- Haskell-Cafe - Haskell.org

Deploying a Binary Haskell Package
by John Van Enk 19 Nov '08

19 Nov '08

This question isn't directly related to Haskell, but I figure some one might know here. I want to deploy an application. I could either: 1) Tell people how to download GHC, have them check out the repository, have them install all the needed hackage packages, ... or 2) Give them a setup.msi/exe I'm curious if any one has done this with a Haskell package. It seems that it's something that might make sense being integrated into Cabal (runhaskell Setup msi). Either way, has some one deployed a Haskell binary as a MSI package? /jve

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Proof of a multi-threaded application
by Silviu ANDRICA 18 Nov '08

18 Nov '08

Hello, I am very new to Haskell, this is my first day, and I wanted to know if it is possible to prove correctness of a multi-threaded application written in Haskell. Basically, I want to check that a multi-threaded implementation of an algorithm that detects cycles in a dynamically changing graph, actually detects the cycles. Also, the algorithm prevents previously detected cycles from happening by not allowing certain edges to be added. And I want to check that this property also holds. Thank you and I hope you can help me, Silviu ANDRICA.

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Re: [Haskell-cafe] implementing python-style dictionary in Haskell
by Tillmann Rendel 18 Nov '08

18 Nov '08

Hello Alberto, I cc this to haskell-cafe again. Alberto G. Corona wrote: > Not so much memory, because data is referentially transparent, the new Map > can point to whole subtrees of the old map that stay the same. is similar > than when a new list is created by prefixing a new element from a old list > ys= x:xs. ys is not at all a fresh copy, but x plus a pointer to the head > of xs. this is the only new data that is needed to create ys. You could just as well compare with appending a new element to the end of the list, which needs a complete copy of the list structure to be made. One has to look more closely to see which case it is here. More specifically, I do not see how this sharing of substructures could be employed in the implementation of hash tables, which rely on O(1) random access into arrays. Tillmann

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Re: Statically dimension-checked hmatrix
by Patrick Perry 18 Nov '08

18 Nov '08

> What is the situation regarding statically dimension-checked linear > algebra libraries? It seems that Frederik Eaton was working on one in > 2006 (see the paper "Statically typed linear algebra in Haskell"), and > he produced the Vectro library from this, based on GSLHaskell. > > Are there any more recent efforts into this, particularly using the > new TFs? If not, I might have a go at it, as a thin wrapper for > hmatrix. The BLAS bindings I wrote use phantom types to make sure the dimensions are consistent. See, for example the functions to get row and column views of a matrix: http://hackage.haskell.org/packages/archive/blas/0.6/doc/html/Data-Matrix-D… Also, the multiplication routines: http://hackage.haskell.org/packages/archive/blas/0.6/doc/html/BLAS-Matrix-I… I've found that phantom types are a good trade off: they provide enough type safety to catch common mistakes without being too much of a hassle to use. Another benefit (which I didn't anticipate) is that they help a *lot* with documentation. I'm skeptical of value that comes from stronger typing. At some point the types become too much of a hassle to be worth using. Even phantom types get in the way sometimes and require use of either GADTs, unsafeCoerce, or both, which is annoying. I'd be interested to hear about any developments you make in this area. Patrick p.s. If you're interested in trying it out, the version of blas on hackage doesn't compile with ghc-6.10.1, but the version in the darcs repository at http://stat.stanford.edu/~patperry/code/blas does.

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simple generic / data view library?
by Conal Elliott 18 Nov '08

18 Nov '08

Is there a simple existing library that provides views of data types in terms of unit, product and sum? Here's what I threw together for my own use. I used associated types, though functional dependencies would work as well. class HasView t where type View t view :: t -> View t unview :: View t -> t -- View instances instance HasView (Maybe a) where type View (Maybe a) = Either () a view Nothing = (Left ()) view (Just a) = (Right a) unview (Left ()) = Nothing unview (Right a) = (Just a) instance HasView [a] where type View [a] = Either () (a,[a]) view [] = (Left ()) view (a:as) = (Right (a,as)) unview (Left ()) = [] unview (Right (a,as)) = (a:as) onView2 :: (HasView a, HasView b, HasView c) => (View a -> View b -> View c) -> (a -> b -> c) onView2 op a b = unview (view a `op` view b) Thanks, - Conal

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Statically dimension-checked hmatrix
by Reiner Pope 18 Nov '08

18 Nov '08

Hi, What is the situation regarding statically dimension-checked linear algebra libraries? It seems that Frederik Eaton was working on one in 2006 (see the paper "Statically typed linear algebra in Haskell"), and he produced the Vectro library from this, based on GSLHaskell. Are there any more recent efforts into this, particularly using the new TFs? If not, I might have a go at it, as a thin wrapper for hmatrix. Cheers, Reiner

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Find unused exports
by Jason Dagit 18 Nov '08

18 Nov '08

Hello, Has anyone already made a tool to check if exported functions, data constructors, types, etc are unused within a set of modules? For my usage it would probably suffice if the tool only compared import lists against export lists as we compile with -Wall and 99% of our imports say exactly which names are imported (and that last 1% could easily be fixed to say as well). If the tool doesn't already exist is there an easy way to approximate it? Thanks, Jason

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How to make interface IO() to IO a in a command-driven tool
by Kyongho Min 18 Nov '08

18 Nov '08

Dear Haskell users, I am working on a command-driven tool (::IO ()). If the system invokes itself again, and the system's returned data type would be 'IO a', say (IO Exp) (Expression). tool:: a -> IO() The nested tool invocation returns (IO Exp) to the previous tool. I am using dynamic error exception handling like (throwDyn exp). If I use 'forkIO', then it works for this situation (e.g. IO Exp) but it is not working for 'quit' command (quit the tool:: thread blocked indefinitely) - quit the subtool and return to the previous tool. Any suggestion would be helpful? tool = {tool1, tool2, tool3, ...} tool1:: (IO ()) invoked tool2:: (IO a) may invoked tool3:: (IO a) tool2 is working basically on IO() and if I got the Exp (proved), then return it to the previous tool (say tool1). Thanks in advance, min

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Haskell Weekly News: Issue 93 - November 15, 2008
by Brent Yorgey 17 Nov '08

17 Nov '08

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20081115 Issue 93 - November 15, 2008 --------------------------------------------------------------------------- Welcome to issue 93 of HWN, a newsletter covering developments in the [1]Haskell community. Community News Congratulations to Ganesh (aka Heffalump) and Amanda on the [2]birth of Alexander Suresh Kerr Sittampalam! Announcements bustle-0.1. Will Thompson [3]announced the [4]release of [5]Bustle, a tool to show diagrams of D-Bus traffic for profiling purposes. It consists of a small C executable to log traffic, and a Gtk+ application which draws diagrams using Cairo. haskell-src-exts 0.4.1. Niklas Broberg [6]announced a new major release of the [7]haskell-src-exts package, an extension of the standard haskell-src package which handles most common syntactic extensions to Haskell. The new release features a cleaned up AST and names without ugly disambiguation prefixes. darcs 2.1.1rc2. Eric Kow (kowey) [8]announced the release of [9]darcs 2.1.1rc2, which adds support for GHC 6.10.1. It also includes a Windows bug fix. If you're using GHC 6.10.1 or Windows, give it a try and let the darcs development team know how it works. hpapi 0.1 release. Michael D. Adams [10]announced the first release of [11]hpapi, Performance API (PAPI) bindings for Haskell. PAPI provides access to various CPU counters such as cache-miss, instruction and pipeline stall counts. Workflow-0.1. Alberto G. Corona [12]announced the release of [13]Workflow, a library for transparent execution of computations across shutdowns and restarts. Reactive library (FRP) and mailing list. Conal Elliott [14]announced the release of [15]Reactive, a library for functional reactive programming (FRP), similar to the original [16]Fran but with a more modern interface (using standard type classes) and a hybrid push/pull implementation. It is designed to be used in a variety of contexts, such as interactive 2D and 3D graphics, graphical user interfaces, web services, and automatic recompilation/re-execution. There is also now a [17]mailing list and a [18]feature/bug tracker. ANN (sorta): OpenGL with extra type safety. Neal Alexander [19]announced a modification of the hOpenGL (and GLFW) source tree to force extra type checking on its various IO actions using the -XGeneralizedNewtypeDeriving extension. The main motivation was for writing concurrent OpenGL applications; the second motivation was to enforce static type checking on commands that can only be executed in certain OpenGL contexts (sending vertex data for example). Hopefully the code will be uploaded to Hackage as a separate package soon. FieldTrip library (functional 3D) and mailing list. Conal Elliott [20]announced the release of [21]FieldTrip, a library for functional 3D graphics. It is intended for building static, animated, and interactive 3D geometry, efficient enough for real-time synthesis and display. FieldTrip also has a [22]mailing list and a [23]feature/bug tracker. gitit 0.2 release - wiki using HAppS, git, pandoc. John MacFarlane [24]announced the upload of an early version of [25]gitit, a Haskell wiki program, to HackageDB. Gitit uses HAppS as a webserver, git for file storage, pandoc for rendering the (markdown) pages, and highlighting-kate for highlighted source code. You can [26]try it out here. Comments and patches welcome. Discussion Proof that Haskell is RT. Andrew Birkett [27]asked whether there exists a formal proof that the Haskell language is referentially transparent. Such a thing cannot exist, since Haskell has no formally defined semantics, but an interesting discussion about referential transparency and semantics ensued anyway. What *not* to use Haskell for. Dave Tapley [28]asked how people answer the question, "what does Haskell not do well?" Unfortunately, it seems that there is no good answer to this question and the thread degenerated into a discussion of all the great things you can do with Haskell. If only Haskell sucked more. Blog noise [29]Haskell news from the [30]blogosphere. * Braden Shepherdson: [31]Pimp Your XMonad #2: SmartBorders. The second in Braden's series on customising xmonad explains how to use the NoBorders extension to get rid of window borders when you don't want them. * Real-World Haskell: [32]Real World Haskell Electronic Edition Now On Sale. * Conal Elliott: [33]More beautiful fold zipping. * >>> Stephen: [34]Endless Cavern. A procedurally-generated tessellated-cavern flying game. * Twan van Laarhoven: [35]Arrays without bounds. Unbounded arrays (with O(1) amortized access) in Haskell! * "The GHC Team": [36]Comparing concurrent linked-list implementations in Haskell. * Ketil Malde: [37]454 sequencing and parsing the SFF binary format. * Tom Schrijvers: [38]Type Invariants for Haskell. Tom, Louis-Julien Guillemette, and Stefan Monnier's paper on Type Invariants for Haskell, which was recently accepted at PLPV'09. * Conal Elliott: [39]Another lovely example of type class morphisms. Conal elaborates on Max Rabkin's recent post on composable folds. * Real-World Haskell: [40]Beautiful Parallelism: Harnessing Multicores with Haskell. Don Stewart will be talking about programming mainstream multicore systems with Haskell at SC'08 next week in Austin, Texas. * Luke Palmer: [41]Sketch of Udon (Version Control/Packaging system). Luke sketches a high-level design for a distributed storage system that could be used as the basis for solving a number of interesting problems. * Galois, Inc: [42]Galois awarded NASA research contract. * Mark Jason Dominus: [43]Representing ordinal numbers in the computer and elsewhere. * The GHC Team: [44]Bootstrapping cabal-install. * Jason Dagit: [45]Phantom Types, Existentials and Controlling Unification -- Part 1. * Ben Moseley: [46]Why does Functional Programming matter?. Quotes of the Week * BMeph: In a functional world, students would ask how that index shadowing works in those funny 'for' statements... * digit: i'm almost annoyed at how brilliant xmonad is. * _pizza_: i think Haskell is undoubtedly the world's best programming language for discovering the first few dozen numbers in the Fibonacci sequence over IRC. * adu: let uncat3 [] = [] ; uncat3 xs = (let (ys, zs) = splitAt 3 xs in ys : uncat3 zs) ; getFrom x y = map (x !!) $ map (fromIntegral . ((\x -> fromIntegral $ foldl (.|.) (0::Word8) (zipWith (\c n -> if c then bit n else (0::Word8)) x [0..2])) :: [Bool] -> Int)) $ reverse . uncat3 . reverse . concat . map (((\x -> map (testBit x) [7,6..0]) :: Word8 -> [Bool]) . fromIntegral . ord) $ y in getFrom " HWdelor" "e\184-\235" * Beelsebob: ((:[]) "pigs eat") <^(++)^> ((:[]) " robot monkies") About the Haskell Weekly News New editions are posted to [47]the Haskell mailing list as well as to [48]the Haskell Sequence and [49]Planet Haskell. [50]RSS is also available, and headlines appear on [51]haskell.org. To help create new editions of this newsletter, please see the information on [52]how to contribute. Send stories to byorgey at cis dot upenn dot edu. The darcs repository is available at darcs get [53]http://code.haskell.org/~byorgey/code/hwn/ . References 1. http://haskell.org/ 2. http://urchin.earth.li/aegean/baby/ 3. http://www.haskell.org//pipermail/haskell-cafe/2008-November/050626.html 4. http://people.collabora.co.uk/~wjt/bustle/releases/bustle-0.1.tar.gz 5. http://resiak.livejournal.com/59590.html 6. http://www.haskell.org//pipermail/haskell-cafe/2008-November/050634.html 7. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/haskell-src-exts… 8. http://www.haskell.org//pipermail/haskell-cafe/2008-November/050378.html 9. http://darcs.net/darcs-2.1.1rc2.tar.gz 10. http://article.gmane.org/gmane.comp.lang.haskell.general/16612 11. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hpapi 12. http://article.gmane.org/gmane.comp.lang.haskell.general/16607 13. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Workflow 14. http://article.gmane.org/gmane.comp.lang.haskell.general/16604 15. http://haskell.org/haskellwiki/Reactive 16. http://conal.net/Fran 17. http://www.haskell.org/mailman/listinfo/reactive 18. http://trac.haskell.org/reactive 19. http://article.gmane.org/gmane.comp.lang.haskell.cafe/47458 20. http://article.gmane.org/gmane.comp.lang.haskell.cafe/47416 21. http://haskell.org/haskellwiki/FieldTrip 22. http://www.haskell.org/mailman/listinfo/FieldTrip 23. http://trac.haskell.org/FieldTrip 24. http://article.gmane.org/gmane.comp.lang.haskell.cafe/47384 25. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/gitit 26. http://johnmacfarlane.net:5001/ 27. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/47569 28. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/47491 29. http://planet.haskell.org/ 30. http://haskell.org/haskellwiki/Blog_articles 31. http://braincrater.wordpress.com/2008/11/15/pimp-your-xmonad-2-smartborders/ 32. http://www.realworldhaskell.org/blog/2008/11/15/real-world-haskell-electron… 33. http://feeds.feedburner.com/~r/conal/~3/453765396/ 34. http://www.maths.tcd.ie/~icecube/2008/11/endless-cavern/ 35. http://twan.home.fmf.nl/blog/haskell/UnboundedArray.details 36. http://ghcmutterings.wordpress.com/2008/11/14/comparing-concurrent-linked-l… 37. http://blog.malde.org/index.php/2008/11/14/454-sequencing-and-parsing-the-s… 38. http://tomschrijvers.blogspot.com/2008/11/type-invariants-for-haskell.html 39. http://feeds.feedburner.com/~r/conal/~3/452607365/ 40. http://www.realworldhaskell.org/blog/2008/11/12/beautiful-parallelism-harne… 41. http://lukepalmer.wordpress.com/2008/11/12/sketch-of-udon-version-controlpa… 42. http://www.galois.com/blog/2008/11/11/galois-awarded-nasa-research-contract/ 43. http://blog.plover.com/math/ordinals.html 44. http://ghcmutterings.wordpress.com/2008/11/10/bootstrapping-cabal-install/ 45. http://blog.codersbase.com/2008/11/10/phantom-types-existentials-and-contro… 46. http://nattermorphisms.blogspot.com/2008/11/why-does-functional-programming… 47. http://www.haskell.org/mailman/listinfo/haskell 48. http://sequence.complete.org/ 49. http://planet.haskell.org/ 50. http://sequence.complete.org/node/feed 51. http://haskell.org/ 52. http://haskell.org/haskellwiki/HWN 53. http://code.haskell.org/~byorgey/code/hwn/

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HAPPS on a major hosting provider?
by Jefferson Heard 17 Nov '08

17 Nov '08

I was wondering if anyone's ever tried to run Haaps on a major hosting provider, like oh, say Site5? I have an app I'd otherwise use Rails for and I thought I'd give Haaps a try... -- Jeff I try to take things like a crow; war and chaos don't always ruin a picnic, they just mean you have to be careful what you swallow. -- Jessica Edwards

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Good name for this operator?
by Ariel J. Birnbaum 16 Nov '08

16 Nov '08

Hi all! When working with Applicative, I often find myself defining and using this operator: (<%>) :: (Applicative f) => f (a -> b) -> a -> f b f <%> x = f <*> pure x and always keep wondering whether it is already known by another name. Can't find it in Control.Applicative. Hoogle didn't give me much either. NB: In general, there's a weird obstacle I notice when writing Haskell: the unshakable feeling that whatever I write, there's already a better name for it and a more elegant implementation lying around. It can get downright paralyzing at times *shudder* Have Fun, -- Ariel J. Birnbaum

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ANNOUNCE: haskell-src-exts 0.4.1
by Niklas Broberg 16 Nov '08

16 Nov '08

Fellow Haskelleers, it is my pleasure to announce the new release of the haskell-src-exts package, version 0.4.1: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/haskell-src-exts… darcs get http://code.haskell.org/HSP/haskell-src-exts This is a new "major" release, the first of the 0.4 branch, and as such it is not backwards compatible with the releases in the 0.3 branch. This is due to two major changes to the design of the library: 1) The AST has been cleaned up, by splitting Haskell expressions in the AST from the "expressions" used while parsing to represent both expressions and patterns. This means that the datatype for expressions will no longer contain constructors for things like wildcards and irrefutable patterns. It now only contains constructors for actual Haskell expressions. If you have been using haskell-src-exts previously, this change should not bite you at all unless you have abused these ugly hacks in the AST, so it is *almost* backwards compatible. However... 2) ... I've finally decided to take the plunge and get rid of the ugly prefixes on all datatypes in the AST. I am of the firm conviction that disambiguation between datatypes and functions with the same name should be handled through the module hierarchy and qualified imports, not by adding prefixes. And the longer I wait, the harder the switch. So now the datatypes that make up the AST are called things like Exp, Pat, Module (the former Module is now ModuleName), Type, QOp etc instead of HsExp, HsPat... . The migration from 0.3.x to 0.4.1 should be really simple: i) replace all occurences of Module with ModuleName ii) remove all occurences of Hs This release also contains a number of smaller, fully backwards compatible bug fixes. These are available for the 0.3 branch in the 0.3.12 release that will mark the end of that branch: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/haskell-src-exts… No further bug fixes or features will be implemented for it, and I urge you to migrate as early as possible, it really isn't hard. :-) Cheers and Happy Haskelling, /Niklas

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GHC 6.10 and scoped variables
by Hugo Pacheco 15 Nov '08

15 Nov '08

Hi, When migrating some code with type families to GHC 6.10, I frequently get the same error. The deal is. If I define some type family and instance: *type family Rep (f :: * -> *) x :: * data (g :+: h) x = Inl (g x) | Inr (h x) type instance Rep (g :+: h) x = Rep g x `Either` Rep h x* and then define a function that has a scoped argument: *test :: Rep (g :+: h) x -> y test (Left x :: Rep (g :+: h) x) = undefined* I get the error: * Pattern signature must exactly match: Rep (g :+: h) x In the pattern: Left x :: Rep (g :+: h) x In the definition of `test': test (Left x :: Rep (g :+: h) x) = undefined* Is this error expected? At least the error message is not clear... Interestingly, when experimenting with a different functor, I get the impossible: * newtype Const t x = Const {unConst :: t} type instance Rep (Const t) x = t** **test2 :: Rep (Const t) x -> y test2 x = undefined* *ghc: panic! (the 'impossible' happened) (GHC version 6.10.1 for i386-unknown-linux): readFilledBox x{tv aoB} [box] Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug > * Sorry for the extensiveness. Thanks, hugo -- www.di.uminho.pt/~hpacheco

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HSDL 0.5.4 on GHC 6.10.1
by Korcan Hussein 15 Nov '08

15 Nov '08

Hi the package at hackage fails to build on GHC 6.10.1 (on windows mingw) this is due to 2 reasons: 1. I believe the order of libraries to be linked needs to change from "-lmingw32 -lSDLmain -lSDL" to "-lSDLmain -lSDL -lmingw32" otherwise you get linker errors which multiple definitions of main. I think the build system should output `sdl-config --cflags --libs` instead of explicitly stating which libraries besides. 2. For some reason the the library & include paths plus the list of which libraries to be linked gets appened to the output twice and thus causing linker errors. I'm a casual user of haskell so I don't much about cabal packages so I manged to figure out a hackish workaround by deleting the entry in the SDL.buildinfo file (the entry for the ld-options). _________________________________________________________________ Win £1000 John Lewis shopping sprees with BigSnapSearch.com http://clk.atdmt.com/UKM/go/117442309/direct/01/

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Re: Haskell-Cafe Digest, Vol 63, Issue 23
by John Lato 15 Nov '08

15 Nov '08

You could use HSoundFile, but I wouldn't recommend it for this specific case. I'm not extremely familiar with the Haskell OpenAL bindings, but IIRC they take buffers (pointers). Since HSoundFile marshals data to [Double], you'd then have to convert it back to CWord16 array. Seems wasteful and slow to me. Here are 3 possible approaches: 1. Look through HSoundFile (or similar) to learn how they work and write your own code. 2. Look at the Codecs or Wave packages, which might be coerced into doing what you want (there is also hsndfile, a binding to libsndfile, however I think that normalizes data like HSoundFile does, although you could likely avoid the marshaling problem. 3. I have a revised HSoundFile, which I think could be much more suitable for this sort of work. If you'd like the code for that, let me know and I'd be happy to pass it along. I'm hoping to do a release next week, but there's a lot of tidying to be done in the current state. How many people care about reading/writing audio files? I've been re-working the HSoundFile API, experimenting with different designs, comparing packages, etc., and I could do a write-up if anyone is interested. John Lato > > Message: 19 > Date: Fri, 14 Nov 2008 08:11:59 +0100 > From: Marc Weber <marco-oweber(a)gmx.de> > Subject: Re: [Haskell-cafe] openal & alut troubles > To: haskell-cafe(a)haskell.org > Message-ID: <20081114071159.GB18112(a)gmx.de> > Content-Type: text/plain; charset=utf-8 > > On Fri, Nov 14, 2008 at 02:33:05AM +0000, Stephen wrote: >> ah, damn I feel stupid. I hadn't it installed. I just tried to, and, >> after verifying with the internet, it seems that ALUT isn't supported on >> macs anymore anyway. Which leads me to the following question: does >> anyone have any example code for saving/loading wav files, say, using >> openal (minus alut) with haskell? I'm not too sure how to go about >> doing it myself (though the people on this thread >> [1]http://groups.google.com/group/fa.haskell/browse_thread/thread/33b57c9452… >> seem to indicate that it would be a relatively easy task). > > Wave files are realitively easy to write .. However you can also try the > encoder from hackage (catergory sound) called HSoundFile.. (I've never > used it before) Also using the haskell wiki search from haskell.org > reveals: http://haskell.org/haskellwiki/Sound_data_structures > > good luck > > Marc

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Calling Haskell from other languages?
by Colin Paul Adams 15 Nov '08

15 Nov '08

Is there a way to call Haskell code from other languages? I have looked on the wiki, and as far as I can see, it only talks about the other way round (when Haskell is the main program). -- Colin Adams Preston Lancashire

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ANN: bustle-0.1, a D-Bus activity charting tool
by Will Thompson 14 Nov '08

14 Nov '08

Hi, For the (probably small) set of people who are interested both in D-Bus and in Haskell, I'm pleased to announce the first release of Bustle, a tool to show diagrams of D-Bus traffic for profiling purposes. It consists of a small C executable to log traffic, and a Gtk+ application which draws diagrams using Cairo. There's no single web page for it yet. http://resiak.livejournal.com/59590.html has slightly more information and context, the release is at http://people.collabora.co.uk/~wjt/bustle/releases/bustle-0.1.tar.gz and the source at git://git.collabora.co.uk/git/user/wjt/bustle.git . Unfortunately, it's not on Hackage, as I haven't written the necessary glue to get Cabal to compile the C executable, but I hope to have time to work on getting Cabal to invoke make appropriately for the next release. Thanks, -- Will

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TimeDiff to Int?
by Lyle Kopnicky 14 Nov '08

14 Nov '08

Hi folks, I had some code using the oldtime package, and want to convert it to use the time package. One of the things I need to do is calculate the number of seconds since midnight. The easy part is getting a TimeDiff result: utc <- getCurrentTime tz <- getCurrentTimeZone let td = timeOfDayToTime $ localTimeOfDay $ utcToLocalTime tz utc Now td is a TimeDiff representation of the number of seconds since midnight. It prints nicely, but I'm having a heck of a time figuring out how to truncate it to an Int. The floor function is only supported by the RealFrac class. Although TimeDiff has an instance of RealFrac and Fractional, it doesn't have an instance of RealFrac. I looked up the various to* and from* functions and have come up short. fromEnum yields an Int but it's the wrong value. I know I could use show and then use readS to get an Integer, or use formatTime (and reparse that), but that's a hack. I can convert it to a TimeOfDay which gives me hours, minutes, and seconds, but then I have to do arithmetic on it, and the seconds are of type Pico, which I can't call floor on either. I can convert it to a Rational via timeOfDayToDayFraction, but a TimeDiff is already a Rational those don't have floor. What am I missing? There has got to be an easy way to count seconds! Thanks, Lyle

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[magnus@galois.com: Re: [Haskell-cafe] Monads for Incremental computing]
by Don Stewart 14 Nov '08

14 Nov '08

Magnus writes: Thanks to Peter Jonsson, the source is now on hackage: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Adaptive Cheers, Magnus Donnie Jones wrote: > Hello sanzhiyan, > > I believe this is the same paper, the pdf is available here: > http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.8.3014 > > Cheers. > __ > Donnie > > On Thu, Nov 13, 2008 at 9:02 PM, Don Stewart <dons(a)galois.com > <mailto:dons@galois.com>> wrote: > > I sit next to the author, CC'd. > > -- Don > > sanzhiyan: > > I'm looking for the source code of the library for adaptive > computations > > exposed in Magnus Carlsson's "Monads for Incremental > Computing"[1], but > > the link in the paper is broken. > > So, does anyone have the sources or knows how to contact the > author? > > > > [1] http://portal.acm.org/citation.cfm?id=581482 > > > _______________________________________________ > > Haskell-Cafe mailing list > > Haskell-Cafe(a)haskell.org <mailto:Haskell-Cafe@haskell.org> > > http://www.haskell.org/mailman/listinfo/haskell-cafe > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org <mailto:Haskell-Cafe@haskell.org> > http://www.haskell.org/mailman/listinfo/haskell-cafe > > ----- End forwarded message -----

3 2

ghci start-up banner
by Cetin Sert 14 Nov '08

14 Nov '08

Hi all, after reading this announcement on the Galois blog: http://www.galois.com/blog/2008/11/13/tech-talk-mechanically-verified-lisp-… I installed Hol4 to play around with it a little bit. I made 2 obvious observations ^_^: 1) It looks like the Hol4 system is just a ML module that gets loaded into the Moscow ML interpreter with the help of a script 2) it prints a custom banner after loading And now I have the following questions: == about proof assistants in general == 1) how many other proof assistants are built the same way as Hol4: as a module loaded into some interpreter? 2) is there a paper or even better a funny but detailed comparison of proof assistants? == about custom banners at module load time == 1) is there a way to do it in ghci? Regards, CS

1 0

openal & alut troubles
by Stephen 14 Nov '08

14 Nov '08

The link to the OpenAL documentation [ http://haskell.org/ghc/docs/latest/html/libraries/OpenAL/Sound-OpenAL.html ] from here [ http://www.haskell.org/haskellwiki/OpenAL ] seems to be down. Also, I tried to use cabal to install ALUT and got the following checking for unistd.h... yes checking AL/alut.h usability... no checking AL/alut.h presence... no checking for AL/alut.h... no checking OpenAL/alut.h usability... no checking OpenAL/alut.h presence... no checking for OpenAL/alut.h... no configure: error: no ALUT header found, so this package cannot be built See `config.log' for more details. cabal: Error: some packages failed to install: ALUT-2.1.0.0 failed during the configure step. The exception was: exit: ExitFailure 1 :/

2 3

Monads for Incremental computing
by sanzhiyan＠gmail.com 14 Nov '08

14 Nov '08

I'm looking for the source code of the library for adaptive computations exposed in Magnus Carlsson's "Monads for Incremental Computing"[1], but the link in the paper is broken. So, does anyone have the sources or knows how to contact the author? [1] http://portal.acm.org/citation.cfm?id=581482

3 2

What is Haskell used for?
by Jason Dagit 14 Nov '08

14 Nov '08

I was looking over the Hackage categories today to figure out what Haskell is *really* used for? I just really quickly sorted the categories by number of packages. It's really interesting to see System, Graphics and Network so high on the list. Clearly, next to data types and text processing, people are doing systems, graphics and network programming. C had better watch out! Jason Categories: Data (89) Text (84) System (83) Graphics (50) Network (48) Development (45) Web (41) Control (37) Language (36) Math (36) Database (33) Sound (31) Codec (26) Game (26) User Interfaces (23) Unclassified (22) Parsing (19) Compilers/Interpreters (16) Data Structures (16) Distribution (15) Testing (15) Algorithms (12) XML (12) Natural Language Processing (10) Monads (9) Pugs (9) Bioinformatics (8) Generics (8) GUI (8) Hardware (3) Foreign (7) FRP (6) Concurrency (6) Reactivity (5) Distributed Computing (5) Source-tools (5) Music (4) Cryptography (4) Editor (4) Interfaces (4) Physics (4) AI (3) Code Generation (3) Codecs (3) Other (3) Search (3) List (2) Data Mining (2) Combinators (2) Console (2) Debug (2) Numerical (2) Theorem Provers (2) Utils (2) Comonads (1) Composition (1) Desktop (1) FFI Tools (1) Finance (1) Help (1) Middleware (1) Monadic Regions (1) Numeric (1) Screensaver (1) Scripting (1) System.Console (1) Test (1) Trace (1) User-interface (1)

1 0

The Gtk Clutter API
by Darrin Thompson 14 Nov '08

14 Nov '08

http://www.clutter-project.org/ What is the degree-of-difficulty for creating Haskell bindings for Clutter? Is it simple to extend gtk2hs to cover it? Or has it been done and I just don't see it? Thanks. -- Darrin

1 0

Getting rid of functional dependencies with type proxies
by Tobias Bexelius 13 Nov '08

13 Nov '08

Hi, some time ago I asked about a problem I had with functional dependencies conflicting when using overlapping instances in a code like this: {-# OPTIONS_GHC -fglasgow-exts -fallow-undecidable-instances -fallow-incoherent-instances #-} data V2 a = V2 a a class Vec v a where dot :: v a -> v a -> a instance Num a => Vec V2 a where V2 a1 a2 `dot` V2 b1 b2 = a1*b1+a2*b2 class Mult a b c | a b -> c where (*.) :: a -> b -> c instance (Num x) => Mult x x x where (*.) = (*) instance (Vec a x) => Mult (a x) (a x) x where (*.) = dot {- Functional dependencies conflict between instance declarations: instance [overlap ok] (Num x) => Mult x x x instance [overlap ok] (Vec a x) => Mult (a x) (a x) x -} The problem here is that the dependency check is occuring too soon. Removing the dependency would solve the problem, but then you would need to put type annotations everywhere you use the multiplication operator, and that's not acceptable. However, I did found a solution I would like to share with you: Creating a "type proxy"! I find it strange that such a simple solution to such a (for me at least) common problem hasn't been documented more. This is the working code: {-# OPTIONS_GHC -fglasgow-exts -fallow-undecidable-instances -fallow-incoherent-instances #-} data V2 a = V2 a a class Vec v a where dot :: v a -> v a -> a instance Num a => Vec V2 a where V2 a1 a2 `dot` V2 b1 b2 = a1*b1+a2*b2 class Mult a b c | a b -> c where (*.) :: a -> b -> c class MultProxy a b c where (*..) :: a -> b -> c instance MultProxy a b c => Mult a b c where (*.) = (*..) instance (Num x) => MultProxy x x x where (*..) = (*) instance (Vec a x) => MultProxy (a x) (a x) x where (*..) = dot Thanks to Emil Axelsson that pointed me to http://haskell.org/haskellwiki/GHC/AdvancedOverlap, where similar problems where discussed. Again, I haven't found links to this page in any of the Haskell tutorials I've read so far. /Tobias

2 1

Proof that Haskell is RT
by Andrew Birkett 13 Nov '08

13 Nov '08

Hi, Is a formal proof that the Haskell language is referentially transparent? Many people state "haskell is RT" without backing up that claim. I know that, in practice, I can't write any counter-examples but that's a bit handy-wavy. Is there a formal proof that, for all possible haskell programs, we can replace coreferent expressions without changing the meaning of a program? (I was writing a blog post about the origins of the phrase 'referentially transparent' and it made me think about this) Andrew -- - http://www.nobugs.org -

17 28

HOpenGL shading problem
by Trin 13 Nov '08

13 Nov '08

Hi, last few days I spent making remake of glxgears. Nothing fancy, I just wanted easily configurable gears. The current performance is only about 70% of glxgears. But I have a problem with shading. Whatever I have been trying, I still don't understand how the shading can be activated. I have light, I have color, but not even Flat shading. Please can you give me a hand? Thanks, Martin PS: I didn't find any attachment size policy for this list, so I hope that the attachment is small enough.

2 1

re: [Haskell-cafe] ANNOUNCE: rewriting-0.1
by Greg Meredith 13 Nov '08

13 Nov '08

Thomas, Did you explore nominal rewrite at all? Do you know if it might be possible to use the scrap-your-nameplate package to implement some useful subset of the nominal rewrite machinery? Best wishes, --greg -- L.G. Meredith Managing Partner Biosimilarity LLC 806 55th St NE Seattle, WA 98105 +1 206.650.3740 http://biosimilarity.blogspot.com

2 1

Turning all the Nothings into Just defaultValue using Data.Generics
by David Fox 13 Nov '08

13 Nov '08

I want to use Data.Generics to write a function to turn all the Nothings in a data structure into Just defaultValue, as shown below. I get the following error because the compiler doesn't know enough about Maybe a for mkT to create the generic function that everywhere requires, I guess. Test.hs:26:16: Ambiguous type variable `a' in the constraints: `Typeable a' arising from a use of `mkT' at Senior/Test2.hs:26:16-30 `Default a' arising from a use of `justDefault' at Senior/Test2.hs:26:20-30 Probable fix: add a type signature that fixes these type variable(s) Here is the example. It all works except for "test". Any suggestions how to do this? {-# LANGUAGE DeriveDataTypeable, FlexibleContexts, FlexibleInstances, MultiParamTypeClasses, RankNTypes, TemplateHaskell, TypeSynonymInstances #-} {-# OPTIONS_GHC -fallow-undecidable-instances #-} module Test where import Data.Generics class Default a where defaultValue :: a instance Default Int where defaultValue = 0 instance Default String where defaultValue = "" instance Default (Maybe a) where defaultValue = Nothing data A = A {b :: Int, c :: Maybe String} deriving (Show, Data, Typeable) instance Default A where defaultValue = A {b = defaultValue, c = defaultValue} test = everywhere (mkT justDefault) (defaultValue :: A) where justDefault Nothing = Just defaultValue justDefault (Just x) = Just x

3 2

Linker errors to OpenGL with GHC 6.10.1
by Greg Fitzgerald 13 Nov '08

13 Nov '08

Do you know how I can fix these linker errors? C:\projects\fun>cat HelloWorld.hs import Graphics.Rendering.OpenGL import Graphics.UI.GLUT main = do (progname, _) <- getArgsAndInitialize createWindow "Hello World" displayCallback $= clear [ColorBuffer] mainLoop C:\projects\fun>ls lib GlU32.Lib glut32.lib OpenGL32.Lib glut.def glut32.dll C:\projects\fun>ghc -Llib -lglut32 -lglu32 -lopengl32 HelloWorld.hs --make Linking HelloWorld.exe ... C:\Program Files\Haskell\GLUT-2.1.1.2\ghc-6.10.1/libHSGLUT-2.1.1.2.a(Begin.o):fake:(.text+0x1cb): undefined reference to `glutGet' C:\Program Files\Haskell\GLUT-2.1.1.2\ghc-6.10.1/libHSGLUT-2.1.1.2.a(Begin.o):fake:(.text+0x8af): undefined reference to `glutMainLoop' C:\Program Files\Haskell\GLUT-2.1.1.2\ghc-6.10.1/libHSGLUT-2.1.1.2.a(Window.o):fake:(.text+0x3cd): undefined reference to `glutEntryFunc' C:\Program Files\Haskell\GLUT-2.1.1.2\ghc-6.10.1/libHSGLUT-2.1.1.2.a(Window.o):fake:(.text+0x40d): undefined reference to `glutVisibilityFunc' C:\Program Files\Haskell\GLUT-2.1.1.2\ghc-6.10.1/libHSGLUT-2.1.1.2.a(Window.o):fake:(.text+0x3595): undefined reference to `glutPassiveMotionFunc' ...hundreds more... Thanks, Greg

2 1

Re: [Haskell-cafe] Proof that Haskell is RT
by Andrew Birkett 13 Nov '08

13 Nov '08

Edsko de Vries wrote: > See "What is a purely functional language" by Sabry. Not quite a formal > proof about *Haskell*, but then we would first need a formal semantics > of Haskell to be able to do that proof ;-) Thanks for the reference, and also to everyone who replied - all very useful and interesting. For what it's worth, the blog posts I was writing are here: http://www.nobugs.org/blog/archives/2008/11/12/why-do-they-call-it-referent… http://www.nobugs.org/blog/archives/2008/11/12/why-do-they-call-it-referent… Andrew

2 1

ANNOUNCE: hpapi 0.1 release
by Michael D. Adams 13 Nov '08

13 Nov '08

I am pleased to announce the first release of hpapi, Performance API (PAPI) bindings for Haskell. The release is on Hackage: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hpapi The source repository is at: http://code.haskell.org/hpapi/ Please send bug reports to <adamsmd [AT] cs.indiana.edu> What is it ========== This is a simple set of bindings for the Performance API (PAPI). PAPI provides access to various CPU counters such as cache-miss, instruction and pipeline stall counts. The easiest way to use this library is the withCounts function: withCounts :: [EventCode] -> IO a -> IO (a, [Integer]) Given a list of events to count and an IO operation it will run the operation and return the resulting counts. So you could do something like: main = do [l1,tlb,fp] <- withCounters [papi_l1_dcm, papi_tlb_dm, papi_fp_ins] ioOperationToMeasure printLn (l1, tlb, fp) To use it one will of course need the PAPI C library and any necessary kernel modifications installed. Status ====== The High Level interface (which will be sufficient for most people's needs) should be usable, but the low level interface is still alpha quality. That is to say, it is ready for people to start banging on it, but it is largely untested and the modules/interfaces may be reorganized based on user feedback. All of PAPI is supported with the exception of the following "advanced" features: - Multiplexing - Threads - Locks - Overflow - Statistical Profiling Future Directions ================= Future directions will be determined largely by user feedback. Principal areas that I am looking for feedback on are: - documentation - module organization - the handling of PAPI errors (currently it throws an IO error) - the design of the Haskell interface build on top of the C level PAPI_get_opt and PAPI_set_opt - what advanced features of PAPI to build bindings for next Comparison with GHC's built-in PAPI =================================== GHC supports a built-in version of PAPI (see http://hackage.haskell.org/trac/ghc/wiki/PAPI) This system is different in a few ways. First, hpapi allows you to measure specific parts of a program while GHCI's PAPI only does whole program measurement Second, since hpapi is a library you can have fine grained and sophisticated control over how things are measured. On the other hand GHC's PAPI as part of the RTS gives you less control, but on the plus side doesn't require any modification to the program. Finally, GHC's PAPI splits apart the counts that come from the garbage collector from those that come from the mutator, while hpapi combines them. This is a limitation of hpapi we hope to correct some time in the future. It remains to be seen whether it would be worth while to unify these two systems. ================ Bug reports as well as suggestions, feedback or contributions to the API or the documentation most welcome. Michael D. Adams

1 0

GHC 6.10, strange behaviour when profiling?
by Aleš Bizjak 13 Nov '08

13 Nov '08

Hello, I'm experiencing some strange behaviour with GHC 6.10 and would like an explanation why. Here's the problem. With GHC 6.8.[23] memory usage of a program was about 250mb (computing pi to 10^6 decimals). Now I tried recompiling and running with GHC 6.10 and I got more than 1.4gb before I killed it, so naturally I tried profiling but here's the strangeness. When I compile for profiling with -prof -auto-all and run with +RTS -p -RTS memory use is still about the same as before (> 1.4gb), but when I try running with +RTS -hc -RTS memory only reaches about 250mb. What is the explanation for this behaviour? I would send a program but it requires HERA, which is not on hackage ... Here is the output of -s ./Test 100000 +RTS -s 47,467,176 bytes allocated in the heap 18,046,776 bytes copied during GC 9,215,104 bytes maximum residency (6 sample(s)) 711,520 bytes maximum slop 80 MB total memory in use (11 MB lost due to fragmentation) Generation 0: 84 collections, 0 parallel, 0.01s, 0.01s elapsed Generation 1: 6 collections, 0 parallel, 0.01s, 0.01s elapsed INIT time 0.00s ( 0.00s elapsed) MUT time 3.66s ( 3.71s elapsed) GC time 0.02s ( 0.02s elapsed) RP time 0.00s ( 0.00s elapsed) PROF time 0.00s ( 0.00s elapsed) EXIT time 0.00s ( 0.00s elapsed) Total time 3.68s ( 3.73s elapsed) %GC time 0.5% (0.6% elapsed) Alloc rate 12,982,553 bytes per MUT second Productivity 99.5% of total user, 97.9% of total elapsed ./Test 100000 +RTS -s -hc 47,471,160 bytes allocated in the heap 18,637,752 bytes copied during GC 13,580,144 bytes maximum residency (37 sample(s)) 810,712 bytes maximum slop 33 MB total memory in use (7 MB lost due to fragmentation) Generation 0: 85 collections, 0 parallel, 0.02s, 0.02s elapsed Generation 1: 37 collections, 0 parallel, 0.00s, 0.01s elapsed INIT time 0.00s ( 0.00s elapsed) MUT time 3.67s ( 3.73s elapsed) GC time 0.02s ( 0.03s elapsed) RP time 0.00s ( 0.00s elapsed) PROF time 0.00s ( 0.00s elapsed) EXIT time 0.00s ( 0.00s elapsed) Total time 3.70s ( 3.77s elapsed) %GC time 0.6% (0.8% elapsed) Alloc rate 12,941,165 bytes per MUT second Productivity 99.2% of total user, 97.4% of total elapsed -- Best regards, Aleš

3 4

Searching for ADT patterns with elem and find
by Paul Keir 13 Nov '08

13 Nov '08

Hi All, If I have an ADT, say data T = A String Integer | B Double | C deriving(Eq) and I want to find if a list (ts) of type T contains an element of subtype "B Double", must my "containsTypeX" function use a second "isTypeX" function as follows: isTypeB :: T -> Bool isTypeB (B _) = True isTypeB _ = False containsTypeB :: [T] -> Bool containsTypeB ts = maybe False (\x -> True) (find isTypeB ts) I understand that while something like "find C ts" will work, "find (isTypeB _) ts" will not, but is there no such thing as a pattern combinator(?), or lambda that could help with this situation. I find I have many individual "isTypeB" functions now. Regards, Paul

6 9

abstract extensible types?
by Alberto G. Corona 13 Nov '08

13 Nov '08

Is there any abstract container that permits the addition of new types of data? I know how to simulate the extension of Algebraic datatypes, but this does not permit the addition of data with new types in the same container and recover them in a type-safe way. Did I reinvent the Weel? I found something, that permits this for any Typeable datatype. For example x=5 list= [put x, put "hello"] [t1,t2 ]= list x' = get t1 :: Int s = get t2 :: String print (x' +1) -- 2 print s -- "hello" x''= get t2 :: Int --"get: casting from String to type Int" The code: data Abstract= forall a. Typeable a => T !String a class FromToAbstract x where put :: x -> Abstract get :: Abstract -> x unsafeGet :: Abstract -> x -- get(put x)== x instance Typeable x => FromToAbstract x where put x= T (typeString x) x get (Abstract type1 a)= if type2 == type1 then v else error ("get: casting "++ "from type "++type1++" to type "++type2) where v= unsafeCoerce a :: x type2= typeString v unsafeGet (Abstract type1 a)= unsafeCoerce a typeString !x= tyConString $ typeRepTyCon $ typeOf x instance Typeable T where typeOf _= mkTyConApp (mkTyCon "Abstract") []

3 2

Hackage web interface
by Hugo Pacheco 13 Nov '08

13 Nov '08

Hi, When previewing some package via the Hackage web interface, I get the following warning: Exposed modules use unallocated top-level names: AI assume that if you define some module A.B, it expects the top-level name A to be a module. Does this make sense? Thanks, hugo -- www.di.uminho.pt/~hpacheco

2 1

problem with boolean splicing in templates in ghc 6.10.1
by Leonidas Fegaras 12 Nov '08

12 Nov '08

Seems that boolean splicing in haskell templates in ghc 6.10.1 does not work correctly. If you do: $((\b -> [| b |]) True) you get the error: Can't find interface-file declaration for data constructor GHC.Base.True Probable cause: bug in .hi-boot file, or inconsistent .hi file Use -ddump-if-trace to get an idea of which file caused the error It seems that GHC.Base.True is now GHC.Bool.True, but the splicing code still generates the former. Leonidas Fegaras

2 1

reliable (bi)directional pipe to a process
by oleg＠okmij.org 12 Nov '08

12 Nov '08

I'd like to point out a reliable, proven and simple way of interacting with another process, via unidirectional or bidirectional pipes. The method supports Unix sockets, pipes, and TCP sockets. I too have noticed insidious bugs in GHC run-time when communicating with another process via a pipe. I tried to use runInteractiveProcess; it worked -- up to file sizes of about 300Kb. Then GHC run-time seems to `loses synchronization' -- and corrupts IO buffers, receiving stuff that cannot have been possibly sent. This is because handle operations are asynchronous and the GHC scheduler seems to have race conditions. That behavior was totally unacceptable. I was writing a production code, and can't afford such errors. Therefore, I wrote a simple foreign function interface to the code sys_open that I have been using for about fifteen years. This code does work, in production, for very large file sizes and long-running processes, on many Unix and Unix-like systems. I was told once about a Cygwin port. http://okmij.org/ftp/syscall-interpose.html#Application http://okmij.org/ftp/packages/sys_open.c http://okmij.org/ftp/Haskell/MySysOpen.hs Please see the test at the end of the file MySysOpen.hs. The test interacts with another process over a bi-directional pipe, repeatedly sending and receiving data. The amount of received data is large (about 510K).

5 6

ByteString/parsec
by Pieter Laeremans 12 Nov '08

12 Nov '08

HI, I want to efficiently parse a large collections of files. The files are in the format : example title TITLE author name AUTHOR some lines with summary here SUMMARY the real text TEXT a list of links LINKS I want to use "ByteString" here, but which library should I use to parse ? "attoparsec" or "bytestringparser", both export the same interface. When I use one of these I thaught it would be nice to write something like this : fileParser :: Parser Content fileParser = do title <- manyTill getInput (string . pack "\nTITLE\n") author <- manyTill getInput (string. pack "\nTITLE\n") .... return Content title author ... But this doesn't work. Even on a small example : parseTest (manyTill getInput (string $ pack "SPLIT") (pack "split the text at SPLIT part two") I get a stack overflow. Obviously I'm not understanding something here. Are there any good examples of open source projects which parse ByteString data ? thanks in advance, Pieter -- Pieter Laeremans <pieter(a)laeremans.org> "The future is here. It's just not evenly distributed yet." W. Gibson

3 2

compiling haskell-src-exts in 6.10
by Hugo Pacheco 12 Nov '08

12 Nov '08

When installing package haskell-src-exts via cabal install, I get the error Language/Haskell/Exts/Syntax.hs:102:7: Could not find module `Data.Data': it is a member of package base, which is hidden However, when manually installing runhaskell Setup.hs configure/build/install It works fine Somehow package base is not available in cabal.. don't know why. hugo -- www.di.uminho.pt/~hpacheco

3 2

Re[2]: [Haskell-cafe] mapping unfreeze over an IntMap of IOUArrays
by Bulat Ziganshin 12 Nov '08

12 Nov '08

Hello Max, Tuesday, November 11, 2008, 11:50:28 PM, you wrote: btw, i made here some time ago proposal about pure hashtables implented over a pure arrays (via accumArray operaion). may be it is somewhat helpful for you >>> > using unsafeFreeze. I'm getting stuck here, since the >>> IntMap library >>> > is not so monad-friendly. >>> >>> Data.Hashtable is >> >> Well, I need mutable update for a while... after that, I prefer a pure >> interface, which is why I'm trying to freeze all the values. > Is there any reason why an immutable Hashtable shouldn't be > implemented, with a pure interface, such that hashtables can be > (unsafe)Freezed into immutable hashtables? Would this be useful? > --Max -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com

2 4

mapping unfreeze over an IntMap of IOUArrays
by Chad Scherrer 12 Nov '08

12 Nov '08

Hello cafe, I've hit a bit of a monadic snag here... I'm scanning a big file, building a table of statistics. I end up with something like IO (IntMap (IOUArray Int Double)) Once I've read in the whole file and built my statistics, I don't need any more updates, so I'd like to do something like IntMap (IOUArray Int Double) -> IO (IntMap (UArray Int Double)), using unsafeFreeze. I'm getting stuck here, since the IntMap library is not so monad-friendly. I could rebuild the whole thing using sequence and lists, but the table is pretty big (4.5 million keys on a first run), so I'd prefer to avoid that. Any ideas? BTW, I probably "should" be using ST for this, but I hit the usual "type s escapes" irritation and gave up. If that would work more easily, that would be fine with me too. Thanks! Chad Scherrer

5 6

Compilation issue with GHC 6.10.1 on Vista
by Alexey Romanov 12 Nov '08

12 Nov '08

I'm trying to update FreshLib <http://homepages.inf.ed.ac.uk/jcheney/programs/freshlib/> to work with the current GHC version. Now it works fine in GHCi, but trying to compile with ghc --make gives this result: [1 of 5] Compiling NominalBase ( NominalBase.hs, NominalBase.o ) Loading package ghc-prim ... linking ... done. Loading package integer ... linking ... done. Loading package base ... linking ... done. Loading package syb ... linking ... done. Loading package base-3.0.3.0 ... linking ... done. Loading package array-0.2.0.0 ... linking ... done. Loading package packedstring-0.1.0.1 ... linking ... done. Loading package containers-0.2.0.0 ... linking ... done. Loading package pretty-1.0.1.0 ... linking ... done. Loading package template-haskell ... linking ... done. Loading package bytestring-0.9.1.4 ... linking ... done. Loading package syb-with-class-0.4 ... linking ... done. C:\Users\Alexey\AppData\Local\Temp\/ghc1892_0/ghc1892_0.s: Assembler messages: C:\Users\Alexey\AppData\Local\Temp\/ghc1892_0/ghc1892_0.s:557: Error: symbol `_N ominalBase_zdgtoName_closure' is already defined C:\Users\Alexey\AppData\Local\Temp\/ghc1892_0/ghc1892_0.s:585: Error: symbol `_N ominalBase_zdgtoName_info' is already defined C:\Users\Alexey\AppData\Local\Temp\/ghc1892_0/ghc1892_0.s:637: Error: symbol `_N ominalBase_zdgfromName_closure' is already defined C:\Users\Alexey\AppData\Local\Temp\/ghc1892_0/ghc1892_0.s:665: Error: symbol `_N ominalBase_zdgfromName_info' is already defined Yours, Alexey Romanov

1 0

Problem installing curl
by Martin Huschenbett 12 Nov '08

12 Nov '08

Hi all, when I try to install curl (needed for hxt) using "cabal install curl" I alwas get the following error message: Resolving dependencies... 'curl-1.3.2.1' is cached. Configuring curl-1.3.2.1... cabal: Error: some packages failed to install: curl-1.3.2.1 failed during the configure step. The exception was: sh: runGenProcess: does not exist (No such file or directory) I don't know what to do here. Can anybody help me please? I'm using the brand new GHC 6.10.1 on Windows Vista. Best regards, Martin.

3 2

compilation question
by Peter Padawitz 12 Nov '08

12 Nov '08

At first a type of arithmetic expressions and its generic evaluator: data Expr = Con Int | Var String | Sum [Expr] | Prod [Expr] | Expr :- Expr | Int :* Expr | Expr :^ Int data ExprAlg a = ExprAlg {con :: Int -> a, var :: String -> a, sum_ :: [a] -> a, prod :: [a] -> a, sub :: a -> a -> a, scal :: Int -> a -> a, expo :: a -> Int -> a} eval :: ExprAlg a -> Expr -> a eval alg (Con i) = con alg i eval alg (Var x) = var alg x eval alg (Sum es) = sum_ alg (map (eval alg) es) eval alg (Prod es) = prod alg (map (eval alg) es) eval alg (e :- e') = sub alg (eval alg e) (eval alg e') eval alg (n :* e) = scal alg n (eval alg e) eval alg (e :^ n) = expo alg (eval alg e) n Secondly, a procedural version of eval (in fact based on continuations): data Id a = Id {out :: a} deriving Show instance Monad Id where (>>=) m = ($ out m); return = Id peval :: ExprAlg a -> Expr -> Id a peval alg (Con i) = return (con alg i) peval alg (Var x) = return (var alg x) peval alg (Sum es) = do as <- mapM (peval alg) es; return (sum_ alg as) peval alg (Prod es) = do as <- mapM (peval alg) es; return (prod alg as) peval alg (e :- e') = do a <- peval alg e; b <- peval alg e'; return (sub alg a b) peval alg (n :* e) = do a <- peval alg e; return (scal alg n a) peval alg (e :^ n) = do a <- peval alg e; return (expo alg a n) My question: Is peval less time- or space-consuming than eval? Or would ghc, hugs et al. optimize eval towards peval by themselves? Peter

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Re: [Haskell-cafe] Calling Haskell from other languages?
by Donn Cave 12 Nov '08

12 Nov '08

Quoth Colin Paul Adams <colin(a)colina.demon.co.uk>: | Is there a way to call Haskell code from other languages? I have looked on | the wiki, and as far as I can see, it only talks about the other way | round (when Haskell is the main program). There sure is a way to call from other languages - cf. "foreign export" - but don't know how hard it would be to make Haskell live without its "main", which performs a lot of runtime initialization. For me (with nhc98) it's a lot easier to use a Haskell "main" that's just a brief wrapper: module Main (main) where import NHC.FFI foreign import ccall "cmain" cmain :: IO () main = cmain (... where "cmain" is an external entry point in the C code, which can then call Haskell as required.) Donn

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announce: Workflow-0.1
by Alberto G. Corona 12 Nov '08

12 Nov '08

I needed to to define multiuser web workflows in the most transparent way. I wondered if a state monad could transparently bring automatic checkpointing of each action and automatic resume after failure. In this way a long living computation could be expressed in a single monadic computation. Additionally, for inter process communications, this package includes a primitive for activating a workflow whenever any action result meet certain condition. There are also primitives for start/restart processes, retrieval of intermediate results and unsafe IO actions inside the state monad... http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Workflow Cabal description: Transparent low level support (state logging, resume of the computation, wait for data condition) for long living, event driven processes. Workflow give the two first services to any monadic computation of type (a-> m a) usually m=IO f x >>=\x'-> g x' >>= \x''->... z by prefixing the user with the method "step": step f x >>= \x'-> step g x' >>= \x''->... This means that a workflow can be described with the familiar "do" notation. In principle, there is no other limitation on the syntax but the restriction (a -> m a): All computations consume and produce the same type of data. do notation is supported fully. Workflow export a few primitives that bring the following services: - transparent checkpointing of each step in permanent storage using TCache (step) - resume of the monadic computation at the last checkpoint after soft or hard interruption - use of versioning techniques for storing object changes (using RefSerialize) - retrieval of the object at any previous step - suspend the computation (waitFor) until the input object meet certain conditions. useful for inter-workflow comunications. At the end of the workflow all the intermediate data is erased. see demos and the header of Control.TCache for documentation. This is a piece of code is a loop that imput numbers (demo.hs). there is another process, that check the numbers entered and return Finish when match the desired number. that is detected by this thread and finalize. When number of tries are 9, The process finish, this is detected by the other process and finalizes also. That ilustrates the use of event handling (waitFor) and step execution. askNumbers name d = do step2 $ threadDelay 5000 -- wait for the other tread to process. r <- step (waitFor anything) d -- get the last value of the object with key "try-finish", to look for the other thread actions case r of Finish msg -> step2 $ print msg --the other thread sent a finalize response Try 9 num -> step1 $ return $ Finish "sorry, no more guesses" --send finalization to the wait thread _ -> do nd <- step (askNumber name) d askNumbers name nd where anything= \_-> True

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GHC 6.10 / Mac OS X / Library problem
by Pieter Laeremans 11 Nov '08

11 Nov '08

Hello, I've got a problem when I want to install pcre-light on OS X, with the latest version of GHC (binary package from haskell.org) It is not clear to me which flags to pass to ghc, to tell it to look at /opt/local/include for the pcre-light.h header. Any suggestions ? thanks, Pieter :cabal-install-0.6.0 pieter$ sudo cabal install pcre-light Password: Resolving dependencies... 'pcre-light-0.3.1' is cached. Configuring pcre-light-0.3.1... Preprocessing library pcre-light-0.3.1... Base.hsc:103:18: error: pcre.h: No such file or directory Base.hsc: In function 'main': Base.hsc:401: error: 'PCRE_ANCHORED' undeclared (first use in this function) Base.hsc:401: error: (Each undeclared identifier is reported only once Base.hsc:401: error: for each function it appears in.) Base.hsc:404: error: 'PCRE_AUTO_CALLOUT' undeclared (first use in this function) Base.hsc:407: error: 'PCRE_CASELESS' undeclared (first use in this function) Base.hsc:410: error: 'PCRE_DOLLAR_ENDONLY' undeclared (first use in this function) Base.hsc:413: error: 'PCRE_DOTALL' undeclared (first use in this function) Base.hsc:416: error: 'PCRE_DUPNAMES' undeclared (first use in this function) Base.hsc:419: error: 'PCRE_EXTENDED' undeclared (first use in this function) Base.hsc:422: error: 'PCRE_EXTRA' undeclared (first use in this function) Base.hsc:425: error: 'PCRE_FIRSTLINE' undeclared (first use in this function) Base.hsc:428: error: 'PCRE_MULTILINE' undeclared (first use in this function) Base.hsc:431: error: 'PCRE_NEWLINE_CR' undeclared (first use in this function) Base.hsc:434: error: 'PCRE_NEWLINE_CRLF' undeclared (first use in this function) Base.hsc:437: error: 'PCRE_NEWLINE_LF' undeclared (first use in this function) Base.hsc:440: error: 'PCRE_NO_AUTO_CAPTURE' undeclared (first use in this function) Base.hsc:443: error: 'PCRE_UNGREEDY' undeclared (first use in this function) Base.hsc:446: error: 'PCRE_UTF8' undeclared (first use in this function) Base.hsc:449: error: 'PCRE_NO_UTF8_CHECK' undeclared (first use in this function) Base.hsc:621: error: 'PCRE_NOTBOL' undeclared (first use in this function) Base.hsc:624: error: 'PCRE_NOTEOL' undeclared (first use in this function) Base.hsc:627: error: 'PCRE_NOTEMPTY' undeclared (first use in this function) Base.hsc:633: error: 'PCRE_PARTIAL' undeclared (first use in this function) Base.hsc:631: error: 'PCRE_ERROR_NOMATCH' undeclared (first use in this function) Base.hsc:634: error: 'PCRE_ERROR_NULL' undeclared (first use in this function) Base.hsc:637: error: 'PCRE_ERROR_BADOPTION' undeclared (first use in this function) Base.hsc:640: error: 'PCRE_ERROR_BADMAGIC' undeclared (first use in this function) Base.hsc:643: error: 'PCRE_ERROR_UNKNOWN_NODE' undeclared (first use in this function) Base.hsc:646: error: 'PCRE_ERROR_NOMEMORY' undeclared (first use in this function) Base.hsc:649: error: 'PCRE_ERROR_NOSUBSTRING' undeclared (first use in this function) Base.hsc:652: error: 'PCRE_ERROR_MATCHLIMIT' undeclared (first use in this function) Base.hsc:655: error: 'PCRE_ERROR_CALLOUT' undeclared (first use in this function) Base.hsc:658: error: 'PCRE_ERROR_BADUTF8' undeclared (first use in this function) Base.hsc:661: error: 'PCRE_ERROR_BADUTF8_OFFSET' undeclared (first use in this function) Base.hsc:664: error: 'PCRE_ERROR_PARTIAL' undeclared (first use in this function) Base.hsc:667: error: 'PCRE_ERROR_BADPARTIAL' undeclared (first use in this function) Base.hsc:670: error: 'PCRE_ERROR_INTERNAL' undeclared (first use in this function) Base.hsc:673: error: 'PCRE_ERROR_BADCOUNT' undeclared (first use in this function) Base.hsc:676: error: 'PCRE_ERROR_DFA_UITEM' undeclared (first use in this function) Base.hsc:679: error: 'PCRE_ERROR_DFA_UCOND' undeclared (first use in this function) Base.hsc:682: error: 'PCRE_ERROR_DFA_UMLIMIT' undeclared (first use in this function) Base.hsc:685: error: 'PCRE_ERROR_DFA_WSSIZE' undeclared (first use in this function) Base.hsc:688: error: 'PCRE_ERROR_DFA_RECURSE' undeclared (first use in this function) Base.hsc:691: error: 'PCRE_ERROR_RECURSIONLIMIT' undeclared (first use in this function) Base.hsc:665: error: 'PCRE_INFO_OPTIONS' undeclared (first use in this function) Base.hsc:668: error: 'PCRE_INFO_SIZE' undeclared (first use in this function) Base.hsc:671: error: 'PCRE_INFO_CAPTURECOUNT' undeclared (first use in this function) Base.hsc:674: error: 'PCRE_INFO_BACKREFMAX' undeclared (first use in this function) Base.hsc:677: error: 'PCRE_INFO_FIRSTBYTE' undeclared (first use in this function) Base.hsc:680: error: 'PCRE_INFO_FIRSTCHAR' undeclared (first use in this function) Base.hsc:683: error: 'PCRE_INFO_FIRSTTABLE' undeclared (first use in this function) Base.hsc:686: error: 'PCRE_INFO_LASTLITERAL' undeclared (first use in this function) Base.hsc:689: error: 'PCRE_INFO_NAMEENTRYSIZE' undeclared (first use in this function) Base.hsc:692: error: 'PCRE_INFO_NAMECOUNT' undeclared (first use in this function) Base.hsc:695: error: 'PCRE_INFO_NAMETABLE' undeclared (first use in this function) Base.hsc:698: error: 'PCRE_INFO_STUDYSIZE' undeclared (first use in this function) Base.hsc:701: error: 'PCRE_INFO_DEFAULT_TABLES' undeclared (first use in this function) Base.hsc:690: error: 'PCRE_CONFIG_UTF8' undeclared (first use in this function) Base.hsc:693: error: 'PCRE_CONFIG_NEWLINE' undeclared (first use in this function) Base.hsc:696: error: 'PCRE_CONFIG_LINK_SIZE' undeclared (first use in this function) Base.hsc:699: error: 'PCRE_CONFIG_POSIX_MALLOC_THRESHOLD' undeclared (first use in this function) Base.hsc:702: error: 'PCRE_CONFIG_MATCH_LIMIT' undeclared (first use in this function) Base.hsc:705: error: 'PCRE_CONFIG_STACKRECURSE' undeclared (first use in this function) Base.hsc:708: error: 'PCRE_CONFIG_UNICODE_PROPERTIES' undeclared (first use in this function) Base.hsc:711: error: 'PCRE_CONFIG_MATCH_LIMIT_RECURSION' undeclared (first use in this function) Base.hsc:724: error: 'PCRE_EXTRA_STUDY_DATA' undeclared (first use in this function) Base.hsc:727: error: 'PCRE_EXTRA_MATCH_LIMIT' undeclared (first use in this function) Base.hsc:730: error: 'PCRE_EXTRA_CALLOUT_DATA' undeclared (first use in this function) Base.hsc:733: error: 'PCRE_EXTRA_TABLES' undeclared (first use in this function) Base.hsc:736: error: 'PCRE_EXTRA_MATCH_LIMIT_RECURSION' undeclared (first use in this function) compiling dist/build/Text/Regex/PCRE/Light/Base_hsc_make.c failed command was: /usr/bin/gcc -c -D__GLASGOW_HASKELL__=610 -I/Library/Frameworks/GHC.framework/Versions/610/usr/lib/ghc-6.10.1/bytestring-0.9.1.4/include -I/Library/Frameworks/GHC.framework/Versions/610/usr/lib/ghc-6.10.1/base-4.0.0.0/include -I/Library/Frameworks/GHC.framework/Versions/610/usr/lib/ghc-6.10.1/include -IPAPI_INCLUDE_DIR dist/build/Text/Regex/PCRE/Light/Base_hsc_make.c -o dist/build/Text/Regex/PCRE/Light/Base_hsc_make.o cabal: Error: some packages failed to install: pcre-light-0.3.1 failed during the building phase. The exception was: exit: ExitFailure 1 -- Pieter Laeremans <pieter(a)laeremans.org> "The future is here. It's just not evenly distributed yet." W. Gibson

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Exporting a Type Class for Type Signatures
by Dominic Steinitz 11 Nov '08

11 Nov '08

In the crypto package, I have two functions > encrypt :: AESKey a => a -> Word128 -> Word128 > decrypt :: AESKey a => a -> Word128 -> Word128 which are exported. I also have > class (Bits a, Integral a) => AESKey a > > instance AESKey Word128 > instance AESKey Word192 > instance AESKey Word256 unexported which stops you using invalid keys. Someone has asked me to export AESKey as they want to write an explicit type signature for a function they are creating e.g. foo :: AESKey a => a -> Word128 -> Word128 foo x y = encrypt x y but this generates an error. Is there a way of allowing someone to use AESKey in a type signature but not allow them to declare new instances? Thanks, Dominic.

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download haskell?
by Johannes Waldmann 11 Nov '08

11 Nov '08

This is nit-picking, but ... when I go to haskell.org, there is a link (top in the left menu) "Download Haskell". Is this for readers who don't know the meaning of the word "implementation" (a few lines below)? Ah, it must be modelled after the perl.org start page... - J.W.

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