- Haskell-Cafe - Haskell.org

Re: [Haskell-cafe] Parallel Haskell stories
by John Lato 10 Mar '11

10 Mar '11

From: Simon Peyton-Jones <simonpj(a)microsoft.com> > > Friends > > I'm giving a talk at a developer conference in London on Friday 18th, about > parallel programming in Haskell. > http://skillsmatter.com/event/scala/functionalpx-2011/ad-1382 > > I know that some of you have been using Haskell for parallel or concurrent > programming quite a bit, so this email is just to ask > > could you contribute a little vignette or story > about using Haskell in a *parallel/concurrent* application > that I could use to illustrate my talk? > I have a physical-model-based audio synthesis application I wanted to convert from an off-line renderer into a real-time engine. I decided upon a concurrent architecture with an interface thread, an engine thread, and an output thread, using STM for communication. It only took a couple hours to make the conversion, most of which was spent modifying the synthesis to work in blocks instead of a single run. I'm particularly happy with this snippet, where the engine collects input from the interface thread: readStrikeVar = do ct <- getCPUTime atomically $ rsv' ct `orElse` return [] -- if the read fails, return an empty list because we can't afford to wait. -- the strikes will eventually catch up... rsv' ct = do strikes <- readTVar tstrikes let carry = map (updateCarry blockdur) $ filter carryOver strikes writeTVar tstrikes carry writeTVar tsync ct return (reverse strikes) This code is the most complicated part of the communication scheme, nearly everything else is at the level of "readTVarIO". A nice feature is that the engine doesn't block waiting for the interface. If the transaction fails because the interface is updating the TVar, the engine moves ahead and can catch up later. On my dual-core macbook, performance is perhaps slightly disappointing compared to the offline renderer which is single-threaded and not parallelized. With one simulation the offline renderer will generate 5 seconds of audio in about 3.3seconds at 100% CPU usage, giving me the equivalent of 66% CPU over 5 seconds. The realtime renderer consistently occupies about 171% CPU for the same simulation. A different simulation has a runtime of 4.4 seconds and realtime usage of 191%. Of course there's going to be some overhead, but I hope to improve this by changing the way data is fed to the engine to a TChan, and also running threadscope to make sure threads yield at the proper times. Speaking of which, threadscope is an awesome tool and deserves a mention. John L.

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ANN: Updates in the monadic regions family
by Bas van Dijk 10 Mar '11

10 Mar '11

Dear all, I released new versions of some of my packages. Here are the changelogs: http://hackage.haskell.org/package/regions-0.9 http://hackage.haskell.org/package/regions-mtl-0.3.1.5 http://hackage.haskell.org/package/regions-monadstf-0.3.1.5 * Switch from monad-peel to monad-control. * Removed Control.Monad.Trans.Region.Concurrent. The fork functions contained bugs which could not be fixed. I'm working on a way to copy handles from one thread to another but the design has not settled yet. * Removed Data.RegionRef. I always considered this module a bit of a wart. * Added support for local regions. Primarily needed for the alloca functions from the regional-pointers package. More on that below. http://hackage.haskell.org/package/regional-pointers-0.6 * Switch from monad-peel to monad-control. * Major API change: Use the new local regions. This means that instead of: alloca ∷ (Storable α, MonadPeelIO pr) ⇒ (∀ s. RegionalPtr α (RegionT s pr) → RegionT s pr β) → pr β I now have: alloca ∷ (Storable α, MonadControlIO pr) ⇒ (∀ sl. LocalPtr α (LocalRegion sl s) → RegionT (Local s) pr β) → RegionT s pr β This allows my alloca to use the native alloca which is more efficient than doing a manual malloc and free as I did before. The type also allows to open resources in the continuation and use them outside the continuation and visa versa. * Have separate types for the three different pointers: - RegionalPtr: for pointers created using malloc. - LocalPtr: for pointers created using alloca. - NullPtr: for the nullPtr. * Add the type classes Pointer and AllocatedPointer to classify them. http://hackage.haskell.org/package/safer-file-handles-0.10 http://hackage.haskell.org/package/safer-file-handles-bytestring-0.2 http://hackage.haskell.org/package/safer-file-handles-text-0.2 * Switch from monad-peel to monad-control. * Support regional-pointers-0.6 and use its overloaded pointers. * Add separate types for standard handles: StdFileHandle and normal handles: RegionalFileHandle. * Add the type class FileHandle to group them. * Overload the filehandle in operations. http://hackage.haskell.org/package/usb-0.8 * getStrDesc and getStrDescFirstLang now return a Text instead of a String. This is a more efficient and cleaner interface. http://hackage.haskell.org/package/usb-enumerator-0.3 * Switch from monad-peel to monad-control. * Support iteratee-0.8.*. * Support usb-0.9. http://hackage.haskell.org/package/usb-safe-0.12 * Switched from monad-peel to monad-control. * Exported the ReadEndpoint, WriteEndpoint and EnumReadEndpoint type classes so you can refer to them in type signatures. * Support usb-0.8: getStrDesc and getStrDescFirstLang now return a Text instead of a String. * Support regions-0.9. * Support usb-enumerator-0.3. * Support iteratee-0.8.*. Regards, Bas

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Re: [Haskell-cafe] Haskell mail server fail?
by wren ng thornton 10 Mar '11

10 Mar '11

Like Kenneth Hoste, I haven't been receiving mails from haskell-cafe@ nor libraries@ for a few days to a week now. What is the status of the mailing lists? (Please CC me off-list, for obvious reasons) -- Live well, ~wren

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Re: [Haskell-cafe] Tagless interpreter, expression problem and zipper
by oleg＠okmij.org 10 Mar '11

10 Mar '11

The Tagless final approach can do context-sensitive evaluation, using the well-known trick from the denotational semantics that explicating the context turns context-sensitive semantics to compositional. The trick isn't out of place given how much tagless-final approach is related to denotational semantics. The non-compositional processing has been discussed at length at lectures last year. Please see the explanation and the code at Non-compositionality: Fold-unlike processing http://okmij.org/ftp/tagless-final/course/course.html#non'compositionality Interestingly, one example FlatF.hs mentioned on the above page specifically talks about the context of being the left operand of the addition (the goal was to `flatten' additions, to re-associate them to the right). That is the same context as you are after, it seems. The detailed lecture notes will be eventually available.

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Update Cabal
by Hauschild, Klaus (EXT) 10 Mar '11

10 Mar '11

Hallo, I'm using Haskell Platform 2010.2.0.0 on a Windows XP machine. This haskell platform includes cabal-1.8.0.6. Now I want to update cabal by "cabal install cabal". Installation works well. Call like "runhaskell ./Setup.hs" will use the updatetd cabal-1.10.0.0. But "cabal --version" says still 1.8.0.6 and I have to re-configure. How I update cabal in my current Haskel Platform? Thanks Klaus

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IPv6 issues for (code|community).haskell.org?
by Erlend Hamberg 10 Mar '11

10 Mar '11

Hi, When I wanted to get the newest xmonad code from darcs today¹ it was really, really slow. Running “host” revealed that code.haskell.org is an alias for community.haskell.org and that it has an IPv6 address associated with it. Being on an IPv6 network, and having been burnt by similar problems before, I tried adding IPv4 address for code.haskell.org in /etc/hosts in order to force the connection to happen over IPv4. This fixed the issue and “darcs get” now takes a few minutes. I just wanted to alert people in case the problem is at the server end. (And in case this isn’t just a temporary problem.) Connecting to code.haskell.org in a Web browser also takes minutes, while e.g. http://ipv6.google.com/ works perfectly. [1] With “darcs get http://code.haskell.org/xmonad” -- Erlend Hamberg ehamberg(a)gmail.com

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Custom monad using ST
by Yves Parès 10 Mar '11

10 Mar '11

Hello, I am trying to make a monad that uses ST internally. But even when reducing this to the simplest case I'm still cramped by the 's' phantom type : {-# LANGUAGE Rank2Types #-} newtype MyST a = MyST (forall s. ST s a) -- ^ I cannot use " deriving (Monad) " through GeneralizedNewtypeDeriving runMyST (MyST m) = runST m -- ^ works thanks to declaration of 's' at rank 2 in the definition of MyST -- It refuses to compile if MyST is declared as such: -- data MyST s a = MyST (ST s a) instance Monad MyST where return = MyST . return -- and this does not compile (MyST m) >>= f = MyST $ do x <- m case f x of (MyST m) -> m If you try it, GHC will complain: Simple.hs:13:20: Couldn't match expected type `forall s. ST s a' with actual type `ST s a' Expected type: a -> forall s1. ST s1 a Actual type: a -> ST s a In the second argument of `(.)', namely `(return :: a -> (forall s. ST s a))' In the expression: MyST . (return :: a -> (forall s. ST s a))

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Automated tests with cabal
by Hauschild, Klaus (EXT) 10 Mar '11

10 Mar '11

Hi Haskellers, I read about the cabal features for running test code from Setup.hs with "defaultMainWithHooks". I'm looking for more generic code that allows me to place any haskell in a subdirectory "test" or so and "cabal test" will run this test without any modification of my Setup.hs. Is there a possibility? Thanks Klaus

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Learn You a Haskell for Great Good - a few doubts
by Karthick Gururaj 10 Mar '11

10 Mar '11

Hello, I'm learning Haskell from the extremely well written (and well illustrated as well!) tutorial - http://learnyouahaskell.com/chapters. I have couple of questions from my readings so far. In "typeclasses - 101" (http://learnyouahaskell.com/types-and-typeclasses#typeclasses-101) there is a paragraph that reads: Enum members are sequentially ordered types - they can be enumerated. The main advantage of the Enum typeclass is that we can use its types in list ranges. They also have defined successors and predecesors, which you can get with the succ and pred functions. Types in this class: (), Bool, Char, Ordering, Int, Integer, Float and Double. What is the "()" type? Does it refer to a tuple? How can tuple be ordered, let alone be enum'd? I tried: Prelude> take 10 [(1,1) ..] <interactive>:1:8: No instance for (Enum (t, t1)) arising from the arithmetic sequence `(1, 1) .. ' at <interactive>:1:8-17 Possible fix: add an instance declaration for (Enum (t, t1)) In the second argument of `take', namely `[(1, 1) .. ]' In the expression: take 10 [(1, 1) .. ] In the definition of `it': it = take 10 [(1, 1) .. ] This is expected and is logical. But, surprise: Prelude> (1,1) > (1,2) False Prelude> (2,2) > (1,1) True Prelude> (1,2) > (2,1) False Prelude> (1,2) < (2,1) True So tuples are in "Ord" type class atleast. What is the ordering logic? Another question, on the curried functions - specifically for infix functions. Suppose I need a function that takes an argument and adds five to it. I can do: Prelude> let addFive = (+) 5 Prelude> addFive 4 9 The paragraph: "Infix functions can also be partially applied by using sections. To section an infix function, simply surround it with parentheses and only supply a parameter on one side. That creates a function that takes one parameter and then applies it to the side that's missing an operand": describes a different syntax. I tried that as well: Prelude> let addFive' = (+5) Prelude> addFive' 3 8 Ok. Works. But on a non-commutative operation like division, we get: Prelude> let x = (/) 20.0 Prelude> x 10 2.0 Prelude> let y = (/20.0) Prelude> y 10 0.5 So a curried infix operator fixes the first argument and a "sectioned infix" operator fixes the second argument? Regards, Karthick

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Finalizer registered with System.Mem.Weak.addFinalizer is called surprisingly early
by balodja 10 Mar '11

10 Mar '11

Hello, I use addFinalizer from System.Mem.Weak for performing some actions on data just before that is reclaimed by GC. Registered in this way finalizer is called surprisingly early for me, much earlier the data is tend to be collected. I've attached source code of simple two-threaded program. Source code also can be found at [1]. It is pretty simple and should be readable enough. Program is intentioned to pass messages through transactional variable (TVar) for printing by worker thread. Messages consist of formatted to String Int values from 1 to 1000000. So the output should look like this: > 1 > 2 > ... > 1000000 But running the program gives something like that: > 1 > 2 > ... > 283 > finalizing > Test: thread blocked indefinitely in an STM transaction As far as I see, finalizer is called too early. If someone could point me out how to do the right thing, that would be helpful. Operaton system: Debian Squeeze Compiler: GHC 6.12.1 Compiling options: none, just "ghc --make Test.hs" Thanks, balodja [1] http://hpaste.org/44648

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Haskell Weekly News: Issue 172
by Daniel Santa Cruz 10 Mar '11

10 Mar '11

Welcome to issue 172 of the HWN, a newsletter covering developments in the [1]Haskell community. This release covers the week of February 27 to March 05, 2011. Announcements Jasper Van der Jeugt [2]announced the release of version 3 of Hakyll. He informs us that this is a complete re-write, and not backwards compatible. Horvath Zoltan [3]informed us about the 4th Central European Functional Programming School (CEFP 2011), which is to take place in Eotvos Lorand University, Budapest, Hungary, from June 14-24, 2011. "The invited lecturers are the most prominent researchers in the field in Europe, and they will present state-of-the-art functional programming techniques." Janis Voigtlander [4]issued a call for papers for the 20th International Workshop on Functional and (Constraint) Logic Programming (WFLP 2011) to be held in Odense, Denmark, on July 19, 2011. Michael Hanus [5]issued a call for papers for the 13th International ACM SIGPLAN Symposium on Principles and Practice of Declarative Programming (PPDP 2011) to be held in Odense, Denmark, on July 20-22, 2011. Trystan Spangler [6]released a new version (0.3.0) of hspec, with "improvements including fixing a base dependency problem, and better reporting of failed examples." Magnus Therming [7]released new versions of dataenc (0.14), and omnicodec (0.5). "It contains a large change to the API. The old, rather simplistic, lazy API has been removed. It has been replaced by an API based on incremental encoding/decoding. This should make the library easier to use together with left-fold enumerators..." Rogan Creswick [8]announced that cabal-dev 0.7.4.0 has been uploaded to hackage. "We strongly suggest that everyone upgrade to this release, since this release specifically addresses changes in Cabal-1.10 and newer, which the latest cabal-install new uses." Frederick Ross [9]announced a minor upgrade to haskell-pgm (0.1.2), with a minor upgrade to the library to make it work with GHC 7. Uwe Schmidt [10]announced an update to hxt to version 9.1. Eric Kow [11]announced that the date and venue for the sixth Darcs Hacking sprint has been confirmed for Paris, April 1-3, 2011. Ian Lynagh and the GHC Team [12]announced a new patchlevel release of GHC. "This release contains a number of bugfixes relative to 7.0.1, so we recommend upgrading." Denis Bueno [13]announced new releases of funsat (0.6.2) and bitset (1.1). Michal Konecny [14]announced version 0.3.2 of hmpfr, bindings to the MPFR arbitrary precision floating point arithmetic library. "The changes in this version are quite small but significant." Jonathan Daugherty [15]announced version 1.0 of the vty-ui terminal user interface library. "The vty-ui library is a complete interactive user interface development toolkit for terminal applications." Jason Dusek [16]announced his now bash-0.0.0, which has "types and functions for generation of Bash scripts, with safe escaping and composition of large subsets of Bash statements and expressions." Quotes of the Week * lpsmith: I didn't take the time to figure out what should be done in finite cases. * <companion_cube> edwardk, you mean it's 2 phD/nick in average ? :) <edwardk> clearly this is why SPJ stays away, he doesn't want to dilute that metric. * edwardk: Haskell 98 is a laudable goal. * douglas-adams: I love deadlines, I especially like the swooshing sound they make as they fly past * kmc: the way to convert imperative code to functional is to think about what your code actually means, and then throw out most of the irrelevant details that imperative programming has forced on you * MonadsSuck: man, I hate it when an adjoint pair of functors get together and compose. So damn annoying * bwright: I don't get it everyone keeps telling me java is a safe language but it melted the plastic on my eeepc900 * danka: you could be a monadic vampire. I hear they bleed semicolons. Top Reddit Stories * ANNOUNCE: GHC version 7.0.2: From (haskell.org) scored 46 with comments. Read on [17]reddit or the [18]original post. * Greenfield Haskell: From (self.haskell), scored 36 with 188 comments. Read on [19]reddit or the [20]original post. * Patches for monad comprehensions are in and will be in the upcoming GHC 7.2 release: From (hackage.haskell.org) scored 34 with 15 comments. Read on [21]reddit or the [22]original post. * GHC 7.0.2 released!: From (haskell.org) scored 32 with 10 comments. Read on [23]reddit or the [24]original post. * Haskell on Android: From (self.haskell), scored 31 with 22 comments. Read on [25]reddit or the [26]original post. * Do you think Haskell will ever catch on?: From (self.haskell), scored 26 with 63 comments. Read on [27]reddit or the [28]original post. * hakyll 3.0 released (static site generator): From (jaspervdj.be), scored 25 with 1 comments. Read on [29]reddit or the [30]original post. * New release of cabal-dev: sandboxed, reproducible build environments for Haskell: From (haskell.org) scored 24 with 9 comments. Read on [31]reddit or the [32]original post. * News on Well-Typed, the Parallel GHC Project, and Eric Kow joins the team.: From (well-typed.com) scored 22 with 3 comments. Read on [33]reddit or the [34]original post. * Build Yourself a Bluetooth Controlled Six-Legged Robot : A Neighborhood of Infinity: From (blog.sigfpe.com) scored 21 with comments. Read on [35]reddit or the [36]original post. Top StackOverflow Answers * [37]Goto in Haskell: Can anyone explain this seemingly insane effect of continuation monad usage? votes: 14 Here's a somewhat informal answer, but hopefully useful. getCC' returns a continuation to the current point of execution; you can think of it as saving a stack frame. The continuation returned by getCC' has not only ContT's state at the point of the call, but also the state of any monad above ContT on the stack. When you restore that state by calling the ... * [38]How do Haskell compilers decide whether to allocate on the heap or the stack? votes: 13 When you call a function like this f 42 (g x y) then the runtime behaviour is something like the following: p1 = malloc(2 * sizeof(Word)) p1[0] = &Tag_for_Int p1[1] = 42 p2 = malloc(3 * sizeof(Word)) p2[0] = &Code_for_g_x_y p2[1] = x p2[2] = y f(p1, p2) That is, arguments are usually passed as pointers to objects on the heap like in Java, but ... * [39]Quick question about Arrow operators votes: 11 (***) :: (Arrow a) => a b c -> a b' c' -> a (b, b') (c, c') So specialize a to -> and we get: (***) :: (Arrow a) => (b -> c) -> (b' -> c') -> (b, b') -> (c, c') And that's great, except we want to, for whatever reason, take the first two arguments as a single pair instead. But that's easy, we just uncurry. Prelude ... * [40]QuickCheck: defining Arbitrary instance in terms of other Arbitraries votes: 9 I'd do it like this: instance Arbitrary C where arbitrary = do a <- arbitrary b <- arbitrary return (C a b) Although sclv's idea of using liftM2 from Control.Monad is probably better: instance Arbitrary C where arbitrary = liftM2 C arbitrary arbitrary Top StackOverflow Questions * Running a Haskell program on the Android OS (votes: 21, answers: 1) [41]read * Goto in Haskell: Can anyone explain this seemingly insane effect of continuation monad usage? (votes: 18, answers: 2) [42]read * Proving equality of streams (votes: 15, answers: 1) [43]read * Rotate the first argument to a function to become nth (votes: 12, answers: 7) [44]read * How do Haskell compilers decide whether to allocate on the heap or the stack? (votes: 9, answers: 2) [45]read About the Haskell Weekly News To help create new editions of this newsletter, please send stories to dstcruz(a)gmail.com. I'm in dire need of finding good "quotes of the week". If you happen to come across any, please don't hesitate to send it along. Until next time, Daniel Santa Cruz References 1. http://haskell.org/ 2. http://article.gmane.org/gmane.comp.lang.haskell.hakyll/128 3. http://article.gmane.org/gmane.comp.lang.haskell.general/18527 4. http://article.gmane.org/gmane.comp.lang.haskell.general/18528 5. http://article.gmane.org/gmane.comp.lang.haskell.general/18530 6. http://article.gmane.org/gmane.comp.lang.haskell.general/18533 7. http://article.gmane.org/gmane.comp.lang.haskell.libraries/15426 8. http://article.gmane.org/gmane.comp.lang.haskell.cafe/86897 9. http://article.gmane.org/gmane.comp.lang.haskell.general/18542 10. http://article.gmane.org/gmane.comp.lang.haskell.cafe/86922 11. http://article.gmane.org/gmane.comp.version-control.darcs.user/25916 12. http://article.gmane.org/gmane.comp.lang.haskell.general/18535 13. http://article.gmane.org/gmane.comp.lang.haskell.cafe/86937 14. http://article.gmane.org/gmane.comp.lang.haskell.cafe/86882 15. http://article.gmane.org/gmane.comp.lang.haskell.general/18540 16. http://article.gmane.org/gmane.comp.lang.haskell.cafe/86975 17. http://www.reddit.com/r/haskell/comments/fwk78/announce_ghc_version_702/ 18. http://www.haskell.org/pipermail/haskell/2011-March/022610.html 19. http://www.reddit.com/r/haskell/comments/fvabx/greenfield_haskell/ 20. file://localhost/r/haskell/comments/fvabx/greenfield_haskell/ 21. http://www.reddit.com/r/haskell/comments/fxjcl/patches_for_monad_comprehens… 22. http://hackage.haskell.org/trac/ghc/ticket/4370#comment:48 23. http://www.reddit.com/r/haskell/comments/fwkdh/ghc_702_released/ 24. http://www.haskell.org/ghc/download_ghc_7_0_2 25. http://www.reddit.com/r/haskell/comments/ful84/haskell_on_android/ 26. http://www.reddit.com/r/haskell/comments/ful84/haskell_on_android/ 27. http://www.reddit.com/r/haskell/comments/ftxc7/do_you_think_haskell_will_ev… 28. http://www.reddit.com/r/haskell/comments/ftxc7/do_you_think_haskell_will_ev… 29. http://www.reddit.com/r/haskell/comments/fusve/hakyll_30_released_static_si… 30. http://jaspervdj.be/hakyll/tutorial.html 31. http://www.reddit.com/r/haskell/comments/fx47b/new_release_of_cabaldev_sand… 32. http://www.haskell.org/pipermail/haskell-cafe/2011-March/089831.html 33. http://www.reddit.com/r/haskell/comments/fw311/news_on_welltyped_the_parall… 34. http://www.well-typed.com/blog/51 35. http://www.reddit.com/r/haskell/comments/ftxzx/build_yourself_a_bluetooth_c… 36. http://blog.sigfpe.com/2011/02/build-yourself-bluetooth-controlled-six.html 37. http://stackoverflow.com/questions/5193876/goto-in-haskell-can-anyone-expla… 38. http://stackoverflow.com/questions/5132350/how-do-haskell-compilers-decide-… 39. http://stackoverflow.com/questions/5200462/quick-question-about-arrow-opera… 40. http://stackoverflow.com/questions/5134259/quickcheck-defining-arbitrary-in… 41. http://stackoverflow.com/questions/5151858/running-a-haskell-program-on-the… 42. http://stackoverflow.com/questions/5193876/goto-in-haskell-can-anyone-expla… 43. http://stackoverflow.com/questions/5179821/proving-equality-of-streams 44. http://stackoverflow.com/questions/5188212/rotate-the-first-argument-to-a-f… 45. http://stackoverflow.com/questions/5132350/how-do-haskell-compilers-decide-…

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Haskell Platform web page is out of date
by Paul Johnson 09 Mar '11

09 Mar '11

The Haskell Platform web page at http://hackage.haskell.org/platform// seems to need updating. (Incidentally, that double slash at the end doesn't look right). * The "next release" is promised in Jan 2011. * The "Release Timetable" schedules the next release for 5 March 2011. I just worry that this is one of the first things someone investigating Haskell sees, and it creates a bad first impression. Paul.

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Haskell Platform 2011.2
by tsuraan 09 Mar '11

09 Mar '11

The wiki page for Haskell Platform is still listing March 5 (today) as the planned release date. Is this still the plan, or should the page be updated?

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Overlaping Parsec rules
by Hauschild, Klaus (EXT) 09 Mar '11

09 Mar '11

Hi, to solve this ICFP task http://www.cs.cornell.edu/icfp/task.htm I'm currnetly working on the parser. With the hint from Thu (reading Phillip Wadlers monadic parser paper) and consulting http://en.wikibooks.org/wiki/Write_Yourself_a_Scheme_in_48_Hours/Parsing I produce a first working version of the parser. After this great moment I completed the token definition and near all parsing rules. For the complete code have a look at http://code.google.com/p/hgmltracer/source/browse/#svn%2Ftrunk%2FhGmlTracer data GmlToken = -- structures FunctionToken TokenSequence | ArrayToken TokenSequence | -- control operators ApplyToken | IfToken | -- number operators AddiToken | AddfToken | ACosToken | ASinToken | ClampfToken | CosToken | DiviToken | DivfToken | EqiToken | EqfToken | FloorToken | FracToken | LessiToken | LessfToken | ModiToken | MuliToken | MulfToken | NegiToken | NegfToken | ToRealToken | SinToken | SqrtToken | SubiToken | SubfToken | -- points GetXToken | GetYToken | GetZToken | PointToken | -- arrays GetToken | LengthToken | -- environment IdentifierToken String | BinderToken String | -- types BoolToken Bool | IntToken Int | RealToken Double | StringToken String deriving Show And parseGml :: String -> [GmlToken] parseGml input = case parse parseList "gml" input of Left err -> error ("Parse error: " ++ (show err)) Right gml -> gml parseList = sepBy parseGml' spaces parseGml' = -- structures -- parseFunction -- <|> parseArray -- control operators parseControlOperators -- number operators <|> parseNumberOperators -- points <|> parsePointOperators -- arrays <|> parseArrayOperators -- types <|> parseBool <|> parseInteger <|> parseString -- environment <|> parseIdentifier <|> parseBinder parseArray = parseSequence '[' ']' parseFunction = parseSequence '{' '}' parseSequence start end = do char start array <- parseList char end return $ ArrayToken array parseControlOperators = parseApply <|> parseIf parseApply = do string "apply" return $ ApplyToken parseIf = do string "if" return $ IfToken parseNumberOperators = do string "addi" return $ AddiToken <|> do string "addf" return $ AddfToken <|> do string "acos" return $ ACosToken <|> do string "asind" return $ ASinToken <|> do string "clampf" return $ ClampfToken <|> do string "cos" return $ CosToken <|> do string "divi" return $ DiviToken <|> do string "divf" return $ DivfToken <|> do string "eqi" return $ EqiToken <|> do string "eqf" return $ EqfToken <|> do string "floor" return $ FloorToken <|> do string "frac" return $ FracToken <|> do string "lessi" return $ LessiToken <|> do string "lessf" return $ LessfToken <|> do string "modi" return $ ModiToken <|> do string "muli" return $ MuliToken <|> do string "mulf" return $ MulfToken <|> do string "negi" return $ NegiToken <|> do string "negf" return $ NegfToken <|> do string "real" return $ ToRealToken <|> do string "sin" return $ SinToken <|> do string "Sqrt" return $ SqrtToken <|> do string "subi" return $ SubiToken <|> do string "subf" return $ SubfToken parsePointOperators = do string "getx" return $ GetXToken <|> do string "gety" return $ GetYToken <|> do string "getz" return $ GetZToken <|> do string "point" return $ PointToken parseArrayOperators = do string "get" return $ GetToken <|> do string "length" return $ LengthToken parseInteger = liftM (IntToken . read) $ many1 digit parseBool = do string "true" return $ BoolToken True <|> do string "false" return $ BoolToken False parseString = do char '"' string <- many (noneOf "\"") char '"' return $ StringToken string parseIdentifier = do identifier <- many (noneOf " ") return $ IdentifierToken identifier parseBinder = do char '/' binder <- many (noneOf " ") return $ BinderToken binder parseComment = do char '%' many (noneOf "") newline return $ () spaces = skipMany1 space After gluing all this together in my mind all worked well. But it doesn't. The test file for parsing looks like: { /self /n n 2 lessi { 1 } { n 1 subi self self apply n muli } if } /fact 12 fact fact apply * I think there is a problem with overlaping rules. There is a parser rule consuming "negi" and resulting in the NegiToken. A single "n" is a valid identifier. For the example file my parser says: unexpected " ", expecting "negi" * I think the same problem is present for "parseInteger" and "parseReal" (currently no in code but looks like "parseReal = do a <- many1 digit \n char '.' \n b <- many1 digit \n return $ RealToken (read (a ++ "." ++ b)" * Something with "parseFunction" is going really wrong. * All parsig rules are designed with the condition that each "construct" is separated by whitespaces. For this before parsing the input will be preprocessed: insert spaces, removing whitespaces and so on. Now in the parsed result appears (IdentifierToken ""). I think my version is not the best way to parse a identifer: parseIdentifier = do identifier <- many (noneOf " ") return $ IdentifierToken identifier Please help me. Klaus

4 15

operations on lists with continuations
by Evan Laforge 09 Mar '11

09 Mar '11

I have a few functions for operating on lists that take continuations: -- | Like takeWhile but with a continuation, so you can chain takes without -- copying. takeWhileThen :: (a -> Bool) -> ([a] -> [a]) -> [a] -> [a] takeWhileThen _ _ [] = [] takeWhileThen f cont (x:xs) | f x = x : takeWhileThen f cont xs | otherwise = cont (x:xs) But of course this isn't enough, then I start wanting a takeThen. And then a filterThen. That makes me think plain explicit recursion would be clearer, but the problem I have with that is that it has an imperative feel. What I mean by that is that the result is a product of the changing state of the recursing function, and it's non-composable. E.g. filterUntil start end msgs = go where go [] = [] go (m:ms) | msg_start m >= start = takeWhile ((<end) . msg_start) (m : ms) | condition m = m : go ms | otherwise = go ms Whereas with filterThen I can write: filterUntil start end = filterThen condition ((>=start) . msg_start) . takeWhile ((<end) . msg_start) This looks much more functional to me, and can be composed: filterUntilPlus1 start end = filterThen condition ((>=start) . msg_start) $ takeWhileThen ((<end) . msg_start) $ take 1 So my question is, am I about to discover this already exists in the Prelude, or is unnecessary because of something I'm overlooking? I imagine it must be a special case of some kind of generalization, right? Surely someone has thought of this and taken it much further than I have. I suppose this starts to look like maybe a CPS version of a parser... but it seems lighter-weight for simple tasks.

3 4

cabal install / upgrade (was: Re: some problem with Cabal)
by Evan Laforge 09 Mar '11

09 Mar '11

> Generally, it shouldn't (and doesn't), but here some packages have to be > reinstalled because they have to be built against different dependencies. > > I'd prefer cabal install to refuse here (overridable with a --force flag) > because reinstalling boot libs (containers, filepath, directory, process, > time) tends to be a bad idea. Seconded! I've had my setup screwed up because some package wanted to recompile base against a tiny version bump on the random package for whatever reason. The presence of two bases with the same version, one in the ghc dir and one in /usr/local/lib proceded to screw up all kinds of things. It took a long time to figure out because I wasn't expecting two copies of base with the same version, and it somehow managed to overwrite the package file in package.conf.d so the original metadata was gone. Eventually I gave up and reinstalled ghc. And all I did was accidentally run cabal upgrade somepackage when I wanted to install a newer version of somepackage. By the time I realized it was apparently still aliased to cabal break-everything and hit ^C it was too late. And it's not like I haven't been warned away from cabal upgrade either... but it made me think, if the command is so dangerous, should it have a scarier name?

1 0

Tagless interpreter, expression problem and zipper
by Roel van Dijk 09 Mar '11

09 Mar '11

Hello everyone, I am stuck rewriting some code in the tagless style. My problem can be thought of as an interpreter for a very simple language: > data Exp = Lit Integer > | Add Exp Exp > | Mul Exp Exp > deriving (Show) But some complexity is added by the fact that my interpreter also needs to know the context in which literals appear in an expression. So given the example > t1 :: Exp > t1 = (Lit 3 `Add` Lit 4) `Mul` Lit 2 I want to have access to the fact that the literal 3 appears on the left side of an addition. Therefore I created a type: > data Ctx = Empty > | AddL Exp Ctx > | AddR Exp Ctx > | MulL Exp Ctx > | MulR Exp Ctx > deriving (Show) This is almost a zipper over the Exp type. I left out a context for literals themselves because it wasn't necessary. Now I can create a simple evaluation function: > eval :: (a -> a -> a) > -> (a -> a -> a) > -> (Integer -> Ctx -> a) > -> Exp > -> a > eval add mul lit = go Empty > where > go ctx (Lit n) = lit n ctx > go ctx (Add x y) = let x' = go (AddL y ctx) x > y' = go (AddR x ctx) y > in x' `add` y' > go ctx (Mul x y) = let x' = go (MulL y ctx) x > y' = go (MulR x ctx) y > in x' `mul` y' This function can evaluate an expression to any type 'a', but it needs some additional functions to accomplish that: add, mul and lit. Notice how the 'lit' function has access to a literal's context. To interpret an Exp as an Integer I use: > evalInt :: Exp -> Integer > evalInt = eval (+) (*) const Or as a String: > evalStr1 :: Exp -> String > evalStr1 = eval addStr mulStr (const . show) > addStr x y = "(" ++ x ++ " + " ++ y ++ ")" > mulStr x y = "(" ++ x ++ " * " ++ y ++ ")" Or a silly example which uses the context: > evalStr2 :: Exp -> String > evalStr2 = eval addStr mulStr lit > where > lit _ (AddL (Lit 4) (MulL _ _)) = "Foo!" > lit n _ = show n The silly example replaces a literal with "Foo!" if it appears on the left side of an addition with 4, and the whole addition is the left side of a multiplication, like in (x + 4) * ?. All of this works. But I want to be able to add additional constructors to the Exp language without changing existing code. This looks like the expression problem. Ignoring the zipper-like context I came up with the following: First define the language: > class Lit a where lit :: Integer -> a > class Add a where add :: a -> a -> a > class Mul a where mul :: a -> a -> a Integer interpreter: > instance Lit Integer where lit = fromInteger > instance Add Integer where add = (+) > instance Mul Integer where mul = (*) String interpreter, using a newtype so I don't need TypeSynonymInstances: > newtype Str = Str {unS :: String} > instance Show Str where show = show . unS > instance Lit Str where lit = Str . show > instance Add Str where add x y = Str $ addStr (unS x) (unS y) > instance Mul Str where mul x y = Str $ mulStr (unS x) (unS y) Same example expression, now polymorphic: > t1 :: (Lit a, Add a, Mul a) => a > t1 = (lit 3 `add` lit 4) `mul` lit 2 This expression can now be interpreted in multiple ways: > t1 :: Integer >> 14 > t1 :: Str >> "((3 + 4) * 2)" This solves the expression problem. I can add new structures to my language in other modules without having to change existing code. The necessary parts are mentioned in the type constraint (Lit a, Add a, Mul a). But I lost the power of the context! How do I get it back? Attached are the two approaches, WithTags.hs and Tagless.hs (but without context). Any help would be greatly appreciated!

2 1

some problem with Cabal
by Qi Qi 09 Mar '11

09 Mar '11

Hi, When I tried the haskell platform 2011.2 source, from here http://code.galois.com/darcs/haskell-platform/download-website/linux.html . Configuration passed successfully. But when making, it gives the following error: scripts/build.sh ************************************************** Scanning system for any installed Haskell Platform components... Found:None. New packages to install: None! All done. ************************************************** Building "/usr/local/bin/ghc" "--make" "Setup" "-o" "Setup" "-package" "Cabal-1.10.1.0" <command line>: cannot satisfy -package Cabal-1.10.1.0: Cabal-1.10.1.0-64e8f05722ea5bbdf07df2e5a3491105 is unusable due to missing or recursive dependencies: directory-1.1.0.0-85d1d0f9d96dffdacf64f3cc6fba6f2f process-1.0.1.5-4cab1bf0666275ac101dd48c7565b64c (use -v for more information) Error: Compiling the Setup script failed make: *** [build.stamp] Error 2 I think this is the same problem as I got during installing some other packages via cabal such as hmatrix, ghc-mod, happy and etc. Does anyone have any idea about how to solve it? Thanks! -- Qi Qi

4 7

have anyone tried GHC 7.0.2
by Qi Qi 09 Mar '11

09 Mar '11

Hi, After I installed GHC 7.0.2 and cabal-install 0.10.0 using Cabal library 1.10.1, I found that some package failed to install. For example like Happy, I got the following error: cabal install happy Resolving dependencies... <command line>: cannot satisfy -package Cabal-1.10.1.0: Cabal-1.10.1.0-64e8f05722ea5bbdf07df2e5a3491105 is unusable due to missing or recursive dependencies: directory-1.1.0.0-85d1d0f9d96dffdacf64f3cc6fba6f2f process-1.0.1.5-4cab1bf0666275ac101dd48c7565b64c (use -v for more information) cabal: Error: some packages failed to install: happy-1.18.6 failed during the configure step. The exception was: ExitFailure 1 Besides happy package, some other packages like ghc-mod, hmatrix also failed to install. Does anyone else have the same issue after installed ghc 7.0.2? By the way, does anyone hear anything about Haskell-platform 2011.2 ? Thanks! -- Qi Qi

4 5

Error recovery in Happy
by Tom 09 Mar '11

09 Mar '11

Hey guys, I was wondering if there were possiblities to ignore certain errors during parsing. I tried using the error token, but that didn't seem to work. I looked at the following topic http://haskell.1045720.n5.nabble.com/Error-detection-in-GLR-Happy-grammar-t… For my parser I need to be able to parse a certain token at any place, but only in some places it is part of a rule. In other cases this token should be ignored after which the parser just procedes to the next token. Is this possible with Happy? Should I use the monadic parser to achieve this? More concretely, I have tokenized some sourcecode which contains comments, these should be ignored except when they are located above a function, in which case I want them to parse. Any ideas about this issue are greatly appreciated! Thanks, Tom

2 5

Haskell IDE
by Hauschild, Klaus (EXT) 08 Mar '11

08 Mar '11

Hi Haskellers, whats your Haskell IDE of choise? Currently I use leksah. Is the EclipseFP Plugin for Eclipse a real alternative? Thanks Klaus

17 25

ANN: theoremquest-0.0.0
by Tom Hawkins 08 Mar '11

08 Mar '11

I have been wanting to gain a better understanding of interactive theorem proving for some time. And I've often wondered: Can theorem proving be made into a user-friendly game that could attract mass appeal? And if so, could a population of gamers collectively solve interesting and relevant mathematical problems? To try to answer these questions -- and to gain some experience myself with theorem proving -- I started a project called TheoremQuest [1]. TheoremQuest intends to be a multi-player game system, where the game server receives requests by clients, such as theorem queries and inference rule applications. The TheoremQuest server validates deductions, compares them with existing theorems in the database, then returns results. TheoremQuest's deductive system borrows that of John Harrison's HOL Light [2]. There are 2 Hackage packages: theoremquest [3] is a library that declares types for terms, inference rules, and client-server transactions, used by both server and clients; and theoremquest-client [4] is an example client (tq). All the code, including the server-side, is hosted at github [5]. Currently the client-server interface is working, but little else. The library has defined most of the core inference rules, but has none of the basic types or axioms. And the "tq" client is nothing at all like a game; at this point it is just a command line tool to test the server. Currently "tq" can ping the server, create a new user, apply inference rules, and print out theorems. Here's how "tq" can prove "x |- x": $ tq newuser tomahawkins tomahawkins(a)gmail.com Ack $ export THEOREMQUEST_USER=tomahawkins $ tq infer 'ASSUME (Var (Variable "x" Bool))' Id 1 $ tq theorem 1 assumptions: Var (Variable "x" Bool) conclusion: Var (Variable "x" Bool) I'd love to have help with this project, if anyone's interested. I'm still grappling with the logical core, but I think the real challenge will be creating game clients that are both capable and yet intuitive enough to appeal to the general population. If the masses can play Sudoku, shouldn't they be capable of interactive theorem proving? -Tom [1] http://theoremquest.org [2] http://www.cl.cam.ac.uk/~jrh13/hol-light/ [3] http://hackage.haskell.org/package/theoremquest [4] http://hackage.haskell.org/package/theoremquest-client [5] http://github.com/tomahawkins/theoremquest

9 12

makeTokenParser + LanguageDef
by Hauschild, Klaus (EXT) 08 Mar '11

08 Mar '11

Hi Haskellers, is there a fine tutorial for building a parser with parsecs (3.*) makeTokenParser and LanguageDef stuff? Klaus

3 2

I think I've found a regression in Haskell Platform, but what do I do next?
by Nick Frolov 08 Mar '11

08 Mar '11

Hi, Recently I had to switch from ghc 6.12.3 to ghc 7.0.1 because of the bug #4235. This switch has introduced a problem with one of third-party libraries I use ('satchmo', an interface for SAT solvers). The problem is that writing to stdin of a process started by System.Process.runInteractiveCommand silently fails provided it's stderr is not read. If stderr of the spawned process is redirected to /dev/null or fully read by the parent process, then problem does not come up. The troubled code is available at http://bit.ly/dNwrIV (lines 43-45). Changes between versions of the 'process' library (1.0.1.3 -> 1.0.1.4) bundled with ghc 6.12.3 and 7.0.1 only include one bug fix, which is not the source of the problem described, as far as I can understand. The problem is not present with ghc 6.12.* at all. Something has definitely changed between these two ghc versions. Since I've spent considerable amount of time on finding a workaround for the problem, I'd like to file a real bug report, but I'm not completely sure where to do it because there are several pieces of software involved (ghc itself, 'process', 'satchmo' and 'minisat2' SAT solver). Could somebody guide me please?

2 2

Questions on list administration
by Karthick Gururaj 08 Mar '11

08 Mar '11

Hello, I recently joined Haskell group and wanted to share a few points. First, I came to Haskell cafe from google groups (groups.google.com -> search for Haskell). Two groups are listed: fa.haskell and haskell-cafe. I became a "member" of Haskell Cafe via the google groups interface (the operation was successful according to google). When I posted a message, I got an automated email (within a few seconds, so I think there was no human moderation): You are not allowed to post to this mailing list, and your message has been automatically rejected. If you think that your messages are being rejected in error, contact the mailing list owner at haskell-cafe-owner(a)haskell.org. I wrote to the email address mentioned and didn't get any response. Funny thing is, google reports that my post was successful, and my post was "visible" on google groups even after I signed out from my google account. I next wrote to the group owner, again from the google groups interface (there is an option to "send email to the owner"). No response here as well. I then went to Haskell.org -> Mailing lists and saw there are atleast three lists of immediate relevance, including one for beginners. The website also describes the posting guidelines and other information. Very useful. I would have stuck to asking questions on the beginner's group if I had known earlier.. Can I ask a couple of changes be done to help others like me? a. In google groups -> https://groups.google.com/group/haskell-cafe/about -> add a link to the haskell.org -> Mailing lists for more info. b. Let users join from google groups interface, or if this is not possible, mention that in the "about" page c. Change the contents of the reject email (reproduced above) to include the following: "If you want to subscribe to the Haskell Cafe mailing list, please visit http://www.haskell.org/mailman/listinfo/haskell-cafe" Aside: the Haskell Cafe mailing list page (at http://www.haskell.org/mailman/listinfo/haskell-cafe) has a dead link at the bottom of the page. The "Overview of all haskell.org mailing lists" points to http://www.haskell.org/cgi-bin/mailman/listinfo (404 error) instead of http://haskell.org/mailman/listinfo. Thanks! Warm regards, Karthick

2 1

AusHack 2011
by Ivan Lazar Miljenovic 08 Mar '11

08 Mar '11

It is time once again to start planning for AusHac (the Hackathon Down Under)! The current proposed dates are 8-10 July. This time we're trying to organise a venue in the Sydney CBD, but if all else fails we'll be at UNSW again. So, is anyone vehemently opposed to having AusHac at this time or place? -- Ivan Lazar Miljenovic Ivan.Miljenovic(a)gmail.com IvanMiljenovic.wordpress.com

1 0

Re: [Haskell-cafe] [Haskell] ANNOUNCE: silently-0.0.1 (prevent IO actions from writing to stdout)
by trystan.s＠comcast.net 07 Mar '11

07 Mar '11

Thanks for the feedback! I'll definitely update the documentation. I agree that temp files are a weird way to go about it but they're the least surprising and dangerous way I could think of handling it. Unix has /dev/null and Windows has a NUL device that works the same way so I could use those. * I could see what OS it is and try those options and use a temp file only if it's an unexpected os. Unfortunately System.Info.os reports windows (and some other os's) as "mingw32", I think it's because of how GHC was compiled. Who knows what the real os is or what each os will be reported as in the future or how they appear to other compilers and runtimes. * I could write to /dev/null or NUL if they exist and use a temp file if neither does, but if there's a legitimate /dev/null or NUL file then having some unrelated program write to them would be very very bad and a major pain for whoever has to figure that one out. I'd rather not use temp files but both of these seem problematic. Does anyone have a better idea or think that either of those are acceptable? Trystan Spangler ----- Original Message ----- From: "Felipe Almeida Lessa" <felipe.lessa(a)gmail.com> To: "Trystan Spangler" <trystan.s(a)comcast.net> Cc: haskell-cafe(a)haskell.org Sent: Monday, March 7, 2011 3:41:07 AM Subject: Re: [Haskell] ANNOUNCE: silently-0.0.1 (prevent IO actions from writing to stdout) Hello! I wouldn't expect that a function that ignores the output directs it to a temporary file. I think that should be clearly stated on the documentation, as this may be undesirable. I don't know if there is a better way of solving this problem, though. (Note, however, that on Unix systems you could probably direct the output to /dev/null.) Cheers, -- Felipe.

2 2

ghc in debian sid
by rustom 07 Mar '11

07 Mar '11

I tried to move from debian testing to sid and got the message that a whole load of libghc**'s would be removed. Are more recent ones lined up?

1 1

groupBy huh?
by Jacek Generowicz 07 Mar '11

07 Mar '11

Hi Cafe, It seems that I don't understand what groupBy does. I expect it to group together elements as long as adjacent ones satisfy the predicate, so I would expect ALL four of the following to give one group of 3 and a group of 1. Prelude> :m + Data.List Prelude Data.List> groupBy (<) "abcb" ["abcb"] Prelude Data.List> groupBy (<) "abca" ["abc","a"] Prelude Data.List> groupBy (<) [1,2,3,2] [[1,2,3,2]] Prelude Data.List> groupBy (<) [1,2,3,1] [[1,2,3],[1]] What am I missing? Thanks.

7 9

Re: [Haskell-cafe] [Haskell] ANNOUNCE: silently-0.0.1 (prevent IO actions from writing to stdout)
by Felipe Almeida Lessa 07 Mar '11

07 Mar '11

Hello! I wouldn't expect that a function that ignores the output directs it to a temporary file. I think that should be clearly stated on the documentation, as this may be undesirable. I don't know if there is a better way of solving this problem, though. (Note, however, that on Unix systems you could probably direct the output to /dev/null.) Cheers, -- Felipe.

1 0

Idiomatic error handling in Haskell
by Rouan van Dalen 07 Mar '11

07 Mar '11

There are quite a few exception handling mechanisms provided by Haskell, as can be seen from this post: http://www.randomhacks.net/articles/2007/03/10/haskell-8-ways-to-report-err… I would like to know what is the preferred Haskell mechanism for handling exceptions in the IO monad? I am not concerned with mechanisms such as Maybe / Either, but would like to know about exception mechanisms inside the IO monad. The 2 I know of are: o) throwDyn o) ioError and catch I do need the exceptions to be extendable. So which is the preferred way to handle exceptions in Haskell for new libs?

2 2

How to daemonize a threaded Haskell program?
by Bas van Dijk 07 Mar '11

07 Mar '11

Hello, I like to turn my Haskell program into a unix daemon. One of the steps in "daemonizing" a process is to fork it then exit the parent and continue with the child. All this is nicely abstracted in hdaemonize[1] which internally calls forkProcess[2]. I would also like to use multiple simultaneous threads in my program. Unfortunately forkProcess is not supported when running with +RTS -N so I can't use hdaemonize. I understand why it's problematic to fork a process which is in the middle of running multiple simultaneous threads. However, in the case of a daemon the fork happens in the beginning of the program. So if I can manage to create a program that first daemonizes my process then starts the Haskell program, all is good. My current plan is to have a custom Haskell main function which is exported using the FFI: --------------------------------------------------------------------- {-# LANGUAGE ForeignFunctionInterface #-} module MyMain where import Control.Monad ( forM_ ) import Control.Concurrent ( threadDelay ) -- from hsyslog: import System.Posix.Syslog ( Priority(Debug), syslog ) foreign export ccall myMain :: IO () myMain :: IO () myMain = forM_ [1..10 :: Int] $ \n -> do syslog Debug $ "test " ++ show n threadDelay 1000000 --------------------------------------------------------------------- Then create a C program that first daemonizes my process (using the 'daemon'[3] function from unistd) then start up my custom Haskell main function: --------------------------------------------------------------------- #include <unistd.h> #include "HsFFI.h" #include "MyMain_stub.h" extern void __stginit_Main ( void ); int main(int argc, char *argv[]) { int r; r = daemon(0,0); if (r < 0) { return r; } hs_init(&argc, &argv); hs_add_root(__stginit_Main); myMain(); hs_exit(); return 0; } --------------------------------------------------------------------- My question is: how can I combine these two into a single program? I very much prefer to do this using Cabal since my actual program contains lots of dependencies. Thanks, Bas [1] http://hackage.haskell.org/package/hdaemonize [2] http://hackage.haskell.org/packages/archive/unix/latest/doc/html/System-Pos… [3] http://www.kernel.org/doc/man-pages/online/pages/man3/daemon.3.html

7 10

can't download haskell-mode for emacs: directory is empty
by Richard Cobbe 06 Mar '11

06 Mar '11

I'm trying to see if I'm running the latest version of haskell-mode.el. Unfortunately, the download link at the top of <http://www.haskell.org/haskellwiki/Haskell_mode_for_Emacs> points to a directory with nothing in it. Is there somewhere else I should be looking? I tried sending email to the maintainer a couple of weeks ago, but I haven't heard a response. What's the status on this package? Thanks, Richard

3 3

Benchmarks game updated
by Don Stewart 06 Mar '11

06 Mar '11

Isaac Gouy from the Language Benchmarks game tells me that they're starting to use GHC 7.0.2, there are a few tweaks, new flags (e.g. the LLVM backend) and other experiments people might like to try. Additionally, there are a couple of build failures that should be fixed. http://shootout.alioth.debian.org/u64q/measurements.php?lang=ghc -- Don

3 2

Creating a darcs repo and trac
by Dominic Steintiz 06 Mar '11

06 Mar '11

I'd like to create a darcs repo for a package I've just created so people can do: darcs get http://code.haskell.org/largeword I can logon to code.haskell.org but I don't have permission to create a directory in /srv/code which is what I thought I had to do. Ditto I would like to create a trac instance on trac.haskell.org. I recall using createtrac but that no longer seems to be available. Is there a wiki page that explains all? Thanks, Dominic.

2 1

Combinatorial Problems
by Richard Senington 06 Mar '11

06 Mar '11

Hello all, I have just uploaded a very early (0.0.1) version of a library I am working on to hackage. The library is for representing some well known combinatorial problems, and provide loading routines for standard repositories of these problems. At the moment is only support SAT-3 and the SATLIB loading routines. It does have a set of functions for TSP, but I have not yet finished reworking the TSPLIB loading code yet. Hopefully that will be coming soon. It is a very early version so not heavily tested, but I thought it would be better to put it up so that if anyone is interested they can have a look and make suggestions. Any comments, bug reports or modification ideas, please feel free to email me. RS

1 0

Use of uninstantiated type class
by Yves Parès 06 Mar '11

06 Mar '11

Hello, For testing purposes, I am trying to make an overlay to IO which carries a phantom type to ensure a context. I define contexts using empty type classes : class CtxFoo c class CtxBar c The overlay : newtype MyIO c a = MyIO (IO a) Then I define some methods that run only a specific context : runFoo :: (CtxFoo c) => MyIO c a -> IO a runFoo (MyIO x) = x runBar :: (CtxBar c) => MyIO c a -> IO a runBar (MyIO x) = x And then an action that runs in context 'Foo' : someAction :: (CtxFoo c) => MyIO c () someAction = putStrLn "FOO" Then I run it : main = runFoo someAction But obiously, GHC complains that my type 'c' remains uninstantiated : Ambiguous type variable `c' in the constraint: (CtxFoo c) arising from a use of `runFoo' Probable fix: add a type signature that fixes these type variable(s) In the expression: runFoo someAction In an equation for `main': main = runFoo someAction Is there a way to deal with this ? The interest of using type classes and not empty types to represent the contexts is that it stays simple, and that I can do that : someAction2 :: (CtxFoo c, CtxBar c) => MyIO c () someAction2 = putStrLn "FOO and BAR" ... a function that can run in both contexts.

4 5

Linking errors when compiling projects with the ncurses-0.2 library
by Román González 06 Mar '11

06 Mar '11

Greetings, Right now I'm developing an app, and I want to use the ncurses library, everything compiles correctly, however when I'm linking, ugly things start to happen: I'm on Mac OS X Snow Leopard, with Haskell Platform 2010.2.0.0<http://hackage.haskell.org/platform/changelog.html> This is the installation process I'm following, everything runs as expected until trying to build the project with Cabal. Thanks in advance. *$ brew install ncursesw --universal* Warning: It appears you have MacPorts or Fink installed. Software installed with MacPorts and Fink are known to cause problems. If you experience issues try uninstalling these tools. ==> Downloading http://ftp.gnu.org/pub/gnu/ncurses/ncurses-5.7.tar.gz File already downloaded and cached to /Users/roman/Library/Caches/Homebrew ==> ./configure --prefix=/Users/roman/.homebrew/Cellar/ncursesw/5.7 --mandir=/Users/roman/.homebrew/Cellar/ncursesw/5.7/share/man --disable-debug --disable-dependency-tracking --e ==> make install /Users/roman/.homebrew/Cellar/ncursesw/5.7: 2734 files, 14M, in 93 seconds *$ cabal install ncurses --extra-include-dirs=/Users/roman/.homebrew/include --extra-lib-dirs=/Users/roman/.homebrew/lib --reinstall* Resolving dependencies... Configuring ncurses-0.2... Preprocessing library ncurses-0.2... Building ncurses-0.2... [1 of 4] Compiling UI.NCurses.Enums ( dist/build/UI/NCurses/Enums.hs, dist/build/UI/NCurses/Enums.o ) [2 of 4] Compiling UI.NCurses.Types ( UI/NCurses/Types.hs, dist/build/UI/NCurses/Types.o ) [3 of 4] Compiling UI.NCurses ( dist/build/UI/NCurses.hs, dist/build/UI/NCurses.o ) [4 of 4] Compiling UI.NCurses.Panel ( dist/build/UI/NCurses/Panel.hs, dist/build/UI/NCurses/Panel.o ) UI/NCurses/Panel.chs:49:0: Warning: The import of `UI.NCurses' is redundant except perhaps to import instances from `UI.NCurses' To import instances alone, use: import UI.NCurses() Registering ncurses-0.2... Installing library in /Users/roman/.cabal/lib/ncurses-0.2/ghc-6.12.3 Registering ncurses-0.2... *$ cabal build* Preprocessing executables for TicTacToe-0.1... Building TicTacToe-0.1... Linking dist/build/TicTacToe/TicTacToe ... ld: warning: in /Users/roman/.homebrew/lib/libncursesw.dylib, file was built for unsupported file format which is not the architecture being linked (i386) Undefined symbols: "_start_color", referenced from: _s9ZP_info in libHSncurses-0.2.a(NCurses.o) "_wget_wch", referenced from: _sfkI_info in libHSncurses-0.2.a(NCurses.o) "_wenclose", referenced from: _s9Fs_info in libHSncurses-0.2.a(NCurses.o) "_beep", referenced from: _ncurseszm0zi2_UIziNCurses_beep1_info in libHSncurses-0.2.a(NCurses.o) (maybe you meant: _ncurseszm0zi2_UIziNCurses_beep2_closure, _ncurseszm0zi2_UIziNCurses_beep1_srt , _ncurseszm0zi2_UIziNCurses_beep_srt , _ncurseszm0zi2_UIziNCurses_beep3_info , _ncurseszm0zi2_UIziNCurses_beep2_srt , _ncurseszm0zi2_UIziNCurses_beep3_srt , _ncurseszm0zi2_UIziNCurses_beep1_closure , _ncurseszm0zi2_UIziNCurses_beep_info , _ncurseszm0zi2_UIziNCurses_beep1_info , _ncurseszm0zi2_UIziNCurses_beep3_closure , _ncurseszm0zi2_UIziNCurses_beep2_info , _ncurseszm0zi2_UIziNCurses_beep_closure ) "_echo", referenced from: _sc50_info in libHSncurses-0.2.a(NCurses.o) (maybe you meant: ___hscore_echo) "_can_change_color", referenced from: _ncurseszm0zi2_UIziNCurses_canDefineColor1_info in libHSncurses-0.2.a(NCurses.o) "_init_color", referenced from: _s97K_info in libHSncurses-0.2.a(NCurses.o) _scw2_info in libHSncurses-0.2.a(NCurses.o) "_wnoutrefresh", referenced from: _s2JC_info in NCurses.o _scSh_info in libHSncurses-0.2.a(NCurses.o) "_noraw", referenced from: _scaE_info in libHSncurses-0.2.a(NCurses.o) "_wtouchln", referenced from: _sd53_info in libHSncurses-0.2.a(NCurses.o) _sd53_info in libHSncurses-0.2.a(NCurses.o) "_wcolor_set", referenced from: _sav6_info in libHSncurses-0.2.a(NCurses.o) "_meta", referenced from: _s9KC_info in libHSncurses-0.2.a(NCurses.o) _scV2_info in libHSncurses-0.2.a(NCurses.o) "_initscr", referenced from: _ncurseszm0zi2_UIziNCurses_runCurses2_info in libHSncurses-0.2.a(NCurses.o) "_stdscr", referenced from: _stdscr$non_lazy_ptr in NCurses.o _stdscr$non_lazy_ptr in libHSncurses-0.2.a(NCurses.o) (maybe you meant: _stdscr$non_lazy_ptr) "_wbkgrndset", referenced from: _scOA_info in libHSncurses-0.2.a(NCurses.o) "_raw", referenced from: _scaE_info in libHSncurses-0.2.a(NCurses.o) (maybe you meant: _ffi_closure_raw_SYSV$non_lazy_ptr, _ffi_closure_raw_SYSV , _ffi_raw_call , _ffi_prep_raw_closure_loc ) "__nc_has_mouse", referenced from: _hsncurses_has_mouse in libHSncurses-0.2.a(hsncurses-shim.o) "_wtimeout", referenced from: _s9KE_info in libHSncurses-0.2.a(NCurses.o) _scV4_info in libHSncurses-0.2.a(NCurses.o) _sfkG_info in libHSncurses-0.2.a(NCurses.o) "_doupdate", referenced from: _ncurseszm0zi2_UIziNCurses_render1_info in libHSncurses-0.2.a(NCurses.o) "_baudrate", referenced from: _ncurseszm0zi2_UIziNCurses_baudrate1_info in libHSncurses-0.2.a(NCurses.o) (maybe you meant: _ncurseszm0zi2_UIziNCurses_baudrate1_info, _ncurseszm0zi2_UIziNCurses_baudrate_info , _ncurseszm0zi2_UIziNCurses_baudrate3_closure , _ncurseszm0zi2_UIziNCurses_baudrate_closure , _ncurseszm0zi2_UIziNCurses_baudrate_srt , _ncurseszm0zi2_UIziNCurses_baudrate2_info , _ncurseszm0zi2_UIziNCurses_baudrate2_closure , _ncurseszm0zi2_UIziNCurses_baudrate1_closure , _ncurseszm0zi2_UIziNCurses_baudrate3_info , _ncurseszm0zi2_UIziNCurses_baudrate1_srt , _ncurseszm0zi2_UIziNCurses_baudrate2_srt , _ncurseszm0zi2_UIziNCurses_baudrate3_srt ) "_whline_set", referenced from: _s9gs_info in libHSncurses-0.2.a(NCurses.o) "_wvline_set", referenced from: _s9fL_info in libHSncurses-0.2.a(NCurses.o) "_cbreak", referenced from: _s9ZJ_info in libHSncurses-0.2.a(NCurses.o) _sc7P_info in libHSncurses-0.2.a(NCurses.o) "_endwin", referenced from: _ncurseszm0zi2_UIziNCurses_endwin_info in libHSncurses-0.2.a(NCurses.o) (maybe you meant: _ncurseszm0zi2_UIziNCurses_endwin_info, _ncurseszm0zi2_UIziNCurses_endwin_closure ) "_wattr_on", referenced from: _saal_info in libHSncurses-0.2.a(NCurses.o) _saal_info in libHSncurses-0.2.a(NCurses.o) _saal_info in libHSncurses-0.2.a(NCurses.o) _saal_info in libHSncurses-0.2.a(NCurses.o) _saal_info in libHSncurses-0.2.a(NCurses.o) _saal_info in libHSncurses-0.2.a(NCurses.o) _saal_info in libHSncurses-0.2.a(NCurses.o) _saal_info in libHSncurses-0.2.a(NCurses.o) _saal_info in libHSncurses-0.2.a(NCurses.o) "_newwin", referenced from: _s9du_info in libHSncurses-0.2.a(NCurses.o) "_getmouse", referenced from: _sfkP_info in libHSncurses-0.2.a(NCurses.o) "_touchwin", referenced from: _sa69_info in libHSncurses-0.2.a(NCurses.o) "_untouchwin", referenced from: _sa6c_info in libHSncurses-0.2.a(NCurses.o) "_has_colors", referenced from: _ncurseszm0zi2_UIziNCurses_supportsColor1_info in libHSncurses-0.2.a(NCurses.o) _s9ZN_info in libHSncurses-0.2.a(NCurses.o) "_mousemask", referenced from: _s9ZL_info in libHSncurses-0.2.a(NCurses.o) "_use_default_colors", referenced from: _s9ZS_info in libHSncurses-0.2.a(NCurses.o) "_waddwstr", referenced from: _sduP_info in libHSncurses-0.2.a(NCurses.o) "_wmove", referenced from: _sdBo_info in libHSncurses-0.2.a(NCurses.o) "_dupwin", referenced from: _scTH_info in libHSncurses-0.2.a(NCurses.o) "_keypad", referenced from: _ncurseszm0zi2_UIziNCurses_zdwa3_info in libHSncurses-0.2.a(NCurses.o) _say8_info in libHSncurses-0.2.a(NCurses.o) _say8_info in libHSncurses-0.2.a(NCurses.o) _scV0_info in libHSncurses-0.2.a(NCurses.o) "_noecho", referenced from: _sc50_info in libHSncurses-0.2.a(NCurses.o) "_flash", referenced from: _ncurseszm0zi2_UIziNCurses_flash1_info in libHSncurses-0.2.a(NCurses.o) (maybe you meant: _ncurseszm0zi2_UIziNCurses_flash1_closure, _ncurseszm0zi2_UIziNCurses_flash_info , _ncurseszm0zi2_UIziNCurses_flash_srt , _ncurseszm0zi2_UIziNCurses_flash_closure , _ncurseszm0zi2_UIziNCurses_flash1_info , _ncurseszm0zi2_UIziNCurses_flash2_info , _ncurseszm0zi2_UIziNCurses_flash3_closure , _ncurseszm0zi2_UIziNCurses_flash1_srt , _ncurseszm0zi2_UIziNCurses_flash2_srt , _ncurseszm0zi2_UIziNCurses_flash2_closure , _ncurseszm0zi2_UIziNCurses_flash3_info , _ncurseszm0zi2_UIziNCurses_flash3_srt ) "_wborder_set", referenced from: _scFt_info in libHSncurses-0.2.a(NCurses.o) "_COLS", referenced from: _COLS$non_lazy_ptr in libHSncurses-0.2.a(NCurses.o) (maybe you meant: _COLS$non_lazy_ptr) "_init_pair", referenced from: _saTg_info in libHSncurses-0.2.a(NCurses.o) _saTg_info in libHSncurses-0.2.a(NCurses.o) _saTg_info in libHSncurses-0.2.a(NCurses.o) _saTg_info in libHSncurses-0.2.a(NCurses.o) _saTg_info in libHSncurses-0.2.a(NCurses.o) _saTg_info in libHSncurses-0.2.a(NCurses.o) _saTg_info in libHSncurses-0.2.a(NCurses.o) _saTg_info in libHSncurses-0.2.a(NCurses.o) _scdx_info in libHSncurses-0.2.a(NCurses.o) _scdx_info in libHSncurses-0.2.a(NCurses.o) _scdx_info in libHSncurses-0.2.a(NCurses.o) _scdx_info in libHSncurses-0.2.a(NCurses.o) _scdx_info in libHSncurses-0.2.a(NCurses.o) _scdx_info in libHSncurses-0.2.a(NCurses.o) _scdx_info in libHSncurses-0.2.a(NCurses.o) _scdx_info in libHSncurses-0.2.a(NCurses.o) "_nocbreak", referenced from: _sc7P_info in libHSncurses-0.2.a(NCurses.o) "_delwin", referenced from: _sb4T_info in libHSncurses-0.2.a(NCurses.o) "_getcurx", referenced from: _s9Iy_info in libHSncurses-0.2.a(NCurses.o) "_getcury", referenced from: _s9Ix_info in libHSncurses-0.2.a(NCurses.o) "_color_content", referenced from: _sff4_info in libHSncurses-0.2.a(NCurses.o) "_COLOR_PAIRS", referenced from: _COLOR_PAIRS$non_lazy_ptr in libHSncurses-0.2.a(NCurses.o) (maybe you meant: _COLOR_PAIRS$non_lazy_ptr) "_wattr_get", referenced from: _s9vO_info in libHSncurses-0.2.a(NCurses.o) "_wattr_off", referenced from: _saaF_info in libHSncurses-0.2.a(NCurses.o) _saaF_info in libHSncurses-0.2.a(NCurses.o) _saaF_info in libHSncurses-0.2.a(NCurses.o) _saaF_info in libHSncurses-0.2.a(NCurses.o) _saaF_info in libHSncurses-0.2.a(NCurses.o) _saaF_info in libHSncurses-0.2.a(NCurses.o) _saaF_info in libHSncurses-0.2.a(NCurses.o) _saaF_info in libHSncurses-0.2.a(NCurses.o) _saaF_info in libHSncurses-0.2.a(NCurses.o) "_wattr_set", referenced from: _s9vS_info in libHSncurses-0.2.a(NCurses.o) "_LINES", referenced from: _LINES$non_lazy_ptr in libHSncurses-0.2.a(NCurses.o) (maybe you meant: _LINES$non_lazy_ptr) ld: symbol(s) not found collect2: ld returned 1 exit status

3 3

GHC 7.0.2 and haddock
by Maciej Marcin Piechotka 06 Mar '11

06 Mar '11

Is there any version of haddock that builds with ghc 7.0.2? For 2.9.1 I get: src/Haddock/Interface/Create.hs:282:11: Couldn't match expected type `Located b0' with actual type `[LTyClDecl id0]' Expected type: HsGroup id0 -> [Located b0] Actual type: HsGroup id0 -> [[LTyClDecl id0]] In the first argument of `mkDecls', namely `hs_tyclds' In the first argument of `(++)', namely `mkDecls hs_tyclds TyClD group_' Regards

3 2

Re: [Haskell-cafe] Use of uninstantiated type class
by John Lato 05 Mar '11

05 Mar '11

> Message: 8 > Date: Sat, 5 Mar 2011 00:45:33 +0100 > From: Yves Par?s <limestrael(a)gmail.com> > Subject: [Haskell-cafe] Use of uninstantiated type class > To: Haskell-Cafe <haskell-cafe(a)haskell.org> > Message-ID: > <AANLkTimBg5TyG6ZNWCKaOT9dP=QE95MtC=q_t7RRPQgv(a)mail.gmail.com> > Content-Type: text/plain; charset="iso-8859-1" > > Hello, > > For testing purposes, I am trying to make an overlay to IO which carries a > phantom type to ensure a context. > I define contexts using empty type classes : > > class CtxFoo c > class CtxBar c > > The overlay : > > newtype MyIO c a = MyIO (IO a) > > Then I define some methods that run only a specific context : > > runFoo :: (CtxFoo c) => MyIO c a -> IO a > runFoo (MyIO x) = x > > runBar :: (CtxBar c) => MyIO c a -> IO a > runBar (MyIO x) = x > > And then an action that runs in context 'Foo' : > > someAction :: (CtxFoo c) => MyIO c () > someAction = putStrLn "FOO" > > Then I run it : > > main = runFoo someAction > > But obiously, GHC complains that my type 'c' remains uninstantiated : > > Ambiguous type variable `c' in the constraint: > (CtxFoo c) arising from a use of `runFoo' > Probable fix: add a type signature that fixes these type variable(s) > In the expression: runFoo someAction > In an equation for `main': main = runFoo someAction > > > Is there a way to deal with this ? > The interest of using type classes and not empty types to represent the > contexts is that it stays simple, and that I can do that : > > someAction2 :: (CtxFoo c, CtxBar c) => MyIO c () > someAction2 = putStrLn "FOO and BAR" > > ... a function that can run in both contexts. > You can accomplish this with Rank2Types (and ScopedTypeVariables). Try this: class CtxFoo c class CtxBar c data Ctx instance CtxFoo Ctx where instance CtxBar Ctx where runFoo :: forall a. (forall c. (CtxFoo c) => MyIO c a) -> IO a runFoo x = case (x :: MyIO CtxFooD a) of (MyIO x') -> x' It's useful to compare the type of this "runFoo" with the old "runFoo" *Main> :t runFoo runFoo :: (forall c. CtxFoo c => MyIO c a) -> IO a *Main> :t runFooOld runBar :: CtxFoo c => MyIO c a -> IO a Note that the "c" type var is no longer universally quantified. This means that "runFoo" can't be used with any actions that specify a concrete context, the action must specify only the "CtxFoo" type class. There's a drawback to this approach though. The number of "run" functions is combinatorial in the number of contexts. With only two contexts, you already need "runFoo", "runBar", and "runFooBar". Unless you'll only ever need a single context, or you won't need to have combinations of them, this approach quickly grows unwieldy. John

1 0

Thoughts on program annotations.
by Jason Dusek 05 Mar '11

05 Mar '11

Hi List, I am working on a Bash config generation system. I've decided to factor out the Bash AST and pretty printer, here in a pre-release state: https://github.com/solidsnack/bash One thing I'd like to support is generic annotations, so that at a future time I can add (and render) comments, mark subscripts with what privilege (package install, sudo) they require or otherwise characterize the script outside its lexical structure. I ended up making my statement type a Functor with a Foldable instance. Given that every statement has an annotation, it seemed better to me to use mutually recursive datatypes, using one datatype to capture "annotatedness", like this: -- From https://github.com/solidsnack/bash/blob/c718de36d349efc9ac073a2c7082742c456… data Annotated t = Annotated t (Statement t) data Statement t = SimpleCommand Expression [Expression] | ... | IfThen (Annotated t) (Annotated t) | ... I wonder what folks think of this approach? It does mean I end up with all leaf-level annotations being potentially without annotations; this allows for relatively generic definitions, on the one hand; but forces type annotations at the use-site in many cases. It also means I have mutually recursive Functor and Foldable instances. Another option for annotations would be a sort of tree of zippers pointing in to the statement tree; this seems horrible at first glance since it leaves open the question of how the annotations are associated with their nodes in the first place. However, it does have the nice feature of simplifying the type of statements and also is just much more modular feeling. What does the list think? -- Jason Dusek Linux User #510144 | http://counter.li.org/

4 5

ANN: hmpfr-0.3.2 (requires integer-simple, supports mpfr 3.0.0)
by Michal Konečný 04 Mar '11

04 Mar '11

Dear all, I am pleased to announce hmpfr-0.3.2, a new version of Aleš Bizjak's bindings to the MPFR arbitrary precision floating point arithmetic library. The changes in this version are quite small but significant: - support for MPFR 3.0.0 as well as MPFR 2.4.* - dependency on integer-simple instead of integer-gmp The latter is most significant because unfortunately it makes it rather more difficult to install hmpfr. Currently almost all binary distributions of ghc have integer-gmp compiled in to provide the Integer type via the standard GMP library. Also haskell platform 2010.2.0.0 assumes that ghc has been compiled with integer-gmp although it makes no specific use of it. Instructions on how to compile ghc and haskell platform with integer-simple instead of integer-gmp are on: http://code.google.com/p/hmpfr/wiki/GHCWithoutGMP The rationale for this change is the fact that despite much effort hmpfr is very unreliable on ghc that includes integer-gmp due to ghc deallocating GMP data that was allocated by MPFR at unpredictable times. Aleš and I hope that hmpfr can return to using integer-gmp once the proposal http://hackage.haskell.org/trac/ghc/wiki/ReplacingGMPNotes#BinaryDropinRepl… to replace gmp with a modified gmp in ghc is implemented and made the default. Best regards, Michal -- |o| Michal Konecny <mikkonecny(a)gmail.com> |o| http://www-users.aston.ac.uk/~konecnym/ |o| office: (+42) (0)121 204 3462 |o| PGP key http://www-users.aston.ac.uk/~konecnym/ki.aston

3 5

Re: [Haskell-cafe] ANN: hmpfr-0.3.2 (requires integer-simple, supports mpfr 3.0.0)
by Michal Konečný 04 Mar '11

04 Mar '11

Hi Dan, On Friday 04 Mar 2011 21:59:12 Daniel Peebles wrote: > I'm adding Ed to the conversation as he's very interested in this topic, > too. I do apologise - I was meant to post the previous email back to haskell-cafe but by mistake it went only to you. I hope you do not mind that I am taking the discussion back to the cafe. I attach my email so that other readers of the cafe can see it. > The experts were right about it being impossible to work with GHC's > GMP – until recently. "foreign import c" calls are indeed going to call GC > when you don't want it, but when they split integer-gmp out of GHC's own > RTS, Duncan Coutts (one of those experts) added the "foreign import prim" > construct so that he could do exactly what you want, and operate on GMP > integers with GHC-allocated memory without worrying about temporary > storage blowing up while you aren't looking. > > So in general, I'd lean more towards replacing all your ccall bindings to > MPFR with cmm bindings. It does require some GHC internals knowledge but > is fairly mechanical, and would solve all the problems, without requiring > a rewrite of GMP (that would be slower anyway). > > Ed is actually going to get started on a fairly simple binding to a subset > of MPFR for one of his projects, using the CMM approach based on the > structure of my natural-gmp package > (https://github.com/pumpkin/natural-gmp, which is itself based heavily on > integer-gmp, but reworked to work fine from cabal rather than depending on > GHC's build process). Once he is done with that, you might want to refer > to his implementation to make your more complete MPFR binding work with > integer-gmp (and thus make no speed sacrifices). If this is the best approach, I would welcome help with this as I will not have much time to work on it until the summer due to teaching commitments and the need to publish work done earlier. > I would also like a gmp-compatible replacement, but it's going to > necessarily be slower and would prefer to be able to have fast > computations over floating-point numbers AND integers/naturals. Eek, I made a mistake, I apologise again - the proposal I was quoting in the announcement is not what I had in mind. I was meant to refer to a mention by igloo at the very end of http://hackage.haskell.org/trac/ghc/ticket/311 which is a very different proposal from the one I linked to and the one you seem to refer to here. I was not at all thinking of writing a gmp compatible replacement. I was thinking of taking gmp sources and mechanically modify the exported names and modify integer-gmp to use those modified names. Thus there would be no difference in the speed of Integer as it would still use an exact clone of the original gmp in exactly the same way as now but not interfere with what the usual gmp code does via other libraries. Please correct me if I this approach is not feasible or if there is some advantage in using cmm over this proposal that I am missing. Michal -- |o| Michal Konecny <mikkonecny(a)gmail.com> |o| http://www-users.aston.ac.uk/~konecnym/ |o| office: (+42) (0)121 204 3462 |o| PGP key http://www-users.aston.ac.uk/~konecnym/ki.aston

1 0

Announce: new releases of bitset and funsat
by Denis Bueno 04 Mar '11

04 Mar '11

Hello all, Just a small announcement. funsat has been bumped to 0.6.2. New in 0.6.2: works with ghc-6.12 and fixed some space leaks. http://hackage.haskell.org/package/funsat bitset has been bumped to 1.1. New in 1.1: can easily convert between the BitSet representation and the underlying Integer. http://hackage.haskell.org/package/bitset -- Denis

1 0

darcs hacking sprint #6 (1-3 April, Paris)
by Eric Kow 04 Mar '11

04 Mar '11

Hi everybody, Following up on my last message, the date and venue for the sixth Darcs Hacking sprint has been confirmed. Get out your berets everybody, because we're going to Paris! Here are three things to know 1. Everybody is welcome to join us. We'd love to have you, whatever your Haskell or Darcs hacking experience. Also, if you've got a wacky idea for the future of version control, or a cool use for the Darcs library, you should join us too :-) 2. Please let us know if you're attending. Just add your name to http://wiki.darcs.net/Sprints/2011-04 and you're good to go. You can also send us an email. 3. We can reimburse travel costs (within reason!). Let us know if you'd like a reimbursement, and save your receipts. Many thanks to everybody who participated in our fundraising drives or who gave money on the side. Thanks also to the Software Freedom Conservancy for making fundraising and reimbursements so painless! If you can't join us in person, but you'd like to cheer us on, say hello at http://darcs.net/donations.html! Looking forward to seeing you! Eric PS. Berets optional. -- Eric Kow <http://www.nltg.brighton.ac.uk/home/Eric.Kow> For a faster response, try +44 (0)1273 64 2905 or xmpp:kowey@jabber.fr (Jabber or Google Talk only)

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A practical Haskell puzzle
by Yitzchak Gale 04 Mar '11

04 Mar '11

You have written a large software system in Haskell. Wishing to play to Haskell's strength, you have structured your system as a series of composable layers. So you have data types Layer1, Layer2, ... and functions layer2 :: Layer1 -> Layer2 layer3 :: Layer2 -> Layer3 ... etc. Of course you'll want to be able to run any range of the layers separately, at least for testing and debugging purposes if not for the functionality itself. So your UI module (command line or whatever) that launches your application provides a data type data Layers = Layers Int Int that indicates which layers to run, and functions deserialize1 :: L.ByteString -> Layer1 deserialize2 :: L.ByteString -> Layer2 ... serialize1 :: Layer1 -> L.ByteString serialize2 :: Layer2 -> L.ByteString ... etc. Now you need a function runLayers :: Layers -> L.ByteString -> L.ByteString so that the effect is for example runLayers (Layers 4 6) = serialize6 . layer6 . layer5 . deserialize4 Typically there could be 20 or 30 layers, so writing out each case could result in hundred of boilerplate definitions for runLayers. Scripting the generation of all that boilerplate, e.g. using TH, doesn't seem very attractive either. On the other hand, it seems silly to have to use super-advanced type olegery for such a trivially simple yet centrally important component of the system. What is the best way to write runLayers? Feel free to change the details of the above design, as long as it meets the functionality requirements expressed. Regards, Yitz

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ANN: Haskell XML Toolbox Version 9.1
by Uwe Schmidt 04 Mar '11

04 Mar '11

Haskell XML Toolbox 9.1 I would like to announce an update hxt-9.1 of the Haskell XML Toolbox. Main changes compared to hxt-9.0 are * space optimization of DOM tree for better performance for lager XML documents * optimization of space used during parsing in native XML and HTML parsers * a binding to the expat parser via hexpat Cheers, Uwe

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Getting started with http-enumerator
by C K Kashyap 04 Mar '11

04 Mar '11

Hi, I'd like to use http-enumerator for things that I've been using perl/Lwp for. I tried looking but was not able to find good documentation for it. Could someone please point me to simple examples? Like posting a form, dealing with cookies etc. Regards, Kashyap

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Project structure
by Hauschild, Klaus (EXT) 04 Mar '11

04 Mar '11

Hi Haskellers, is there a recommended structure for Haskell projects. I like the Maven way (http://maven.apache.org/guides/introduction/introduction-to-the-standard-di…) for Java projects. How to separate productive from test code, how to separate source code from other resources? Thanks Klaus

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ANN: cabal-dev-0.7.4.0
by Rogan Creswick 04 Mar '11

04 Mar '11

We're happy to announce that cabal-dev-0.7.4.0 is now on hackage. We strongly suggest that everyone upgrade to this release, since this release specifically addresses changes in Cabal-1.10 and newer, which the latest cabal-install now uses. The ticket for the bug is here, for anyone interested: https://github.com/creswick/cabal-dev/issues/2 --Rogan

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