31M in use, 0.00 INIT (0.00 elapsed), 0.07 MUT (0.55 elapsed), 0.02 GC (0.02 elapsed) :ghc>> make[2]: *** [ghc-pkg.bin] Error 1 Failed making install in ghc-pkg: 1 make[1]: *** [install] Error 1 make: *** [install] Error 1 Have I got some of the steps wrong? Regards, Reid Barton

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Access to Oracle database from Haskell
by Henning Thielemann 26 Jun '08

26 Jun '08

Is there a way of accessing a remote Oracle database by one of the common Haskell database interfaces (HaskellDB, Takusen, etc.) ? I tried to get unixODBC and Oracle's Instant Client running on a Linux machine, but I'm trapped in the notorious error: $ isql USER -v [IM004][unixODBC][Driver Manager]Driver's SQLAllocHandle on SQL_HANDLE_HENV failed [ISQL]ERROR: Could not SQLConnect This error message is discussed in various web forums, but there seems to be no systematic way to track down the problem. So I wonder whether there is another way to access the Oracle data base from Haskell.

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Stupid question about Cabal file
by Fernand 26 Jun '08

26 Jun '08

Hi, Excuse me in advance if this is a trivial question, but I have been unable to find (understand?) the answer in Cabal's documentation. My issue is simple : I build a Cabal package named, let's say, "foo". That package is a library (libHSfoo.a, something like that), which exposes its Foo.Bar and Foobar modules. I wrote the cabal file, register it, everything seems fine. The issue comes when I try to use that package when compiling a main program, like this : ghc -package foo MyMain.hs [other options] I get an error about the compiler not finding the interface files Foobar.hi and Bar.hi, as I have "import Bar" and "import Foo.Bar" in my "MyMain.hs" file. Of course, I could add "-l" flags to point to the ".hi" files that I used to compile my package, but I get the well-known issue about the fact that the package's names of the interface files (which were compiled with the "-package-name foo" option) are not the correct ones ("Bad interface file: ../foo/Foobar.hi, Something is amiss; requested module main:Foobar differs from name found in the interface file foo:Foobar") ; and that solution is ugly anyway. So far, I found some Cabal documentation talking about the import-dirs property, but I did not manage to "make it work", I mean, my package does not seems to "include" the interface files. I am sure, on the other hand, that it is possible :) Sincerely yours, Fernand

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history of tuples vs pairs
by Conal Elliott 26 Jun '08

26 Jun '08

I have a foggy memory that early ML had only binary pairing, nesting for n-tuples. Can anyone confirm this memory. If so, does anyone remember the rationale for going to n-tuples? Performance, perhaps? Similarly, did the Haskell designers consider pairs as an alternative to n-ary tuples? The reason I ask is that while ghc and libraries suppors n-tuples for some values of n, the support is generally incomplete and inconsistent. And some abstractions are very heavily biased toward pairing, particularly Arrow and the pair instances of Monad and Applicative. And of course, inclusion of fst and snd in the prelude but lack of similar standard functions for n-tuples with n>2. - Conal

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looking for advice on "lifting" and FFI
by Galchin, Vasili 26 Jun '08

26 Jun '08

Hello, I am thinking about "glue"/"binding" code for POSIX listio and aio_suspend. E.g. http://docs.hp.com/en/B9106-90009/lio_listio.2.html 1) It seems to me that this is a "lifting" problem where we lift to a Haskell list of "aiocb's" to a C array of pointers?? An example of the "C array of pointers" is described by http://docs.hp.com/en/B9106-90009/lio_listio.2.html 2) Is it reasonable for the domain of the 1) mapping to be a Haskell list of "aiocb's"?? Kind regards, Vasili

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Haskell Weekly News: Issue 74 - June 25, 2008
by Brent Yorgey 25 Jun '08

25 Jun '08

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20080625 Issue 74 - June 25, 2008 --------------------------------------------------------------------------- Welcome to issue 74 of HWN, a newsletter covering developments in the [1]Haskell community. This week, you'll notice a bit more detail in the 'Blogs' section. I've added summaries to some of the posts, to help you decide which you might be interested to read (only a few this week, since I added them at the last minute). I've also >>> highlighted blogs not syndicated on Planet Haskell---mostly people who have just begun learning Haskell and decided to blog about it. Go show them some comment love, and invite them into the community! Community News Andrew Wagner (chessguy) recently flew out to Microsoft for an interview with their Live Search team. In [2]an email to the cafe, he shares some stories from his experience and some interesting coding challenges. Announcements HAppS self-demoing tutorial. Thomas Hartman [3]announced a self-demoing, HStringTemplate-using intro to HAppS. Check out the [4]live demo or obtain it [5]from Hackage. NWFP Interest Group. Greg Meredith [6]announced the next monthly meeting of the NW Functional Programmers Interest group, 6:30 on June 25 at the Seattle Public Library. Greg will talk about a very cool [7]compositional representation of graphs he's been tinkering with recently. ICFP final call for posters. Matthew Fluet [8]announced the final call for proposals for the ICFP 2008 poster session, which should be [9]submitted by June 30. Let people know what you're working on! type-level and parameterized-data packages. Alfonso Acosta [10]announced the release of the [11]type-level and parameterized-data packages, which provide type-level computation and parameterized types a la a dependently-typed system. Lambda in the sun. James Iry [12]announced the creation of [13]Southern California Functional Programmers (SoCalFP), a group for people in LA, Orange County, and San Diego to meet to discuss, debate, present, and learn about functional programming concepts and techniques in various languages. Real World Haskell. Bryan O'Sullivan [14]announced the availability of ten new draft chapters of [15]Real World Haskell, the upcoming O'Reilly book being written by Bryan, John Goerzen, and Don Stewart. In case you were worried, yes, you'll be able to have one in your Christmas stocking! Pugs on hackage!. Audrey Tang has uploaded to Hackage [16]version 6.2.13.2 of [17]Pugs, an implementation of Perl 6 in Haskell. Literal programming with rst-literals. Martin Blais [18]described a neat use of his utility [19]rst-literals to extract Haskell code from ReST documents, enabling a different style of literate programming. Pipe 1.0. Matti Niemenmaa [20]announced the release of [21]Pipe, a library for piping data through a pipeline of processes. HUnit. Richard Giraud [22]announced that he has improved the HUnit documentation and published the changes in a [23]darcs repository. hback. Norbert Wojtowicz [24]announced a new release of [25]hback, a Haskell implementation of the [26]dual n-back memory game using [27]gtk2hs. Google Summer of Code Progress updates from participants in the 2008 [28]Google Summer of Code. Hoogle 4. Neil Mitchell (ndm) is working on Hoogle 4, and recently [29]added two new features, multi-word search and intelligent suggestions. DPH physics engine. Roman Cheplyaka (Feuerbach) is working on a physics engine using [30]Data Parallel Haskell. [31]This week he intended to implement simple ad-hoc cubic collision geometry to test collisions with rotation, but the code became too cumbersome and non-extensible. He took a break to read some papers, and found [32]a better solution. GHC plugins. Max Bolingbroke is working on dynamically loaded plugins for GHC. [33]This week he worked on adding arbitrary user-specified phases to GHC, implementing a control system, pipeline generation, and [34]Template Haskell integration. Next he plans to work on a plugin annotation system. Cabal dependency framework. Andrea Vezzosi (Saizan) is working on a make-like dependency analysis framework for Cabal. He has posted [35]a detailed explanation of his project, some of the issues involved, and his progress so far. Language.C. Benedikt Huber (visq) is working on Language.C, a standalone parser/pretty printer library for C99. This week he worked on AST documentation and improvements, prepared to port the AST analysis from c2hs, and worked on the pretty printer's internals. Generic tries. Jamie Brandon is working on a library for efficient maps using generalized tries. Recently he has worked on implementing some [36]bitpacking tools to save memory. GHC API. Thomas Schilling (nominolo) is supposedly working on [37]improvements to the GHC API. However, officials at HWN headquarters have begun privately speculating that Thomas does not, in fact, exist. Discussion history of tuples vs pairs. Conal Elliott [38]asked about the history of support for n-tuples in Haskell and ML. hackageDB maintainer policy. Ross Paterson began a lengthy [39]discussion towards agreeing on a policy for uploading packages to Hackage, specifying whether the package is maintained and who is maintaining it, and other related issues. What is a rigid type variable?. Xiao-Yong Jin [40]asked what the 'rigid type variables' are that are sometimes referred to in GHC error messages. Read the thread for a concise discussion and the solution to the original problem. Map interface. Jamie Brandon started a [41]thread asking for feedback on his proposed API for generic tries, and the discussion is still ongoing. Left and right folds. George Kangas [42]exhibited a pair of very elegant alternate definitions for left and right fold, and showed how this alternate viewpoint makes obvious several algebraic identities as well as the generalization to [43]Data.Foldable. A must-read for the aspiring functional programmer. ribbonsPerLine. Alfonso Acosta asked an interesting [44]question about "ribbonsPerLine" in the Text.PrettyPrint.HughesPJ library. Do you know what it does? The answer can be found in the [45]original paper describing the library. Jobs PhD position at University of Strathclyde, Glasgow. Simon Marlow [46]announced, on behalf of Patricia Johann, an open PhD position in operational and categorical approaches to parametricity. The funded position is in the newly-formed Mathematically Structured Programming group at the University of Strathclyde, comprising Neil Ghani, Patricia Johann, and Conor McBride. Quantitative Trading Developer Position at Hutchin Hill Capital. Neil Mehra [47]announced an open position for a Quantitative Trading Developer at Hutchin Hill Capital, a newly formed multi-strategy hedge fund located in midtown Manhattan. Blog noise [48]Haskell news from the [49]blogosphere. * >>> Blockcipher: [50]Converting Geospatial Coordinates. Blockcipher has had enough of reading Haskell tutorials, and is itching to actually create something useful! * Roman Cheplyaka: [51]V-Clip algorithm (status update). An update on Roman's Google Summer of Code project. * Andy Gill: [52]Memo class using type families. * >>> blueapple: [53]Project Euler. blueapple is hooked on [54]Project Euler and has been using it as an opportunity to learn Haskell. * >>> Dinesh Pillay: [55]Haskell & Type Inference. Dinesh has been learning Haskell for just a few days now and is really enjoying it. In this post he shares a problem he was having with types and its solution. * Don Stewart (dons): [56]Daily Haskell: Download and analyse logs, then generate sparklines. A new series on gluing Hackage libraries together to get things done. * Max Bolingbroke: [57]Compiler Plugins For GHC: Week Two. An update on Max's Google Summer of Code project. * Edward Kmett: [58]Paramorphism. * Edward Kmett: [59]Catamorphism. * Edward Kmett: [60]Recursion Schemes: A Field Guide. Edward is writing up a 'field guide' to all those 'foomorphism' recursion schemes. * Neil Mitchell: [61]GSoC Hoogle: Week 4. * Real World Haskell: [62]Ten new draft chapters. * Jamie Brandon: [63]Bitpacking. Updates on Jamie's Google Summer of Code project. * Jamie Brandon: [64]Finally!. * Brent Yorgey: [65]ZipEdit. Brent describes a new library for creating simple interactive list editors. * Real-World Haskell: [66]Video of my concurrent/multicore Haskell talk is up. * Roman Cheplyaka: [67]Status report: week 4. An update on Roman's Google Summer of Code project. * Osfameron: [68]More Countdown: laziness, Scheme, and German frogs. * Andrea Vezzosi (Saizan): [69]a dependency analysis framework for Cabal. * Osfameron: [70]Schwartzian transform in Haskell. * Neil Mitchell: [71]Hoogle 4 New Features. * Thomas M. DuBuisson: [72]Past and Future libraries. * >>> codeflow: [73]Haskell + a grain of Python. codeflow talks about his experience learning Haskell and functional programming. * >>> Peter Christensen: [74]Hey Language Snobs: Don't Pinch Pennies. * >>> Micah Elliott: [75]1983-96: The Golden Age of Programming Languages. Quotes of the Week * povman: when does ghc6.10 plan to release itself? * Baughn: So I just rewrote a fairly complex text extraction/indexing system to pipeline its work across several processors - painlessly, in less than five minutes. Bravo, haskell! * monochrom: We need to cabalise Cale. * Botje: h0t (monoid `mappend` monoid) action? * quicksilver: the only tool we have in haskell98 for performing an action is the magic sigil 'main =' * solrize: haskell has a very steep unlearning curve :) * Botje: drug users pass around needles, haskell users pass around Oleg papers * qwe1234: i know haskell, ocaml, scheme and prolog better than you ever will. About the Haskell Weekly News New editions are posted to [76]the Haskell mailing list as well as to [77]the Haskell Sequence and [78]Planet Haskell. [79]RSS is also available, and headlines appear on [80]haskell.org. Headlines are available as [81]PDF. To help create new editions of this newsletter, please see the information on [82]how to contribute. Send stories to byorgey at seas dot upenn dot edu. The darcs repository is available at darcs get [83]http://code.haskell.org/~byorgey/code/hwn/ . References 1. http://haskell.org/ 2. http://article.gmane.org/gmane.comp.lang.haskell.cafe/41760 3. http://www.haskell.org/pipermail/haskell-cafe/2008-June/044696.html 4. http://rippledeals.com:5001/ 5. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/happs-tutorial 6. http://www.haskell.org/pipermail/haskell-cafe/2008-June/044671.html 7. http://biosimilarity.blogspot.com/2008/06/algebra-of-graphs-individually-an… 8. http://article.gmane.org/gmane.comp.lang.haskell.general/16263 9. https://www.softconf.com/s08/icfp08-posters/submit.html 10. http://www.haskell.org/pipermail/haskell-cafe/2008-June/044630.html 11. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/type-level 12. http://article.gmane.org/gmane.comp.lang.haskell.general/16260 13. http://socalfp.blogspot.com/ 14. http://www.realworldhaskell.org/blog/2008/06/22/ten-new-draft-chapters/ 15. http://www.realworldhaskell.org/blog/ 16. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Pugs-6.2.13.2 17. http://pugscode.org/ 18. http://article.gmane.org/gmane.comp.lang.haskell.cafe/41621 19. http://furius.ca/pubcode/pub/conf/common/bin/rst-literals.html 20. http://article.gmane.org/gmane.comp.lang.haskell.cafe/41619 21. http://iki.fi/matti.niemenmaa/pipe/ 22. http://article.gmane.org/gmane.comp.lang.haskell.glasgow.user/14661 23. http://richardg.name/ 24. http://article.gmane.org/gmane.comp.lang.haskell.general/16252 25. http://code.google.com/p/hback/ 26. http://www.pnas.org/cgi/content/abstract/0801268105v1 27. http://www.haskell.org/gtk2hs/ 28. http://hackage.haskell.org/trac/summer-of-code/wiki/SoC2008 29. http://neilmitchell.blogspot.com/2008/06/hoogle-4-new-features.html 30. http://www.haskell.org/haskellwiki/GHC/Data_Parallel_Haskell 31. http://physics-dph.blogspot.com/2008/06/status-report-week-4.html 32. http://physics-dph.blogspot.com/2008/06/v-clip-algorithm-status-update.html 33. http://blog.omega-prime.co.uk/2008/06/23/compiler-plugins-for-ghc-week-two/ 34. http://www.haskell.org/haskellwiki/Template_Haskell 35. http://vezzosi.blogspot.com/2008/06/my-summer-of-code-project-dependency.ht… 36. http://jamiiecb.blogspot.com/2008/06/gsoc-week-1.html 37. http://hackage.haskell.org/trac/ghc/wiki/GhcApiStatus 38. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/41749 39. http://article.gmane.org/gmane.comp.lang.haskell.libraries/9334 40. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/41651 41. http://thread.gmane.org/gmane.comp.lang.haskell.libraries/9259 42. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/41607 43. http://www.haskell.org/ghc/docs/latest/html/libraries/base/Data-Foldable.ht… 44. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/41506 45. http://www.cs.chalmers.se/~rjmh/Papers/pretty.ps 46. http://article.gmane.org/gmane.comp.lang.haskell.general/16253 47. http://article.gmane.org/gmane.comp.lang.haskell.cafe/41584 48. http://planet.haskell.org/ 49. http://haskell.org/haskellwiki/Blog_articles 50. http://idea-guy.blogspot.com/2008/06/converting-geosptial-coordinates.html 51. http://physics-dph.blogspot.com/2008/06/v-clip-algorithm-status-update.html 52. http://blog.unsafeperformio.com/?p=30 53. http://blueappledev.wordpress.com/2008/06/24/project-euler/ 54. http://projecteuler.net/ 55. http://dpillay.blogspot.com/2008/06/haskell-type-inference.html 56. http://www.cse.unsw.edu.au/~dons/blog/2008/06/24#daily-haskell-one 57. http://blog.omega-prime.co.uk/2008/06/23/compiler-plugins-for-ghc-week-two/ 58. http://comonad.com/reader/2008/paramorphism/ 59. http://comonad.com/reader/2008/catamorphism/ 60. http://comonad.com/reader/2008/recursion-schemes/ 61. http://neilmitchell.blogspot.com/2008/06/gsoc-hoogle-week-4.html 62. http://www.realworldhaskell.org/blog/2008/06/22/ten-new-draft-chapters/ 63. http://jamiiecb.blogspot.com/2008/06/bitpacking.html 64. http://jamiiecb.blogspot.com/2008/06/finally.html 65. http://byorgey.wordpress.com/2008/06/21/zipedit/ 66. http://www.realworldhaskell.org/blog/2008/06/20/video-of-my-concurrentmulti… 67. http://physics-dph.blogspot.com/2008/06/status-report-week-4.html 68. http://osfameron.vox.com/library/post/more-countdown-laziness-scheme-and-ge… 69. http://vezzosi.blogspot.com/2008/06/my-summer-of-code-project-dependency.ht… 70. http://osfameron.vox.com/library/post/schwartzian-transform-in-haskell.html… 71. http://neilmitchell.blogspot.com/2008/06/hoogle-4-new-features.html 72. http://tommd.wordpress.com/2008/06/18/past-and-future-libraries/ 73. http://codeflow.wordpress.com/2008/06/18/haskell-a-grain-of-python/ 74. http://www.pchristensen.com/blog/articles/hey-language-snobs-dont-pinch-pen… 75. http://micahelliott.blogspot.com/2008/06/1983-96-golden-age-of-programming.… 76. http://www.haskell.org/mailman/listinfo/haskell 77. http://sequence.complete.org/ 78. http://planet.haskell.org/ 79. http://sequence.complete.org/node/feed 80. http://haskell.org/ 81. http://code.haskell.org/~byorgey/code/hwn/archives/20080625.pdf 82. http://haskell.org/haskellwiki/HWN 83. http://code.haskell.org/~byorgey/code/hwn/

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Two questions regarding Alex/Parsec
by Niels Aan de Brugh 25 Jun '08

25 Jun '08

Hello Haskellers, As an experiment I'm writing a parser for MediaWiki language. I'm using the Alex lexer and Parsec. I have novice two questions. (I've tried using Happy but I was unable to get a grammar file to compile, which must be because I have no real experience using Yacc and the like. I've also attempted to write an ad-hoc recursive descent parser, but that become too complex to be fun very quickly.) == SourcePos and AlexPosn == My first question is about Parsec's SourcePos. I have a definition like: type LexToken = (AlexPosn, Token) type MWP a = GenParser LexToken () a toSourcePos :: AlexPosn -> SourcePos toSourcePos (AlexPn _ line col) = undefined mwtok :: (Token -> Maybe a) -> MWP a mwtok test = token showToken posToken posTest where showToken = show . snd posToken = toSourcePos . fst posTest = test . snd The definition of toSourcePos isn't 100% satisfactory. The constructor SourcePos is hidden, so I cannot simply use (SourcePos line col). Is there a way to convert an AlexPosn value to a SourcePos? == Data Constructors as Parameters and Tags == Secondly, I frequently encounter the pattern where I try to match a token, return Just some result if it matches, and Nothing otherwise. So I tried to fix this pattern in a nice reusable function. onTok0 :: Token -> a -> MWP a onTok0 t x = mwtok (\tok -> if tok `isTok` t then Just x else Nothing) This seems to work, but I'd also like a definition for data constructors taking one parameter: onTok1 :: (a -> Token) -> (a -> b) -> MWP b onTok1 t f = mwtok (\tok -> case tok of (t n) = Just $ f n _ = Nothing) This doesn't work, the pattern match (t n) fails, which is understandable: n is used as a parameter to t and a matched result, which looks like a paradox. t is a function (constructor) but also a tag. Is it possible to pass a tag as an argument? Or is there another way to extract this pattern? Regards, Niels

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Simple question about processing XML with HaXml
by Dominic Espinosa 25 Jun '08

25 Jun '08

Hello, I'm trying to learn how to use HaXml, but I'm having trouble getting off the ground. I can see from the documentation how to process XML using the combinators and processXmlWith, but processXmlWith seems to "hide" the actual process of reading and parsing the XML. Suppose that processXmlWith isn't suitable for a program. How then do you load the XML and apply filters to it? I guess what I'm asking is, given the following code: load filename = do handle <- IO.openFile filename IO.ReadMode contents <- IO.getContents handle IO.hclose handle return $ xmlParse filename contents myTest fname = do -- read file d <- load fname --- ?? now what? I'm sure the answer to this is quite simple, but I'm coming from a background of OO and SAX, and the HaXml docs are a bit cryptic as yet. Additionally, if anyone knows of any tutorials pertaining to HaXml, other than the papers on the HaXml website and the blog entries on cleaning legacy HTML, I'd appreciate some pointers. Thanks.

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ICFP08 Final Call for posters
by Matthew Fluet (ICFP Publicity Chair) 25 Jun '08

25 Jun '08

ICFP 2008 poster session September 21, 2008 Call for presentation proposals ICFP 2008 will feature a poster session for researchers and practitioners, including students. The session will provide friendly feedback for work that is in gestation or ongoing, as well as opportunities to meet each other and exchange ideas. We welcome poster submissions on all ICFP topics, especially presentations of - applications of and to functional programming; - recent work presented at more distant venues; and - ongoing work, whether or not submitted to ICFP. There will be no formal proceedings, but presenters will be invited to submit working notes, demo code, and other materials to supplement their abstract and poster. These materials will be released informally on a Web page dedicated to the poster session. An accepted submission is not intended to replace conference or journal publication. Persons interested in presenting a poster are invited to submit a one-page abstract in SIGPLAN conference style http://www.acm.org/sigs/sigplan/authorInformation.htm to the Web site https://www.softconf.com/s08/icfp08-posters/submit.html by June 30, 2008. The program committee will review the submissions for relevance and interest, and notify the authors by July 14, 2008. Accepted posters must be presented by the authors in person on Sunday, September 21, 2008. Important dates: Submission: Monday, June 30, 2008 Notification: Monday, July 14, 2008 Presentation: Sunday, September 21, 2008 Program committee: Benjamin Pierce (University of Pennsylvania) Colin Runciman (University of York) Chung-chieh Shan (Rutgers University)

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Help with generalizing function
by leledumbo 25 Jun '08

25 Jun '08

I've successfully create a function to return lists of N-ple that satisfy the following function: x1 + x2 + x3 + ... + xN = C But unfortunately, it's not generic. The N is supposed to be an input, too. I don't know how to make a dynamic N-ple (is it possible anyway?). Currently, here's the implementation: [code] findAllAns c = [ (x1,x2,x3,x4,x5) | x1 <- [0..c], x2 <- [0..c], x3 <- [0..c], x4 <- [0..c], x5 <- [0..c], x1 + x2 + x3 + x4 + x5 == c ] [/code] I tried using lists of lists, like this: [code] findAllAns c n = [ [x] | x <- [0..c], length [x] == n ] [/code] but [x] doesn't mean "a list of x", instead it's "a list that contains an x, where x in [0..c]". Can anyone help me? -- View this message in context: http://www.nabble.com/Help-with-generalizing-function-tp18063291p18063291.h… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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