August 2011 - Haskell-Cafe

library on common sub-expression elimination?
by Anton Kholomiov 15 Aug '11

15 Aug '11

Is there a library on common sub-expression elimination?

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FLOPS 2012: 1st Call for Papers
by Tom Schrijvers 15 Aug '11

15 Aug '11

First Call For Papers ===================== *Eleventh International Symposium on Functional and Logic Programming (FLOPS 2012)* May 23-25, 2012 Kobe, Japan [http://www.org.kobe-u.ac.jp/flops2012/] _Submission deadline : December 9, 2011_ FLOPS is a forum for research on all issues concerning declarative programming, including functional programming and logic programming, and aims to promote cross-fertilization and integration between the two paradigms. Previous FLOPS meetings were held in Fuji Susono (1995), Shonan Village (1996), Kyoto (1998), Tsukuba (1999), Tokyo (2001), Aizu (2002), Nara (2004), Fuji Susono (2006), Ise (2008), and Sendai (2010). Topics ====== FLOPS solicits original papers in all areas of functional and logic programming, including (but not limited to): - Declarative Pearls: new and excellent declarative programs with illustrative applications. - Language issues: language design and constructs, programming methodology, integration of paradigms, interfacing with other languages, type systems, constraints, concurrency and distributed computing. - Foundations: logic and semantics, rewrite systems and narrowing, type theory, proof systems. - Implementation issues: compilation techniques, memory management, program analysis and transformation, partial evaluation, parallelism. - Applications: case studies, real-world applications, graphical user interfaces, Internet applications, XML, databases, formal methods and model checking. The proceedings will be published as an LNCS volume. The proceedings of the previous meeting (FLOPS 2010) were published as LNCS 6009. PC co-Chairs ============ - Tom Schrijvers (Ghent University, Belgium) - Peter Thiemann (University of Freiburg, Germany) PC Members ========== - Salvador Abreu (University of Evora, Portugal) - Thorsten Altenkirch (University of Nottingham, UK) - Sebastian Brand (NICTA, Australia) - Giuseppe Castagna (CNRS Univ Paris 7, France) - Sebastian Fischer (Germany) - Marco Gavanelli (University of Ferrara, Italy) - Joxan Jaffar (National University of Singapore, Singapore) - Barry Jay (University of Sydney, Australia) - Andy King (University of Kent, UK) - Claude Kirchner (INRIA, France) - Neelakantan R. Krishnaswami (Microsoft Cambridge, UK) - Yulya Lierler (University of Kentucky, USA) - Keiko Nakata (Tallinn University of Technology, Estonia) - Peter Schneider-Kamp (University of Southern Denmark, Denmark) - Olin Shivers (Northeastern University, USA) - Paul Tarau (University of Northern Texas, USA) - Kazunori Ueda (Waseda University, Japan) - Meng Wang (Chalmers Technical University, Sweden) General Chair and Local co-Chairs ================================= - Naoyuki Tamura (Kobe University, Japan) - Mutsunori Banbara (Kobe University, Japan) - Katsutoshi Hirayama (Kobe University, Japan) Submission ========== Submissions must be unpublished and not submitted for publication elsewhere. Work that already appeared in unpublished or informally published workshops proceedings may be submitted. Submissions should fall into one of the following categories: - Regular research papers: they should describe new results and will be judged on originality, correctness, and significance. - System descriptions: they should contain a link to a working system and will be judged on originality, usefulness, and design. Submissions must be written in English and can be up to 15 pages long, though pearls are typically considerably shorter. Authors are required to use LaTeX2e and the Springer llncs class file, available at [http://www.springer.de/comp/lncs/authors.html] Regular research papers should be supported by proofs and/or experimental results. In case of lack of space, this supporting information should be made accessible otherwise (e.g., a link to a web page, or an appendix). Papers should be submitted electronically at [https://www.easychair.org/conferences/?conf=flops2012] Important Dates =============== - Submission deadline : December 9, 2011 - Author notification : February 3, 2012 - Camera-ready copy : March 2, 2012 Place and Related Events ======================== Takikawa Memorial Hall, Kobe University, 1-1 Rokkodai, Nada, Kobe 657-8501 Japan. The 23rd International Conference on Rewriting Techniques and Applications (RTA 2012) and satellite workshops including WFLP 2012 will be held in the week after FLOPS at Nagoya, Japan. Some Previous FLOPS =================== - FLOPS 2010, Sendai: [http://www.kb.ecei.tohoku.ac.jp/flops2010/] - FLOPS 2008, Ise: [http://www.math.nagoya-u.ac.jp/~garrigue/FLOPS2008/] - FLOPS 2006, Fuji Susono: [http://hagi.is.s.u-tokyo.ac.jp/FLOPS2006/] Sponsors ======== - Japan Society for Software Science and Technology (JSSST) SIGPPL In Cooperation with =================== - ACM SIGPLAN (pending approval) - Asian Association for Foundation of Software (AAFS) - Association for Logic Programming (ALP)

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strictness properties of monoidal folds
by Sebastian Fischer 14 Aug '11

14 Aug '11

Hello Cafe, left- and rightwards folds come in strict and lazy variants foldl/fold' and foldr/foldr' which makes sense because strict versions sometimes use less stack space while lazy versions support infinite data. For example, head (foldr (:) [] [1..]) returns in an instant while head (foldr' (:) [] [1..]) diverges. On the other hand foldl' (flip (:)) 0 [1..10^9] runs in constant space while foldl (flip (:)) 0 [1..10^9] consumes all memory available on my machine (at least without optimizations. With optimizations GHC's strictness analyzer seems to be smart enough to make the accumulator strict.) Data.Foldable also provides the monoidal fold function foldMap. It is left unspecified whether the elements are accumulated leftwards, rightwards or in some other way, which is possible because the combining function is required to be associative. Does this additional freedom for implementors go so far as to allow for strict accumulation? Is it safe to implement foldMap (without prime) with a strict accumulator or are there examples where lazy accumulation is useful like in the above foldr example and distinguishable from strict accumulation without breaking the monoid laws? Sebastian P.S. I thought the `Last` monoid would be an example that requires a lazy accumulator but it is not because the `Just` constructor guards list elements.

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how to read CPU time vs wall time report from GHC?
by Wishnu Prasetya 14 Aug '11

14 Aug '11

Hi guys, I'm new in parallel programming with Haskell. I made a simple test program using that par combinator etc, and was a bit unhappy that it turns out to be slower than its sequential version. But firstly, I dont fully understand how to read the runtime report produced by GHC with -s option: SPARKS: 5 (5 converted, 0 pruned) INIT time 0.02s ( 0.01s elapsed) MUT time 3.46s ( 0.89s elapsed) GC time 5.49s ( 1.46s elapsed) EXIT time 0.00s ( 0.00s elapsed) Total time 8.97s ( 2.36s elapsed) As I understand it from the documentation, the left time-column is the CPU time, whereas the right one is elapses wall time. But how come that the wall time is less than the CPU time? Isn't wall time = user's perspective of time; so that is CPU time + IO + etc? Any help? --Wish.

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Evolving faster Haskell programs - where are the files?
by Robert Clausecker 14 Aug '11

14 Aug '11

I just read the enlightening article by Don Stewart[1], and wanted to test this method on one of my own programs, but it seems that there some of the attached files are missing, namely [2], [3] and [4]. Is there anybody who knows, where I can get those files? I don't really want to rewrite those file by hand. Yours, Robert Clausecker [1]: http://donsbot.wordpress.com/2009/03/09/evolving-faster-haskell-programs [2]: http://galois.com/~dons/acovea/gcc43_core2.acovea [3]: http://galois.com/~dons/acovea/ghc-basic.acovea [4]: http://galois.com/~dons/acovea/ghc-6_10.acovea

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Invitation to connect on LinkedIn
by Andrew Smith B.Sc(Hons),MBA 14 Aug '11

14 Aug '11

LinkedIn ------------ I'd like to add you to my professional network on LinkedIn. - Andrew Andrew Smith B.Sc(Hons),MBA Founder and CEO at VTRL - Value Technology Research Ltd Edinburgh, United Kingdom Confirm that you know Andrew Smith B.Sc(Hons),MBA https://www.linkedin.com/e/uc6lxc-grc8ge3y-3d/isd/3853824536/atjCCKYr/ -- (c) 2011, LinkedIn Corporation

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Re: [Haskell-cafe] Proposal #3339: Add (+>) as a synonym for mappend
by Brandon Allbery 14 Aug '11

14 Aug '11

On Sun, Aug 14, 2011 at 13:38, Yitzchak Gale <gale(a)sefer.org> wrote: > Brandon Allbery wrote: > > Umm, I think the semigroups package will break everything that creates > > Monoid instances anyway. > > It has never broken anything for me. What do you mean? > Anything useful has to be modified to depend on SemiGroup as well to get mconcat or its replacement; that's why you jumped the proposal to begin with.... As others have noted, this is a rather intrusive change to the Haskell ecosystem. *If* it has in fact been decided to go ahead with it, *then* this proposal should be merged with yours since the best time to do it is when mconcat is being relocated anyway. I don't think we've made it past the "if", especially given the comments so far. -- brandon s allbery allbery.b(a)gmail.com wandering unix systems administrator (available) (412) 475-9364 vm/sms

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Array and Ix for custom Graph ADT
by Mark Spezzano 13 Aug '11

13 Aug '11

Hi, I'm creating a Graph data structure, and I want to use the array list approach, implemented as an Array. I need my Nodes to be instances of Ix for this to work and my Node type is roughly as follows: data Node = MyNode Int [Int] Type1 Type2 (Type1 and Type2 are nullary algebraic datatypes--enumerations in other words) How can I "index" the Array with an instance of a Node. I think I need to make Node an instance of Ix somehow?? Is this a sensible approach? Sample code of the instance declaration for Ix would be helpful. Thanks Mark Spezzano

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Diffs for hackage
by Luite Stegeman 13 Aug '11

13 Aug '11

hi all, often when a new version of a package is available on hackage, I want to see what has changed since the previous release. Unfortunately many packages don't have a changelog or a public source code repository. That's why I have made a simple website with git repositories that contain all versions of all hackage packages: http://hdiff.luite.com/ The home page contains a bookmarklet that takes you directly from the index page of a package version (for example http://hackage.haskell.org/package/parsec-3.1.0 ) to the commit diff, showing the difference with the previous version ( http://hdiff.luite.com/cgit/parsec/commit?id=3.1.0 ) I hope some people will find this useful, luite

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Subtitles for "Programming in Haskell" videos
by José Romildo Malaquias 13 Aug '11

13 Aug '11

Hello. Are there subtitles (in English or Portuguese) for the video lectures[1] given by Erik Meijer using the book "Programming in Haskell", by Graham Hutton? [1] http://www.cs.nott.ac.uk/~gmh/book.html Romildo

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