February 2003 - Haskell

Re : escape from existential quantification
by George Russell 27 Feb '03

27 Feb '03

Wang Meng wrote > I understand that existentially bound types cannot escape. > > For example, say we have > data Foo = forall a. Foo Int a > > Then we cannot define a function > extract (Foo i a) = a > > However,this limitation makes it extremly difficult to program with local > quantifications.Is there any way to by pass this? It occasionally happens that I *know* what type is (or at least ought to be) inside an existential type, but unfortunately GHC doesn't, and I need to get the value out. This can be solved using dynamic types, for example you declare the datatype as > data Foo = forall a. Typeable a => Foo Int a (or something like that), then you can extract the a value by going to Dynamic and back.

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escape from existential quantification
by Wang Meng 27 Feb '03

27 Feb '03

I understand that existentially bound types cannot escape. For example, say we have data Foo = forall a. Foo Int a Then we cannot define a function extract (Foo i a) = a However,this limitation makes it extremly difficult to program with local quantifications.Is there any way to by pass this? -W-M- @ @ | \_/

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does this irritate anyone else?
by Mike T. Machenry 26 Feb '03

26 Feb '03

I am trying to use type classes to get some percollate actions through a nested data structure. The problem is I can't make an instance of a class unless the type is defined with newtype or data. This means all of my functions look something like this: findFugitive :: DetectiveLocations -> FugitiveLocations -> Move -> FugitiveLocat findFugitive (DetectiveLocations dL) (FugitiveLocations fL) StartGame = (FugitiveLocations minusSet fL (occupiedStops dL)) instead of this: findFugitive :: DetectiveLocations -> FugitiveLocations -> Move -> FugitiveLocat findFugitive dL fL StartGame = minusSet fL (occupiedStops dL) which is much simpler to read. Why can't I make a normal type an instance of a type class? I get errors that it's an ambiguous type. thanks, -mike

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fundeps for extended Monad definition
by Hal Daume III 26 Feb '03

26 Feb '03

Hi all, I'm hoping someone can explain some weirdnesses to me. I want to have a class that's like the standard Monad class, but is a bit more general. That is, I want: class Monad2 m a ma | m a -> ma, ma -> m a where return2 :: a -> ma bind2 :: Monad2 m b mb => ma -> (a -> mb) -> mb _unused :: m a -> () _unused = \_ -> () Here, all the real work happens in the combined "mb" parameter. The _unused definition is just to get Hugs to realize that 'm' should be of kind * -> * (for GHC, a kind definition does the same thing). I want to be able to define instances like: instance Monad2 [] a [a] where return2 x = [x] bind2 l f = concatMap f l However, in GHC, if I just give the instance declaration (without the function definitions), we get: Cannot unify the type-signature variable `mb' with the type `[b]' Expected type: [b] Inferred type: mb When using functional dependencies to combine Monad2 [] a [a], arising from the instance declaration at /nfs/isd/hdaume/projects/Trials/UsefulDTs/UsefulDTs.hs:114 Monad2 [] b mb, arising from a type signature at /nfs/isd/hdaume/projects/Trials/UsefulDTs/UsefulDTs.hs:114 When trying to generalise the type inferred for `bind2' Signature type: forall a mb1 b1. (Monad2 [] b1 mb1) => [a] -> (a -> mb1) -> mb1 Type to generalise: forall mb1 b1. (Monad2 [] b1 mb1) => [a] -> (a -> mb1) -> mb1 This doesn't make sense to me. Hugs accepts this without complaint. Here's why I don't understand it: We know that m is []. We have an instance definition (the one we're defining) that says that for any type x, we have 'Monad2 [] x [x]' where [] and x determine [x]. This should tell us that mb=[b], but somehow GHC doesn't get that (or there's something wrong with my reasoning). When the funciton definitions are provided for the instance, GHC complains: /nfs/isd/hdaume/projects/Trials/UsefulDTs/UsefulDTs.hs:119: Cannot unify the type-signature variable `mb' with the type `[b]' Expected type: a -> [b] Inferred type: a -> mb In the first argument of `concatMap', namely `f' In the definition of `bind2': concatMap f l and Hugs complains similarly: *** Expected type : (Monad2 [] a [a], Monad2 [] b c) => [a] -> (a -> c) -> c *** Inferred type : (Monad2 [] a [a], Monad2 [] b [c]) => [a] -> (a -> [c]) -> [c] Both are saying that they don't know that mb=[b], but I think the fundeps guarentee this. Note that if we change the type definition of bind2 to: bind2 :: Monad2 m b mb => ma -> (a -> m b) -> m b then Hugs accepts the instance declaration but GHC complains as it did the first time. Can someone explain which is right and why? Thanks! - 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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Question about How use the ports in haskell
by Cesar Augusto Acosta Minoli 26 Feb '03

26 Feb '03

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CfP: ACL2003 Resources Infrastucture Workshop
by steven.krauwer＠elsnet.org 26 Feb '03

26 Feb '03

ACL2003 Resources Information Infrastructure Workshop _________________________________________________________________ CALL for PAPERS Towards a Resources Information Infrastructure Workshop at ACL2003 in Sapporo (Japan) July 11 and 12 2003 Organised by ENABLER / ELSNET Description The problem addressed by this workshop is the well-known information problem. People are creating, exploring and exploiting language resources all over the world. Those who are working with resources know a lot about their own and other resources, and they are generally prepared to share this knowledge, their expertise and in many cases even their resources with others via publications in journals, presentations at conferences, and via the web. Unfortunately this information, however public, is not accessible in any systematic way for those who need resources, who want to know what sort of resources exist, how resources should be annotated, which standards to adhere to, which tools to use, etc etc. We will call this problem the 'Resources Information Problem'. The problem has also a geographical dimension: As work on specific languages is very often concentrated in specific parts of the world, much relevant information has a tendency to stay in one geographical place. This is an obstacle for those who are working on these same languages in different parts of the world, and it makes it harder to port knowledge and expertise gained on one language to other languages. The above observation are far from novel, and it would be naive to think that the problems will ever go away. At the same time one can observe that there are organisations (associations, agencies, projects, networks, etc) that have access to parts or fragments of this information and that have their own infrastructures that facilitate access to this information by internal or external people. The purpose of this workshop is to investigate how we can exploit the existing infrastructures to a maximum in order to facilitate world-wide access to information on language resources. The role of the workshop will be to bootstrap this process. Approach * First of all we will try to make an initial map of the language resources landscape world-wide. This map will include actors, organisations, repositories, standards, projects, tool libraries, etc etc. All participants will be asked beforehand to submit pointers to such items. They will be collected and published. * At the workshop we will invite representatives of a number of organisations that can be seen as key actors in the field, and they will be asked to present ideas about the way their organisation could contribute to solving the Resources Information Problem. These ideas could range from very concrete and immediately implementable proposals to longer term and visionary actions. * A round table discussion at the workshop will aim at the creation of convergence, coherence and synergies between the proposed actions. The intended output is a catalogue of actions to facilitate access to resources information that could be implemented (almost) immediately, a skeleton plan for longer term actions, and firm commitment from key players to make these things happen. Target audience Representatives of parties that could play a key role in providing access to resources information, such as (but not limited to) * Resources distribution agencies, e.g. LDC and ELDA/ELRA * Professional organisations, e.g. ACL, ISCA, and their regional branches, e.g. EACL, AACL, JACL, Asian NLP federation * Networks and resources infrastructure projects, e.g. ENABLER, ISLE. ELSNET * Committees, e.g. ICWLR, COCOSDA * National resources or infrastructure projects, e.g. Technolangue, Collate * International actions, e.g. OLAC * Researchers and developers interested in improving the language resources infrastructure for our community Invited and submitted papers We expect to invite some 15 representatives to give their presentations, but in addition we are issuing an open call for papers addressing the resources information problem and possible solutions. These papers will be reviewed in the usual way. Submission format Please submit full papers of maximum 8 pages (including references, figures etc). Authors should follow the main conference ACL style format. Electronic submission only. Send the pdf, postscript, or MS Word form of your submission to: Steven Krauwer (steven.krauwer(a)elsnet.org) who will also answer any queries regarding the submission. Important Dates Submission deadline for workshop papers: 13 April 2003 Notification of accepted papers: 14 May 2003 Deadline for camera ready copies 29 May 2003 Workshop dates: 11-12 July 2003 Workshop Format It will be a two-day workshop, with invited and submitted presentations in the mornings, and topical panels and round table discussion in the afternoons, including an open meeting of the newly created International Coordination Committee for Written Language Resources. Programme Committee As this workshop is jointly proposed by ELSNET and ENABLER (two EU funded projects aimed at providing collaboration infrastructures), we have invited all ca 60 members of the ELSNET and ENABLER Boards to constitute the core programme committee. We may want to invite additional members from Asia and other parts of the world in order to ensure sufficient geographical coverage. A full list of PC members will be published on the workshop website at http://www.elsnet.org/acl2003-workshop The workshop will be jointly chaired by Steven Krauwer (ELSNET) and Nicoletta Calzolari/Antonio Zampolli (ENABLER) Historical note This workshop can be seen as a follow-up of the workshop organised at ACL2000 in Hong Kong, entitled 'Towards infrastructures for global collaboration'. One of the conclusions of this workshop was that the field of language resources would offer good opportunities for collaborative actions, and the first concrete goal was the creation of an international resources federation, a first step towards which is now embodied by the proposal to set up an International Committee for Written Language Resources. The proposed workshop should lead to the definition of concrete actions to be carried out under the auspices of ICWLR, in collaboration with other organisations. Contact info Steven Krauwer (steven.krauwer(a)elsnet.org) ELSNET (http://www.elsnet.org)

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Haskell running on JVM?
by Graham Klyne 26 Feb '03

26 Feb '03

This is something of a long-shot enquiry. Are there any known tools that will allow Haskell programs to be packages as .class files to run on a Java VM? A friend of mine pointed out this reference: http://www.students.cs.uu.nl/people/rjchaaft/jHaskell/old/ which looks to be a defunct project. (I've noticed that there are Java environment interfaces, but my question is about projects which will run Haskell programs "natively" in a Java environment; e.g. like the Jython system for Python.) #g ------------------- Graham Klyne <GK(a)NineByNine.org>

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Regular expressions as Haskell Type Generators?
by Steffen Mazanek 26 Feb '03

26 Feb '03

Hello, I am wondering if it would be worth while (and possible) to allow the definition of types by regular expressions, e.g. data Date = Date #RegExp([0-9][0-9]-[0-9][0-9]-[0-9][0-9][0-9][0-9]) or easier with some auxiliary constructs. Clearly there would be some drawbacks with the use of standard String-operations or type checking. But in praxi it may be absolutely relevant. Or is some work already done in this direction? Ciao, Steffen

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profiling problems
by Damien R. Sullivan 26 Feb '03

26 Feb '03

I have this code which compiles and runs normally, but gives bus errors or segfaults at run time when compiled with -prof -auto-all. ghc-5.04 SunOS cownose.cs.indiana.edu 5.8 Generic_108528-18 sun4u sparc SUNW,Ultra-5_10 What's wrong? import Numeric import Ratio import System top 1 = 1 top n = 9*n*top (n-2) + oddfact (n-2) lfact :: [Integer] lfact = 1 : zipWith (*) [3,5 .. ] lfact oddfact :: Integer -> Integer oddfact n = lfact!!ni where ni = nint `div` 2 nint = fromInteger n log_two :: Int -> Rational log_two lim = 2* top n % (3^lim * oddfact n) where n = fromIntegral lim log_tup :: Int -> (Rational, Rational) log_tup lim = -- TODO any chance I can drop the br? Would it get me more than a digit? (l + lo_err, l + hi_err) where l = log_two lim -- TODO double check these lo_err = (2)/(n+1)*(d/(1+c))^(lim+1) hi_err = (2)/(n+1)*d^(lim+1) -- original logs -- lo_err = (-2)/(n+1)*(d/(1+c))^(lim+1) -- hi_err = -lo_err -- lo_err = (-1)/(n+1)*x^(lim+1) -- c = 0 n = toRational lim d = 1%3 c = d log_tup_str lim = (floatlo, floathi, diff) where (lo, hi) = log_tup lim floatlo = floatRat lo lim floathi = floatRat hi lim diff = floathi - floatlo floatRat :: Rational -> Int -> Integer floatRat r lim = num*10^lim `div` den where num = numerator r den = denominator r main :: IO () main = do args <- System.getArgs let lim :: Int lim = read (args!!0) let (s1, s2, s3) = log_tup_str lim let sh1 = show s1 let l1 = length sh1 let shd = show s3 let ld = length shd putStrLn (show s1) putStrLn (show s2) putStrLn (show s3) putStr "digits: " putStrLn (show (l1-ld))

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WFLP'03 - Second Call for Papers
by German Vidal 24 Feb '03

24 Feb '03

[ Apologies if you receive this message more than once ] ====================================================================== SECOND CALL FOR PAPERS WFLP 2003 12th Int'l Workshop on Functional and (Constraint) Logic Programming June 12-13, 2003, Valencia (Spain) http://www.dsic.upv.es/~rdp03/wflp/ ====================================================================== WFLP is the International Workshop on Functional and (Constraint) Logic Programming. WFLP'03, the twelfth in the series, will be held in Valencia, Spain, June 12-13, 2003, at the Federated Conference on Rewriting, Deduction and Programming (RDP'03) http://www.dsic.upv.es/~rdp03/ The WFLP workshops aim at bringing together researchers interested in functional programming, (constraint) logic programming, as well as their integration. It promotes the cross-fertilizing exchange of ideas and experiences among researches and students from the different communities interested in the foundations, applications, and combina- tions of high-level, declarative programming languages and related areas.The technical program of the workshop will include invited talks, presentations of refereed papers and demo presentations. Previous editions of the workshop have been held in Grado (Italy), Kiel (Germany), Benicassim (Spain), Grenoble (France), Bad Honnef (Germany), Schwarzenberg (Germany), Marburg (Germany), Rattenberg (Germany), and Karlsruhe (Germany). ---------------------------------------------------------------------- TOPICS OF INTEREST WFLP'03 solicits papers in all areas of functional and (constraint) logic programming, including (but not limited to): * Language Design: modules and type systems, multi-paradigm languages, concurrency and distribution, objects * Foundations: formal semantics, rewriting and narrowing, nonmonotonic reasoning, dynamics, type theory * Implementation: abstract machines, parallelism, compile-time and run-time optimizations, interfacing with external languages * Transformation and Analysis: abstract interpretation, specialization, partial evaluation, program transformation, meta-programming * Software Engineering: design patterns, specification, verification and validation, debugging, test generation * Applications: declarative programming in education and industry, domain-specific languages, visual/graphical user interfaces,embedded systems, WWW applications, knowledge representation and machine learning, deductive databases, advanced programming environments and tools The main focus is on new and original research results but submissions describing innovative products, prototypes under development or interesting experiments (e.g., benchmarks) are also encouraged. ---------------------------------------------------------------------- IMPORTANT DATES Submission of papers: Sunday, March 23, 2003 Notification of acceptance: Friday, April 25, 2003 Camera-ready papers: Sunday, May 11, 2003 Workshop: June 12 - 13, 2003 ---------------------------------------------------------------------- SUBMISSION Authors are invited to submit an extended abstract (no longer than 12 pages including figures and references) or a system description (no longer than 4 pages) in Postscript or PDF format (Springer LNCS style) via email to gvidal(a)dsic.upv.es before March 23, 2003. Submissions should include the title, authors' names, affiliations, addresses, and e-mail. ---------------------------------------------------------------------- PUBLICATION Accepted papers will be included in the preliminary proceedings that will be available at the workshop. After the workshop, authors of the best abstracts will be invited to submit full papers.These full papers will be reviewed and accepted papers will appear in the Electronic Notes in Theoretical Computer Science (Elsevier). ---------------------------------------------------------------------- BEST NEWCOMER AWARD An award will be given to the best paper exclusively written by one or several young researchers who have not yet obtained their PhD degrees. Papers written in this category should be clearly marked "Student papers" in the submission. ---------------------------------------------------------------------- PROGRAM COMMITTEE Maria Alpuente (Technical University of Valencia, Spain) Sergio Antoy (Portland State University, USA) Annalisa Bossi (Universita Ca' Foscari di Venezia, Italy) Olaf Chitil (University of York, UK) Rachid Echahed (Institut IMAG, France) Sandro Etalle (University of Twente, The Netherlands) Moreno Falaschi (Universita di Udine, Italy) Michael Hanus (CAU Kiel, Germany) Herbert Kuchen (University of Muenster, Germany) Michael Leuschel (University of Southampton, UK) Juan Jose Moreno-Navarro (Universidad Politecnica de Madrid, Spain) Ernesto Pimentel (University of Malaga, Spain) Mario Rodriguez-Artalejo (Universidad Complutense de Madrid, Spain) Yukiyoshi Kameyama (University of Tsukuba, Japan) German Vidal (Technical University of Valencia, Spain) ---------------------------------------------------------------------- LOCAL ORGANIZING COMMITTEE Elvira Albert Santiago Escobar Cesar Ferri Jose Hernandez Carlos Herrero Pascual Julian Marisa Llorens Gines Moreno Javier Oliver German Vidal Alicia Villanueva ---------------------------------------------------------------------- FURTHER INFORMATION WFLP 2003: http://www.dsic.upv.es/~rdp03/wflp Workshop contact: gvidal(a)dsic.upv.es RDP 2003: http://www.dsic.upv.es/~rdp03

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