- Haskell - Haskell.org

Could not deduce .. why ?
by Marc Weber 13 Oct '08

13 Oct '08

Surely I've overseen a small point. But I can't see it: Why doesn't ghc recognize taht elc_ (class decl), elc (instance decl) and elc_1 are the same type To help you find the connecting pieces faster I've marked them with ## ## Marc data PT a b = PT b -- phantom type containing state a and the result b class AddEl el_ el2_ elc_ where addEl :: el_ -> elc -> el2_ -- el, child -- ========== adding sub elements (tags) ============================= class AddElT est el_ estc ##elc_## est2 el2_ | estc est -> est2 , est est2 estc el2_ -> el_ , est est2 estc el2_ -> elc_ where addElT :: PT est el_ -> PT estc ##elc_## -> PT est2 el2_ -- first child ? attrs ok? instance ( AddEl el el2 ##elc## <-- this is not recognized because elc != elc_1 , Consume st (Elem celType) st' , DetermineElAddEl (NYV (Element elType AttrsOk st HFalse)) el (Valid celType) elc (NYV (Element elType AttrsOk st' HTrue)) el2 ) => AddElT (NYV (Element elType AttrsOk st HFalse)) el (Valid celType) ##elc## <-- elc_ from class declaration (NYV (Element elType AttrsOk st' HTrue)) el2 where addElT (PT t) (PT ##c##) = PT $ addEl t c -- <<<<<<<<< line 435, c should have type elc, not elc_1 src/Text/XML/Validated/Types.hs|435 col 32 error| || Could not deduce (AddEl el el2 elc_1) || from the context (AddElT || (NYV (Element elType AttrsOk st HFalse)) || el || (Valid celType) || elc || (NYV (Element elType AttrsOk st' HTrue)) || el2, || AddEl el el2 elc, || Consume st (Elem celType) st', || DetermineElAddEl || (NYV (Element elType AttrsOk st HFalse)) || el || (Valid celType) || elc || (NYV (Element elType AttrsOk st' HTrue)) || el2) || arising from a use of `addEl' || at src/Text/XML/Validated/Types.hs:435:32-40 || Possible fix: || add (AddEl el el2 elc_1) to the context of the instance declaration || In the second argument of `($)', namely `addEl t c' || In the expression: PT $ addEl t c || In the definition of `addElT': || addElT (PT t) (PT c) = PT $ addEl t c

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ANNOUNCE: Graphalyze-0.4 and SourceGraph-0.2
by Ivan Lazar Miljenovic 13 Oct '08

13 Oct '08

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 I'd like to announce version 0.4 of my Graphalyze library [1] and 0.2 of my SourceGraph programme [2]. [1] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Graphalyze [2] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/SourceGraph This should fix the bugs reported by Gwern Branwen, Magnus Therning (thanks to Niklas Broberg for stating the correct version for Haskell-Src-Exts) and Christopher Hinson. No really new features are included in this release. I was planning on fixing this and releasing it sooner but - to utilise what seems to be a current meme [3] - "I accidentally my Gentoo" on Tuesday night and only fixed it yesterday. [3] http://encyclopediadramatica.com/I_accidentally_X Since I'm more awake now than I was when I made the initial release, here's a run-down of what SourceGraph is: SourceGraph is a programme designed to help you analyse the static complexity of your Haskell code when represented as a graph. At the moment, it does the following (M == for each module, I = for imports, C = the whole codebase): * Visualise it {M,I,C} * See a "collapsed" visualisation {M} * Proposed module/directory layout using two different algorithms {I,C} * See the "core" visualisation (recursively strip off roots/leaves) {M} * Calculate the Cyclomatic complexity [4] {M,I,C} * Root analysis (compare what's exported to what actually is a root) {M,I,C} * Determine how many components you have, to see if you should split {M,I,C} * Clique Analysis (find co-recursive functions) {M,C} * Cycle analysis (non-cliques) {M,I,C} * Chain detection (e.g. "straight-line" functions/imports) {M,I,C} [4] http://en.wikipedia.org/wiki/Cyclomatic_complexity Current limitations: * An automatic refactoring tool: SourceGraph gives *you* information on how you might want to possibly refactor your code. It's not smart: it can't tell that you've clumped functions foo and bar in the same module because they do similar things or because it's a utility module, even though they're not related. For automatic refactoring, see something like HaRe [5]. * SourceGraph ignore's "data-based" functions, i.e. record-functions and class/instance declarations, as it's too confusing (IMHO) which actual function you mean (if you see "show" being called, is it for Int, Double, or something else?). * Despite using Haskell-Src-Exts, some extensions (e.g. TH) are ignored, mainly because I have no idea how they work and nothing to test it on. GHC extensions should be supported (read the parser won't choke on them) though. * Reporting output is currently rather limited: - The report will be generated in a subdirectory called "SourceGraph" of the codebase directory; this is currently hardwired in. - It will produce an all-in-one html file report, with no fancy CSS magic to make it look pretty. Ideally, it would produce a split-file, and allow you to choose output format. - Large graphs are shrunk down to being a maximum of 15"x10". Ideally, I'd like to extend this later so that large graphs will have a shrunk version in the graph, which link to a larger version (note though that these graphs get very large very fast). - The output of individual function names, etc. could be improved. [5] http://www.cs.kent.ac.uk/projects/refactor-fp/hare.html SourceGraph can be installed with cabal-install. Once you've done so, you can analyse a cabalized library/application Foo as follows: $ SourceGraph /path/to/codebase/Foo.cabal Report generated at: /path/to/codebase/SourceGraph/Foo.html This has been written as part of my mathematics Honours Thesis, "Graph-Theoretic Analysis of the Relationships in Discrete Data". Since I've actually got to write the thesis up now, I won't be making any more releases for a while. After uni is over for the semester though, I hope to tidy it up and extend it. If you want to check the code out yourselves, there's also darcs repositories for Graphalyze [6] and SourceGraph [7]. [6] http://code.haskell.org/Graphalyze [7] http://code.haskell.org/SourceGraph/ Note that whilst Graphalyze is fully documented, etc., the internals of SourceGraph are a bit fugly (mainly due to time constraints). Enjoy! - -- Ivan Lazar Miljenovic Ivan.Miljenovic(a)gmail.com IvanMiljenovic.wordpress.com -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.9 (GNU/Linux) iEYEARECAAYFAkjyAacACgkQfEfFJ9JhvyiHEACfVVuRk2FR3ZQiJ6H18FFK/de/ sukAn0tuCLwqxmzlQvWicQKQ3qEJKC1K =HRUK -----END PGP SIGNATURE-----

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Re: [Haskell-cafe] ANNOUNCE: Salsa: A .NET Bridge for Haskell
by Don Stewart 10 Oct '08

10 Oct '08

This could be a game changer. Great work Andrew!! -- Don andrew.appleyard: > I'd like to announce the first release of Salsa, an experimental Haskell > library that allows Haskell programs to access .NET libraries. > > Here's a taste: > > > type Hello.hs > import Foreign.Salsa > import Bindings > > main = withCLR $ do > _Console # _writeLine ("Hello .NET World!") > > > type Hello.imports > System.Console: WriteLine > > > msbuild > > .\hello > Hello .NET World! > > Salsa operates by loading the .NET runtime into your Haskell process and > using the FFI (and run-time code generation) to marshall calls between > the .NET and Haskell runtimes. It includes a code generator and a > type-level library (which uses type families) to provide type-safe > access to .NET libraries in Haskell with C#-style method overload > resolution and implicit conversions. > > The adventurous can find version 0.1.0.1 of Salsa on Hackage [1], the > darcs repository on code.haskell.org [2], and some (limited) > documentation on the Haskell wiki [3]. > > The library is experimental and by no means complete (refer to the wiki > page [3] for some of its limitations). Be prepared to end up with > incomprehensible error messages and/or a broken compiler! :-) > > At the moment you'll need Windows, GHC 6.8, and version 3.5 of the .NET > Framework to use it. > > Have fun! > > [1] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Salsa > [2] http://code.haskell.org/Salsa > [3] http://haskell.org/haskellwiki/Salsa > > -- > Andrew > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe

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Re: [Haskell-cafe] ANNOUNCE: Salsa: A .NET Bridge for Haskell
by Alfonso Acosta 10 Oct '08

10 Oct '08

Great! Are there any chances of getting support for non-Win32 platforms with Mono? On Fri, Oct 10, 2008 at 2:12 PM, Andrew Appleyard <andrew.appleyard(a)gmail.com> wrote: > I'd like to announce the first release of Salsa, an experimental Haskell > library that allows Haskell programs to access .NET libraries. > > Here's a taste: > > > type Hello.hs > import Foreign.Salsa > import Bindings > > main = withCLR $ do > _Console # _writeLine ("Hello .NET World!") > > > type Hello.imports > System.Console: WriteLine > > > msbuild > > .\hello > Hello .NET World! > > Salsa operates by loading the .NET runtime into your Haskell process and > using the FFI (and run-time code generation) to marshall calls between the > .NET and Haskell runtimes. It includes a code generator and a type-level > library (which uses type families) to provide type-safe access to .NET > libraries in Haskell with C#-style method overload resolution and implicit > conversions. > > The adventurous can find version 0.1.0.1 of Salsa on Hackage [1], the darcs > repository on code.haskell.org [2], and some (limited) documentation on the > Haskell wiki [3]. > > The library is experimental and by no means complete (refer to the wiki page > [3] for some of its limitations). Be prepared to end up with > incomprehensible error messages and/or a broken compiler! :-) > > At the moment you'll need Windows, GHC 6.8, and version 3.5 of the .NET > Framework to use it. > > Have fun! > > [1] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Salsa > [2] http://code.haskell.org/Salsa > [3] http://haskell.org/haskellwiki/Salsa > > -- > Andrew > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe >

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ANNOUNCE: ListZipper-1.1.0.0
by Ryan Ingram 10 Oct '08

10 Oct '08

I was surprised to find there was no simple zipper for [] on hackage, so I made one: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/ListZipper-1.1.0… (1.0.0.0 had a dumb bug where I switched right and left!) Example in ghci: Prelude Data.List.Zipper> let z = fromList [1,2,3] Prelude Data.List.Zipper> toList (replace 5 $ right z) [1,5,3] -- ryan

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Catching error / making library functions monadic (in failure)
by Philip K.F. Hölzenspies 10 Oct '08

10 Oct '08

Dear Hask'lers, I'm working on a graph generator that involves a lot of random selection out of a list of vertices. Basically, there are functions that look a little like this: select vs = randomRM (0,length vs - 1) >>= return . (vs !!) where randomRM is a lot like Random.randomRIO, except that it is not in the IO monad, but rather in any monad, i.e. class Monad m => RandomM m where randomM :: m a randomRM :: (a,a) -> m a instance RandomM IO where randomM = randomIO randomRM = randomRIO The problem is, obviously, that when the list of vertices (vs) is empty, "select vs" will result in an error. The Prelude defines (!!) as: xs !! n | n < 0 = error "Prelude.!!: negative index" [] !! _ = error "Prelude.!!: index too large" (x:_) !! 0 = x (_:xs) !! n = xs !! (n-1) The function 'error' is implemented (at least in GHC) using Control.Exception.throw. Unfortunately, 'catch' does not seem to work. From ghci: Prelude> catch (return $ [] !! 0) (const $ putStrLn "foo" >> return 42) *** Exception: Prelude.(!!): index too large Is there any way to catch errors in functions in libraries (like the Prelude)? This is made even more necessary by the fact that the default implementation for 'fail' in a monad is 'error'. I would already be happy if I could make all applications of error change into applications of fail, as defined in my monad. Preferably, though, I would not even need a failure mechanism in my own monad, but rather have an ErrorMonad (or something similar) and just have class Monad m => ErrorMonad error m | m -> error where onError :: m a -> (error -> a) -> a For now, I simply reimplement the functions I need that give errors. Regards, Philip

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ANNOUNCE: darcs 2.1.0
by Eric Kow 09 Oct '08

09 Oct '08

Hi all, I am delighted to announce the release of darcs 2.1.0, available at http://darcs.net/darcs-2.1.0.tar.gz What has changed? ----------------- This version provides over 40 bug fixes and 20 new features since darcs 2.0.2. The most notable changes are: * Defaulting to darcs-2. The darcs initialize command now creates darcs-2 format repositories by default. This change will make the the improved conflict handling and merging semantics from darcs 2 available to more users. Note that no action is required on your part. Darcs will continue working with all pre-existing repositories. You can explicitly request an old-fashioned repository if needed. * Better HTTP support. Dmitry Kurochkin has refined our HTTP support and fixed several http-related bugs from darcs 2.0.2. There is also an experimental --http-pipelining feature you can enable on the command line (or in your defaults file) for faster downloading. Note: --http-pipelining is enabled by default for libwww, and also for libcurl 7.19.1 (not yet released at the time of this writing) * Repository correctness. David Roundy has resolved a longstanding 'pending patch' regression (originally reported on 2008-02). Needless to say the offending case has been moved to our regression testing suite See the attached ChangeLog for more details. What should I do? ----------------- Upgrade! Binary versions should be available shortly, either from your favourite package distributor or by third party contributors. Other than installing the new darcs, no action is required on your part to perform this upgrade. Darcs 2, including this particular version, is 100% compatible with your pre-existing repositories. If you have not done so already, you should consider using the hashed repository format in place of your current old-fashioned repositories. This format offers greater protection against accidental corruption, better support for case insensitive file systems. It also provides some very nice performance features, including lazy fetching of patches and a global cache (both optional). If darcs 1 compatibility is not a concern, you could also upgrade your repositories all the way to the darcs 2 format. In addition to the robustness and performance features above, this gives you the improved merging semantics and conflicts handling that give darcs 2 its name. More details about upgrading to darcs 2 here: http://wiki.darcs.net/index.html/DarcsTwo What comes next? ---------------- We will now be shifting to a time based release model, with the next darcs release planned for January 2009. For the next release of darcs, we will be focusing on optimising darcs's day to day performance issues. We want darcs to fetch repositories as fast as it possibly can over a network, and we especially want to rehabilitate known slow commands like darcs annotate. We believe that a few simple and practical changes can really improve the darcs experience for most users. Think you can help? We would love to hear from you. In fact, the first darcs hacking sprint (25-26 October) is fast approaching! We have three venues available: Brighton, Paris and Portland and everybody is invited to come hack. See http://wiki.darcs.net/index.html/Sprints for details. Thanks everybody, and enjoy! -- Eric Kow <http://www.nltg.brighton.ac.uk/home/Eric.Kow> PGP Key ID: 08AC04F9

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Call for Contributions - Haskell Communities and Activities Report, November 2008 edition
by Janis Voigtlaender 08 Oct '08

08 Oct '08

Dear Haskellers, so much has happened in the Haskell world in the past months. Therefore, I would very much like to collect contributions for the 15th edition of the ================================================================ Haskell Communities & Activities Report http://www.haskell.org/communities/ Submission deadline: 31 October 2008 (please send your contributions to hcar(a)haskell.org, in plain text or LaTeX format) ================================================================ This is the short story: * If you are working on any project that is in some way related to Haskell, please write a short entry and submit it. Even if the project is very small or unfinished or you think it is not important enough -- please reconsider and submit an entry anyway! * If you are interested in any project related to Haskell that has not previously been mentioned in the HC&A Report, please tell me, so that I can contact the project leaders and ask them to submit an entry. * Feel free to pass on this call for contributions to others that might be interested. More detailed information: The Haskell Communities & Activities Report is a bi-annual overview of the state of Haskell as well as Haskell-related projects over the last, and possibly the upcoming six months. If you have only recently been exposed to Haskell, it might be a good idea to browse the May 2008 edition -- you will find interesting topics described as well as several starting points and links that may provide answers to many questions. Contributions will be collected until the submission deadline. They will then be compiled into a coherent report that is published online as soon as it is ready. As always, this is a great opportunity to update your webpages, make new releases, announce or even start new projects, or to talk about developments you want every Haskeller to know about! Looking forward to your contributions, Janis (current editor) FAQ: Q: What format should I write in? A: The best format is a LaTeX source file, adhering to the template that is available at: http://haskell.org/communities/11-2008/template.tex There is also a LaTeX style file at http://haskell.org/communities/11-2008/hcar.sty that you can use to preview your entry. If you do not know LaTeX, then use plain text. If you modify an old entry that you have written for an earlier edition of the report, you should have received your old entry as a template already (provided I have your valid email address). Please modify that template, rather than using your own version of the old entry as a template. Do not worry about writing correct LaTeX, I will be able to handle your file. Please do not use HTML or even DOC. Q: Can I include images? A: Yes, you are even encouraged to do so. Please use .jpg format, then. Q: How much should I write? A: Authors are asked to limit entries to about one column of text. This corresponds to approximately one page, or 40 lines of text, with the above style and template. A general introduction is helpful. Apart from that, you should focus on recent or upcoming developments. Pointers to online content can be given for more comprehensive or ``historic'' overviews of a project. Images do not count towards the length limit, so you may want to use this opportunity to pep entries up. There is no minimum length of an entry! The report aims at being as complete as possible, so please consider writing an entry, even if it is only a few lines long. Q: Which topics are relevant? A: All topics which are related to Haskell in some way are relevant. We usually had reports from users of Haskell (private, academic, or commercial), from authors or contributors to projects related to Haskell, from people working on the Haskell language, libraries, on language extensions or variants. We also like reports over distributions of Haskell software, Haskell infrastructure, books and tutorials on Haskell. Reports on past and upcoming events related to Haskell are also relevant. Finally, there might be new topics we do not even think about. As a rule of thumb: if in doubt, then it probably is relevant and has a place in the HCAR. You can also ask the editor. Q: Is unfinished work relevant? Are ideas for projects relevant? A: Yes! You can use the HCAR to talk about projects you are currently working on. You can use it to look for other developers that might help you. You can use it to write ``wishlist'' items for libraries and language features you would like to see implemented. Q: If I do not update my entry, but want to keep it in the report, what should I do? A: Tell the editor that there are no changes. The old entry will be reused in this case, but it might be dropped if it is older than a year, to give more room and more attention to projects that change a lot. Do not resend complete entries if you have not changed them. -- Dr. Janis Voigtlaender http://wwwtcs.inf.tu-dresden.de/~voigt/ mailto:voigt@tcs.inf.tu-dresden.de

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Announce: Yi 0.5.0.1
by Jean-Philippe Bernardy 08 Oct '08

08 Oct '08

I'm pleased to announce the 0.5 release of the Yi editor. ## Yi Yi is a text editor written and extensible in Haskell. The long-term goal of the Yi project is to provide the editor of choice for Haskell programmers. Yi is not a finished product. This is a beta-quality release. However, Yi has become a lot more usable than previously, so if you feel like testing it, now might be a good time to take a look. ## Installation Using cabal install: cabal install yi-0.5.0.1 If you want unix console support, pass the -fvty option to cabal install. ## Features * A purely functional editor core * Key-bindings written as parsers of the input * Emacs, Vim and partial Cua emulations provided by default * Unix Console front-end (Gtk2Hs frontend is not supported in this release) * Static configuration (XMonad style) for fast load * Haskell support: * Lexical highlighting * Layout-aware parenthesis-matching * Auto-indentation * cabal-build within the editor ## Links * [download](http://hackage.haskell.org/cgi-bin/hackage-scripts/package/yi) * [FAQ](http://haskell.org/haskellwiki/Yi/FAQ) * [homepage](http://haskell.org/haskellwiki/Yi) * [blog and release notes](http://yi-editor.blogspot.com/) * [check and report issues](http://code.google.com/p/yi-editor/issues/list) * [darcs repository](http://code.haskell.org/yi) * [get involved](mailto:yi-devel@googlegroups.com) ## Credits This release is brought to you by: * Allan Clark * Corey O'Connor * Gustav Munkby * Gwern Branwen * Jean-Philippe Bernardy * Jeff Wheeler * Nicolas Pouillard * Thomas Schilling * Tristan Allwood and all the contributors to the previous versions.

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DAMP 2009 CFP reminder & revised full paper deadline
by Manuel M T Chakravarty 07 Oct '08

07 Oct '08

[Note the revised full paper submission date.] CALL FOR PAPERS DAMP 2009: Workshop on Declarative Aspects of Multicore Programming Savannah, GA, USA (co-located with POPL 2009) January 20, 2009 ABSTRACT SUBMISSION DEADLINE: OCTOBER 10 http://www.cse.unsw.edu.au/~pls/damp09/ Important Dates: Deadline for abstract submission: October 10, 2008 Deadline for full paper submission: October 14, 2008 Notification of acceptance: November 10, 2008 Final papers due: November 17, 2008 DAMP 2009: January 20, 2009 DAMP 2009 is the fourth in a series of one-day workshops seeking to explore ideas in programming language design that will greatly simplify programming for multicore architectures, and more generally for tightly coupled parallel architectures. DAMP 2009 is co-located with the ACM SIGPLAN - SIGACT Symposium on Principles of Programming Languages (POPL 2009). Scope The emphasis will be on functional and (constraint-)logic programming, but any programming language ideas that aim to raise the level of abstraction are welcome. DAMP seeks to gather together researchers in declarative approaches to parallel programming and to foster cross fertilization across different approaches. Specific topics include, but are not limited to: * suitability of functional and (constraint-)logic programming languages to multicore applications; * run-time issues such as garbage collection or thread scheduling; * architectural features that may enhance the parallel performance of declarative languages; * type systems and analysis for accurately knowing or limiting dependencies, aliasing, effects, and nonpure features; * ways of specifying or hinting at parallelism; * ways of specifying or hinting at data placement which abstract away from any details of the machine; * compiler techniques, automatic parallelization, automatic granularity control; * experiences of and challenges arising from making declarative programming practical; * technology for debugging parallel programs; * design and implementation of domain-specific declarative languages for multi-core; Accepted papers will be published in the ACM Digital Library and in a physical proceedings. Papers must adhere to the SIGPLAN Republication Policy: http://www.sigplan.org/republicationpolicy.htm Concurrent submissions to other conferences, workshops, journals, or similar forums of publication are not allowed. However, DAMP is intended to be a venue for discussion and exploration of works-in-progress, and so publication of a paper at DAMP 2009 is not intended to preclude later publication as appropriate. Submission Details: Authors should submit an abstract of at most 300 words and a full paper of no more than 10 pages (including bibliography and appendices) in the ACM SIGPLAN conference format. Further details are on the workshop web page: http://www.cse.unsw.edu.au/~pls/damp09/submission.html Program Chair: Manuel Chakravarty University of New South Wales Program Committee: Guy Blelloch Carnegie Mellon University Manuel Carro Universidad Politécnica de Madrid Koen Claessen Chalmers University of Technology Matthew Fluet Toyota Technological Institute at Chicago Vivek Sarkar Rice University Sven-Bodo Scholz University of Hertfordshire Satnam Singh Microsoft Research, Cambridge Martin Sulzmann IT University of Copenhagen Don Syme Microsoft Research, Cambridge Phil Trinder Heriot-Watt University General Chair: Leaf Petersen Intel Corporation Past DAMPs: http://www.cliplab.org/Conferences/DAMP08 http://glew.org/damp2006 http://www.cs.cmu.edu/~damp

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