- Haskell - Haskell.org

Gaussian Integers
by dominic.j.steinitz＠britishairways.com 19 Mar '02

19 Mar '02

On holiday, I started reading about Gaussian integers (as you do) and I thought this should be a piece of cake for Haskell. I get the following error in Hugs: ERROR "D:\Temp\comptst2.hs" (line 4): Cannot build superclass instance *** Instance : Num (Gaussian a) *** Context supplied : () *** Required superclass : Eq (Gaussian a) and a similar one using GHCi: Could not deduce `Eq b' from the context () Probable fix: Add `Eq b' to the instance declaration context arising from an instance declaration at comptst1.hs:4 I've already declared Gaussian a as being of class Eq so why does it need to be told again? data Integral a => Gaussian a = Gaussian a a deriving (Eq, Show) instance Num (Gaussian a) where Gaussian a b - Gaussian a' b' = Gaussian (a-a') (b-b') Gaussian a b + Gaussian a' b' = Gaussian (a+a') (b+b') Gaussian a b * Gaussian a' b' = Gaussian (a*a' - b*b') (a*b' + b*a') negate (Gaussian a b) = Gaussian (negate a) (negate b) fromInteger a = Gaussian (fromIntegral a) 0

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Re: Strictness!
by cwitty＠newtonlabs.com 19 Mar '02

19 Mar '02

Jay Cox <sqrtofone(a)yahoo.com> writes: > On Thu, 14 Mar 2002, Brian Huffman wrote: > > > In Haskell you can produce the desired behavior by using pattern guards. > > Since the pattern guards always get evaluated before the result does, they > > can be used to make things more strict. Here is the foldl example: > > > > strict x = seq x True > > > > foldl' :: (a -> b -> a) -> a -> [b] -> a > > foldl' f z [] = z > > foldl' f z (x:xs) > > | strict z = foldl' f (f z x) xs > > > > You can make multiple arguments strict by using && or similar, e.g.: > > > > f x y | strict x && strict y = ... > > f x y | all strict [x,y] = ... > > > > Of course, with the second example x and y must have the same type. > > Hope this helps. > > > > - Brian Huffman > > Thanks! that looks like a great haskell idiom to use! > > Jay Cox I also like this for trace: f x y | trace (show (x, y)) True = ... (Putting the trace on a separate line like that makes it easy to comment out.) Or, if you've got a function with a lot of cases, you can trace all of them by adding: f x y | trace (show (x, y)) False = undefined above all the other cases. Carl Witty

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Hello
by promos＠motolev.com 18 Mar '02

18 Mar '02

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Haskell slicing tool?
by senganb＠ia.nsc.com 18 Mar '02

18 Mar '02

Are there any tools to perform program slicing on Haskell? I often find myself wanting to find all "fromJusts" invoked from the current function, or all functions that use a particular member of my monad's ADT. Sengan

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Haskell 98 report: March release
by Simon Peyton-Jones 18 Mar '02

18 Mar '02

Folks Before I get buried in ICFP submissions I thought I should get out the H98 report draft. It's in the usual place: http://research.microsoft.com/~simonpj/haskell98-revised Main changes since the Dec release are: Much improved informal semantics of pattern matching (3.17). Minor changes to the lexical syntax for white space (!). Two extra productions for expressions, which makes the treatment of sections align with the text in 3.5. Add notes in three places about hard-to-parse constructs. This is my eventual solution to some dark corners in the grammar (Chapter 3). Allow duplicates in the subordinate names of export lists (5.2). Remark that Eq and Ord are strict in both arguments (Appendix D.1). plus quite a few other minor corrections. As ever, your careful proofreading, esp of the new parts, would be most helpful.

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PhD studentship in Nottingham
by Graham Hutton 18 Mar '02

18 Mar '02

Dear all, I'm seeking applicants for a PhD studentship in the area of functional programming, to start on 1st October 2002 for a period of three years. You will normally require a first-class Honours degree (or equivalent qualification) in Computer Science and/or Mathematics, and some experience of functional programming. If you are interested in the possibility of such a PhD position, in the first instance please email your full CV, including the results of all your university examinations to date. Best wishes, Graham +---------------------------------------------------------------------+ | Dr Graham Hutton Email : gmh(a)cs.nott.ac.uk | | Foundations of Programming Group Web : www.cs.nott.ac.uk/~gmh | | School of Computer Science and IT | | University of Nottingham | | Jubilee Campus, Wollaton Road | | Nottingham NG8 1BB Phone : +44 (0)115 951 4220 | | United Kingdom Fax : +44 (0)115 951 4254 | +---------------------------------------------------------------------+

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Reminder: GCSE/SAIG Submissions
by Don Batory 18 Mar '02

18 Mar '02

Please excuse multiple listings of this announcement. CALL FOR PAPERS Submission Deadline: March 21, 2002 The First ACM SIGPLAN/SIGSOFT Conference on Generators and Components (GCSE/SAIG'02) Supported by the National Science Foundation (NSF) Pittsburgh, PA, October 6-8, 2002. http://www.cs.yale.edu/~taha/gcse-saig/cfp02.html Invited Speakers: * Neil Jones, University of Denmark * Catuscia Palamidessi, Penn State University * Janos Sztipanovits, Vanderbilt University Program generation has the prospect of being an integral part of a wide range of software development processes. Many recent studies investigate different aspects of program generation, including their semantics, their application, and their implementation. Existing theories and systems address both high-level (source) language and low-level (machine) language generation. A number of programming languages now support program generation and manipulation, with different goals, implementation techniques, and targeted at different applications. The goal of this conference is to provide a meeting place for researchers and practitioners interested in this topic. A particular area of interest is component-based software development, which bears the promise of considerable productivity increases to software development comparable to the introduction of the assembly line in manufacturing. But due to the very same sophistication that makes components useful, their maintenance can be hard. Generative programming presents a promising approach to alleviating the above problems, as changes affecting components can now be more effectively managed during the generation process rather than at the component level. The goal of this joint event is to foster further cross-fertilization between the software engineering research community on the one hand, and the programming languages community on the other, in addition to supporting the original research goals of both GCSE and SAIG communities. We seek papers both in software engineering and programming languages, and especially those that bridge the gap. Being accessible to both communities at the same time is also valued. The conference solicits submissions related (but not limited) to: * Generative Programming: Reuse, meta-programming, partial evaluation, multi-stage and multi-level languages, * Semantics, type systems, symbolic computation, linking and explicit substitution, in-lining and macros, templates, program transformation, * Runtime code generation, compilation, active libraries, synthesis from specifications, development methods, generation of non-code artifacts, formal methods. Reflection. * Component-Based Software Engineering: Reuse, distributed platforms, distributed systems, evolution, analysis and design patterns, development methods, formal methods * Integration of Generative and Component-Based Approaches * Domain Engineering, analysis, and languages * Separation of Concerns: Aspect-Oriented Programming, Intentional * Programming, and Multi-Dimensional Separation of Concerns * Product Lines and generic architectures for that purpose. * Industrial Applications of Components and Generative Programming Reports on applications of these techniques to real-world problems are especially encouraged, as are submissions that relate ideas and concepts from several of these topics, or bridge the gap between theory and practice. The program committee is happy to advise on the appropriateness of a particular subject. General Chair: Walid Taha, Yale University, USA. Program Chair (GCSE focus): Don Batory, University of Texas at Austin, USA. Program Chair (SAIG focus): Charles Consel, INRIA, LaBRI, France. Program Committee (GCSE focus): Jan Bosch , University of Groningen Greg Butler, Concordia University Prem Devanbu, University of California at Davis Cristina Gacek, University of Newcastle upon Tyne Stan Jarzabek, National University of Singapore Kyo Kang, Pohang University of Science and Technology Peter Knauber, Fraunhofer Institute for Experimental Software Engineering Hausi Muller, University of Victoria Nenad Medvidovic, University of Southern California Wolfgang Pree, University of Constance Yannis Smaragdakis, Georgia Institute of Technology Douglas R. Smith , Kestrel Institute Program Committee (SAIG focus): Craig Chambers, University of Washington Shigeru Chiba, Tokyo Institute of Technology Pierre Cointe, Ecole des Mines de Nantes Dawson Engler, Stanford University Siau cheng Khoo, National University of Singapore Gregor Kiczales, University of British Columbia Martin Odersky, Ecole Polytechnique Fédérale de Lausanne Calton Pu, Georgia Institute of Technology Peter Thiemann, Universität Freiburg Andrew Tolmach, Portland State University Submission Details: Authors are invited to submit papers of at most 5000 words (excluding figures), in postscript format (letter or A4), using the electronic submission form by March 21st, 2002. This deadline is firm. Both position and technical papers are welcome (Please indicate at time of submission.) Authors will be notified of acceptance by May 14th, 2002. Final version of the papers must be submitted by July 14, 2002. Format: The three day conference will contain slots for technical papers (45 minutes) and position papers (30 minutes). Both times include discussion. Position papers are expected to describe important future directions, ongoing work, and survey previous results. This category is best thought of as one for "competitive invited papers". Technical papers are expected to contain novel results. All papers will be reviewed by the program committee for the above-mentioned criteria, in addition to correctness and clarity. Simultaneous submission to other venues is not allowed, as is submission of previously published material. In addition, there will be time allocated for open discussions at the end of the conference. Proceedings will be published as an LNCS volume. Special Note on Combined Event: While the Program Committee is divided into two focus areas corresponding the parent events (GCSE and SAIG), there will be one unified program committee meeting. At the time of submission, authors must indicate whether they intend the paper for the GCSE audience, SAIG audience, or BOTH. The last category is the default, and is strongly encouraged. Papers submitted explicitly to only one focus will be accepted or rejected by the respective Program Chair. For papers submitted to BOTH, it is enough that one of the two Program Chairs accepts the paper. All members of the PC will allowed to bid for and review all papers, and cross-bidding is encouraged. The conference itself will not be divided along focus lines. Rather, an attempt will be made to ensure that each session is of interest to both parent communities.

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Functional and Declarative Programming in Education (FDPE02)
by S.J.Thompson 18 Mar '02

18 Mar '02

Functional and Declarative Programming in Education (FDPE02) A one day workshop at PLI'02 Monday 7 October 2002, Pittsburgh, PA, USA CALL FOR SUBMISSIONS Functional and declarative programming plays an increasingly important role in computing education at all levels. The aim of this workshop is to bring together educators and others who are interested in exchanging ideas on how to use a functional or declarative programming style in the classroom. Submissions are sought in a variety of forms, including: - Standard presentations (30 minutes) - Short talks or "tricks of the trade" presentations (10 minutes) The organisers would also welcome other sorts of submissions, such as software demos, panels, very short talks and so on. Michael Hanus, University of Kiel, Germany Shriram Krishnamurthi, Brown University, RI, USA Simon Thompson, University of Kent, UK More details at the FPDE02 website: FDPE02: http://www.cs.ukc.ac.uk/people/staff/sjt/fdpe02/description.html PLI'02: http://pli2002.cs.brown.edu/

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Final CFP: Unification in non-classical logics
by Manuel Ojeda Aciego 18 Mar '02

18 Mar '02

======================================================================= We apologize if you receive this more than once ======================================================================= Final call for papers Unification in Non-Classical Logics --co-located with ICALP 2002-- July, 12-13, 2002, Málaga, Spain http://www.satd.uma.es/aciego/icalp-ws.html ======================================================================= The workshop on Unification in Non-Classical Logics will be held in Málaga, as a workshop of the 29-th International Colloquium on Automata, Languages, and Programming (ICALP 2002), which is a very convenient forum for an open discussion of the subject of non-canonical unification, roughly depicted below. Aims and scope -------------- Unification in non-classical logics, with various approaches to handling generalised terms, has drawn more and more attention in recent years. It turns out to be among the most promising areas of research on non-classical logics and its applications. So far, most popular lines of research include fuzzy unification of (conventional) databases and the use of fuzzy concepts in information retrieval. Some international events based on these topics have been held so far, for instance, the 2nd Intl Workshop on Logic Programming and Soft Computing (LPSC'98), or the special session on Advances in Possibilistic Logic and Related Issues at the IFSA Congress in Vancouver, Canada (2001), have non-classical unification among their topics. This workshop at ICALP is conceived as a forum for the exchange of ideas relevant for the concept of unification in non-classical logics, including, but not limited to, the following topics (practical implementations and experiences as well as theoretical advances): * Unification in multiple-valued and fuzzy logic programming. * Unification based on similarities and fuzzy equivalence relations. * Categorical unification. * Practical use of non-classical unification, e.g. in expert systems and information retrieval. We expect potential participants from the following areas: multiple-valued logic, fuzzy logic, uncertainty in logic programming, categorical applications to computer science. The workshop will have a limited number of presentations and the organizers will apply a refereeing procedure accordingly. The format will be as a set of presentations followed by a round table discussion. As the number of participants is estimated not to be very large, time enough will be allocated for each presentation (between 30 and 40 minutes), thus helping to have a relaxed workshop atmosphere in which discussions are encouraged. Submission ---------- Authors are invited to submit an extended abstract of their papers, presenting original contributions to the workshop themes. The workshop proceedings will be published as an issue in the ENTCS series (Electronic Notes on Theoretical Computer Science). Submissions should be written in English and not exceed 15 pages using the ENTCS style, and sent to the organizers in either PS or PDF form, together with a text-only message containig: title, abstract and keywords, the author's full names, and address and e-mail for correspondence. Simultaneous submission to other meetings with published proceedings is not allowed. Important dates --------------- * 20.03.2002 Workshop paper submission deadline * 21.04.2002 Workshop paper acceptance notification * 10.05.2002 Workshop paper camera-ready deadline Organizing Committee -------------------- Patrik Eklund Manuel Ojeda-Aciego Dept. Computing Science Dept. Matematica Aplicada Umea University Universidad de Malaga mailto:peklund@cs.umu.se mailto:aciego@ctima.uma.es ----------------------------------------------------------

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RE: Standard Library report: List union
by Simon Peyton-Jones 17 Mar '02

17 Mar '02

There's a remark at the beginning of 7.2 that says: delete, (\\), union and intersect preserve the invariant that lists don't contain duplicates, provided that their first argument contains no duplicates. The same applies to unionBy etc. This design is one you might reasonably disagree with. I'd have thought it would be more sensible to have the invariant that *both* arguments to union and intersect are assumed to be sets (no dups). But I don't propose to change this now. Simon | -----Original Message----- | From: Jay Cox [mailto:sqrtofone@yahoo.com] | Sent: 05 March 2002 01:51 | To: Jon Fairbairn | Cc: haskell(a)haskell.org | Subject: Re: Standard Library report: List union | | | On Mon, 4 Mar 2002, Jon Fairbairn wrote: | | > The current library report defines unionBy like this: | > | > unionBy eq xs ys = xs ++ deleteFirstsBy eq (nubBy eq ys) xs | > | > why does it take the nub of ys, but not xs? I'd have expected | > | > unionBy eq xs ys = (nubBy eq xs) ++ deleteFirstsBy eq | (nubBy eq ys) | > xs | > | > Jón | | Pure guess, but... (no really!) | | | For the sake of argument, lets define a ulist as a list where | for all elements x in list l, there is no element n with | index not equal to that of x (index being position of the | element in the list) such that eq n x == True. | | In other words every element in a ulist appears only once. | | Suppose you (unionBy eq x y) to get a result. | Suppose also that x is a ulist | A. x is a ulist by argument. | B. the result of (nubBy eq ys), lets call it z, is a ulist. | C. the result of (deleteFirstsBye eq z xs) is a list which | has no elements in common with xs). because (deleteFirstsBy | eq) "deletes" elements and doesnt add,the result is a ulist. | D. Adding new, unique, elements (elements not equal to a | element in the ulist in question) to a ulist results in a | ulist. E. Therefore (unionBy eq x y) is a ulist. | | | Why should this be important? | | what if you wanted to fold the function (unionBy eq) over a | list of lists to get a ulist? Assuming you start with an | initial ulist, by your suggestion you'd be applying (nubBy | eq) to a ulist (generated by the the repeated application | (unionByeq), which would be the same as applying the identity | function to a ulist. (meaning you have essentially one big | nasty no-op)! | | | However, in taking a look at unionBy, one might wonder why it | isnt defined like so (assuming xs would be the accumulated | ulist in the fold. | | | unionBy eq xs ys = (deleteFirstsBy eq (nubBy eq ys) xs) ++ xs | | or maybe better (to mirror (++)) | | unionBy' eq ys xs = (deleteFirstsBy eq (nubBy eq ys) xs) ++ xs | | in using this definition, the number of conses with (:) | should be linear (or less) with with the number of elements | to be added to the first_ulist in the following folds. | | | foldl (unionBy eq) first_ulist list_of_lists | foldr (unionBy' eq) first_ulist list_of_lists | | So, is there aother reason I cannot think of? I'm sure I | haven't covered all bases here. | | Thanks, | | Jay Cox | | _______________________________________________ | Haskell mailing list | Haskell(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell |

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