January 2002 - Haskell

ANNOUNCE: hmake-3.00
by Malcolm Wallace 22 Jan '02

22 Jan '02

hmake-3.00 ---------- We are pleased to announce the release of version 3.00 of 'hmake', the Haskell program compilation manager. http://www.cs.york.ac.uk/fp/hmake/ Features of hmake: * compiler independent * aware of .hi files in re-compilation analysis * respects cpp directives * supplies an optional Hugs-like interactive environment (hi) New features in 3.00: * improved detection and configuration of compilers * multiple compilers of the same type are now permitted simultaneously (e.g. ghc 4.08 + 5.02) * you can refer to compilers by simple name or absolute paths * a new separate tool 'hmake-config' manages hmakerc files * various Haskell preprocessors are now recognised and invoked (e.g. happy, hsc2hs, c2hs, greencard) if the corresponding file extension is found (.ly/.y, .hsc, .chs, .gc) * hooks for the forthcoming compiler-independent Haskell tracing system ('portable' Hat) are included Bug reports: Please send bug reports for 'hmake' to the mailing list nhc-bugs(a)haskell.org

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SBLP'2002 First Call for Papers
by Carlos Camarao de Figueiredo 21 Jan '02

21 Jan '02

=============================================== SBLP'2002 VI Brazilian Symposium on Programming Languages http://www.inf.puc-rio.br/sblp Departamento de Informática PUC-Rio Rio de Janeiro, RJ, Brazil June 05-07, 2002 =============================================== First Call for Papers --------------------- The VI Brazilian Symposium on Programming Languages (SBLP'2002) will be held at Pontifícia Universidade Católica do Rio de Janeiro (PUC-Rio) in Rio de Janeiro, Brazil, on June 05-07, 2002. The symposium is sponsored by the Brazilian Computer Society (SBC) and aims to provide a forum where researchers, educators, and practitioners present and discuss the latest theoretical and practical work on programming languages. We invite authors to contribute to SBLP'2002 with the following kinds of submission: * Technical research papers introducing original research results on topics such as (but not limited to): - Programming language design and implementation - Formal semantics of programming languages - Domain-specific programming languages - Visual programming languages - Programming languages for mobile, WWW, and network computing - Script languages - Design and implementation of programming tools and environments - New programming models - Theoretical foundations of programming languages - Teaching programming languages * Experience reports on the use of programming languages, tools, and environments. The reports should clearly state the problems and difficulties identified on using those programming languages or technologies on projects, possibly giving solutions to those problems or hints to avoid them. * Tutorial proposals on subjects related to programming languages, APIs, tools, environments or theories. There will be also invited lectures, tutorials, panels, and working meetings to closely group together professionals interested on specific research topics. Important dates --------------- Deadline for submissions: February 28, 2002 Notification of acceptance: March 28, 2002 Camera-ready version: May 15, 2002 Conference chair ---------------- Edward Hermann Haeusler Departamento de Informática Pontifícia Universidade Católica do Rio de Janeiro Tel.: +55 (21) 3114-1500 R: 4345 email: hermann(a)inf.puc-rio.br Program Chair ------------- Carlos Camarão Departamento de Ciência da Computação Universidade Federal de Minas Gerais Tel: +55 (31) 3499 5889 email: camarao(a)dcc.ufmg.br Submission details ------------------- Contributions can be written in Portuguese, English or Spanish. Those written in English can be selected for publication elsewhere (probably Elsevier Electronic Notes in Theoretical Computer Science). All papers and experience reports will be published in the conference proceedings. Papers should have at most 14 pages and experience reports at most 8 pages. ---- Tutorials will be published in a separate proceedings. They should cover material of postgraduate level. The tutorial submission may be only a proposal, containing: - title - author names - motivation, describing the relevance of the subject in the area of programming languages - abstract - description of the presentation (optional) Tutorial proposals will be selected according to i) its technical quality and ii) expected relevance and interest from the community. The final tutorial should contain at most 30 pages. ---- Contributions should use the standard format of SBC (Brazilian Computer Society). They are available in: - LaTeX: http://www.sbc.org.br/templates/sbc-template-latex.zip - PDF/Adobe Acrobat: http://www.sbc.org.br/templates/sbc-template-latex.zip - Word: http://www.sbc.org.br/templates/sbc-template-dot.zip Use of LaTeX is preferred. Examples of the use of the SBC format can be found in these zip files. (You can also obtain them by visiting the site http://www.sbc.org.br and following the links *eventos* and, afterwards, *Informações úteis*.) For submission of contributions, fill out the required information at http://www.dcc.ufmg.br/~camarao/sblp/forms/authpaper_reg.html ======================================================================

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ESSLLI 2002 Student Session
by Malvina Nissim 21 Jan '02

21 Jan '02

!!! Concerns all students in Logic, Linguistics and Computer Science !!! !!! Please circulate and post among students !!! We apologise if you receive this message more than once. ESSLLI-2002 STUDENT SESSION SECOND CALL FOR PAPERS August 5-16 2002, Trento, Italy Deadline: February 25th, 2002 www.iccs.informatics.ed.ac.uk/~malvi/esslli02 We are pleased to announce the Student Session of the 14th European Summer School in Logic, Language and Information (ESSLLI-2002) organised by the Centre for scientific and technological research (ITC-irst) in Trento and by the University of Trento, under the auspices of the European Association for Logic, Language and Information (FoLLI). ESSLLI-2002 will be held in Trento from August 5-16 2002. We invite submission of papers for presentation at the ESSLLI-2002 Student Session and for appearance in the proceedings. PURPOSE: This seventh ESSLLI Student Session will provide, like the other editions, an opportunity for ESSLLI participants who are students to present their own work in progress and get feedback from senior researchers and fellow-students. The ESSLLI Student Session encourages submissions from students at any level, from undergraduates (before completion of the Master Thesis) as well as postgraduates (before completion of the PhD degree). Papers co-authored by non-students will not be accepted. Papers may be accepted for full presentation (30 minutes including 10 minutes of discussion) or for a poster presentation. All the accepted papers will be published in the ESSLLI-2002 Student Session proceedings, which will be made available during the summer school. KLUWER BEST PAPER AWARD: As in previous years, the best paper will be selected by the programme committee and will be offered a prize of 600 euros by Kluwer Academic Publishers to be spent on books. REQUIREMENTS: The Student Session papers should describe original, unpublished work, completed or in progress that demonstrates insight, creativity, and promise. No previously published papers should be submitted. Note that the ESSLLI02 school will be focused on the three main interdisciplinary areas (Logic & Language, Logic & Computation, and Language & Computation), while the single areas have been dropped. Given the high interest shown over the years, the Student Session will keep two of the single areas, namely Logic and Language, welcoming thus submissions within the following topics: Logic, Language, Logic & Language, Logic & Computation, Language & Computation. FORMAT OF SUBMISSION: Student authors should submit an anonymous full paper headed by the paper title, not to exceed 7 pages of length exclusive of references and send a separate identification page (see below). Note that the length of the final version of the accepted papers will not be allowed to exceed 10 pages. Since reviewing will be blind, the body of the paper should omit author names and addresses. Furthermore, self-references that reveal the author's identity (e.g., "We previously showed (Smith, 1991)... ") should be avoided. It is possible to use instead references like "Smith (1991) previously showed...". For any submission, a plain ASCII text version of the identification page should be sent separately, using the following format: Title: title of the submission First author: firstname lastname Address: address of the first author ...... Last author: firstname lastname Address: address of the last author Short summary: abstract (5 lines) Subject area (one of): Logic | Language | Logic and Language | Logic and Computation | Language and Computation If necessary, the programme committee may reassign papers to a more appropriate subject area. The submission of the paper should be in one of the following formats: PostScript, PDF, RTF, or plain text. But note that, in case of acceptance, the final version of the paper has to be submitted in LaTeX format. Please, use A4 size pages, 11pt or 12pt fonts, and standard margins. Submissions outside the specified length and formatting requirements may be subject to rejection without review. The paper and separate identification page must be sent by e-mail to: malvi(a)cogsci.ed.ac.uk by FEBRUARY 25th 2002 ESSLLI-2002 INFORMATION: In order to present a paper at ESSLLI-2002 Student Session, at least one student author of each accepted paper has to register as a participant at ESSLLI-2002. The authors of accepted papers will be eligible for reduced registration fees. For all information concerning ESSLLI-2002, please consult the ESSLLI-2002 web site at www.esslli2002.it IMPORTANT DATES: Deadline for submission of papers: February 25, 2002. Authors notifications: April 22, 2002. Final version due: May 20, 2002. ESSLLI-2002 Student Session: August 5-16, 2002. PROGRAMME COMMITTEE: David Ahn, University of Rochester (Language and Computation) Carlos Areces, University of Amsterdam (Logic) Reinhard Blutner, University of Berlin (Language) Kees van Deemter, University of Brighton (Language and Computation) Paul Dekker, University of Amsterdam (Logic and Language) Juergen Dix, University of Manchester (Logic and Computation) Marta Garcia-Matos, University of Helsinki (Logic) Juan Heguiabehere, University of Amsterdam (Logic and Computation) Elsi Kaiser, University of Pennsylvania (Language) Malvina Nissim, University of Edinburgh (Chair) Rick Nouwen, University of Utrecht (Logic and Language) For any specific questions concerning ESSLLI-2002 Student Session, please, do not hesitate to contact me: Malvina Nissim ICCS, University of Edinburgh 2 Buccleuch Place, Edinburgh EH8 9LW, UK phone: +44 +(0)131 +650 4630 fax: +44 +(0)131 +650 6626 e-mail: malvi(a)cogsci.ed.ac.uk

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H98 Report: semantics of pattern matching
by Ross Paterson 21 Jan '02

21 Jan '02

In section 3.17 Pattern Matching, there are some inconsistencies between the informal and formal semantics: (1) Section 3.17.2 Informal Semantics of Pattern Matching needs an extra rule (before rule 2): Matching _|_ against the pattern con pat, where con is a constructor defined by newtype, is equivalent to matching _|_ against the pattern pat. (2) Rule 3 "Matching _|_ against a refutable pattern always diverges" is untrue, because rules 4(b) and (c) (numeric literals and n+k patterns) are also applicable to _|_, and it is possible to define the Eq, Ord and Num classes so that pattern matching is non-strict: > data Foo = Foo > instance Eq Foo where _ == _ = True > instance Ord Foo where _ > _ = False > instance Show Foo > instance Num Foo > f :: Foo -> Int > f 0 = 20 > g :: Foo -> Int > g (n+1) = 20 -- Hugs incorrectly requires the Integral class so f undefined = g undefined = 20. Other definitions could be hyperstrict, so _|_/non-_|_ distinction isn't relevant. I'd suggest changing rule 3 to Matching _|_ against a pattern whose outermost component is a constructor defined by data always diverges. deleting rule 4 and promoting the subrules, removing "non-_|_" from (c) and changing "if x < k" to "otherwise". You might wish to say it diverges if x >= k does, but maybe that's too formal. (3) Section 3.17.3 Formal Semantics of Pattern Matching needs an extra equation: case _|_ of { K x1 ... xn -> e; _ -> e' } = _|_ where K is a data constructor of arity n (4) Equation (r) uses let, suggesting the possibility of polymorphism -- I'd suggest changing the rhs to if v >= k then case v-k of { x -> e } else e'

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Re: Ambiguous types
by Ashley Yakeley 21 Jan '02

21 Jan '02

At 2002-01-21 00:25, Janis Voigtlaender wrote: >Hope that helps and doesn't just make the story more obscure ;-) I'm not convinced. Here's a simplified case... This compiles fine: emptyList :: [a] emptyList = [] isempty :: Bool isempty = null emptyList But this gives an error: emptyList :: (Ord a) => [a] emptyList = [] isempty :: Bool isempty = null emptyList ghci says: Ambiguous type variable(s) `a' in the constraint `Ord a' arising from use of `emptyList' at ActorTest.hs:7 In the first argument of `null', namely `emptyList' In the definition of `isempty': null emptyList Hugs says: ERROR "ActorTest.hs" (line 7): Cannot justify constraints in explicitly typed binding *** Expression : isempty *** Type : Bool *** Given context : () *** Constraints : Ord a -- Ashley Yakeley, Seattle WA

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Ambiguous types
by Daniel . 21 Jan '02

21 Jan '02

Hi there, I've just starting learning Haskell and, to be quite frank, it gives me a cold sweat at times. What has me confused at present is why the following code gives me :- ActorTest.hs:8: Ambiguous type variable(s) `a' in the constraint `Action a' arising from use of `validActions' at ActorTest.hs:8 In the first argument of `(==)', namely `validActions actor' In the definition of `canAct': (validActions actor) == [] {-code-} module ActorTest where class Actor t where canAct :: t -> Bool validActions :: (Action u) => t -> [u] canAct actor = validActions actor == [] validActions actor = [] class Eq t => Action t {-end code-} Is the error saying that it is impossible to tell what specific type instance of the Action class will be returned by validActions? If so, why should it matter? Isn't it enough to know that they results will be of the class Action? Thanks Daniel -- _______________________________________________ Sign-up for your own FREE Personalized E-mail at Mail.com http://www.mail.com/?sr=signup 1 cent a minute calls anywhere in the U.S.! http://www.getpennytalk.com/cgi-bin/adforward.cgi?p_key=RG9853KJ&url=http:/…

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RE: dependent type query
by Simon Peyton-Jones 21 Jan '02

21 Jan '02

| >Furthermore, I can't even write: | > | >data (MyClass f a) => MyData2 f = MyData2 f | | Well now this is odd. I had no trouble simulating it with this: | | data MyData2 f = MyData2 f | | mkMyData2 :: (MyClass f a) => f -> MyData2 f | mkMyData2 = MyData2 | | Looks like extended Haskell is being excessively restricted. Comments? I think you are correct here. But as you point out, contexts in data declarations only restrict what programs you can write, by adding extra constraints to the constructors. They have no useful purpose at all, so far as I know, and I wish Haskell didn't have them. So I am disinclined to invest much effort in fixing this infelicity in GHC's handling of them. Simon

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(no subject)
by Peter Stuckey 21 Jan '02

21 Jan '02

------- Blind-Carbon-Copy To: pjs Subject: Date: Mon, 21 Jan 2002 13:27:08 +1100 Message-ID: <21510.1011580028(a)muldi.cs.mu.oz.au> From: Peter Stuckey <pjs(a)muldi.cs.mu.oz.au> Apologies for Receiving Multiple Copies of this Message - ---------------------------------------------------------- CALL FOR PAPERS ICLP'02 Eighteenth International Conference on Logic Programming Copenhagen, Denmark July 29th - August 1, 2002 http://floc02.diku.dk/ICLP/ ICLP'02, the Eighteenth International Conference on Logic Programming will be be held this year as part of the 2002 Federated Logic Conference (http://floc02.diku.dk/) in conjunction with CADE, CAV, FME, LICS, RTA and TABLEAUX. ICLP'02 is sponsored by IF/Prolog (http://www.ifcomputer.de) TOPICS Since the first ICLP, held in Marseilles in 1982, ICLP has been the premier international conference for presenting research into logic programming. Original papers are sought in all areas of logic programming including (but not restricted to): Theory Implementation Semantic Foundations Compilation Formalisms Memory Management Non-monotonic Reasoning Virtual Machines Knowledge Representation Parallelism Language Issues Environments Constraints Program Analysis Concurrency Program Transformation Objects Validation and Verification Coordination Debugging Mobilility Higher Order Applications Types Modes Deductive Databases Programming Techniques Software Engineering Natural Language Web tools Internet Agents Artificial Intelligence Papers describing innovative applications of logic programming (in the broadest sense, e.g. including constraint programming, non-monotonic systems, etc.) are particularly sought. We welcome submission in, but not limited to, the following topics: surveys of an application area, problems to which logic programming may be applied, experience in applying logic programming, software engineering aspects of logic programming and areas where further research is required to meet industrial needs. There will be an award for the best application paper sponsored by IF/Prolog. SUBMISSION Papers must describe original, previously unpublished work, be written and presented in English, not exceed 15 pages (A4 or letter format, up to 5,000 words), and not be simultaneously submitted for publication elsewhere. The proceedings will be published by Springer Verlag in the Lecture Notes in Computer Science series. Authors are strongly encouraged to use LaTeX2e and the Springer llncs class file, available at http://www.springer.de/comp/lncs/authors.html Submission is Web-based. In order to submit a paper, authors should upload it via the web at http://www.cs.mu.oz.au/~pjs/ICLP2002/ where more detailed instructions are given. If submission through the Web is not possible, five hard copies may be sent to the program chair. Authors intending to submit a paper are requested to submit an abstract of their paper, through the same web interface, before February 10, to help expedite the paper assignment process. Submission Agenda: Submission of abstracts: February 10, 2002 Submission of papers: February 17, 2002 Notification of acceptance: April 14, 2002 Camera-ready papers due: May 14, 2002 Workshops: The following workshops will be held in conjunction with ICLP'02. August 1: CLIMA - Computational Logic In Multi-Agent Systems July 28: CLPSE - (Constraint) Logic Programming and Software Engineering July 31: LPE - Workshop on Logic Programming Environments July 27-28: NLULP - Natural Language Understanding and Logic Programming July 27: PCL - Paraconsistent Computational Logic July 27: SAVE - Specification, Analysis and Validation for Emerging Technologies in Computational Logic July 28: UNKB - Updating Non-Monotonic Knowledge Bases Conference Location: The conference will be held at the University of Copenhagen. Program Chair: Conference Chair: Peter J. Stuckey Henning Christiansen Department of Computer Science Department of Computer Science and Software Engineering Roskilde University University of Melbourne PO Box 260 3010, AUSTRALIA DK-4000 Roskilde, DENMARK Email: pjs(a)cs.mu.oz.au Email: henning(a)ruc.dk Tel: +613-8344-9155 Tel: +45 46 74 38 32 Fax: +613-9348-1184 Programme Committee: Jose Alferes, Universidade Nova de Lisboa Francisco Bueno, Universidad Polytecnica de Madrid Henning Christiansen, Roskilde University Sandro Etalle, University of Twente Francois Fages, INRIA Maurizio Gabbrielli, University of Bologna Maria Garcia de la Banda, Monash University Michael Gelfond, Texas Tech University Gopal Gupta, UT Dallas Katsumi Inoue, Kobe University Joxan Jaffar, National University of Singapore Gerda Janssens, K.U.Leuven Bharat Jayaraman, State University of New York at Buffalo Michael Leuschel, University of Southampton Michael Maher, Loyola University Chicago Dale Miller, The Pennsylvania State University Ulf Nilsson, Linkoping University Francesca Rossi, Universita' di Padova Konstantinos Sagonas, Uppsala University Christian Schulte, Universitat des Saarlandes Harald Sondergaard, University of Melbourne Francesca Toni, Imperial College London Miroslaw Truszczynski, University of Kentucky Pascal Van Hentenryck, Brown University David S. Warren, State University of New York at Stony Brook ------- End of Blind-Carbon-Copy

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question about kinds
by Hal Daume III 20 Jan '02

20 Jan '02

I have the following definition: > class Traversable d where > traverse :: d a -> (Maybe a, [d a]) And the standard binary tree data type: > data Tree a = Branch (Tree a) (Tree a) > | Leaf a I can define both Tree and [] to be instances of Traversable: > instance Traversable Tree where > traverse (Leaf a) = (Just a, []) > traverse (Branch t1 t2) = (Nothing, [t1,t2]) > instance Traversable [] where > traverse [] = (Nothing, []) > traverse (x:xs) = (Just x, [xs]) Now, I want to say that if some data type 'd' is Traversable and another data type 'e' is Traversable, then the "combined data type" is Traversable. That is, for example, I want to say that a Tree of Lists is traversable, or that a List of Trees, or a List of Lists is traversable. But I can say neither: > instance Traversable (Tree []) where ... or: > instance (Traversable a, Traversable b) => Traversable (a b) where .. Because of the obvious kind errors. What I suppose I need is some sort of lambda expansion over kinds, so I could say: > instance (Traversable a, Traversable b) => Traversable (\x -> a b x) or something like that. Obviously this doesn't exist. How can I get around this? - Hal -- Hal Daume III "Computer science is no more about computers | hdaume(a)isi.edu than astronomy is about telescopes." -Dijkstra | www.isi.edu/~hdaume

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Re: question about kinds
by Ashley Yakeley 19 Jan '02

19 Jan '02

At 2002-01-18 13:19, Hal Daume III wrote: >In theory, I could write: > >class Traversable d a where > traverse :: d a -> (Maybe a, [d a]) > >instance Traversable Tree a where > traverse (Leaf a) = (Just a, []) > traverse (Branch t1 t2) = (Nothing, [t1,t2]) > >instance Traversable [] a where > traverse [] = (Nothing, []) > traverse (x:xs) = (Just x, [xs]) > >instance (Traversable d (e a), Traversable e a) => Traversable d (e >a) where > traverse = ... > >but then both ghc and hugs complain about overlapping instances, even with >-fallow-overlapping-instances/-fallow-undecidable-instances in ghc and +o >in hugs. Try this: class Traversable t a where -- note no fundep traverse :: t -> (Maybe a, [t]) instance Traversable (Tree a) a where traverse (Leaf a) = (Just a, []) traverse (Branch t1 t2) = (Nothing, [t1,t2]) instance Traversable [a] a where traverse [] = (Nothing, []) traverse (x:xs) = (Just x, [xs]) instance (Traversable (d (e a)) (e a), Traversable (e a) a) => Traversable (d (e a)) a where traverse = ... ...or even, more generally... instance (Traversable a b, Traversable b c) => Traversable a c where traverse = ... -- Ashley Yakeley, Seattle WA

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