May 2002 - Haskell - Haskell.org

ANN: Functional Metapost 1.2
by Ferenc Wagner 28 May '02

28 May '02

Dear Haskell Community, version 1.2 of Functional Metapost is now available at http://afavant.elte.hu/~wferi/funcmp/ News: * This version includes English translations of the most important parts of the documentation! Thanks to Meik Hellmund, who contributed the translations. * 8-bit color depth bitmaps work. Cheers, Feri.

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RE: Negative literals and the meaning of case -2 of -2 -> True
by Simon Peyton-Jones 27 May '02

27 May '02

Fixed. Simon | -----Original Message----- | From: Simon Marlow [mailto:simonmar@microsoft.com] | Sent: 17 May 2002 10:34 | To: Thomas Hallgren; haskell(a)haskell.org | Subject: RE: Negative literals and the meaning of case -2 of | -2 -> True | | | | > To find out how Haskell implementations treat negated | > literals, I tested | > the following program: | > | > ------------------------------------------------ | > main = print (minusTwo,trueOrFalse) | > | > minusTwo = -2::N | > | > trueOrFalse = | > case minusTwo of | > -2 -> True | > _ -> False | > | > data N = Negate N | FromInteger Integer deriving (Eq,Show) | > | > instance Num N where | > negate = Negate | > fromInteger = FromInteger | > ------------------------------------------------- | > | > The result is: | > | > * ghc 5.02.2: main outputs: (FromInteger (-2),True) | | GHC has two bugs in this area, one of which has been fixed | recently. The current output is (Negate (FromInteger | 2),False) (i.e. the same as hbc). We were being a little too | eager to replace 'negate (fromInteger N)' by 'fromInteger | (-N)'. There is also a bug in the pattern handling, however. | | Thanks for a nice test case... | | Cheers, | Simon | | _______________________________________________ | Haskell mailing list | Haskell(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell |

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RE: minor H98 anomaly: class declarations
by Simon Peyton-Jones 27 May '02

27 May '02

Yes, I agree, and I shall make this change forthwith unless anyone disagrees. thanks Simon | -----Original Message----- | From: Ross Paterson [mailto:ross@soi.city.ac.uk] | Sent: 27 May 2002 13:04 | To: haskell(a)haskell.org | Subject: minor H98 anomaly: class declarations | | | 4.3.1 has | | topdecl -> class [scontext =>] simpleclass [where cdecls] | scontext -> simpleclass | | ( simpleclass[1] , ... , simpleclass[n] ) | (n>=0) | simpleclass -> qtycls tyvar | | implying that the class being declared can be qualified: | | class Foo.C a where ... | | in contrast to every other kind of declaration. Nor does the | text explain what this could mean. Shouldn't the first line be | | topdecl -> class [scontext =>] tycls tyvar [where cdecls] | | (GHC doesn't allow qualification; Hugs and Nhc allow it and | do strange things.) _______________________________________________ | Haskell mailing list | Haskell(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell |

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minor H98 anomaly: class declarations
by Ross Paterson 27 May '02

27 May '02

4.3.1 has topdecl -> class [scontext =>] simpleclass [where cdecls] scontext -> simpleclass | ( simpleclass[1] , ... , simpleclass[n] ) (n>=0) simpleclass -> qtycls tyvar implying that the class being declared can be qualified: class Foo.C a where ... in contrast to every other kind of declaration. Nor does the text explain what this could mean. Shouldn't the first line be topdecl -> class [scontext =>] tycls tyvar [where cdecls] (GHC doesn't allow qualification; Hugs and Nhc allow it and do strange things.)

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Problem with FFI?
by John Meacham 26 May '02

26 May '02

I may be missing something obvious here, but from the current FFI spec it appears that it is impossible to create libraries in haskell which are meant to be called from c code without running into undefined behavior. The problem is in the definition of hs_init() and hs_exit() . now, it is acceptable to have hs_init and hs_exit called in the initialization and finalization of your library, but the problem arrises when you link against more than one library which is implemented in haskell, suddenly whichever library is initialized secondly segfaults! (or whatever undefined behaviour means.). programs could suddenly stop working when a library is changed from a c implementation to a haskell one, which seems to be a bad thing. proposed fix: allow nested calls to hs_init, hs_exit, a counter is incremented when hs_init is called more than once, and decremented on hs_exit. only the last call to hs_exit will actually do whatever needs to be done. note that this cannot be implemented by the programmer himself since there might be several third party libraries also implemented in haskell which an app wishes to link against. this is sort of a showstopper for people (like me!) who wish to just use haskell as an implementation language for a library which is meant to be called from C. but then again, perhaps i am missing something obvious. John -- --------------------------------------------------------------------------- John Meacham - California Institute of Technology, Alum. - john(a)foo.net ---------------------------------------------------------------------------

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Re: arrows
by David Feuer 25 May '02

25 May '02

I strongly suspect that arrows without arr could be quite useful... not sure about ones without first. -- Night. An owl flies o'er rooftops. The moon sheds its soft light upon the trees. David Feuer

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arrows
by Wolfgang Jeltsch 24 May '02

24 May '02

Hello, in his paper "Generalising monads to arrows" John Hughes introduces an Arrow class with the members arr and (>>>) and extends this with a member first. The Arrow module by Ross Paterson adopts the practice of including first in the Arrow class. Now, I have a type which would fit wonderfully into the Arrow concept if arrows wouldn't be expected to have a first operator. To be precise, I have a type Parser of kind * -> * -> * with Parser a b being a parser which reads from a list of tokens of type a and produces a value of type b. Parser a is an instance of Monad and MonadPlus, thus providing sequencing, handling of alternatives and the like. Now I want to implement scanners via my parser type. A scanner shall simply be described by a parser which parses one higher-level token from a stream of lower-level tokens. I want to provide a function of type Parser a b -> Parser b c -> Parser a c which constructs a parser which reads a value of type c from a stream of type a tokens by repeatedly invoking the first argument parser to produce higher-level tokens which are then consumed by the second argument parser in order to produce the final output. Of course this function looks like a candidate for being (>>>) in a Parser arrow. And there is also a meaningful definition for pure (arr). pure f just has to be a parser which reads exactly one token, applies f to it and outputs the resulting value. The problem is that there seems to be no appropriate definition for first. That's why, in my opinion, it would be very good to have only the members pure (arr) and (>>>) in Arrow and to define a subclass which adds first, similar to ArrowChoice which adds left. This would have also the advantage that the handling of first, second, (***) and (&&&) on the one hand, and the handling of left, right, (+++) and (|||) on the other would be totally analogous. What do you think of this approach? Are there any of you who think that modifying the Arrow module this way would be a good idea? I'm waiting for your comments. Wolfgang

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WFLP2002: Call for PARTICIPATION
by Marco Comini 24 May '02

24 May '02

=============================================================================== CALL FOR PARTICIPATION 11th International Workshop on Functional and (Constraint) Logic Programming Grado, Italy June 20 - 22, 2002 =============================================================================== Please find attached (in PDF format) the fully detailed CALL FOR PARTICIPATION. Here is a text-only summary. ------------------------------------------------------------------------------- GENERAL The 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. Recent edition of the workshop have been held in Kiel (Germany), Benicassim (Spain), Grenoble (France), Bad Honnef (Germany). This workshop aims to promote the cross-fertilizing exchange of ideas and experiences among researches and students from the different communities interested in the foundations, applications, software engineering techniques and combinations of high-level, declarative (constraint) programming languages and related areas. The technical program of the workshop will include invited talks, presentations of refereed papers and demo presentations. The WWW page of the workshop is http://www.dimi.uniud.it/~wflp2002/ ------------------------------------------------------------------------------- LOCATION WFLP 2002 will take place in Grado, Italy. Grado is an island located on the Adriatic coast in a beautiful lagoon. It is famous for its attractive beaches, for its Roman history, and for the pleasant middleuropean atmosphere. Venezia is 100 km away and Trieste is 60 km away. The Conference Site is: Hotel Diana Via G. Verdi, 3 I-34073, Grado (Gorizia), Italy Tel. +39 043 182 247 / +39 043 180 026 Fax. +39 043 183 330 http://www.hoteldiana.it/ ------------------------------------------------------------------------------- PROGRAM The workshop will be a 3-day event including presentations of the accepted papers, system demos, and 3 INVITED TALKS: Yike Guo: "Declarative Programming in the Post-Internet Era" Peter Thiemann: "Programmable Type Systems for Domain SpecificLanguages" Giorgio Delzanno: "Verification of logic programs based on constraints" ------------------------------------------------------------------------------- PROGRAM COMMITTEE Maria Alpuente (Technical University of Valencia) Sergio Antoy (Portland State University) Manuel Chakravarty (University of New South Wales, Sidney) Rachid Echahed (IMAG, Grenoble) Francois Fages (INRIA Rocquencourt) Moreno Falaschi (Univ. Udine, chair) Thom Fruewirth (LMU Munich) Robert Glück (Waseda Univ., Japan and DIKU, Denmark) Michael Hanus (CAU Kiel) Tetsuo Ida (University of Tsukuba) Helene Kirchner (Univ. Nancy) Herbert Kuchen (Univ. Muenster) Michael Maher (Loyola University Chicago) Juan Jose Moreno Navarro (UP Madrid) Ernesto Pimentel (Univ. Malaga) Mario Rodriguez-Artalejo (UC Madrid) ------------------------------------------------------------------------------- LOCAL ORGANIZING COMMITTEE Gianluca Amato Demis Ballis Marco Comini Luca Di Gaspero Agostino Dovier Moreno Falaschi Alicia Villanueva ------------------------------------------------------------------------------- Please find attached (in PDF format) the fully detailed CALL FOR PARTICIPATION. This was a text-only summary. We hope to see you in Grado, Best Regards, -- WFLP 2002 Organizing Committee http://www.dimi.uniud.ut/~wflp2002/

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CSMR 2003 - CALL FOR PAPERS
by csmr2003＠unisannio.it 24 May '02

24 May '02

Dear colleague: We would like to invite you to participate in the Seventh European Conference on Software Maintenance and Reengineering, which will be held in Benevento, Italy, March 26-28, 2003, and to submit a paper. ======================================================================== (Please apologize for multiple copies) Seventh European Conference on Software Maintenance and Reengineering Benevento, Italy March 26-28, 2003 http://rcost.unisannio.it/csmr2003 CALL FOR PAPERS CSMR is the premier European Conference on Software Maintenance and Reengineering. Its purpose is to promote both discussion and interaction about evolution, maintenance and reengineering. Topics of interest include, but are not restricted to: Evolution, maintenance and reengineering: + pattern languages + experience reports (successes and failures) + tools + enabling technologies + formal methods + system assessment + web-site Metrics and economics Software evolution and architecture recovery Migration and maintenance issues Dealing with legacy systems towards new technologies Wrapping and interfacing legacy systems Data reengineering Reverse engineering of embedded (control, mobile, ...) systems Evaluation and assessment of reverse engineering tools One of the basic intentions of this conference is to offer a European forum for discussion and exchange of experiences among researchers and practitioners. Therefore, besides academics, we kindly invite all those in companies developing maintenance tools, offering reengineering services or going through legacy systems migration experiences to contribute by submitting papers or presenting innovative tools, solutions or experience reports. This conference is not limited to European participants; authors from outside Europe are also welcomed. SUBMISSIONS: ============ IEEE Computer Society Press will publish the CSMR 2003 Proceedings. Two types of submissions will be accepted: full length papers (not exceeding 10 proceeding pages, IEEE Style) and short papers (not exceeding 4 proceeding pages, IEEE Style). All papers must be in English. Authors are requested to submit electronically a PostScript or PDF version of their papers. For submission details please look at the web site IMPORTANT DATES: ================ Deadline for submissions October 10, 2002 Author's notification November 27, 2002 Deadline for camera-ready of accepted papers December 20, 2002 SPECIAL SESSIONS: ================= Sessions of special interest proposed by delegates will be welcomed. Please send suggestions to the program chair before the submissions closing date. PROGRAM CHAIR: Mark van den Brand, CWI,The Netherlands e-mail: Mark.van.den.Brand(a)cwi.nl PROGRAM CO-CHAIR: Tibor Gyimóthy, University of Szeged, Hungary e-mail: gyimi(a)cc.u-szeged.hu GENERAL CHAIR: Gerardo Canfora, Research Centre on Software Technology, Italy e-mail: canfora(a)unisannio.it

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name of List.nub function
by Brian Huffman 24 May '02

24 May '02

Hi, This is just for fun, really, but does anyone know how the nub function from the standard List module got its name? (It is the function that removes duplicates from a list, in case you are not familiar with it.) I looked up the word "nub" in the online Merriam-Webster dictionary (www.m-w.com) and it gives: 1 : KNOB, LUMP 2 : NUBBIN 3 : GIST, POINT Then the entry for "nubbin" says: 1 : something (as an ear of Indian corn) that is small for its kind, stunted, undeveloped, or imperfect 2 : a small usually projecting part or bit 3 : NUB 3 So which sense of the word was the function named for? Could a list with stuff removed from it be considered "stunted"? Or maybe the set of unique elements from a list would be like the "main point" or "gist" of the list? If so, maybe "List.nub" could just as well have been named "List.gist" instead. Anyway, I'd be interested to learn anything about the history and naming of "nub", or any other library functions, for that matter. - Brian Huffman

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