November 2003 - Haskell

ANNOUNCE: HC&A Report (5th edition, November 2003)
by C.Reinke 11 Nov '03

11 Nov '03

On behalf of the many contributors, I am happy to announce that the ----------------------------------------- Haskell Communities and Activities Report (5th edition, November 2003) http://www.haskell.org/communities/ ----------------------------------------- is now available from the Haskell Communities home page in several formats: in PDF (for those who haven't noticed: that format is not just for printing, but also for online viewing, with working links and table of contents) or, for those who have problems with the PDF, in HTML (using John's secret weapon yet again) and Postscript. A big thanks here to everyone who contributed, be it by making sure that there are so many interesting activities to report on, or by sending in descriptions to make sure that we can read about these activities! I hope you will find it as interesting to read as we did. For those of you who haven't heard of these reports before (and have filtered all previous calls into the spam-folder..), the first edition of the HC&A Report was released in November 2001, with the goal of helping to improve the communication between the increasingly diverse groups, projects, and individuals working on, with or inspired by Haskell. The idea of these reports is simple: Every six months, a call goes out to all of you on the Haskell mailing list to contribute brief summaries of your own area of work. Many of you respond (eagerly, unprompted, and well in time for the deadline;-) to the call. The editor then collects all these into a single report and feeds it back to this very mailing list. And when we try for the next update in six months, you might want to add your own work, project, research area or group as well. So, please, put that item into your diary now! --------------------------------------- End of April 2004: target deadline for contributions to the May 2004 edition of the HC&A Report --------------------------------------- It has become clear that many Haskellers who work on interesting projects no longer have the time to follow the Haskell mailing list closely and may thus miss the calls for contribution. If you are a member, user or friend of such projects, please point them to the current edition, and invite them to "register" with me for a simple email-reminder in the middle of April (and no, you can't register anyone else:). Of course, they'll still have to act on that reminder, but perhaps we can extend our reach this way.. Enjoy (and communicate;-)! Claus Reinke -- Computing Laboratory University of Kent http://www.cs.kent.ac.uk/~cr3/ PS. Please note the preface: as announced at this year's Haskell workshop, there'll be a change of editor after this edition. Andres Loeh has kindly offered to take over starting with the November 2004 edition, but we are still looking for someone to take on the May 2004 edition. If you're interested, please get in touch with me!

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A question about monads
by Ryoko Nanase 11 Nov '03

11 Nov '03

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neat trick: parallel show
by John Meacham 11 Nov '03

11 Nov '03

while working on a random project, I had opprotunity to write a 'parallel show' which concurrently evaluates everything needed to show a structure and lets you print succesivly refined versions as vaules are calculated and filled in. it is nice because a value that takes a long time (or perhaps forever) to evaluate at the front of your structure doesn't keep you from seeing what else is in it. I must say it has been a very useful little bit of code so thought I might share the concept and was curious if anyone else does things like this.. it works something like foo = [Right "foo", Left undefined, undefined, Right "here"] parShow (parPretty foo) >>= putStrLn => "(Right foo) (Left _|_) _|_ (Right here)" and succesive calls to parShow will fill in the _|_ values as they get evaluated. my attached implementation is rather weak (my real one is tied into a project and does wierd things with ANSI escape codes to redraw the screen as things get evaluated and handles exceptions differently) but the gist is the same. would people be interesting in me( or someone else :) ) turning this into a full fledged library? does one alreoady exist which does this? I was thinking integrating it into a real pretty printing system would be handy but might be too much work, if there were a way to reuse an existing pretty printing library without change and somehow add this capability then that would be cool. I couldn't think of a way to do it since the final 'render' routine obviously needs to be in the IO monad so the MVars can be checked again when rerendering.. John -- --------------------------------------------------------------------------- John Meacham - California Institute of Technology, Alum. - john(a)foo.net ---------------------------------------------------------------------------

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CfP: ESSLLI'04 Student Session
by Paul Egré 10 Nov '03

10 Nov '03

CALL FOR PAPERS ESSLLI-2004 STUDENT SESSION 9-20 August, 2004 in Nancy, France Deadline: February 22, 2004 http://esslli2004.loria.fr/ We are pleased to announce the Student Session of the 16th European Summer School in Logic, Language and Information (ESSLLI-2004), which will be held in Nancy from August 9-20, 2004. We invite submission of papers for presentation at the ESSLLI-2004 Student Session and for appearance in the proceedings. PURPOSE: This ninth ESSLLI Student Session will provide, like the previous editions, an opportunity for ESSLLI participants who are students to present their own work in progress and get feedback from senior researchers and fellow-students. The ESSLLI Student Session encourages submissions from students at any level, undergraduates (before completion of the Master Thesis) as well as postgraduates (before completion of the PhD degree). Papers co-authored by non-students will not be accepted. Papers may be accepted for full presentation (30 minutes including 5 to 10 minutes of discussion) or for a poster presentation. All the accepted papers will be published in the ESSLLI-2004 Student Session proceedings, which will be made available during the summer school. REQUIREMENTS: The Student Session papers should describe original, unpublished work, completed or in progress, that demonstrates insight, creativity, and promise. No previously published papers should be submitted. We welcome submissions with topics within the areas of Logic, Language and Computation. SUBMISSION DETAILS: Student authors are invited to submit a full paper, not to exceed 7 pages of length exclusive of references. Note that the length of the final version of the accepted papers will not be allowed to exceed 10 pages. The submissions will be reviewed by the student session programme committee and additional reviewers. A plain ASCII text version of the identification page should be sent separately, using the following format: Title: title of the submission First author: firstname lastname Address: address of the first author ...... Last author: firstname lastname Address: address of the last author Short summary: abstract (5 lines) Subject area (one or two of): Logic | Language | Computation In case the paper is being submitted to another conference or workshop, this must be clearly indicated on the identification page. The preferred formats of submissions are PostScript, PDF, or plain text, although other formats will also be accepted. In case of acceptance, the final version of the paper will have to be submitted in LaTeX format. The papers must use single column A4 size pages, 11pt or 12pt fonts, and standard margins. Submissions not in accordance with the specified formatting and length requirements may be subject to rejection without review. The paper and separate identification page must be sent electronically to: paulegre(a)magic.fr by FEBRUARY 22, 2004. PROGRAMME COMMITTEE: Laura Alonso i Alemany (Universitat de Barcelona, Barcelona) Carlos Areces (LORIA, Nancy) Jaume Baixeries (Universitat Politècnica de Catalunya, Barcelona) Willem Comradie (Rand Afrikaans University, South Africa) Benoit Crabbé (LORIA, Nancy) Paul Egré (IHPST, Université Paris 1, IJN) Judit Gervain (SISSA, Trieste) Bart Geurts (University of Nijmegen, Nijmegen) Ivana Kruijff-Korbayova (Universität des Saarlandes, Saarbrücken) Marco Kuhlmann (Universität des Saarlandes, Saarbrücken) Mª Magdalena Ortiz de la Fuente (Universidad de las Americas, Puebla) Benjamin Spector (Laboratoire de Linguistique Formelle, Université Paris 7, ENS) IMPORTANT DATES: Deadline for submission of papers : February 22, 2004. Authors notifications : April 19, 2004. ESSLLI early registration : May 1, 2004. Final papers for proceedings : May 15, 2004. ESSLLI-2004 Student Session : August 9-20, 2004. ESSLLI-2004 INFORMATION: In order to present a paper at ESSLLI-2004 Student Session, at least one student author of each accepted paper has to register as a participant at ESSLLI-2004. The authors of accepted papers will be eligible for reduced registration fees even after the deadline for early registration. For all information concerning ESSLLI-2004, please consult the ESSLLI-2004 main website at http://esslli2004.loria.fr/ For more information about the ESSLLI'04 student session, consult the ESSLLI'04 student session website at: http://lingua.fil.ub.es/~lalonso/stusESSLLI04/. If you have any further question about the student session, do not hesitate to contact us: Laura Alonso i Alemany Paul Egré lalonso(a)fil.ub.es paulegre(a)magic.fr Departament de Lingüística General IHPST / Université Paris 1 / Institut Jean-Nicod Gran Via de les Corts Catalanes, 585 Institut d'Histoire et de Philosophie des Sciences et Techniques Universitat de Barcelona 13, rue du Four Barcelona, SPAIN 75006 Paris, FRANCE telephone number: +34 93 403 56 93 telephone number: + (33) (0)1 43 54 60 36 fax number: +34 93 318 98 22 fax number: + (33) (0)1 44 07 16 49

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Inspecting reduced/optimized code
by andrew cooke 10 Nov '03

10 Nov '03

Is it possible/easy in any of the compilers/interpreters to see what the results of rewriting/optimisations are? (I'm sure it is *possible*, I'm really asking if any produce simple output in a well documented format that I'm likely to understand). The reason I ask is because I'm curious whether the "well known" fold (foldr) (I don't have it to hand, but it's something like fold (\x g -> \n -> g x n) id) that is equivalent to foldl generates the same code as foldl itself (ie defined recursively). I know I can do timing, or look at the C code from GHC, which would tell me whether they are identical, I guess, but I was hoping for something higher level (I suupose transformed Haskell code is too much to ask for?). Should I be looking at some kind of debugging tool (never used a debugger in Haskell)? Thanks, Andrew PS Despite its sweet naivete, this post comes from a balding middle aged programmer looking for something to relieve the tedium of working shifts away from home, and not some grasping, lazy, evil student that wants to save time on homework to indulge in yet more wild, drunken orgies [sighs wistfully, looks at clock, gets back to work...]. -- http://www.acooke.org/andrew

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Preliminary CFP: GPCE'04 -- Generative Programming and Component Engineering
by Eelco Visser 09 Nov '03

09 Nov '03

PRELIMINARY CALL FOR PAPERS ---------------------------------------------------------------------- Third International Conference on Generative Programming and Component Engineering (GPCE'04) Vancouver, October 24-28, 2004 co-located with OOPSLA 2004 http://gpce04.gpce.org ---------------------------------------------------------------------- ------------------------------------ Scope ------------------------------------ Generative and component approaches have the potential to revolutionize software development in a similar way as automation and components revolutionized manufacturing. Generative Programming (developing programs that synthesize other programs), Component Engineering (raising the level of modularization and analysis in application design), and Domain-Specific Languages (elevating program specifications to compact domain-specific notations that are easier to write and maintain) are key technologies for automating program development. GPCE arose as a joint conference, merging the prior conference on Generative and Component-Based Software Engineering (GCSE) and the Workshop on Semantics, Applications, and Implementation of Program Generation (SAIG). The goal of GPCE is to provide a meeting place for researchers and practitioners interested in cutting edge approaches to software development. We aim 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 the GCSE and the SAIG communities. We seek papers both in software engineering and in programming languages, and especially those that bridge the gap and are accessible to both communities at the same time. ------------------------------------ Topics of Interest ------------------------------------ The conference solicits submissions related (but not limited) to: * Generative programming o Reuse, meta-programming, partial evaluation, multi-stage and multi-level languages, step-wise refinement o Semantics, type systems, symbolic computation, linking and explicit substitution, in-lining and macros, templates, program transformation o Runtime code generation, compilation, active libraries, synthesis from specifications, development methods, generation of non-code artifacts, formal methods, reflection * Generative techniques for o Product lines and architectures o Embedded systems o Model-driven architecture * Component-based software engineering o Reuse, distributed platforms, distributed systems, evolution, analysis and design patterns, development methods, formal methods * Integration of generative and component-based approaches * Domain engineering and domain analysis o Domain-specific languages (DSLs) including visual and UML-based DSLs * Separation of concerns o Aspect-oriented programming, feature-oriented programming, o Intentional programming, and multi-dimensional separation of concerns * Industrial applications 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. ------------------------------------ Important Dates ------------------------------------ * Pre-submission: March 12, 2004 (title + abstract) * Submission: March 19, 2004 * Conference: 24-28 October 2004 ------------------------------------ Organization ------------------------------------ General chair * Tim Sheard (OGI School of Science & Engineering at OHSU) Program committee chairs * Gabor Karsai (Vanderbilt University) * Eelco Visser (Utrecht University) Program committee * Uwe Assmann (Linkopings Universitet) * Don Batory (University of Texas) * Jan Bosch (Universiteit Groningen) * Jean Bezivin (Université de Nantes) * Jim Cordy (Queen's University) * Krzysztof Czarnecki (University of Waterloo) * Mathew Flatt (University of Utah) * Robert Glueck (University of Copenhagen) * George Heineman (Worcester Polytechnic Institute) * Michael Leuschel (University of Southampton) * Karl Lieberherr (Northeastern University) * Simon Peyton Jones (Microsoft Research) * Douglas R. Smith (Kestrel Institute) * Gabriele Taentzer (Technical University of Berlin) * Todd Veldhuizen (Indiana University) * Kris de Volder (University of Britisch Columbia) * Dave Wile (Teknowledge Corp.) * Alexander Wolf (University of Colorado at Boulder) Contact * gpce-chairs(a)cs.uu.nl

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A question about overloading
by Ryoko Nanase 09 Nov '03

09 Nov '03

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Number conversions, like floats to doubles
by Ben Escoto 09 Nov '03

09 Nov '03

Quick and probably stupid question: If I want to convert a Float to a Double, should I use fromRational . toRational ? It seems to work, but isn't this a bit weird? It took a while for me to figure this out. I suppose they are rationals because of the finite precision of Floats and Doubles? And similarly, (fromInteger . toInteger) is the right way to convert the integral types? Why not just have a function like: convertIntegral :: (Integral a, Integral b) => a -> b -- Ben Escoto

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type class problem / GHC bug
by Brandon Michael Moore 08 Nov '03

08 Nov '03

Hi everyone I've built GHC from CVS and I'm getting some odd errors about overlapping instances. This is different from 6.0.1, but it's not obvious it is wrong, so I'm probably missing something here. The example is class A x class (A x) => B x instance A x instance B x The new GHC complains that the second instance overlapps with the first. Maybe because of the context on B x the instance for B x is interpreted as a claim we have A x too, but shouldn't it be the other way, that you need an instance A x from somewhere along with an instance for B x? Also, I tried to update and rebuild, but the makefiles seem to have the dependencies wrong or something. I compiles THSyntax.hs by hand, then ran into some trouble with files that needed some modules from GHCI trying (and dying) to build before the ghci files.Is there a guide to building GHC from CVS anywhere? I had the same problem with alex, but that's small enough to build by hand. Thanks Brandon

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happy Haskell hacking for compiler writers
by nr＠eecs.harvard.edu 07 Nov '03

07 Nov '03

I'm curious about using purely functional data structures to represent a control-flow graph in a compiler. I'm working on a compiler that uses this model: 1. Build a control-flow graph 2. Execute a million optimization steps, each of which makes a small mutation to the control-flow graph 3. Linearize the control-flow graph and emit assembly code Right now we're using mutable data structures, and I'm curious about using functional ones. I figure readers of this list are more likely than most to know how to write things like ``rewrite every basic block as a new subgraph with one entry and one exit.'' Any suggestions about what data structures I should use, what the interface should look like, and especially what the critical higher-order functions are and how they should be implemented? (I should add that I care about efficiency---one of the reasons I'm interested in a functional data structure is that I believe I'm paying a lot for all the mutation I'm doing.) Pointers to papers are code are also very welcome. Norman

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