- Haskell-Cafe - Haskell.org

Record update fusion (or how should I call it?)
by Peter Verswyvelen 06 Sep '09

06 Sep '09

I've seen a couple of package being announced that provide first class labels, and other packages already existed for this (Grapefruit Record, HList, Accessor, ...) Regarding this, I have a question about the performance of multiple composed field updates. Maybe an example. Suppose I have a large record - say WindowDescription - which contains a lot of fields. Suppose I have a couple of default window description values, e.g. defaultWindowDesc, dialogBoxDesc, etc Using accessors it is easy to take such a default value, and "modify" a couple of fields, like: let myWindowDesc = set title "Haskell" . set size (640,480) . set background Blue . set fontFamily Arial $ defaultWindowDesc However, I guess this would make a lot of intermediate WindowDescription copies no (whether the fields are strict or not)? So ideally for performance, all these "updates" should be fused, maybe running inside an ST monad? I'm not sure if any of this is valid, but I would like to understand more about this, so any links and hints are welcome :-) Peter Verswyvelen

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Re: How to customize dyre recompile?
by Will Donnelly 06 Sep '09

06 Sep '09

Hi Andy, I feel that I should offer a disclaimer here: You are misusing Dyre somewhat by attempting to make it handle whole-program recompilation. It is designed to recompile a single configuration file, generally against an installed library form of the application. Some of its code, specifically the part that decides when to recompile, is based almost entirely on this assumption. That aside, you should be able to accomplish your goals like this: 1. Set the 'forceRecomp' parameter (just added in Dyre 0.7.3) to 'False'. This will remove the '-fforce-recomp' flag from GHC's options. 2. Run your executable with the '--force-reconf' flag, which will cause Dyre to always enter the recompilation code. In a test project I just created, this seems to do what you desire. Hope this helps clear things up - Will Donnelly On Sun, Sep 6 2009 at 1:41 PM, Andy Stewart <lazycat.manatee(a)gmail.com> wrote: > > Hi all, > > I use below params for configure dyre: > > rebootParams :: Params Config > rebootParams = defaultParams > {projectName = "Main" > ,realMain = manatee > ,showError = rebootShowError > ,cacheDir = Just $ return "/test/Download/cache/" > ,configDir = Just getCurrentDirectory > } > > There have two version of function `reboot` to reboot Master binary: > > reboot :: IORefObject -> IO () > reboot ioRefObject = do > rs <- rebootGetState ioRefObject > relaunchWithBinaryState rs Nothing > > reboot :: IORefObject -> IO () > reboot ioRefObject = do > output <- customCompile rebootParams > case output of > Just o -> putStrLn o -- output recompile error > Nothing -> do -- otherwise relaunch > rs <- rebootGetState ioRefObject > relaunchWithBinaryState rs Nothing > > Becuase i setup `projectName` with `Main`, so i want `dyre` recompile > NECESSARY module when i change any module in my project. > > In first version of function `reboot`, i just use > `relauncheWithBinaryState`, i found `dyre` just recompile all project when i > modified Main.hs, if i modified any others module in project, `dyre` > won't recompile those modified modules. > > In second version, i use `customCompile` for recompile, but this have > another problem, `customComiple` use `-fforce-recomp` flags to remove > all object files, so function `customComiple` will recompile all modules > in project, and not just recompile NECESSARY modules. > > So how to make `dyre` just recompile NECCESSARY modules whatever i > change any modules in project? > > Maybe add new option "--dyre-reconf-necessary" in `dyre`? > > Thanks! > > -- Andy

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Re: memoization
by John Lato 06 Sep '09

06 Sep '09

I just discovered that changing DiffArray to a plain Array improves performance of my code by almost a factor of 10. Bitten by DiffArray yet again! John -- this is no good, just change DiffArray to Array. > update :: (Char -> [Int]) -> DiffArray Int ModP -> Char -> DiffArray Int ModP > update lookup arr c = arr // (map calc . lookup $ c) > where > calc i = (i, (arr ! i) + (arr ! (i-1)))

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Averting QuickCheck Madness
by Christopher Lane Hinson 06 Sep '09

06 Sep '09

There are some libraries that depend on QuickCheck 2, and others that depend on QuickCheck 1. This can be a problem. AIUI, the Haskell Platform current depends on QC1, but intends to move to QC2 soon. I also know that the cabal mailing list has talked about some kind of private-depends capability to mitigate this kind of thing in the future. However, I don't see how it can possibly be a best practice to depend on QuickCheck from a shipping library. End users never use this, and for users of upstream packages who may compile from source and contribute the occasional (but valuable!) patch, this is nothing but a compile-time problem waiting to happen. (Note that a user who contributes to a library should be encouraged to run test suites, but I'm talking about users of upstream packages.) There are some good ideas discussed on this list last year*, but none of them seem to have been blessed by the community. * http://www.haskell.org/pipermail/haskell-cafe/2008-September/047216.html Friendly, --Lane

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Re: [Haskell-cafe] Trying to reduce memory costs of String duplicates - Oh my god it works
by Günther Schmidt 06 Sep '09

06 Sep '09

Hi Luke, Brian, oh my god it works! I'm just saying it because that's a first! Late last night I had already suspected that laziness might be one of the reasons why the memoization technique showed no effect on memory consumption and after Brian's email that's exactly where I tried again, using Bang Patterns. IT WORKED! The memory consumption is now down by 20 fold! Thank you guys very very much! Günther Am 06.09.2009, 03:24 Uhr, schrieb Brian Sniffen <bts(a)evenmere.org>: > Remember that each string will still be read, so you may still > allocate a great deal of memory and generate a great deal of garbage. > You will just release it before long, rather than hold it for the life > of your program. Remember also that the memoization itself is lazy: > it does no good if you read all the file in, then force the > memoizations along with the computation of interest. > > -Brian > > 2009/9/5 Günther Schmidt <gue.schmidt(a)web.de>: >> Hi Luke, >> >> thanks, this is some very good advice as I find many duplicates in the >> data >> I have to iterate over. >> >> However so far I'm unable to tell wether this actually works or not, I >> tried >> it a couple of times under different settings but it showed to >> difference in >> memory consumption. The same mem peeks as before. >> >> Do you have some code that where you could see a before and after? >> >> Günther >> >> >> Am 05.09.2009, 19:38 Uhr, schrieb Luke Palmer <lrpalmer(a)gmail.com>: >> >>> 2009/9/5 Günther Schmidt <gue.schmidt(a)web.de>: >>>> >>>> Hi all, >>>> >>>> I'm reading in a data of 216k records into a map of Key, Values Pairs, >>>> the >>>> values being strings. >>>> >>>> As it happens out of 216k String values there really are only about >>>> 6.6k >>>> distinct string values, so I could save a lot of RAM if I was able to >>>> "insert" only actually *new* string values into the map and use >>>> references >>>> to (string) values that already are in memory instead. >>>> >>>> Is there a container that would, if I wanted to insert an element, >>>> return >>>> a >>>> pair of either the previously inserted, equal value and the container >>>> unchanged, or the new, previously unknown value and the new container >>>> amended by that element? >>> >>> I believe a memoization of the identity function will do what you want: >>> >>> import qualified Data.MemoCombinators as Memo >>> >>> share = Memo.list Memo.char id >>> >>> Then pass any string through share to make/get a cached version. >>> >>> You might want to limit the scope of share -- eg. put it in a where >>> clause for the function where you're using it -- so that it doesn't >>> eat memory for the lifetime of your program, only for when you need >>> it. >>> >>> Luke >> >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> > > >

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Re: memoization
by John Lato 06 Sep '09

06 Sep '09

Hello, I agree that your answer is elegant, but it's not an efficient algorithm in any language. How about this, keeping the rest of your code the same? import Data.Array.Diff import Data.IArray update :: (Char -> [Int]) -> DiffArray Int ModP -> Char -> DiffArray Int ModP update lookup arr c = arr // (map calc . lookup $ c) where calc i = (i, (arr ! i) + (arr ! (i-1))) solve line sol = (foldl' (update lookup) iArray line) ! snd (bounds iArray) where iArray = listArray (0, length sol) $ 1 : map (const 0) sol lookup c = map (+1) . findIndices (== c) $ sol I would expect that at least some of the C programs would use the same algorithm. It's not the most efficient Haskell implementation, but on my computer it runs the large dataset in a little under 3 seconds, which is probably good enough. Cheers, John > > Hi, > > I participating in de google code jam this year and I want to try to use > haskell. The following > simple http://code.google.com/codejam/contest/dashboard?c=90101#s=p2 > problem > would have the beautiful haskell solution. > > import Data.MemoTrie > import Data.Char > import Data.Word > import Text.Printf > > newtype ModP = ModP Integer deriving Eq > > p=10000 > > instance Show ModP where > show (ModP x) = printf "%04d" x > > instance Num ModP where > ModP x + ModP y = ModP ((x + y) `mod` p) > fromInteger x = ModP (x `mod` p) > ModP x * ModP y = ModP ((x * y) `mod` p) > abs = undefined > signum = undefined > > solve _ [] = 1::ModP > solve [] _ = 0::ModP > solve (hs:ts) t@(ht:tt) | hs==ht = solve ts tt + solve ts t > | otherwise = solve ts t > > go (run, line) = "Case #"++show run++": "++show (solve line "welcome to code > jam") > > main = interact $ unlines . map go . zip [1..] . tail . lines > > > Which is unfortunately exponential. > > Now in earlier thread I argued for a compiler directive in the lines of {-# > Memoize function -#}, > but this is not possible (it seems to be trivial to implement though). Now I > used memotrie which > runs hopelessly out of memory. I looked at some other haskell solutions, > which were all ugly and > more clumsy compared to simple and concise C code. So it seems to me that > haskell is very nice > and beautiful until your are solving real algorithmic problems when you want > to go back to some > imperative language. > > How would experienced haskellers solve this problem? > > Thanks > -- > View this message in context: http://www.nabble.com/memoization-tp25306687p25306687.html > Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. >

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Don't “accidentallyparallelize”
by Gracjan Polak 06 Sep '09

06 Sep '09

Hi all, In "DEFUN 2009: Multicore Programming in Haskell Now!" (http://donsbot.wordpress.com/2009/09/05/defun-2009-multicore-programming-in…) slide 30 I see: Don't “accidentally parallelize”: – f `par` f + e and that the correct way of achieving parallelism is: – f `par` e `pseq` f + e Actually I don't understand the difference between these two forms. Could any brave soul explain it to me, please? As a bonus question: what is the difference between `seq` and `pseq`? -- Gracjan

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How to customize dyre recompile?
by Andy Stewart 06 Sep '09

06 Sep '09

Hi all, I use below params for configure dyre: rebootParams :: Params Config rebootParams = defaultParams {projectName = "Main" ,realMain = manatee ,showError = rebootShowError ,cacheDir = Just $ return "/test/Download/cache/" ,configDir = Just getCurrentDirectory } There have two version of function `reboot` to reboot Master binary: reboot :: IORefObject -> IO () reboot ioRefObject = do rs <- rebootGetState ioRefObject relaunchWithBinaryState rs Nothing reboot :: IORefObject -> IO () reboot ioRefObject = do output <- customCompile rebootParams case output of Just o -> putStrLn o -- output recompile error Nothing -> do -- otherwise relaunch rs <- rebootGetState ioRefObject relaunchWithBinaryState rs Nothing Becuase i setup `projectName` with `Main`, so i want `dyre` recompile NECESSARY module when i change any module in my project. In first version of function `reboot`, i just use `relauncheWithBinaryState`, i found `dyre` just recompile all project when i modified Main.hs, if i modified any others module in project, `dyre` won't recompile those modified modules. In second version, i use `customCompile` for recompile, but this have another problem, `customComiple` use `-fforce-recomp` flags to remove all object files, so function `customComiple` will recompile all modules in project, and not just recompile NECESSARY modules. So how to make `dyre` just recompile NECCESSARY modules whatever i change any modules in project? Maybe add new option "--dyre-reconf-necessary" in `dyre`? Thanks! -- Andy

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ANN: vty-4.0.0.1 released
by Corey O'Connor 06 Sep '09

06 Sep '09

Vty is a terminal UI library. Release 4.0.0.1 brings a number of important fixes, features, and performance enhancements. - Completely rewritten output backend. - Efficient, "scanline rasterization" style output span generator. Has not been fully optimized, but should be fast enough. - Terminfo based display terminal implementation. With specialized derivitives for xterm, Terminal.app, and iTerm.app. - Attempts to robustly handle even terminals that don't support all display attributes. - I've tested the following terminals with success: iTerm.app, Terminal.app, xterm, rxvt, mlterm, Eterm, gnome-terminal, konsole, screen, linux vty. Hopefully you will be as successfull. - Improved unicode support. Double wide characters will display as expected. - 256 color support. See Graphics.Vty.Attributes.Color240. The actual output color is adjusted according to the number of colors the terminal supports. - The Graphics.Vty.Image combinators no longer require matching dimensions to arguments! Unspecified areas are filled in with a user-customizable background pattern. See Graphics.Vty.Picture. - output picture will be cropped to display size as expected. - GHC 6.8 support is broken :-( - Unknown Windows platform support. - API changes: - "getSize" has been removed. Use "terminal vty >>= display_bounds" where "vty" is an instance of the Vty data structure. - added a "terminal" field to the Vty data structure. Accesses the TerminalHandle associated with the Vty instance. See Graphics.Vty.Terminal for details on the API usable with a TerminalHandle. - Graphics.Vty.Types has undergone a number of changes. Summary: - Partitioned into Graphics.Vty.Attributes for display attributes. Graphics.Vty.Image for image combinators. Graphics.Vty.Picture for final picture construction. - Graphics.Vty.Attributes: - "setFG" and "setBG" are now "with_fore_color" and "with_back_color" - All other "set.." equations similarly replaced. - "attr" is now "def_attr", short for "default display attributes" Also added a "current_attr" for "currently applied display attributes" - Graphics.Vty.Image: - "horzcat" is now "horiz_cat" - "vertcat" is now "vert_cat" - "renderBS" is now "utf8_bytestring" - "renderChar" is now "char" - "renderFill" is now "char_fill" - added a "utf8_string" and "string" (AKA "iso_10464_string") for UTF-8 encoded Strings and ISO-10464 encoded Strings. String literals in GHC have an ISO-10464 runtime representation. - Graphics.Vty.Picture: - exports Graphics.Vty.Image - "pic" is now "pic_for_image" - added API for setting background fill pattern. issues resolved: - "gnome terminal displays non-basic attributes as strikethrough" - http://trac.haskell.org/vty/ticket/14 - "Multi-byte characters are not displayed correctly on update" - http://trac.haskell.org/vty/ticket/10 - "Redraw does not handle rendering a line that extends beyond screen width characters" - http://trac.haskell.org/vty/ticket/13 - "The <|> and <-> combinators should be more forgiving of mismatched dimensions" - http://trac.haskell.org/vty/ticket/9 - "256-color support" - http://trac.haskell.org/vty/ticket/19

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Trying to reduce memory costs of String duplicates
by Günther Schmidt 06 Sep '09

06 Sep '09

Hi all, I'm reading in a data of 216k records into a map of Key, Values Pairs, the values being strings. As it happens out of 216k String values there really are only about 6.6k distinct string values, so I could save a lot of RAM if I was able to "insert" only actually *new* string values into the map and use references to (string) values that already are in memory instead. Is there a container that would, if I wanted to insert an element, return a pair of either the previously inserted, equal value and the container unchanged, or the new, previously unknown value and the new container amended by that element? Günther

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Haskell Weekly News: Issue 129 - September 5, 2009
by Brent Yorgey 05 Sep '09

05 Sep '09

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20090905 Issue 129 - September 05, 2009 --------------------------------------------------------------------------- Welcome to issue 129 of HWN, a newsletter covering developments in the [1]Haskell community. The [2]Haskell Symposium was a great success, with many [3]interesting talks and a good discussion on the future of Haskell. Watch this space for links to video from the Symposium as it becomes available! Announcements HStringTemplate 0.6.2. Sterling Clover [4]announced some new features in the [5]HStringTemplate library, including simple quasiquotation; proper Unicode support; creation of groups from hierarchies of directories; separators applied within iterated template application; depthwise chained iterated template application; generalized encoding functions; and more. fclabels-0.4.0 - First class accessor labels. Sebastiaan Visser [6]announced a new release of the [7]fclabels package, straight from ICFP in Edinburgh. The package provides first-class labels which act as fully composable, bidirectional record fields, as well as support for automatically generating them from record types. vty-4.0.0.1 released. Corey O'Connor [8]announced release 4.0.0.1 of [9]vty, a terminal UI library. This release brings a number of important fixes, features, and performance enhancements, including a completely rewritten output backend; efficient, "scanline rasterization" style output span generator; terminfo based display terminal implementation; improved Unicode support; 256 color support; and more. haskell-src-exts-1.1.4. Niklas Broberg [10]announced the release of [11]haskell-src-exts-1.1.4, a package for Haskell source code manipulation. The experimental code in Language.Haskell.Annotated{.*} has changed quite a lot, although the stable portion of the package interface has not changed. Significantly, the package now includes an exact-printer which allows round-tripping between parsing and pretty-printing to be the identity. Next BostonHaskell meeting: September 16th at MIT (32G-882). Ravi Nanavati [12]announced the September meeting of the Boston Area Haskell Users' Group, to be held Wednesday, September 16th from 7pm - 9pm. As usual, it will be held in the MIT CSAIL Reading Room (32-G882, on the 8th floor of the Gates Tower of the MIT's Stata Center at 32 Vassar St in Cambridge, MA). The featured speaker will be Edward Kmett, who will be presenting the second part of his monoids and parsing presentation: "A Parallel Parsing Trifecta: Iteratees, Parsec, and Monoids". lenses -- Simple Functional Lenses. Job Vranish [13]announced the release of [14]lenses, a simple but powerful implementation of function lenses (aka functional references/accessors). This library provides a convenient way to access and update the elements of a structure. It is very similar to Data.Accessors, but simpler, a bit more generic and has fewer dependencies. Dutch HUG: meeting next week (September 11th) in Utrecht. Tom Lokhorst [15]invited functional programmers in The Netherlands to the [16]Dutch Haskell User Group, meeting Friday, September 11 at 19:00 in the [17]Booth Hall of the Utrecht University Library. Thomas (noknok) will be talking about his system for doing propositional logic in Haskell. Pedro will give an introductory talk about generic programming, and Sean will talk about xformat, a library for extensible and type-safe formatting with scanf- and printf-like functions. There is also still space for short 5-minute lighting talk about something related to Haskell or functional programming; contact Tom if you're interested. moe html combinator. Jinjing Wang [18]announced the release of [19]moe, a DSL for generating HTML. jail-0.0.1 - Jailed IO monad. Sebastiaan Visser [20]announced the first release of the [21]jail package, a jailed IO monad that can restrict filesystem access for your code. scion 0.1. Thomas Schilling [22]announced the first release of [23]Scion, a Haskell library that aims to implement those parts of a Haskell IDE which are independent of a particular front-end. Scion is based on the GHC API and Cabal. It provides both a Haskell API and a server for non-Haskell clients such as Emacs and Vim. Blog noise [24]Haskell news from the [25]blogosphere. Blog posts from people new to the Haskell community are marked with >>>, be sure to welcome them! * Don Stewart (dons): [26]DEFUN 2009: Multicore Programming in Haskell Now!. * Bryan O'Sullivan: [27]Slides from my CUFP 2009 keynote talk. * LHC Team: [28]Yet another unfair benchmark.. * Alex McLean: [29]Hackpact documentation. * >>> Jeff Foster: [30]Exploring Haskell's List Functions. * Don Stewart (dons): [31]Parallel Programming in Haskell: A Reading List. * David Amos: [32]Finite fields, part 2. * >>> Jeff Foster: [33]Debugging in Haskell. * apfelmus: [34]Fun with Morse Code. * Ketil Malde: [35]Parsing ints. * Alex McLean: [36]Hackpact. * Greg Bacon: [37]Finding duplicates with Perl and Haskell. * Colin Adams: [38]Selecting software for a replacement for this website. * Don Stewart (dons): [39]Haskell Popularity Rankings: September 2009. * Mikael Vejdemo-Johansson: [40][Stanford] MATH 198: Category Theory and Functional Programming. * Jeff Heard: [41]HDR imaging library for Haskell based on pfsutils. * David Amos: [42]Extension fields. * Magnus Therning: [43]Trying to work out iteratees. Quotes of the Week * benmachine: ho hum. I understand both your positions. but i don't understand mine, now :( * ksf: agda is actually a secret mindwar-weapon of the illuminati, who want to wrack your nerves with excessively big symbol sets requiring a keyboard with 10 modifier keys. just like APL. * Axman6: does anyone else think that C++ looks like a dead fish? (C++<) * Cale: The difference between Many Worlds and Copenhagen is a garbage collector ;) * apfelmus: Lambda Fu, form 72 - three way dragon zip: 'averages3 xs = zipWith3 avg xs (drop 1 xs) (drop 2 xs); where avg a b c = (a+b+c) / 3' About the Haskell Weekly News New editions are posted to [44]the Haskell mailing list as well as to [45]the Haskell Sequence and [46]Planet Haskell. [47]RSS is also available, and headlines appear on [48]haskell.org. To help create new editions of this newsletter, please see the information on [49]how to contribute. Send stories to byorgey at cis dot upenn dot edu. The darcs repository is available at darcs get [50]http://code.haskell.org/~byorgey/code/hwn/ . References 1. http://haskell.org/ 2. http://www.haskell.org/haskell-symposium/2009/ 3. http://www.haskell.org/haskell-symposium/2009/schedule.html 4. http://article.gmane.org/gmane.comp.lang.haskell.cafe/63108 5. http://hackage.haskell.org/package/HStringTemplate 6. http://article.gmane.org/gmane.comp.lang.haskell.cafe/63082 7. http://hackage.haskell.org/package/fclabels 8. http://article.gmane.org/gmane.comp.lang.haskell.cafe/63072 9. http://hackage.haskell.org/package/vty 10. http://article.gmane.org/gmane.comp.lang.haskell.cafe/63068 11. http://hackage.haskell.org/package/haskell-src-exts 12. http://article.gmane.org/gmane.comp.lang.haskell.cafe/63067 13. http://article.gmane.org/gmane.comp.lang.haskell.cafe/63059 14. http://hackage.haskell.org/package/lenses 15. http://article.gmane.org/gmane.comp.lang.haskell.cafe/63000 16. http://www.haskell.org/haskellwiki/Dutch_HUG 17. http://www.uu.nl/EN/library/contact/university_library/zaalverhuur/Pages/de… 18. http://article.gmane.org/gmane.comp.lang.haskell.cafe/62865 19. http://hackage.haskell.org/package/moe 20. http://article.gmane.org/gmane.comp.lang.haskell.cafe/62839 21. http://hackage.haskell.org/package/jail 22. http://article.gmane.org/gmane.comp.lang.haskell.cafe/62820 23. http://hackage.haskell.org/package/scion 24. http://planet.haskell.org/ 25. http://haskell.org/haskellwiki/Blog_articles 26. http://donsbot.wordpress.com/2009/09/05/defun-2009-multicore-programming-in… 27. http://www.serpentine.com/blog/2009/09/04/slides-from-my-cufp-2009-keynote-… 28. http://lhc-compiler.blogspot.com/2009/09/yet-another-unfair-benchmark.html 29. http://yaxu.org/hackpact-documentation/ 30. http://www.fatvat.co.uk/2009/09/exploring-haskells-list-functions.html 31. http://donsbot.wordpress.com/2009/09/03/parallel-programming-in-haskell-a-r… 32. http://haskellformaths.blogspot.com/2009/09/finite-fields-part-2.html 33. http://www.fatvat.co.uk/2009/09/debugging-in-haskell.html 34. http://apfelmus.nfshost.com/fun-with-morse-code.html 35. http://blog.malde.org/index.php/2009/08/31/parsing-ints/ 36. http://yaxu.org/hackpact/ 37. http://feedproxy.google.com/~r/gbacon/~3/aaZePz6Gv2Q/finding-duplicates-wit… 38. http://colina.demon.co.uk/?q=node/753 39. http://donsbot.wordpress.com/2009/08/29/haskell-popularity-rankings-septemb… 40. http://blog.mikael.johanssons.org/archive/2009/08/stanford-math-198-categor… 41. http://vis.renci.org/jeff/2009/08/28/hdr-imaging-library-for-haskell-based-… 42. http://haskellformaths.blogspot.com/2009/08/extension-fields.html 43. http://therning.org/magnus/archives/735 44. http://www.haskell.org/mailman/listinfo/haskell 45. http://sequence.complete.org/ 46. http://planet.haskell.org/ 47. http://sequence.complete.org/node/feed 48. http://haskell.org/ 49. http://haskell.org/haskellwiki/HWN 50. http://code.haskell.org/~byorgey/code/hwn/

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Re: Problem on existential type.
by John Lato 05 Sep '09

05 Sep '09

Also, the two definitions for liftGW are exactly equivalent. You have: liftGW (GridWidget label) f = f label liftGW (GridWidget textView) f = f textView The only difference between the two is name to which the data parameter to GridWidget is bound, which doesn't change the meaning at all. You should properly have liftGW (GridWidget widget) f = f widget There's no way to determine if that widget is a label or textView, which is the whole point of existential types. Cheers, John > From: Miguel Mitrofanov <miguelimo38(a)yandex.ru> > Subject: Re: [Haskell-cafe] Problem on existential type. > To: Magicloud Magiclouds <magicloud.magiclouds(a)gmail.com> > > Your data type GridWidget doesn't have a parameter, yet you use it > like it has one. > >> data GridWidget = forall widget. (WidgetClass widget) => GridWidget >> widget > ^ > | > NB:-------------+ > >> liftGW :: (GridWidget widget) -> (widget -> t) -> t >

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Re: [Haskell-cafe] haskelldb + sqlite problem.
by Colin Paul Adams 05 Sep '09

05 Sep '09

>>>>> "Magicloud" == Magicloud Magiclouds <magicloud.magiclouds(a)gmail.com> writes: Magicloud> Hi, I am using haskelldb and Magicloud> haskelldb-hdbc-sqlite3. Well, I finally got the source Magicloud> compiled and ran, I got this error: App: user error Magicloud> (SQL error: SqlError {seState = "", seNativeError = 21, Magicloud> seErrorMsg = "prepare 74: SELECT subject,\n Magicloud> timestamp\nFROM notes as T1\nORDER BY timestamp DESC: Magicloud> library routine called out of sequence"}) Any clue what Magicloud> I should check? Did you get this working? If so, what was the problem and how did you go about resolving it. I have the identical problem. I had the database code working fine, but then I added a state monad into the monad stack for the program, and now I get this problem. I see that John Goerzen suggested it might be a result of reading the data lazily. So I tried changing my import statements from import Control.Monad.State to import Control.Monad.State.Strict in case the StateT was indirectly causing the problem, but that doesn't make any difference. -- Colin Adams Preston Lancashire

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How to preload the module of my own
by zaxis 05 Sep '09

05 Sep '09

I want to preload the module automatically when starting ghci. The module located in ~/work directory contains some functions i use everyday. Now i use an alias: alias ghci='ghci -i ~/money/Money.hs' which works fine. However i feel there maybe are more elegant way. thanks! -- View this message in context: http://www.nabble.com/How-to-preload-the-module-of-my-own-tp25304154p253041… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Native windowing for glut applications on OS X.
by Lyndon Maydwell 05 Sep '09

05 Sep '09

Hi haskell-cafe. I recently updated glut through cabal to version GLUT-2.2.1.0, and where once I had native windowing, now I can only seem to use X11. Does anyone know how to use native windowing?

2 1

forkM fails
by Alberto G. Corona 04 Sep '09

04 Sep '09

Hi I need to execute a procedure not in the IO monad, but in an any monad: I defined: forkM :: Monad m=> m a -> IO ThreadId forkM proc=forkIO $ proc `seq` return() I assumed that seq will force the evaluation of proc and after, it will discard his type (m a) and return () in the IO monad.as forkIO expect. however proc is not executed Prelude> Control.Concurrent.forkIO $ print "hola" ThreadId 331 "hola" Prelude> Prelude> let forkM p=Control.Concurrent.forkIO $ p `seq` return () Prelude> forkM $ print "hola" ThreadId 493 Prelude> Any idea?. Thanks in advance

3 2

ANN: HStringTemplate 0.6.2
by Sterling Clover 04 Sep '09

04 Sep '09

I haven't sent out a release announcement for HStringTemplate in some time. In that time, there's been a host of new users, and consequently a host of feature requests and bug reports. Among the relatively recent changes: * Simple quasiquotation. * Proper unicode support (files are read in UTF-8, Data.Text templates are supported). * Creation of groups from hierarchies of directories. * Separators are applied within iterated template application. * Chained iterated template application now occurs depthwise rather than breadthwise. * Encoding functions generalized from String -> String to (Stringable a) => a -> a * Trailing newlines stripped from templates. * Initial newlines stripped after conditionals. * Functions to check templates for proper parsing, and existence of all necessary parameters and invoked templates. Current version is, as always, on Hackage: http://hackage.haskell.org/package/HStringTemplate User-maintained documentation on the wiki: http://www.haskell.org/haskellwiki/HStringTemplate Patches, bug reports, requests, and especially additional work on the documentation always welcome. Cheers, Sterl.

1 0

[Long] 'Fun' with types
by Maciej Piechotka 04 Sep '09

04 Sep '09

I'm somehow experimenting with GADT. I'm implementing FRP system and I get such error: Occurs check: cannot construct the infinite type: a = (a, b) In the pattern: CircuitSplit f g In the definition of `createChannel': createChannel (CircuitSplit f g) = let (df, cf) = createChannel f (dg, cg) = createChannel g .... in (df <<< dg, Map.map merge $ Map.unionWith (\ (First x) (Second y) -> Both x y) (Map.map First cf) (Map.map Second cf)) On code: import Control.Applicative import Control.Arrow import Control.Category (Category) import qualified Control.Category import Control.Monad import Control.Monad.Fix import Data.IORef import Data.Monoid hiding (First) import Data.Map (Map) import qualified Data.Map as Map import Data.Unique import Foreign import Foreign.C import Unsafe.Coerce -- | "CSignal" is a continous signal - i.e. signal which have a value at each -- point of time data CSignal a = CSignal (IO a) instance Functor CSignal where f `fmap` (CSignal v) = CSignal $ f <$> v instance Applicative CSignal where pure x = CSignal $ pure x (CSignal f) <*> (CSignal v) = CSignal $ f <*> v -- | "DSignal" is a discret signal - i.e. signal which is point-like. data DSignal a = DSignal (Map Unique ((a -> IO ()) -> IO ())) instance Functor DSignal where f `fmap` (DSignal l) = DSignal $ Map.map (. (. f)) l instance Monoid (DSignal a) where mempty = DSignal Map.empty (DSignal l) `mappend` (DSignal s) = DSignal $ Map.union l s -- | Convers the discret signal into a continous signal readAndCacheSignal :: a -- ^ Inital value -> DSignal a -- ^ Discret signal -> IO (CSignal a) -- ^ Continous signal readAndCacheSignal v (DSignal l) = do vr <- newIORef v Map.fold (>>) (return ()) $ Map.map ($ writeIORef vr) l return $ CSignal $ readIORef vr data Circuit a b where CircuitCSignal :: CSignal a -> Circuit () a CircuitDSignal :: DSignal a -> Circuit () (Maybe a) CircuitArr :: Kleisli IO a b -> Circuit a b CircuitJoint :: Circuit b c -> Circuit a b -> Circuit a c CircuitSplit :: Circuit a c -> Circuit b d -> Circuit (a, b) (c, d) CircuitChoice :: Circuit a c -> Circuit b d -> Circuit (Either a b) (Either c d) CircuitLoop :: Circuit (a, c) (b, c) -> Circuit a b instance Category Circuit where id = CircuitArr returnA f . g = CircuitJoint f g instance Arrow Circuit where arr f = CircuitArr $ arr f first = flip CircuitSplit returnA second = CircuitSplit returnA (***) = CircuitSplit instance ArrowChoice Circuit where left = flip CircuitChoice returnA right = CircuitChoice returnA (+++) = CircuitChoice instance ArrowLoop Circuit where loop = CircuitLoop data CircuitChannel a b where CircuitChannel :: Kleisli IO (c, a) b -> ((c -> IO ()) -> IO ()) -> CircuitChannel a b data ChannelJoin a b = First a | Second b | Both a b createChannel :: Circuit a b -> (Kleisli IO a b, Map Unique (CircuitChannel a b)) createChannel (CircuitCSignal (CSignal v)) = (Kleisli (const v), Map.empty) createChannel (CircuitDSignal (DSignal l)) = (arr $ const Nothing, Map.map (CircuitChannel (arr $ Just . snd)) l) createChannel (CircuitArr a) = (a, Map.empty) createChannel (CircuitJoint f g) = let (df, cf) = createChannel f (dg, cg) = createChannel g merge (First (CircuitChannel a r)) = CircuitChannel (dg <<< a) r merge (Second (CircuitChannel a r)) = CircuitChannel (a <<< second df) r merge (Both (CircuitChannel a r) (CircuitChannel b _)) = CircuitChannel (proc (d, v) -> do v' <- b -< (d, v) a -< (d, v')) r in (df <<< dg, Map.map merge $ Map.unionWith (\(First x) (Second y) -> Both x y) (Map.map First cf) (Map.map Second cf)) createChannel (CircuitSplit f g) = let (df, cf) = createChannel f (dg, cg) = createChannel g merge (First (CircuitChannel a r)) = CircuitChannel (proc (e, (c, d)) -> do c' <- a -< (e, c) d' <- dg -< d returnA -< (c', d')) r merge (Second (CircuitChannel b r)) = CircuitChannel (proc (e, (c, d)) -> do c' <- df -< c d' <- b -< (e, d) returnA -< (c', d')) r merge (Both (CircuitChannel a r) (CircuitChannel b _)) = CircuitChannel (proc (e, (c, d)) -> do c' <- a -< (e, c) d' <- b -< (e, d) returnA -< (c', d')) r in (df <<< dg, Map.map merge $ Map.unionWith (\(First x) (Second y) -> Both x y) (Map.map First cf) (Map.map Second cf)) createChannel (CircuitChoice f g) = let (df, cf) = createChannel f (dg, cg) = createChannel g merge (First (CircuitChannel a r)) = CircuitChannel (proc (e, c) -> case c of Left x -> a -< (e, x) Right x -> dg -< x) r merge (Second (CircuitChannel a r)) = CircuitChannel (proc (e, c) -> case c of Left x -> df -< x Right x -> a -< (e, x)) r merge (Both (CircuitChannel a r) (CircuitChannel b _)) = CircuitChannel (proc (e, c) -> case c of Left x -> a -< (e, x) Right x -> b -< (e, x)) r in (df ||| dg, Map.map merge $ Map.unionWith (\(First x) (Second y) -> Both x y) (Map.map First cf) (Map.map Second cf)) createChannel (CircuitLoop f) = let (df, cf) = createChannel f in (loop df, Map.map (\(CircuitChannel a r) -> CircuitChannel (proc (e, a) -> do rec (b, c) <- a -< (e, (a, c)) returnA -< b) r) cf) I know that it will require some sort of type voodoo but where's error now? Regards

3 3

Is this Parsec code idiomatic?
by Serge LE HUITOUZE 04 Sep '09

04 Sep '09

Hi Haskellers, I'm asking some advice on a small piece of code representing a simplified version of a treatment I need to perform. I have a line-oriented string/file, from which I want to extract only a substring of those lines starting with char '+' (the detail of the extraction is irrelevant here, I'll just return what follows the '+'). [I also simplified the "eol" parser for shorter code.] I came out with the code below. The line parser returns a "Maybe String". The complete parser return a "[Maybe String]" by mere concatenation. The main function filters the 'Nothing' with 'catMaybes'. > import Text.ParserCombinators.Parsec > import Data.Maybe > > maybePlusFile :: GenParser Char st [Maybe String] > maybePlusFile = endBy maybePlusLine eol > > maybePlusLine :: GenParser Char st (Maybe String) > maybePlusLine = try (do char('+') > result <- many (noneOf "\n") > return $ Just result) > <|> do many (noneOf "\n") > return $ Nothing > > eol = char '\n' > > selectPlus :: String -> Either ParseError [String] > selectPlus input = > case parse maybePlusFile "(input)" input of > Left e -> Left e > Right mblist -> Right $ catMaybes mblist This works as expected (or so it seems), as the ghci dump shows: > GHCi, version 6.10.1: http://www.haskell.org/ghc/ :? for help > ... > Prelude> :l selectPlus.hs > [1 of 1] Compiling Main ( selectPlus.hs, interpreted ) > Ok, modules loaded: Main. > *Main> selectPlus "abc\n+123\ndef\n+456\n" > Loading package parsec-2.1.0.1 ... linking ... done. > Right ["123","456"] > *Main> I'd like to know if this code is good style, and how you would possibly improve it. Thanks in advance. --Serge

6 5

NFData question
by Peter Verswyvelen 04 Sep '09

04 Sep '09

When ones makes an ADT with data constructors that has strict (and maybe unpacked) fields, e.g. data Vec2 a = Vec2 {-# UNPACK #-} !a {-# UNPACK #-} !a how does one define an NFData instance? Like this? instance NFData a => NFData (Vec2 a) where rnf (Vec2 x y) = rnf x `seq` rnf y Or is it enough to just do instance NFData a => NFData (Vec2 a) since Vec2 is fully strict anyway, so that default rnf implementation will do? Thanks, Peter

3 2

greencard error message
by mf-hcafe-15c311f0c＠etc-network.de 04 Sep '09

04 Sep '09

greetings, greencard is confusing me: I copied an example from the command line and was hoping to look at some generated Haskell code to understand what's going on, but got this instead: | $ cat M1.gc | module M1 where | %enum PosixError Int [EACCES, ENOENT] | $ greencard M1.gc | greencard: user error (<unknown>, line <unknown>: | Don't know how to unmarshall (int res1) | | <unknown>, line <unknown>: | Don't know how to unmarshall (int res1) | | ) (is there any live code out there that i could use as an example to study? most of the links from haskell.org/greencard are dead. anybody agree to earlier comments that greencard is obsolete? i really like it so far and would be glad to hear otherwise.) thanks, mattias

1 0

How to derive instance for type without exported constructor?
by Grigory Sarnitskiy 04 Sep '09

04 Sep '09

In System.Random StdGen is defined as data StdGen = StdGen Int32 Int32 but its constructor StdGen is not exported. How to make StdGen to be an instance of Binary? The following won't work: instance Data.Binary.Binary StdGen where put (StdGen aa ab) = do Data.Binary.put aa Data.Binary.put ab get = do aa <- get ab <- get return (StdGen aa ab)

3 7

Parallel programming in Haskell : a reading list
by Don Stewart 04 Sep '09

04 Sep '09

Here's a reading list for parallel programming in Haskell (via GHC) I've collected while preparing a tutorial. Might be interesting to those trying to get into multicore Haskell right now, http://donsbot.wordpress.com/2009/09/03/parallel-programming-in-haskell-a-r… Are there any good resources I'm missing? -- Don

2 1

ANN: haskell-src-exts-1.1.4
by Niklas Broberg 03 Sep '09

03 Sep '09

Fellow Haskelleers, I'm pleased to announce the release of haskell-src-exts-1.1.4! * On hackage: http://hackage.haskell.org/package/haskell-src-exts * Via cabal: cabal install haskell-src-exts * Via darcs: darcs get http://code.haskell.org/haskell-src-exts * Report bugs: http://trac.haskell.org/haskell-src-exts haskell-src-exts is a package for Haskell source code manipulation. In particular it defines an abstract syntax tree representation, and a parser and pretty-printer to convert between this representation and String. It handles (almost) all syntactic extensions to the Haskell 98 standard implemented by GHC, and the parsing can be parametrised on what extensions to recognise. haskell-src-exts-1.1.4 follows version 1.1.3 in being a mostly experimental release. From a PVP perspective, the version number indicates that no incompatible changes have been made to the *stable* portion of the package, i.e. anything that doesn't contain Annotated in its module name. The experimental stuff in Language.Haskell.Annotated{.*} has changed quite a lot, but those of you who depend on it already must obviously know what you're doing. ;-) haskell-src-exts-1.1.4: =================== * For the stable part, the only new thing in haskell-src-exts-1.1.4 is a bug fix that allows declaration headers surrounded by parentheses to be parsed, e.g. "data (a :< b) = ...". * For the experimental part, the new and cool feature is a full exact-printer, allowing full round-tripping of parsing plus printing. In other words, using the parser and the exact-printer in conjunction gives the same result back: exactPrint . parse == id . (Well, that's half a lie since you need to use parseWithComments and some uncurrying if you want to so easily compose, but that's the gist of it anyway. :-)) * There have also been a number of further changes to the (annotated) AST to allow it to retain enough source information to allow for said exact-printing. In particular there have been changes to the way contexts and declaration heads are treated, and literals have been embellished to remember just how they were given (e.g. did we use 0xFF or 255? \BEL or \a?). * With a few small caveats, the round-tripping works over the full (alas somewhat small) test suite that comes with (the darcs version of) haskell-src-exts: - Trailing whitespace on a line is not retained. (The test suite uses reverse . dropWhile (isSpace) . reverse on each line to disregard that issue.) - Tab characters in the source are converted to (8) spaces (except when they appear inside comments or literals). (The test suite doesn't contain tabs.) - Exact specification of literals is only remembered for literals used as literals :-). What I mean is, source literals appearing in other positions in the source than as Haskell literals will be converted to a basic form. E.g. 'infixl 0x02 %%' will become 'infixl 2 %%'. Apart from infix declarations (tell me you never considered writing them that way!) this mostly matters for various pragmas. - Parentheses used around the function symbol in a function declaration will not be remembered (I can't figure out how to make a non-outrageous change to the AST to cope with them). E.g. '(foo a) b = ...' will be printed as 'foo a b = ...'. If anyone has an idea for a neat (or at least non-outrageous) AST fix that could handle these cases, drop me a line. - Literate source files are not handled by the exact-printer (can't re-literate them). Please, help me test this on your source code! If you grab a darcs version of the package from the repository, you can put any and all source files you want to test in the "haskell-src-exts/Test/examples" directory and then just run 'cabal test'. Please report any failing cases to my trac! :-) Cheers and Happy Haskelling, /Niklas

2 2

Fwd: [BostonHaskell] Next meeting: September 16th at MIT (32G-882)
by Ravi Nanavati 03 Sep '09

03 Sep '09

I'm pleased to announce the September meeting of the Boston Area Haskell Users' Group. Based on the feedback from the meeting polls and the constraints of our speaker, the September meeting has been scheduled for Wednesday, September 16th from 7pm - 9pm. I've decided to move the meeting time back half an hour since that seems closer to what we've ended up doing in practice. Like the past three meetings, it will be held in the MIT CSAIL Reading Room (32-G882, i.e. a room on the 8th floor of the Gates Tower of the MIT's Stata Center at 32 Vassar St in Cambridge, MA). Based on the topic poll, our featured speaker will be Edward Kmett, who will be presenting the second part of his monoids and parsing presentation: "A Parallel Parsing Trifecta: Iteratees, Parsec, and Monoids". Edward's slides from August are here: http://comonad.com/reader/wp-content/uploads/2009/08/IntroductionToMonoids.… I'd recommend looking at them if you weren't at the August meeting (or want a refresher on the material) since the two parts of his presentation were originally designed to go concurrently. There's also a preview of the September presentation as part of this post on Edward's blog: http://comonad.com/reader/2009/iteratees-parsec-and-monoid/ We don't have any other presenters for September, so there are still openings for Lightning Talks or other relevant announcements / advertisements. If you're interested in one of those openings or in presenting something (large or small) at a future meeting, please let me know as we're still very hungry for content overall. The September attendance poll is at: http://doodle.com/gew97steggwhrnue As always, responding to this poll will help with two things: 1. Getting an idea of what fraction of the Boston-area Haskell community can and can't attend this meeting (to help with future scheduling). 2. Giving me an estimated count of attendees, so my wife can scale her baking of goodies appropriately. Sponsorship of or other assistance with refreshments is still being eagerly solicited. I'm also still having trouble embedding this poll in a page on our Google Group, so if anyone has any ideas about that, please feel free to try (any group member can edit pages) and/or offer other assistance or suggestions. If you have any questions about the meeting please send them to the BostonHaskell mailing list: bostonhaskell(a)googlegroups.com or contact me directly. I look forward to seeing many Boston-area Haskellers at the September meeting! Thank you, - Ravi Nanavati

1 0

ANNOUNCE: lenses -- Simple Functional Lenses
by Job Vranish 03 Sep '09

03 Sep '09

A simple but powerful implementation of function lenses (aka functional references, accessors, etc..). This library provides a convenient way to access and update the elements of a structure. It is very similar to Data.Accessors, but simpler, a bit more generic and has fewer dependencies. I particularly like how cleanly it handles nested structures in state monads. It also contains a couple simple functions that can be used to easily convert a function that fetches data from a structure to a function that modifies data in the structure. Hackage hasn't generated the haddock documentation yet, but there is a mini-tutorial in Data.Lenses that explains it's use. Also for those that are interested it's also hosted on github here: http://github.com/jvranish/Lenses/tree/master Let me know what you think, Criticism is welcome, - Job

3 3

Re: Snow Leopard Breaks GHC
by Christian Maeder 03 Sep '09

03 Sep '09

It might help to add -optc-m32 -opta-m32 -optl-m32 to /usr/bin/ghci, too. (TH uses ghci) Cheers Christian Brian Sniffen wrote: > Having edit the Haskell Platform's /usr/bin/ghc in place, most > packages install fine. I'm still having trouble with Pandoc, even > given the advice: > >> Once cabal works, options --ld-option=-m32 (and also --gcc-option=-m32) >> may be used. These options may also be passed to "./Setup configure" > > The problem appears to come when linking an incompatible zlib version: > > src/Text/Pandoc/ODT.hs:49:26: > Exception when trying to run compile-time code: > user error (Codec.Compression.Zlib: incompatible zlib version) > Code: ($) makeZip "data" </> "odt-styles" > In the first argument of `read', namely > `$(makeZip $ "data" </> "odt-styles")' > In the expression: read ($(makeZip $ "data" </> "odt-styles")) > In the definition of `refArchive': > refArchive = read ($(makeZip $ "data" </> "odt-styles")) > > I do have a universal zlib installed by MacPorts, as well as the > universal zlib that shipped with Snow Leopard and the universal zlib > that came with Cabal. I'm not sure whether this message indicates > that TH code is searching a different library path than non-TH code or > what. Advice is most welcome. >

1 0

WXHaskell problem
by Seb 03 Sep '09

03 Sep '09

I just installed WXHaskell via Cabal and tried one of the examples BouncingBalls.hs. But every time I run it I get this error message in a dialog saying: "assert "m_dynamicEvents" failed in SearchDynamicEventTable(): caller should check that we have dynamic events" It also asks me if I want to stop the program or suppress further warnings. And if I press Cancel in the dialog to suppress further warnings the BouncingBalls-program seems to work just fine. How can i make this warning message go away?

1 0

Can't get my head round monad transformers
by Colin Adams 03 Sep '09

03 Sep '09

I'm trying to add a state monad onto the IO monad for use in a happstack application. I thought this should involve using StateT and Happstack.Server.SimpleHTTP.simpleHTTP', but I can't figure out how to plumb it all together. Any tips will be welcome. -- Colin Adams Preston, Lancashire, ENGLAND

3 3

Re: cabal: : openFile: does not exist (No such file or directory)
by Thomas Hartman 03 Sep '09

03 Sep '09

cabal -v3 update will give you a more verbose version of what is going wrong. cabal --help regrettably, cabal --help doesn't tell you this but there is always the man page I suppose. 2009/7/16 Tony Hannan <tonyhannan2(a)gmail.com>: > Hello, > > I'm on Ubuntu 8.10. > I installed ghc 6.10.4 (from binary package: > ghc-6.10.4-i386-unknown-linux-n.tar.bz2). > I installed haskell-platform-2009.2.0.1 (from source package: > haskell-platform-2009.2.0.1.tar.gz). It contains cabal-install-0.6.2. > > Then when I run "cabal update", I get the following error: > cabal: : openFile: does not exist (No such file or directory) > > Any ideas? > > Thanks, > Tony > > _______________________________________________ > Libraries mailing list > Libraries(a)haskell.org > http://www.haskell.org/mailman/listinfo/libraries > >

6 11

cannot build greencard
by mf-hcafe-15c311f0c＠etc-network.de 02 Sep '09

02 Sep '09

hi, i am stuck with a linker error in greencard, and haven't found anything online, so i am addressing you for fresh ideas. as soon as i get this sorted out, i will try to turn the answer into a patch that you can consider for the next release. SYMPTOMS: greencard 3.0.3 and 3.01 do not compile with ghc-6.8 (debian lenny package) and 6.10 (darcs copy, checked out yesterday). here is what happens: 4 (0) 19:27:19 mf@yoyo:/tmp2 $ tar xvpzf greencard-3.0.3.tar.gz greencard-3.0.3/ greencard-3.0.3/ANNOUNCE greencard-3.0.3/dist/ greencard-3.0.3/dist/build/ greencard-3.0.3/dist/build/greencard/ greencard-3.0.3/dist/build/greencard/greencard-tmp/ greencard-3.0.3/dist/build/greencard/greencard-tmp/Parse.hs greencard-3.0.3/examples/ greencard-3.0.3/examples/Gdbm/ greencard-3.0.3/examples/Gdbm/diffs greencard-3.0.3/examples/Gdbm/Gdbm.gc greencard-3.0.3/examples/Gdbm/gdbmplus.h greencard-3.0.3/examples/Gdbm/Main.hs greencard-3.0.3/examples/Gdbm/Makefile greencard-3.0.3/examples/Gdbm/README greencard-3.0.3/examples/Makefile greencard-3.0.3/examples/world/ greencard-3.0.3/examples/world/Main.hs greencard-3.0.3/examples/world/Makedefs.ghc greencard-3.0.3/examples/world/Makedeps greencard-3.0.3/examples/world/Makefile.ghc-linux greencard-3.0.3/examples/world/Makefile.ghc-win32 greencard-3.0.3/examples/world/Makefile.hugs-linux greencard-3.0.3/examples/world/Makefile.hugs-win32 greencard-3.0.3/examples/world/README.txt greencard-3.0.3/examples/world/World.gc greencard-3.0.3/greencard.cabal greencard-3.0.3/INSTALL greencard-3.0.3/lib/ greencard-3.0.3/lib/Foreign/ greencard-3.0.3/lib/Foreign/GreenCard.hs greencard-3.0.3/lib/GreenCard.gc greencard-3.0.3/lib/Makefile greencard-3.0.3/lib/package.conf.in greencard-3.0.3/LICENSE greencard-3.0.3/Makefile greencard-3.0.3/README greencard-3.0.3/Setup.hs greencard-3.0.3/src/ greencard-3.0.3/src/Casm.lhs greencard-3.0.3/src/Decl.lhs greencard-3.0.3/src/DIS.lhs greencard-3.0.3/src/ErrMonad.lhs greencard-3.0.3/src/ErrorHook.c greencard-3.0.3/src/FillIn.lhs greencard-3.0.3/src/FillInMonad.lhs greencard-3.0.3/src/GCToken.lhs greencard-3.0.3/src/greencard.ghc.in greencard-3.0.3/src/greencard.hugs.in greencard-3.0.3/src/GreenCard.lhs greencard-3.0.3/src/Lex.lhs greencard-3.0.3/src/LexM.lhs greencard-3.0.3/src/ListUtils.lhs greencard-3.0.3/src/Makefile greencard-3.0.3/src/MarshallMonad.lhs greencard-3.0.3/src/Name.lhs greencard-3.0.3/src/NameSupply.lhs greencard-3.0.3/src/Package.lhs greencard-3.0.3/src/Package.lhs.in greencard-3.0.3/src/Parse.ly greencard-3.0.3/src/PrettyUtils.lhs greencard-3.0.3/src/Proc.lhs greencard-3.0.3/src/Process.lhs greencard-3.0.3/src/Target.lhs greencard-3.0.3/src/Type.lhs 5 (0) 19:27:22 mf@yoyo:/tmp2 $ cd greencard-3.0.3 6 (0) 19:27:24 mf@yoyo:/tmp2/greencard-3.0.3 $ make prefix=/tmp2/ make[1]: Entering directory `/hime/tmp2/greencard-3.0.3/src' happy Parse.ly unused terminals: 1 rm -f .depend touch .depend ghc -M -optdep-f -optdep.depend -optdep-xFiniteMap -optdep-xPretty -recomp -O -fglasgow-exts Casm.lhs DIS.lhs Decl.lhs ErrMonad.lhs FillIn.lhs FillInMonad.lhs GCToken.lhs GreenCard.lhs Lex.lhs LexM.lhs ListUtils.lhs MarshallMonad.lhs Name.lhs NameSupply.lhs Package.lhs PrettyUtils.lhs Proc.lhs Process.lhs Target.lhs Type.lhs Parse.hs make[1]: Leaving directory `/hime/tmp2/greencard-3.0.3/src' make[1]: Entering directory `/hime/tmp2/greencard-3.0.3/src' ghc -recomp -O -fglasgow-exts -c Target.lhs -o Target.o ghc -recomp -O -fglasgow-exts -c PrettyUtils.lhs -o PrettyUtils.o ghc -recomp -O -fglasgow-exts -c Casm.lhs -o Casm.o Casm.lhs:544:1: Warning: Pattern match(es) are overlapped In a case alternative: _ -> ... Casm.lhs:577:1: Warning: Pattern match(es) are overlapped In a case alternative: _ -> ... Casm.lhs:616:4: Warning: Pattern match(es) are overlapped In a case alternative: _ -> ... Casm.lhs:631:5: Warning: Pattern match(es) are overlapped In a case alternative: _ -> ... ghc -recomp -O -fglasgow-exts -c ListUtils.lhs -o ListUtils.o ghc -recomp -O -fglasgow-exts -c ErrMonad.lhs -o ErrMonad.o ghc -recomp -O -fglasgow-exts -c Name.lhs -o Name.o ghc -recomp -O -fglasgow-exts -c DIS.lhs -o DIS.o ghc -recomp -O -fglasgow-exts -c Type.lhs -o Type.o ghc -recomp -O -fglasgow-exts -c Decl.lhs -o Decl.o ghc -recomp -O -fglasgow-exts -c FillInMonad.lhs -o FillInMonad.o ghc -recomp -O -fglasgow-exts -c NameSupply.lhs -o NameSupply.o ghc -recomp -O -fglasgow-exts -c FillIn.lhs -o FillIn.o ghc -recomp -O -fglasgow-exts -c GCToken.lhs -o GCToken.o ghc -recomp -O -fglasgow-exts -c MarshallMonad.lhs -o MarshallMonad.o ghc -recomp -O -fglasgow-exts -c Proc.lhs -o Proc.o ghc -recomp -O -fglasgow-exts -c LexM.lhs -o LexM.o ghc -recomp -O -fglasgow-exts -c Lex.lhs -o Lex.o ghc -recomp -O -fglasgow-exts -Onot -c Parse.hs -o Parse.o Parse.hs:1733:1: Warning: Pattern match(es) are overlapped In a case alternative: _ -> ... ghc -recomp -O -fglasgow-exts -c Process.lhs -o Process.o ghc -recomp -O -fglasgow-exts -c Package.lhs -o Package.o ghc -recomp -O -fglasgow-exts -cpp -DBEGIN_GHC_ONLY='-}' -DEND_GHC_ONLY='{-' -DBEGIN_NOT_FOR_GHC='{-' -DEND_NOT_FOR_GHC='-}' -DPURE_WIN32=0 -c GreenCard.lhs -o GreenCard.o ghc -c ErrorHook.c -o ErrorHook.o ghc -recomp -O -fglasgow-exts -o greencard-bin Casm.o DIS.o Decl.o ErrMonad.o FillIn.o FillInMonad.o GCToken.o GreenCard.o Lex.o LexM.o ListUtils.o MarshallMonad.o Name.o NameSupply.o Package.o PrettyUtils.o Proc.o Process.o Target.o Type.o Parse.o ErrorHook.o Casm.o: In function `s201_info': (.text+0x168): undefined reference to `prettyzm1zi0zi0zi0_TextziPrettyPrintziHughesPJ_Str_con_info' Casm.o: In function `s201_info': (.text+0x17b): undefined reference to `prettyzm1zi0zi0zi0_TextziPrettyPrintziHughesPJ_TextBeside_con_info' Casm.o: In function `s201_info': (.text+0x19d): undefined reference to `prettyzm1zi0zi0zi0_TextziPrettyPrintziHughesPJ_Empty_closure' Casm.o: In function `s201_info': (.text+0x1b7): undefined reference to `prettyzm1zi0zi0zi0_TextziPrettyPrintziHughesPJ_Str_con_info' Casm.o: In function `s201_info': (.text+0x1ca): undefined reference to `prettyzm1zi0zi0zi0_TextziPrettyPrintziHughesPJ_TextBeside_con_info' Casm.o: In function `s201_info': (.text+0x1e9): undefined reference to `prettyzm1zi0zi0zi0_TextziPrettyPrintziHughesPJ_Empty_closure' Casm.o: In function `s201_info': (.text+0x1f0): undefined reference to `prettyzm1zi0zi0zi0_TextziPrettyPrintziHughesPJ_Beside_con_info' [... these continue for every object file on the command line; a bit over 2000 message of the same type in total...] Type.o: In function `sBv_info': (.text+0x1b2b): undefined reference to `prettyzm1zi0zi0zi0_TextziPrettyPrintziHughesPJ_Beside_con_info' Type.o: In function `sZT_info': (.text+0x1ed3): undefined reference to `__stginit_prettyzm1zi0zi0zi0_TextziPrettyPrint_' Type.o: In function `sBb_info': (.text+0x1988): undefined reference to `prettyzm1zi0zi0zi0_TextziPrettyPrintziHughesPJ_go6_info' Type.o: In function `sBf_info': (.text+0x1a12): undefined reference to `prettyzm1zi0zi0zi0_TextziPrettyPrintziHughesPJ_go6_info' Type.o: In function `sZU_info': (.text+0x1b96): undefined reference to `prettyzm1zi0zi0zi0_TextziPrettyPrintziHughesPJ_text_info' Type.o: In function `rvv_closure': (.data+0x8): undefined reference to `prettyzm1zi0zi0zi0_TextziPrettyPrintziHughesPJ_Chr_static_info' Type.o: In function `rvH_closure': (.data+0x64): undefined reference to `prettyzm1zi0zi0zi0_TextziPrettyPrintziHughesPJ_TextBeside_static_info' Type.o: In function `rvH_closure': (.data+0x6c): undefined reference to `prettyzm1zi0zi0zi0_TextziPrettyPrintziHughesPJ_lvl3_closure' Type.o: In function `rvH_closure': (.data+0x70): undefined reference to `prettyzm1zi0zi0zi0_TextziPrettyPrintziHughesPJ_Empty_closure' Type.o: In function `rvN_closure': (.data+0xb0): undefined reference to `prettyzm1zi0zi0zi0_TextziPrettyPrintziHughesPJ_Str_static_info' collect2: ld returned 1 exit status make[1]: *** [greencard-bin] Error 1 make[1]: Leaving directory `/hime/tmp2/greencard-3.0.3/src' make[1]: Entering directory `/hime/tmp2/greencard-3.0.3/lib' ghc -package-name greencard -cpp -fglasgow-exts -fno-prune-tydecls -c Foreign/GreenCard.hs -o Foreign/GreenCard.o -hisuf hi ghc-6.8.2: unrecognised flags: -fno-prune-tydecls Usage: For basic information, try the `--help' option. make[1]: *** [Foreign/GreenCard.o] Error 1 make[1]: Leaving directory `/hime/tmp2/greencard-3.0.3/lib' make[1]: Entering directory `/hime/tmp2/greencard-3.0.3/src' make[1]: Nothing to be done for `all'. make[1]: Leaving directory `/hime/tmp2/greencard-3.0.3/src' make[1]: Entering directory `/hime/tmp2/greencard-3.0.3/lib' ghc -package-name greencard -cpp -fglasgow-exts -fno-prune-tydecls -prof -c Foreign/GreenCard.hs -o Foreign/GreenCard.p_o -hisuf p_hi ghc-6.8.2: unrecognised flags: -fno-prune-tydecls Usage: For basic information, try the `--help' option. make[1]: *** [Foreign/GreenCard.p_o] Error 1 make[1]: Leaving directory `/hime/tmp2/greencard-3.0.3/lib' make: *** [all] Error 2 the errors about no-prune-tydecls are easy enough to fix: $ diff -r greencard-3.0.3{,-patched} diff -r greencard-3.0.3/examples/Gdbm/Makefile greencard-3.0.3-patched/examples/Gdbm/Makefile 28d27 < HC_OPTS += -fno-prune-tydecls diff -r greencard-3.0.3/lib/Makefile greencard-3.0.3-patched/lib/Makefile 6c6 < GHC_OPTS = -cpp -fglasgow-exts -fno-prune-tydecls --- > GHC_OPTS = -cpp -fglasgow-exts $ this helps, but the linker errors are unrealted, and i don't know what to make of them. (I guess I should study how ghc generates C code at this point? it does feel like something obvious...) thanks, cheers, matthias

4 5

Can GHC produce dylib on MacOSX/Intel?
by Pavel Perikov 02 Sep '09

02 Sep '09

Is it possible? Is it possible with binary distribution? Regards, Pavel

2 1

Documentation on the internals of Hugs
by KwangYul Seo 02 Sep '09

02 Sep '09

Hello, I want to study the internals lof Hugs, but the only document I got is: The implementation of the Gofer functional programming system http://web.cecs.pdx.edu/~mpj/pubs/goferimp.html I see Gofer is the predecessor of Hugs, but I am not sure how much the code base has been changed since then. Are there more recent documents on the internals of Hugs? Regards, Kwang Yul Seo

1 0

Cleaning up stable names?
by Peter Verswyvelen 02 Sep '09

02 Sep '09

>From the documentation, I don't think I grasp how stable names work. >From the docs: "There is no deRefStableName operation. You can't get back from a stable name to the original Haskell object. The reason for this is that the existence of a stable name for an object does not guarantee the existence of the object itself; it can still be garbage collected." >From this I can conclude that stable names behave a bit like weak pointers. However, suppose I have a hash table of these stable names. How can I remove the redundant stable names from the table? I mean removing stable names that refer to an object that is garbage collected? I don't see any function for checking that (e.g. isStableNameTargetAlive or something) Thanks, Peter

4 8

Slow IO?
by Steve 02 Sep '09

02 Sep '09

Hi, I'm tackling a Sphere Online Judge tutorial question where it tests how fast you can process input data. You need to achieve at least 2.5MB of input data per second at runtime (on an old machine running ghc 6.6.1). This is probably close to the limit of Haskell's ability. https://www.spoj.pl/problems/INTEST/ I can see that 24 haskell programmers have solved it, but most are very close to the 8 secs limit (and 6/24 are even over the limit!). Here's my code. It fails with a "time limit exceeded" error. (I think it would calculate the correct result, eventually). module Main where import qualified Data.List as DLi import qualified System.IO as SIO main :: IO () main = do line1 <- SIO.hGetLine SIO.stdin let k = read $ words line1 !! 1 s <- SIO.hGetContents SIO.stdin print $ count s k count :: String -> Int -> Int count s k = DLi.foldl' foldFunc 0 (map read $ words s) where foldFunc :: Int -> Int -> Int foldFunc a b | mod b k == 0 = a+1 | otherwise = a I tried using Data.ByteString but then found that 'read' needs a String, not a ByteString. I tried using buffered IO, but it did not make any difference. Any suggestions on how to speed it up? Regards, Steve

8 24

Question about Lazy.IO
by staafmeister 02 Sep '09

02 Sep '09

Hi, I've been wondering about Lazy IO for a while. Suppose we have a program like main = interact (unlines . somefunction . lines) then somefunction is a pure function. With the semantic interpretation of: given a input list return an output list. However I, the user, can change my input depending on the output of this function. Now in simple cases like this, this will not be a problem. But suppose you are reading and writing to a file. Now the result of pure functions become dependent on the order of execution, breaking (I think) referential transparency. Am I wrong here or how could you prove that Lazy IO is consistent nonetheless? Greetings, Gerben -- View this message in context: http://www.nabble.com/Question-about-Lazy.IO-tp25236848p25236848.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

4 4

Re: [Haskell-cafe] GUI library
by Job Vranish 01 Sep '09

01 Sep '09

If you're already used to C++ Qt and PyQt, qtHaskell should be relatively straightforward (though probably with a few gotchas). You could download qtHaskell and look at the examples to get an idea for the feel of it. If you're already used to Qt they should look familiar. Subclassing _is_ done a little weird: First you declare a dummy datatype: data MyQPushButton = MyQPushButton And then you use the qSubClass function: myQPushButton :: String -> IO (QPushButton MyQPushButton) myQPushButton s = qSubClass $ qPushButton1 s The type signature here is necessary. It's the only thing that forces the new (QPushButton a) to be a QPushButton MyQPushButton. Then you can use your subclassed buttons like so: main :: IO () main = do app <- qApplication dialog <- qDialog button1 <- myQPushButton "Click for Stuff" qObject_connectSlot1 button1 "clicked()" button1 "click()" $ on_pbutton_clicked dialog mainLayout <- qVBoxLayout qLayout_addWidget mainLayout button1 qWidget_setLayout dialog mainLayout qWidget_setWindowTitle dialog "Stuff Test" ok <- qDialog_exec dialog return() on_pbutton_clicked :: QDialog () -> QPushButton MyQPushButton -> IO () on_pbutton_clicked _dlg _this = do mb <- qMessageBox1 _dlg qMessageBox_setText mb $ "Stuff" qWidget_show mb return () Hmmm, though it doesn't look like you can currently overload methods of your parent class, usually you don't need too though as you can just tie into a signal (so you still can do things like paint). Though I'm kinda suprised I didn't notice this before, I'll have to email the guy and see if this is actually an issue. Also, qtHaskell doesn't fully support all the Qt widgets (though it covers most of them) but there is a new version coming out soon that should be more complete. Overall qtHaskell has served my perposes well. There is also a good listing of GUI toolkits for Haskell at http://www.haskell.org/haskellwiki/Applications_and_libraries/GUI_libraries - Job On Tue, Sep 1, 2009 at 1:49 AM, Michael Mossey <mpm(a)alumni.caltech.edu>wrote: > Thanks for the info. Interesting. I'm already familiar with C++ Qt and also > PyQt. I am also a fan of Qt. > > However, as a beginner to Haskell, I want to be sure I don't get myself > into trouble. I hope that qtHaskell is straightforward. > > Qt depends on deriving user classes. How is this handled in qtHaskell? > > Thanks, > > -Mike > > > Job Vranish wrote: > >> I recommend qtHaskell. >> I am a big fan of Qt in general. It has good documentation and extensive >> examples, is very well designed, and has a good license. I'd even say the >> C++ version is good choice for beginners (certainly easier to understand/use >> than say GTK). >> The qtHaskell bindings are also pretty good. The documentation and >> examples are not as extensive, but you can usually use the C++ documentation >> to fill in the gaps. >> Being already familiar with C++ Qt, using qtHaskell was a snap. However, >> if you're unfamiliar with both Qt and Haskell it will probably be confusing >> at first. Though I'd bet money the GTK bindings aren't any better in that >> regard. >> I'd still say you'd be more productive with qtHaskell in the long run. >> >> - Job >> >> >> On Sat, Aug 29, 2009 at 11:03 AM, Michael Mossey <mpm(a)alumni.caltech.edu<mailto: >> mpm(a)alumni.caltech.edu>> wrote: >> >> I want to choose a GUI library for my project. Some background: I'm >> a beginner to functional programming and have been working through >> Haskell books for a few months now. I'm not just learning Haskell >> for s**ts and giggles; my purpose is to write >> music-composition-related code; in particular, I want to write a >> graphical musical score editor. (Why write my own editor, you may >> ask? Because I want to fully integrate it with >> computer-assisted-composition algorithms that I plan to write, also >> in Haskell.) I decided to use Haskell for its great features as a >> functional programming language. >> >> Regarding a choice of GUI library, I want these factors: >> >> - it needs to provide at a minimum a drawing surface, a place I can >> draw lines and insert characters, in addition to all the standard >> widgets and layout capabilities we have to come to expect from a GUI >> library. >> >> - This is a Windows application. >> >> - it needs to be non-confusing for an intermediate-beginner >> Haskeller. Hopefully good documentation and examples will exist on >> the web. >> >> - It might be nice to have advanced graphics capability such as Qt >> provides, things like antialiasied shapes, and a canvas with >> efficient refresh (refereshes only the area that was exposed, and if >> your canvas items are only primitives, it can do refreshes from >> within C++ (no need to touch your Haskell code at all). However I'm >> wondering if qtHaskell fits my criteria "well-documented" and "lots >> of examples aimed at beginners". >> >> Thanks, >> Mike >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org <mailto:Haskell-Cafe@haskell.org> >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> >> >>

1 0

GUI library
by Michael Mossey 01 Sep '09

01 Sep '09

I want to choose a GUI library for my project. Some background: I'm a beginner to functional programming and have been working through Haskell books for a few months now. I'm not just learning Haskell for s**ts and giggles; my purpose is to write music-composition-related code; in particular, I want to write a graphical musical score editor. (Why write my own editor, you may ask? Because I want to fully integrate it with computer-assisted-composition algorithms that I plan to write, also in Haskell.) I decided to use Haskell for its great features as a functional programming language. Regarding a choice of GUI library, I want these factors: - it needs to provide at a minimum a drawing surface, a place I can draw lines and insert characters, in addition to all the standard widgets and layout capabilities we have to come to expect from a GUI library. - This is a Windows application. - it needs to be non-confusing for an intermediate-beginner Haskeller. Hopefully good documentation and examples will exist on the web. - It might be nice to have advanced graphics capability such as Qt provides, things like antialiasied shapes, and a canvas with efficient refresh (refereshes only the area that was exposed, and if your canvas items are only primitives, it can do refreshes from within C++ (no need to touch your Haskell code at all). However I'm wondering if qtHaskell fits my criteria "well-documented" and "lots of examples aimed at beginners". Thanks, Mike

5 6

Problems installing documentation and sources using Cabal on Mac OSX
by Colin Adams 01 Sep '09

01 Sep '09

I noticed today on the train (no internet connection!) that the documentation for packages I had installed with cabal was missing, and that there was no source in .cabal/packages for them. Now I'm in the offiice, I tried --reinstall --enable-documentation. There was a warning about haddock and ghc version mismatch (so much for the haskell platform install), so I did a --reinstall of haddock. Now the message I see is: cabal: can't find source for module Paths_happstack_server (happstack_server is the first package I'm trying to reinstall to get docs). So I think the documentation failure is because haddock can't find the source code (nor can I), but I don't know why there is no source installed in .cabal/packages - what should I do to further track this problem down? -- Colin Adams Preston, Lancashire, ENGLAND

1 0

Re: [Haskell-cafe] Takusen - is anyone currently using it on Win32 - ODBC?
by Günther Schmidt 01 Sep '09

01 Sep '09

Hi Anton, well the problem isn't really accessing the data as such, it's quite easy to use HDBC.ODBC for instance to read in the data in a very comfortable way. I was explicitly asking for Takusen because it make certain guarantees regarding resources, memory consumption and such. One of the files for instance has 298 k lines. A glance over sushi revealed that parsec is involved so I can only presume it is read into memory all at once. That would certainly be a problem. Thanks, Günther Am 31.08.2009, 19:47 Uhr, schrieb Anton van Straaten <anton(a)appsolutions.com>: > Günther Schmidt wrote: >> My app then needs to read in dynamic data, a set of 4 CSV files, and I >> had been using Microsofts ODBC driver with HDBC.ODBC and that worked >> too. >> When I try to swap it for Takusen though I get an >> *** Exception: DBError ("HY","C00") 106 "[Microsoft][ODBC Text >> Driver] >> Optional Feature was not implemented >> Which is a bit of a shame, because using the ODBC text driver was much >> simpler than parsing the CSV files. > > A simple but powerful way to access CSV files is via TxtSushi, which > gives SQL access to CSV files, without needing ODBC: > > Home page: http://keithsheppard.name/txt-sushi/ > Hackage: http://hackage.haskell.org/package/txt-sushi > > You'd have to use it directly, since afaik it won't work with Takusen, > although a Takusen back end for it ought to be possible. > > Anton >

2 1

How to fix such a TYPE problem ?
by zaxis 01 Sep '09

01 Sep '09

>let [y,m,d] = map (\x -> read x::Int) $ splitRegex (mkRegex "-") "2009-08-31" >fromGregorian y m d Couldn't match expected type `Integer' against inferred type `Int' In the first argument of `fromGregorian', namely `y' In the expression: fromGregorian y m d In the definition of `it': it = fromGregorian y m d thanks! -- View this message in context: http://www.nabble.com/How-to-fix-such-a-TYPE-problem---tp25233906p25233906.… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

2 2

Dutch HUG: meeting next week (September 11th) in Utrecht
by Tom Lokhorst 31 Aug '09

31 Aug '09

>From lovely Edinburgh, I'd like to invite functional programmers in The Netherlands to the Dutch Haskell User Group [1, 2] meeting next Friday at 19:00. For the first time, we'll have people giving talks! Thomas (noknok) will be talking about his system for doing propositional logic in Haskell. Pedro will give an introductory talk about generic programming, and Sean will talk about xformat, a library for extensible and type-safe formatting with scanf- and printf-like functions. If you're interested in giving a short 5-minute lighting talk about something related to Haskell or functional programming, we'd very much like to hear from you! The meeting will be in the Booth Hall [3] of the Utrecht University Library. There's free car parking [4] at the library, and it's easily accessible by bike and bus [5]. We have a poll [6] that shows all people who plan to attend. See you next Friday! - Tom Lokhorst [1]: http://www.haskell.org/haskellwiki/Dutch_HUG [2]: http://groups.google.com/group/dutch-hug [3]: http://www.uu.nl/EN/library/contact/university_library/zaalverhuur/Pages/de… [4]: http://www.uu.nl/EN/library/contact/university_library/Parkeren/Pages/defau… [5]: http://www.uu.nl/EN/library/contact/university_library/plattegrondenrou/Pag… [6]: http://doodle.com/a7vx3a6imcue4ghr

1 0

Get data from HTML pages
by José Romildo Malaquias 31 Aug '09

31 Aug '09

Hello. I am porting to Haskell a Java application I have written to manage collections of movies. Currently the application has an option to indirectly import movie data from web pages. For that first the user should access the page in a web browser. Then the user should copy the rendered text in the web browser into an import window in my application and click an "import" button. In response the application parses the given text and collects any relevant data it knows about, using regular expressions. For instance, to get the director information from a movie in the AllCenter web site I use the following regular expression: ^Direção:\s+(.+)$ I want to modify this scheme in order to eliminate the need to copy the rendered text from a web browser. Instead my application should download and parse the HTML page directly. Which libraries are available in Haskell that would make it easy to get content information from a HTML document, in the way described above? Regards, Romildo

4 3

Takusen ODBC - MS Access
by Günther Schmidt 31 Aug '09

31 Aug '09

Hi all, recently I had problems getting Takusen ODBC to work with MS-Access on Win32. It seems, that the problems originated from Takusens UTF8 code, the path of the Access Database contains an Umlaut. This even causes problems when one does not specify a connection String but merely a DSN, no further problems occured when I moved the Access file directly to C:\. I also could not get takusen to work with MS Text / CSV ODBC driver, irregardless of Umlauts, the exception was about some optional feature not implemented (on MS's ODBC site). Could anyone suggest a work around? I notice that when you're a haskeller on Win32 *and* German (the Umlauts), things become a bit more difficult than for the English / linux haskellers. Günther

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Takusen - is anyone currently using it on Win32 - ODBC?
by Günther Schmidt 31 Aug '09

31 Aug '09

Hi all, is anyone currently using takusen with odbc on Win32? In particular with MS Access? I'm asking because I noticed that when database libraries are declared to work with ODBC no one seems to mean Win32 ODBC, but rather Unix ODBC. Günther

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Re: How to use dyre relaunch/restore State of Gtk2hs Object?
by Will Donnelly 31 Aug '09

31 Aug '09

Hi Andy, Your program didn't compile as given, so I cut out some of the event handling fanciness you were doing. Also, my modified version restarts whenever the 'r' key is pressed. I figure those changes aren't important to the problem at hand. Anyway, I don't think it's ever going to be possible to define a Binary instance for a TextView, since all of the functions which can yield information about it are impure. I would recommend extracting the relevant data beforehand, and then persisting it in a tuple. You could use some 'marshal<WIDGET>' and 'recreate<WIDGET>' functions if you need to persist many different widget types. Saving just the text can be done as follows: <code> module DyreExample where import Graphics.UI.Gtk hiding (get) import qualified Graphics.UI.Gtk.Gdk.Events as E import qualified Config.Dyre as Dyre import Config.Dyre.Relaunch import System.IO import Data.Binary data Config = Config { message :: String, errorMsg :: Maybe String } defaultConfig :: Config defaultConfig = Config "Dyre Example v0.1" Nothing showError :: Config -> String -> Config showError cfg msg = cfg { errorMsg = Just msg } realMain Config{message = message, errorMsg = errorMsg } = do initGUI textView <- textViewNew textBuffer <- textViewGetBuffer textView text <- restoreBinaryState "" putStrLn $ "Restored state: " ++ text textBufferSetText textBuffer text rootWindow <- windowNew rootWindow `onDestroy` mainQuit windowFullscreen rootWindow rootWindow `containerAdd` textView widgetShowAll rootWindow rootWindow `onKeyPress` (\event -> dyreKeyTest event textView) mainGUI dyreExample = Dyre.wrapMain $ Dyre.defaultParams { Dyre.projectName = "Main" , Dyre.realMain = realMain , Dyre.showError = showError } dyreKeyTest :: E.Event -> TextView -> IO Bool dyreKeyTest ev textView = do case E.eventKeyName ev of "r" -> do textBuffer <- textViewGetBuffer textView sI <- textBufferGetStartIter textBuffer eI <- textBufferGetEndIter textBuffer text <- textBufferGetText textBuffer sI eI True putStrLn $ "Relaunching with state: " ++ text relaunchWithBinaryState text Nothing return True _ -> return False </code> Other comments: 1. It isn't necessary to explicitly tell Dyre to do a custom compile. It will take care of figuring that out once you restart it. 2. Instead of manually setting paths in the code, you can use the '--dyre-debug' command-line flag, which will cause Dyre to look for configurations in the current directory, and store temporary files in a 'cache' subdirectory. 3. Giving a project name of 'Main' causes Dyre to see the file 'Main.hs' as a custom configuration. I'm not sure if that's what you intended, but it will make testing custom configurations harder than it needs to be. 4. Good luck with the rest of your project! - Will Donnelly

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Edinburgh Hackathon round-up
by Dougal Stanton 31 Aug '09

31 Aug '09

Hello Haskellers, On Saturday & Sunday (28th & 29th August) we held a Hackathon in Edinburgh, before the ICFP got fully underway. If you were there, thank you for coming. We'll be writing a summary of what happened soon, and we'd love to hear what you did. If you started a new project or fixed some insidious bug, identified a major bottleneck or just enriched the testing structure around your chosen project, it would be great to know. Just a line or two is all we need! I am hoping that everyone who attended will see this message, as they must have seen Eric's original advertising emails. But please pass this message along if you know there's someone we missed. Cheers, Dougal -- Dougal Stanton dougal(a)dougalstanton.net // http://www.dougalstanton.net

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specialised monad transformers
by Alberto G. Corona 31 Aug '09

31 Aug '09

Hi all I want to define a partial monad transformer i.e not defined for all kinds of data but the ones that have instances of certain classes. That is because in my lift instance code there are some hidden use of these classes. But because in the MonadTrans definition does not refers to the data, no specialised lift seems possible: class MonadTrans t where lift :: Monad m => m a -> t m a Is that true? A possible adition could be to define (note: I did not test it, it is just an idea): class SpecialisedMonadTrans (t m a) where lift :: Monad m => m a -> t m a liftMN :: Monad m => m a -> t a The whole problem has certain relation with effect control. This kind of definition permits a more fine control of effect handling when passing from a monad to other depending on the idiosyncrasy of the monad m and the kind of a.

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happstack-helpers fails to install on Mac OSX
by Colin Paul Adams 31 Aug '09

31 Aug '09

I've just installed the Haskell Platform (2009.2.0.2) on Mac OSX 10.5.6, including GHC 6.10.4. Then I started added some packahges with cabal install. But happstack-helpers-0.30 fails with: Happstack/Helpers/DirBrowse.hs:88:105 Couldn't match expected type `String' against inferred type `Bool' In the third argument of `hscolour', namely `False' In the second argument of `(.)', namely `BrowseHtmlString . (hscolour defaultColourPrefs False False f)' Is this a known error, and if so, is there a workaround? -- Colin Adams Preston Lancashire

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Data.Time is so weak ?!
by zaxis 31 Aug '09

31 Aug '09

today = fromGregorian 2009 8 31 then how to calculate the day passing 150 days ? today + 150 doesnot work ! -- View this message in context: http://www.nabble.com/Data.Time-is-so-weak--%21-tp25218462p25218462.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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