September 2002 - Haskell

Re: Lazy IO?
by Sengan.Baring-Gould＠nsc.com 03 Sep '02

03 Sep '02

On Tue, 3 Sep 2002 20:08:32 +0100 "Duncan Coutts" <duncan(a)coutts.uklinux.net> wrote: > On Tue, 3 Sep 2002 14:49:45 -0400 > Sengan.Baring-Gould(a)nsc.com wrote: > > > Is there any way to make the IO Monad lazy? > > > > The simplified version of my problem is that I want to > > generate an infinite structure from an IOArray and then > > consume only the relevant part of it. > > Yes, unsafeInterleaveIO. > > http://www.haskell.org/ghc/docs/latest/html/base/System.IO.Unsafe.html#unsa… > > This is how getContents is implemented so that it reads the file lazily. > > Be careful of course it is "unsafe". > > Duncan Excellent. Thanks a lot, Sengan

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PLI 2002 early registration deadline approaching
by Shriram Krishnamurthi 03 Sep '02

03 Sep '02

[This is the last announcement we will send about PLI 2002. Please note that the early registration deadline is just over a week away. We look forward to your participation in the events!] PLI 2002 Principles, Logics, and Implementations of High-Level Programming Languages Early Registration Deadline: SEPTEMBER 12, 2002 Pittsburgh, PA, USA October 3-8, 2002 http://pli2002.cs.brown.edu/ PLI is a confederation of conferences and workshops aimed at the advancement of high-level programming languages. This year, PLI consists of three conferences: ICFP (International Conference on Functional Programming) PPDP (International Conference on Principles and Practice of Declarative Programming) GPCE (Generative Programming and Component Engineering) and seven workshops: Haskell PLAN-X (Programming Languages for XML) Scheme Rule (Rule-Based Programming) VCL (Verification and Computational Logic) Erlang FDPE (Functional and Declarative Programming in Education) The hotel's cut-off date for guaranteed reservations at the group rate is also September 12, 2002, so do register and reserve soon. We look forward to seeing you in Pittsburgh! Shriram Krishnamurthi Publicity Chair PLI 2002

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Re: A question concerning functional dependencies
by Ashley Yakeley 02 Sep '02

02 Sep '02

At 2002-09-02 07:47, Dylan Thurston wrote: >GHC (and Hugs) check for potential conflicts like this unless you >explicitly allow overlapping instances. AFAIK, even with overlapping instances allowed, GHC will still complain if there's a fundep. See <http://sourceforge.net/tracker/?func=detail&aid=441389&group_id=8032&atid= 108032>. -- Ashley Yakeley, Seattle WA

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CFP: AMAI Special Issue on Computational Logic in Multi-Agent Systems
by João Alexandre Leite 02 Sep '02

02 Sep '02

[We apologize if you receive multiple copies of this message.] -------------------------------------------------------------------- Call for Papers Annals of Mathematics and Artificial Intelligence Special Issue on Computational Logic in Multi-Agent Systems Special Issue Editors: Jürgen Dix (The University of Manchester, UK) João Alexandre Leite (New University of Lisbon, Portugal) KenSatoh (National Institute of Informatics, Japan) http://centria.di.fct.unl.pt/~jleite/amai03/ Submission Deadline: October 1st, 2002 -------------------------------------------------------------------- About the Special Issue: 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 Special Issue is to present techniques, based on computational logic (CL), for reasoning about multi-agent systems in a formal way. This is clearly a major and exciting challenge for computational logic. We have to develop techniques to deal with real world issues and applications. We solicit papers that address CL-related 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 (but are not limited to): Nonmonotonic reasoning in MAS Planning in MAS Adaptability and learning in MAS Knowledge representation in MAS Temporal reasoning in MAS Negotiation, co-operation, competition and communication in MAS Verification of MAS Decision theory for MAS Distributed problem solving in MAS Significant applications of MAS Submission Details: We are expecting full papers to describe original, previously unpublished research, be written in English, and not be simultaneously submitted for publication elsewhere (previous publication of partial results at workshops with informal proceedings is allowed). Papers should be formatted according to the Instructions for AMAI submissions (to be found at http://www.kluweronline.com/issn/1012-2443 ) and should be between 20 and 40 pages long: We also require the following issues to be addressed: CL: An introduction that includes statements about how the paper addresses the exploitation of CL for MAS; MAS: An explanation of which aspect/functionality of MAS the paper formalises; Examples: Example(s) which give an intuitive motivation and explanation of the formalisation. Please submit a PostScript or PDF file of your paper to dix(a)cs.man.ac.uk by the 1st of October 2002. Important Dates: Submission Deadline: October 1, 2002 Author Notification: December 15, 2002 Final Paper Deadline: February 15, 2003 Special Issue: September 2003 About the Special Issue Editors: Jürgen Dix is a Reader at The University of Manchester, UK. He is also member of the CS Department at the Technical University of Vienna, where he is lecturing regularly. He worked since 1989 in several areas of Computational Logic (nonmonotonic reasoning, logic programming, deductive databases, knowledge representation) and, lately, also in Multi-Agent Reasoning. João Alexandre Leite is a researcher at the Center for Artificial Intelligence (CENTRIA), New University of Lisbon, Portugal. He has been doing research on logic programming and non-monotonic reasoning, with particular emphasis on the problem of representing and reasoning about dynamic knowledge, and its application to multi-agent systems. Ken Satoh is a professor of National Institute of Informatics, Japan. He has been doing research on theoretical foundations of AI such as nonmonotonic reasoning, preference-based reasoning and case-based reasoning. He is also interested in formalization of multi-agent systems and application of the above reasoning to multi-agent systems. About Annals of Math and AI: Annals of Mathematics and Artificial Intelligence (AMAI) is devoted to reporting significant contributions on the interaction of mathematical and computational techniques reflecting the evolving disciplines of artificial intelligence. Annals of Mathematics and Artificial Intelligence publishes edited volumes of original manuscripts, survey articles, monographs and well refereed conference proceedings of the highest caliber within this increasingly important field. All papers will be subject to the peer reviewing process with at least two referees per paper. Inquiries: ------------------------------ Please send your inquires to dix(a)cs.man.ac.uk.

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Re: A question concerning functional dependencies
by Ashley Yakeley 02 Sep '02

02 Sep '02

At 2002-09-02 02:46, Jerzy Karczmarczuk wrote: >class Module v s | v->s . ... >instance Num s => Module (v->s) s ... >instance ...=> Module ((v->s)->(v->s)) s ... >But GHCi yells that two instances in view of the functional >dependency declared are in conflict. GHCi is correct. Bear in mind GHC ignores contexts in instance declarations when calculating conflicts. This is unfortunate, but apparently fixing it would be hard. ((v->s)->(v->s)) is a substitution instance of (v->s). So from the first instance, instance ...=> Module (v->s) s GHC can derive instance ...=> Module ((v->s)->(v->s)) (v->s) ...which conflicts with your second instance per the fundep: instance ...=> Module ((v->s)->(v->s)) s The solution of course is to declare new datatypes: newtype Vector v s = MkVector (v->s) newtype Operator v s = MkOperator ((v->s)->(v->s)) etc. -- Ashley Yakeley, Seattle WA

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A question concerning functional dependencies
by Jerzy Karczmarczuk 02 Sep '02

02 Sep '02

I wanted to write a small package implementing vector spaces, etc. A part of it is class Module v s where (*>) :: s->v->v defining the multiplication of a vector by a scalar: w = a*>v Now, as in many other circumstances, concrete vectors are based on concrete scalars, and I defined really: class Module v s | v->s . One typical instance of vectors is the orthodox functional construction instance Num s => Module (v->s) s where (s*>f) x = s * (f x) and such tests: u = 2.5 *> sin; res = u 3.14 pass without tears. But I wanted also that operators of the type (b->s) -> (b->s), for example: inver f = recip . f . recip be vectors. So: instance ...=> Module ((v->s)->(v->s)) s where (s*>op) f = s*>(op f) But GHCi yells that two instances in view of the functional dependency declared are in conflict. Since I believe that I do not really understand fundeps in Haskell, and this is not a GHC 'feature' only, I send this query to the haskell list. I don't see this conflict. I could remove the fundep, but then I have other (smaller, but a bit annoying) problems, so I want to keep it, if only for my own instruction. Good people, help, please. Why v [->s] cannot "coexist" in this context with ((v->s)->v) [->s] Of course all extensions, including overlapping instances are on. Jerzy Karczmarczuk Caen, France

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