March 2005 - Haskell - Haskell.org

No Pattern Guards
by Yitzchak Gale 28 Mar '05

28 Mar '05

I posted a link to the following on the HaskellTwo wiki page. Please comment. I would like to suggest that PatternGuards NOT be included in HaskellTwo. While I enjoyed Simon Peyton Jones' well-written note on pattern guards [http://research.microsoft.com/Users/simonpj/Haskell/guards.html] very much, it was written a long time ago. Today it is easy to recognize that the problem he identifies is just the need for a monad, and that his proposed solution is a new syntax for introducing monadic calculations. The new syntax is messier and less general than the existing "do". Furthermore, the new syntax confuses the semantics of existing constructs. Referring to Simon's principal example in his note, here is one way to write "clunky" without PatternGuards: > clunky env var1 var2 = fromMaybe (var1 + var2) $ do > val1 <- lookup env var1 > val2 <- lookup env var2 > return (val1 + val2) Simple, clear, and scalable. -YitzGale

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Re: [Haskell] How to substract a list?
by Bright Sun 28 Mar '05

28 Mar '05

Hi, Tks, this is not what I wanted. I want remove pairs list, [(5,1),(4,1),(3,1),(2,1),(1,1)] remove [(2,1),(1,1)] [(5,1),(4,1),(3,1)] so pairs [(2,1),(1,1)] removed. Tks. --- Pierre Barbier de Reuille <pierre.barbier(a)cirad.fr> wrote: > One answer is the infix operator (\\) defined in the > List module (or in > Data.List ...) > > But it's in ont of the "set" operations. For example > try : > > [1..10] \\ [3..6] > [1,2,7,8,9,10] > > But also : > > ([1..10]++[1..10]) \\ [3..6] > [1,2,7,8,9,10,1,2,7,8,9,10] > > So _all_ the elements with values in [3..6] where > removed !! > If that's what you want ! Perfect ... if not : what > do you want exactly > ? List substraction is not uniq. > > Pierre > > Bright Sun a �crit : > > In Haskell, ++ can spends second list argument > onto > > the end of first list argument. How to substract > the > > second list from the first list? > > > > For example, > > [(5,1),(4,1),(3,1),(2,1),(1,1)] > > substract > > [(2,1),(1,1)] > > I want to get result list: > > [(5,1),(4,1),(3,1)] > > > > Tks. > > > > > > > > __________________________________ > > Do you Yahoo!? > > Make Yahoo! your home page > > http://www.yahoo.com/r/hs > > _______________________________________________ > > Haskell mailing list > > Haskell(a)haskell.org > > http://www.haskell.org/mailman/listinfo/haskell > > > > -- > Pierre Barbier de Reuille > > INRA - UMR Cirad/Inra/Cnrs/Univ.MontpellierII AMAP > Botanique et Bio-informatique de l'Architecture des > Plantes > TA40/PSII, Boulevard de la Lironde > 34398 MONTPELLIER CEDEX 5, France > > tel : (33) 4 67 61 65 77 fax : (33) 4 67 61 > 56 68 > __________________________________ Do you Yahoo!? Yahoo! Small Business - Try our new resources site! http://smallbusiness.yahoo.com/resources/

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Superclass default methods
by Yitzchak Gale 28 Mar '05

28 Mar '05

Thomas Hallgren wrote: > If classes were allowed to declare default > methods for superclasses... Benjamin Franksen wrote (on Haskell Libraries): > Robert Will has written a fully specified proposal for this. He calls it > "delayed method definition", see > http://www.stud.tu-ilmenau.de/~robertw/dessy/fun/, sections... 4.3.2. > Looks like a really good idea to me. Cale Gibbard wrote: > One issue might be which default instance gets chosen > when two classes both provide default instances for a > given class. Perhaps in this case, we can just force the > user to provide an instance, In other words, we either (a) throw a compile-time error, or (b) issue a compile-time warning and bind the method to undefined. Robert Will's specification is not completely explicit about which of these to choose, but he implies (a). > or produce a compile-time warning and select one > automatically in some canonical fashion. No, that would lead to problems. See below. Simon Peyton-Jones wrote: > It seems overkill to have a whole new language feature > to deal with one library issue. Ross Paterson wrote: > It's not just here -- this would make lots of fairly > fine-grained class hierarchies a lot less painful. Right. This is not just one library issue. In my opinion it is a major limitation in Haskell's type system. This restriction has often forced me to write gobs of boiler-plate code, and to make awkward distortions in what should have been simple hierarchies of classes. > The idea comes up very occasionally... For me it comes up all the time. This is an upward-compatible change that is very intuitive. Ross Paterson also wrote: > But I agree that there's a cross-module problem. No. A cross-module problem only arises if we arbitrarily choose a default method when there is an ambiguity. If we choose (a) or (b) above, there is no problem. -Yitz

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ESSLLI 2005 - Registration now Open!
by Carlos Areces 28 Mar '05

28 Mar '05

ESSLLI 2005 17th European Summer School in Logic, Language and Information The annual summer school of FoLLI, the Association for Logic, Language and Information. Heriot-Watt University Edinburgh, Scotland 8-19 August, 2005 -------------------------- |REGISTRATION IS NOW OPEN| -------------------------- Go to http://www.macs.hw.ac.uk/esslli05/ and follow the registration page at: http://www.macs.hw.ac.uk/esslli05/give-page.php?17 (Note, this is during the Edinburgh famous international festival, so accommodation must be reserved promptly to guarantee accommodation). The main focus of ESSLLI is on the interface between linguistics, logic and computation. The school has developed into an important meeting place and forum for discussion for students, researchers and IT professionals interested in the interdisciplinary study of Logic, Language and Information. ESSLLI courses cover a wide variety of topics within six areas of interest: Logic, Computation, Language, Logic and Computation, Computation and Language, Language and Logic. Foundational courses aim to provide truly introductory courses into a field. The courses presuppose absolutely no background knowledge. In particular, they should be accessible to people from other disciplines. Introductory courses are intended to equip students and young researchers with a good understanding of a field's basic methods and techniques, and to allow experienced researchers from other fields to acquire the key competences of neighboring disciplines, thus encouraging the development of a truly interdisciplinary research community. Advanced courses are intended to enable participants to acquire more specialized knowledge about topics they are already familiar with. Workshops are intended to encourage collaboration and the cross-fertilization of ideas by stimulating in-depth discussion of issues which are at the forefront of current research in the field. In these workshops, students and researchers can give presentations of their research. In addition to courses and workshops there are evening lectures, a student session and a number of satellite events (to be announced later). The aim of the student session is to provide Masters and PhD students with an opportunity to present their own work to a professional audience, thereby getting informed feedback on their own results. Unlike workshops, the student session is not tied to any specific theme. Looking forward to seeing you at ESSLLI 2005 in beautiful Edinburgh during the impressive Edinburgh international festival (see http://www.eif.co.uk/festival2005/) Fairouz Kamareddine (ESSLLI 2005 organising chair) and FOLLI (the Association for Logic, Language and Information)

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ANNOUNCE: yi 0.1.0
by dons＠cse.unsw.edu.au 28 Mar '05

28 Mar '05

yi-0.1.0 Yi is a text editor written and extensible in Haskell. The goal of Yi is to provide a flexible, powerful and correct editor core dynamically scriptable in Haskell. Yi as it stands implements most of vi by default. Keybindings for vim and nano are also provided. Other editor interfaces can be written by the user to extend Yi, through lexer specifications. Yi uses hs-plugins for runtime configuration via Haskell source, and to allow components of the editor to be dynamically recompiled without needing to restart Yi. Yi is quite fast and lightweight, thanks to GHC's excellent profiling tools. Source and more information is available at: http://www.cse.unsw.edu.au/~dons/yi.html Yi would not exist without the support of the members of the #haskell irc channel - thanks guys :) Patches, comments, criticism welcome! -- Don Stewart

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ANNOUNCE: HWSProxyGen version 0.1
by Andre W B Furtado 28 Mar '05

28 Mar '05

We are glad to present version 0.1 of HWSProxyGen, a web services proxy generator for the Haskell functional language, implemented in Haskell and C#. The final purpose is to show that Haskell and functional languages in general can be used as a viable way to the implementation of distributed components and applications, interacting with services implemented in different languages and/or platforms. Plese note that this first version is guaranteed to work only for web services generated with Visual Studio .NET. Binaries, source code and more information can be found in: http://www.cin.ufpe.br/~haskell/hwsproxygen/ HWSProxyGen was conceived and implemented in the Informatics Center of the Federal University of Pernambuco, Brazil, by: - Andre W. B. Furtado - Andre L. M. Santos - Carlos A. G. Ferraz - Gustavo A. Santos - Adeline S. Silva - Carla M. P. Nascimento Cheers, -- AFurtado

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Re: [Haskell] How to substract a list?
by Bright Sun 28 Mar '05

28 Mar '05

Tks Arjun, This is what I want. Thanks very much. Bright --- Arjun Guha <guhaarju(a)grinnell.edu> wrote: > Try this: > > > remove theList toRemove = filter (\x -> not (elem > x toRemove)) theList > > -Arjun > > On Mar 27, 2005, at 18:28, Bright Sun wrote: > > > Hi, > > > > Tks, this is not what I wanted. > > > > I want remove pairs list, > > > > [(5,1),(4,1),(3,1),(2,1),(1,1)] remove > [(2,1),(1,1)] > > [(5,1),(4,1),(3,1)] > > > > so pairs [(2,1),(1,1)] removed. > > > > Tks. > > > > --- Pierre Barbier de Reuille > > <pierre.barbier(a)cirad.fr> wrote: > > > One answer is the infix operator (\\) defined > in the > > > List module (or in > > > Data.List ...) > > > > > > But it's in ont of the "set" operations. For > example > > > try : > > > > > > [1..10] \\ [3..6] > > > [1,2,7,8,9,10] > > > > > > But also : > > > > > > ([1..10]++[1..10]) \\ [3..6] > > > [1,2,7,8,9,10,1,2,7,8,9,10] > > > > > > So _all_ the elements with values in [3..6] > where > > > removed !! > > > If that's what you want ! Perfect ... if not : > what > > > do you want exactly > > > ? List substraction is not uniq. > > > > > > Pierre > > > > > > Bright Sun a �crit : > > > > In Haskell, ++ can spends second list > argument > > > onto > > > > the end of first list argument. How to > substract > > > the > > > > second list from the first list? > > > > > > > > For example, > > > > [(5,1),(4,1),(3,1),(2,1),(1,1)] > > > > substract > > > > [(2,1),(1,1)] > > > > I want to get result list: > > > > [(5,1),(4,1),(3,1)] > > > > > > > > Tks. > > > > > > > > > > > > > > > > __________________________________ > > > > Do you Yahoo!? > > > > Make Yahoo! your home page > > > > http://www.yahoo.com/r/hs > > > > > _______________________________________________ > > > > Haskell mailing list > > > > Haskell(a)haskell.org > > > > > http://www.haskell.org/mailman/listinfo/haskell > > > > > > > > > > -- > > > Pierre Barbier de Reuille > > > > > > INRA - UMR Cirad/Inra/Cnrs/Univ.MontpellierII > AMAP > > > Botanique et Bio-informatique de l'Architecture > des > > > Plantes > > > TA40/PSII, Boulevard de la Lironde > > > 34398 MONTPELLIER CEDEX 5, France > > > > > > tel : (33) 4 67 61 65 77 fax : (33) 4 67 > 61 > > > 56 68 > > > > > > > > > > > > > __________________________________ > > Do you Yahoo!? > > Yahoo! Small Business - Try our new resources > site! > > http://smallbusiness.yahoo.com/resources/ > > _______________________________________________ > > Haskell mailing list > > Haskell(a)haskell.org > > http://www.haskell.org/mailman/listinfo/haskell > > __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com

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How to substract a list?
by Bright Sun 27 Mar '05

27 Mar '05

In Haskell, ++ can spends second list argument onto the end of first list argument. How to substract the second list from the first list? For example, [(5,1),(4,1),(3,1),(2,1),(1,1)] substract [(2,1),(1,1)] I want to get result list: [(5,1),(4,1),(3,1)] Tks. __________________________________ Do you Yahoo!? Make Yahoo! your home page http://www.yahoo.com/r/hs

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Profiling strategies
by Andreas Marth 25 Mar '05

25 Mar '05

Hallo! Does anybody have some profiling strategies other than from the ghc user guide? Any references, suggestions and so on are very welcome. Thanks, Andreas

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RE: [Haskell] The FunctorM library
by Simon Peyton-Jones 25 Mar '05

25 Mar '05

| > Yes, I think this should be fixed, and perhaps it could be done in a | > backward compatible way? If classes were allowed to declare default | > methods for superclasses, then you could have | > | > class Functor f where fmap :: ... | > class Functor m => Monad m where | > ...the usual stuff... | > fmap = liftM | > | > Then declaring | > | > instance Monad T where ... | > | > for some T, would implicitly introduce an instance Functor T, if it is | > not defined explicitly... It seems overkill to have a whole new language feature to deal with one library issue. It would take a bit of implementing too, and it's not clear to me what the specification is. For example, what if Functor T *is* defined explicitly, but in a later module? The idea comes up very occasionally, but I wouldn't say it's been a hot issue. Simon

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