November 2005 - Haskell

Haskell-mode 2.0
by Stefan Monnier 02 Feb '09

02 Feb '09

I have recently taken over maintainership of Haskell-mode, and after making a bunch of changes, I figured it would be a good idea to make a new release. You can find this new release at: http://www-perso.iro.umontreal.ca/~monnier/elisp/ If you think it should also be found at http://www.haskell.org/haskell-mode/, then please tell John Peterson to get back to me (my email to him seem to go straight to the bitbucket. John?). This release has several changes that have all been only lightly tested, especially w.r.t compatibility with various Emacsen. See appended the NEWS file that describes some of the notewirthy changes. Stefan Changes since 1.45: * keybindings C-c <char> have been replaced by C-c C-<char> so as not to collide with minor modes. * The following modules are now automatically activated without having to add anything to haskell-mode-hook: haskell-font-lock (just turn on global-font-lock-mode). haskell-decl-scan (just bind `imenu' to some key). * In recent Emacsen, haskell-doc hooks into eldoc-mode. * haskell-hugs and haskell-ghci are superceded by inf-haskell. * Indentation rules have been improved when using layout inside parens/braces. * Symbols like -> and \ can be displayed as actual arrows and lambdas. See haskell-font-lock-symbols. * Tweaks to the font-lock settings. Among other things paren-matching with things like \(x,y) should work correctly now. * New maintainer <monnier(a)gnu.org>.

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GADTs and GHC
by Simon Peyton-Jones 27 Dec '05

27 Dec '05

Dear Haskell folk One of the interesting things about ICFP was the number of times GADTs came up, either in papers or in discussions in the breaks. Francois's invited talk was very inspiring, and that was just the beginning. Stephanie and Dimitrios and I are now busy revising our wobbly-types GADT paper (which is implemented in GHC, but never published http://research.microsoft.com/%7Esimonpj/papers/gadt/index.htm) We have a *far* simpler story now... but that means it'll reject some programs that would be accepted by the earlier version. We don't think this loss of expressiveness is important, but we'd like to check. Hence this message: If you use GADTs, would you to send us your GADT code, so we can check that we can still compile it? (A secondary reason for asking is that it'd be interesting just to see the way you are using GADTs.) If you send your code just to me, I'll collect it. You could a) send a complete Haskell program, which should compile and run b) send a Haskell module, or collection of modules, which should compile, but which isn't a complete program c) send a Haskell module using GADTs, but lacking the support modules that would enable it to compile d) send Omega code, which GHC won't understand, but which demonstrates some cunning use of GADTs All of these would be useful, even (c) and (d) --- we can eyeball the code. As a bonus, in the case of (a) or (b) I'll add your code to GHC's regression suite, so that all future releases will guarantee to run your code. [Or at least if not it'll be deliberate!] Tell me if you'd like this; it'll become visible in GHC's CVS repository. Thanks Simon

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fptools mirror in darcs ready for testing
by John Goerzen 08 Dec '05

08 Dec '05

Hello everyone, Finally! Simon Marlow's plan[1] for moving from CVS to darcs for fptools, GHC, etc. is happening. Thanks to some feedback from him and the author of Tailor, as well as some free time finally, I've been able to convert things from CVS to darcs according to the plan. So, the first phase is to have live, updated darcs mirrors of CVS repos as appropriate. We now have that. Please feel free to darcs get --partial any of these. (Trust me, you *REALLY* want to use --partial. You'd be downloading over 13,000 patches otherwise on some of these.) http://cvs.haskell.org/darcs/ghc GHC HEAD http://cvs.haskell.org/darcs/ghc.ghc-6.4 GHC ghc-6-4-branch http://cvs.haskell.org/darcs/libraries libraries dir from fptools, HEAD http://cvs.haskell.org/darcs/libraries.ghc-6.4 libraries dir from fptools, ghc-6-4-branch http://cvs.haskell.org/darcs/nofib nofib dir from fptools, HEAD (there were no commits on ghc-6-4-branch for nofib) http://cvs.haskell.org/darcs/testsuite testsuite dir from fptools, HEAD http://cvs.haskell.org/darcs/testsuite.ghc-6.4 testsuite dir from fptools, ghc-6-4-branch Please note that you cannot pull patches between branches. This is because it is not really possible to have an automated CVS to darcs conversion that preserves enough information to do so. However, once the 6.4 branches go away, this will become nicely possible with future branches. Also please note that these repos are READ ONLY for now. Nobody will be accepting darcs patches until Simon (or someone) gives the word. These will all be updating daily as soon as I get around to writing a cron job. [1] http://www.haskell.org//pipermail/cvs-ghc/2005-November/027174.html

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ANNOUNCE: hmp3, an ncurses mp3 player
by dons＠cse.unsw.edu.au 04 Dec '05

04 Dec '05

hmp3 0.1 : an ncurses mp3 player hmp3 is a lightweight ncurses-based mp3 player written in Haskell. It uses mpg321 or mpg123 as its decoding backend. It is designed to be simple, fast and robust. A screenshot can be found at: http://www.cse.unsw.edu.au/~dons/hmp3.html The source: darcs get http://www.cse.unsw.edu.au/~dons/code/hmp3 Thanks go to Stefan Wehr and Sam Bronson, who helped a lot with beta testing. In particular Sam, who burnt many cpu cycles. Thanks! Cheers, Don

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Haskell Weekly News: November 29, 2005
by John Goerzen 29 Nov '05

29 Nov '05

Haskell Weekly News: November 29, 2005 Greetings, and thanks for reading the 17th issue of HWN, a weekly newsletter for the Haskell community. Each Tuesday, new editions will be posted (as text) to [1]the Haskell mailing list and (as HTML) to [2]The Haskell Sequence. 1. http://www.haskell.org/mailman/listinfo/haskell 2. http://sequence.complete.org/ Discussion Monads in other languages. A very interesting [3]thread covering availability of monads for other programming languages. 3. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/9430 Haskell in higher education. John Hughes posted a [4]survey aimed at those teaching Haskell in higher education. 4. http://thread.gmane.org/gmane.comp.lang.haskell.general/12680 GHC 6.6 progress. Jim Apple mentioned the [5]wiki page on GHC 6.6. 5. http://haskell.org/hawiki/GHC_206_2e6 GHC targetting Java. John Goerzen [6]asked about the apparent support for a Java target in the GHC source tree. Simon Peyton-Jones noted that it is no longer supported. 6. http://thread.gmane.org/gmane.comp.lang.haskell.glasgow.user/8970 Darcs Corner P2P repositories. There was a lot of [7]discussion on the Darcs lists about using a P2P network for storing Darcs information. 7. http://thread.gmane.org/gmane.comp.version-control.darcs.user/8883 About Haskell Weekly News Want to continue reading HWN? Please help us create new editions of this newsletter. Please see the [8]contributing information, or send stories to hwn -at- complete -dot- org. There is also a Darcs repository available. 8. http://sequence.complete.org/hwn-contrib

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Survey of Haskell in Higher Education
by John Hughes 28 Nov '05

28 Nov '05

I'm carrying out another survey of the Haskell community, this time to find out how Haskell is being used in university teaching. If you're teaching a course and using Haskell in any way, then this survey is aimed at you! You can find the survey form at http://www.cs.chalmers.se/~rjmh/Wash/Survey/TeachingSurvey.cgi Once again, as a reward for completing the form, you will see the results so far! I'm only surveying courses being taught this academic year, but I would like to gather as complete information as possible. I know that not all teachers using Haskell read this list, so I would appreciate it if you could help me by informing colleagues who are using Haskell about the existence of the survey. The information gathered will be used in the "History of Haskell" paper that I, Simon PJ, Phil Wadler and Paul Hudak are working on. Thanks very much for you help! John Hughes PS I now have over 500 responses to my earlier survey on use of Haskell--thank you very much! The results are interesting, and can be obtained from http://www.cs.chalmers.se/~rjmh/Wash/Survey/Survey.cgi.

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Records (was Re: [Haskell] Improvements to GHC)
by Georg Martius 28 Nov '05

28 Nov '05

Hi folks, rather than discussing about which operator symbol to use for record access, which is really a question of personal taste we should try to seriously discuss the proposals and get to a solutions! We all seem to agree that records are broken in Haskell. In order to fix that we need a new and most probably incompatible solution. However, I think the new solution should go in a new version of the Haskell standard (among other things :-) ). I would strongly disadvice to try to stick with the old system and improve it. Just because there are lots of different opinions we should still try to find a reasonable solution soon. Desite the minor problem of '.' that dominated the discussion so far, what are the REAL offences against Simons proposal [1] (denoted as SR in the following)? To me it sounds like a very reasonable starting point. Which other proposals exist? I quote David Roundy's list of problems [2] with a short annotation whether SR solves them: 1. The field namespace issue. solved by not sharing the same namespace with functions 2. Multi-constructor getters, ideally as a function. not solved. only possible by hand - As stated by Wolfgang Jeltsch [3] another datatype design might be better - I can image a solution is within SR example: > data Decl = DeclType { name :: String, ... } > | DeclData { name :: String, ... } > | ... > d :: Decl in addition to > d.DeclType.name > d.DeclData.name we provide (only if save, see 3.) > d.name 3. "Safe" getters for multi-constructor data types. not supported as it is - with the above suggestion it could be possible (don't know if desireable) 4. Getters for multiple data types with a common field. - solved with contrains > getx :: (r <: { x :: a }) => r -> a 5. Setters as functions. doesn't seem to be supported, or I don't see it right now. 6. Anonymous records. Supported 7. Unordered records. I don' t understand it. points added from me: 8. Subtyping Supported, quite nicely 9. higher order versions for selecting, updateing ... [4] not supported seems important to me, any solutions? Regards Georg [1] http://research.microsoft.com/~simonpj/Haskell/records.html [2] http://www.haskell.org//pipermail/haskell-cafe/2005-November/012226.html [3] http://www.haskell.org//pipermail/haskell-cafe/2005-November/012227.html [4] http://www.haskell.org//pipermail/haskell-cafe/2005-November/012162.html Am Donnerstag, 17. November 2005 19:08 schrieb Dimitry Golubovsky: > Sebastian Sylvan wrote: > >Personally I think that the dot is way to good of a symbol to be > >"wasted" on function composition. I mean, how often do you really use > >function composition in a way which doesn't obfuscate your code? I use > >($) way more often than (.). Some people do use it more often than I > > I found it useful to use (mainly for debugging purposes) > > mapM (putStrLn . show) <some list> > > if I want to print its elements each on a new line. > > -- > Dimitry Golubovsky > > Anywhere on the Web -- ---- Georg Martius, Tel: (+49 34297) 89434 ---- ------- http://www.flexman.homeip.net ---------

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RE: [Haskell] Re: Records
by Ralf Lammel 28 Nov '05

28 Nov '05

Good questions. You can't have a polymorphic typecase like "`extQ` (show :: Show a => a -> String )" because that's not really a *type*case. It is too polymorphic. You can have a polymorphic typecase like "`extQ` ( lshow :: [ a ] -> String )" because that's covered by the SYB2 paper; you need ext1Q (extQ1, depending on version). With SYB3, the second case is easier; it's just an instance. The first case ... still doesn't work ... this time for reasons of the class system. The type system doesn't allow to write one "default" instance for the case that a certain constraint is satisfiable (here: Show a) and to have yet another "default" instance to kick in *otherwise* to the SYB version. It would be great to have typeclass case to deal with this issue. Questions asking for typeclass case pop every now and then. The idea of the example is that you would need to define your own generic show function from scratch. The limitation of SYB1/SYB2 is that you would hit a closed-world-assumption. That's why SYB3! It allows you to add instances to the new generic show, as you go. Because of the lack of typeclass case, you still wouldn't be able to use the normal Prelude show function as default. You can use it instance-per-instance, by adopting each (attractive) show instances to be become instance of the new generic show function. However, you need to clone code because you probably want to re-tie the recursive knot in the new generic function. SYB3 is shipped separately, please use the distribution you pointed to. Simon PJ and I are still undecided regarding the modalities for adding SYB3 to the GHC libraries. Basically, we don't like the idea of having two libraries; SYB3 is more powerful but the combinator types are somewhat more complicated. However, using the separate SYB3 distribution is safe because it comes with TH support and a standalone mini SYB library. Regards, Ralf > -----Original Message----- > From: haskell-bounces(a)haskell.org [mailto:haskell-bounces@haskell.org] > On Behalf Of Johannes Waldmann > Sent: Monday, November 28, 2005 7:33 AM > To: haskell(a)haskell.org > Subject: [Haskell] Data.Generics question > > Dear all, in Data.Generics.Text > http://cvs.haskell.org/cgi- > bin/cvsweb.cgi/fptools/libraries/base/Data/Generics/Text.hs?rev=1.10 > I find this nice example > > gshow = ( \t -> > "(" > ++ showConstr (toConstr t) > ++ concat (gmapQ ((++) " " . gshow) t) > ++ ")" > ) `extQ` (show :: String -> String) > > but I couldn't figure out how to use this to declare a useful show > instance. I would need something like > > `extQ` (show :: Show a => a -> String ) > > i. e. use Show instance if available, or > > `extQ` ( lshow :: [ a ] -> String ) > > i. e. use another function if argument type is a list type > > > BTW: I guess the above is related to > http://homepages.cwi.nl/~ralf/syb3/ > Do the current (6.4) ghc compiler/libraries correspond to what's in > that paper? > -- > -- Johannes Waldmann -- Tel/Fax (0341) 3076 6479/80 -- > ---- http://www.imn.htwk-leipzig.de/~waldmann/ ------- > > > _______________________________________________ > Haskell mailing list > Haskell(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell

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Call for Proposals: FM08: The 15th International Symposium on Formal Method s
by events-admin＠fmeurope.org 28 Nov '05

28 Nov '05

Formal Methods Europe Call for Proposals FM08: The 15th International Symposium on Formal Methods Formal Methods Europe invites proposals from organisations interested in hosting the 15th International Symposium on Formal Methods (FM08), to be held in Europe in Spring 2008. Formal Methods Europe (FME, http://www.fmeurope.org/) is a worldwide association bringing together researchers and practitioners in all aspects of formal methods for the evelopment, analysis and maintenance of computing systems and software. Its activities include the dissemination of research findings and industrial experience through symposia and sponsored events, notably the long running and highly regarded series of FM symposia. The 14th symposium in the series (http://fm06.mcmaster.ca/) is being organised by McMaster University, Ontario, Canada for August 2006. We invite enquiries and proposals from potential hosts for the 15th Symposium (FM08), which will be held at a European location, in spring 2008. Symposia take place approximately every 18 months and have at their core an international technical conference based on high quality refereed papers with published proceedings. A programme of workshops, tutorials and exhibitions adds to the event. However, there are few fixed rules regarding the format and potential hosts are invited to discuss options with FME. Attendances typically range from 125 to 260 participants. Important Dates - January 15, 2006 Proposals due Following receipt of proposals, FMEs board will discuss proposals by email with the proposers. - April 15, 2006 Latest date for notification of proposal acceptance Proposal Submission Proposals should be regarded as expressions of interest and will serve as a basis for discussion. They are not binding agreements and acceptance of a proposal does not constitute a final commitment on either side. Proposals should be no more than 3 pages in length and should contain: A brief description of why hosting the symposium is of interest to the proposing institution. The names and contact information (web page, email address) of the proposed organising committee. Previous experience in events organisation. A description of the facilities that will be available for the symposium. We welcome informal enquiries. Please send your proposals and any enquiries by electronic mail to: info(a)fmeurope.org. Proposals should be submitted in PDF. _______________________________________________ events mailing list events(a)fmeurope.org http://www.fmeurope.org/mailman/listinfo/events

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Data.Generics question
by Johannes Waldmann 28 Nov '05

28 Nov '05

Dear all, in Data.Generics.Text http://cvs.haskell.org/cgi-bin/cvsweb.cgi/fptools/libraries/base/Data/Gener… I find this nice example gshow = ( \t -> "(" ++ showConstr (toConstr t) ++ concat (gmapQ ((++) " " . gshow) t) ++ ")" ) `extQ` (show :: String -> String) but I couldn't figure out how to use this to declare a useful show instance. I would need something like `extQ` (show :: Show a => a -> String ) i. e. use Show instance if available, or `extQ` ( lshow :: [ a ] -> String ) i. e. use another function if argument type is a list type BTW: I guess the above is related to http://homepages.cwi.nl/~ralf/syb3/ Do the current (6.4) ghc compiler/libraries correspond to what's in that paper? -- -- Johannes Waldmann -- Tel/Fax (0341) 3076 6479/80 -- ---- http://www.imn.htwk-leipzig.de/~waldmann/ -------

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