- Haskell - Haskell.org

stack overflow - nonobvious thunks?
by Scherrer, Chad 27 Jul '05

27 Jul '05

I'm trying to write a function to build a table of values from a list. Here's my current attempt: table :: (Ord a) => [a] -> [(a,Int)] table xs = Map.assocs $! foldl' f Map.empty xs where f m x = Map.insertWith (+) x 1 m The ($!) and the foldl' were my clumsy attempts to avoid the stack overflows I keep getting, but it's not working right yet. If I set unif :: [Int] unif = randomRs (1,10) $ mkStdGen 1 then I should be able to use f :: Int -> [(Int, Int)] f n = table $ take n unif I would think this should work using very little memory, since unif is evaluated lazily, and the table is built eagerly. But I must be keeping around more thunks than I think, since I get (in ghci) *Main> f 1000000 [(1,99816),(2,100187),(3,99969),(4,99892),(5,100194),(6,100190),(7,99776 ),(8,100347),(9,100125),(10,99504)] *Main> f 10000000 [(1,*** Exception: stack overflow So it works on big lists, but not huge ones. What am I missing? Is there a way to do this other than just increasing the memory allocation? Thanks, Chad Scherrer

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Haskell SOE Question
by Alex Edelsburg 27 Jul '05

27 Jul '05

Hello! I'm a student in Professor John Peterson's Elements of Computing (class site located here: http://cs.yale.edu/cs110-05) and he's having me learn Haskell with Paul Hudak's SOE book. I'm working on the PaddleBall in 20 lines at the end of Chapter 15 and I'm having a problem with HUGS. I downloaded the version from http://haskell.org/soe/software.htm which is recommended but I'm still having trouble. I copied the code verbatim from the book and I still get the following error. ERROR "Animation.hs" - Unknown entity "word32ToInt" imported from module "Word" It looks like this is a problem with one of the Haskell or Hugs libraries, not an SOE library. If anyone has any suggestions, they would be greatly appreciated. If anyone would like to see my code, please let me know and I'll post it ASAP. ~Alex

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CFP: Computational Models of Scientific Reasoning and Applications (CMSRA-IV)
by Luis Moniz Pereira 23 Jul '05

23 Jul '05

Please relay --------------------------- Computational Models of Scientific Reasoning and Applications (CMSRA-IV) Lisbon, 21-23 September 2005 http://centria.di.fct.unl.pt/~greg/conf/CMSRA-IV.html Program Invited speakers: Teddy Seidenfeld H. A. Simon Professor of Philosophy and Statistics, Carnegie Mellon University, USA Wiebe van der Hoek Professor of Computer Science, Head of the (Agent ART) Group University of Liverpool, UK Accepted papers: The Mathematics of Family Resemblance R. Jennings and D. Nicholson Nonmonotonic Conditionals that Behave Like Conditional Probabilities Above a Threshold J. Hawthorne An Adaptive Logic for Compassionate Relevantism H. Lycke Preferential Theory Revision P. Dell'Acqua and L.M. Pereira Defeasible Reasoning Partial Models: a Formal Framework for the Methodology of Research Programs F. Tohmé, C. Delrieux and O. Bueno Some Comments on History Based Structures E. Pacuit Types of Coherence and Coherence among Types P. Bandyopadhyay Conditionals and Consequences H. E. Kyburg, C. M. Teng and G. Wheeler Confirmation Theory and the Logic of Inductive Implication R. Silvestre, H. Tarcisio and C. Pequeno A Mathematical Comment on the Fundamental Difference between Legal Theory Formation and Scientific Theory Formation R. Loui

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Ambiguity problem
by Mads Lindstrøm 22 Jul '05

22 Jul '05

Hi I am struggling with an ambiguity problem. I have the following code: > foo :: Constr -> Int > foo = numChildren . fromConstr > > numChildren :: (Data a) => a -> Int > numChildren x = sum $ gmapQ (\_ -> 1) x which I thought would work, but the GHC-6.4 says: > Ambiguous type variable `a' in the constraint: > `Data a' arising from use of `numChildren' at AutoForm.hs:87:6-16 > Probable fix: add a type signature that fixes these type variable(s) I cannot see why I need to add (Data a), as fromConstr signatur is: fromConstr :: forall a. (Data a) => Constr -> a I do not know where to add it either. Hope, somebody can enlighten me. Greetings, Mads Lindstrøm

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Haskell workshop 2005 -- Call for participation.
by Daan Leijen 22 Jul '05

22 Jul '05

2005 Haskell Workshop Tallinn, Estonia, 30 September, 2005 http://www.cs.uu.nl/~daan/hw2005 Call for participation -- Important Dates --------------------------------------------------- Early registration deadline : July 29 Late registration deadline : September 2 Haskell workshop : September 30 Registration is available from <http://www.cs.ioc.ee/tfp-icfp-gpce05>. -- Preliminary Programme --------------------------------------------- The preliminary programme is available from the Haskell workshop website at <http://www.cs.uu.nl/~daan/hw2005> and is appended in plain text to this section. This year, David Roundy gives an invited talk about Darcs: a popular distributed version control system written Haskell. 8:45 Welcome by Daan Leijen 9:00 - 10:30 Invited talk: Lessons from Darcs David Roundy Visual Haskell – A full-featured Haskell development environment Krasimir Angelov and Simon Marlow Haskell ready to Dazzle the real world Martijn M. Schrage, Arjan van IJzendoorn, and Linda C. van der Gaag 11:00 - 12:30 Dynamic applications from the ground up Don Stewart and Manuel M. T. Chakravarty Haskell server pages through dynamic loading Niklas Broberg Haskell on a shared-memory multiprocessor Tim Harris, Simon Marlow, and Simon Peyton Jones 14:00 - 15:30 Verifying Haskell programs using constructive type theory Andreas Abel, Marcin Benke, Ana Bove, John Hughes, Ulf Norell Putting Curry-Howard to work Tim Sheard There and Back Again – Arrows for Invertible Programming Artem Alimarine, Sjaak Smetsers, Arjen van Weelden, Marko van Eekelen, and Rinus Plasmeijer 16:00 - 17:15 TypeCase: A design pattern for type-indexed functions Bruno C. d. S. Oliveira and Jeremy Gibbons Functional pearl: Polymorphic pattern matching Richard S. Bird Tool demonstration: Halfs – the Haskell file system Isaac Jones 17:15 - 17:45 Discussion: The future of Haskell -- The Haskell Workshop ---------------------------------------------- The Haskell Workshop 2005 is an ACM SIGPLAN sponsored workshop affiliated with the 2005 International Conference on Functional Programming (ICFP). Previous Haskell Workshops have been held in La Jolla (1995), Amsterdam (1997), Paris (1999), Montreal (2000), Firenze (2001), Pittsburgh (2002), Uppsala (2003), and Snowbird (2004). -- Scope ------------------------------------------------------------- The purpose of the Haskell Workshop is to discuss experience with Haskell, and future developments for the language. The scope of the workshop includes all aspects of the design, semantics, theory, application, implementation, and teaching of Haskell. Topics of interest include, but are not limited to, the following: * Language Design, with a focus on possible extensions and modifications of Haskell as well as critical discussions of the status quo; * Theory, in the form of a formal treatment of the semantics of the present language or future extensions, type systems, and foundations for program analysis and transformation; * Implementations, including program analysis and transformation, static and dynamic compilation for sequential, parallel, and distributed architectures, memory management as well as foreign function and component interfaces; * Tools, in the form of profilers, tracers, debuggers, pre-processors, and so forth; * Applications, Practice, and Experience, with Haskell for scientific and symbolic computing, database, multimedia and Web applications, and so forth as well as general experience with Haskell in education and industry; * Functional Pearls, being elegant, instructive examples of using Haskell. Papers in the latter two categories need not necessarily report original research results; they may instead, for example, report practical experience that will be useful to others, re-usable programming idioms, or elegant new ways of approaching a problem. The key criterion for such a paper is that it makes a contribution from which other practitioners can benefit. It is not enough simply to describe a program! -- Program committee ------------------------------------------------- Martin Erwig Oregon State University John Hughes Chalmers University of Technology Mark Jones OGI School of Science and Engineering at OHSU Ralf Lämmel Microsoft Corp. Daan Leijen Universiteit Utrecht (Program Chair) Andres Löh Universiteit Utrecht Andrew Moran Galois Connections Inc. Simon Thompson University of Kent Malcolm Wallace University of York

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WS-FM 2004 Call For Participation
by Mario Bravetti 20 Jul '05

20 Jul '05

---------------------------------------------------------------------- We apologize if you receive multiple copies of this announcement. ---------------------------------------------------------------------- ====================================================================== 1st International Workshop on Web Services and Formal Methods (WS-FM 2004) February 23-24, 2004, Pisa, Italy Workshop affiliated to COORDINATION 2004, February 24-27, 2004 WS-FM 2004 homepage: http://www.cs.unibo.it/~lucchi/ws-fm04/ ====================================================================== - The technical program is available at: http://www.cs.unibo.it/~lucchi/ws-fm04/ - Information about registration, travel and accomodation can be found at the COORDINATION 2004 web site: http://www.di.unipi.it/Coordination2004/ If you intend to participate, we recommend you to register and book the hotel as soon as possible. The Coordination 2004 Organizing Committee informed us that hotels are going to be fully booked in short time.

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ICLP 2005: Call for Participation
by ICLP 2005 18 Jul '05

18 Jul '05

Dear Colleague, Please note that ICLP 2005 registration is now open. In fact, the early registration deadline is not too far (July 31st). More details can be found at the ICLP 2005 website: http://www.iiia.csic.es/iclp2005/ Highlights include invited talks by Ian Horrocks, Peter Stuckey, Francesca Rossi, a tutorial on "Inductive Logic Programmng, Statistical Relational Learning and its applications" by Vitor Santos Costa, contributed papers, posters, programming competition, panels, conference workshops, and of course the Solar Eclipse that will take place during the conference and will be visible in Barcelona (time has been set aside during the conference to view the eclipse). We look forward to seeing all of you in Barcelona. Best wishes, Gopal Gupta and Maurizio Gabbrielli ---------------------------------------------------------------------- LIST OF ACCEPTED PAPERS: ---------------------- Full papers (26 papers) ----------------------- Use of Logic Programming for Complex Business Rules Walter Wilson Semantics of Framed Temporal Logic Programs Zhenhua Duan, Xiaoxiao Yang and Maciej Koutny. On the relation between Answer Set and SAT procedures (or, between smodels and cmodels) Enrico Giunchiglia and Marco Maratea. HYPROLOG: a new logic programming language with assumptions and abduction Henning Christiansen and Veronica Dahl. A Generator of Efficient Abstract Machine Implementations and its Application to Emulator Minimization Jose Morales, Manuel Carro, German Puebla and Manuel Hermenegildo. Nondeterminism Analysis of Functional Logic Programs Bernd Brabel and Michael Hanus. Testing for Termination with Size Change Graphs Michael Codish, Vitaly Lagoon and Peter Stuckey. Towards an Integration of Answer Set and Constraint Solving Sabrina Baselice, Piero A. Bonatti and Michael Gelfond. Symbolic Support Graph: A Space Efficient Data Structure For Incremental Tabled Evaluation Diptikalyan Saha and C. R. Ramakrishnan. Towards Implementations for Advanced Equivalence Checking in Answer-Set Programming Hans Tompits and Stefan Woltran. Hybrid Probabilistic Logic Programs With Non-monotonic Negation Emad Saad and Enrico Pontelli. Reducing Inductive Definitions to Propositional Satisfiability Nikolay Pelov and Eugenia Ternovska. A Comparison of CLP(FD) and ASP Solutions to NP-Complete Problems Agostino Dovier, Andrea Formisano and Enrico Pontelli. A Well-Founded Semantics with Disjunction Joao Alcantara, Carlos Damasio and Luis Moniz Pereira. An optimised Semantic Web query language implementation in Prolog Jan Wielemaker. Practical Higher-Order Pattern Unification via On-the-Fly Raising Gopalan Nadathur and Natalie Linnell. Dynamic Mixed-Strategy Evaluation of Tabled Logic Programs Ricardo Rocha, Fernando Silva and Vitor Santos Costa. Small proof witnesses for LF Susmit Sarkar, Brigitte Pientka and Karl Crary. Guard and Continuation Optimization for Occurrence Representations of CHR Jon Sneyers, Tom Schrijvers and Bart Demoen. Abduction of Linear Arithmetic Constraints Michael Maher. Coordination of Many Agents Joxan Jaffar, Roland Yap and Kenny Zhu. Parallelizing Union-Find in Constraint Handling Rules Using Confluence Thom Fruehwirth. Luca Bortolussi and Herbert Wiklicky. A Distributed and Probabilistic Concurrent Constraint Programming Language Deductive Multi-valued Model Checking Ajay Mallya. Techniques for Scaling Up Analyses Based on Pre-Interpretations John P. Gallagher, Kim Henriksen and Gourinath Banda. Polynomial Interpretations as a Basis for Termination An Manh Thang Nguyen and Danny De Schreye. ----------------------------- Accepted posters (18 posters) ----------------------------- Inconsistency-based Strategy For Clarifying Vague Software Requirements Kedian Mu, Zhi Jin and Ruqian Lu. A Type System for CHR Emmanuel Coquery and Francois Fages. Decision Support for Personalization on Mobile Devices Thomas Kleemann and Alex Sinner. Algorithms for FO(ID) model generation Maarten Marikn, Rudradeb Mitra and Marc Denecker. Abstract Interpretation with Specialized Definitions German Puebla, Elvira Albert and Manuel Hermenegildo. Induction of causal ramifications for action descriptions in ASP Ramon Otero. The need for Ancestor Resolution when answering queries in Horn Clause Logic Oliver Ray. Modeling Systems in CLP with Coinductive Tabling Joxan Jaffar, Andrew Edward Santosa and Razvan Voicu. A Sufficient Condition for Strong Equivalence under the Well-Founded Semantics Chistos Nomikos, Panos Rondogiannis and William Wadge. Analyses, Optimizations and Extensions of Constraint Handling Rules: Ph.D. Summary Tom Schrijvers. IMPACT: Innovative Models for Prolog with Advanced Control and Tabling Ricardo Rocha, Ricardo Lopes, Fernando Silva and Vitor Santos Costa. Using CLP to characterise linguistic lattice boundaries in a text mining process Alexandre Saidi. Hybridization of Genetic Algorithms and Constraint Propagation for the BACP Tony Lambert, Carlos Castro, Eric Monfroy, Maria Cristina Riff and Fridiric Saubion. The MYDDAS Project: Using a Deductive Database for Traffic Characterization Michel Ferreira. Open World Reasoning in Datalog Gergely Lukacsy and Zsolt Nagy. Optimizing Queries for Heterogeneous Information Sources Andras Gyvrgy Bikis. Denotational semantics using Horn Concurrent Transaction Logic Marcus Santos. Gentra4cp: a Generic Trace Format for Constraint Programming Ludovic Langevine and The OADymPPaC team.

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offside rule question
by Frederik Eaton 18 Jul '05

18 Jul '05

Compiling the following module (with ghc) fails with error message "parse error (possibly incorrect indentation)", pointing to the let statement. The error goes away when I indent the lines marked "--*". But I don't understand how what I've written could be ambiguous. If I am inside a parenthesized expression, then I can't possibly start another let-clause. The fact that the compiler won't acknowledge this fact ends up causing a lot of my code to be squished up against the right margin when it seems like it shouldn't have to be. module Main where main :: IO () main = do let a = (map (\x-> x+1) --* [0..9]) --* print a return () Is there a reason for this behavior or is it just a shortcoming of the compiler? Frederik

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Re: A MonadPlusT with fair operations and pruning
by oleg＠pobox.com 16 Jul '05

16 Jul '05

on Jun 22 Andrew Bromage wrote about the usefulness of soft-cuts and "don't care" non-determinism in non-deterministic computations in Haskell. > http://www.haskell.org/pipermail/haskell/2005-June/016037.html Thank you very much for your explanation, it was helpful indeed. You noted, > Some of the interesting examples in Prolog are moot in Haskell by virtue > of the fact that Haskell is "strongly moded" And hence was our quandary. Even the leanTAP theorem prover looked too simple in Haskell to serve as a good example of advanced non-determinism. Your Tic-Tac-Toe example is thus even more appreciated. We have extended your code to boards of arbitrary NxN size (with M consecutive marks needed for winning). There is also a function for a human to play against the machine. We added some limits on the breadth and the depth of the search -- to keep both the reasonable response time and the pride. All in all, playing on the 5x5 board (with 4 marks needed for winning) is fairly entertaining. The archive LogicT.tar.gz mentioned previously now contains the tic-tac-toe code. The paper has been updated with its description. BTW, > best p b ... > | otherwise > = ifte (once (do > m <- choose [1..9] > b' <- move m p b > guard (win p b) > return (Win, b'))) > return > return > (ifte (once (do > m <- choose [1..9] > b' <- move m (otherPlayer p) b > guard (win (otherPlayer p) b') > return m)) > (\m -> do > b' <- move m p b > (w,_) <- best (otherPlayer p) b' > return (w,b')) The last statement should probably be `return (otherState w,b')', right? on Jan 5 2005, Andrew Bromage wrote on Haskell-Cafe: > Logical if-then-else has this signature: > > mif :: LogicT m a -> (a -> LogicT m b) -> LogicT m b -> LogicT m b > > Intuitively, this takes three arguments: the "condition", the "then" > case and the "else" case. This obeys the "obvious" laws of if-then-else: > > mif (return a) t e = t a > mif (mzero) t e = e > mif (mif c t' e') t e = mif c (\x -> mif (t' x) t e) (mif e' t e) Chung-chieh Shan has pointed out a problem with the last law: Let us consider the following instance of that law. We use Prolog, which implements soft-cuts (aka mif aka ifte) natively. In Prolog, `mif test t e' is written as `test *-> t ; e' He chose t === true, e === true, e' === fail, t' === X = 1, c === (X=1 ; X=2) mif (mif c t' e') t e translates to ((X=1 ; X=2) *-> X=1 ; fail) *-> true; true. and gives one answer, 1. mif c (\x -> mif (t' x) t e) (mif e' t e) translates to (X=1 ; X=2) *-> ( X=1 *-> true ; true) ; (fail *-> true; true). and gives two answers, 1 and 2. So, it seems the law has to be formulated in a more complex way, mif (mif c t' e') t e = mif (once c) (const $ mif (c >>= t') t e) (mif e' t e) with a surprising occurrence of `once'. That formulation isn't particularly useful for a backtracking _transformer_. In any case, we haven't encountered a need to simplify "mif (mif c t' e') t e" algebraically. It is interesting to see when such a law may be required.

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Early registration: GPCE'05 -- Generative Programming and Component Engineering
by Eelco Visser 15 Jul '05

15 Jul '05

CALL for EARLY REGISTRATION (deadline July 29) ---------------------------------------------------------------------- 4th International Conference on Generative Programming and Component Engineering (GPCE'05) Sep 29 - Oct 1, 2005, Tallinn (Estonia) http://www.gpce.org/05 Sponsored by ACM SIGPLAN, in cooperation with ACM SIGSOFT co-located with ICFP'05 and TFP'05 ---------------------------------------------------------------------- Please consult http://www.gpce.org/05 for the UP-TO-DATE and DETAILED programme http://www.cs.ioc.ee/tfp-icfp-gpce05/ for the ON-LINE REGISTRATION, hotel and travel information ---------------------------------------------------------------------- IMPORTANT DATES * Jul 29, 2005: EARLY REGISTRATION DEADLINE (and hotel discount rates) * Sep 02, 2005: Late registration deadline * Sep 27-28, 2005: GPCE workshops and tutorials * Sep 29 - Oct 1, 2005: GPCE papers and demos ---------------------------------------------------------------------- SCOPE. Generative and component approaches have the potential to revolutionize software development in a similar way as automation and components revolutionized manufacturing. Generative Programming (developing programs that synthesize other programs), Component Engineering (raising the level of modularization and analysis in application design), and Domain-Specific Languages (elevating program specifications to compact domain-specific notations that are easier to write and maintain) are key technologies for automating program development. GPCE arose as a joint conference, merging the conference on Generative and Component-Based Software Engineering (GCSE) and the workshop on Semantics, Applications, and Implementation of Program Generation (SAIG). The goal of GPCE is to provide a meeting place for researchers and practitioners interested in cutting edge approaches to software development. We aim to foster further cross-fertilization between the software engineering research community and the programming languages community, in addition to supporting the original research goals of both the GCSE and the SAIG communities. ---------------------------------------------------------------------- 3 INVITED SPEAKERS: * Oscar Nierstrasz: Object-oriented Reengineering Patterns * Oege de Moor: The AspectBench Compiler for AspectJ * Bernd Fischer: Certifiable Program Generation 25 TECHNICAL PAPERS 2 DEMONSTRATIONS: * Developing Dynamic and Adaptable Applications with CAM/DAOP: a Virtual Office Application * Metamodeling made easy - MetaEdit+ 2 TUTORIALS T1: Multi-stage Programming in MetaOCaml (Presenters: W.Taha, C.Calcagno) T2: Implementing Domain-Specific Modelling Languages and Generators (Presenters: R.Pohjonen and J-P.Tolvanen) 3 WORKSHOPS W1: Seventh Young Researchers Workshop (Organizers: D.R.Dechow, D.Foetsch, S.Kiebusch, S.Perugini, M.J.Rutherford, D.Shestakov) W2: Second MetaOCaml Workshop (Organizers: K.Swadi, W.Taha) W3: Graph and Model Transformations Workshop (Organizers: G.Karsai, G.Taentzer) ---------------------------------------------------------------------- PROGRAM COMMITTEE Chairs: * Robert Glück (U. of Copenhagen) * Michael Lowry (NASA) Members: * Don Batory (U. of Texas, USA) * Ira Baxter (Semantic Designs) * Cristiano Calcagno (Imperial College) * Prem Devanbu (U. of California at Davis) * Ulrich Eisenecker (U. of Leipzig) * Tom Ellman (Vassar College) * Robert Filman (NASA) * Zhenjiang Hu (U. of Tokyo) * Patricia Johann (Rutgers U.) * John Launchbury (Galois) * Anne-Françoise Le Meur (U. of Sci. and Tech. Lille) * Hong Mei (Peking U.) * Nicolas Rouquette (NASA) * William Scherlis (CMU) * Yannis Smaragdakis (Georgia Inst. of Tech.) * Walid Taha (Rice U.) * Todd Veldhuizen (Chalmers U. of Tech.) ORGANIZING COMMITTEE General Chair * Eugenio Moggi (Genova U.) Publicity Chair: * Eelco Visser (U. Utrecht) Workshops and Tutorials Chairs * Jeff Gray (U. of Alabama at Birmingham) * Andrew Malton (Waterloo U.) Local Arrangements Chair * Tarmo Uustalu (Inst. of Cybernetics, Tallinn) ----------------------------------------------------------------------

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