March 2002 - Haskell - Haskell.org

2nd CfP: WRS'02 - 2nd WS on Reduction Strategies in Rewriting and Programming
by Bernhard Gramlich 09 Mar '02

09 Mar '02

[Apologies for multiple copies of this announcement] ************************************************************************** **************** 2nd call for papers and participation ***************** ************************************************************************** Second International Workshop on Reduction Strategies in Rewriting and Programming (WRS 2002) http://www.dsic.upv.es/users/elp/WRS2002 affiliated with RTA 2002, held as part of FLoC 2002 Copenhagen, Denmark, July 21, 2002 -------------------------------------------------------------------------- BACKGROUND AND AIMS Reduction strategies in rewriting and programming have attracted an increasing attention within the last years. New types of reduction strategies have been invented and investigated, and new results on rewriting / computation under particular strategies have been obtained. Research in this field ranges from primarily theoretical questions about reduction strategies to very practical application and implementation issues. The need for a deeper understanding of reduction strategies in rewriting and programming, both in theory and practice, is obvious, since they bridge the gap between unrestricted general rewriting (computation) and (more deterministic) rewriting with particular strategies (programming). Moreover, reduction strategies provide a natural way to go from operational principles (e.g., graph and term rewriting, narrowing, lambda-calculus) and semantics (e.g., normalization, computation of values, infinitary normalization, head-normalization) to implementations of programming languages. Therefore any progress in this area is likely to be of interest not only to the rewriting community, but also to neighbouring fields like functional programming, functional-logic programming, and termination proofs of algorithms. The workshop wants to provide a forum for the presentation and discussion of new ideas and results, recent developments, new research directions, as well as of surveys on existing knowledge in this area. Furthermore we aim at fostering interaction and exchange between researchers and students actively working on such topics. The workshop will be held in conjunction with RTA 2002 in Copenhagen (Denmark) on July 21, 2002. The workshop is (co-)organized by TU Valencia and TU Wien. TOPICS OF INTEREST Topics of interest include, but are not restricted to: - theoretical foundations for the definition and semantic description of reduction strategies - strategies in different frameworks (term rewriting, graph rewriting, infinitary rewriting, lambda calculi, higher order rewriting and explicit substitutions, conditional rewriting, rewriting with built-ins, narrowing, constraint solving, etc.) and their application in (equational, functional, functional-logic) programming (languages) - properties of reduction strategies / computations under strategies (e.g., completeness, computability, decidability, complexity, optimality, (hyper-)normalization, cofinality, fairness, perpetuality, context-freeness, neededness, laziness, eagerness, strictness) - interrelations, combinations and applications of reduction under different strategies (e.g., equivalence conditions for fundamental properties like termination and confluence, applications in modularity analysis, connections between strategies of different frameworks, etc.) - program analysis and other semantics-based optimization techniques dealing with reduction strategies - rewrite systems / tools / implementations with flexible / programmable strategies as essential concept / ingredient - specification of reduction strategies in (real) languages - data structures and implementation techniques for reduction strategies. SUBMISSIONS We solicit papers on all aspects of reduction strategies in rewriting and programming. Submissions should describe unpublished work, except for survey papers which are explicitly welcome, too. Submissions should not exceed 10 pages (however, survey papers may be longer) and be sent in postscript format to the PC co-chairs at wrs02(a)dsic.upv.es before April 15, 2002. Submissions should include the title, authors' names, affiliations, addresses, and e-mail. Selection of papers by the PC will be based on originality, significance, and correctness. Final versions will be due by June 17, 2002. PUBLICATION The final workshop proceedings will be published in the Electronic Notes in Theoretical Computer Science (ENTCS) series of Elsevier. Preliminary hardcopy proceedings will be available at the workshop. A special issue of the Journal of Symbolic Computation (JSC) on Reduction Strategies in Rewriting and Programming will be designated for revised and extended versions of selected contributions from both WRS 2001 (Utrecht, May 2001) and WRS 2002. PROGRAM COMMITTEE Sergio Antoy Portland (USA) Roberto Di Cosmo Paris VII (France) Bernhard Gramlich (co-chair) Wien (Austria) Michael Hanus Kiel (Germany) Claude Kirchner Nancy (France) Paul Klint CWI Amsterdam (The Netherlands) Salvador Lucas (co-chair) Valencia (Spain) Manfred Schmidt-Schauss Frankfurt am Main (Germany) Yoshihito Toyama Tohoku (Japan) ORGANIZERS Bernhard Gramlich (co-chair) Technische Universitaet Wien Salvador Lucas (co-chair) Universidad Politecnica de Valencia INVITED TALKS (with tentative titles) Aart Middeldorp, Tsukuba (Japan): Strategies for Term Rewriting Vincent van Oostrom, Utrecht (The Netherlands): Optimal Strategies in Higher-Order Rewriting IMPORTANT DATES Deadline for submissions: April 15, 2002 Notification: May 27, 2002 Final versions due: June 17, 2002 Workshop: July 21, 2002 FURTHER INFORMATION WRS 2002 website: http://www.dsic.upv.es/users/elp/WRS2002 WRS 2002 e-mail address: wrs02(a)dsic.upv.es RTA 2002 website: http://www.ericsson.com/cslab/rta2002/ FLoC 2002 website: http://floc02.diku.dk WRS 2002 website at FLoC: http://floc02.diku.dk/WRS **************************************************************************

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scholarship information
by To Chieu Cuong 09 Mar '02

09 Mar '02

Dear Sir or Madam, I'm working at Department of Engineering Mechanics, Ho Chi Minh city University of Technology, Viet Nam as a teaching assistant. I have a M.E. of Civil Engineering and a B.S. of Computer Science. I'm looking for a scholarship. Would you please send me scholarship information of your university? I look forward to hearing from you. With best regards, Cuong. _________________________________________________________ Do You Yahoo!? Get your free @yahoo.com address at http://mail.yahoo.com

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Debugging Haskell
by Jerry, JiJie 09 Mar '02

09 Mar '02

Good day everyone, I was fiddling around with this tiny echo client/server haskell program from 'The Great Language Shootout' site (http://www.bagley.org/~doug/shootout/) and got stuck. The code (attached) has been reformatted with minimal API tweak (mkPortNumber, writeSocket, readSocket) to please my ghc-5.02.2, and all what I get is something stuck forever after the first iteration: $ ./echo 3 Client wrote: Hello there sailor Server recv: Hello there sailor Server read: Hello there sailor Server wrote: Hello there sailor After adding all these print statement, I still don't have a clue what's jammed there. Hope someone here can shred some light. BTW, I'd also like to take this chance to ask how to debug a haskell program in general? Regards, Jerry

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Concurrent Haskell (GHC) and Win32 Applications ?
by Antony Blakey 09 Mar '02

09 Mar '02

Hi, I'm experimenting with GHC as a platform for writing a Win32 GUI application, and I've hit what I think is a brick wall. The problem I think is with the lightweight thread implementation - Win32 calls can (and will) block the OS thread that makes the call, which blocks the entire system. Given that I'm wanting to write a network server with a Win32 GUI, this is obviously a Bad Thing. So, does any know if I missing some vital piece of information? I am using the following reduced test case, which I don't think is clueless. import Win32 import Concurrent endless:: Char -> IO () endless c = do { putChar c; endless c } main = do { task1; task2; endless 'b' } where task1 = forkIO ( do { messageBox nullHANDLE "Hey" "Yeah" mB_OK; return () } ) task2 = forkIO ( endless 'a' ) It does intersperse the 'a' and 'b' output nicely, but stops while the message box is on the screen. I'm not keen on writing a seperate GUI management thread in C++ and linking - the point is to do all of this in Haskell and write an application indistinguishable from a C++ GUI app e.g. imagine Simon Peyton Jones' sample webserver with a realtime GUI monitor. Thanks in advance for any pointers!

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RE: first-class polymorphism beats rank-2 polymorphism
by Ralf.Laemmel＠cwi.nl 08 Mar '02

08 Mar '02

Simon Peyton-Jones wrote: > In fact GHC does "forall-lifting" on type signatures to bring the > foralls to the front. But there's a bug in 5.02's forall-lifting... > ... > Perhaps you can try the 5.03 snapshot release? Certain things work there. In fact, it is fascinating. But now I did a new experiment ... It seems that forall-lifting does not work as expected for type synonyms in 5.03. Here is an example from my upcoming ICFP submission :-) Here is an innocent type synonym for generic functions with three parameters of kind * -> *: type Generic i o m = forall x. i x -> m (o x) This is a good candidate for all the parameters: type Id x = x Now I tried to define sequential composition. In fact, the following type deals with a very restricted case for simplicity: sequ :: forall t. (Generic t t Id) -> (Generic t t Id) -> (Generic t t Id) sequ f g = undefined Looking at the type of sequ, the foralls for t end up at the top. Hence, I have no chance to define sequential composition. Main> :t sequ forall t x1 x11 x. (t x1 -> Id (t x1)) -> (t x11 -> Id (t x11)) -> t x -> Id (t x) Main> Please let me know if this is a bug. Please don't fix it too soon :-) because otherwise I had to rewrite some material which is now based on first-class polymorphism and datatypes for i, o, and m. Such code will probably look better in proper rank-2 style with type synonyms for type constructor parameters. I just realized that type synonyms in GHC seem to be valid arguments even when not completely instantiated? This is wonderful. It is not supported in hugs. How difficult is it to cope with this? Does it make a real difference for the type system? Ralf

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[E-CFP] WFLP2002 - deadline is approaching
by Marco Comini 08 Mar '02

08 Mar '02

Dear Colleague I would like to remind you that the WFLP 2002 paper submission deadline is approaching. WFLP 2002 is the 11th international workshop on functional and (constraint) logic programming. WFLP 2002 aims to bring together researchers interested in functional programming, (constraint) logic programming, as well as their integration. For further details about the workshop please visit the web site http://www.dimi.uniud.it/~wflp2002/ Papers are due by March 20, 2002 You can sumbit papers following the electronic sumbission process at: http://www.dimi.uniud.it/~wflp2002/submit/ We hope that this "Call For Papers" will be useful for your work. Please forward the following to anybody who you think may be interested. Our apologies if you received multiple copy of this. -- Marco.

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pattern-matching with labelled types
by Andre W B Furtado 08 Mar '02

08 Mar '02

If I have: > data MyType = MT { > x :: Int, > y :: Char > } How do I update the Int value of MyType leaving the Char value unaffected? I tryied something like: > MT {x = newValue} but GHC gave me a warning about the Char value and it indeed caused strange effects. Of course, it is possible to do something like > update :: MyType -> Int -> MyType > update mt newValue = MT {x = newValue, y = oldValue} > where oldValue = y mt but this really annoys me when MyType has too many fields. Suggestions? Thanks a lot, -- Andre

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RE: rank-n polymorphism
by Simon Peyton-Jones 08 Mar '02

08 Mar '02

Mark Shields and I are writing a paper. The technical basis is in "Putting type annotations to work" Odersky/Laufer, POPL'96. Simon | -----Original Message----- | From: Artem S Alimarine [mailto:alimarin@cs.kun.nl] | Sent: 07 March 2002 16:27 | To: haskell(a)haskell.org | Subject: rank-n polymorphism | | | Dear all, | | GHC 5.0.3 supports rank-n polymorphism. | Could anyone please point me to a paper that describes type | inference algorithm used. | | Thanks in advance | Artem Alimarine | | _______________________________________________ | Haskell mailing list | Haskell(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell |

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RE: first-class polymorphism beats rank-2 polymorphism
by Simon Peyton-Jones 08 Mar '02

08 Mar '02

| So I would claim that these two types are the same: | | forall x. Class x => (forall y. Class y => y -> y) -> x -> x | (forall y. Class y => y -> y) -> (forall x. Class x => x -> x) | | ...so you should be able to do this: | | combinator :: (forall y. Class y => y -> y) -> (forall x. | Class x => x -> x) | combinator f x = combinator' f x | | but for some reason GHC 5.02.2 complains. I think this is a bug. Indeed the two types are the same. In fact GHC does "forall-lifting" on type signatures to bring the foralls to the front. But there's a bug in 5.02's forall-lifting... it doesn't bring the constraints to the front too. I fixed this in 5.03 a while ago, but didn't back-propagate the fix to 5.02. And indeed, 5.03 is happy with the pure rank-2 program. class Class x where combinator' :: (forall y. Class y => y -> y) -> x -> x combinator :: (forall y. Class y => y -> y) -> (forall x. Class x => x -> x) combinator f = combinator' f It's quite a bit of extra work propagating fixes into the 5.02 branch, so I probably won't do so for this one, since only a small minority of people will trip over it. Perhaps you can try the 5.03 snapshot release? Simon

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rank-n polymorphism
by Artem S Alimarine 08 Mar '02

08 Mar '02

Dear all, GHC 5.0.3 supports rank-n polymorphism. Could anyone please point me to a paper that describes type inference algorithm used. Thanks in advance Artem Alimarine

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