- Haskell - Haskell.org

Pure File Reading (was: Dealing with configuration data)
by Koen Claessen 11 Oct '02

11 Oct '02

Dear all, At the moment, a discussion on haskell-cafe is going on about how to neatly program the fact that an entire program depends on a number of parameters that are read in once at the beginning of a program. The suggestion that many people came up with was using unsafePerformIO in the beginning to read the file. Here is my version of that: | data Configuration = ... -- config data | | getConfig :: Configuration | getConfig = unsafePerformIO $ | do ...read configuration from file... | return configuration | | main = | do doStuff It is quite disturbing that there is no other easy way to do this than using unsafePerformIO (except for using implicit parameters perhaps, but there are other reasons for not using those). I have been thinking a little bit more about this and here is what I found. Remember the Gofer days, when Gofer had a "function": openFile :: FilePath -> String This was of course a cheap and dirty way of implementing things like the getConfig above, but it is impure. However, one could imagine a functional version of this function: readFileOnce :: FilePath -> Maybe String This function will read the contents of the file (and return Nothing if something went wrong), but it is memoized, so that the second time you use this function you get the same result. So, it is a pure function. (Admittedly, it is somewhat unpredictable, but you will always get the same result for the same arguments.) It is no more strange than GHC's pure version of the getArgs function (I forgot what it was/is called). How about space behavior, you say? Reading a file, and memoizing the result means storing the whole contents of the file in memory! The point is that the use of this function will typically happen at the beginning of a program, when reading the configuration file(s). When all this has happened, the function readFileOnce, and its memo table, will be garabage collected. (Of course there is no guarantee that all calls to readFileOnce will be evaluated at the beginning of a program, and it is not required, but when you do, there are no space problems.) There could of course be pure "-Once" versions of other IO operations. Here is a list of possibilities: - reading a file - getting arguments - getting environment variables - downloading a webpage - ... What do you think? Regards, /Koen. -- Koen Claessen http://www.cs.chalmers.se/~koen Chalmers University, Gothenburg, Sweden.

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The future of Haskell discussion at the Haskell workshop, Oct 3, 2002
by Johan Jeuring 11 Oct '02

11 Oct '02

This is a brief account of the discussion on the future of Haskell at the Haskell workshop, Oct 3, 2002, in Pittsburgh. After Simon Peyton Jones discussed the copy-right issue of publishing the report, we had a brief discussion about the future of Haskell. The first point raised was that the addition of unsafe extensions to Haskell, like unsafePerformIO and unsafeCoerce, goes against the original design requirements for Haskell. The presence of unsafe extensions makes quick but dirty solutions possible, for example for problems that need concurrency. This hampers the development of semantically clean theories, and makes building tools that reason about Haskell much harder. Reactions on this point differed: some people heartily agreed, some other people thought unsafePerformIO was often just a cosmetic thing, and that whenever a theory/abstraction/method for an application for which unsafe extensions are used now is in sight, people will try to develop it. Another suggestion was to develop methods for separation of threads so that you can reason locally about threads. -- Johan Jeuring

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RE: Reversi
by Jan de Wit 11 Oct '02

11 Oct '02

Hi, > Hello!!! > > Thank you for the answer. > I would like to know about games two-player. > I´m having problems with interface of user. I've written a Go-program (also black and white stones on a board :-) with an interface in TclHaskell. If you could be a bit more specific about your user-interface problems, I might be able to help out... Cheers, Jan de Wit > > Thank you > Tatiana -----Original Message----- From: Tatiana [mailto:tatianam@escelsa.com.br] Sent: Thursday, October 10, 2002 2:29 PM To: haskell(a)haskell.org Subject: Reversi Hello!!! Thank you for the answer. I would like to know about games two-player. I´m having problems with interface of user. Thank you Tatiana On 2002-10-08T17:13:35-0300, Tatiana wrote: > Hello! > > Does anybody have the game reversi in Haskell??? > I need this code to understand a problem. > If you have another game in Haskell, please help me. I need see any > game in Haskell. How about games in general (more specifically, two-player zero-sum games)? Check out section 5 of: @Article{ hughes-why, author = "John Hughes", title = "Why Functional Programming Matters", journal = "The Computer Journal", year = 1989, volume = 32, number = 2, pages = "98--107", url = "http://www.cs.chalmers.se/~rjmh/Papers/whyfp.html", abstract = "As software becomes more and more complex, it is more and more important to structure it well. Well-structured software is easy to write, easy to debug, and provides a collection of modules that can be re-used to reduce future programming costs. Conventional languages place conceptual limits on the way problems can be modularised. Functional languages push those limits back. In this paper we show that two features of functional languages in particular, higher-order functions and lazy evaluation, can contribute greatly to modularity. As examples, we manipulate lists and trees, program several numerical algorithms, and implement the alpha-beta heuristic (an algorithm from Artificial Intelligence used in game-playing programs). Since modularity is the key to successful programming, functional languages are vitally important to the real world." } -- Edit this signature at http://www.digitas.harvard.edu/cgi-bin/ken/sig When a strange flattened eel gives a bite you can feel, that's a moray. __________________________________________________________________ Tatiana Coco ICQ#: 111963224 Current ICQ status: + More ways to contact me __________________________________________________________________ ########################################### This message has been scanned by F-Secure Anti-Virus for Microsoft Exchange. For more information, connect to http://www.F-Secure.com/ ###########################################

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CFP for LDTA 2003
by Pierre-Etienne.Moreau＠loria.fr 11 Oct '02

11 Oct '02

Please apologize if you receive multiple copies of this message. ********************************************************** *** LDTA 2003 *** *** APRIL, 6, 2003 *** *** WARSAW, POLAND *** *** *** *** http://www-sop.inria.fr/LDTA2003 *** ********************************************************** Scope: ------ The aim of this one day workshop is to bring together researchers from academia and industry interested in the field of formal language definitions and language technologies, with a special emphasis on tools developed for or with these language definitions. Benefits of such active research fields are, among others: - Program analysis, transformation, generation - Formal analysis of language properties - Automatic generation of language processing tools Although these benefits are well-known, they are in current practices hardly exploited. For example, language definitions can be augmented in a manner that not only compilers/interpreters can be automatically generated but also other tools such as syntax-directed editors, debuggers, partial evaluators, test case generators, documentation generators, etc. Domains of applications that are of interest for this workshop are among others: - Language components, modeling languages - Re-engineering, re-factoring - Aspect-oriented programming, adaptive programming - Domain-specific languages - XML processing - Visualization and graph transformation Invited Talk: ------------- Hassan Ait Kaci, Distinguished Scientist, Research an Development, ILOG, France. Tool demonstrations: -------------------- The one day LDTA 2003 workshop program will also include a session on tool demonstrations. Submission procedure and publication: ------------------------------------- Accepted papers will be published and available during the workshop. After revision, final copies of the accepted papers will be published in Electronic Notes in Theoretical Computer Science (ENTCS), Elsevier Science. Author's instructions are given here. The authors of the best papers will be invited to write a journal version of their paper which will be separately reviewed and after acceptance be published in a special issue devoted to LDTA 2003 of the journal Science of Computer Programming (Elsevier Science). Organizing Committee: --------------------- Isabelle Attali, INRIA Sophia Antipolis Mark van den Brand, CWI Amsterdam Pierre-Etienne Moreau, INRIA-Loria Nancy Program committee co-chairs: ---------------------------- Barrett R. Bryant, University of Alabama at Birmingham, USA Joao Saraiva, University of Minho, Portugal Program Committee members: -------------------------- Don Batory, University Texas / Austin (USA) Uwe Glaesser, Technical University of British Columbia (Canada) Katsuhiko Gondow, JAIST (Japan) Uwe Kastens, University Paderborn (Germany) Paul Klint, CWI (The Netherlands) Jan Madey, University of Warsaw (Poland) Marjan Mernik, University of Maribor (Slovenia) Thomas Noll, University Aachen (Germany) Oege de Moor, Oxford University Computing Laboratory, (England) Peter D. Mosses, BRICS, University Aarhus (Denmark) Eelco Visser, Utrecht (The Netherlands) ----------------------------------------------------------------------- IMPORTANT DATES ----------------------------------------------------------------------- December 1st 2002 Submission of full paper January 20th 2003 Notification February 15th 2003 Final version due April 6th 2003 LDTA 2003

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Yampa 0.9 released
by nilsson＠cs.yale.edu 10 Oct '02

10 Oct '02

We are pleased to announce the first official release of Yampa An implementation of Functional Reactive Programming Version 0.9 Yampa is the culmination of our efforts to provide domain-specific embedded languages for the programming of hybrid systems using the concepts of functional reactive programming (FRP). Yampa is structured using *arrows*, which greatly reduce the chance of introducing space- and time-leaks into reactive, time-varying systems. This release contains the following major components: * The Yampa Base Library, containing generic functions for the expression of continuous behaviors, discrete events, and the interactions between behaviors and events. * The Yampa Robotics Library, containing entities tailored for controlling mobile robots, both real and simulated, in the style of Frob, our FRP-based robotics language. The simulator is written using Yampa's Base and HGL, and performs physical modelling of mobile differential-drive robots equipped with several kinds of sensors. A pre-configured version of the simulator allows one to play RoboCup Soccer. Note: With the Base Library and HGL (or any other graphics library), it is easy to write reactive animation programs in the style of Fran. Thus there is no need for a special library to support graphics and animation. For information on down-loading Yampa, please visit the Yampa website at: http://www.haskell.org/yampa There is also a Yampa mailing list. To subscribe, point your browser at: http://mailman.cs.yale.edu/mailman/listinfo/yampa-users YaMPA doesn't really mean anything, but this work started at Yale, ended with Arrows, and had Much Programming in the middle. Yampa is also a river in Colorado that combines continuous, placid sections with an occasional abrupt transition - a perfect metaphor for hybrid systems. The Yale Haskell Group http://haskell.cs.yale.edu/yale -- Henrik Nilsson Yale University Department of Computer Science nilsson(a)cs.yale.edu

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Re: Java representation in Haskell
by Paulo Sequeira 10 Oct '02

10 Oct '02

mmmm...The paper look very interesting and may also prove itself quite useful for the same project I mentioned before. I see there are some related downloads. I'll check them. Thanks a lot. >From: Ralf Laemmel <Ralf.Laemmel(a)cwi.nl> >To: Dean Herington <heringto(a)cs.unc.edu> >CC: Paulo Sequeira <otro_paulo(a)hotmail.com>, Haskell <haskell(a)haskell.org>, > Joost Visser <Joost.Visser(a)software-improvers.com> >Subject: Re: Java representation in Haskell >Date: Thu, 10 Oct 2002 00:09:37 +0200 > >Paulo Sequeira wrote: > > > > Anyone knows of a module that provides data structures and functions >for > > > representing and manipulating Java source code, so we don't have to >start > > > from scratch? It would be wonderful if the module also includes some > > > "out-of-the-box" pretty-printing facilities for the representation. > >Dean Herington wrote: > > > The paper described at http://www.cs.vu.nl/Strafunski/sf/ suggests that >the > > authors might have something relevant to your request. > >In fact, >the paper to look at would be preferrable >this one (the above cited one, actually deals with >a Java subset): > > Strafunski against Autism and Hypersensitivity > --- Application Letter > http://www.cwi.nl/~ralf/tiptoe/ > (Draft) > >It describes how to do some metrics for Java >in Haskell. To this end, it uses an external Java >parser the parse trees of which are then read in >as terms of alg. datatypes for the Java syntax. It >then advocates strategic programming (say, generic >programming) to manipulate parse trees. In the code >that we have, pretty printing is not an issue. As for the >parsing technology, we use generalized LR parsing based >on sglr/sdf. > >This appl. will be included in the next >release of Strafunski coming very soon now. > >Ralf > >-- >Dr.-Ing. Ralf Laemmel >CWI & VU, Amsterdam, The Netherlands >http://www.cwi.nl/~ralf/ >http://www.cs.vu.nl/~ralf/ _________________________________________________________________ MSN Photos is the easiest way to share and print your photos: http://photos.msn.com/support/worldwide.aspx

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Reversi
by Tatiana 10 Oct '02

10 Oct '02

Hello!!! Thank you for the answer. I would like to know about games two-player. I´m having problems with interface of user. Thank you Tatiana On 2002-10-08T17:13:35-0300, Tatiana wrote: > Hello! > > Does anybody have the game reversi in Haskell??? > I need this code to understand a problem. > If you have another game in Haskell, please help me. I need see any > game in Haskell. How about games in general (more specifically, two-player zero-sum games)? Check out section 5 of: @Article{ hughes-why, author = "John Hughes", title = "Why Functional Programming Matters", journal = "The Computer Journal", year = 1989, volume = 32, number = 2, pages = "98--107", url = "http://www.cs.chalmers.se/~rjmh/Papers/whyfp.html", abstract = "As software becomes more and more complex, it is more and more important to structure it well. Well-structured software is easy to write, easy to debug, and provides a collection of modules that can be re-used to reduce future programming costs. Conventional languages place conceptual limits on the way problems can be modularised. Functional languages push those limits back. In this paper we show that two features of functional languages in particular, higher-order functions and lazy evaluation, can contribute greatly to modularity. As examples, we manipulate lists and trees, program several numerical algorithms, and implement the alpha-beta heuristic (an algorithm from Artificial Intelligence used in game-playing programs). Since modularity is the key to successful programming, functional languages are vitally important to the real world." } -- Edit this signature at http://www.digitas.harvard.edu/cgi-bin/ken/sig When a strange flattened eel gives a bite you can feel, that's a moray. __________________________________________________________________ Tatiana Coco ICQ#: 111963224 Current ICQ status: + More ways to contact me __________________________________________________________________

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Java representation in Haskell
by Paulo Sequeira 09 Oct '02

09 Oct '02

Hi, A friend is considering to start a project of building a generator of certain particular (pieces of) programs. The code generated is most likely to be Java. Anyone knows of a module that provides data structures and functions for representing and manipulating Java source code, so we don't have to start from scratch? It would be wonderful if the module also includes some "out-of-the-box" pretty-printing facilities for the representation. Thanks in advance. Paulo Sequeira

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Reversi
by Tatiana 09 Oct '02

09 Oct '02

Hello! Does anybody have the game reversi in Haskell??? I need this code to understand a problem. If you have another game in Haskell, please help me. I need see any game in Haskell. Thank you very much. Tatiana

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CSMR2003 - New Deadline for Submission
by csmr2003＠unisannio.it 09 Oct '02

09 Oct '02

Please note that the deadline for submitting papers to the European Conference on Software Maintenance and Reengineering has been extended to October 18, 2002. ======================================================================== (Apologies for multiple copies) Seventh European Conference on Software Maintenance and Reengineering Benevento, Italy March 26-28, 2003 http://rcost.unisannio.it/csmr2003 CALL FOR PAPERS CSMR is the premier European Conference on Software Maintenance and Reengineering. Its purpose is to promote both discussion and interaction about evolution, maintenance and reengineering. Topics of interest include, but are not restricted to: Evolution, maintenance and reengineering: + pattern languages + experience reports (successes and failures) + tools + enabling technologies + formal methods + system assessment + web-site Metrics and economics Software evolution and architecture recovery Migration and maintenance issues Dealing with legacy systems towards new technologies Wrapping and interfacing legacy systems Data reengineering Reverse engineering of embedded (control, mobile, ...) systems Evaluation and assessment of reverse engineering tools One of the basic intentions of this conference is to offer a European forum for discussion and exchange of experiences among researchers and practitioners. Therefore, besides academics, we kindly invite all those in companies developing maintenance tools, offering reengineering services or going through legacy systems migration experiences to contribute by submitting papers or presenting innovative tools, solutions or experience reports. This conference is not limited to European participants; authors from outside Europe are also welcomed. SUBMISSIONS: ============ IEEE Computer Society Press will publish the CSMR 2003 Proceedings. Two types of submissions will be accepted: full length papers (not exceeding 10 proceeding pages, IEEE Style) and short papers (not exceeding 4 proceeding pages, IEEE Style). All papers must be in English. Authors are requested to submit electronically a PostScript or PDF version of their papers. For submission details please look at the web site IMPORTANT DATES: ================ Deadline for submissions October 18, 2002 Author's notification November 27, 2002 Deadline for camera-ready of accepted papers December 20, 2002 SPECIAL SESSIONS: ================= Sessions of special interest proposed by delegates will be welcomed. Please send suggestions to the program chair before the submissions closing date. PROGRAM CHAIR: Mark van den Brand, CWI,The Netherlands e-mail: Mark.van.den.Brand(a)cwi.nl PROGRAM CO-CHAIR: Tibor Gyimóthy, University of Szeged, Hungary e-mail: gyimi(a)cc.u-szeged.hu GENERAL CHAIR: Gerardo Canfora, Research Centre on Software Technology, Italy e-mail: canfora(a)unisannio.it ========================================================================

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