October 2005 - Haskell

Dazzle sources
by Arjan van IJzendoorn 14 Oct '05

14 Oct '05

Hello everyone, After the Dazzle presentation at the Haskell workshop, several people have asked us whether the source code is available. There is the possibility of commercialising Dazzle at some point in the future and for that reason we don't want to give away all our algorithms. However, the diagram editor part of Dazzle is something we would like to share with the community. Already Malcolm Wallace has been using this as a basis for another editor and has made some really nice improvements and generalisations. We plan to make an open-source project out of the diagram editor because we think that that is the part people will be most interested in. Here are some of the features of the diagram editor that will be called Blobs: - editing diagrams - arcs with "via points", in other words polylines - saving to and reading from file, XML format (using HaXml) - unlimited undo & redo (using the PersistentDocument library) - printing a diagram - save a diagram to JPG/PNG - labels at nodes and arcs - resizing a diagram - based on wxHaskell and can therefore run on Windows, Linux and Mac OS X - the XTC library (eXtended and Typed Controls) will be included - and much more Our plan is to set up a project website, a version management system and to reintegrate Dazzle with Malcolm's extended Blobs. Once we feel people can start using it, we will make an official announcement. Regards, the Dazzle team (Martijn Schrage & Arjan van IJzendoorn)

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RE: [Haskell-cafe] Interest in helping w/ Haskell standard
by Simon Marlow 14 Oct '05

14 Oct '05

On 12 October 2005 23:50, Sebastian Sylvan wrote: > (I'm specifically interested in seeing SPJ's records proposal > included, and a new module system). Highly unlikely, IMHO. A new revision of the Haskell standard is not the place for testing new research, rather it's a clear specification of existing well-understood language features. If you want a new record system, or a new module system, now is the time to start designing and implementing them ready for the next standardisation process. Cheers, Simon

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Interest in helping w/ Haskell standard
by Isaac Jones 14 Oct '05

14 Oct '05

At the end of the Haskell Workshop at ICFP, we had the traditional "Future of Haskell" discussion (chaired by Andres Loeh). One of the main topics was the perceived need of a new standard, because the Haskell 98 standard is quite old already, and Haskell has evolved in the meantime, leading to a situation where almost none of the actually existing Haskell programs is according to the 98 standard. No clear opinion was visible on what form a new standard would take. There was, however, considerable support for the idea to standardize an incremental and moderate extension to Haskell 98 (working name "Haskell 06" or "Industrial Haskell"). This effort would then be separate from discussion about the Real Next Version (dubbed "Haskell 2"). John Launchbury asked for a show of hands of those who would be interested in helping out with the "Haskell 06" standard. I think "helping" means "willing to spend a non-trivial amount of time". That is, it's pretty well expected that most Haskellers will be willing to contribute to discussion on the mailing lists, but we're trying to get a list of those who want to take it to the next level. If you raised your hand, or if you think this describes you, please email John Launchbury at john(a)galois.com. peace, Isaac Jones & Andres Loeh

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How to zip folds: A library of fold transformers
by oleg＠pobox.com 14 Oct '05

14 Oct '05

We show how to merge two folds into another fold `elementwise'. Furthermore, we present a library of (potentially infinite) ``lists'' represented as folds (aka streams, aka success-failure-continuation--based generators). Whereas the standard Prelude functions such as |map| and |take| transform lists, we transform folds. We implement the range of progressively more complex transformers -- from |map|, |filter|, |takeWhile| to |take|, to |drop| and |dropWhile|, and finally, |zip| and |zipWith|. Emphatically we never convert a stream to a list and so we never use value recursion. All iterative processing is driven by the fold itself. The implementation of zip also solves the problem of ``parallel loops''. One can think of a fold as an accumulating loop. One can easily represent a nested loop as a nested fold. Representing parallel loop as a fold is a challenge, answered at the end of the message. We need recursive types -- but again, never value recursion. This library is inspired by Greg Buchholz' message on the Haskell-Cafe list and is meant to answer open questions posed at the end of that message http://www.haskell.org/pipermail/haskell-cafe/2005-October/011575.html This message a complete literate Haskell code. > {-# OPTIONS -fglasgow-exts #-} > module Folds where First we define the representation of a list as a fold: > newtype FR a = FR (forall ans. (a -> ans -> ans) -> ans -> ans) > unFR (FR x) = x It has a rank-2 type. The defining equations are: if flst is a value of a type |FR a|, then unFR flst f z = z if flst represents an empty list unFR flst f z = f e (unFR flst' f z) if flst represents the list with the head 'e' and flst' represents the rest of that list >From another point of view, |unFR flst| can be considered a _stream_ that takes two arguments: the success continuation of the type |a -> ans -> ans| and the failure continuation of the type |ans|. The LogicT paper discusses such types in detail, and shows how to find that "rest of the list" flst'. The slides of the ICFP05 presentation by Chung-chieh Shan point out to more related work in that area. But we are here to drop, take, dropWhile, etc. Our functions will take a stream and return another stream, of the |FR a| type, which represents truncated, filtered, etc. source stream. Let us define two sample streams: a finite and an infinite one: > stream1 :: FR Char > stream1 = FR (\f unit -> foldr f unit ['a'..'i']) > stream2 :: FR Int > stream2 = FR (\f unit -> foldr f unit [1..]) and the way to show the stream. This is the only time we convert |FR a| to a list -- so we can more easily show it. > instance Show a => Show (FR a) where > show l = show $ unFR l (:) [] The map function is trivial: > smap :: (a->b) -> FR a -> FR b *> smap f l = FR(\g -> unFR l (g . f)) which can also be written as > smap f l = FR((unFR l) . (flip (.) f)) For example, > test1 = show $ smap succ stream1 Next is the filter function: > sfilter :: (a -> Bool) -> FR a -> FR a > sfilter p l = FR(\f -> unFR l (\e r -> if p e then f e r else r)) > test2 = sfilter (not . (`elem` "ch")) stream1 The function takeWhile is quite straightforward, too > stakeWhile :: (a -> Bool) -> FR a -> FR a > stakeWhile p l = FR(\f z -> unFR l (\e r -> if p e then f e r else z) z) > test3 = stakeWhile (< 'z') stream1 > test3' = stakeWhile (< 10) stream2 As we can see, stakeWhile well applies to an infinite stream. The functions take, drop, dropWhile ask for more complexity. > stake :: (Ord n, Num n) => n -> FR a -> FR a > stake n l = FR(\f z -> > unFR l (\e r n -> if n <= 0 then z else f e (r (n-1))) (const z) n) > test4 = stake 20 stream1 > test4' = stake 5 stream1 > test4'' = stake 11 stream2 > test4''' = (stake 11 . smap (^2)) stream2 The function sdrop shows the major deficiency: we're stuck with the (<=0) test for the rest of the stream. In this case, some delimited continuation operators like `control' can help, in limited circumstances. > sdrop :: (Ord n, Num n) => n -> FR a -> FR a > sdrop n l = FR(\f z -> > unFR l (\e r n -> if n <= 0 then f e (r n) else r (n-1)) (const z) n) > test5 = sdrop 20 stream1 > test5' = sdrop 5 stream1 > test5'' = stake 5 $ sdrop 11 stream2 The function dropWhile becomes straightforward > sdropWhile :: (a -> Bool) -> FR a -> FR a > sdropWhile p l = FR(\f z -> > unFR l (\e r done -> > if done then f e (r done) > else if p e then r done else f e (r True)) (const z) False) > test6 = sdropWhile (< 'z') stream1 > test6' = sdropWhile (< 'd') stream1 > test6'' = stake 5 $ sdropWhile (< 10) stream2 The zip function is the most complex. Here we need a recursive type: an iso-recursive type to emulate the equi-recursive one. > newtype RecFR a ans = RecFR (a -> (RecFR a ans -> ans) -> ans) > unRecFR (RecFR x) = x This is still a newtype: there is no extra consing. I will not pretend that the following is the most perspicuous piece of code: *> szip :: FR a1 -> FR a2 -> FR (a1,a2) *> szip l1 l2 = FR(\f z -> *> let l1' = unFR l1 (\e r x -> unRecFR x e r) (\r -> z) *> l2' = unFR l2 (\e2 r2 e1 r1 -> f (e1,e2) (r1 (RecFR r2))) (\e r-> z) *> in l1' (RecFR l2')) It can be simplified to the following: > szipWith :: (a->b->c) -> FR a -> FR b -> FR c > szipWith t l1 l2 = FR(\f z -> > unFR l1 (\e r x -> unRecFR x e r) (\x -> z) > (RecFR $ > unFR l2 (\e2 r2 e1 r1 -> f (t e1 e2) (r1 (RecFR r2))) (\e r -> z))) > > szip :: FR a -> FR b -> FR (a,b) > szip = szipWith (,) One can easily prove that this function does correspond to zip for all finite streams. The proof for infinite streams requires more elaboration. > test81 = szip stream1 stream1 > test82 = szip stream1 stream2 > test83 = szip stream2 stream1 > test84 = stake 5 $ szip stream2 (sdrop 10 stream2) As one may expect (or not), these tests give the right results *Folds> test83 [(1,'a'),(2,'b'),(3,'c'),(4,'d'),(5,'e'),(6,'f'),(7,'g'),(8,'h'),(9,'i')] *Folds> test84 [(1,11),(2,12),(3,13),(4,14),(5,15)]

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Re: Network Exception
by Arias 13 Oct '05

13 Oct '05

I've tryed to connect using the telnet and it connects properly, I've try also with another servers/ports and it allways throws the exception > On Thu, Oct 13, 2005 at 12:18:44PM +0200, > Arias <arias(a)elleondeoro.com> wrote > a message of 35 lines which said: > > > In the port 8080 I have apache listening, so the server and port is > > correct. > > Excuse me but I prefer actual tests to claims. "telnet localhost > 8080". (Apache may be listening only on the public IP address, for > instance.) > > > the other one had the same matter than me, both using the GHC > > compiler version 6.4. > > I tried with ghc 6.4 (FreeBSD and Debian) and it worked. > > >

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Network Exception
by Arias 13 Oct '05

13 Oct '05

Hi, My name Iván Arias, I'm trying to connect to a server using the Network library, the code that I'm using is something like this: --- BEGIN --- module Main where import System.IO import Network main = withSocketsDo $ do handle <- connectTo "localhost" ( PortNumber 8080 ) hClose handle --- END --- It compiles correctly, but when I try to run this code, it throws an exception at connectTo. The exception's message is: - getServiceEntry: does not exists (No such service entry) Do somebody know why this happens and how to fix it? Thanks

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setSocketOption unusable?
by John Goerzen 12 Oct '05

12 Oct '05

I'm wanting to set the SO_RCVTIMEO and SO_SNDTIMEO options on a socket from Haskell. socket(7) say that these take a struct timeval ad a parameter. (Other options, such as SO_LONGER, also could have this problem.) In Haskell, we see: setSocketOption :: Socket -> SocketOption -> Int -> IO () Now, there are SocketOption constructors (RecvTimeOut and SendTimeOut) for what I want. But there is no way to give it a proper timeval (and yes, I checked the source.) setSocketOption definately wants an Int, and is passing the length of the Int to setsockopt(2) as well, so it appears to me that there is absolutely no way to correctly specify SO_RCVTIMEO or SO_SNDTIMEO through Haskell's socket layer. Is that correct? If so, how can we fix it? -- John

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i-C&P 2006 France
by Computational Philosophy Laboratory - Univ. of Pavia 12 Oct '05

12 Oct '05

CALL FOR PAPERS - Deadline November 18, 2005 --------------------------------------------------------------- i-C&P 2006 quick link COMPUTERS & PHILOSOPHY, an International Conference Le Mans University, Laval, France, 3-5 May, 2006 Chair: C.T.A. SCHMIDT Colin.Schmidt(a)univ-lemans.fr e-mail --------------------------------------------------------------- http://www.iut-laval.univ-lemans.fr/i-CaP_2006/ IMPORTANT DATES (check conference url for up-to-date information) Friday November 18 th 2005 Submission deadline for extended abstracts (1000 wds.) 3-5 May 2006, Conference in Laval France GENERAL INFORMATION >From Wednesday 3rd to Friday 5th May 2006 The International Conference on COMPUTERS & PHILOSOPHY will be held at Le Mans University in Laval (near Rennes, France). Overview: Those interested in the study of philosophical problems and related technological applications are encouraged to participate. Philosophical, epistemological, theological and anthropological stances on the construction and use of machines are of relevance to the conference. Within the framework of the programme, we are looking forward to the contributions of some eminent thinkers: USA Daniel DENNETT, Philosophy, Tufts USA Rodney BROOKS, Robotics, MIT Italy Lorenzo MAGNANI, Logic & Philosophy, Pavia UK Margaret BODEN, Art. Intelligence, Cognitive Sc. & Philosophy, Sussex Canada Daniel VANDERVEKEN, Logic & Language, UQTR Thailand Darryl MACER, UNESCO Reg. Adviser for Soc.& Human Sc. in Asia-Pacific UK Noel SHARKEY, Computation & Robotics, Sheffield Please see web site for full details; programme, topics, accommodation, registration as well as detailed information on plenary session talks. RELEVANT RESEARCH AREAS In addition to main-stream areas of research -Philosophy of Artificial Intelligence, Intelligent Robotics, Cognitive Science, Computer Ethics- we are looking for cross-cultural studies on the place of machines in society, as well as the following: 1. Evolution & Technologies a.. Evolutionary Computation and Evolutionary Language Development b.. Information Systems and the Philosophy of Design c.. Biologically-Incorporated Intelligence; the Use of Organic Components for Robotics d.. Bio-computation, Bio-Robotics, Artificial Life & Meaning e.. Robotics (Humanoid, Cognitive, Epigenetic, "Autonomous", Service, etc.) f.. Humanoid Hosts and Guides for Museums, Galleries and Virtual Reality Environments 2. Pragmatics & Comp. Linguistics a.. Speech Acts and the Limits of Machine-embedded Use of Dialogue b.. Obstacles to Parsing (Accents, Intonations, Emotional States, etc.) c.. Relations, Reference and Communicability d.. Artificial Affectivity in (non-)Dialogical Settings e.. All Language, Meaning and Dialogue Issues 3. Minds and Intentionality a.. Evocative Objects and Presumed Intelligence a.. Personification of Artefacts b.. Other Minds Theories and Simulating Co-intentionality c.. The Mind/Body Problem in Cognitive Science d.. European Versions (and Anti-theses) of the Intentional Stance 4. Culture & Adaptability a.. All Anthropological Views on Computers and Robots b.. Context-embedded Computer Learning c.. In-class Robotic Teachers, Vulgarisation and (non-)Acceptance Issues d.. The Pros and Cons of Computer-Mediated Communication & Learning e.. Virtual Reality & Digitally-supported Personalities f.. Post-modernism and Fiction related to Machines and Individuals 5. History, Ethics & Theology a.. Issues arising from the Automation of Thought b.. Designing Users' Beliefs, Beliefs Designing Machines, Religious Deontology c.. Robo-Ethics, Moral Agents, Spirituality of Machines, Technological Souls d.. The Impacts of Intelligent Computers and Robotics on Society throughout History e.. Cognitive Epistemology or Science as Applied Technology Other a.. Transdisciplinary attempts to link Philosophy, Computing and/or Robotics b.. cf. full scientific programme and printable version of the Call for Papers at quick link For further information about the conference, please consult the i-C&P 2006 website or contact the Chair for the complete version of the Call for Papers and related information. VENUE Laval is known to be a city of character for its history, art and culture. Located on the Mayenne River in beautiful Western France (see film at http://www.lamayenne.fr/front.aspx?sectionId=3D452&publiId=3D3996&controlle r =3DVi= e wpublication ), it offers all the amenities of a large city while maintaining a small town feel. SCIENTIFIC COMMITTEE General Chair: Colin T. Schmidt, Communication, Philosophy & Cognition, Le Mans University, France Local Organisations Chair: Xavier Dubourg, Computer Science & Learning, Le Mans University & Director of the Laval Technological Institute, France Honorary Chair: Francis Jacques, Emeritus Professor of Philosophy, Sorbonne University, France Varol Akman, Philosophy and Computer Science, Bilkent University, Turkey Jean Caelen, Cognition and Interaction, CNRS/Grenoble University, France Raja Chatila, Robotics, CNRS/Toulouse University, France Nathalie Colineau, Language & Multi-modality, CSIRO, Australia Roberto Cordeschi, Computation & Communication, Salerno University, Italy Liu Gang, Information & Philosophy, Inst. of Philosophy, Chinese Acad. of Soc. Sciences, China Deborah G. Johnson, Technology and Ethics, University of Virginia, USA Fr=E9d=E9ric Kaplan, Artificial Intelligence, SONY CSL =AD Paris Nik Kasabov, Computer and Information Sciences, Auckland University, New Zealand Oussama Khatib, Robotics & Artificial Intelligence, Stanford University, USA Boicho Kokinov, Cognitive Science, New Bulgarian University, Sofia, Bulgaria Felicitas Kraemer, Philosophy & Intentionality, Bielefeld University, Germany Jean Lass=E8gue, Philosophy, CNRS/Ecole Normale Sup=E9rieur Paris, France Ping Li, Cognitive Science & Philosophy of Science, Sun Yat-sen University, China Daniel Luzzati, Linguistics, Le Mans University, France M.C. Manes Gallo, Info. & Communication Sciences, Bordeaux University, France Anne Nicolle, Computer Science & Interdisciplinarity, CNRS/University of Caen, France Teresa Numerico, Communication, Salerno University, Italy James Moor, Philosophy, Dartmouth College, USA Bernard Moulin, Computer Science, Laval University, Canada Denis Vernant, Logic & Philosophy, Grenoble University, France Ming Xie, Robotics, Nanyang Technological University, Singapore LOCAL CONTACT POINT Tel +33 2 43 59 49 20 & Dr. Colin Schmidt (Chair) Computers & Philosophy, an International Conference i-C&P 2006 Computer Science Laboratory LIUM CNRS FRE 2730 Le Mans University France Phone: +33 2 43 59 49 25 Fax: +33 2 43 59 49 28 E-mail: Colin.Schmidt(a)lium.univ-lemans.fr Conference: quick link

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ANNOUNCE: Haskell XML Toolbox Version 5.3
by Uwe Schmidt 12 Oct '05

12 Oct '05

Haskell XML Toolbox 5.3 I would like to announce a new version of the Haskell XML Toolbox for processing XML. main new features: * a cookbook for using the new arrow programming interface of the toolbox * an integrated Relax NG validator implemented with the arrow interface More information and download: http://www.fh-wedel.de/~si/HXmlToolbox/index.html Please email comments, bugs, etc. to hxmltoolbox(a)fh-wedel.de Uwe Schmidt <uwe(a)fh-wedel.de> -- University of Applied Sciences, Wedel, Germany http://www.fh-wedel.de/~si/index.html

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RE: [Haskell] getArgs, maxBound, float division: pure functions?
by Ralf Lammel 12 Oct '05

12 Oct '05

Just for the record, Cobol has a long history of specifying local rounding options. More recently, the options for rounding are elaborated in the context of adding standard arithmetic. http://www.cobolportal.com/j4/files/05-0152.doc Ralf > -----Original Message----- > From: haskell-bounces(a)haskell.org [mailto:haskell-bounces@haskell.org] On > Behalf Of Bjorn Lisper > [...] > He was very careful to give > the language a good design also regarding floating-point computations. His > design choice, as regards rounding, was to allow the compiler to choose > rounding mode by default (thus allowing more freedom for optimization), > while providing a set of special arithmetic operators, with specified > rounding modes, to use when more explicit control is needed. > > He also proposed a special construct "letctrl ... in e", where the "..." > are > a list of directives telling how to interpret and evaluate the expression > e. One possible directive is "RoundingMode = ..." to set the rounding mode > locally in e. Other directives control, for instance, whether > optimizations > like x*0.0 -> 0.0 are allowed in e, whether to force strict evaluation of > all subexpressions (so optimizations cannot affect exceptions), to set > allowed miminum accuracy, etc. > > The language has exception handling (including a "handle" construct to > catch > exceptions), which also takes care of floating-point exceptions.

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