- Haskell - Haskell.org

Re[2]: [Template-haskell] new TH tutorial (request for comments)
by Bulat Ziganshin 24 Jan '06

24 Jan '06

Hello Johannes, Monday, January 23, 2006, 11:27:58 AM, you wrote: JW> I'd like to read some overview and comparison on "second-level JW> programming" in Haskell (and if there is none, I'm willing to contribute): citating my another letter: "when i was interested in generic programmimg with Haskell, i found 7 projects, which can be used for it: drift -fgenerics TH generic haskell polyp SYB strafunski" JW> what is the relation between Preprocessors (DrIFT), Template Haskell, JW> Data.Generics/Typeable (so perhaps have one example presented in each JW> of these frameworks) i also had an idea of small overview of these all tools. i divided them to 3 categories: general preprocessors/code generators TH DrIFT compile-time generic programming tools GH PolyP -fgenerics dynamic generic programming libraries SYB strafunski it's interesting that GHC itself armored with just one tool in each category! :) of course, -fgenerics is very weak tool, so compile-time generic programming is the area where GHC has lesser power JW> and how it compares to Reflection (including Annotations) as in JW> http://java.sun.com/j2se/1.5.0/docs/api/java/lang/reflect/package-summary.h… JW> I have the feeling that annoations (in the Java sense, see JLS 9.6/9.7) JW> are a clever and powerful idea that we might want to copy. no opinion, just citating for haskell maillist :) -- Best regards, Bulat mailto:bulatz@HotPOP.com

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Visual Haskell for Visual Studio 2005
by Lars Schouw 24 Jan '06

24 Jan '06

Simon, All, First of all congratulations on a great product and all the time spend on this. Is there any plans to let Visual Haskell support Visual Studio 2005 like f#? Regards Lars Schouw Tokyo, Japan --------------------------------- Yahoo! Photos Got holiday prints? See all the ways to get quality prints in your hands ASAP.

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RE: [Haskell] IO Regions in Haskell98
by Simon Peyton-Jones 24 Jan '06

24 Jan '06

| however that there is a Haskell98 implementation of IO regions. The | solution involves no higher-ranked types, and works both in GHC and | Hugs. The idea is trivial: given | | > newtype Q = Q Handle | > newtype IOM a = IOM (IO a) | > qGetChar :: Q -> IOM Char | > withFile :: FilePath -> (Q -> IOM a) -> IOM a | | we wish to assure that the handle Q never escapes, neither explicitly | nor implicitly. Don't side effects kill you? withFile "foo" (\q -> writeIORef var q) So would unsafePerformIO withFile "foo" (\q -> return (unsafePerformIO (qGetChar q))) Simon

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Modelling languages for FP (like UML for OO)
by Mads Lindstrøm 23 Jan '06

23 Jan '06

Hi all In object-oriented programming, UML is used to model programs. In functional programming (especially Haskell) we use ??? The only graphical modellering language I have found is FAD: http://www.cs.kent.ac.uk/pubs/2001/1152/ . Are there other approaches? Are anybody, except for the creates of FAD, using it? If you are using FAD, what are your experiences with it? I am mainly interested in the macro level. That is modules, classes, class instances, ... Not in modellering the internals of a function. Greetings, Mads Lindstrøm

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RE: [Haskell] Pattern Matching with rank-2 types
by Simon Peyton-Jones 23 Jan '06

23 Jan '06

Well spotted! Yes, I changed this some time ago. Handling polymorphic subsumption when matching patterns just turned to be a lot of hassle, with little obvious payoff. Types in patterns must now match exactly. I could conceivably back-pedal on this, but you are the first person to even notice the change (or at least to comment on it). Simon | -----Original Message----- | From: haskell-bounces(a)haskell.org [mailto:haskell-bounces@haskell.org] On Behalf Of Bruno Oliveira | Sent: 21 January 2006 18:44 | To: Haskell Mailing List | Subject: [Haskell] Pattern Matching with rank-2 types | | Hello, | | The following function is a valid function in ghc6.2.2: | | > func :: (forall a . [a]) -> [b] | > func [] = [] | | However, in ghc6.4.1 it does not work anymore: | | Iterators4.lhs:56:6: | Couldn't match `forall a. [a]' against `[a]' | When checking the pattern: [] | In the definition of `func': func [] = [] | | Is this supposed to happen? | | Cheers, | | Bruno | | | _______________________________________________ | Haskell mailing list | Haskell(a)haskell.org | http://www.haskell.org/mailman/listinfo/haskell

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Haskell Weekly News: January 23, 2006
by dons＠cse.unsw.edu.au 22 Jan '06

22 Jan '06

Haskell Weekly News: January 23, 2006 Greetings, and thanks for reading the 21st issue of HWN, a weekly newsletter for the Haskell community. Each Monday, new editions are posted to [1]the Haskell mailing list and to [2]The Haskell Sequence. [3]RSS is also available. 1. http://www.haskell.org/mailman/listinfo/haskell 2. http://sequence.complete.org/ 3. http://sequence.complete.org/node/feed New Releases * Haskell' This week Isaac Jones announced that the Haskell' standardisation process is underway. Haskell' will be a conservative refinement of Haskell 98: "Announcing the Haskell' ("Haskell-Prime") process. A short time ago, I asked for volunteers to help with the next Haskell standard. A brave group has spoken up, and we've organized ourselves into a committee in order to coordinate the community's work. It will be the committee's task to bring together the very best ideas and work of the broader community in an "open-source" way, and to fill in any gaps in order to make Haskell' as coherent and elegant as Haskell 98." Read the full announcement [4]here. Presently, the following resources are available: + [5]The haskell-prime mailing list + The Haskell' [6]issue tracking system/wiki + A [7]darcs repository for larger code examples and experiments Please join us in making Haskell' a success. 4. http://article.gmane.org/gmane.comp.lang.haskell.general/13138 5. http://haskell.org/mailman/listinfo/haskell-prime 6. http://hackage.haskell.org/trac/haskell-prime 7. http://hackage.haskell.org/trac/haskell-prime/wiki/SourceCode Resources and Tools * Cabal. Isaac Jones [8]announced some changes to Cabal, including new changes to the `hooks' interface. Feedback is encouraged. Secondly, a move is underway to build [9]an exhaustive list of all Cabalised packages. Add a link if you have something! Isaac is asking people to re-send any Cabal bug reports or feature requests yet to be addressed. Report them on the [10]Cabal Wiki & Bug Tracker 8. http://article.gmane.org/gmane.comp.lang.haskell.libraries/4145 9. http://hackage.haskell.org/trac/hackage/wiki/CabalPackages 10. http://hackage.haskell.org/trac/hackage/ * Darcs switchover GHC has [11]switched to darcs. The era of CVS is at an end: From: Simon Marlow Subject: TAG final switch to darcs, this repo is now live Fri Jan 20 05:46:30 PST 2006 Simon Marlow microsoft.com> tagged final switch to darcs, this repo is now live 11. http://article.gmane.org/gmane.comp.lang.haskell.cvs.ghc/13186 Discussion * IO Regions. Oleg Kiselyov [12]describes a simple implementation of monadic regions. The technique provides static guarantees that neither a file handle nor any computation involving the handle can leak outside of the region that created it. The technique has no runtime overhead and induces no runtime errors. For some background, John Launchbury and Simon Peyton Jones's 94 paper [13]Lazy Functional State Threads is useful. 12. http://article.gmane.org/gmane.comp.lang.haskell.general/13106 13. http://www.cse.ogi.edu/~jl/Papers/stateThreads.ps * Lexically scoped type variables. Simon Peyton-Jones [14]released a proposal to change the way in which lexically-scoped typed variables work in GHC, as part of a revision to make type inference for GADTs simpler and more uniform. 14. http://article.gmane.org/gmane.comp.lang.haskell.glasgow.user/9219 * Providing an alternative to GMP. Esa Ilari Vuokko [15]began a discussion on modifying the GHC runtime and build system to support alternative arbtirary precision arithmetic libraries, other than the GPL'd GMP. 15. http://article.gmane.org/gmane.comp.lang.haskell.cvs.ghc/13198 * Arrays interfaces. (clarification) The Haskell'98 library report contains only basic Array implementation. The Hierarchical Libraries, shipped with modern versions of GHC, Hugs and NHC, includes much richer arrays library. [16]Bulat Ziganshin started [17]a wiki page describing how to use these new array interfaces. 16. http://article.gmane.org/gmane.comp.lang.haskell.general/12992 17. http://haskell.org/haskellwiki/Arrays Papers This is a new HWN section collecting paper or article abstracts on Haskell-related topics. If you have submitted a new Haskell paper, send your abstract to HWN, and the abstract will appear in the next issue. * Ralf L�mmel. Book review, "The Haskell Road to Logic, Maths and Programming" by Kees Doets and Jan van Eijck. To appear in JoLLI journal; 13 pages. [18]http://www.cs.vu.nl/~ralf/JoLLI06. The "Haskell road" is an excellent book worth considering as course material and reading anyhow. A non-Haskell road is also discussed in the review. 18. http://www.cs.vu.nl/~ralf/JoLLI06 * Ralf L�mmel. "Google's MapReduce Programming Model -- Revisited" Draft; To be submitted; feedback appreciated; 27 pages. [19]http://www.cs.vu.nl/~ralf/MapReduce. The seminal MapReduce paper had been briefly discussed at LTU without really going into technical details. The present paper discovers the concepts from a functional programming perspective. Did you ever wonder why MapReduce is called MapReduce? 19. http://www.cs.vu.nl/~ralf/MapReduce Darcs Corner * Darcs Blogging. Zooko [20]wrote an interesting blog entry on the PR issues darcs has, and on the various activities undertaken by the darcs developers. 20. http://article.gmane.org/gmane.comp.version-control.darcs.user/9258 Quote of the Week <monochrom> monadic regions? sounds neat. <monochrom> "monadic ___" sounds neat :) <dons> forall a. Monad a => Neat a Contributing to HWN Thanks to Bulat Ziganshin and Isaac Jones for contributing material to this edition of HWN. You can help us create new editions of this newsletter. Please see the [21]contributing information, send stories to dons -at- cse.unsw.edu.au. The darcs repository is available at darcs get http://www.cse.unsw.edu.au/~dons/code/hwn 21. http://sequence.complete.org/hwn-contrib

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duplicate elements in Data.Set
by Walter Moreira 22 Jan '06

22 Jan '06

Hello list. Are there situations where a set can contain duplicate elements? I have a newtype and it is an instance of 'Eq' via the 'compare' method, and it is also an instance of 'Ord'. After some Data.Set operations with sets of that type I get a set which contains two elements which compare equal. What am I doing wrong? The function 'Set.valid' returns 'False' when applied to the set. I use the function 'Set.fromList' sometimes. Is it supposed to always yield a valid set? or it may depend on the order or equality? Sorry the question is a little vague. When I try to construct small examples the problem disappear. Thanks, Walter

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Pattern Matching with rank-2 types
by Bruno Oliveira 21 Jan '06

21 Jan '06

Hello, The following function is a valid function in ghc6.2.2: > func :: (forall a . [a]) -> [b] > func [] = [] However, in ghc6.4.1 it does not work anymore: Iterators4.lhs:56:6: Couldn't match `forall a. [a]' against `[a]' When checking the pattern: [] In the definition of `func': func [] = [] Is this supposed to happen? Cheers, Bruno

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Haskell': Kicking off the process of defining the next Haskell standard.
by Isaac Jones 21 Jan '06

21 Jan '06

let haskell' = succ haskell98 in Announcing the Haskell' ("Haskell-Prime") process. A short time ago, I asked for volunteers to help with the next Haskell standard. A brave group has spoken up, and we've organized ourselves into a committee in order to coordinate the community's work. It will be the committee's task to bring together the very best ideas and work of the broader community in an "open-source" way, and to fill in any gaps in order to make Haskell' as coherent and elegant as Haskell 98. Our task is broadly defined by our mission statement: The Haskell programming language is more-or-less divided into two "branches". The Haskell 98 standard is the "stable" branch of the language, and that has been a big success. A lot of progress has been made over the last few years in the "research" branch of the Haskell language. It is constantly advancing, and we feel that it is time for a new standard which reflects those advancements. Haskell' will be a conservative refinement of Haskell 98. It will be the work of this committee to adopt a set of language extensions and modifications and to standardize a new set of libraries. We will strive to only include tried-and-true language features, and to define them at least as rigorously as Haskell 98 was defined. This standard will reflect the realities of developing practical applications in the Haskell language. We will work closely with the rest of the Haskell community to create this standard. Your Haskell' Committee is as follows (slightly munged email addresses follow): * Manuel M T Chakravarty <chak at cse.unsw.edu.au> * John Goerzen <jgoerzen at complete.org> * Bastiaan Heeren <bastiaan at cs.uu.nl> * Isaac Jones <ijones at galois.com> * John Launchbury <john at galois.com> * Andres Loeh <loeh at iai.uni-bonn.de> * Simon Marlow <simonmar at microsoft.com> * John Meacham <john at repetae.net> * Ravi Nanavati <ravi at bluespec.com> * Henrik Nilsson <nhn at cs.nott.ac.uk> * Ross Paterson <ross at soi.city.ac.uk> * Simon Peyton-Jones <simonpj at microsoft.com> * Don Stewart <dons at cse.unsw.edu.au> * Audrey Tang <autrijus at gmail.com> * Simon J. Thompson <S.J.Thompson at kent.ac.uk> * Malcolm Wallace <Malcolm.Wallace at cs.york.ac.uk> * Stephanie Weirich <sweirich at cis.upenn.edu> The editors are Isaac Jones and John Launchbury. Feel free to contact any of us with any concerns or questions. If you don't know who to direct your questions to, email Isaac Jones ijones(a)syntaxpolice.org. Community involvement is vital to our task, and there will be a way for members of the community to make formal proposals. In the opening phases, please use these more informal resources to help us coordinate Haskell': * The haskell-prime mailing list. All technical discussion will take place here, or (if other meetings take place) be reported here. Anyone can subscribe, and any subscriber can post questions and comments, and participate in discussions. Anyone can read the list archives. http://haskell.org/mailman/listinfo/haskell-prime * A wiki / issue tracking system to document consensus and to track ongoing tasks. This system is publicly readable, but only committee writable so that we may present it as the "official" output of the committee. If you ever feel that the wiki is not accurate as to the consensus, please alert the committee! http://hackage.haskell.org/trac/haskell-prime * A darcs code repository for experiments, proposed libraries,and complex examples. darcs is a decentralized system, so anyone can use it, but patches should be sent to Isaac Jones: http://hackage.haskell.org/trac/haskell-prime/wiki/SourceCode Please join us in making Haskell' a success. your, Haskell' Committee p.s. Please feel free to forward this announcement to appropriate forums.

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Re: [Haskell] Modelling languages for FP (like UML for OO)
by David Barton 19 Jan '06

19 Jan '06

Philippa Cowderoy and Mads Lindstrom wrote: ----- Original Message ----- From: "Philippa Cowderoy" <flippa(a)flippac.org> To: "Mads Lindstrøm" <mads_lindstroem(a)yahoo.dk> Cc: <haskell(a)haskell.org> Sent: Thursday, January 19, 2006 8:16 AM Subject: Re: [Haskell] Modelling languages for FP (like UML for OO) On Thu, 19 Jan 2006, Mads [ISO-8859-1] Lindstrøm wrote: > Hi all > > In object-oriented programming, UML is used to model programs. In > functional programming (especially Haskell) we use ??? > Haskell :-) > I am mainly interested in the macro level. That is modules, classes, > class instances, ... Not in modellering the internals of a function. > I tend to just write the equivalent haskell code with the function definitions left out. I suspect the only thing that can really be gained with a more graphical language is drawing dependancy lines between modules and the like - though I was never big on the formalised modelling languages in the first place, so I may not be the best person to conclude that. ------------------------------------------------------- I do not wish to take away anything from Philippa's reply, but I do wish to toot my own project. Dr. Perry Alexander and myself are in the final stages of moving a Systems Level Design Language (SLDL) to standardization. It is called Rosetta, and is suited to the kind of modeling you are referring to (among other things). It is logic based rather than lamda calculus based, but the "execution subset" that is coming to be a kind of defacto standard (as opposed to the standard itself) is pretty much Haskell --- the CADSTONE product is called R-Haskell, as it translates that subset directly into Haskell. More information may be found at http://www.sldl.org And, by the way, we at EDAptive Computing are looking for someone to work on our own Rosetta projects, particularly with direct experience with theorem provers and model checkers --- using as much as designing and implementing. If anyone is interested, or has any questions about Rosetta, by all means drop me a line. Dave Barton EDAptive Computing

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