January 2009 - Haskell-Cafe

how to link to external documentation with haddock ?
by minh thu 12 Jan '09

12 Jan '09

Hi, When generating haddock documention (I use runhaskell Setup.lhs haddock), haddock warns me : "could not find link destinations for:" and lists for instance GHC.Show.Show or Data.Either.Either. Is it possible to instruct Haddock to links against http://www.haskell.org/ghc/docs/latest/html/libraries/ for those unfound destinations ? Thanks, Thu

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Understanding type synonym families
by Martijn van Steenbergen 11 Jan '09

11 Jan '09

Hello everybody, I think I'm finally beginning to understand how type synonym families [1] work, in the way that works best for me: running into a problem to which type synonyms offer a solution. I wrote down my train of thoughts [2] and I was hoping you could give me some feedback: are there any mistakes in my conclusions? Did I miss any obvious corollaries? Are the points I make valid? Also, I'm hoping it will be valuable to read for those wanting to understand type synonym families. Thank you in advance, Martijn. [1] http://www.haskell.org/haskellwiki/GHC/Type_families#Detailed_definition_of… [2] http://martijn.van.steenbergen.nl/journal/type-synonym-families/

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git mirrors for GHC boot libraries
by Manlio Perillo 11 Jan '09

11 Jan '09

Hi. Where can I find git mirrors for GHC boot libraries? From http://hackage.haskell.org/trac/ghc/wiki/Design/VersionControlSystem it is not clear if the mirrors are already available. Thanks Manlio Perillo

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Space leak with Data.Binary and decodeFile
by Maxime Henrion 11 Jan '09

11 Jan '09

Hello all, I've been observing a huge space leak with some code using Data.Binary that I cannot make sense of and I hope someone here can shed some light on this, so I'll try to explain my problem as clearly as possible. I qualify the space leak as huge because if I let the program run, it will soon consume the whole memory available (~3G) and finally will get killed by the system. The code I'm writing implements a search algorithm using an inverted index. This index is built from a Trie [Int] (from the bytestring-trie package) and an Array Int ByteString. The trie maps each referenced word to an integer list that is a list of indices into the array. Here is the code for the Index datatype and the obvious Binary instance: data Index = Index { entries :: Array Int ByteString , invidx :: Trie [Int } instance Binary Index where put (Index dirs idx) = put dirs >> put idx get = liftM2 get get I have no problems creating and seralizing this data structure to a file. The huge leak appears instead when I'm reading this data structure from a file and try to do something with it. This is the smallest test case I came up with that can reproduce the problem : main = do idx <- decodeFile "list.idx"; mapM_ (B.putStrLn . snd) (assocs (entries idx)) The space leak also appears when I try to touch the trie instead of the array. I've been trying tons of combinations involving adding or removing strictness annotations and seq calls in various places with no luck. I have also been adding SCC annotations and tried to profile the code. This seemed to suggest the space leak happens in the get method of the Array instance of Binary : instance (Binary i, Ix i, Binary e) => Binary (Array i e) where [...] get = do bs <- get n <- get -- read the length xs <- replicateM n get -- now the elems. return (listArray bs xs) The output of the profiler tells me that all the space gets allocated from the "replicateM n get" expression. Now for the really weird part: if I load my code in GHCi and type "main", I can observe the space leak. However, if I copy paste the definition of main instead, the code runs fine! This is the only circumstance I've seen this code work instead of eating all the RAM... I have been using GHC 6.10.1, binary 0.4.4 and bytestring-trie 0.1.2. If there's anything else that I can do to understand what's going on, I would gladfully hear about it. Please also tell me if I should provide more information. Thanks, -- Maxime Henrion

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Declaring each instance of a typeclass to be also an instance of another typeclass
by Mikhail Glushenkov 11 Jan '09

11 Jan '09

Hi, Is it possible to write something like this: > {-# LANGUAGE FlexibleInstances, UndecidableInstances #-} > > import Control.Monad (liftM) > > instance (Monad a) => Functor a where > fmap = liftM without having to use UndecidableInstances (and preferably, other type system extensions too)?

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Propositional logic implementation
by Andrew Wagner 10 Jan '09

10 Jan '09

All, Is there some better way to do this? It seems like a lot of boilerplate. Thanks! http://hpaste.org/13807#a1

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ANN: Haskell BLAS bindings version 0.7
by Patrick Perry 10 Jan '09

10 Jan '09

Here's the haddock documentation; I'm not sure if Hackage honors {-# OPTIONS_HADDOCK hide #-} when it displays the exposed modules: http://quantile95.com/blas/ Patrick

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Haskell Weekly News: Issue 100 - January 10, 2009
by Brent Yorgey 10 Jan '09

10 Jan '09

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20090110 Issue 100 - January 10, 2009 --------------------------------------------------------------------------- Welcome to issue 100 of HWN, a newsletter covering developments in the [1]Haskell community. Welcome to the 100th (!) issue of the Haskell Weekly News, suitably published on your friendly neighborhood HWN editor's 1000th birthday (base 3). If you ever have content to be included in the HWN (announcements, blog posts, major life news) or a suggestion on how the HWN could be more useful to you as a window into the goings-on of the Haskell community, please don't hesitate to send it along, using the contact information at the end of each issue. Announcements Haskell BLAS bindings version 0.7. Patrick Perry [2]announced the [3]release of version 0.7 of the [4]blas package, Haskell bindings to the BLAS (Basic Linear Algebra Subprograms) library. According to Patrick, this release is "a major milestone---it is finally the library with all of the features that I want." X Haskell Bindings. Antoine Latter [5]announced a preview release of the [6]X Haskell Bindings. The goal of the library is to provide low-level access to the X11 protocol, in the spirit of the [7]X C Bindings. Data.TCache 0.5.5. Alberto G. Corona [8]announced the 0.5.5 release of the [9]TCache package, a transactional data cache with configurable persistence. This version adds the the capability to safely handle transactions, and incrementally serialize many data types simultaneously in the same piece of code. haskell-src-exts 0.4.8. Niklas Broberg [10]announced a new release (0.4.8) of the [11]haskell-src-exts package. This is a bug-fix release in the wake of the flurry of bug reports due to [12]hlint. bytestring-trie 0.1.2 (bugfix). wren ng thornton [13]announced a bugfix release for [14]bytestring-trie, efficient finite maps from (byte)strings to values. This release fixes a bug in alterBy, and adds an Eq instance. wxHaskell 0.11.1. Jeremy O'Donoghue [15]announced the release of [16]wxHaskell 0.11.1, a Haskell binding for the wxWidgets GUI library. The main highlights include support for XRC resource files, support for wxWidgets 2.8.x and GHC 6.10, and preliminary support for Cabal and Hackage. cabal2doap 0.1. Greg Heartsfield [17]announced the [18]release of [19]Cabal2doap, which generates Description of a Project (DOAP) XML/RDF data representing a Haskell project. This should make it possible for semantic web project aggregation sites to find and index Haskell projects. Jobs Jane Street is hiring functional programmers. Yaron Minsky [20]reminded everyone that [21]Jane Street is still hiring! Jane Street now has over 30 OCaml developers, and is actively looking to hire more in Tokyo, London and New York. PhD, postdoc, and engineering positions at HATS. CFP [22]announced the availability of 10 PhD, postdoc, and engineering positions within the HATS project (Highly Adaptable and Trustworthy Software using Formal Models), a new Integrated Project funded by the European Union, within the programme "Future and Emerging Technologies" (FET). The goal of HATS is a tool-supported framework and formal methodology for the development of long-lived and trustworthy software systems. Hypothetical Haskell job in New York. Tony Hannan [23]asked how many would be interested in applying to a hypothetical Haskell job in New York, assuming his boss can be convinced to use Haskell. Blog noise [24]Haskell news from the [25]blogosphere. * Lennart Augustsson (augustss): [26]LLVM arithmetic. * GHC / OpenSPARC Project: [27]Bootstrapping 6. * Patrick Perry: [28]New Haskell BLAS bindings!. * Clemens Fruhwirth: [29]Liskell standalone. * The GHC Team: [30]Benchmarking recent improvements in parallelism. * Galois, Inc: [31]Tech Talk: OpenTheory: Package Management for Higher Order Logic Theories. * Eric Kow (kowey): [32]fold diagram revisited?. * GHC / OpenSPARC Project: [33]Bootstrapping 5. * Lennart Augustsson (augustss): [34]LLVM. * Sebastian Fischer: [35]Monadic and Queue-Based Tree Search. * Philip Wadler: [36]Well-typed programs can't be blamed. * GHC / OpenSPARC Project: [37]Bootstrapping 4. * Manuel M T Chakravarty: [38]GPU Kernels as Data-Parallel Array Computations in Haskell.. * GHC / OpenSPARC Project: [39]Bootstrapping 3. * Tom Schrijvers: [40]Monadic Constraint Programming. * Conal Elliott: [41]Another angle on functional future values. * >>> Greg Heartsfield: [42]Cabal2doap. * Christopher Lane Hinson: [43]MaybeArrow?. * GHC / OpenSPARC Project: [44]Bootstrapping 2. * Darcs: [45]darcs 2.2.0pre2 ready for testing!. * Alson Kemp: [46]Sad about Import Cycles. * GHC / OpenSPARC Project: [47]Bootstrapping. * gamr7: [48]Accessing Recursive Haskell Data Structures from C/Python. Quotes of the Week * jml: A wise man once said, "the program isn't debugged until the last user is dead". * pumpkin: OMG I <3 RECORD SYNTAX * Olathe: <Olathe> > floor (1.0/0.0) <lambdabot> 179769... <Olathe> But you can see that Haskell can calculate the maximum Integer. * lilac: <drdozer> gha! I'm drowning in the haskell number hierarchy again <lilac> drdozer: magic 8-ball says 'add calls to fromIntegral' * monopoly: do not exit IO. go directly to the REPL, do not pass any parameters or continuations. * EvilTerran: [on category theory] the same place of nightmares that spawned zygohistomorphic prepromorphisms :P About the Haskell Weekly News New editions are posted to [49]the Haskell mailing list as well as to [50]the Haskell Sequence and [51]Planet Haskell. [52]RSS is also available, and headlines appear on [53]haskell.org. To help create new editions of this newsletter, please see the information on [54]how to contribute. Send stories to byorgey at cis dot upenn dot edu. The darcs repository is available at darcs get [55]http://code.haskell.org/~byorgey/code/hwn/ . References 1. http://haskell.org/ 2. http://article.gmane.org/gmane.comp.lang.haskell.cafe/50195 3. http://quantile95.com/2009/01/09/new-haskell-blas-bindings/ 4. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/blas 5. http://article.gmane.org/gmane.comp.lang.haskell.cafe/50170 6. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/xhb 7. http://xcb.freedesktop.org/ 8. http://article.gmane.org/gmane.comp.lang.haskell.cafe/50169 9. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/TCache 10. http://article.gmane.org/gmane.comp.lang.haskell.cafe/50119 11. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/haskell-src-exts 12. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlint 13. http://article.gmane.org/gmane.comp.lang.haskell.cafe/49956 14. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/bytestring-trie 15. http://article.gmane.org/gmane.comp.lang.haskell.cafe/49898 16. http://wxhaskell.sourceforge.net/ 17. http://article.gmane.org/gmane.comp.lang.haskell.general/16718 18. http://blog.gregheartsfield.com/2009/01/04/cabal2doap/ 19. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/cabal2doap 20. http://article.gmane.org/gmane.comp.lang.haskell.general/16741 21. http://janestreet.com/ 22. http://article.gmane.org/gmane.comp.lang.haskell.general/16736 23. http://article.gmane.org/gmane.comp.lang.haskell.cafe/50015 24. http://planet.haskell.org/ 25. http://haskell.org/haskellwiki/Blog_articles 26. http://augustss.blogspot.com/2009/01/llvm-arithmetic-so-we-want-to-compute-… 27. http://ghcsparc.blogspot.com/2009/01/bootstrapping-6.html 28. http://quantile95.com/2009/01/09/new-haskell-blas-bindings/ 29. http://blog.clemens.endorphin.org/2009/01/liskell-standalone.html 30. http://ghcmutterings.wordpress.com/2009/01/09/46/ 31. http://www.galois.com/blog/2009/01/08/tech-talk-opentheory-package-manageme… 32. http://koweycode.blogspot.com/2009/01/fold-diagram-revisited.html 33. http://ghcsparc.blogspot.com/2009/01/bootstrapping-5.html 34. http://augustss.blogspot.com/2009/01/llvm-llvm-low-level-virtual-machine-is… 35. http://www-ps.informatik.uni-kiel.de/~sebf/projects/monad-vs-queue.html 36. http://wadler.blogspot.com/2009/01/well-typed-programs-cant-be-blamed.html 37. http://ghcsparc.blogspot.com/2009/01/bootstrapping-4.html 38. http://justtesting.org/post/68696876 39. http://ghcsparc.blogspot.com/2009/01/bootstrapping-3.html 40. http://tomschrijvers.blogspot.com/2009/01/monadic-constraint-programming.ht… 41. http://conal.net/blog/posts/another-angle-on-functional-future-values/ 42. http://blog.gregheartsfield.com/2009/01/04/cabal2doap/ 43. http://blog.downstairspeople.org/2009/01/04/maybearrow/ 44. http://ghcsparc.blogspot.com/2009/01/test-run-of-patched-ghc-6.html 45. http://blog.darcs.net/2009/01/darcs-220pre2-ready-for-testing.html 46. http://www.alsonkemp.com/haskell/sad-about-import-cycles/ 47. http://ghcsparc.blogspot.com/2009/01/building.html 48. http://gamr7.com/blog/?p=66 49. http://www.haskell.org/mailman/listinfo/haskell 50. http://sequence.complete.org/ 51. http://planet.haskell.org/ 52. http://sequence.complete.org/node/feed 53. http://haskell.org/ 54. http://haskell.org/haskellwiki/HWN 55. http://code.haskell.org/~byorgey/code/hwn/

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Looking for Haskellers on Windows
by Günther Schmidt 10 Jan '09

10 Jan '09

Hi all, I'm looking for Haskell programmer that use Windows as their OS-Plattform. I developing an application in Haskell on Windows and run into problems that seem to have a lower priority with the greater Haskell community as most of them are using Linux where the problems do not occur or are already solved. So it'd be nice to get in touch with other Haskellers that face the same problems. Günther

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Re: [Haskell-cafe] Haskell not ready for Foo [was: Re: Hypothetical Haskell job in New York]
by John A. De Goes 10 Jan '09

10 Jan '09

If you're looking for a project to take on, I would suggest starting with the following: A high-level, type-safe AMQP client written in 100% Haskell, which provides a clean way of handling hundreds of unique message types. Then it would be possible to hook it up to any AMQP broker (most likely RabbitMQ). There are logical steps beyond the above (an embedded Haskell broker), but the above project is far from trivial. And the main undertaking, I think, consists not in coding to the spec (for which there is some help; a JSON representation of the AMQP specification can be processed and used to emit language-specific code), but in finding a design that works well in Haskell. Regards, John On Jan 8, 2009, at 1:16 PM, Creighton Hogg wrote: > On Thu, Jan 8, 2009 at 2:02 PM, John A. De Goes <john(a)n-brain.net> > wrote: >> >> On Jan 8, 2009, at 12:56 PM, Tim Newsham wrote: >>> >>> You replied to someone discussing using Haskell at a CDN to >>> implement >>> things like web servers by saying that Haskell wasn't suitable for >>> the task. >> >> >> That is incorrect. I replied to Achim's message asking for >> elaboration on >> Haskell's unsuitability. It was a convenient point to discuss >> Haskell's >> networking deficiencies. > > Part of the problem I'm having with this discussion, though, is that > it's still not clear to me what critical features are lacking. I know > you've said Haskell doesn't have anything quite like the Erlang OTP > library, but that doesn't really help me much. I've only looked a > little at OTP & I don't think I understand what you get from its > behaviors that you don't get from Control.Concurrent + mtl, i.e. > various forms of state & error handling independent of the concurrency > underneath. > > Can you elucidate a bit more? I don't want the conversation to > degenerate.

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