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Re: Union Types for Haskell!?
by Pixel 24 Nov '00

24 Nov '00

Fergus Henderson <fjh(a)cs.mu.oz.au> writes: [...] > (2) Allow pattern matching on values of particular types, > using `case'. [...] > If we allow (2), then some programming mistakes that previously > were type errors would instead become just inexhaustive pattern > matches for which you get a run-time error. > > For example: > > foo :: Maybe a -> b -> Maybe b > foo x y = case list of > [] -> Nothing > (x:xs) -> Just x > where list = case x of > Nothing -> 0 -- oops, meant [] instead of 0 > Just foo -> [y] > > If union types were allowed, with (2) above, this example would be > legal, with `list' having the union type { [a], Integer }. if you disallow undeclared union types, you'll catch easily this kind of errors. > But `foo Nothing 42' would evaluate to bottom, since the `case list' > expression has no case with a pattern of type Integer. > > So allowing union types in this way would reduce static type safety, > at least unless we also forbid inexhaustive pattern matches. well allowing inexhaustive pattern matching always leads to less type safetyness, no news :) And of course subtyping also reduce type safetyness. But it is the same for type classes. No one is more safe than using '+' for integers and '+.' for floats... > > If instead you only allow (1), then probably union types would > not be suitable for expressing the kinds of things that you want > to express with them. sure, you don't win anything. > > > Is there any reason for this restriction > > in the Haskell type system? Does this lead to losing the principal type > > property? > > If you allow (2) above, there may be serious problems for > principal types. For example, consider > > f x = case x of > Nothing -> False > Just _ -> True > > What's the most general type for `f'? > The type `f :: Maybe a -> Bool' is less general than > e.g. `f :: Union { Maybe a, ... } -> Bool', > but you certainly don't want to infer the latter type. not necessarily. If you disallow undeclared union types, the only occurence of Union { Maybe a, ... } will be Maybe a, unless one really wants to extend Maybe... cu Pixel.

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Re: Union Types for Haskell!?
by Ashley Yakeley 24 Nov '00

24 Nov '00

At 2000-11-24 03:14, Fergus Henderson wrote: >> Is there any reason for this restriction >> in the Haskell type system? Does this lead to losing the principal type >> property? > >If you allow (2) above, there may be serious problems for >principal types. For example, consider > > f x = case x of > Nothing -> False > Just _ -> True > >What's the most general type for `f'? >The type `f :: Maybe a -> Bool' is less general than >e.g. `f :: Union { Maybe a, ... } -> Bool', >but you certainly don't want to infer the latter type. There are two different kinds of 'general' here. Informally, you want the type most general in the type-substitution sense, but probably most specific in the subtype sense. -- Ashley Yakeley, Seattle WA

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Four lectureships in Nottingham
by gmh＠marian.cs.nott.ac.uk 24 Nov '00

24 Nov '00

Dear all, We are currently advertising four new lectureships in Nottingham. There are no particular research areas specified for these positions, but applications in the area of the Languages and Programming research group (http://www.cs.nott.ac.uk/Research/lap/) would be most welcome. Graham Hutton ---------------------------------------------------------------------- THE UNIVERSITY OF NOTTINGHAM School of Computer Science and Information Technology Four Lectureships Applications are invited for the above posts in a rapidly-expanding School based at one of the UK's strongest research-led universities. The School was graded 4 in the 1996 Research Assessment Exercise and is now building up its research strengths for a further improvement in grade. These posts are part of a steady increase in the size of the School accompanied by a move to new purpose-built accommodation in September 1999. Although the successful candidates will have the opportunity of teaching within their specialist area at undergraduate and postgraduate level, there will also be a requirement to teach general computer science and information technology modules outside of any particular specialisation. Candidates should already have a PhD in computer science, or another closely related discipline, together with strong evidence of existing research work and the potential for future research at Grade 5 level. Outstanding candidates will be welcomed from any area of computer science. Salary will be within the range #18,731 - #30,967 per annum, depending on qualifications and experience. Informal enquiries may be addressed to Professor P H Ford, Head of School, tel: +44 (0)115 951 4251 or Email: Peter.Ford(a)Nottingham.ac.uk. Further information about the School is available on the WWW at: http://www.cs.nott.ac.uk. Further details and application forms are available from the Personnel Office, Highfield House, The University of Nottingham, University Park, Nottingham, NG7 2RD. Tel: +44 (0)115 951 5927. Fax: +44 (0)115 951 5205. Email: Carole.Matthews(a)Nottingham.ac.uk. Please quote ref. LEG/537. Closing date: 5 January 2001. ----------------------------------------------------------------------

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Release: Mondrian and Haskell for .NET
by Nigel Perry 23 Nov '00

23 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. Documentation is provided in the form of a paper and example programs, i.e. we haven't written proper documentation yet ;-) Also released is our first 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, in particular there is no support for floats, file I/O and other odds'n'ends. This will improve over time (have you looked at the GHC Prelude, it takes time!) Both compilers, demo 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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Parser Combinators in C
by Koen Claessen 23 Nov '00

23 Nov '00

Hi all, A while ago, I worked on a project where I was forced to write code in C. (Yuck!) One of the things that I wrote was a parser. I hate using yacc, so, in order to have some fun on my project, I decided to develop a parser combinator library in C! This would be a parser combinator library inspired by the monadic library described in Meijer's and Hutton's paper. Since then, I completely reimplemented the library, cleaning up the interface and adding new features to it. I started writing a little bit about it. A first draft can be found on: http://www.cs.chalmers.se/~koen/ParserComboC/parser-combo-c.html I thought it could be fun for Haskell programmers to see this. (One of the problems with this webpage is that I do not really know for who I am writing it...) So if you have any comments or suggestions, please tell me! Regards, Koen. PS. This is not a joke. Some people have looked at my code and thought nobody would ever be able to write code like that! Well, I wrote and used this code for real! :-) I guess we functional programmers are (considered to be) weird sometimes :-) :-) Or maybe it is just me... -- 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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Attn: Corporate Training Coordinator - Windows 2000 Courseware Content
by fibonaci＠smartt.com 22 Nov '00

22 Nov '00

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HAPPY QUESTION
by Franck Delaplace 21 Nov '00

21 Nov '00

I wish to test Happy. Where can I find an example the use of Happy ? Thank sfor your answer -- Franck Delaplace @w3:http://taillefer.lami.univ-evry.fr:8090/~delapla/ La.M.I-U.M.R C.N.R.S Université d'Evry Val d'Essonne Cours Monseigneur Roméro 91025 Evry CEDEX (France)

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Static Analysis Symposium 2001, Paris : 1st CfP
by Radhia Cousot 21 Nov '00

21 Nov '00

========My apologies for duplicates of this announcement========= ================================================================= = = = First Call For Papers = = = = 8th INTERNATIONAL STATIC ANALYSIS SYMPOSIUM = = = = = = La Sorbonne, Paris = = 16-18 July, 2001 = = = = http://www.ens.fr/sas01/ = = = ================================================================= Static Analysis is increasingly recognized as a fundamental technique for high performance implementations and verification systems of high-level programming languages. The series of Static Analysis Symposia has served as the primary venue for presentation of theoretical, practical and applicative in the area. The Eigth International Static Analysis Symposium (SAS2'01) will be held at La Sorbonne in Paris and followed immediately at La Mutualite by the Thirteenth Conference on Computer Aided Verification (CAV'01, http://www.lsv.ens-cachan.fr/cav01/}. Previous symposia were held in Santa Barbara, Venice, Pisa, Paris, Aachen, Glasgow and Namur. The technical program for SAS'01 will consist of invited lectures, tutorials, panels, presentations of refereed papers, and software demonstrations. Contributions are welcome on all aspects of Static Analysis, including, but not limited to abstract interpretation data flow analysis verification systems optimizing compilers abstract domains program specialization theoretical frameworks type inference abstract model checking complexity analysis abstract testing security analysis Submissions can address any programming paradigm, including concurrent, constraint, functional, imperative, logic and object-oriented programming. Survey papers that present some aspect of the above topics with a new coherence are also welcome. Submitted papers must not substantially overlap with papers that have been published or that are simultaneously submitted to a journal or a conference with a refereed proceedings. Submitted papers should be at most 15 single space 11-point font pages excluding bibliography and well-marked appendices. Program committee members are not required to read any appendices, and so a paper should be intelligible without them. The papers should be submitted as PostScript documents that are interpretable by Ghostscript and/or in PDF format, and they must be printable on both US letter and A4 paper; to facilitate this, extensive use of special fonts and colors should be avoided. Submissions should arrive by February 15, 2001. All submissions must be done electronically at http://www.ens.fr/sas01/. Authors will be notified of the acceptance or rejection of their papers by April 2, 2001. Final versions of the accepted papers must be received in electronic form by April 30, 2001. Important Dates: Submission: February 15, 2001. Notification: April 2, 2001. Final Version: April 30, 2001. Program Chair: Patrick Cousot Ecole Normale Superieure Departement d'Informatique 45, Rue d'Ulm 75230 Paris Cedex 05, France Email: sas01(a)ens.fr Phone: & + 33 1 44 32 20 64 Fax: & + 33 1 44 32 21 52 Program Committee: M. Bruynooghe (KU, Leuven) P. Cousot (ENS, Paris) G. Fil'e (Padova) M. Hagiya (Tokyo) C. Hankin (IC, London) L. Hendren (McGill, Montreal) M. Hermenegildo (UPM, Madrid) N. Jones (DIKU, Denmark) J. Larus (Microsoft, Redmond) J. Palsberg (Purdue) S. Sagiv (Tel Aviv) D. Sands (Chalmers, Goteborg) D. Schmidt (Kansas S.) M.L. Soffa (Pittsburgh) H. Sondergaard (Melbourne) R. Wilhelm (Saarbruken) K. Yi (KAIST, Taejon) General Chair: Radhia Cousot CNRS & Ecole polytechnique rcousot(a)lix.polytechnique.fr

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CFP: "Information Stucture, Discourse Structure and Discourse Semantics" -Workshop at ESSLLI 2001
by Ivana Kruijff-Korbayova 21 Nov '00

21 Nov '00

We apologize if you receive multiple copies. %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %% %% %% CALL FOR PAPERS %% %% %% %% ESSLLI Workshop on %% % Information Stucture, Discourse Structure and Discourse Semantics % %% %% %% http://www.cogsci.ed.ac.uk/~ivana/esslli01-wsh/ %% %% %% %% %% %% August 20-24, 2001 %% %% %% %% Helsinki, Finland %% %% %% %% The workshop is endorsed by SIGSEM: http://www.sigsem.org/ %% %% %% %% ESSLLI: http://www.helsinki.fi/esslli %% %% %% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% BRIEF MISSION STATEMENT: --------------------------------------------- This workshop aims to provide a forum for recent research on interactions between information structure (as a component of sentence-level semantics), discourse structure and discourse-level semantics. Both Information Structure (IS) and Discourse Structure (DS) are construed broadly here: -- IS, as comprising structural and semantic properties of utterances relating to the discourse status of their content, the actual and attributed attentional states of the discourse participants, and the participants' prior and changing attitudes. -- DS, as covering all aspects of the internal organizational structure of a discourse, an essential aspect being the use of explicit and implicit devices signifying links between clause and sentences. Understanding IS in light of DS and vice versa is not only justified on theoreticalgrounds: Experience with applications such as translating telephony and interactive query-answering makes it clear that a theory relating IS and DS is essential for accurate Natural Language Processing. The workshop aims to attract researchers in computational and theoretical linguistics and logic who are investigating IS-sensitive discourse processing and to facilitate contact, exchange of ideas and cooperation between them. We hope that the participants will transcend the difficulties caused by proliferating terminologies, and concentrate instead on investigating the interactions between IS and DS, with the goal of understanding how sentence-level semantic devices that make up IS symbiotically serve the needs of discourse cohesion and coherence. We seek contributions advancing beyond descriptive frameworks towards an explanatory account of how IS and DS, in whatever framework, interact to refer to and update a dynamically evolving representation of discourse context. The submitted papers will be refereed by the PC. See http://www.cogsci.ed.ac.uk/~ivana/esslli01-wsh/ for more details. SUBMISSION GUIDELINES: ----------------------------------------- Full papers addressing the above issues are solicited, not exceeding 5000 words including references. Each paper must contain a 5-10 lines abstract. A postscript or pdf version of the paper should be submitted (zipped) by e-mail to ivana(a)cogsci.ed.ac.uk by the submission deadline given below. In an accompanying email message, please provide the following information: Paper title: Contact author: Email(s): 5-10 lines abstract: We strongly encourage the use of LaTeX. The workshop proceedings will be prepared using LaTeX and authors will be required to provide the final versions of their papers in LaTeX. IMPORTANT DATES: ------------------------------- March 30 Submission deadline April 30 Notifications of acceptance/rejection to authors May 20 Final version of papers in LaTeX for the proceedings due August 20-24 Workshop dates Note that all workshop participants must register as particpants of ESSLLI. The early registration fees apply to authors of accepted papers. PROGRAMME COMMITTEE: ------------------------------------------ Ivana Kruijff-Korbayova (organizer, co-chair) Mark Steedman (organizer, co-chair) John Bateman Daniel Buering Elisabet Engdahl Bart Geurts David Traum Maria Vilkuna Bonnie Webber We are looking forward to your submissions :-) -------------------------------------------------------------------------- ing. Ivana Kruijff-Korbayova, Dr. Center for Computational Linguistics ICCS, Division of Informatics Charles University University of Edinburgh Malostranske nam. 25. 2 Buccleuch Place 118 35 Praha 1 Edinburgh, EH8 9NW Czech Republic Scotland tel. 00420 - 2 - 2191 4288 tel. +44-(0)-131-6504412 fax. 00420 - 2 - 2191 4309 fax. +44-(0)-131-6506626 korbay(a)ufal.mff.cuni.cz ivana(a)cogsci.ed.ac.uk -------------------------------------------------------------------------

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Origins of the G-Machine
by Frank Atanassow 20 Nov '00

20 Nov '00

At the Sunday Times website, there is a very odd story about the recovery of the Enigma machine stolen from Bletchley Park. http://www.sunday-times.co.uk:80/news/pages/sti/2000/11/19/stinwenws02039.h… It includes this fun fact, which Haskellers may find of interest: Enigma machines vary and the official designation of this one is a Type G, or the G-machine; it was sometimes called the counter machine or "Zahlwerk-Enigma", because it has a letter counter. Will this hinder the adoption of Haskell compiler technology in France and Israel...? -- Frank Atanassow, Information & Computing Sciences, Utrecht University Padualaan 14, PO Box 80.089, 3508 TB Utrecht, Netherlands Tel +31 (030) 253-3261 Fax +31 (030) 251-3791

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