- Haskell - Haskell.org

RE: [Haskell] Why is newChan in the IO Monad?
by Nick Benton 23 Apr '04

23 Apr '04

Double is a pretty poor choice of "whatever" (just thinking about equality of floating point numbers puts one in a state of sin :-)). Worse still, your newChanSafe would be type-unsafe if you gave it that polymorphic type (think about it). So let's assume channels aren't polymorphic and that we were were going to use ints or strings or something as identities. Then since your newChan has got to be injective, you could just identify chan with int and be done with it. Even then, there's still quite a lot going on: Firstly, of course, the equation I wrote *does* actually hold in Haskell with the current definitions. But it would fail to hold if newchan were a non-normal form, each evaluation of which returned a new name, which was what was intended. Secondly, if you manage your own channel identities you'll end up carrying around a "current" identity/name supply and having an operation which takes a supply and gives you a fresh name and a new supply. That's just another monad (TX = supply->X*supply, gensym : Tname). If the type you use for names isn't abstract (e.g. you just use int) then the resulting equational theory will be weak (because contexts can supply all the names). A more refined treatment is possible. If (and only if) you make the type of names and their operations more abstract then there is a very nice monad just for name generation, which you could separate from the monad for actually sending and receiving values. One advantage of doing that is that the dynamic allocation monad satisfies more equations than the IO monad (it's commutative, for example). Then there's a monad morphism that lets you lift new name generation into the IO monad when you want to use the channels (IO is definitely not commutative). If you want to do fancy program transformations then this extra refinement is helpful. If you don't, having two monads instead of one just makes life even more complicated. Now, giving newChan a non-monadic type amounts to making this new name monad *implicit* - allowing divergence and/or name-generation to happen during evaluation without reflecting either possibility in the types. As I said, this breaks the equational theory of the language. But other people have taken the position that maybe it doesn't break it all that badly, and that one can make sure that the compiler's transformations respect the weaker theory [1]. This is what happens in "observable sharing", which was suggested precisely because others, like you, found doing gensym monadically in Haskell to be a bit tedious: K. Claessen and D. Sands. Observable sharing for functional circuit description. In ASIAN'99, volume 1742 of Lecture Notes in Computer Science, pages 62--73. Springer-Verlag, 1999. Names in circuit descriptions are used to express the sharing which distinguishes cyclic circuits from infinite ones. In the case of channels, however, you don't just compare the names for equality - all non-trivial uses of them are going to involve sends and receives and hence put you into the IO monad anyway. So messing up the theory of the whole language just to to have a few fewer IOs doesn't seem a good tradeoff. If you're interested in the theory, there's a big (and rapidly growing!) literature on the semantics of name generation - see the work of Pitts & Stark on the \nu-calculus, for example. To summarize the above ramble: it's an excellent question, but you almost certainly want to leave newChan where it is. Nick [1] arguably, including strict constructs (pattern matching, strict sequencing) is already a step down this road. But the Haskell/Miranda "war of the bottoms" was all a long time ago... -----Original Message----- From: S. Alexander Jacobson [mailto:alex@alexjacobson.com] Sent: 23 April 2004 20:05 To: Nick Benton Cc: Haskell Mailing List Subject: RE: [Haskell] Why is newChan in the IO Monad? Yes, that makes sense, but I'm ok with passing in an identity. I'd like a function like this: newChanSafe::Identity -> Chan a type Identity = Double -- or whatever -Alex- _________________________________________________________________ S. Alexander Jacobson mailto:me@alexjacobson.com tel:917-770-6565 http://alexjacobson.com On Fri, 23 Apr 2004, Nick Benton wrote: > Channels have identity, so allocating a new one is a side effecting > operation. Having it outside the IO monad would require (for example): > > (newChan, newChan) = (let x = newChan in (x,x)) > > which is wrong. If you wrap newChan in unsafePerformIO then the compiler > will feel free to apply rewrites like the above, which is unlikely to be > what you wanted. > > Nick > -----Original Message----- > From: haskell-bounces(a)haskell.org [mailto:haskell-bounces@haskell.org] > On Behalf Of S. Alexander Jacobson > Sent: 23 April 2004 19:22 > To: Haskell Mailing List > Subject: [Haskell] Why is newChan in the IO Monad? > > Nothing actually happens when newChan is called > except construction of a new datastructure. It > would be nice to have non IO monad code be able to > create a new Chan that gets passed to IO code that > uses it somewhere else. > > Alternatively, is there a way to create a Chan > outside the IO monad? > > -Alex- > > _________________________________________________________________ > S. Alexander Jacobson mailto:me@alexjacobson.com > tel:917-770-6565 http://alexjacobson.com > _______________________________________________ > Haskell mailing list > Haskell(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell >

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AFP 2004 - Call for Participation
by afp04＠cs.ut.ee 23 Apr '04

23 Apr '04

[Early registration deadline: 14 May 2004.] Call for Participation AFP 2004 5th International Summer School on Advanced Functional Programming Tartu, Estonia 14-21 August 2004 http://www.cs.ut.ee/afp04 AFP is a series of international summer schools which aims to bring computer scientist, in particular young researchers and programmers, up to date with the latest advances in practical functional programming. The main focus of the school is on the interface between results presented at programming conferences and the programming in the real world. This is the fifth event in the series organized by the Department of Computer Science of the University of Tartu in conjuction with the Centre for Dependable Computing. The previous schools were held in Båstad (Sweden, 1995), Olympia (Washington, USA, 1996), Braga (Portugal, 1998) and Oxford (UK, 2002). PROGRAMME The scientific programme of AFP'04 consists of short courses by renowned experts of the field and a student session. The school offers eight main courses, each composed of lectures and accompanied by lab sessions. The course list is the following: John Hughes (Chalmers University of Technology): Arrows Conor McBride (University of Durham): Epigram: dependent types for practical programming Alberto Pardo (Universidad de la Republica, Montevideo): Combining datatypes and effects Rinus Plasmeijer (University of Nijmegen): Generic programming techniques for the construction of graphical user interfaces A strongly typed functional operating system based on dynamics Bernie Pope (University of Melbourne): Declarative debugging with Buddha Doaitse Swierstra (Utrecht University) and Atze Dijkstra (Utrecht University): Typing Haskell with an Attribute Grammar Peter Thiemann (University of Freiburg): Server-side Web programming in WASH Simon Thompson (University of Kent): Refactoring Functional Programs In addition, there will be some introductory and intermediate functional programming courses serving as a preparation for the advanced courses. The purpose of the student session is to give students an opportunity to present their work and get feedback. Everyone intending to give a presentation should submit an extended abstract (max 10 pp) along with the registration form. VENUE Tartu, with 100,000 inhabitants, is the second largest city in Estonia, situated 180 km south-east from Tallinn. Tartu University, founded 1632, is one of the oldest universities in Northern Europe. The school will be held in the new building of the Faculty of Mathematics and Computer Science. Tartu is accessible from Tallinn by coach. The coaches run very frequently (1-2 departures per hour) and the ride takes 2-2.5 hrs. Tallinn, with 400,000 inhabitants, is the capital city of Estonia, that used to be a member of the Hansa League. Tallinn's medieval Old Town is on the UNESCO World Heritage List. There are direct flights to Tallinn from London, Paris, Amsterdam, Frankfurt, Hamburg, Munich, Berlin, Prague, Warsaw, Moscow, Copenhagen, Oslo, Stockholm, Helsinki. IMPORTANT DATES May 14, 2004 Early registration deadline July 9, 2004 Late registration deadline REGISTRATION AND COST The registration is done through internet (http://www.cs.ut.ee/afp04/submreg.ht ml). The deadline for registration is July 9, 2004 and the registration fee is 330 EUR. For early registrants, until May 14, there is a reduced registration fee 280 EUR. The registration fee includes course materials distributed during the school, revised lecture notes published by Springer after the school, lunches, refreshments for coffee breaks and conference dinner. AFP'04 is an APPSEM II affiliated event, hence APPSEM II sites can use the project funds to support their students' participation in the school. PROGRAMME COMMITTEE / ORGANIZING COMMITTEE Varmo Vene University of Tartu Tarmo Uustalu Institute of Cybernetics Johan Jeuring Utrecht University SPONSORS Ministry of Education and Research (via the centres of excellence in research programme) APPSEM II - FP5 IST thematic network Applied Semantics II CONTACT afp04(a)cs.ut.ee

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Why is newChan in the IO Monad?
by S. Alexander Jacobson 23 Apr '04

23 Apr '04

Nothing actually happens when newChan is called except construction of a new datastructure. It would be nice to have non IO monad code be able to create a new Chan that gets passed to IO code that uses it somewhere else. Alternatively, is there a way to create a Chan outside the IO monad? -Alex- _________________________________________________________________ S. Alexander Jacobson mailto:me@alexjacobson.com tel:917-770-6565 http://alexjacobson.com

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ACL2 Workshop
by Matt Kaufmann 23 Apr '04

23 Apr '04

Greetings [and apologies if you get multiple copies]: The fifth ACL2 Workshop will be held November 18-19, 2004, in Austin Texas, USA, in conjunction with (and immediately following) FMCAD. We invite users of ACL2, users of other theorem provers, and persons interested in the applications of theorem proving technology to attend. ACL2 is a state-of-the-art automated reasoning system, which grew out of the Boyer-Moore theorem prover and has been used successfully on a number of industrial and academic projects. ACL2 is described at http://www.cs.utexas.edu/users/moore/acl2. The ACL2 workshops provide a forum for the presentation and discussion of projects using ACL2 as well as the evolution of the tool. Topics include the following. o applications of the theorem prover o improvements and extensions to the theorem prover o comparisons of ACL2 to other theorem provers, programming languages, or specification languages o solved challenge problems for ACL2 users (especially challenges that help newcomers learn the system) o implementations connecting ACL2 and other systems For more information, including a call for papers, see: http://www.cs.utexas.edu/users/moore/acl2/workshop-2004/ Relevant dates are as follows: Submission Deadline: July 26, 2004 Acceptance Notification: August 23, 2004 Registration without late fee: October 4, 2004 Workshop: November 18-19, 2004 Regards, Matt Kaufmann and J Moore (Organizing Committee)

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evaluate function as a string
by Ay Joselito 23 Apr '04

23 Apr '04

Hello! I am new to Haskell. I want to develop an application in which the user enters a mathematical equation, presumably as a string (any arbitrary equation, using any of the standard mathematical operators : +,*,^, etc, and any of the standard functions: sin, exp, etc.). I need to take that string, convert it to a real function, and evaluate it. Thank you. ______________________________________________________________________ Correo Yahoo! - 6MB, más protección contra el spam ¡Gratis! http://correo.yahoo.es

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Correct interpretation of the curry-howard isomorphism
by Bruno Oliveira 23 Apr '04

23 Apr '04

Hi all! I would like to know what is the right interpretation of one of the consequences of the curry-howard isomorphism. I know that there is a relation between being able to implement coerse :: a -> b, and the fact that a type system is sound. I thought this would be the right consequence: ------------------------------------------ if we can write a function: coerce :: a -> b then, this would mean (by the curry-howard isomorphism) that the type system is not sound. ------------------------------------------ but then, it would be too easy to write this in haskell: coerce :: a -> b coerce x = undefined As an obvious consequence, Haskell type system would be unsound. So, I assumed that this would be a wrong interpretation. Would the following be more correct? ------------------------------------------ if we can write a function: coerce :: a -> b without calling any other function or primitive (that is, just with making use of the type system), then this would mean that the type system is unsound. ------------------------------------------ I would appreciate if someone could provide me with the right interpretation. Thanks, in advance! Best Regards, Bruno Oliveira

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CICLOPS 2004: Extended deadline [May 7th]
by Manuel Carro 22 Apr '04

22 Apr '04

[ N O T E: E X T E N D E D D E A D L I N E ] [ Please accept our apologies if you receive this message several times ] --------------------------------------------------------------------------- C A L L F O R P A P E R S CICLOPS 2004 Colloquium on Implementation of Constraint and LOgic Programming Systems to be held at Saint-Malo (France) at the occasion of ICLP'04 September, 2004 http://clip.dia.fi.upm.es/Conferences/CICLOPS-2004 --------------------------------------------------------------------------- Important dates --------------- * submission deadline: May 7 [EXTENDED] * notification of acceptance: June 7 * final version: June 28 * workshop dates: still to be decided (they depend on the organization of ICLP 2004) Topics of interest ------------------ This workshop aims at discussing and exchanging experience on the design, implementation, and optimization of logic, constraint (logic) programming systems, and systems intimately related to logic as a means to express computations. Experience backed up by real implementations and their evaluation will be given preference, as well as descriptions of work in progress in that direction. Topics include, but are not limited to: * Standard and alternative sequential implementation schemes (e.g., generalization / modification of the WAM, translation to lower-level and/or general-purpose languages, etc.) * Interaction between high-level optimizations / transformations / specialization and low-level issues. * Compile-time analysis and its application to code generation. * Low-level cost models to guide high-level optimizations. * Memory management, indexing, and garbage collection issues. * Balance between compile-time effort and run-time machinery. * Implementation of parallel and concurrent logic and constraint programming systems. * Implementation techniques for declarative programming paradigms with basis on, or extending, logic and constraint programming, such as non-monotonic reasoning, inductive logic programming, etc. * Implementation of systems closely related to, or based on, logic, such as theorem provers and natural language processing systems. * Performance evaluation of logic and constraint programming systems. * User oriented tools for performance evaluation and profiling. * Software design with and for LP/CP systems: components, patterns, etc. * Design and implementation of programming environments. * Experiences from using systems in real-life applications. Workshop Goals -------------- Our intent is to bring together, in an informal setting, people involved in research on sequential and parallel implementation technologies for logic and constraint programming languages and systems, in order to promote the exchange of ideas and feedback on recent developments. We hope that the workshop will provide a meeting point for people working on implementation technology for different aspects of logic and constraint-based languages and systems. Rationale and History --------------------- The last years have witnessed continuous progress in the technology available both for academic and commercial computing environments. Examples include more processor performance, increased memory capacity and bandwidth, faster networking technology, and operating system support for cluster computing. These improvements, combined with recent advances in compilation and implementation technologies, are causing high-level languages to be regarded as good candidates for programming complex, real world applications. Techniques aiming at achieving flexibility in the language design make powerful extensions easier to implement; on the other hand, implementations which reach good performance in terms of speed and memory consumption make declarative languages and systems amenable to develop non-trivial applications. Logic Programming and Constraint Programming, in particular, seem to offer one of the best options, as they couple a high level of abstraction and a declarative nature with an extreme flexibility in the design of their implementations and extensions and of their execution model. This adaptability is key to, for example, the implicit exploitation of alternative execution strategies tailored for different applications (e.g., for domain-specific languages) without jeopardizing efficiency unnecessarily. This workshop continues a tradition of successful workshops on Implementations of Logic Programming Systems, previously held with in Budapest (1993) and Ithaca (1994), the Compulog Net workshops on Parallelism and Implementation Technologies held in Madrid (1993 and 1994), Utrecht (1995) and Bonn (1996), the Workshop on Parallelism and Implementation Technology for (Constraint) Logic Programming Languages held in Port Jefferson (1997), Manchester (1998), Las Cruces (1999), and London (2000), and more recently the Colloquium on Implementation of Constraint and LOgic Programming Systems in Paphos (Cyprus, 2001), Copenhagen (2002), and Mumbai (2003), and the CoLogNet Workshops on Implementation Technology for Computational Logic Systems held in Madrid (2002) and Pisa (2003). Submission Information ---------------------- Authors are invited to submit papers written in English and not exceeding 12 pages. To speed up the process of refereeing, authors are requested to submit their paper in Postscript or PDF form. Hard copies may be sent to the contact address below only if access to electronic media is not available; please contact the organizers beforehand if that is the case. Submissions should contain full return mail and email address (if applicable) and FAX number (if applicable) of the contact author. Prospective authors are kindly requested to first send an indication of interest together with a paper title and abstract, in plain text format, to the organizers at the e-mail address at the bottom of the page. LaTeX style files are available via WWW at the Workshop web site. We strongly encourage their use, both in the preparation of submissions and, specially, for the final version. In order to obtain homogeneous workshop proceedings, authors of accepted papers will be requested to send the sources to the organizers. Authors who wish to prepare papers in formats other than LaTeX are kindly requested to contact the organization beforehand in order to make sure that we have available the right tools to process the files (if needed), or in order to receive detailed format instructions otherwise. Organization ------------ Program Committee: * Manuel Carro (Spain) * Ricardo Lopes (Portugal) * José F. Morales (Spain) * Enrico Pontelli (USA) * Vítor Santos (Brazil) * Tom Schrijvers (Belgium) * Christian Schulte (Sweden) * Paul Tarau (USA) * Neng-Fa Zhou (USA) Workshop Coordinators: Manuel Carro (contact person) http://lml.ls.fi.upm.es/~mcarro Phone: +34-91-3367455 Fax: +34-91-3366595 José F. Morales http://clip.dia.fi.upm.es/~jfran Phone: +34-91-3367448 Fax: +34-91-3366595 Invited Speaker: To be announced Contact Please address any question regarding the workshop organization to the address ciclops-org(a)clip.dia.fi.upm.es

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FM 2005: Call for Papers
by events-admin＠fmeurope.org 22 Apr '04

22 Apr '04

Call for Papers FM 2005 The 13th International Symposium of Formal Methods Europe Newcastle upon Tyne, UK 18-22 July 2005 www.csr.ncl.ac.uk/fm05/ Important dates: 24 January 2005 Paper submission deadline 07 March 2005 Last date for Workshop & Tutorial proposals 09 April 2005 Decisions on papers 02 May 2005 Final versions of papers due 09 May 2005 Last date for Tools Exhibition & Demonstration proposals FM'05 is the thirteenth in a series of symposia organized by Formal Methods Europe, an independent association whose aim is to stimulate the use of, and research on, formal methods for software development. The symposia have been notably successful in bringing together innovators and practitioners in precise mathematical methods for software development, industrial users as well as researchers. Submissions will be welcomed in the form of original papers on research and practice, proposals for workshops and tutorials, and entries for the exhibition of software tools, publications and companies. FM'05 welcomes papers in all aspects of formal methods for computer systems, including, but not restricted to, the following: * introducing formal methods in industrial practice (technical, organizational, social, psychological aspects) * reports on practical use and case studies (reporting positive or negative experiences) * formal methods in hardware and system design * reusable domain theories * theoretical foundations (specification and modelling, refining, verification, calculation etc.) * tool support and software engineering * environments for formal methods * method integration Papers ====== Full papers should be submitted electronically via the Web by 24 January 2005. Full submission details will be published on the conference web site. Papers will be evaluated by the Program Committee according to their originality, significance, soundness, quality of presentation and relevance with respect to the main issues of the symposium. Papers should have not been submitted elsewhere for publication. Accepted papers will be published in the Symposium Proceedings, to appear in Springer-Verlag's Lecture Notes in Computer Science Series. Papers should not exceed 16 pages and should be in LNCS format: see http://www.springer.de/comp/lncs/authors.html Please include a short list of keywords on a separate line at the end of the abstract, beginning with "Keywords:" in boldface. Workshops ========= We welcome proposals for one-day or two-day workshops related to FM'05. Proposals may be considered and evaluated at any time up to 7 March 2005 and should be directed to the Workshop Chair Juan Bicarregui (J.C.Bicarregui(a)rl.ac.uk) Early contact is recommended. Tutorials ========= We welcome proposals for half-day or full-day tutorials related to formal methods. Tutorial proposals will be evaluated on the basis of their potential benefit for participants, and should contain an outline of the objectives, format, content and, if appropriate, history of the tutorial. Proposals may be considered and evaluated at any time up to 7 March 2005, and should be sent to the Tutorial Chair, Neil Henderson (Neil.Henderson(a)ncl.ac.uk) Early contact is recommended. Exhibition & Sponsors' Presentations ==================================== An exhibition of projects and tools will also take place during the symposium, with the opportunity of holding presentations for each tool. The opportunity also exists to give a presentation as a sponsor. Proposals are welcomed at any time up to 9 May 2005 and should be directed to the Exhibition and Sponsors' Chair, Joan Atkinson (Joan.Atkinson(a)ncl.ac.uk) Early contact is recommended. Contacts ======== General Chair: John Fitzgerald, University of Newcastle upon Tyne, UK John.Fitzgerald(a)ncl.ac.uk Programme Chairs: Ian Hayes, University of Queensland, Australia Ian.Hayes(a)itee.uq.edu.au Andrzej Tarlecki, Warsaw University, Poland tarlecki(a)mimuw.edu.pl Organisers: Claire Smith & Jon Warwick, University of Newcastle upon Tyne, UK Claire.Smith(a)ncl.ac.uk, Jon.Warwick(a)ncl.ac.uk Workshops Chair: Juan Bicarregui, Rutherford Appleton Laboratory, UK J.C.Bicarregui(a)rl.ac.uk Tutorials Chair: Neil Henderson, University of Newcastle upon Tyne, UK Neil.Henderson(a)ncl.ac.uk Exhibitions & Sponsorship: Joan Atkinson, University of Newcastle, UK Joan.Atkinson(a)ncl.ac.uk Programme Committee =================== Bernhard Aichernig, UNU-IIST, UN Keijiro Araki, Kyushu University, Japan Michel Bidoit, LSV, CNRS & ENS de Cachan, France Juan Bicarregui, Rutherford Appleton Laboratory, UK Ed Brinksma, University of Twente, The Netherlands Luca Cardelli, Microsoft Research, UK Ernie Cohen, Microsoft, USA Jin Song Dong, National University of Singapore, Singapore Jose Fiadeiro, University of Leicester, UK John S. Fitzgerald, Centre for Software Reliability, UK Stefania Gnesi, CNR, Italy Anthony Hall, Praxis Critical Systems, UK Ian Hayes, University of Queensland, Australia (Co-chair) Anne E. Haxthausen, Technical University of Denmark, Denmark Thomas Henzinger, University of California, Berkeley, USA He Jifeng, UNU-IIST, UN Cliff Jones, University of Newcastle upon Tyne, UK Shaoying Liu, Hosei University, Japan Mícheál Mac an Airchinnigh, Trinity College, Dublin, Ireland Tom Maibaum, King's College, London, UK Dino Mandrioli, Politecnico di Milano, Italy Richard Moore, IFAD A/S, Denmark Tobias Nipkow, Technische Universität München, Germany José Oliveira, Universidade do Minho, Portugal Sam Owre, CRI, USA Alexander Petrenko, ISPRAS, Russia Nico Plat, West Consulting, Netherlands Ken Robinson, University of New South Wales, Australia Mark Saaltink, ORA, Canada Shin Sahara, JFITS, Japan Steve Schneider, Royal Holloway, UK Kaisa Sere, Åbo Akademi, Finland Ketil Stølen, SINTEF, Norway Andrzej Tarlecki, Warsaw University, Poland (Co-chair) Martyn Thomas, Martyn Thomas Associates, UK Mark Utting, Waikato University, New Zealand Marcel Verhoef, Chess IT & Radboud University, Nijmegen, Netherlands Alan Wassyng, McMaster University, Canada Martin Wirsing, Ludwig-Maximilians-Universität, München, Germany _______________________________________________ events mailing list events(a)fmeurope.org http://www.fmeurope.org/mailman/listinfo/events

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EuroHaskell - come to sweden, write code
by Shae Matijs Erisson 21 Apr '04

21 Apr '04

You are cordially invited to come to EuroHaskell for fun and code. EuroHaskell is a sprint[1] and gathering happening at Chalmers University of Technology in Gothenburg, Sweden on June 10th, 11th, and 12th. The goal is to meet, learn, and code. The [dis]organizers are Björn Bringert and Shae Erisson. There is no entrance fee. Food and drink are not supplied, but feel free to bring your own. More information is available on the EuroHaskell wiki page: http://www.haskell.org/hawiki/EuroHaskell [1]A sprint is a focussed development session based on the principles of Extreme Programming, in which developers pair off together in a room and focus on a particular subsytem or task. for more info see : http://www.zopemag.com/Guides/miniGuide_ZopeSprinting.html -- Shae Erisson - putStr $ fix("HELLO\n"++) - http://www.ScannedInAvian.org/ OSDir: Community building... interesting... what's the secret sauce? Limi: Irresponsible sleep patterns. -- Alexander Limi, one of the Plone founders http://osdir.com/Article199.phtml

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Haskell and Artificial Intelligence
by GAYLE, Orrett Orville 21 Apr '04

21 Apr '04

I am having great difficulty finding resources with AI sysytems implemented in Haskell. If anyones knows of a book or site which covers AI techniques implemented using haskell, could you please help me. Thanks in advance.

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