- Haskell - Haskell.org

Haskell 98 lexical syntax again
by Simon Peyton-Jones 13 Feb '02

13 Feb '02

To meet Ian's observation below, I propose to replace the lexical production newline -> a newline (system dependent) by newline -> return linefeed | return | linefeed which, given maximal munch, will behave decently on any normal system. Any objections? Simon | -----Original Message----- | From: Ian Lynagh [mailto:igloo@earth.li] | The report says | | whitechar -> newline | return | linefeed | vertab | formfeed | | space | tab | uniWhite | newline -> a newline (system dependent) | return -> a carriage return | linefeed -> a line feed | | so, if your system defines a newline to be a line feed, an | implementation is free to choose whether to lex a line feed | as a whitechar or a newline, which makes quite a difference | when you consider the layout rule! | | newline can't be arbitrarily determined by the system - | certainly "x" or "let" would not be acceptable - and having | it system dependent means that Haskell scripts are not | portable between different systems. I haven't looked but I | would be surprised if current implementations behaved | differently on different platforms - I assume they all look | for something matching (<CR><LF>?)|<LF> everywhere.

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Sendind mail
by Monique Louise 13 Feb '02

13 Feb '02

Hi, I'd like to know if there's any Hugs compatible library with functionalities to send mail.

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Re: what does fixST do?
by Levent Erkok 12 Feb '02

12 Feb '02

A couple of days ago, Hal Daume III asked > what does fixST do? Briefly, fixST allows recursive definitions of values in the ST monad. As you can guess, there's a bunch of such operators for different monads, the most famous being "fixIO", the corresponding operator for the IO monad. These operators are known as "value recursion operators". Maybe, list, IO, lazy and strict ST monads, the output monad, environment monad (and various combinations thereof) are examples of monads that have such operators. However, it is not necessarily the case that every monad has an associated value recursion operator. For instance, as far as I know, there is no such operator for the continuation monad. To understand how these operators work, may be I can suggest an exercise. It's a variant of Richard Bird's "replaceMin" problem. Given a datatype of the form: data Tree a = L a | B (Tree a) (Tree a) the aim is to write a function: replaceMin :: Tree Int -> Tree Int such that replaceMin replaces all the elements with the minimum one in the tree. For instance: Main> replaceMin (B (L 2) (B (L 3) (L 4))) B (L 2) (B (L 2) (L 2)) It is indeed very easy to write a two-pass solution: First traverse to get the minimum, then reconstruct the tree using this value. The challenge is to solve this problem in one pass. Richard Bird gave a solution in 1984. (I'm not going to copy the solution here, it's quite a well known algorithm..) Now consider an extension to the problem, where we not only want to transform the tree, but also want to print the nodes as we traverse it. The type of replaceMin becomes: replaceMin :: Tree Int -> IO (Tree Int) For instance: Main> replaceMin (B (L 2) (B (L 3) (L 4))) >>= print 2 3 4 B (L 2) (B (L 2) (L 2)) Again, a two pass solution is easy. Can you solve this in one pass as well? To do so, you'll have to use fixIO.. This exercise should clear up the use of fixIO, and indirectly that of fixST. You can easily imagine numbering the nodes for instance, where you can use the ST monad to keep track of numbers. Than, you'd need fixST. For a solution to this problem (and a more detailed discussion), visit: http://www.cse.ogi.edu/PacSoft/projects/rmb/repMin.html For info on value recursion operators in general: http://www.cse.ogi.edu/PacSoft/projects/rmb/ -Levent.

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CFP: Unification in non-classical logics
by Manuel Ojeda Aciego 12 Feb '02

12 Feb '02

======================================================================= We apologize if you receive this more than once ======================================================================= Preliminary call for papers Unification in Non-Classical Logics --co-located with ICALP 2002-- July, 12-13, 2002, Málaga, Spain http://www.satd.uma.es/aciego/icalp-ws.html ======================================================================= The workshop on Unification in Non-Classical Logics will be held in Málaga, as a workshop of the 29-th International Colloquium on Automata, Languages, and Programming (ICALP 2002), which is a very convenient forum for an open discussion of the subject of non-canonical unification, roughly depicted below. Aims and scope -------------- Unification in non-classical logics, with various approaches to handling generalised terms, has drawn more and more attention in recent years. It turns out to be among the most promising areas of research on non-classical logics and its applications. So far, most popular lines of research include fuzzy unification of (conventional) databases and the use of fuzzy concepts in information retrieval. Some international events based on these topics have been held so far, for instance, the 2nd Intl Workshop on Logic Programming and Soft Computing (LPSC'98), or the special session on Advances in Possibilistic Logic and Related Issues at the IFSA Congress in Vancouver, Canada (2001), have non-classical unification among their topics. This workshop at ICALP is conceived as a forum for the exchange of ideas relevant for the concept of unification in non-classical logics, including, but not limited to, the following topics (practical implementations and experiences as well as theoretical advances): * Unification in multiple-valued and fuzzy logic programming. * Unification based on similarities and fuzzy equivalence relations. * Categorical unification. * Practical use of non-classical unification, e.g. in expert systems and information retrieval. We expect potential participants from the following areas: multiple-valued logic, fuzzy logic, uncertainty in logic programming, categorical applications to computer science. The workshop will have a limited number of presentations and the organizers will apply a refereeing procedure accordingly. The format will be as a set of presentations followed by a round table discussion. As the number of participants is estimated not to be very large, time enough will be allocated for each presentation (between 30 and 40 minutes), thus helping to have a relaxed workshop atmosphere in which discussions are encouraged. Submission ---------- Authors are invited to submit an extended abstract of their papers, presenting original contributions to the workshop themes. The workshop proceedings will be published as an issue in the ENTCS series (Electronic Notes on Theoretical Computer Science). Submissions should be written in English and not exceed 15 pages using the ENTCS style, and sent to the organizers in either PS or PDF form, together with a text-only message containig: title, abstract and keywords, the author's full names, and address and e-mail for correspondence. Simultaneous submission to other meetings with published proceedings is not allowed. Important dates --------------- * 20.03.2002 Workshop paper submission deadline * 21.04.2002 Workshop paper acceptance notification * 10.05.2002 Workshop paper camera-ready deadline Organizing Committee -------------------- Patrik Eklund Manuel Ojeda-Aciego Dept. Computing Science Dept. Matematica Aplicada Umea University Universidad de Malaga mailto:peklund@cs.umu.se mailto:aciego@ctima.uma.es ----------------------------------------------------------

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CFP: CLIMA'02 - Computational Logic in Multi-Agent Systems
by João Alexandre Leite 12 Feb '02

12 Feb '02

[We apologize if you receive multiple copies of this message.] ****************************************************************** Preliminary Call for Papers Computational Logic in Multi-Agent Systems (CLIMA'02) Copenhagen, Denmark August 1, 2002 http://centria.di.fct.unl.pt/~jleite/clima02/ Affiliated with FLOC'2002 and ICLP'2002 Submission Deadline: April 30th, 2002 ****************************************************************** Multi-agent systems (MAS) have become an increasingly important area of research, not least because of the advances in the Internet and Robotics. However multi-agent systems can become very complicated, and, consequently, reasoning about the behaviour of such systems can become extremely difficult. Therefore, it is important to be able to formalise multi-agent systems and, to do so in such a way that allows automated reasoning about agents' behaviour. The purpose of this workshop is to present techniques, based on computational logic (CL), for multi-agent systems in a formal way. In 1999, the ICLP'99 Workshop on Multi-Agent Systems in Logic Programming was held and constituted the first in this series. It was followed by CLIMA'00 at CL2000 and CLIMA'01 at ICLP'01. In 2000, we announced a special issue of the Annals of Math and AI and we especially invited all accepted papers of CLIMA'00 for submission to this issue. We got over 20 submissions and the issue will appear early in 2002. We are planning to continue this series of workshops in the following years in order to foster interaction between the multi-agent and the computational logic communities. We solicit unpublished papers that address formal approaches to multi-agent systems. The approaches as well as being formal must make a significant contribution to the practice of multi-agent systems. Relevant techniques include the following: * Non-monotonic reasoning in multi-agent systems * Planning under incomplete information in multi-agent systems * Usage of abduction in multi-agent systems * Representation of knowledge and belief in multi-agent systems * Temporal reasoning for multi-agent systems * Theory of argumentation for multi-agent negotiation and co-operation * Communication languages for multi-agent systems * Distributed constraint satisfaction in multi-agent systems * Decision theory for multi-agents * Distributed theorem proving for multi-agent systems ------------------------------ SUBMISSION INSTRUCTIONS ------------------------------ Papers should be written in English, unpublished, and not simultaneously submitted for publication elsewhere. Papers should be formatted according to the Springer LNCS style and not exceed 12 pages including figures, references, etc. Please send your paper in PostScript (PS) or Portable Document Format (PDF) file format to jleite(a)di.fct.unl.pt. ------------------------------ IMPORTANT DATES ------------------------------ * Submission: April 30th, 2002 * Notification of Acceptance: May 31st, 2002 * Final version due: June 20th, 2002 * CLIMA'02: August 1st, 2002 ------------------------------ PROCEEDINGS ------------------------------ Informal workshop proceedings will be available. As in 2000, we are planning to have a special issue of the Annals of Math and AI on "Computational Logic and Multi-Agency". Authors of the best CLIMA'02 papers will be invited to submit extended drafts for the special issue as a part of the volume. Further details will be announced shortly. ------------------------------ PROGRAM COMMITTEE ------------------------------ * Thomas Eiter, Vienna University of Technology, Austria * Klaus Fischer, DFKI, Germany * Michael Fisher, University of Liverpool, UK * James Harland, Royal Melbourne Institute of Technology, Australia * Wiebe van der Hoek, Utrecht University, The Netherlands * Katsumi Inoue, Kobe University, Japan * Luís Moniz Pereira, New University of Lisbon, Portugal * V.S. Subrahmanian, University of Maryland, USA * Francesca Toni, Imperial College, UK * Paolo Torroni, University of Bologna, Italy ------------------------------ WORKSHOP ORGANIZERS: ------------------------------ * Jürgen Dix The University of Manchester UK dix(a)cs.man.ac.uk * João Alexandre Leite New University of Lisbon Portugal jleite(a)di.fct.unl.pt * Ken Satoh National Institute of Informatics, Japan ksatoh(a)nii.ac.jp ------------------------------ INQUIRIES: ------------------------------ Please send program suggestions and inquires to either of the organizers.

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CFP Generators and Components (GCSE/SAIG'02)
by Walid Taha 12 Feb '02

12 Feb '02

CALL FOR PAPERS The First ACM SIGPLAN/SIGSOFT Conference on Generators and Components (GCSE/SAIG'02) Supported by the National Science Foundation (NSF) Pittsburgh, PA, October 6-8, 2002. http://www.cs.yale.edu/~taha/gcse-saig/cfp02.html Invited Speakers: * Neil Jones, University of Denmark * Catuscia Palamidessi, Penn State University * Janos Sztipanovits, Vanderbilt University Program generation has the prospect of being an integral part of a wide range of software development processes. Many recent studies investigate different aspects of program generation, including their semantics, their application, and their implementation. Existing theories and systems address both high-level (source) language and low-level (machine) language generation. A number of programming languages now support program generation and manipulation, with different goals, implementation techniques, and targeted at different applications. The goal of this conference is to provide a meeting place for researchers and practitioners interested in this topic. A particular area of interest is component-based software development, which bears the promise of considerable productivity increases to software development comparable to the introduction of the assembly line in manufacturing. But due to the very same sophistication that makes components useful, their maintenance can be hard. Generative programming presents a promising approach to alleviating the above problems, as changes affecting components can now be more effectively managed during the generation process rather than at the component level. The goal of this joint event is to foster further cross-fertilization between the software engineering research community on the one hand, and the programming languages community on the other, in addition to supporting the original research goals of both GCSE and SAIG communities. We seek papers both in software engineering and programming languages, and especially those that bridge the gap. Being accessible to both communities at the same time is also valued. The conference solicits submissions related (but not limited) to: * Generative Programming: Reuse, meta-programming, partial evaluation, multi-stage and multi-level languages, * Semantics, type systems, symbolic computation, linking and explicit substitution, in-lining and macros, templates, program transformation, * Runtime code generation, compilation, active libraries, synthesis from specifications, development methods, generation of non-code artifacts, formal methods. Reflection. * Component-Based Software Engineering: Reuse, distributed platforms, distributed systems, evolution, analysis and design patterns, development methods, formal methods * Integration of Generative and Component-Based Approaches * Domain Engineering, analysis, and languages * Separation of Concerns: Aspect-Oriented Programming, Intentional * Programming, and Multi-Dimensional Separation of Concerns * Product Lines and generic architectures for that purpose. * Industrial Applications of Components and Generative Programming Reports on applications of these techniques to real-world problems are especially encouraged, as are submissions that relate ideas and concepts from several of these topics, or bridge the gap between theory and practice. The program committee is happy to advise on the appropriateness of a particular subject. General Chair: Walid Taha, Yale University, USA. Program Chair (GCSE focus): Don Batory, University of Texas at Austin, USA. Program Chair (SAIG focus): Charles Consel, INRIA, LaBRI, France. Program Committee (GCSE focus): Jan Bosch , University of Groningen Greg Butler, Concordia University Prem Devanbu, University of California at Davis Cristina Gacek, University of Newcastle upon Tyne Stan Jarzabek, National University of Singapore Kyo Kang, Pohang University of Science and Technology Peter Knauber, Fraunhofer Institute for Experimental Software Engineering Hausi Muller, University of Victoria Nenad Medvidovic, University of Southern California Wolfgang Pree, University of Constance Yannis Smaragdakis, Georgia Institute of Technology Douglas R. Smith , Kestrel Institute Program Committee (SAIG focus): Craig Chambers, University of Washington Shigeru Chiba, Tokyo Institute of Technology Pierre Cointe, Ecole des Mines de Nantes Dawson Engler, Stanford University Siau cheng Khoo, National University of Singapore Gregor Kiczales, University of British Columbia Martin Odersky, Ecole Polytechnique F�d�rale de Lausanne Calton Pu, Georgia Institute of Technology Peter Thiemann, Universit�t Freiburg Andrew Tolmach, Portland State University Submission Details: Authors are invited to submit papers of at most 5000 words (excluding figures), in postscript format (letter or A4), using the electronic submission form by March 21st, 2002. This deadline is firm. Both position and technical papers are welcome (Please indicate at time of submission.) Authors will be notified of acceptance by May 14th, 2002. Final version of the papers must be submitted by July 14, 2002. Format: The three day conference will contain slots for technical papers (45 minutes) and position papers (30 minutes). Both times include discussion. Position papers are expected to describe important future directions, ongoing work, and survey previous results. This category is best thought of as one for "competitive invited papers". Technical papers are expected to contain novel results. All papers will be reviewed by the program committee for the above-mentioned criteria, in addition to correctness and clarity. Simultaneous submission to other venues is not allowed, as is submission of previously published material. In addition, there will be time allocated for open discussions at the end of the conference. Proceedings will be published as an LNCS volume. Special Note on Combined Event: While the Program Committee is divided into two focus areas corresponding the parent events (GCSE and SAIG), there will be one unified program committee meeting. At the time of submission, authors must indicate whether they intend the paper for the GCSE audience, SAIG audience, or BOTH. The last category is the default, and is strongly encouraged. Papers submitted explicitly to only one focus will be accepted or rejected by the respective Program Chair. For papers submitted to BOTH, it is enough that one of the two Program Chairs accepts the paper. All members of the PC will allowed to bid for and review all papers, and cross-bidding is encouraged. The conference itself will not be divided along focus lines. Rather, an attempt will be made to ensure that each session is of interest to both parent communities. ------------------------------------------------------------------------- A printable version of this CFP is available at: http://www.cs.yale.edu/~taha/gcse-saig/cfp02.pdf

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FW: Haskell 98 report
by Simon Peyton-Jones 11 Feb '02

11 Feb '02

I propose to adopt Olaf's suggestion here. It makes for a nice simple specification, even though *in principle* data T = MkT deriving( Eq ) needn't have a strict (==) operation. It's certainly a vagueness at the moment. Simon -----Original Message----- From: Olaf Chitil [mailto:olaf@cs.york.ac.uk] Sent: 08 February 2002 18:50 To: Simon Peyton-Jones Subject: Haskell 98 report In D.1 Derived instances of Eq and Ord. there is the statement Derived comparisons always traverse constructors from left to right. These examples illustrate this property: (1,undefined) == (2,undefined) => False (undefined,1) == (undefined,2) => _|_ This statement makes me wonder, if for example False <= undefined should evaluate to True, because False is the least constructor. However, all Haskell implementations yield "undefined". To resolve this ambiguity of the report I suggest to add the sentence: However, all derived comparisons are strict in all arguments. -- OLAF CHITIL, Dept. of Computer Science, The University of York, York YO10 5DD, UK. URL: http://www.cs.york.ac.uk/~olaf/ Tel: +44 1904 434756; Fax: +44 1904 432767

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RE: Specifying Kinds of Types
by Simon Peyton-Jones 11 Feb '02

11 Feb '02

OK, it's done. In GHC you can specify kinds in data type decls type synonym decls class decls explicit for-alls For example data T (x :: *->*) = MkT type Composer c = forall (x :: * -> *) (y :: * -> *) (z :: * -> *). (c y z) -> (c x y) -> (c x z); And you can put kind signatures on arbitrary types, rather like you can put type signatures on arbitrary expressions. No kind polymorphism though! All this is in the HEAD. You'll need to build from source to get it until we make a release. Simon | -----Original Message----- | From: Ashley Yakeley [mailto:ashley@semantic.org] | Sent: 08 February 2002 11:26 | To: Haskell List | Subject: Specifying Kinds of Types | | | I'd like to be able to declare the kinds of new types and synonyms, | because sometimes Haskell can't infer them. For instance: | | data CMap0 p q = MkCMap0; | | Without evidence, Haskell assumes that p and q have kind '*' | (as per sec. | 4.6), and therefore CMap0 has kind '* -> * -> *'. Actually, I | wanted p | and q to both have kind '* -> *', giving CMap0 kind '(* -> *) | -> (* -> *) | -> *'. | | Here's another example: | | type Composer c = forall x y z. (c y z) -> (c x y) -> (c x z); | | Haskell gives x, y and z all the kind '*'. But I wanted them | to have kind | '* -> *', giving c the kind '(* -> *) -> (* -> *) -> *' and | Composer the | kind '(* -> *) -> (* -> *) -> * -> *'. | | It's not currently possible to specify kinds, is it? Actually I think | polymorphic kinds would be nice, but I can't say I | desperately need them. | I'd just like to be able to specify kinds somehow. For instance: | | data CMap0 (p ::: * -> *) (q ::: * -> *) = MkCMap0; | | ...or perhaps | | data ({* -> *} p,{* -> *} q) => CMap0 p q = MkCMap0; | | ...or whatever. | | | -- | Ashley Yakeley, Seattle WA | | _______________________________________________ | Haskell mailing list | Haskell(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell |

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Tour of Prelude - HTML version
by Arjan van IJzendoorn 11 Feb '02

11 Feb '02

Hello, Earlier Bernie Pope wrote: > announce: tour of Haskell Prelude document (for teaching etc) > It is intended as a study aid. Typically our students take a printed copy > with them to lab classes (yes we still print things here). Although > it may be converted into HTML and presented online. I've converted Bernie Pope's "Tour of the Haskell Prelude" to HTML. Here, at Utrecht University, we prefer clicking over printing and I wanted an online reference just like Java has. You can find it at: http://www.cs.uu.nl/~afie/haskell/tourofprelude.html I'll be using and updating it while I teach functional programming (March, April). This will help our students when writing Haskell programs. Thanks, Bernie! Greetings, Arjan -------------------------------------------------------------------------- Arjan van IJzendoorn Institute of Information and Computing Sciences, Utrecht University P.O. Box 80089, 3508 TB Utrecht, The Netherlands mail:afie@cs.uu.nl Phone: +31-30-253 1012 Fax: +31-30-251 3791 --------------------------------------------------------------------------

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Announce: new Online Bibliography of Haskell Research
by Jim Bender 11 Feb '02

11 Feb '02

I have created a new "Online Bibliography of Haskell Research". This bibliography collects together references to conference papers, technical reports, theses, etc. related to Haskell, and where available, provides a link to online copies of the document. The bibliography is available at http://haskell.readscheme.org. Also available, of course, is the Bibliography of Scheme-related Research (http://library.readscheme.org) and the "reading list" of research on XML and Web programming in the context of functional programming languages, available at http://readscheme.org. Jim Bender jim(a)benderweb.net

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