October 2003 - Haskell

hscairo 0.3
by Abraham Egnor 20 Oct '03

20 Oct '03

The haskell bindings for cairo have reached 0.3, which is enough of a milestone to warrant this post, I think. Main improvements include: * better (i.e. more Haskellish) wrappers for the Matrix functions * better status handling - status is now checked automatically, and errors reported properly. * Attributes are parameterized by object type as well as value type. What this means is that things other than the implicit Cairo object can have Attributes; for example, Matrix objects have an "affine" Attribute. * all current cairo functions wrapped. A few had been left out of the prior version due to implementation difficulty. * a better backend. Specifically, a running hscairo program no longer uses up all CPU time. The new version is available at http://ofb.net/~abe/hscairo-0.3.tar.bz2. Abe

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how to do lazy IO like getContents?
by Ben Escoto 19 Oct '03

19 Oct '03

Hi, I'm trying to do IO and it isn't lazy enough. My problem seems similar to this one: Write a function that lazily reads characters from stdin, just like getContents does. These two don't work: lazyRead :: IO String lazyRead = do first_char <- getChar rest <- lazyRead return $ first_char:rest lazyRead2 :: IO String lazyRead2 = (liftM2 (:)) getChar lazyRead2 because neither has the intended behavior, because if I type: lazyRead >>= putChar . head Then it seems that all of stdin is read, not just the first character, which is different from: getContents >>= putChar . head which only reads one character. So how do you write getContents in haskell? Thanks for any insight. -- Ben Escoto

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calling FunPtr's?
by John Meacham 18 Oct '03

18 Oct '03

I need to call some dynamically linked routines recieved via Posix.DynamicLinker but am unsure how to do this from haskell. I do not know the types of the functions I wish to call at compile time so can't create appropriate foreign import statements. What would be nice is something like callFunPtr :: (Storable a, Storable b) => FunPtr z -> a -> IO b with a being a tuple if I want to push multiple arguments onto the stack perhaps. this function should be straightforward to implement, as it just needs to place the arguments on the stack in the appropriate fashion and pull the return value of out the proper register or memory location, but would obviously be very architecture specific so should be provided by the compiler. does something like this exist? is there another way to do this? John -- --------------------------------------------------------------------------- John Meacham - California Institute of Technology, Alum. - john(a)foo.net ---------------------------------------------------------------------------

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Announce: buddha 1.0 released
by Bernard James POPE 18 Oct '03

18 Oct '03

Announcing buddha version 1.0 ----------------------------- www.cs.mu.oz.au/~bjpop/buddha A declarative debugger for Haskell 98. It is based on program transformation and works with GHC 5 and 6. buddha offers a declarative debugging algorithm and a browsing mechanism. It is useful for finding logical errors in programs and for exploring computations in a high-level manner. The interface is designed to be simple to use, and may be an ideal aid for teaching Haskell. Version 1.0 is known to work on unix platforms, including OS X, GNU/linux and freeBSD. It does not work on Windows. buddha is released under the GPL license. Enjoy, Bernie.

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forkIO implemenation
by Feingold, Jason (WingspanTech) 17 Oct '03

17 Oct '03

I infer from a discussion from March 2002 that concurrency in Haskell is not implemented in native threads, at least in Windows. Is this true? The discussion also implies that an implementation is in the works. The reason I ask is that when I forkIO and accept from a socket in the new thread everything seems blocked. Is this the expected behavior? It would be really nice to be able to listen on multiple sockets in a single process. Thanks, Jason Feingold

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How do I derive a type class for different type parameters?
by Ben_Yu＠asc.aon.com 16 Oct '03

16 Oct '03

Hi there, I'm having a problem with type classes. I have a class called PrettyPrintable, For data type: data Generic a = ...... I need to provide instance of Generic a for type class PrettyPrintable. The parameter type a could be either PrettyPrintable or Show. If I write the following, it won't compile: instance Show a => PrettyPrintable (Generic a) where ...... instance PrettyPrintable a => PrettyPrintable (Generic a) where ... How do I achieve this? Another alternative that I think may work is if I can say "all Show a will be PrettyPrintable a in terms of this implementation". But it seems that the following code won't compile either: instance Show a => PrettyPrintable a where ...... Am I doing the design totally wrong? Or there is actually some clever scheme in Haskell that can do this elegantly? Thanks. Ben. This message is intended only for the addressee and may contain information that is confidential or privileged. Unauthorized use is strictly prohibited and may be unlawful. If you are not the intended recipient, or the person responsible for delivering to the intended recipient, you should not read, copy, disclose or otherwise use this message, except for the purpose of delivery to the addressee. If you have received this email in error, please delete and advise us immediately.

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Final call: Formal Methods for Components and Objects
by M.M. Bonsangue 16 Oct '03

16 Oct '03

(We apologize for the reception of multiple copies) ********************LAST CALL FOR PARTICIPATION ********************** Second International Symposium on Formal Methods for Components and Objects (FMCO 2003) DATES 4 - 7 November 2003 PLACE Lorentz Center, Leiden University, Leiden, The Netherlands REGISTRATION FORM http://fmco.liacs.nl/fmco03.html REGISTRATION FEES 400 euro for regular participants and 275 euro for students FINAL PROGRAM TUESDAY 4th, November 2003 8:45 - 9:00 Welcome 9:00 - 10:00 Keynote: David Parnas (University of Limerick, IE) Mathematical Documentation of Software 10:00 - 10:30 Break 10:30 - 11:15 Razvan Diaconescu (IMAR, RO) Behavioural specification for hierarchical object composition 11:15 - 12:00 Heike Wehrheim (University of Oldenburg, DE) Preserving Properties under Change 12:00 - 13:30 Lunch break 13:30 - 14:30 Keynote: Andrew D. Gordon (Microsoft Research, UK) Formal Tools for Securing Web Services 14:30 - 15:00 Break 15:00 - 15:45 Jeannette Wing (Carnegie Mellon University, USA) Vulnerability Analysis Using Attack Graphs 15:45 - 16:30 Yassine Lakhnech (University of Grenoble, FR) Security protocols, their modes and analysis: a survey 16:30 - 16:45 Break 16:45 - 17:30 Albert Benveniste (IRISA/INRIA - Rennes, FR) Heterogeneous reactive systems formal modeling WEDNESDAY 5th, November 2003 9:00 - 10:00 Keynote: Tony Hoare (Microsoft Research Cambridge, UK) The Verifying Compiler: a Grand Challenge for Computing Research 10:00 - 10:30 Break 10:30 - 11:15 Willem-Paul de Roever (University of Kiel, DE) Data Refinement: model-oriented proof methods and their comparison 11:15 - 12:00 Frank de Boer (CWI, Amsterdam, NL) Hoare Logics for Object-Oriented Programming: State of the Art 12:00 - 13:30 Lunch break 13:30 - 14:15 Jean-Marc Jezequel (IRISA, Rennes, FR) Model-Driven Engineering: Basic Principles and Open Problems 14:15 - 15:00 Jan Friso Groote (Eindhoven University, NL) Visualisation of HUGE state spaces 17:00 - 19:15 Social Event 19:30 - Dinner THURSDAY 6th, November 2003 9:00 - 10:00 Keynote: Yuri Gurevich (Microsoft Research Redmond, USA) The Semantics of AsmL 10:00 - 10:30 Break 10:30 - 11:15 Egon Boerger (Pisa University, IT) Exploiting the "A" in Abstract State Machines for Specification Reuse. A Java/C# Case Study. 11:15 - 12:00 Werner Damm (University of Oldenburg, DE) t.b.a. 12:00 - 13:30 Lunch break 13:30 - 14:30 Keynote: Joseph Sifakis (Verimag, FR) Component-based construction of deadlock-free systems 14:30 - 15:00 Break 15:00 - 15:45 Philippe Schnoebelen (CNRS, Cachan, FR) The Verification of Lossy Channel Systems 15:45 - 16:30 Bengt Jonsson (Uppsala University, SE) t.b.a. 16:30 - 16:45 Break 16:45 - 17:30 Jan Rutten (CWI, Amsterdam, NL) A case study in coinductive stream calculus: signal flow graphs for dummies FRIDAY 7th, November 2003 9:00 - 10:00 Keynote: E. Allen Emerson (University of Texas, USA) Model checking many components 10:00 - 10:30 Break 10:30 - 11:15 Amir Pnueli (The Weizmann Institute of Science, ISR) t.b.a. 11:15 - 12:00 Natalia Sidorova (Eindhoven University, NL) Practical approaches for the verification of asynchronous components: model checking, abstraction and static analysis 12:00 - 13:30 Lunch break 13:30 - 14:30 Keynote: Desmond D'Souza (Kinetium, Austin, USA) Component Architectures - Some meeting points of practice, trend, and theory 14:30 - 15:00 Break 15:00 - 15:45 Jose Luiz Fiadeiro (University of Leicester, UK) CommUnity on the move: architectures for distribution and mobility 15:45 - 16:30 Gregor Engels (University of Paderborn, DE) Consistent interaction of components 16:30 - 17:15 Rob van Ommering (Philips Research Laboratories, NL) Component Based Architectures and Formalization MOBI-J AFFILIATED WORKSHOP On Monday 3rd, November 2003 from 13:30 till 17:00 there will at the Lorentz Center be a half-day Mobi-J workshop on "Assertional Methods for Java and its Extension with Mobile Asynchronous Channels". REGISTRATION Participation is limited to about 80 people, using a first-in first-served policy. To register, please fill in the registration form at http://fmco.liacs.nl/fmco03.html. The registration fee is 400 euro for regular participants and 275 euro for students It includes the participation to the symposium, a copy of the proceedings, all lunches and refreshments, and a social event (with dinner). ORGANIZING COMMITTEE F.S. de Boer (CWI and Utrecht University) M.M. Bonsangue (LIACS-Leiden University) S. Graf (Verimag) W.P. de Roever (CAU) For more information about participation and registration see the FMCO site above or consult either F.S. de Boer (frb(a)cwi.nl) or M.M. Bonsangue (marcello(a)liacs.nl)

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RTA'04: call for papers
by Femke van Raamsdonk 16 Oct '03

16 Oct '03

****************************** * * * RTA'04 CALL FOR PAPERS * * * ****************************** http://www-i2.informatik.rwth-aachen.de/RTA04/ The 15th Int. Conf. on Rewriting Techniques and Applications (RTA'04) will be part of the Federated Conference on Rewriting, Deduction and Programming (RDP'04). IMPORTANT DATES: Jan 15 2004: Deadline electronic submission of title+short abstract Jan 22 2004: Deadline electronic submission of papers Mar 14 2004: Notification of acceptance of papers Apr 4 2004: Deadline for final versions of accepted papers Jun 3-5 2004: Conference. RTA is the major forum for the presentation of research on all aspects of rewriting. Typical areas of interest include (but are not limited to): * APPLICATIONS: case studies; rule-based (functional and logic) programming; symbolic and algebraic computation; theorem proving; system synthesis and verification; proof checking. * FOUNDATIONS: matching and unification; narrowing; completion techniques; strategies; constraint solving; explicit substitutions; tree automata. * FRAMEWORKS: string, term, and graph rewriting; lambda-calculus and higher-order rewriting; proof nets; constrained rewriting/deduction; categorical and infinitary rewriting. * IMPLEMENTATION: compilation techniques; parallel execution; rewriting tools. * SEMANTICS: equational logic; rewriting logic. INVITED TALKS will be given at RTA'04 by: * Neil Jones (Copenhagen) * Aart Middeldorp (Innsbruck) * Robin Milner (Cambridge) BEST PAPER AWARDS: A 1000 Euro award wil be given to the best paper or papers as decided by the PC. The award may also totally or partially go to the best paper with a student as main author, according to the submission letter. RTA'04 PROGRAM COMMITEE: * Zena Ariola (Oregon) * J�rgen Giesl (Aachen) * Masahito Hasegawa (Kyoto) * H�l�ne Kirchner (Nancy) * Pierre Lescanne (Lyon) * Klaus Madlener (Kaiserslautern) * Narciso Mart�-Oliet (Madrid) * Paul-Andr� Melli�s (Paris) * Oege de Moor (Oxford) * Vincent van Oostrom (Utrecht, Chair) * Frank Pfenning (Carnegie Mellon) * Ashish Tiwari (SRI) * Ralf Treinen (ENS Cachan) * Roel de Vrijer (Amsterdam) RTA'04 SUBMISSIONS: Submissions must be original and not submitted for publication elsewhere. Submission categories include regular research papers and system descriptions. Also problem sets and submissions decribing interesting applications of rewriting techniques will be very welcome. As usual, accepted papers will appear in the Springer-Verlag Lecture Notes in Computer Science series. More information about paper submission will be available at the RDP'04 web page <http://www-i2.informatik.rwth-aachen.de/RDP04/> For further questions please contact the program chair: RTA'04 PROGRAM CHAIR: Vincent van Oostrom Universiteit Utrecht Department of Philosophy Heidelberglaan 8 3584 CS Utrecht, Netherlands Vincent.vanOostrom(a)phil.uu.nl

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changed link
by Christian Maeder 15 Oct '03

15 Oct '03

Hi, on: http://www.haskell.org/bookshelf/ the link for: Online Haskell Course by Ralf Hinze (in German). should be changed from: http://www.informatik.uni-bonn.de/~ralf/teaching/HsKurs_toc.html to: http://www.informatik.uni-bonn.de/~ralf/teaching/Hskurs_toc.html At least my browser seems to be case sensitive. Christian

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Re: IO behaves oddly if used nested
by blaat blaat 14 Oct '03

14 Oct '03

[snip] > Neither example is odd behavior, unless >you consider Hugs providing a perfectly reasonable instance of Show for >IO a odd. True, every program behaves exactly as according to the definition of the run-time behavior of Haskell programs. (Hugs deviates a bit from ghc but ah well) The odd is not in the run-time behavior. The odd is in the conceptual explanation. If I give a description of some f x = y function in Haskell I expect that some program f x is reduced to y and the result is given back (possibly printed). A good story to sell to students. This is almost everywhere the case except for the IO monad. In the former example, the inner putStr is _not_ evaluated but a message is shown (hinting that a IO has some structure we can observe before evaluation). In the latter example, it is shown that we are not interested in a result of a IO program, but only in its (lazily generated) side-effects. The monad behaves oddly with respect to the f x = y behavior. I think I observe the following reactions when I explain IO: 1* Can't the guy in front of me stop poking his nose? (the blank faces and parse errors) 2* Hmm, feels like Java, looks like Java, ahah! is Java! (coders) 3* Hmm, feels like math, looks like math, ahah! is math! (designers and thinkers) Group 1 will mimic, group 2 will produce obfuscuated Java code in Haskell, group 3 has great difficulty with the IO monad (although they are the first group who will write OK haskell programs) because it behaves differently from what they expect. The usual questions of group 3: * Why is an IO a evaluated if I am not interested in it's result? (opposite to the f x = y lazy behavior) * Why is in the putStr "hello world" example Hello World not shown? (opposite to expected f x = y eval-first-then-show behavior) * Why is in the IO (IO ()) example the inner IO () not evaluated? (somewhat opposite to expected f (f x) behavior - I personally wonder if it is even sound in a category theoretical setting) * ...Lots of other questions... Hmm, have to finish this email now - time constraints. I guess the short story just is: IO monads == sometimes bad conceptual story to sell. Especially so since the "best" group has the biggest problems and non-trivial examples are only explainable in the end in terms of run-time behavior. What was that remark again about pointy headed people and Haskell? ;-) For that I also gave the Nomad datatype as a possible solution (needs a pretty hefty type checker though). A nice (old) idea would be to represent IO as programs which are interpreted by some _outside_ RTS in a given manner, and leave the Haskell language clean. (It might even be a good idea with respect to the compiler implementation since it removes checking against unsafe IO behavior from the compiler -- just a thought) Bye now, and cheers, l4t3r _________________________________________________________________ The new MSN 8: smart spam protection and 2 months FREE* http://join.msn.com/?page=features/junkmail

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