November 2013 - Haskell-Cafe

ANN: New Haskell.org committee members
by Jason Dagit 21 Nov '13

21 Nov '13

The Haskell.org committee has selected new members following the October self-nomination period. The new members are: * Adam Foltzer * Nicolas Wu * Andres Loeh Thank you to everyone who submitted a self-nomation. We had many very strong candidates and it was not easy for us to narrow the selection down to just three people. I would like to add, that if you've self-nominated in the past but not be picked, please self-nominate again in the future. Cheers, Jason

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Product Profunctor and Contravariant
by Tom Ellis 20 Nov '13

20 Nov '13

Does anyone recognise these typeclasses: import Data.Profunctor (Profunctor) import Data.Functor.Contravariant (Contravariant) class Profunctor p => ProductProfunctor p where empty :: p () () (***!) :: p a b -> p a' b' -> p (a, a') (b, b') class Contravariant f => ProductContravariant f where point :: f () (***<) :: f a -> f b -> f (a, b) They are both a bit like Applicative, and ProductProfunctor is basically Arrow without the Category part. I'm finding ProductProfunctor useful for marshalling data from a database into Haskell, and both of them come up a lot inside my database library. Has anyone ever seen these before? Has Edward Kmett written a library for these already? Thanks, Tom

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QuickCheck-like tests with GHC.Generic deriving
by Alexander Solla 20 Nov '13

20 Nov '13

I am looking for a QuickCheck-like test framework which exposes data generators (like QuickCheck's Arbitrary class) with Generic defaults. I have seen that SmallCheck's Serial class has Generic defaults, but it isn't particularly good for my purpose (I'd like to use the generator to populate deeply nested data types, and SmallCheck's generator requires computing a few million values before I get any interesting ones) Something "random" would be more useful for my purpose. I know that the plan depends on my vaguely abusing the test-case generator, but I plan on doing some testing anyway, so I figured I should reuse the instance. That said, I'd be willing to use any random value type class with Generic-default instances. Does anybody have any suggestions?

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Re: [Haskell-cafe] QuickCheck-like tests with GHC.Generic, deriving
by Janis Voigtlaender 20 Nov '13

20 Nov '13

Alexander Solla writes: > I am looking for a QuickCheck-like test framework which exposes data > generators (like QuickCheck's Arbitrary class) with Generic defaults. > > I have seen that SmallCheck's Serial class has Generic defaults, but it > isn't particularly good for my purpose (I'd like to use the generator to > populate deeply nested data types, and SmallCheck's generator requires > computing a few million values before I get any interesting ones) > Something "random" would be more useful for my purpose. > > I know that the plan depends on my vaguely abusing the test-case generator, > but I plan on doing some testing anyway, so I figured I should reuse the > instance. > > That said, I'd be willing to use any random value type class with > Generic-default instances. > > Does anybody have any suggestions? I think what you want is: http://hackage.haskell.org/package/testing-feat See also the paper: http://dx.doi.org/10.1145/2430532.2364515 Specifically, the technique solves the "populate deeply nested data types" issue. You can efficiently jump to the so-and-so-many-millionth value in the enumeration without having to create all smaller values. Best, Janis.

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Need help with very simple C++ FFI call
by Thiago Padilha 19 Nov '13

19 Nov '13

Hi I'm trying write a ffi binding to the v8 javascript engine (C++ library). Theres one already at https://github.com/sol/v8 but I want to do it again as an exercise to improve by haskell skills. I chose this library be because it will force me to deal with impure functions using monads. Since its not a trivial library, it will also improve my knowledge of writing FFI bindings and cabal packages in case I want to wrap more C++ libraries in the future. My first step is to port the 'hello world' example in v8 embedders guide(https://developers.google.com/v8/get_started) as a haskell binding. So I have downloaded/compiled v8 and created the following directory structure: src/V8.hs cbits/haskell-v8.cpp # v8 libraries deps/lib/libv8_base.a deps/lib/libv8_snapshot.a # v8 headers deps/include/ Here's the contents of the haskell-v8.cpp file: http://pastebin.com/RfYCCxFQ (basically a copy of the v8 embedders example function, except that it returns a char pointer). and here's the haskell module: http://pastebin.com/fnXVbEeU I compiled a shared library exposing the c "hello" function with the following command: $ g++ \ -shared -o libhaskellv8.so \ -I./deps/include \ -L./deps/lib \ ./cbits/haskell-v8.cpp \ -lv8_base \ -lv8_snapshot \ -lpthread \ -lrt And loaded into ghci with the following: $ ghci -L. -lhaskellv8 src/V8.hs The problem is that I get a segmentation fault when I call the 'hello' function from ghci. To ensure the library was compiled correctly, I successfully called it from python: $ python -c \ 'from ctypes import CDLL, c_char_p; lv8=CDLL("libhaskellv8.so"); lv8.hello.restype = c_char_p; print lv8.hello()' Hello, World! I have selectively uncommented lines from the c++ file, and the segmentation faults starts happening when I uncomment line 14 (HandleScope handle_scope(isolate)). What am I missing here?

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FLOPS 2014 2nd CFP
by Eijiro Sumii 19 Nov '13

19 Nov '13

NEWS: - Journal publications in JFP (Jounral of Functional Programming) and TPLP (Theory and Practice of Logic Programming) are planned (see below). - Hyakumangoku Matsuri ( https://www.google.com/search?q=hyakumangoku%20matsuri&tbm=isch ) is scheduled *just* after FLOPS 2014. Call For Papers =============== Twelfth International Symposium on Functional and Logic Programming (FLOPS 2014) June 4-6, 2014 Kanazawa, Japan http://www.jaist.ac.jp/flops2014/ 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 at Fuji Susono (1995), Shonan Village (1996), Kyoto (1998), Tsukuba (1999), Tokyo (2001), Aizu (2002), Nara (2004), Fuji Susono (2006), Ise (2008), Sendai (2010), and Kobe (2012). Topics ====== FLOPS solicits original papers in all areas of functional and logic programming, including (but not limited to): - 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 meetings (FLOPS 1999, 2001, 2002, 2004, 2006, 2008, 2010, and 2012) were published as LNCS 1722, 2024, 2441, 2998, 3945, 4989, 6009, and 7294. PC Co-Chairs ============ Michael Codish (Ben-Gurion University of the Negev) Eijiro Sumii (Tohoku University) PC Members ========== Lars Birkedal (Aarhus University) Michael Codish (Ben-Gurion University of the Negev) [co-chair] Marina De Vos (University of Bath) Moreno Falaschi (Universita degli studi di Udine) Carsten Fuhs (University College London) John Gallagher (Roskilde Universitet / IMDEA Software Institute) Samir Genaim (Universidad Complutense de Madrid) Laura Giordano (Universita del Piemonte Orientale) Ichiro Hasuo (University of Tokyo) Fritz Henglein (University of Copenhagen) Andy King (University of Kent) Oleg Kiselyov Vitaly Lagoon (MathWorks) Shin-Cheng Mu (Academia Sinica) Keiko Nakata (Institute of Cybernetics at Tallinn University of Technology) Luke Ong (University of Oxford) Peter Schachte (University of Melbourne) Takehide Soh (Kobe University) Eijiro Sumii (Tohoku University) [co-chair] Tachio Terauchi (Nagoya University) Joost Vennekens (KU Leuven) Janis Voigtlaender (Universitaet Bonn) Stephanie Weirich (University of Pennsylvania) Local Chair =========== Yuki Chiba (JAIST) 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. See also ACM SIGPLAN Republication Policy: http://www.sigplan.org/Resources/Policies/Republication 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. - Declarative pearls: new and excellent declarative programs or theories with illustrative applications. System descriptions and declarative pearls must be explicitly marked as such in the title. Submissions must be written in English and can be up to 15 pages long including references, though pearls are typically 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=flops2014 Important Dates =============== Submission deadline: December 13, 2013 Author notification: February 10, 2014 Camera-ready copy: March 7, 2014 Journal Publication =================== - Journal of Functional Programming and - Theory and Practice of Logic Programming 2-4 of the best papers in each of the two areas: Functional Programming and Logic Programming, will be invited for inclusion in a designated FLOPS section within each of the two journals. The Theory and Practice of Logic Programming papers will appear as "Rapid Publications". All of the these submissions are expected to represent high-quality revisions and extensions of the selected FLOPS papers and will be reviewed under the standard criteria of each journal. Venue ===== Main Hall, Ishikawa Prefectural Museum of Art, 2-1 Dewa-machi, Kanazawa, Ishikawa 920-0963 JAPAN. Some Previous FLOPS =================== FLOPS 2012, Kobe: http://www.org.kobe-u.ac.jp/flops2012/ FLOPS 2010, Sendai: http://www.kb.ecei.tohoku.ac.jp/flops2010/ FLOPS 2008, Ise: http://www.math.nagoya-u.ac.jp/~garrigue/FLOPS2008/ Sponsor ======= Japan Society for Software Science and Technology (JSSST), Special Interest Group on Programming and Programming Languages (SIG-PPL) In Cooperation With =================== ACM SIGPLAN Asian Association for Foundation of Software (AAFS) Association for Logic Programming (ALP)

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New Functional Programming Job Opportunities
by Functional Jobs 18 Nov '13

18 Nov '13

Here are some functional programming job opportunities that were posted recently: Compiler Engineer at BAE Systems http://functionaljobs.com/jobs/8656-compiler-engineer-at-bae-systems Cheers, Sean Murphy FunctionalJobs.com

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Incorrect behavior in Data.Complex ?
by jared simpson 18 Nov '13

18 Nov '13

Prelude Data.Complex> 0**2 0.0 Prelude Data.Complex> 0**2 :: Complex Double NaN :+ NaN Prelude Data.Complex> exp $ 2 * log 0 :: Complex Double NaN :+ NaN Prelude Data.Complex> log 0 :: Complex Double (-Infinity) :+ 0.0 Prelude Data.Complex> 2 * it :: Complex Double (-Infinity) :+ NaN Prelude Data.Complex> exp it :: Complex Double NaN :+ NaN So Complex uses the default implementation of **. Then when 2*(-inf :+ 0) is evaluated. We do (2 * -inf - 0*0) :+ (2*0 + -inf*0). Which because of -inf*0 sets the imaginary part to NaN. Then exp (-inf :+ NaN) = exp x cos y :+ exp x sin y which becomes 0 * cos NaN :+ 0 * sin NaN. So we end up with NaN :+ NaN. So is there a library I should be using, or is this a bug?

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FP Complete Launches Free Community edition of FP Haskell Center
by Natalia Muska 18 Nov '13

18 Nov '13

https://www.fpcomplete.com/business/blog/fp-complete-launches-free-communit… -- Natalia Muska Marketing Manager FP Complete, Inc. Natalia(a)fpcomplete.com 865-506-6513 skype: natalia.s.muska

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Error cabal update: "Unsucessful HTTP code: 404"
by Vaniax 18 Nov '13

18 Nov '13

Hi, I have a big problem with a fresh installation of the Haskell-Platform 2013.2 on Windows 7. When I try to run `cabal update` I get the following error message: "|Downloading the latest package list from hackage.haskell.org cabal: Failed to download http://hackage.haskell.org/packages/archive/00-index.tar.gz : ErrorMisc "Unsucessful HTTP code: 404" When I try ||`wget http://hackage.haskell.org/packages/archive/00-index.tar.gz`everything works alright. I'm using no proxies or something like that. Maybe someone know whats going wrong? A parallel Windows-XP installation of the platform works fine. Vaniax |

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