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The Haskell store is open ....
by John Peterson 01 Dec '00

01 Dec '00

Head to http://www.cafepress.com/haskell for your holiday shopping. Thanks to Conal Elliott and Fritz Ruehr for their artwork. Conal's design was produced by Pan so this shirt is in fact powered by Haskell! I'll be glad to add more designs in the future. Once cafepress lets me put more than one design in a store I'll consolidate everything. Meanwhile, if you want to set up a separate store I can link it into haskell.org for you. John

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Beginner: error when using multiple where stmts in hugs98
by Wim-Jan Hilgenbos 01 Dec '00

01 Dec '00

Hi, I've been trying some examples in functional programming. Most things work fine, but I have trouble with expressions with 'where' clauses that define more then one local definition. (I work with hugs98 version september 1999 under Linux) For example: ----------[ Mydiff.hs ]---------------------- module Mydiff where mydiff f = f' where f' x = ( f (x+h) - f x) / h h = 0.0001 ----------[ end Mydiff.hs ]------------------- When I try to load this module I get ERROR "Mydiff.hs" (line 5): Syntax error in input (unexpected `=') line 5 is the line h = 0.0001 I tried other examples like this one, played around with line-breaks white-space etc. Rewriting the f' line to f' x = (f (x+0.0001) - f x) / 0.0001 does the trick, but is not very satisfying. Can anyone help? WJ PS. I attached above example -- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Disclaimer: "These opinions are my own, though for a small fee they be yours too." -- Dave Haynie module Mydiff where mydiff f = f' where f' x = ( f (x+h) - f x) / h h = 0.0001

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Re: a trap for the unwary
by Jan-Willem Maessen 01 Dec '00

01 Dec '00

Malcolm Wallace writes: > Quick quiz: without running this through a compiler, who can spot > the mistake? :-) > > > module Main where > > import Char > > f x = y > > where > > y | isSpace x = True > > y | otherwise = False -- ** The problem line? > > main = print (f 'x') Without running this through the compiler, but based on similar problems I've had recently, I'd assume the problem is the marked line. Two outer-level patterns are each presented with guards. This would be correct for a function definition: > f x = y () > where > y _ | isSpace x = True > y _ | otherwise = False -- ** Does this work? This is a tricky issue. I'd like the original program to be all right. We end up sowing confusion with erroneous programs like this one: > f x = y > where > y | otherwise = False -- ** Now this pattern overlaps! > y | isSpace x = True But of course an analogous problem occurs in the function definition, and I think can be caught by turning on warnings in ghc. -Jan-Willem Maessen jmaessen(a)mit.edu

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a trap for the unwary
by Malcolm Wallace 01 Dec '00

01 Dec '00

Today, I thought I had discovered a bug in ghc. Then I tried hbc and Hugs, and they also rejected my program with the same error. nhc98 alone accepts it without complaint. I looked up the Report, and it seems that the program is indeed incorrect. Quick quiz: without running this through a compiler, who can spot the mistake? :-) > module Main where > import Char > f x = y > where > y | isSpace x = True > y | otherwise = False > main = print (f 'x') Regards, Malcolm

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Release 2: Mondrian and Haskell for .NET
by Nigel Perry 30 Nov '00

30 Nov '00

We have just released a new version of Mondrian, a new functional language for OO environments. This version is a prototype which targets Microsoft's new .NET platform. Mondrian is a non-strict functional language with threads, exceptions and interlanguage working - think of it as Haskell "light" with extras. Also released is our prototype of Haskell for .NET. This is a modified version of GHC which outputs an internal language which is read and compiled by the Mondrian for .NET compiler. This is the full GHC compiler but not all the Prelude is there. The following are the major changes between Release 1 and Release 2: * The Mondrian language is now better documented. * The standard packages have had a number of functions added to them and are now documented. * The Haskell compiler is now designed to install over a GHC installation. * Much more of the Haskell Prelude is supported. You now get all the standard high-level I/O operations, including file I/O. Haskell exceptions are also supported. Any .NET exception thrown by code called from Haskell appears to Haskell as an IOError. * There is some documentation describing interlanguage calling, both Mondrian <=> Haskell and Haskell & Mondrian <=> .NET languages Both compilers, sample programs, etc. are available now from: <http://www.mondrian-script.org> You will need Windows 2000 and .NET to use this software. Have fun and feedback is welcome. Cheers, Nigel for the Mondrian Team -- -- Nigel Perry, New Zealand/Utrecht, The Netherlands

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Re: "Green Card" for untyped lambda calculus?
by C.Reinke 29 Nov '00

29 Nov '00

> nil :: List a > cons :: a -> List a -> List a > forlist :: b -> (a -> List a -> b) -> List a -> b .. > The implementation I'm interested in (one without > constructors) is: > > nil fornil forcons = fornil > cons x xs fornil forcons = forcons x xs > forlist fornil forcons ls = ls fornil forcons .. > As one might guess, this implementation relies on infinite > types, which becomes obvious when offering for example > > map f = forlist nil (\x xs -> cons (f x) (map f xs)) I have to admit that I misread your definitions at first, because they are very similar to the representation of data structures as their own folds. As your original question has been answered by now, it might be interesting to have a look at this alternative. In the case of lists: nil c n = n cons x xs c n = c x (xs c n) -- pass c and n to xs fold c n l = l c n The reversed order of the cons and nil replacements is just for consistency with the standard fold, but note that the replacements get passed down to the rest of the list in the definition of cons, ensuring a consistent interpretation for all constructors in a given structure. This gives you the obvious non-recursive map f = fold (cons.f) nil and all those other golden foldies sum = fold (+) 0 length = fold (const (+1)) 0 append l1 l2 = fold cons l2 l1 .. Instead of an explicit recursion over an unknown structure, with pattern-matching at each stage, these functions utilize the recursive structure of the list parameter, and work uniformly on the whole list. [This fold representation of lists just uses a parameterized variant of the successor function known from Church numerals. I seem to remember that Church himself used continuation-passing representations of data structures, but I don't have access to his presentation here:-( Could someone please confirm whether or not he used it for recursive structures (other than naturals) or only for pairs, products, conditionals and the like?] To make things more visible, the following conversions are useful: fromlist = foldr cons nil tolist = fold (:) [] Then you have, for instance Main> fromlist [1..4] <<function>> Main> tolist $ fromlist [1..4] [1,2,3,4] Main> tolist $ map (+1) $ fromlist [1..4] [2,3,4,5] What I don't know is whether this representation is an option for you or whether you need the "flat" pattern-matching. Your initial definitions seem to correspond not to the standard lists but rather to: data L a b = N | C a b which doesn't fix the recursive structure and allows, among other things, for heterogeneous lists and trees. You'll find it hard to write some recursive functions even for this non-functional variant. And if you fix (L a) to give you something equivalent to data List a = N | C a (List a) the flat functional representation is no longer the only possible choice - it represents the "sums of products"-part, but leaves the recursive structure unattended. The variant given above would take care of that, but has other problems: As mentioned, the variant that represents data structures as their own folds corresponds -for lists- to Church numerals with parameterized successor. Unfortunately, the predecessor for these numerals is known to be slightly non-obvious, so the definition of tail for the fold-style lists is left as an exercise to the reader;-) If you absolutely need to operate on parts of your lists and want to treat each cons individually, the modified definitions of the "flat", pattern-matching-style representation given in other postings will be more convenient but, where it is applicable, the whole-structure approach supported by the "deep", fold-style representation is quite attractive. Claus

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MBR'01 Deadline extension
by Lorenzo Magnani 29 Nov '00

29 Nov '00

********** DEADLINE EXTENSION TO DECEMBER 15, 2000 *************** We have extended the submission deadline to December 15. Please send electronically (Microsoft Word, RTF, PDF, or Postcript) the extended abstract (about 1000 words) - No hard copies - to the program chair at the address lmagnani(a)cc.gatech.edu NEW Web Site Address of MBR'01 http://www.unipv.it/webphilos_lab/courses/progra1.html Last updated November 25, 2000 ********************************************************************** MODEL-BASED REASONING: SCIENTIFIC DISCOVERY, TECHNOLOGICAL INNOVATION, VALUES (MBR'01), Pavia, Italy, May 17-19, 2001. ********************************************************************** Up-to date information on the conference will be found at http://www.unipv.it/webphilos_lab/courses/progra1.html ********************************************************************** GENERAL INFORMATION >From Thursday 17 to Saturday 19 May 2001 (three days) the International Conference "MODEL-BASED REASONING. SCIENTIFIC DISCOVERY, TECNOLOGICAL INNOVATION, VALUES" will be held at the University of Pavia (near Milan, Italy). PROGRAM The conference will deal with the logical, epistemological, and cognitive aspects of modeling practices employed in scientific discovery and technological innovation, including computational models of such practices. Abduction is widely recognized as a significant reasoning process in discovery whose features are in need of explication. We will solicit papers that examine various forms of model-based reasoning, such as analogical and visual modeling, from philosophical, historical, sociological, psychological, or computational perspectives. We also plan to address the problem of model-based reasoning in ethics reasoning, especially pertaining to science and technology. RELEVANT RESEARCH AREAS We shall call for papers that cover topics from the following list: - abduction - analogical reasoning - causal and counterfactual reasoning in model construction - computational models of model-based reasoning and scientific reasoning - conceptual combination and theory formation - hypothetical and explanatory reasoning - logical analyses that may contribute to our understanding of the issues in model-based reasoning - model-based reasoning in ethics - models and manipulative reasoning - models and technological innovation - thought experimenting - visual, spatial, imagistic modeling, reasoning, and simulation SUBMISSIONS OF PAPERS All submitted papers will be carefully refereed. The precise format of the conference will be fixed after we have an idea of the number of accepted papers. We are thinking in terms of presentations of 40 and 20 minutes. The funding is Italian and US, but we are also looking elsewhere for further financing (and would appreciate any suggestions). A selected subset will be invited for inclusion (subject to refereeing) in a book which will constitute an advanced handbook for scientists and researchers. The book will be published by an international publishing house. Moreover another selected subset will be invited for inclusion (subject to refereeing) in special issues of suitable international Journals. FORMAT Authors must submit three printed copies and an electronic version - formatted in Microsoft Word, RTF, PDF, or Postcript format - of an extended abstract (about 1000 words) not later than December 18, 2000. Please send electronically the extended abstract to the program chair at the address lmagnani(a)cc.gatech.edu in case of problem with the above address please use lorenzo(a)philos.unipv.it or lmagnaniusa(a)netscape.net REGISTRATION AND FURTHER INFORMATION Registration Fees: Before 15 March 2001: Normal: ITL. 300.000 = appr. US$ 155 (EUR 154.93) (to participate in all the activities of the Conference) Students: Free After 15 March 2001: Normal: ITL. 350.000 = appr. US$ 175 (EUR 180.75) (to participate in all the activities of the Conference) Students: Free METHOD OF PAYMENT AND REGISTRATION DEADLINE: Bank (Swift) Transfer to BANCA REGIONALE EUROPEA S.p.A BRANCH PAVIA - Sede SWIFT BREUITM2 301 Bank Code 06906.11301 Acc. n. 520 Dipartimento di Filosofia indicating CONVEGNO INTERNAZIONALE MBR'01 PLEASE REGISTER by email, fax or air mail (before March 15, 2001) by sending PROGRAM CHAIR first and last name, function, institution, full address, phone, fax and email. For information about paper submission and the program that is not available on the web site, please contact the program chair. IMPORTANT DATES Registration deadline............................15 March 2001 Submission deadline..............................15 Dec 2000 Notification of acceptance.....................28 Feb 2001 Final papers (from those selected for publication) due........30 June 2001 Conference....................................17-19 May 2001 PROGRAM CHAIR Lorenzo MAGNANI School of Public Policy and College of Computing Program in Philosophy, Science, & Technology Georgia Institute of Technology, 685 Cherry Street Atlanta, GA, 30332 - 0345, USA Office: 404-894-0950 & 404-385-0884, Home: 404-875-3566 Fax: 404-385-0504 & 404-894-2970 Email: lorenzo.magnani(a)cc.gatech.edu Address in Italy: Department of Philosophy and Computational Philosophy Laboratory University of Pavia, Piazza Botta 6, 27100 Pavia, Italy Office: +39-0382-506283, Home: +39-0383-371067 Fax: +39-0382-23215 Email: lorenzo(a)philos.unipv.it PROGRAM CO-CHAIR Nancy J. NERSESSIAN (Program Co-Chair) Program in Cognitive Science School of Public Policy and College of Computing, Georgia Institute of Technology, Atlanta, USA Email: nancyn(a)cc.gatech.edu PROGRAM CO-CHAIR Kenneth J. KNOESPEL (Program Co-Chair) School of History, Technology, and Society, and Program in Cognitive Science Georgia Institute of Technology, Atlanta, USA Email: kenneth.knoespel(a)hts.gatech.edu PROGRAM COMMITTEE - Ann Bostrom, School of Public Policy, Georgia Institute of Technology, Atlanta, GA, USA - Elena Gagliasso, Department of Philosophical and Epistemological Studies, University of Rome La Sapienza, Rome, ITALY - Dedre Gentner, Psychology Department, Northwestern University, Evanston, IL 60208, USA - Ronald N. Giere, Department of Philosophy, University of Minnesota, MN, USA - Mark L. Johnson, Department of Philosophy, 1295 University of Oregon, Eugene, OR, USA - Kenneth Knoespel, School of History, Technology, and Society, Georgia Institute of Technology, Atlanta, GA, USA - Lorenzo Magnani, Department of Philosophy, University of Pavia, Pavia, ITALY and School of Public Policy and College of Computing, Georgia Institute of Technology, Atlanta, GA, USA - Pat Langley, Adaptive Systems Group, DaimlerChrysler Research & Technology Center, Palo Alto, CA, USA - Nancy J. Nersessian, School of Public Policy and College of Computing, Georgia Institute of Technology, Atlanta, GA, USA - Brian Norton, School of Public Policy, Georgia Institute of Technology, Atlanta, GA, USA - Claudio Pizzi, Department of Philosophy and Social Sciences, University of Siena, Siena, ITALY - Mario Stefanelli, Department of Computer Science, University of Pavia, Pavia, ITALY - Paul Thagard, Department of Philosophy, University of Waterloo, Waterloo, CANADA - Ryan D. Tweney, Bowling Green State University, Bowling Green, OH, USA - Stella Vosniadou, Department of Philosophy and History of Science, Brain and Cognitive Science Division, National and Capodistrian University of Athens, Athens, GREECE. LOCAL ORGANIZING COMMITTEE Riccardo Dossena (riki.dox@libero), Elena Gandini (elegand(a)yahoo.com) Rosella Gennari (gennari(a)hum.uva.nl) Lorenzo Magnani (lmagnani(a)cc.gatech.edu) Massimo Manganaro (triskel(a)worldonline.it) Stefania Pernice (stepernice(a)libero.it) Matteo Piazza (pimat(a)yahoo.com) Giulio Poletti (philosophia(a)libero.it) Stefano Rini (s.rini(a)philos.unipv.it) Andrea Venturi (aventuri@philos.unipv.,it) (Department of Philosophy, University of Pavia, Pavia, Italy), Mario Stefanelli (mstefa(a)ipvstefa.unipv.it) (Department of Computer Science, University of Pavia, Pavia, Italy). IMPORTANT ADDRESSES LORENZO MAGNANI (Conference Chair) School of Public Policy and College of Computing Program in Philosophy, Science, & Technology Georgia Institute of Technology, 685 Cherry Street Atlanta, GA, 30332 - 0345, USA Office: 404-894-9050 & 404-385-0884, Home: 404-875-3566 Fax: 404-385-0504 & 404-894-2970 Email: lorenzo.magnani(a)cc.gatech.edu Address in Italy: Department of Philosophy and Computational Philosophy Laboratory University of Pavia, Piazza Botta 6, 27100 Pavia, Italy Office: +39-0382-506283, Home: +39-0383-371067 Fax: +39-0382-23215 Email: lorenzo(a)philos.unipv.it CONFERENCE SITE: Collegio Ghislieri, Piazza Ghislieri, 27100 PAVIA, Italy, phone +39 0382 22044. The Conference is sponsored by UNIVERSITY OF PAVIA, ITALY GEORGIA INSTITUTE OF TECHNOLOGY, ATLANTA, GA, USA UNIVERSITY OF SIENA, ITALY UNIVERSITY OF ROME "LA SAPIENZA", ITALY, MURST (Ministero dell'Università e della Ricerca Scientifica e Tecnologica), ITALY, CARIPLO (CASSA DI RISPARMIO DELLE PROVINCIE LOMBARDE, MILAN, ITALY) HOW TO REACH PAVIA LINATE Airport: People arriving by plane at LINATE should take the bus to the CENTRAL STATION of Milan (cf below fron this Station to Pavia). In LINATE it could be convenient to take a Taxi because the airport is close to the center of Milan. Moreover, The bus company SGEA offers six runs from LINATE to Pavia at 9.00, 10.00, 12.00 AM and 2.00, 5.00, 8.30 PM. The last stop is Pavia, near the station (see again our updated web page for possible alterations of this time-table) (from Pavia to LINATE six runs at 5,00, 7.45, 10.00 AM, 1.00, 4.00, 6.00 PM) (one hour trip). In Pavia there is only one station. The easiest way to reach the center of the town is to get off at the station and than take the bus n. 3. MALPENSA 2000 and OLD MALPENSA Airports (usually people arrive to Malpensa 2000 and not to OLD MALPENSA): People arriving by plane at MALPENSA 2000 (also called MALPENSA 2000 Terminal 1) or at "old" MALPENSA (now called MALPENSA NORTH but also called Malpensa 2000 Terminal 2) should take the bus to the CENTRAL STATION of Milan. There is also a bus AND A TRAIN from Malpensa 2000 to the NORTH STATION (Piazzale Cadorna) of Milan, in this case from NORTH Station you will have to take the underground MM1 to the Central Station: trains to Pavia leave from Central station). Moreover, the bus company SGEA offers four runs from MALPENSA 2000 to Pavia at 9.00 AM, 1:30 PM, 5.00 PM, and 9:30 PM - from Malpensa North (OLD Malpensa or Malpensa 2000 Terminal 2 5 munutes later) (from Pavia to MALPENSA 2000 and to OLD MALPENSA four runs at 7.00 AM, 11:00 AM, 3.15 PM, and 7:00 PM) (one hour and half trip). The last stop is Pavia, near the station (see again our updated web page for possible alterations of this time-table) In Pavia there is only one station. The easiest way to reach the center of the town is to get off at the station and than take the bus n. 3. There are trains from MILAN (Central Station) to PAVIA and vice Versa about every an hour (routes: MILAN-GENOVA; MILAN-VENTIMIGLIA; MILAN-LA SPEZIA; MILAN-SAVONA; MILAN-SESTRI LEVANTE; MILAN-IMPERIA; MILAN-ALBENGA; Pavia is the first stop only if the train is not slow, that is, if it is not, in ITALIAN, "L", locale). In Pavia there is only one rail station. The easiest way to reach the center of the town is to get off at the station and than take the bus n. 3. ACCOMMODATION The WEB site of the Tourist Office is http://www.systemy.it/pavia/home.html (new! sorry, only in Italian). The email address is info(a)apt.pv.it. When available you will find the whole list of hotels and other information concerning Pavia and its history. See also http://www.itwg.com/ct_00036.asp. In case of accommodation problems remember we will have at our disposal some rooms at special "conference rates" in the Colleges of the University. For further information please contact the Program Chair. As the the conferences dates are very close to summer holidays we recommend making your reservations as early as possible and before March 31, 2000 at the latest. ALL ACCOMMODATIONS (EXCEPT FOR INVITED SPEAKERS) WILL BE PROCESSED BY: Agenzia Viaggi ALOHATOUR Corso Cairoli 11 I - 27100 PAVIA Italy Phone: +39-0382-539565 Fax: +39-0382-539572 +39-0382-539504 email (only to request information): aloha(a)buonviaggio.it (cut here) ********************************************************************** ACCOMMODATION FORM - MBR'01 ---------------------------------------------------------------------- TO BE FAXED: +39-0382-539572 +39-0382-539504 OR MAILED: Agenzia Viaggi ALOHATOUR Corso Cairoli 11 I - 27100 PAVIA Italy email (only to request information): aloha(a)buonviaggio.it ---------------------------------------------------------------------- FILL IN CAPITAL LETTERS, PLEASE LAST NAME:___________________FIRST NAME:_____________Prof./Dr./Mr./Ms. AFFILIATION/UNIVERSITY/DEPT.__________________________________________ STREET:_______________________________________________________________ TOWN:___________________________CODE:_____________COUNTRY:____________ PHONE:__________________FAX:__________________E-MAIL:_________________ TYPE OF TRAVELLING:__________________DATE OF ARRIVAL:_________________ DATE OF DEPARTURE:___________________NUMBER OF NIGHTS:________________ CREDIT CARD NUMBER AND TYPE__________________________ EXPIRATION_____________ (you can also pay by bank transfer and postal order, please see below) ACCOMMODATION INCL. BREAKFAST SINGLE ROOM+BATH. / DOUBLE ROOM+BATH. ***HOTEL EXCELSIOR, Piazza Stazione, PAVIA LIT. 100.000 / LIT. 150.000 ______________ (EUR. 51.64 / EUR. 77.46) ****HOTEL ARISTON, Via Scopoli, PAVIA LIT. 130.000 / LIT. 190.000 +_____________ (EUR. 67.13 / EUR. 98.12) ****HOTEL MODERNO, Viale V. Emanuele, PAVIA LIT. 170.000 / LIT. 230.000 +_____________ (EUR. 87.79 / EUR. 118.78) RESERVATION CHARGE LIT. 25.000 +_______ (EUR. 12.91) TOTAL AMOUNT: =_____________ ACCOMMODATION DEPOSIT: ONE NIGHT LIT......... - _____________ (EUR) ACCOMMODATION BALANCE: LIT......... =_____________ (EUR)........ Hotel Excelsior (from the station walk east) Hotel Moderno (from the station walk north) To reach Hotel Ariston take the bus n. 3 or taxi. ____________________________________________________________________ PLEASE FAX OR MAIL THIS FORM AND PAY BY *CREDIT CARD* BEFORE *15 MARCH 2001* TO: FAX: +39-0382-539572 +39-0382-539504 MAIL ADDRESS: Agenzia Viaggi ALOHATOUR Corso Cairoli 11 I - 27100 PAVIA Italy email (only to request information): aloha(a)buonviaggio.it DATE OF PAYMENT____________YOUR SIGNATURE____________________ ________________________________________________________________________ PLEASE FAX OR MAIL THIS FORM AND PAY BY *BANK TRANSFER* BEFORE *15 MARCH 2001* (fax or mail also a copy of the bank transfer) TO: BANCA REGIONALE EUROPEA S.p.A.BRANCH PAVIA - SedeSWIFT BREUITM2 301Bank Code 6906.11301 Agenzia Viaggi ALOHATOUR S.r.l. Acc.n 19952/4 DATE OF PAYMENT____________YOUR SIGNATURE___________________ ________________________________________________________________________ PLEASE FAX OR MAIL THIS FORM AND PAY BY *POSTAL ORDER* BEFORE* 15 MARCH 2001* (fax or mail also a copy of the postal receipt) TO: Agenzia Viaggi ALOHATOUR Corso Cairoli 11 I - 27100 PAVIA Italy DATE OF PAYMENT______________________YOUR SIGNATURE______________________ _________________________________________________________________________ ALHOATOUR WILL MAIL OR FAX YOU THE RESERVATION VOUCHER ALOHATOUR WILL SATISFY THE REQUESTS AS FAR AS POSSIBLE. IF NOT POSSIBLE, ANOTHER SIMILAR ACCOMMODATION WILL BE ARRANGED.

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Showing Haskell
by Koen Claessen 29 Nov '00

29 Nov '00

Hi all, I just send this message to share some Haskell code with you. I hope it might be useful to some people. (Maybe even to the haskell.org crowd!) Recently I experimented a little bit with an easy way of writing CGI scripts that generate HTML in Haskell. I know many people have done this already, but I was inspired by the paper "Haskell Server Pages" by Erik Meijer et al., which uses an HTML datatype where one can also do IO inside. This makes it a lot more convenient to write CGI scripts I think. The idea is to have an HTML datatype of the following kind: type Html = [HtmlEl] data HtmlEl = Text String | Tag String [(String,String)] Html | Action (IO Html) I wrote a very modest CGI library making use of this datatype, and also providing some other useful functions for writing CGI scripts (such as locked variables). I also implemented some CGI scripts of course. One script is a script that "shows" a Haskell module, using syntax highlighting. One can also click on imported modules and see their definitions. To see the Haskell CGI library displyed by this CGI script, go to the following link: http://www.cs.chalmers.se/Cs/Grundutb/Kurser/afp/Cgi/show-haskell.cgi?file=… (I used it in my course, so there is some extra junk there.) You can click on the bottom of the page, and look at the implementation of the "show-haskell" script. Regards, Koen. -- Koen Claessen http://www.cs.chalmers.se/~koen phone:+46-31-772 5424 mailto:koen@cs.chalmers.se ----------------------------------------------------- Chalmers University of Technology, Gothenburg, Sweden

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"Green Card" for untyped lambda calculus?
by Elke Kasimir 29 Nov '00

29 Nov '00

I'm concerned with the following problem: A possible (though probably unusual) characterization of list data structures is three functions nil :: List a cons :: a -> List a -> List a forlist :: b -> (a -> List a -> b) -> List a -> b for which forlist fornil forcons nil = fornil forlist fornil forcons (cons x xs) = forcons x xs holds, that is, 'forlist' is a kind of case with pattern matching for lists. The straightforward implementation with buildt-in lists is nil = [] cons = (:) forlist fornil forcons [] = fornil forlist fornil forcons (x:xs) = forcons x xs The implementation I'm interested in (one without constructors) is: nil fornil forcons = fornil cons x xs fornil forcons = forcons x xs forlist fornil forcons ls = ls fornil forcons As one might guess, this implementation relies on infinite types, which becomes obvious when offering for example map f = forlist nil (\x xs -> cons (f x) (map f xs)) to the Haskell type checker. I have made two other attempts to fit my implementation in the haskell type system, without finding a usable solution (see attachment). (By the way, the map definition above can be easily optimized to: map f ls fnil fcons = ls fnil (\x xs -> fcons (f x) (map f xs)) via straight inlining plus one optimization rule, which allows for even more inlining if the consumer (fnil,fcons) is known.) Has anyone an idea of how to express my lists in haskell or some haskell type system extension? Just a thought... Would it be possible for a Haskell Compiler/ Interpreter to provide a "Green Card" for untyped lambda calculus...? Elke. --- Elke Kasimir Skalitzer Str. 79 10997 Berlin (Germany) fon: +49 (030) 612 852 16 mail: elke.kasimir(a)catmint.de> see: <http://www.catmint.de/elke> for pgp public key see: <http://www.catmint.de/elke/pgp_signature.html>

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WoLLIC'2001 - Call for Papers
by Ruy de Queiroz 28 Nov '00

28 Nov '00

[please post. apologies for multiple copies] Call for Papers 8th Workshop on Logic, Language, Information and Computation (WoLLIC'2001) July 31 to August 3, 2001 Scientific Co-Sponsorship: IGPL, FoLLI, ASL, SBC, SBL Brasília, Brazil (NEW!: (MODEST) STUDENT GRANTS) THE EVENT The "8th Workshop on Logic, Language, Information and Computation" (WoLLIC'2001), the eighth version of a series of workshops which started in 1994 with the aim of fostering interdisciplinary research in pure and applied logic, will be held in Brasília, Brazil, from July 31st to August 3rd 2001. SCOPE Contributions are invited in the form of short papers (10 A4 10pt pages) in all areas related to logic, language, information and computation, including: pure logical systems, proof theory, model theory, algebraic logic, type theory, category theory, constructive mathematics, lambda and combinatorial calculi, program logic and program semantics, logics and models of concurrency, logic and complexity theory, nonclassical logics, nonmonotonic logic, logic and language, discourse representation, logic and artificial intelligence, automated deduction, foundations of logic programming, logic and computation, and logic engineering. SCIENTIFIC SPONSORSHIP The 8th WoLLIC'2001 has the scientific sponsorship of the Association for Symbolic Logic (ASL), the Interest Group in Pure and Applied Logics (IGPL), the European Association for Logic, Language and Information (FoLLI), the Sociedade Brasileira de Computação (SBC), and the Sociedade Brasileira de Lógica (SBL). THE LOCATION Brasília, the youthful capital of Brazil - famous for its innovating architecture and futuristic urbanism, is situated in the geographical center of the country, inside the Brazilian Cerrados that is a rich Tropical Savannah, with a unique and diverse flora and fauna. In August, during the Brazilian winter, the weather is dry with an average temperature of 22 C, that makes ideal aquatic sports and visits to the natural attractions of the city as the Zoo, the Botanical Garden and the National Park. GUEST SPEAKERS There will be a number of guest speakers, including: Walter Carnielli (State Univ Campinas, Brazil) Bruno Courcelle (Univ Bordeaux 1, France) Gilles Dowek (INRIA, France) Petr Hajek (Inst Computer Sci, Czech Acad of Sciences, Czech Republic) Dexter Kozen (Cornell Univ, USA) (TO BE CONFIRMED) Jouko Väänänen (Helsinki Univ, Finland) SUBMISSION Papers (up to 10 pages A4 10pt, sent preferably in postscript format by e-mail to wollic(a)cin.ufpe.br, or in 5(five) copies to postal address) must be RECEIVED by APRIL 2nd, 2001 by one of the Chairs of the Organising Committee. Papers must be ANONYMOUS (a separate identification page must be included), written in English and give enough detail to allow the programme committee to assess the merits of the work. Papers should start with a brief statement of the issues, a summary of the main results, and a statement of their significance and relevance to the workshop. References and comparisons with related work is also expected. Technical development directed to the specialist should follow. Results must be unpublished and not submitted for publication elsewhere, including the proceedings of other symposia or workshops. One author of each accepted paper will be expected to attend the conference in order to present it. Authors will be notified of acceptance by MAY 7th, 2001, and final versions will have to be delivered (in LaTeX format) by MAY 31st, 2001. The abstracts of the papers will be published in a "Conference Report" section of the Logic Journal of the IGPL (ISSN 1367-0751) (Oxford Univ Press) as part of the meeting report. Papers presented at the meeting will be invited for submission (in full version) to the Logic Journal of the IGPL (http://www.oup.co.uk/igpl/) STUDENT GRANTS WoLLIC'2001 will make available modest grants to graduate students in logic and to recent PhDs so that they may attend the meeting in Brasília. To be considered for a grant, please (1) send a letter of application, and (2) ask your thesis supervisor to send a brief recommendation letter. The application letter should be brief (one page) and should include (1) your name, (2) your home institution, (3) your thesis supervisor's name, (4) a one-paragraph description of your studies and work in logic, (5) your estimate of the travel expenses you will incur, (6) (for citizens or residents of Brazil) citizenship or visa status, and (7) (voluntary) indication of your gender and minority status. Only modest grants will be possible, partially covering travel costs and perhaps some of the living expenses during the meeting. Women and members of minority groups are strongly encouraged to apply. In addition to funds provided by WoLLIC, it is expected that this program of student grants will be supported by a grant from the Brazilian National Council for the Scientific and Technological Development (CNPq); CNPq funds may be awarded only to students at Brazilian universities and to citizens and permanent residents of Brazil. Application by email is encouraged; put "WoLLIC grant application" in the subject line of your message. Applications and recommendations should be received before the deadline of MARCH 1st, 2001, by one of the Co-Chairs of the Organising Committee. IMPORTANT DATES Submission: APRIl 2nd, 2001 Notification of acceptance/rejection: MAY 7th, 2001 Delivery of final (in LaTeX): MAY 31st, 2001 PROGRAMME COMMITTEE John Baldwin (Univ Illinois at Chicago, USA) Mads Dam (Swedish Inst Computer Sci, Sweden) Marcelo Finger (Univ Sao Paulo, Brazil) Edward Hermann Haeusler (Pont Cathol Univ Rio de Janeiro, Brazil) David Israel (SRI International, USA) Fairouz Kamareddine (Heriot-Watt Univ, Scotland) Claude Kirchner (LORIA & INRIA, France) Phokion Kolaitis (Univ Calif at Santa Cruz, USA) Daniel Leivant (Indiana Univ, USA) Michael Moortgat (Utrecht Univ, The Netherlands) Pavel Pudlák (Maths Inst, Czech Acad. of Sciences, Czech Rep) ORGANISING COMMITTEE Mauricio Ayala-Rincon (UnB) (Co-Chair) Sandra A. de Amo (UFU) Ana Teresa de Castro Martins (UFC) Anjolina G. de Oliveira (UFPE/UFBA) Haydée W. Poubel (UnB) Ruy de Queiroz (UFPE) (Co-Chair) Renata Wassermann (USP) FURTHER INFORMATION Contact one of the Co-Chairs of the Organising Committee: Ruy de Queiroz, Centro de Informática, Univ. Federal de Pernambuco, CP 7851, 50732-970 Recife, PE, Brazil. E-mail: ruy(a)cin.ufpe.br, tel.: (+55 81) 3271-8430, fax: (+55 81) 3271-8438. Mauricio Ayala Rincon, Departamento de Matemática, Universidade de Brasília, 70910-900 Brasília, DF, Brazil. E-mail: ayala(a)mat.unb.br, tel.: (+55 61) 307-2441, fax: (+55 61) 273-2737. WEB PAGE http://www.cin.ufpe.br/~wollic/wollic2001/ -------

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