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Trouble installing ghc-6.10.1 on linux
by Bit Connor 07 Dec '08

07 Dec '08

I'm trying to install ghc 6.10.1 on a machine with the crux distro. libc version 2.3.6 gcc 4.0.3 linux version 2.6.15.6 First I tried the binary version ghc-6.10.1-i386-unknown-linux.tar.bz2 and I very quickly get this error: $ ./configure checking build system type... i686-pc-linux-gnu checking host system type... i686-pc-linux-gnu checking target system type... i686-pc-linux-gnu Which we'll further canonicalise into: i386-unknown-linux checking for path to top of build tree... configure: error: cannot determine current directory $ Next I tried building the source version ghc-6.10.1-src.tar.bz2 using ghc 6.6 that is already installed. configure works but make eventually dies with: ... Configuring ghc-6.10.1... cabal-bin: At least the following dependencies are missing: Cabal -any, base <3, filepath >=1 && <1.2, haskell98 -any, hpc -any, template-haskell -any, unix -any make[2]: *** [boot.stage.2] Error 1 Any ideas? Thanks, Bit

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latest Hood ?
by Simon Michael 07 Dec '08

07 Dec '08

Hugo Pacheco wrote: > The library also features the visualization of the intermediate data > structure of hylomorphisms with GHood. I hadn't come across GHood and Hood before, and they look quite a useful addition to the toolbox. http://www.haskell.org/hood says "The current released version of HOOD is the July 2000 release, but there is also a patch to all HOOD to work with GHC 5.00.". The Observe.lhs there doesn't immediately work with current GHC. Has anyone got an updated version, or is this available in some more recent library or package ? Or, I may have misunderstood, and Debug.Trace may do everything that Hood did. Still, a working Hood would be useful to get the nice visualisations of GHood. Thanks - Simon

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Can't cabal install readline
by Martijn van Steenbergen 06 Dec '08

06 Dec '08

Hello, This week I upgraded to GHC 6.10 using the .pkg installer. It installed without a single hiccup -- thanks! I've noticed two odd things: the standard library haddock that comes with the installer doesn't have links to the hs-coloured sources anymore (and neither does the online documentation); I miss that a lot. I also can't Ctrl+R anymore in GHCi to search my command history. But I can learn to live without those. Another minor inconvenience is that the packages I had installed (using cabal) are no longer available to GHC -- I think I will have to reinstall them. But I cannot continue working on my Yogurt project anymore, because it depends on readline, which fails to build: <snip> checking for rl_readline_version... yes checking for rl_begin_undo_group... no configure: error: readline not found, so this package cannot be built See `config.log' for more details. cabal: Error: some packages failed to install: Yogurt-0.2 depends on readline-1.0.1.0 which failed to install. readline-1.0.1.0 failed during the configure step. The exception was: exit: ExitFailure 1 The build failure mentions config.log which I cannot find anywhere on my system. I have readline installed using MacPorts without problems, and the cabal package worked fine too on the previous version of GHC. I'm on Intel Leopard. How can I get cabal install readline to succeed on the new GHC? Thanks much, Martijn.

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Haskell Weekly News: Issue 96 - December 6, 2008
by Brent Yorgey 06 Dec '08

06 Dec '08

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20081206 Issue 96 - December 06, 2008 --------------------------------------------------------------------------- Welcome to issue 96 of HWN, a newsletter covering developments in the [1]Haskell community. Announcements Haskell haikus. Gwern Branwen [2]announced that he has collected all known haikus about Haskell and put them on a [3]wiki page. Add more! Platforms that GHC supports. Simon Peyton-Jones [4]linked to a [5]new page clearly articulating what platforms GHC supports, and what platforms its maintainers would like it to support. If you're interested and willing to help sponsor a "Tier 2" platform, let them know! Using Data Parallel Haskell. Manuel Chakravarty [6]announced a new [7]wiki page with documentation for Data Parallel Haskell. DrHylo 0.0.1. Hugo Pacheco [8]announced the [9]release of [10]DrHylo, a tool for deriving hylomorphisms from a restricted Haskell syntax. It is based on the algorithm first presented in the paper Deriving Structural Hylomorphisms From Recursive Definitions at ICFP'96 by Hu, Iwasaki, and Takeichi. The generated code can be run with [11]Pointless Haskell, allowing the visualization of the recursion trees of Haskell functions. pointless-haskell 0.0.1. Hugo Pacheco [12]announced the [13]release of [14]Pointless Haskell, a library for point-free programming with recursion patterns defined as hylomorphisms, inspired in ideas from the PolyP library. The re-implementation of the library using type functions (in opposition to classes with functional dependencies) enables a type-level view of data types as the fixed points of functors and provides a better experience to the users in terms of code sanity. The library also features the visualization of the intermediate data structure of hylomorphisms with GHood. Projects that depend on the vty package?. Corey O'Connor [15]asked whether there are any other projects that depend on the [16]vty package. If so, let him know! The package also has a new [17]trac and wiki. haskell-src-exts 0.4.4. Niklas Broberg [18]announced the release of [19]haskell-src-exts 0.4.4, which adds support for pragmas. ChristmasTree 0.1. S. Doaitse Swierstra [20]announced the release of the [21]ChristmasTree package, which stands for "Changing Haskell's Read Implementation Such That by Manipulating Abstract Syntax Trees it Reads Expressions Efficiently". TTTAS. S. Doaitse Swierstra [22]announced the release of [23]TTTAS, a library for typed transformations of typed abstract syntax. GHood. Hugo Pacheco [24]announced that GHood, a graphical backend for the lightweight Hood Haskell debugger, has now been [25]released as a Cabal package. Discussion Animated line art. Andrew Coppin [26]asked for ideas on writing Haskell to generate some animations. Jobs Scala job in Boston writing quantitative finance software. Paul Chiusano [27]announced that [28]ClariFI is looking to hire developers with a strong background in functional programming to do a mixture of Scala and Java programming. ClariFI is a small company (about 15 developers) that specializes in software for quantitative investment management. This position is for the Boston office. If you're interested, send him an email. Blog noise [29]Haskell news from the [30]blogosphere. * Bryan O'Sullivan: [31]Functional programmers on Twitter. * Conal Elliott: [32]Sequences, segments, and signals. * >>> Gianfranco Alongi: [33]QuickCheck(ing) the code i C. * Edward Kmett: [34]The Pointed-Set Comonad. * Twan van Laarhoven: [35]Knight in n, part 3: rings. * "The GHC Team": [36]Explicit Stack Traces. * Real-World Haskell: [37]The Real World Haskell Book Club. * Real-World Haskell: [38]Real World Haskell: Now in Brazil. * >>> Matt Hellige: [39]Pointless fun. * Chung-chieh Shan: [40]The pointed-set monad. * Holumbus: [41]Status Update. * Paul R Brown: [42].editrc Tidbit for ghci. * Roman Cheplyaka: [43]DPH docs and project status. * David Sankel: [44]Introducing Reactive: Behaviors. * Manuel M T Chakravarty: [45]How to use Data Parallel Haskell.. * Conal Elliott: [46]Prettier functions for wrapping and wrapping. * Twan van Laarhoven: [47]Knight in n, part 2: combinatorics. * Yi: [48]Prototypes: Encoding OO-style inheritance in Haskell. * "Osfameron": [49]Functional Pe(a)rls v2 (now with Monads!) at the London Perl Workshop 2008. * Conal Elliott: [50]Sequences, streams, and segments. * Conal Elliott: [51]Early inspirations and new directions in functional reactive programming. * Clemens Fruhwirth: [52]XMonad GridSelect. 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/2008-December/051529.html 3. http://haskell.org/haskellwiki/Haiku 4. http://article.gmane.org/gmane.comp.lang.haskell.glasgow.user/15958 5. http://hackage.haskell.org/trac/ghc/wiki/Platforms 6. http://www.haskell.org//pipermail/glasgow-haskell-users/2008-December/01627… 7. http://haskell.org/haskellwiki/GHC/Data_Parallel_Haskell 8. http://article.gmane.org/gmane.comp.lang.haskell.general/16668 9. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/DrHylo 10. http://haskell.di.uminho.pt/wiki/DrHylo 11. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/pointless-haskell 12. http://article.gmane.org/gmane.comp.lang.haskell.cafe/48598 13. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/pointless-haskell 14. http://haskell.di.uminho.pt/wiki/Pointless+Haskell 15. http://article.gmane.org/gmane.comp.lang.haskell.cafe/48471 16. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/vty 17. http://trac.haskell.org/vty/ 18. http://www.haskell.org//pipermail/haskell-cafe/2008-December/051444.html 19. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/haskell-src-exts… 20. http://www.haskell.org//pipermail/haskell/2008-December/020847.html 21. http://en.wikipedia.org/wiki/Sinterklaas 22. http://www.haskell.org//pipermail/haskell/2008-December/020848.html 23. http://www.cs.uu.nl/wiki/bin/view/Center/TTTAS 24. http://www.haskell.org//pipermail/haskell/2008-December/020849.html 25. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/GHood-0.0.2 26. http://www.haskell.org//pipermail/haskell-cafe/2008-December/051451.html 27. http://www.haskell.org//pipermail/haskell-cafe/2008-December/051295.html 28. http://clarifi.com/ 29. http://planet.haskell.org/ 30. http://haskell.org/haskellwiki/Blog_articles 31. http://www.serpentine.com/blog/2008/12/05/functional-programmers-on-twitter/ 32. http://conal.net/blog/posts/sequences-segments-and-signals/ 33. http://writert.blogspot.com/2008/12/quickchecking-code-i-c.html 34. http://comonad.com/reader/2008/the-pointed-set-comonad/ 35. http://twan.home.fmf.nl/blog/haskell/Knight3.details 36. http://ghcmutterings.wordpress.com/2008/12/04/explicit-stack-traces/ 37. http://www.realworldhaskell.org/blog/2008/12/03/the-real-world-haskell-book… 38. http://www.realworldhaskell.org/blog/2008/12/03/real-world-haskell-now-in-b… 39. http://matt.immute.net/content/pointless-fun 40. http://conway.rutgers.edu/~ccshan/wiki/blog/posts/Pointed_set/ 41. http://holumbus.fh-wedel.de/blog/?p=16 42. http://mult.ifario.us/p/editrc-tidbit-for-ghci 43. http://physics-dph.blogspot.com/2008/12/dph-docs-and-project-status.html 44. http://netsuperbrain.com/blog/posts/introducing-reactive-behaviors/ 45. http://justtesting.org/post/62610924 46. http://conal.net/blog/posts/prettier-functions-for-wrapping-and-wrapping/ 47. http://twan.home.fmf.nl/blog/haskell/Knight2.details 48. http://yi-editor.blogspot.com/2008/12/prototypes-encoding-oo-style.html 49. http://greenokapi.net/blog/2008/12/01/functional-pearls-v2-now-with-monads-… 50. http://conal.net/blog/posts/sequences-streams-and-segments/ 51. http://conal.net/blog/posts/early-inspirations-and-new-directions-in-functi… 52. http://blog.clemens.endorphin.org/2008/11/xmonad-gridselect.html 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/

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Fwd: problems with hs-plugins load-eval
by Alberto G. Corona 06 Dec '08

06 Dec '08

I have a web server which load server extensions. these extensions eval-uate configuration files that contains code (user-editable workflow descriptions). The problem is that I need common definitions for the extensions and for the configurration files. This is not permitted by ha-plugins. The minimal code example are the files below. main loads eval.hs , that evaluate a expression. The common definitions are in Include.hs. The error is: *GHCi runtime linker: fatal error: I found a duplicate definition for symbol Include_sum1_srt whilst processing object file /home/magocoal/haskell/devel/votesWorkflow/src/unused/tests/Include.o This could be caused by: * Loading two different object files which export the same symbol * Specifying the same object file twice on the GHCi command line * An incorrect `package.conf' entry, causing some object to be loaded twice. GHCi cannot safely continue in this situation. Exiting now. Sorry. * ** Do you kno how to solve the problem while maintaining the functionality? -------Include.hs------- module Include where sum [x,y]= x+y ------Main.hs----- module Main where import Include import System.Plugins main= do s <-loadExec "eval.o" "mainc" print s loadExec:: String-> String->IO String loadExec file method = do mv <- load file ["."] [] method case mv of LoadSuccess mod v -> v :: IO String LoadFailure msg -> return $ concat msg ------------Eval.hs-------- module Eval(mainc) where import System.IO.Unsafe import System.Eval.Haskell mainc= do i <- unsafeEval_ "sum1 [1,2]" ["Include"] [] []["."] :: IO (Either [String] Int) return $ show i

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ANNOUNCE: pointless-haskell 0.0.1
by Hugo Pacheco 06 Dec '08

06 Dec '08

Dear Haskelleers, Alcino Cunha and me are pleased to announce the release of the Pointless Haskell library in Hackage: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/pointless-haskell Pointless Haskell is library for point-free programming with recursion patterns defined as hylomorphisms, inspired in ideas from the PolyP library. The re-implementation of the library using type functions (in opposition to classes with functional dependencies) enables a type-level view of data types as the fixed points of functors and provides a better experience to the users in terms of code sanity. The library also features the visualization of the intermediate data structure of hylomorphisms with GHood. I am giving birth to a website with some examples: http://haskell.di.uminho.pt/wiki/Pointless+Haskell Any feedback is welcome. Cheers, hugo -- www.di.uminho.pt/~hpacheco

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Functional version of this OO snippet
by Andrew Wagner 06 Dec '08

06 Dec '08

Hi all, public interface IEngine { void foo(); void bar(string bah); ... } public class Program { public void Run(IEngine engine){ while(true){ string command = GetLine(); if (command.startsWith("foo")){ engine.foo(); } else if (command.startsWith("bar")){ engine.bar(command); ... else break; } In other words, I want to provide the same UI across multiple implementations of the engine that actually processes the commands. Thanks in advance.

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Fun with type functions
by Simon Peyton-Jones 05 Dec '08

05 Dec '08

Friends GHC has embodied data type families since 6.8, and now type synonym families (aka type functions) in 6.10. However, apart from our initial papers there isn't much published material about how to *use* type families. But that hasn't stopped you: quite a few people are using them already, and of course there is a rich seam of work on using functional dependencies to express type-level computation. Ken Shan and Oleg Kiselyov and I are collaborating to write a paper for an upcoming workshop, under the general rubric of "Fun with type functions" (in homage to Thomas Hallgren's paper "Fun with functional dependencies" and Ralf Hinze's paper "Fun with phantom types"). So this message is to ask you: can you tell us about the most persuasive, fun application you've encountered, for type families or functional dependencies? Simple is good. It doesn't have to be elaborate: just something that does something useful you could not have done otherwise. Pointers to email threads are fine. Don't assume we already know about them (even if we participated in the thread :-) Part of what we're interested in is that *you* found the example compelling. Many thanks Simon, Ken, Oleg PS: I'm broadcasting this message to GHC-users and Haskell-cafe, but to avoid deluging ghc-users, please reply just to us and Haskell cafe. (Interested ghc-users can follow the threads there from the archives if they want.)

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efficient combination of foldl' and foldr -> foldl'r
by Henning Thielemann 05 Dec '08

05 Dec '08

I want to do a foldl' and a foldr in parallel on a list. I assumed it would be no good idea to run foldl' and foldr separately, because then the input list must be stored completely between the calls of foldl' and foldr. I wanted to be clever and implemented a routine which does foldl' and foldr in one go. But surprisingly, at least in GHCi, my clever routine is less efficient than the naive one. Is foldl'rNaive better than I expect, or is foldl'r worse than I hope? module FoldLR where import Data.List (foldl', ) import Control.Arrow (first, second, (***), ) foldl'r, foldl'rNaive :: (b -> a -> b) -> b -> (c -> d -> d) -> d -> [(a,c)] -> (b,d) foldl'r f b0 g d0 = first ($b0) . foldr (\(a,c) ~(k,d) -> (\b -> k $! f b a, g c d)) (id,d0) foldl'rNaive f b g d xs = (foldl' f b *** foldr g d) $ unzip xs test, testNaive :: (Integer, Char) test = second last $ foldl'r (+) 0 (:) "" $ replicate 1000000 (1,'a') {- *FoldLR> test (1000000,'a') (2.65 secs, 237509960 bytes) -} testNaive = second last $ foldl'rNaive (+) 0 (:) "" $ replicate 1000000 (1,'a') {- *FoldLR> testNaive (1000000,'a') (0.50 secs, 141034352 bytes) -}

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Gluing pipes
by Matt Hellige 05 Dec '08

05 Dec '08

>From time to time, I've wanted to have a more pleasant way of writing point-free compositions of curried functions. One might want to transform both the first and second arguments, for instance, or only the third argument, of a curried function. I've never known a (non-cryptic) way to do this. For example, given: f :: a -> b -> c g :: a1 -> a h :: b2 -> b I'd like to be able to write something like: \ x y -> f (g x) (h y) in a way that is both point-free and applicative. In other words, I'd like to apply a function to "pipes" or transformers rather than to values. Recent posts by Conal Elliott [1,2] got me thinking about this again, and I've found a simple solution. I use two of Conal's combinators: argument = flip (.) result = (.) And now we define: infixr 2 ~> f ~> g = argument f . result g infixl 1 $. ($.) = flip ($) Which lets us write: -- transform both arguments f $. g ~> h ~> id -- transform just the second argument f $. id ~> h ~> id The name ($.) is chosen to indicate that this is (roughly) a composition disguised as an application. The transformer spec to the right of ($.) looks like the type of the function to the left, and consists of a transformer for each argument and one for the result type. Of course, (~>) is right associative, and id can match the entire tail "in bulk", so we can also write something like: f $. g ~> id And of course, each transformer can be a pipeline, so assuming proper types, we can do things like: f $. id ~> (length.snd.unWrap) ~> wrap More details here: http://matt.immute.net/content/pointless-fun Questions: 1. Is there already another well-known way to do this? It seems a common enough problem... 2. Do these particular combinators already exist somewhere with other names? 3. Are there better names for these functions? Thanks! Matt [1] http://conal.net/blog/posts/semantic-editor-combinators/ [2] http://conal.net/blog/posts/prettier-functions-for-wrapping-and-wrapping/

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