- Haskell-Cafe - Haskell.org

Doing people's homework?
by Michael P Mossey 29 Sep '09

29 Sep '09

I'm not really hip to the culture here so this is just an observation, but some of the recent questions posted to this list (and beginners(a)haskell.org) look a lot like someone's homework. Is anyone here concerned about avoiding giving the full answer, or maybe it's really none of our business (we aren't responsible for anyone's learning process)?

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Writing tool question (may be out of scope here)
by Saul Malesac 29 Sep '09

29 Sep '09

Hi, Excuse me if that is out of subject here, but does anyone know which tool/writing framework was used to write the "Real world Haskell" book ? I'm wondering, in particular, about the capability to write/edit/publish it online while allowing people to leave comments, then have a paperback/PDF version. Thanks in advance, -- Saul

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Ghci dynamic linking (Was: C++ libraries and GHCI)
by Paolo Losi 29 Sep '09

29 Sep '09

Hi all, I would really appreciate if anyone could give a look to the following problem. Thanks in advance!!! Paolo ---------- Forwarded message ---------- From: Paolo Losi <paolo.losi(a)gmail.com> Date: Mon, Sep 14, 2009 at 10:33 AM Subject: C++ libraries and GHCI To: glasgow-haskell-users(a)haskell.org Hi all, I'm working on a tentative implementation of haskell binding to libsvm [1]: http://hackage.haskell.org/package/HSvm The package includes libsvm C++ sources. While it works perfectly with ghc --make (try to install the package and compile http://bitbucket.org/pao/hsvm/raw/6cf7ca91f1e5/test/test.hs) it fails with ghci: (hsvm)(env)paolo@moltrasio:~/trash$ ghci test.hs GHCi, version 6.10.4: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer ... linking ... done. Loading package base ... linking ... done. Ok, modules loaded: Main. Prelude Main> main Loading package syb ... linking ... done. Loading package array-0.2.0.0 ... linking ... done. Loading package containers-0.2.0.1 ... linking ... done. Loading package HSvm-0.1.0.2.89 ... linking ... <interactive>: /home/paolo/trash/hsvm/lib/HSvm-0.1.0.2.89/ghc-6.10.4/HSHSvm-0.1.0.2.89.o: unknown symbol `_ZTV6Kernel' ghc: unable to load package `HSvm-0.1.0.2.89' Please note that the symbol is available in libHSHSvm-0.1.0.2.89.a $ nm HSHSvm-0.1.0.2.89.o |grep _ZTV6Kernel 00000000 V _ZTV6Kernel $ nm libHSHSvm-0.1.0.2.89.a |grep _ZTV6Kernel 00000000 V _ZTV6Kernel Can anyone give a look to the problem? Thanks Paolo [1] http://www.csie.ntu.edu.tw/~cjlin/libsvm/ -- Paolo Losi e-mail: paolo(a)enuan.com mob: +39 348 7705261 ENUAN Srl Via XX Settembre, 12 - 29100 Piacenza

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ANNOUNCE: SourceGraph-0.5.0.0
by Ivan Lazar Miljenovic 29 Sep '09

29 Sep '09

SourceGraph [1] is a tool to statically analyse your Haskell code by applying graph-theoretic techniques on the call graph. It utilised the Graphalyze [2] library to do so, both of which were originally written as part of my Honours thesis last year [3]. [1] http://hackage.haskell.org/package/SourceGraph [2] http://hackage.haskell.org/package/Graphalyze [3] http://ivanmiljenovic.wordpress.com/2008/11/03/graph-theoretic-analysis-of-… I have been meaning to update SourceGraph since last year, but was waiting for improvements to the graphviz [4] library first. Now that these are done and I have fewer excuses, I've started to improve upon it. [4] http://hackage.haskell.org/package/graphviz When I first released SourceGraph last year, several people (e.g. Gwern) wanted support for CPP and command-line options. Unfortunately, I haven't yet gotten around to that; what I have done is added support for type classes and data structures, something I originally said I wasn't going to do. This support isn't perfect, especially when dealing with type classes from outside the scope of the code base, but in most cases works (except that the virtual instance functions don't always get positioned in the correct spots for some reason). The produced graphs are now also much prettier, with various colours and shapes being used. The useful features that SourceGraph offers include: * Visualisation of each module, the relations between modules and the entire code base. * Finds functions that are exported from a module that isn't in exposed in the .cabal file. * Alternate module splits. Please note that SourceGraph is _not_ a refactoring tool: it is designed to give you the programmer more information about what is in your code. I'd appreciate it if people could give SourceGraph a whirl and at least check how well the conversion from Haskell code to the graph is, as I'm not that sure how well I've converted haskel-src-ext's [5] internal state to SourceGraph's state. Please note that there are already various aspects that I know don't work properly; these can be found in the ParsingProblems.txt file (KnownProblems.txt contains other non-parsing problems that I'm aware of). In particular, TH, etc. aren't supported. [5] http://hackage.haskell.org/package/haskell-src-exts-1.1.4 To use SourceGraph after it's been installed, at a prompt do the following: > SourceGraph path/to/project.cabal The resulting report will then be found in a directory called "SourceGraph" in the same directory as the cabal file. -- Ivan Lazar Miljenovic Ivan.Miljenovic(a)gmail.com IvanMiljenovic.wordpress.com

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A thought about liberating Haskell's syntax
by George Pollard 29 Sep '09

29 Sep '09

Dear all, Here is a note concerning a thought I just had. I have written a rough sketch/outline and would like feedback upon this. The beginning thought: I would like to be able to write new bracket-like operators without having to rewrite GHC. (Case in point: applicative brackets.) First idea is to make them Template Haskell so we can mess with the internals (write custom list/set comprehension implementations). However a type (String → Exp) is not good enough; parsing the String is too much work! (Think precedence, etc.) We want to be able to have something (Exp → Exp). For this, we probably also need Template Haskell versions of normal (infix) operators, so that we can have something like: template infixr , (-1) -- lower precedence than $ a, b = if isList b then a : b else a : [b] Problem with this; [x, [y,z]] would have type :: [α] Lists constructed with ',' should have a different type from normal lists; call it QList. , :: Exp → Exp → Exp a, b@(AppE (ConE 'QCons) _) = a `qcons` b a, b = a `qcons` (b `qcons` QNil) where qcons a b = (ConE 'QCons) `AppE` a `AppE` b {- NB: we also need to provide implementations for type and pattern contexts, see next section. -} I believe that with this we can have the tuple and list syntax not hard-coded in. An example: -- note we need to provide the context for TH: Pattern, Expression, or Type -- no thought to sections here -- how to add tuple sections? -- perhaps relax operator rules for templates so that a, , , b is legitimate template outfix ( ) expression = (\x → case x of (QCons _ _) → TupE $ fromQList x _ → x template outfix ( ) pattern = (\x → case x of (QCons _ _) → TupP $ fromQList x _ → x template outfix ( ) type = (\x → case x of (QCons _ _) → foldl (\z x → z `AppT` x) (TupleT (length x)) x _ → x Anyway, we could then have easily-written syntax for; - sets - applicative brackets - parallel list comprehensions wouldn't have to be hardcoded (provide something like the above ',' but '|' returning something else. Perhaps QList should be tagged by a phantom type.) - statically-lengthed vectors Problems I can see: - QList (or other use-only-for-x types) could turn up in an actual program; l = a, b :: QList α -- is this actually a problem? - "Hidden" rewriting/macros not really the Template Haskell way, this is more scheme-like. A further (possibly evil) extension: template outfix do {-outdent-} expression = ... >:) -- would require thinking about EOL handling/semi-colon insertion

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Re: [Haskell-cafe] unicode text libraries
by Don Stewart 29 Sep '09

29 Sep '09

tittoassini: > 2009/9/28 Don Stewart <dons(a)galois.com>: > > titto: > >> Hi, > >> > >> I am looking for an unicode strings library, I found on hackage: > >> > >> http://hackage.haskell.org/package/compact-string > >> > >> http://hackage.haskell.org/package/text > >> > >> They both look solid and functionally complete so ... I don't know which > >> one to use :-) > >> > >> As I am sure I am not the first one facing this choice, may I ask > >> which one you preferred and why? > > > Data.Text > > Thanks , but .. why? Sorry, was on the way out the door. Data.Text has growing use, is well designed, and builds on the pedigree of bytestring and the vector* series of fusion libraries. I trust that code. -- Don

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Haskell Weekly News: Issue 131 - Semptember 25, 2009
by Joe Fredette 29 Sep '09

29 Sep '09

This week is an experiment, I'm eliminating the mail client from the sendout, and simply using sendmail directly. If this doesn't fix the line ending problem, then I'm pretty sure it's a software issue, and not a client issue. If you notice problems, please email me at this address, put [HWN] in the subject line so my filters will catch it. Please _don't_ email me if there are no problems. Thanks, /Joe --------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20090926 Issue 133 - September 26, 2009 --------------------------------------------------------------------------- Welcome to issue 133 of HWN, a newsletter covering developments in the [1]Haskell community. This week, we have a few new libraries, some interesting discussion about EDSLs, a comment from Oleg, and dons extolling the virtues of SCIENCE! On the new HWN software front, I've decided to jump right into something I had planned for far further down the development chain. Specifically, rather than scraping GMane for messages, I've been working on a way to grab the messages directly from the mailing-lists. I'm not entirely sure how I'm going to create links as they are now for the messages, but one crisis at a time. Till next week, here's the Haskell Weekly News! Announcements epoll bindings 0.2. Toralf Wittner [2]announced the release of epoll bindings 0.2 available [3]here. Epoll is an I/O event notification facility for Linux similar to poll but with good scaling characteristics. This release adds a buffer abstraction on top of the existing low-level bindings, so client code can write and read to buffers without having to deal directly with the underlying epoll event handling. diagrams 0.2.1, and planned major improvements. Brent Yorgey [4]announced version 0.2.1 of the diagrams library, available now on [5]Hackage. This minor release which fixes a few bugs and adds a few new combinators, most notably a grid layout combinator contributed by Ganesh Sittampalam. Workflow-0.5.5, TCache-0.6.4 RefSerialize-0.2.4. Alberto G. Corona [6]announced Workflow 0.5.5. Workflow provides a monad transformer that encapsulates any monad in a state monad that bring automatic state logging and recovery. A workflow can be viewed as a thread that persist across planeed or unplanned application shutdowns. When recovering the execution is resumed at the last action that was logged. The process continues at the same state as if not interruption took place. graphviz-2999.5.1.1. Ivan Lazar Miljenovic [7]announced version 2999.5.1.1 of the [8]graphviz library. This is another bug-fix release, fixing the problem spotted by Kathleen Fisher where Dot keywords need to be explicitly quoted if used as labels, etc. There is no change to the API. histogram-fill, library for creating histograms. Khudyakov Alexey [9]announced [10]histogram-fill. histogram-fill provides a generic and convenient API for making histograms. Features include, multiple simultaneous histogram creation, Immutable histograms, and Serialization to and from human readable text. Darcs Hacking Sprint - 14-15 November Vienna. Eric Kow [11]announced the third Darcs Hacking Sprint. Which will take place 14-15 November, 2009 at the University of Technology, Vienna, Austria. Anybody who wants to hack on Darcs (or Camp, Focal, SO6, etc) -- Beginners especially -- are welcome! 2nd CFP: TLDI 2010. Andrew Kennedy [12]announced a second call for papers for TLDI2010, the Types in Language Design and Implementation Workshop. darcs 2.3.1: better docs, fewer bugs. Reinier Lamers [13]announced a new stable version of darcs, with bugfixes from 2.3.0, improved documentation, and removal of the old autoconf build system. TFM09: Call for Participation (FMWeek, Eindhoven, November 2009). J.N. Oliveira [14]announced a Call for Participation in TFM2009 2nd Int. FME Conference on Teaching Formal Methods Friday, November 6th 2009, co-located with FM2009 : 16th Int. Symposium on Formal Methods Eindhoven, the Netherlands, November 2 - November 6, 2009. Discussion Monad Tutorial in C++. Adrian May [15]wrote a tutorial about monads in some other niche language... Beginning of a meta-Haskell. Oleg -- [16]as if he needs any introduction -- commented on things far above my ability to understand. Evidently, however, it involves extensible, modular interpreters in the ``tagless final'' style. It was a reply to an earlier thread [17]here. An issue with EDSLs in the ``finally tagless'' tradition. Brad Larsen [18]talked about his run in with [19]the expression problem while experimenting with EDSLs. Blog noise [20]Haskell news from the [21]blogosphere. Blog posts from people new to the Haskell community are marked with >>>, be sure to welcome them! * Bryan O'Sullivan: [22]Riddle me this. * David Amos: [23]Finite geometries, part 3: Points in PG(n,Fq). David's continuing series on Finite Geometries. * Neil Brown: [24]Concurrent Pearl: The Expanding Prime Pipeline. * Mikael Vejdemo Johansson (Syzygy-): [25][MATH198] Lecture 1 now online. Mikael's first Category Theory Lecture is up online. * Brent Yorgey: [26]diagrams 0.2.1, and future plans. * Alex McLean: [27]hackpact week 4. Part of the continuing series on Alex's hackpact progress. * Manuel M T Chakravarty: [28]Heads Up: GHC devs on Macs - GHC's testsuite crashes spotlight indexer on SL. * Clint Moore: [29]8 Cores of Awesome. * Bryan O'Sullivan: [30]Video of my CUFP keynote. * Chris Smith: [31]Thoughts on Hackage and the Haskell Platform. * Manuel M T Chakravarty: [32]Haskell Bindings to C -> c2hs. * Neil Brown: [33]Functions into processes, using arrows. * Brent Yorgey: [34]Functional MetaPost. * Malcolm Wallace: [35]Haskell Symposium 2009 - videos now online. * DEFUN 2009: [36]DEFUN and CUFP 2009 registration are now open!. * Chris Smith: [37]Type Classes With An Easier Example. * Darcs: [38]darcs weekly news #41. * Greg Bacon: [39]Haskell craps. * Bryan O'Sullivan: [40]A new pseudo-random number generator for Haskell. * Thomas M. DuBuisson: [41]HacPDX is Coming. * Dan Piponi (sigfpe): [42]More Parsing With Best First Search. * Osfameron: [43]Coin Tricks. Quotes of the Week * lilac: ponders whether unsafePerformIO would be better as simonSaysPerformIO * bos: [On the type signature of hPrintf] This makes me a sad Irish panda. * ksf: (But if (on the other hand)) (I think only a number in general (whether it be five or a hundred)) (this thought is rather the representation of a method (whereby a multiplicity (for instance a thousand) may be represented (in an image in conformity with a certain concept)) than the image itself. * dons: ah, via the magic of SCIENCE * dobblego: many of my colleagues used to be [fond of ruby] as well until I was let loose on them * dons: (on whether a library is wanted) *yes* put it on Hackage! * BMeph: (about parsec) 'Cause it's light-years ahead of the competition! * switch: Comeon people! You make the news! * ray: I think programmers make the worst programmers, also the worst people, and I'm saying this having not looked at programming reddit in a while. * Orclev: ... a lot of haskell still looks greek to me, and I'm not talking about lambdas. * Jason Dusek: "Some day, we're going to need a short, catchy name for Cabal packages. Let's call them cabbages." [see http://thread.gmane.org/gmane.comp.lang.haskell.cafe/63649] * Reinier Lamers: If we keep up the current pace of performance hacking, darcs will be complete before you even hit the enter key in a few years * Trent Buck: [To Reiner Lamers] With the appropriate (ie unbuffered) terminal, this is already the case for interactive prompts. About the Haskell Weekly News New editions are posted to [44]the Haskell mailing list as well as to [45]the Haskell Sequence and [46]Planet Haskell. [47]RSS is also available, and headlines appear on [48]haskell.org. To help create new editions of this newsletter, please see the information on [49]how to contribute. Send stories to jfredett . at . gmail . dot . com. The darcs repository is available at darcs get [50]http://patch-tag.com/r/HWN2/home . References 1. http://haskell.org/ 2. http://article.gmane.org/gmane.comp.lang.haskell.cafe/63815 3. http://hackage.haskell.org/package/epoll 4. http://article.gmane.org/gmane.comp.lang.haskell.cafe/63791 5. http://hackage.haskell.org/package/diagrams 6. http://article.gmane.org/gmane.comp.lang.haskell.cafe/63786 7. http://article.gmane.org/gmane.comp.lang.haskell.cafe/63770 8. http://hackage.haskell.org/package/graphviz-2999.5.1.1 9. http://article.gmane.org/gmane.comp.lang.haskell.cafe/63640 10. http://hackage.haskell.org/package/histogram-fill 11. http://article.gmane.org/gmane.comp.lang.haskell.general/17511 12. http://article.gmane.org/gmane.comp.lang.haskell.general/17508 13. http://article.gmane.org/gmane.comp.lang.haskell.general/17507 14. http://article.gmane.org/gmane.comp.lang.haskell.general/17506 15. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/63800 16. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/63761 17. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/63751 18. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/63751 19. http://www.daimi.au.dk/~madst/tool/papers/expression.txt 20. http://planet.haskell.org/ 21. http://haskell.org/haskellwiki/Blog_articles 22. http://www.serpentine.com/blog/2009/09/25/riddle-me-this/ 23. http://haskellformaths.blogspot.com/2009/09/finite-geometries-part-3-points… 24. http://chplib.wordpress.com/2009/09/24/the-expanding-prime-pipeline/ 25. http://blog.mikael.johanssons.org/archive/2009/09/math198-lecture-1-now-onl… 26. http://byorgey.wordpress.com/2009/09/24/diagrams-0-2-1-and-future-plans/ 27. http://yaxu.org/hackpact-week-3-2/ 28. http://justtesting.org/post/195668539 29. http://www.l2mlogistics.com/2009/09/8-cores-of-awesome.html 30. http://www.serpentine.com/blog/2009/09/23/video-of-my-cufp-keynote/ 31. http://cdsmith.wordpress.com/2009/09/23/thoughts-on-hackage-and-the-haskell… 32. http://justtesting.org/post/194790750 33. http://chplib.wordpress.com/2009/09/22/functions-into-processes-using-arrow… 34. http://byorgey.wordpress.com/2009/09/21/functional-metapost/ 35. http://feedproxy.google.com/~r/malcolm/~3/wxsdwfUArJ8/haskell-symposium-200… 36. http://www.defun2009.info/blog/2009/06/defun-2009-registration-is-now-open/ 37. http://cdsmith.wordpress.com/2009/09/20/side-computations-via-type-classes/ 38. http://blog.darcs.net/2009/09/darcs-weekly-news-41.html 39. http://feedproxy.google.com/~r/gbacon/~3/QILx5EtQN4o/haskell-craps.html 40. http://www.serpentine.com/blog/2009/09/19/a-new-pseudo-random-number-genera… 41. http://tommd.wordpress.com/2009/09/19/hacpdx-is-coming/ 42. http://blog.sigfpe.com/2009/09/language-nomonomorphismrestrictiongener.html 43. http://greenokapi.net/blog/2009/09/19/coin-tricks/ 44. http://www.haskell.org/mailman/listinfo/haskell 45. http://sequence.complete.org/ 46. http://planet.haskell.org/ 47. http://sequence.complete.org/node/feed 48. http://haskell.org/ 49. http://haskell.org/haskellwiki/HWN 50. http://patch-tag.com/r/HWN2/home

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Re: [Haskell-cafe] unicode text libraries, and the winner is ...
by Pasqualino "Titto" Assini 29 Sep '09

29 Sep '09

By unanimous opinion the "text" library is the man. Thanks to all who answered. titto

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ANNOUNCE: Graphalyze-0.7.0.0
by Ivan Lazar Miljenovic 29 Sep '09

29 Sep '09

Graphalyze [1] is a library for using graph-theoretic techniques to analyse the relationships inherent within discrete data. It was originally written for my Honours thesis [2] last year, and I have now started updating it. [1] http://hackage.haskell.org/package/Graphalyze [2] http://ivanmiljenovic.wordpress.com/2008/11/03/graph-theoretic-analysis-of-… Graphalyze provides helper functions to import discrete data, analyse it using various algorithms (a dodgy term, I know, but I couldn't think of a better one) and then create a report with the results. The main changes since the previous version are: * The ability to have graphs with edge labels. * More of a focus on applying changes to the overall information state of the data rather than just extracting the graph and applying a function to it. * Usage of the updated features in the graphviz library (http://hackage.haskell.org/package/graphviz) to visualise graphs. Changes to come: * Re-do the reporting framework to use more of a pretty-printing approach and make it more customisable. -- Ivan Lazar Miljenovic Ivan.Miljenovic(a)gmail.com IvanMiljenovic.wordpress.com

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So I wrote this performance measurement library thingy
by Bryan O'Sullivan 29 Sep '09

29 Sep '09

Which I will not blather on too long about here, but point you at a blog posting instead: http://www.serpentine.com/blog/2009/09/29/criterion-a-new-benchmarking-libr…

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