- Haskell-Cafe - Haskell.org

source from hayoo
by Doug McIlroy 16 Dec '13

16 Dec '13

Apologies for a false send of a part message. Here's the whole: It is a shame that when you look something up in Hayoo, you can immediately see the source, but you can't use it. To get plain source, not gussied up as HTML, you have to switch to another, multistep retrieval mechanism. It would be nice if the HTML included a link to the real source file from which it was constructed. Doug McIlroy

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Using unsafePerformIO and free with CString
by Nikita Karetnikov 16 Dec '13

16 Dec '13

I’m trying to write a wrapper for a C function. Here is an example of such code: {-# LANGUAGE ForeignFunctionInterface #-} import Foreign.C.String import Foreign.C.Types import System.IO.Unsafe import Foreign.Marshal.Alloc foreign import ccall "string.h strcmp" c_strcmp :: CString -> CString -> CInt strcmp :: String -> String -> Ordering strcmp s t = unsafePerformIO $ do s' <- newCString s t' <- newCString t let n = c_strcmp s' t' -- free s' -- free t' return $ case () of _ | n == 0 -> EQ | n < 0 -> LT | otherwise -> GT Two questions: 1. May I safely use unsafePerformIO in such cases? 2. What’s the proper way of using free here? If I uncomment the above, the function returns incorrect results.

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Re: [Haskell-cafe] ANN: hledger 0.22
by Simon Michael 15 Dec '13

15 Dec '13

Well that's a mystery to me. Given that we've both done a cabal update, I can't think what is causing my cabal to find an install plan with default maxjump and yours not to. Maybe a someone will enlighten us. (I've belatedly dropped the haskell list from this thread.) On Sun, Dec 15, 2013, at 11:31 AM, Marko Kocić wrote: Yes, I have the same problem with cabal sandbox. I'm on Ubuntu 12.04 with binary downloaded ghc-7.6.3, cabal-1.18.0.2 and cabal-dev-0.9.2 Regards, Marko On Sun, Dec 15, 2013 at 7:43 PM, Simon Michael <[1]simon(a)joyful.com> wrote: That's odd. Here I have ubuntu raring, ghc 7.6.3, cabal-dev 0.9.2 using Cabal 1.16.0, cabal-install 1.18.0.2 using Cabal 1.18.1. Do you see the same problem with cabal sandbox init; cabal install ./hledger-lib ./hledger ./hledger-web ? On Sun, Dec 15, 2013, at 03:36 AM, Marko Kocić wrote: I also had fresh cabal-dev repo, and it didn't work. However, I was able to build when I added --max-backjumps=10000 to the build line. Regards, Marko On Sunday, December 15, 2013 4:50:30 AM UTC+1, Simon Michael (sm) wrote: It works for me in a fresh cabal-dev package db, which I think yours is not, right ? Installs into an already-populated package db are more troublesome than usual right now because of the recent major version bumps to text, wai, warp, http-conduit etc. On Sat, Dec 14, 2013, at 10:27 AM, Marko Kocić wrote: I have build problems again after pulling from git. ~/src/hledger$ cabal-dev install ./hledger ./hledger-lib/ ./hledger-web/ Resolving dependencies... cabal: Could not resolve dependencies: trying: hledger-0.22 (user goal) trying: utf8-string-0.3.7 (dependency of hledger-0.22) rejecting: utf8-string-0.3.7:+bytestring-in-base (conflict: base==[2]4.6.0.1/installed-ced..., utf8-string-0.3.7:bytestring-in-base => base>=2.0 && <2.2) trying: utf8-string-0.3.7:-bytestring-in-base trying: bytestring-0.10.0.2/installed-0b6... (dependency of utf8-string-0.3.7:-bytestring-in-base) trying: text-1.0.0.0 (dependency of hledger-0.22) trying: shakespeare-text-1.0.0.10 (dependency of hledger-0.22) trying: shakespeare-1.2.0.3 (dependency of shakespeare-text-1.0.0.10) next goal: system-fileio (dependency of shakespeare-1.2.0.3) rejecting: system-fileio-0.3.11, 0.3.10 (conflict: text==1.0.0.0, system-fileio => text>=0.7.1 && <0.12) rejecting: system-fileio-0.3.9, 0.3.8, 0.3.7, 0.3.6, 0.3.5, 0.3.4, 0.3.3, 0.3.2.1, 0.3.2, 0.3.1, 0.3 (conflict: bytestring==[3]0.10.0.2/installed-0b6..., system-fileio => bytestring>=0.9 && <0.10) rejecting: system-fileio-0.2.7, 0.2.6, 0.2.5, 0.2.4, 0.2.3, 0.2.2.1, 0.2.2, 0.2.1, 0.2, 0.1.1, 0.1 (conflict: shakespeare => system-fileio>=0.3) Backjump limit reached (change with --max-backjumps). marko@monet:~/src/hledger$ ghc --version The Glorious Glasgow Haskell Compilation System, version 7.6.3 -- -- You received this message because you are subscribed to the Google Groups hledger group. To post to this group, send email to hle...(a)googlegroups.com. To unsubscribe from this group, send email to hledger+u...(a)googlegroups.com. For more options, visit this group at [4]https://groups.google.com/d/forum/hledger?hl=en --- You received this message because you are subscribed to the Google Groups "hledger" group. To unsubscribe from this group and stop receiving emails from it, send an email to hledger+u...(a)googlegroups.com. For more options, visit [5]https://groups.google.com/groups/opt_out. -- -- You received this message because you are subscribed to the Google Groups hledger group. To post to this group, send email to [6]hledger(a)googlegroups.com. To unsubscribe from this group, send email to [7]hledger+unsubscribe(a)googlegroups.com. For more options, visit this group at [8]https://groups.google.com/d/forum/hledger?hl=en --- You received this message because you are subscribed to the Google Groups "hledger" group. To unsubscribe from this group and stop receiving emails from it, send an email to [9]hledger+unsubscribe(a)googlegroups.com. For more options, visit [10]https://groups.google.com/groups/opt_out. -- -- You received this message because you are subscribed to the Google Groups hledger group. To post to this group, send email to [11]hledger(a)googlegroups.com. To unsubscribe from this group, send email to [12]hledger+unsubscribe(a)googlegroups.com. For more options, visit this group at [13]https://groups.google.com/d/forum/hledger?hl=en --- You received this message because you are subscribed to a topic in the Google Groups "hledger" group. To unsubscribe from this topic, visit [14]https://groups.google.com/d/topic/hledger/FdWGTSAVzYU/unsubscribe. To unsubscribe from this group and all its topics, send an email to [15]hledger+unsubscribe(a)googlegroups.com. For more options, visit [16]https://groups.google.com/groups/opt_out. -- -- You received this message because you are subscribed to the Google Groups hledger group. To post to this group, send email to hledger(a)googlegroups.com. To unsubscribe from this group, send email to hledger+unsubscribe(a)googlegroups.com. For more options, visit this group at [17]https://groups.google.com/d/forum/hledger?hl=en --- You received this message because you are subscribed to the Google Groups "hledger" group. To unsubscribe from this group and stop receiving emails from it, send an email to hledger+unsubscribe(a)googlegroups.com. For more options, visit [18]https://groups.google.com/groups/opt_out. References 1. mailto:simon@joyful.com 2. http://4.6.0.1/installed-ced.. 3. http://0.10.0.2/installed-0b6.. 4. https://groups.google.com/d/forum/hledger?hl=en 5. https://groups.google.com/groups/opt_out 6. mailto:hledger@googlegroups.com 7. mailto:hledger%2Bunsubscribe@googlegroups.com 8. https://groups.google.com/d/forum/hledger?hl=en 9. mailto:hledger%2Bunsubscribe@googlegroups.com 10. https://groups.google.com/groups/opt_out 11. mailto:hledger@googlegroups.com 12. mailto:hledger%2Bunsubscribe@googlegroups.com 13. https://groups.google.com/d/forum/hledger?hl=en 14. https://groups.google.com/d/topic/hledger/FdWGTSAVzYU/unsubscribe 15. mailto:hledger%2Bunsubscribe@googlegroups.com 16. https://groups.google.com/groups/opt_out 17. https://groups.google.com/d/forum/hledger?hl=en 18. https://groups.google.com/groups/opt_out

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Re: [Haskell-cafe] ANN: hledger 0.22
by Simon Michael 15 Dec '13

15 Dec '13

That's odd. Here I have ubuntu raring, ghc 7.6.3, cabal-dev 0.9.2 using Cabal 1.16.0, cabal-install 1.18.0.2 using Cabal 1.18.1. Do you see the same problem with cabal sandbox init; cabal install ./hledger-lib ./hledger ./hledger-web ? On Sun, Dec 15, 2013, at 03:36 AM, Marko Kocić wrote: I also had fresh cabal-dev repo, and it didn't work. However, I was able to build when I added --max-backjumps=10000 to the build line. Regards, Marko On Sunday, December 15, 2013 4:50:30 AM UTC+1, Simon Michael (sm) wrote: It works for me in a fresh cabal-dev package db, which I think yours is not, right ? Installs into an already-populated package db are more troublesome than usual right now because of the recent major version bumps to text, wai, warp, http-conduit etc. On Sat, Dec 14, 2013, at 10:27 AM, Marko Kocić wrote: I have build problems again after pulling from git. ~/src/hledger$ cabal-dev install ./hledger ./hledger-lib/ ./hledger-web/ Resolving dependencies... cabal: Could not resolve dependencies: trying: hledger-0.22 (user goal) trying: utf8-string-0.3.7 (dependency of hledger-0.22) rejecting: utf8-string-0.3.7:+bytestring-in-base (conflict: base==[1]4.6.0.1/installed-ced..., utf8-string-0.3.7:bytestring-in-base => base>=2.0 && <2.2) trying: utf8-string-0.3.7:-bytestring-in-base trying: bytestring-0.10.0.2/installed-0b6... (dependency of utf8-string-0.3.7:-bytestring-in-base) trying: text-1.0.0.0 (dependency of hledger-0.22) trying: shakespeare-text-1.0.0.10 (dependency of hledger-0.22) trying: shakespeare-1.2.0.3 (dependency of shakespeare-text-1.0.0.10) next goal: system-fileio (dependency of shakespeare-1.2.0.3) rejecting: system-fileio-0.3.11, 0.3.10 (conflict: text==1.0.0.0, system-fileio => text>=0.7.1 && <0.12) rejecting: system-fileio-0.3.9, 0.3.8, 0.3.7, 0.3.6, 0.3.5, 0.3.4, 0.3.3, 0.3.2.1, 0.3.2, 0.3.1, 0.3 (conflict: bytestring==[2]0.10.0.2/installed-0b6..., system-fileio => bytestring>=0.9 && <0.10) rejecting: system-fileio-0.2.7, 0.2.6, 0.2.5, 0.2.4, 0.2.3, 0.2.2.1, 0.2.2, 0.2.1, 0.2, 0.1.1, 0.1 (conflict: shakespeare => system-fileio>=0.3) Backjump limit reached (change with --max-backjumps). marko@monet:~/src/hledger$ ghc --version The Glorious Glasgow Haskell Compilation System, version 7.6.3 -- -- You received this message because you are subscribed to the Google Groups hledger group. To post to this group, send email to hle...(a)googlegroups.com. To unsubscribe from this group, send email to hledger+u...(a)googlegroups.com. For more options, visit this group at [3]https://groups.google.com/d/forum/hledger?hl=en --- You received this message because you are subscribed to the Google Groups "hledger" group. To unsubscribe from this group and stop receiving emails from it, send an email to hledger+u...(a)googlegroups.com. For more options, visit [4]https://groups.google.com/groups/opt_out. -- -- You received this message because you are subscribed to the Google Groups hledger group. To post to this group, send email to hledger(a)googlegroups.com. To unsubscribe from this group, send email to hledger+unsubscribe(a)googlegroups.com. For more options, visit this group at [5]https://groups.google.com/d/forum/hledger?hl=en --- You received this message because you are subscribed to the Google Groups "hledger" group. To unsubscribe from this group and stop receiving emails from it, send an email to hledger+unsubscribe(a)googlegroups.com. For more options, visit [6]https://groups.google.com/groups/opt_out. References 1. http://4.6.0.1/installed-ced.. 2. http://0.10.0.2/installed-0b6.. 3. https://groups.google.com/d/forum/hledger?hl=en 4. https://groups.google.com/groups/opt_out 5. https://groups.google.com/d/forum/hledger?hl=en 6. https://groups.google.com/groups/opt_out

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Re: [Haskell-cafe] ANN: hledger 0.22
by Simon Michael 15 Dec '13

15 Dec '13

It works for me in a fresh cabal-dev package db, which I think yours is not, right ? Installs into an already-populated package db are more troublesome than usual right now because of the recent major version bumps to text, wai, warp, http-conduit etc. On Sat, Dec 14, 2013, at 10:27 AM, Marko Kocić wrote: I have build problems again after pulling from git. ~/src/hledger$ cabal-dev install ./hledger ./hledger-lib/ ./hledger-web/ Resolving dependencies... cabal: Could not resolve dependencies: trying: hledger-0.22 (user goal) trying: utf8-string-0.3.7 (dependency of hledger-0.22) rejecting: utf8-string-0.3.7:+bytestring-in-base (conflict: base==4.6.0.1/installed-ced..., utf8-string-0.3.7:bytestring-in-base => base>=2.0 && <2.2) trying: utf8-string-0.3.7:-bytestring-in-base trying: bytestring-0.10.0.2/installed-0b6... (dependency of utf8-string-0.3.7:-bytestring-in-base) trying: text-1.0.0.0 (dependency of hledger-0.22) trying: shakespeare-text-1.0.0.10 (dependency of hledger-0.22) trying: shakespeare-1.2.0.3 (dependency of shakespeare-text-1.0.0.10) next goal: system-fileio (dependency of shakespeare-1.2.0.3) rejecting: system-fileio-0.3.11, 0.3.10 (conflict: text==1.0.0.0, system-fileio => text>=0.7.1 && <0.12) rejecting: system-fileio-0.3.9, 0.3.8, 0.3.7, 0.3.6, 0.3.5, 0.3.4, 0.3.3, 0.3.2.1, 0.3.2, 0.3.1, 0.3 (conflict: bytestring==0.10.0.2/installed-0b6..., system-fileio => bytestring>=0.9 && <0.10) rejecting: system-fileio-0.2.7, 0.2.6, 0.2.5, 0.2.4, 0.2.3, 0.2.2.1, 0.2.2, 0.2.1, 0.2, 0.1.1, 0.1 (conflict: shakespeare => system-fileio>=0.3) Backjump limit reached (change with --max-backjumps). marko@monet:~/src/hledger$ ghc --version The Glorious Glasgow Haskell Compilation System, version 7.6.3 -- -- You received this message because you are subscribed to the Google Groups hledger group. To post to this group, send email to hledger(a)googlegroups.com. To unsubscribe from this group, send email to hledger+unsubscribe(a)googlegroups.com. For more options, visit this group at [1]https://groups.google.com/d/forum/hledger?hl=en --- You received this message because you are subscribed to the Google Groups "hledger" group. To unsubscribe from this group and stop receiving emails from it, send an email to hledger+unsubscribe(a)googlegroups.com. For more options, visit [2]https://groups.google.com/groups/opt_out. References 1. https://groups.google.com/d/forum/hledger?hl=en 2. https://groups.google.com/groups/opt_out

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Writing a Storable instance for a C union
by Nikita Karetnikov 14 Dec '13

14 Dec '13

Could anyone explain how to write a Storable instance for MyStruct? (The key field allows to determine the type of a value inside the union.) typedef enum Key_ { ONE = 1, FOUR = 4, TWENTY = 20 } Key; struct MyStruct { Key key; union { Foo one; uint64_t four; void *twenty; }; }; Also, should I use hsc2hs to make the resulting code portable?

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Munich Haskell Christmas Meeting
by Heinrich Hördegen 14 Dec '13

14 Dec '13

Dear all, on Thursday, 19th of December, we will meet for a Christmas get-together. The event is organised together with the Munich Lambda Group. We will have Glühwein & Lebkuchen (mulled wine & gingerbread). Check out the details: http://www.meetup.com/Munich-Lambda/events/155219402/ I also updated our homepage. New meeting dates are available for next year: http://www.haskell-munich.de/dates And check out also the links that were sent for our last meeting. Thanks to everyone who contributed interesting links for our web site during this year. I wish all of you happy Chrismas and a happy new year! Heinrich

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Deadline extended: FLOPS 2014 call for papers
by Eijiro Sumii 14 Dec '13

14 Dec '13

********************************************************************** NEWS: Submission deadline extended. - Title, abstract, and draft paper by December 13, 2013 - Full paper by December 15, 2013 (23:59 anywhere in the world) ********************************************************************** 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/ ---------------------------------------------------------------------- - 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. ---------------------------------------------------------------------- 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 (EXTENDED): - Title, abstract, and draft paper by December 13, 2013 - Full paper by December 15, 2013 (23:59 anywhere in the world) 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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ANN: hledger 0.22
by Simon Michael 14 Dec '13

14 Dec '13

Hi all. I have released hledger and hledger-web 0.22. hledger is a command-line tool and haskell library for tracking financial transactions, which are stored in a human-readable plain text format. In addition to reporting, it can also help you record new transactions, or convert CSV data from your bank. Add-on packages include hledger-web (providing a web interface), hledger-irr and hledger-interest. hledger is inspired by and compatible with John Wiegley's Ledger. For more, see http://hledger.org . Install it: cabal update; cabal install hledger [hledger-web] For more installation help, see http://hledger.org/MANUAL.html#installing . Or, sponsor a ready-to-run binary for your platform: http://hledger.org/DOWNLOAD.html . Release notes (http://hledger.org/NEWS.html#hledger-0.22) **New:** - balance: with a reporting interval (monthly, yearly etc.), the [balance command](MANUAL.html#balance) will now show a multi-column report, showing either the per-period changes in balance (by default), the period ending balances starting from zero (`--cumulative`), or the actual period ending balances (`--historical`). A more detailed specification of the balance command's behaviour has been added to Hledger.Cli.Balance. - csv: rules files can now include other rules files, useful for factoring out common rules - queries: `sym:REGEXP` matches commodity symbols - register: `--average/-A` shows a running average, like ledger - in period expressions, `-` (hyphen) can be used as a more compact synonym for `from` and `to`. Eg: `-p 2012/12/1-2013/2/1` or `date:aug-`. - the add-on script examples in extra/ have been updated; get the hledger source and add .../hledger/extra/ to your PATH to make them available. They include: hledger-accountnames.hs - print account names hledger-balance-csv.hs - print a balance report as CSV hledger-equity.hs - print an entry matching all account balances hledger-print-unique.hs - print only journal entries unique descriptions hledger-register-csv.hs - print a register report as CSV **Improved:** - balancesheet: now shows just assets and liabilities, not equity - print: comment positions (same line or next line) are now preserved - queries: `amt` now uses the = operator by default, eg `amt:50` is equivalent to `amt:=50` - command line processing has been overhauled and made more consistent, and now has tests and debug output. More flags now work both before and after COMMAND: `-f`, `--rule-file`, `--alias`, `--help`, `--debug`, `--version`. Command line help, command aliases, API docs and code have been improved. - `--debug` now takes an optional numeric argument to set the debug level higher than 1, for more verbose debug output in a few cases. **Fixed:** - csv: CSV data containing non-ascii characters is now supported - build with latest versions of dependencies (text, warp, http-conduit etc.) **Release contributors:** Marko Kocić, Max Bolingbroke, and a big welcome to first-time committer John Wiegley! :) There's a rumour that a 1.0 release could be next, depending on how this one fares. All feedback welcome. Best! - Simon

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GLUT, FLGW, FLGW-b
by Vlad Lopatin 14 Dec '13

14 Dec '13

Hey guys, I keep reading (wiki) that GLUT is a legacy package and some libraries (e.g. GLFW) are meant to replace it. I also see that some of the GLUT functionality is based on fixed pipeline. What is the current status of Haskell GLUT? Is it 'to stay' or something that is going to be deprecated at some point? Should one try replacing it with GLFW(-b) in a project, if fixed pipeline is not expected to be used? Regards, Vladimir.

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Odd behavior with Num instance for lists (was: f^n for functional iteration)
by Mark Fredrickson 14 Dec '13

14 Dec '13

On Fri, Dec 13, 2013 at 8:59 AM, Antonio Nikishaev <me(a)lelf.lu> wrote: > > http://hackage.haskell.org/package/NumInstances > The previous exchange prompted me to whip up a Num instance for lists: instance Num a => Num [a] where negate = fmap negate (+) = zipWith (+) (*) = zipWith (+) fromInteger x = [fromInteger x] abs = fmap abs signum = fmap signum It mostly behaves how one would expect: let a = [1,2,3] ghci> let b = [4,5,6,7] ghci> a + b [5,7,9] ghci> 1 + a [2] I was wondering whey `1 + a` succeeds. At first I thought it could be the `fromInteger` definition, but this explanation were true, I should be able to add integers and doubles freely, which I can't: ghci> fromInteger (1::Integer) + (1.0::Double) 2.0 ghci> (1::Integer) + (1.0::Double) <interactive>:30:17: Couldn't match expected type `Integer' with actual type `Double' In the second argument of `(+)', namely `(1.0 :: Double)' ... Thanks for enlightening me. -M

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Re: [Haskell-cafe] f^n for functional iteration
by Doug McIlroy 13 Dec '13

13 Dec '13

Agreeing with the analysis, I will sharpen my question. Is option 2 possible at all, regardless of sanity concerns (e.g. incomplete implementation of Num). Doug > On Tue, 10 Dec 2013 at 10:51 AM, Danny Gratzer <danny.gratzer(a)gmail.com> wrote > > Well (^) is already used for their traditional meaning and using this exact > operator would require > > 1. Shadowing (^) from prelude > 2. Making (a -> a) an instance of Num (impossible to do sanely) > > You can just use a different operator > > f .^. n = foldl (.) id $ replicate n f > > On Tue, Dec 10, 2013 at 10:45 AM, Doug McIlroy <doug(a)cs.dartmouth.edu>wrote: > > > Is there a trick whereby the customary notation f^n for iterated > > functional composition ((\n f -> foldl (.) id (replicate n f)) n f) can > > be defined in Haskell? > > > > Doug McIlroy

4 4

Way to implement toFloat :: (Num a) => a -> Float
by EatsKittens 13 Dec '13

13 Dec '13

Is there a way to add a method to a typeclass like num to implement this concept? A function that converts any number to floats?

6 6

ANN - csound-expression 3.1 library for electronic music
by Anton Kholomiov 12 Dec '13

12 Dec '13

I'm glad to announce the new version of the csound-expression [1] package. It's the library for electronic music and sound design. Here is a full description [2] In the new version it supports GUI-widgets. You can not only create sound instruments but update parameters onlne with sliders, knobs and buttons. There are many other widgets. You can find out the details in the quick start guide [3] and the examples [4]. Anton [1] http://hackage.haskell.org/package/csound-expression [2] https://github.com/anton-k/csound-expression [3] https://github.com/anton-k/csound-expression/blob/master/tutorial/QuickStar… [4] https://github.com/anton-k/csound-expression/tree/master/examples/Gui

2 1

SENIOR HASKELL OPPORTUNITY
by Neena Singh 12 Dec '13

12 Dec '13

Hello, I have been retained by a leading Hedge Fund who are looking for an experienced Haskell developer to join their highly regarded front office technology team. This is a great opportunity for a passionate technologist to join a group working very closely with the trading floor on advanced Haskell projects. Previous finance experience is not a pre-requisite however a passion for Haskell is a must. If you are interested learning more about this opportunity and potential salary ranges please call me on 020 7871 4482 or email me Neena.singh(a)henlowgroup.com<mailto:Neena.singh@henlowgroup.com>. I look forward to hearing from you, Regards, Neena Neena Singh Analyst Henlow Recruitment Group +44(0)20 7871 1834 neena.singh(a)henlowgroup.com<mailto:neena.singh@henlowgroup.com> www.henlowgroup.com<http://www.henlowgroup.com/> [cid:image017.jpg@01CECB15.783A6E10]<https://twitter.com/Henlow_Group> [cid:image019.png@01CECB15.783A6E10] <http://www.linkedin.com/profile/view?id=300878083&authType=OUT_OF_NETWORK&a…> [cid:image005.png@01CEDA27.B1142430] <http://www.linkedin.com/profile/view?id=300878083&authType=OUT_OF_NETWORK&a…> This e-mail contains proprietary information some or all of which may be legally privileged. It is for the intended recipient only. If an address or transmission error has misdirected this email, please notify the author by replying to this e-mail. If you are not the intended recipient you must not use, disclose, distribute, copy, print, rely on or retain this e-mail. This email and any attached files have been scanned for the presence of computer viruses, however you are advised that you open any attachments at your own risk. All e-mails including CV's are subject to our standard terms and conditions of business. The acceptance of any CV's constitutes the acceptance of our standard terms and conditions of business unless there has been written prior agreement. Any views or opinions presented here may be solely those of the originator and are not necessarily those of Henlow Recruitment Group. Henlow Recruitment Group reserves the right to share information between companies within our group. Please read Henlow Recruitment Groups' privacy policy at http://www.henlowgroup.com/privacy-policy to understand how Henlow Recruitment Group uses and protects the information you provide.

8 9

GLFW/GLFW-b ambiguity
by Vlad Lopatin 12 Dec '13

12 Dec '13

Hey guys, I am messing with OpenGL and here's the question: GLFW-b is supposed to be based on GLFW and extend it. How come GLFW-b naming is ambiguous with GLFW? GLFW-b main module is named the same as GLFW (import Graphics.UI.GLFW), making it necessary to hide one of the libraries via ghc-pkg hide, or to use a language extension in order to solve ambiguity. I am tempted to consider it a bug, unless somebody knows a good reason for it to be called a feature. Am I missing something? Regards, Vladimir

3 4

Haskell Weekly News: Issue 287
by Daniel Santa Cruz 12 Dec '13

12 Dec '13

Welcome to (the "I'm not dead yet") issue 287 of the HWN, an issue covering crowd-sourced bits of information about Haskell from around the web. This issue covers the very long span of time from November 10 to December 07, 2013. Quotes of the Week * chrisdone: monads are like a finger pointing away to the moon. *smack* don't look at the finger or you will miss all that heavenly glory * quchen: A group with an associative law is called a group. * chrisdone: i swim in a sea of parens and it warms me like rays of the sun * zomg: my client tells me weekly how I've saved his company. Then I goto haskell and I'm like "I have no idea what I'm doing lul" * pigworker: The usual style is to write as if everything is inductive, and if it still works on infinite data, to pat ourselves on the back for using Haskell rather than ML. Top Reddit Stories * Honorary Doctorate for Simon Peyton Jones - On December 3 2013 Simon Peyton Jones was honoured by the University of Glasgow with the honorary degree of Doctor of Science. Domain: dcs.gla.ac.uk, Score: 166, Comments: 18 On Reddit: [1] http://goo.gl/XLezZO Original: [2] http://goo.gl/WqC2EN * Hell: A Haskell shell Domain: github.com, Score: 114, Comments: 53 On Reddit: [3] http://goo.gl/6ogD6n Original: [4] http://goo.gl/YCzNT3 * Löb and möb: strange loops in Haskell Domain: github.com, Score: 95, Comments: 35 On Reddit: [5] http://goo.gl/8bF5Op Original: [6] http://goo.gl/GqzuP0 * Explanation of the new Haskell records extension Domain: well-typed.com, Score: 88, Comments: 70 On Reddit: [7] http://goo.gl/419sYv Original: [8] http://goo.gl/g24kLB * FP Complete IDE now free for community use. Give it a try! Domain: fpcomplete.com, Score: 86, Comments: 65 On Reddit: [9] http://goo.gl/OJh2Oz Original: [10] http://goo.gl/2FYHa * The Haskell Cast #4 - Simon Marlow on Parallelism and Concurrency Domain: haskellcast.com, Score: 82, Comments: 13 On Reddit: [11] http://goo.gl/kzNEz3 Original: [12] http://goo.gl/yrUDXL * 24 Days of Hackage: scotty Domain: ocharles.org.uk, Score: 74, Comments: 16 On Reddit: [13] http://goo.gl/CoUanr Original: [14] http://goo.gl/a83HZg * Idris 0.9.10 released Domain: idris-lang.org, Score: 73, Comments: 21 On Reddit: [15] http://goo.gl/0OnlPV Original: [16] http://goo.gl/MKtbxu * 24 Days of Hackage: threepenny-gui Domain: ocharles.org.uk, Score: 68, Comments: 4 On Reddit: [17] http://goo.gl/vSTpc0 Original: [18] http://goo.gl/Hmjqzq * 24 Days of Hackage: linear Domain: ocharles.org.uk, Score: 66, Comments: 43 On Reddit: [19] http://goo.gl/dcFHGg Original: [20] http://goo.gl/R9c0bh * 24 Days of Hackage: tasty Domain: ocharles.org.uk, Score: 65, Comments: 4 On Reddit: [21] http://goo.gl/xIwvgk Original: [22] http://goo.gl/aUJGLJ * 24 Days of Hackage: 2013 in Review Domain: ocharles.org.uk, Score: 64, Comments: 11 On Reddit: [23] http://goo.gl/ideT63 Original: [24] http://goo.gl/DQYDar * Hacking Haskell in nightclubs (x-post from /r/programming) Domain: vice.com, Score: 60, Comments: 30 On Reddit: [25] http://goo.gl/ezuhIJ Original: [26] http://goo.gl/bD3vnN * 24 Days of Hackage: extensible-effects Domain: ocharles.org.uk, Score: 60, Comments: 25 On Reddit: [27] http://goo.gl/5T2brL Original: [28] http://goo.gl/q2hVM0 * From Object Oriented Programming to Functional Programming - Inheritance and the Expression Problem Domain: github.com, Score: 58, Comments: 62 On Reddit: [29] http://goo.gl/fFldOR Original: [30] http://goo.gl/n5nHYo * I've been working on a small roguelike in Haskell Domain: github.com, Score: 56, Comments: 26 On Reddit: [31] http://goo.gl/mojdIu Original: [32] http://goo.gl/fT9DLB * Chordify: Get the chords to any song, using Haskell ! Domain: chordify.net, Score: 55, Comments: 19 On Reddit: [33] http://goo.gl/YfcHEu Original: [34] http://goo.gl/19apd * Merging, Folding, Monoids, and Foldable Domain: mtnviewmark.wordpress.com, Score: 53, Comments: 5 On Reddit: [35] http://goo.gl/GtoDKp Original: [36] http://goo.gl/QJsd7L * 24 Days of Hackage: persistent & esqueleto Domain: ocharles.org.uk, Score: 49, Comments: 14 On Reddit: [37] http://goo.gl/97eeUF Original: [38] http://goo.gl/TL8P7V * Haskell From Scratch - Series about making a non-trivial app from the ground up. Domain: youtube.com, Score: 46, Comments: 2 On Reddit: [39] http://goo.gl/sPV7rs Original: [40] http://goo.gl/KslDE4 Top StackOverflow Questions * What does (f .) . g mean in Haskell? votes: 17, answers: 2 Read on SO: [41] http://goo.gl/2i3GNc * LaTeX natural deduction proofs using Haskell votes: 13, answers: 0 Read on SO: [42] http://goo.gl/uH1K2u * Lazily Tying the Knot for 1 Dimensional Dynamic Programming votes: 13, answers: 4 Read on SO: [43] http://goo.gl/1kZQkK * What does Clojure borrow from Haskell? [on hold] votes: 12, answers: 0 Read on SO: [44] http://goo.gl/DsqKhp * Meaning of `<-` in do block in Haskell votes: 10, answers: 4 Read on SO: [45] http://goo.gl/JOJiFy * Why is function composition in Haskell right associative? votes: 10, answers: 1 Read on SO: [46] http://goo.gl/mURUDZ * Is there a library or typeclass for getting the transformer version of a monad? votes: 9, answers: 1 Read on SO: [47] http://goo.gl/k81E1h * How to implement B+ tree in Haskell? votes: 9, answers: 2 Read on SO: [48] http://goo.gl/lkwh8Z * Delimiting the IO monad votes: 9, answers: 2 Read on SO: [49] http://goo.gl/x3RlXO Until next time, [50]+Daniel Santa Cruz References 1. http://www.dcs.gla.ac.uk/~muffy/SPJ_oration.pdf 2. http://www.reddit.com/r/haskell/comments/1sbfmb/honorary_doctorate_for_simo… 3. https://github.com/chrisdone/hell 4. http://www.reddit.com/r/haskell/comments/1r755t/hell_a_haskell_shell/ 5. https://github.com/quchen/articles/blob/master/loeb-moeb.md 6. http://www.reddit.com/r/haskell/comments/1qwjk6/l%C3%B6b_and_m%C3%B6b_stran… 7. http://www.well-typed.com/blog/84 8. http://www.reddit.com/r/haskell/comments/1rpte3/explanation_of_the_new_hask… 9. https://www.fpcomplete.com/ 10. http://www.reddit.com/r/haskell/comments/1qzioh/fp_complete_ide_now_free_fo… 11. http://www.haskellcast.com/episode/004-simon-marlow-on-parallelism-and-conc… 12. http://www.reddit.com/r/haskell/comments/1rexqq/the_haskell_cast_4_simon_ma… 13. http://ocharles.org.uk/blog/posts/2013-12-05-24-days-of-hackage-scotty.html 14. http://www.reddit.com/r/haskell/comments/1s65bl/24_days_of_hackage_scotty/ 15. http://www.idris-lang.org/idris-0-9-10-released/ 16. http://www.reddit.com/r/haskell/comments/1rn4d6/idris_0910_released/ 17. http://ocharles.org.uk/blog/posts/2013-12-07-24-days-of-hackage-threepenny-… 18. http://www.reddit.com/r/haskell/comments/1sc67q/24_days_of_hackage_threepen… 19. http://ocharles.org.uk/blog/posts/2013-12-02-24-days-of-hackage-linear.html 20. http://www.reddit.com/r/haskell/comments/1rximk/24_days_of_hackage_linear/ 21. http://ocharles.org.uk/blog/posts/2013-12-03-24-days-of-hackage-tasty.html 22. http://www.reddit.com/r/haskell/comments/1s0t1f/24_days_of_hackage_tasty/ 23. http://ocharles.org.uk/blog/posts/2013-12-01-24-days-of-hackage-intro.html 24. http://www.reddit.com/r/haskell/comments/1rv45n/24_days_of_hackage_2013_in_… 25. http://www.vice.com/read/algorave-is-the-future-of-dance-music-if-youre-an-… 26. http://www.reddit.com/r/haskell/comments/1riror/hacking_haskell_in_nightclu… 27. http://ocharles.org.uk/blog/posts/2013-12-04-24-days-of-hackage-extensible-… 28. http://www.reddit.com/r/haskell/comments/1s3oba/24_days_of_hackage_extensib… 29. https://github.com/Dobiasd/articles/blob/master/from_oop_to_fp_-_inheritanc… 30. http://www.reddit.com/r/haskell/comments/1quhrl/from_object_oriented_progra… 31. https://github.com/dvolk/hoodie 32. http://www.reddit.com/r/haskell/comments/1r248j/ive_been_working_on_a_small… 33. http://chordify.net/ 34. http://www.reddit.com/r/haskell/comments/1r7sh1/chordify_get_the_chords_to_… 35. https://mtnviewmark.wordpress.com/2013/12/02/mfmf/ 36. http://www.reddit.com/r/haskell/comments/1rz8cn/merging_folding_monoids_and… 37. http://ocharles.org.uk/blog/posts/2013-12-06-24-days-of-hackage-persistent-… 38. http://www.reddit.com/r/haskell/comments/1s9fyb/24_days_of_hackage_persiste… 39. https://www.youtube.com/playlist?list=PLxj9UAX4Em-Ij4TKwKvo-SLp-Zbv-hB4B 40. http://www.reddit.com/r/haskell/comments/1s48bm/haskell_from_scratch_series… 41. http://stackoverflow.com/questions/20279306/what-does-f-g-mean-in-haskell 42. http://stackoverflow.com/questions/19919431/latex-natural-deduction-proofs-… 43. http://stackoverflow.com/questions/20159269/lazily-tying-the-knot-for-1-dim… 44. http://stackoverflow.com/questions/20411148/what-does-clojure-borrow-from-h… 45. http://stackoverflow.com/questions/19961941/meaning-of-in-do-block-in-haske… 46. http://stackoverflow.com/questions/20342860/why-is-function-composition-in-… 47. http://stackoverflow.com/questions/20066858/is-there-a-library-or-typeclass… 48. http://stackoverflow.com/questions/20309501/how-to-implement-b-tree-in-hask… 49. http://stackoverflow.com/questions/20318936/delimiting-the-io-monad 50. https://plus.google.com/105107667630152149014/about

1 0

striping non-alphanumericals
by Joerg Fritsch 12 Dec '13

12 Dec '13

I have the following code snippet: import System.IO import Data.String.Utils main = withFile "test.txt" ReadMode $ \handle -> do xs <- getwords handle sequence_ $ map putStrLn (escapeRe xs) getwords :: Handle -> IO [String] getwords h = hGetContents h >>= return . words What I want to to there is to get i.e. "word," or "word!" etc. and arrive at "word". I understand that escapeRe may do this. However, I always get some sort of mismatch errors like this: test.hs:6:38: Couldn't match type `Char' with `[Char]' Expected type: [String] Actual type: String In the return type of a call of `escapeRe' In the second argument of `map', namely `(escapeRe xs)' In the second argument of `($)', namely `map putStrLn (escapeRe xs)' test.hs:6:47: Couldn't match type `[Char]' with `Char' Expected type: String Actual type: [String] In the first argument of `escapeRe', namely `xs' In the second argument of `map', namely `(escapeRe xs)' In the second argument of `($)', namely `map putStrLn (escapeRe xs)' Now I have three questions: 1. Is escapeRe the right function to use here? 2. What do I do wrong? 3. I read in the Real World Haskell book that actually all these file/string operations are very very slow. The recommendation is to work with bytestrings instead. Is there any (fast) way to strip non-alphanumericals from bytestrings? Thanks, --Joerg

3 2

Re: [Haskell-cafe] Does anyone use ghc-mod with Yesod?
by Carlo Hamalainen 11 Dec '13

11 Dec '13

On 11/12/13 01:36, Curtis Carter wrote: > I believe you just need to install that lib. It's not in the main > dependencies but in the test ones. That did the trick. I thought that yesod-test would be installed automatically when I ran cabal install in the Yesod project directory. I can confirm that ghc-mod works fine on a Yesod project via ghcmod-vim. Thanks, -- Carlo Hamalainen http://carlo-hamalainen.net

1 0

ANN: tasty-0.5
by Roman Cheplyaka 11 Dec '13

11 Dec '13

The new version of Tasty, a modern and extensible testing framework for Haskell, is out. The major new feature in this release is resources, described in detail in the article http://ro-che.info/articles/2013-12-10-tasty-resources.html Although I haven't posted here since the very first release of tasty, there have been many small improvements and some new big features, such as resources and ingredients. The core Tasty packages are now part of Stackage, which means that you can use them in FP Haskell Center™ and School of Haskell. It's also great to see third-party packages appearing, which was the main motivation behind Tasty's extensible design: http://hackage.haskell.org/package/tasty-th, by Benno Fünfstück http://hackage.haskell.org/package/tasty-hspec, by Mitchell Rosen http://hackage.haskell.org/package/tasty-ant-xml, by Oliver Charles To learn more about Tasty, please see: http://documentup.com/feuerbach/tasty — the README http://hackage.haskell.org/package/tasty-0.5.1/docs/Test-Tasty.html — the haddock documentation https://github.com/feuerbach/tasty/blob/master/CHANGES.md — the changelog http://ocharles.org.uk/blog/posts/2013-12-03-24-days-of-hackage-tasty.html — this year's «24 days of Hackage» article about Tasty Roman

1 0

Re: [Haskell-cafe] XEventPtr in Xlib?
by EatsKittens 11 Dec '13

11 Dec '13

Hmm, I think I now know how to work with XEventPtr's with allocaXEvent event, what I have now is this: raiseWin :: Win -> IO (); raiseWin w = let { d = disp w; r = root w; xID = xid w; } in do { ctime <- Monad.liftM (\(Time.TOD t _) -> fromIntegral t) Time.getClockTime; atom <- Xlib.Atom.internAtom d "_NET_ACTIVE_WINDOW" True; Xlib.Event.allocaXEvent $ \ePtr -> do { Xlib.Extras.setEventType ePtr XTypes.clientMessage; Xlib.Extras.setClientMessageEvent ePtr xID atom 32 2 ctime; Xlib.Event.sendEvent d r False (Xlib.substructureNotifyMask .|. Xlib.substructureRedirectMask) ePtr; }; }; where root in the Win record is derived from: (root, parent, _) <- Xlib.Extras.queryTree d xid; The code compiles and type checks, it just doesn't... work, it does nothing. Replacing the code with: raiseWin w = System.Process.rawSystem "xdotool" ["windowactivate", show x] >> return () where { x = xid w; } Makes it work without errors, inspecting the code of xdotool makes it reveal to use the "_NET_ACTIVE_WINDOW" client message to the root hole? Any idea what I could be doing wrongly, is this the correct root window? On 10 December 2013 06:22, Brandon Allbery <allbery.b(a)gmail.com> wrote: > On Mon, Dec 9, 2013 at 10:57 PM, EatsKittens < > temporalabstraction(a)gmail.com> wrote: > >> Xlib.Event seems to define the interestingly recursive type data XEvent = >> XEvent (Ptr XEvent) and otherwise give no information about that type. >> > > Anything on the far side of a Ptr is defined by C and accessed via the > FFI. In this case, you're looking for the XEvent structure defined by the C > Xlib and described in X11/X.h (constants) and X11/Xlib.h (structs; note > that there is a separate struct for each event type although they all have > a common preamble). > > You may be better served by the event definitions in > http://xmonad.org/xmonad-docs/X11/Graphics-X11-Xlib-Extras.html which is > a Haskell, instead of FFI, interface. (I pointed to the xmonad copy of the > docs because that's what I already have loaded in a tab, but it's part of > the same X11 binding as Graphics.X11.Xlib.Event.) > > I need this type to send an XEvent message to a window, is this a mistake >> or am I overlooking something in how to use it, or is the idea that the >> only way to make XEvent data is to make it in C and import it from there? >> > > allocaXEvent is defined in Graphics.X11.Xlib.Event, but you need to refer > to the C Xlib definitions and use FFI marshaling to work with it (and may > need to know C type sizes and how the C compiler packs structs on your > system). There's some code in xmonad-contrib which uses that interface to > send custom events. > > -- > brandon s allbery kf8nh sine nomine > associates > allbery.b(a)gmail.com > ballbery(a)sinenomine.net > unix, openafs, kerberos, infrastructure, xmonad > http://sinenomine.net >

2 2

f^n for functional iteration
by Doug McIlroy 10 Dec '13

10 Dec '13

Is there a trick whereby the customary notation f^n for iterated functional composition ((\n f -> foldl (.) id (replicate n f)) n f) can be defined in Haskell? Doug McIlroy

2 1

No instance for (Constructor Main.D1MyData)
by Maarten Faddegon 10 Dec '13

10 Dec '13

Dear list, I try to implement the generic show of section 3.6 from the paper Magelheas et al., "A Generic Deriving Mechanism for Haskell" but run into problems with the Constructor class. If someone could point out what is wrong here I would be most grateful. I import generics: > import GHC.Generics And I define my own "Show" class named "Toonbaar", and a generic version of the class "GToonbaar": > class Toonbaar a where > toon :: a -> String > > default toon :: (Generic a, GToonbaar (Rep a)) => a -> String > toon a = gtoon (from a) > > instance Toonbaar Int where > toon i = show i > > class GToonbaar f where > gtoon :: f a -> String Next I want implement instances of gtoon for the 5 primitive types that are used to by the "from" function to represent data types. Most interisting is the meta-information instance here, where I use the "conName" function. Most of the rest I copied from the serialization example on the wiki: http://www.haskell.org/haskellwiki/GHC.Generics#Complete_working_example > -- | Meta-information (constructor names, etc.) > instance (GToonbaar a, Constructor c) => GToonbaar (M1 i c a) where > gtoon m@(M1 _) = conName m > > -- | Unit: used for constructors without arguments > instance GToonbaar U1 where > gtoon _ = "Unit" > > -- | Constants, additional parameters and recursion of kind * > instance (GToonbaar a, GToonbaar b) => GToonbaar (a :*: b) where > gtoon _ = "Constant" > > > -- | Sums: encode choice between constructors > instance (GToonbaar a, GToonbaar b) => GToonbaar (a :+: b) where > gtoon x = gtoon x > > -- | Products: encode multiple arguments to constructors > instance (Toonbaar a) => GToonbaar (K1 i a) where > gtoon (K1 x) = toon x I define a data type, deriving Generic and make it an instance of Toonbaar. > data MyData = MyInt Int > deriving (Generic) > instance Toonbaar MyData > > main = putStrLn (toon (MyInt 42)) When I try to compile the above, ghc emits the following error: No instance for (Constructor Main.D1MyData) arising from a use of `Main.$gdmtoon' Possible fix: add an instance declaration for (Constructor Main.D1MyData) In the expression: (Main.$gdmtoon) In an equation for `toon': toon = (Main.$gdmtoon) In the instance declaration for `Toonbaar MyData' There are 2 things here that I do not understand: 1. I was under the impression that Constructor can be derived, but this does not seem to be the case. (I tried adding it to the line where I also derive Generic). Is there another way to derive it? 2. Why is the error message referring to D1MyData and not to MyData? And $gdmtoon instead of toon or gtoon? Thanks, Maarten

2 1

[ANN] SFML and SFML-control
by Alfredo Di Napoli 10 Dec '13

10 Dec '13

Hello guys, I will send you the link back to the original Reddit discussion that, for some unfathomable reason is not showing up directly in /r/haskell. http://www.reddit.com/r/haskell/comments/1sjemq/ann_sfml_and_sfmlcontrol/ Feedback appreciated! Alfredo

1 0

Does anyone use ghc-mod with Yesod?
by Carlo Hamalainen 10 Dec '13

10 Dec '13

Hi, I have been using ghc-mod (via ghcmod-vim) recently and it's fantastic but I can't get it to work on one of my Yesod projects. This is what happens on a minimal scaffolded Yesod project: $ yesod init # create project Foo, sqlite, no other options $ cd Foo $ cabal install # builds ok, no issues $ ghc-mod check Handler/Home.hs Handler/Home.hs:0:0:Error:<command line>: cannot satisfy -package yesod-test (use -v for more information) I've reported the error on github [1] but I was wondering if anyone here had a workaround, maybe using cabal-dev or sandboxing or something? Cheers, -- Carlo Hamalainen http://carlo-hamalainen.net [1] https://github.com/kazu-yamamoto/ghc-mod/issues/170

1 0

XEventPtr in Xlib?
by EatsKittens 10 Dec '13

10 Dec '13

Xlib.Event seems to define the interestingly recursive type data XEvent = XEvent (Ptr XEvent) and otherwise give no information about that type. I need this type to send an XEvent message to a window, is this a mistake or am I overlooking something in how to use it, or is the idea that the only way to make XEvent data is to make it in C and import it from there?

2 1

cmm
by Alexander Pakhomov 10 Dec '13

10 Dec '13

Hi. Trying to compile ghc-7.7.20130828 on OpenBSD I got an error: rts/HeapStackCheck.cmm:97:18: parse error on input `[' The code is following: 96 if (HpAlloc <= BLOCK_SIZE 97 && bdescr_link(CurrentNursery) != NULL) { which preprocesses to: if (HpAlloc <= (1<<12) && b0[CurrentNursery+15] != (0::bits64)) { This is the first occurrence of b0 in preprocessed file. I believe that it is due to undefined b0. Command that fails is: "inplace/bin/ghc-stage1" -static -H32m -O -Iincludes -Iincludes/dist -Iincludes/dist-derivedconstants/header -Iincludes/dist-ghcconstants/header -Irts -Irts/dist/build -DCOMPILING_RTS -package-name rts -dcmm-lint -i -irts -irts/dist/build -irts/dist/build/autogen -Irts/dist/build -Irts/dist/build/autogen -O2 -c rts/HeapStackCheck.cmm -o rts/dist/build/HeapStackCheck.o To preprocess do the following: cpp -O -Iincludes -Iincludes/dist -Iincludes/dist-derivedconstants/header -Iincludes/dist-ghcconstants/header -Irts -Irts/dist/build -DCOMPILING_RTS -Irts/dist/build -Irts/dist/build/autogen rts/HeapStackCheck.cmm | less Can you please find source of b0 in preprocessed file?

2 5

Call for Participation PEPM 2014 (co-located with POPL 2014)
by Jurriaan Hage 09 Dec '13

09 Dec '13

Dear all, Note the presence of Haskell papers in the program. Hope to see many of you there. best, Jur (co-chair of PEPM 2014) =========== PEPM 2014 =============== ACM SIGPLAN Workshop on Partial Evaluation and Program Manipulation http://www.program-transformation.org/PEPM14 January 20-21, 2014 San Diego, CA, USA (Affiliated with POPL 2014) CALL FOR PARTICIPATION IMPORTANT DATES * Hotel reservation deadline: December 21, 2013 * Early registration deadline: December 31, 2013 VENUE PEPM'14 and all POPL'14 affiliated events will take place at the US Grant in San Diego, CA, USA. SCOPE The PEPM Symposium/Workshop series aims at bringing together researchers and practitioners working in the areas of program manipulation, partial evaluation, and program generation. PEPM focuses on techniques, theory, tools, and applications of analysis and manipulation of programs. INVITED TALKS: * Manuel Fahndrich (Microsoft Research, USA) on Lessons from a Web-Based IDE and Runtime * Sven-Bodo Scholz (Heriott-Watt University, Scotland) on Partial Evaluation as Universal Compiler Tool (experiences from the SAC eco system) PROGRAM CHAIRS Wei Ngan Chin (National University of Singapore, Singapore) Jurriaan Hage (Utrecht University, Netherlands) PROGRAM COMMITTEE Evelyne Contejean (LRI, CNRS, Université Paris-Sud, France) Cristina David (University of Oxford, UK) Alain Frisch (LexiFi, France) Ronald Garcia (University of British Columbia, Canada) Zhenjiang Hu (National Institute of Informatics, Japan) Paul H J Kelly (Imperial College, UK) Oleg Kiselyov (Monterey, USA) Naoki Kobayashi (University of Tokyo, Japan) Jens Krinke (University College London, UK) Ryan Newton (University of Indiana, USA) Alberto Pardo (Universidad de la República, Uruguay) Sungwoo Park (Pohang University of Science and Technology, South Korea) Tiark Rompf (Oracle Labs & EPFL, Switzerland) Sukyoung Ryu (KAIST, South Korea) Kostis Sagonas (Uppsala University, Sweden) Max Schaefer (Nanyang Technological University, Singapore) Harald Søndergaard (The University of Melbourne, Australia) Eijiro Sumii (Tohoku University, Japan) Eric Van Wyk (University of Minnesota, USA) Jeremy Yallop (University of Cambridge, UK) PRELIMINARY PROGRAM DAY 1: Monday, January 20th, 2014 ================================== 09:00 - 10:00 Invited Talk =========================== Lessons from a Web-Based IDE and Runtime Manuel Fahndrich 10:30 - 12:00 Meta-Programming ------------------------------- Combinators for Impure yet Hygienic Code Generation Yukiyoshi Kameyama, Oleg Kiselyov, Chung-Chieh Shan Effective Quotation James Cheney, Sam Lindley, Gabriel Radanne, Philip Wadler Compile-time Reflection and Metaprogramming for Java Weiyu Miao, Jeremy Siek 14:00 - 15:25 Bidirectional Transformations -------------------------------------------- Monadic Combinators for "Putback" Style Bidirectional Programming Hugo Pacheco, Zhenjiang Hu and Sebastian Fischer Semantic Bidirectionalization Revisited Meng Wang and Shayan Najd Generating Attribute Grammar-based Bidirectional Transformations from Rewrite Rules Pedro Martins, Joao Paulo Fernandes, Joao Saraiva and Eric Van Wyk 16:00 - 17:00 Static Analysis and Optimization ----------------------------------------------- Optimizing SYB is Easy! Michael D. Adams, Andrew Farmer, Jose Pedro Magalhaes: QEMU/CPC: Static Analysis and CPS Conversion for Safe, Portable, and Efficient Coroutines Gabriel Kerneis, Charlie Shepherd, Stefan Hajnoczi ================================= DAY 2: Tuesday, January 21, 2014 ================================= 09:00 - 10:00 Invited Talk --------------------------- Partial Evaluation as Universal Compiler Tool (experiences from the SAC eco system) Sven-Bodo Scholz 10:30 - 12:00 Program Transformation -------------------------------------- The HERMIT in the Stream Andrew Farmer, Christian Hoener Zu Siederdissen, Andy Gill Type-Changing Rewriting and Semantics-Preserving Transformation Sean Leather, Johan Jeuring, Andres Loeh, Bram Schuur An Operational Semantics for Android Activities Etienne Payet, Fausto Spoto 14:00 - 15:30 Type Systems ---------------------------- Early Detection of Type Errors in C++ Templates Sheng Chen, Martin Erwig Lazy Stateless Incremental Evaluation Machinery for Attribute Grammars Jeroen Bransen, Atze Dijkstra, Doaitse Swierstra Deriving Interpretations of the Gradually-Typed Lambda Calculus. Alvaro Garcia-Perez, Pablo Nogueira, Ilya Sergey 16:00 - 17:20 Program Analysis/Testing ---------------------------------------- Automating Property-based Testing of Evolving Web Services Huiqing Li, Simon Thompson, Pablo Lamela Seijas, Miguel Angel Francisco A Modular and Generic Analysis Server System for Functional Logic Programs Michael Hanus, Fabian Skrlac HIPimm: Verifying Granular Immutability Guarantees Andreea Costea, Asankhaya Sharma, Cristina David

1 0

Is anyone currently working on SDL2 FFI ?
by Ömer Sinan Ağacan 09 Dec '13

09 Dec '13

Hello everyone, I was wondering if anyone is currently working on SDL2 FFI. I really need that library and I'm willing to contribute to the work, but I can't currently spare enough time to start it from scratch(it's very big library). I know we have OpenGL and GLFW bindings and gloss for 2D stuff etc. but for several reasons I want this particular library. (just wanted to make this clear because I presume people point me alternatives otherwise :-) ) Thanks, --- Ömer Sinan Ağacan http://osa1.net

4 4

GHCi linker
by Alexander Pakhomov 09 Dec '13

09 Dec '13

Hi. Trying to runhaskell following: import Graphics.UI.Gtk main = print "OK" I got GHCi runtime linker: fatal error: I found a duplicate definition for symbol locale_charset whilst processing object file /usr/local/lib/libintl.a This could be caused by: * Loading two different object files which export the same symbol * Specifying the same object file twice on the GHCi command line * An incorrect `package.conf' entry, causing some object to be loaded twice. GHCi cannot safely continue in this situation. Exiting now. Sorry. ghc works fine and creates working executable. In ghci "import Graphics.UI.Gtk" works too. What is the difference between runhaskell, ghci interactive and ghc linkers? ghc 7.6.3 running on OpenBSD. It is built from ports system with default patches. I don't see any patch that touches GHCi linker.

2 1

FLOPS 2014 Final CFP (Reminder)
by Eijiro Sumii 09 Dec '13

09 Dec '13

Final 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/ ---------------------------------------------------------------------- - Submission deadline: December 13, 2013 - 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. ---------------------------------------------------------------------- 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)

1 0

Re: [Haskell-cafe] converting between a Ptr a and an Integer
by keydana＠gmx.de 08 Dec '13

08 Dec '13

Hi, thanks for your answers, I've found a way (or rather, was pointed to it ;-) ) in the meantime, using something like nullPtr `plusPtr` <desired address> Thanks all the same, Sigrid

1 0

existential quantification
by TP 08 Dec '13

08 Dec '13

Hi everybody, I try to understand existential quantification. I have two questions. 1/ I have just read the answer of yairchu at http://stackoverflow.com/questions/3071136/what-does-the-forall-keyword-in-… He writes: """ So with Existential-Quantification, foralls in data definitions mean that, the value contained *can* be of *any* suitable type, not that it *must* be of *all* suitable types. """ This made me think to an error I obtained with the code: --------------- test :: Show s => s test = "foobar" --------------- The error is: Could not deduce (s ~ [Char]) from the context (Show s) bound by the type signature for test :: Show s => s [...] `s' is a rigid type variable bound by the type signature for test :: Show s => s Indeed, `test :: Show s => s` means "for any type s which is an instance of Show, test is a value of that type s". But for example "foobar" can't be an Int that is an instance of Show, so it yields an error. By comparison, --------------- test :: Num a => a test = 42 --------------- works because 42 can be a value of type Int or Integer or Float or anything else that is an instance of Num. So I thought that by using existential quantification, the first example could work: --------------- {-# LANGUAGE ExistentialQuantification #-} test :: forall s . Show s => s test = "asd" --------------- But I obtain the same error, why? 2/ Is the notion of existential type related in some way to the classical mathematical quantifier "∃" (Unicode symbol U+2203: "There exists")? If yes, then why using "forall" for an "existential type"? At the following address http://www.haskell.org/ghc/docs/6.12.1/html/users_guide/data-type-extension… we read """ 7.4.4.1. Why existential? What has this to do with existential quantification? Simply that MkFoo has the (nearly) isomorphic type MkFoo :: (exists a . (a, a -> Bool)) -> Foo But Haskell programmers can safely think of the ordinary universally quantified type given above, thereby avoiding adding a new existential quantification construct. """ But I don't understand the explanation. Thanks in advance, TP

7 10

STM interfacing with GLFW
by Pavel Krajcevski 08 Dec '13

08 Dec '13

Hi, I'm new to STM and to Haskell in general. I've been writing a small library to try some graphics algorithms in Haskell, but using GLFW's callbacks seems to be causing me problems. I have a (relatively heavyweight?) object wrapped in a TVar (Data.Set) that I'm sharing across all threads. Unfortunately, once I run the program, it becomes unresponsive although the main loop is still running. I'm not sure exactly what the semantics are for getting STM right, but ideally I'm trying to modify the TVar in GLFW event callbacks and then finally read out the value of the TVar at the end (or beginning) of my rendering loop. I've been able to get a small program working that reproduces my problem: https://gist.github.com/Mokosha/34eda7bd2d6b5cafd5a3 Any help would be great! Thanks! - Pavel

1 1

converting between a Ptr a and an Integer
by keydana＠gmx.de 07 Dec '13

07 Dec '13

Hi, is there any way to convert between a Ptr a and an Integer? (I would like to attach to shared memory and dereference pointers to certain memory addresses, as you would do in C.) If there is no way at all, I think I could still get along by defining c_shmat as c_shmat :: CInt -> CInt -> CInt -> IO (Ptr a) and perform calculations using plusPtr, but then how do I check if I got back the correct address, and not (void *) -1, which is what shmat returns on error? Any help very much appreciated! Thanks Sigrid

3 2

Higher order functions and strictness
by Joachim Breitner 07 Dec '13

07 Dec '13

Hi, we currently have a pattern where a higher order function (like foldl, or Map.unionWith), which naively build thunks without the passed function having a chance to prevent that. Therefore, there are variants like foldl', which seq the result of the function. Can one have one function that allows for both? I take mapMaybe :: (a -> b) -> Maybe a -> Maybe b as an (simple, and not very relevant) example. With that signature, there is not much "mapMaybe f x" can do. It either applies f lazily to x, or strictly. One could have data Box a = Box a mapMaybe :: (a -> Box b) -> Maybe a -> Maybe b and have mapMaybe pattern-match on Box. Then it will evaluate _something_ of the return value of f, and f can have control over whether the thing inside the box is evaluated or not. So this is nice, but unfortunately we now allocate and destruct a box that we do not care about. But since I had been looking at some unboxed tuples recently, I noticed that the singleton unboxed tuple allows for exactly that: Call a function in a way that it has control (i.e. can force stuff), but do not necessarily evaluate its result, and all that without extra allocations. Here is some example code: {-# LANGUAGE UnboxedTuples #-} import GHC.HeapView mapMaybe :: (a -> (# b #) ) -> Maybe a -> Maybe b mapMaybe _ Nothing = Nothing mapMaybe f (Just x) = case f x of (# y #) -> Just y f_plain :: Int -> Int f_plain x = x + 1 f_lazy :: Int -> (# Int #) f_lazy x = (# x + 1 #) f_strict :: Int -> (# Int #) f_strict x = let y = x + 1 in y `seq` (# y #) main = do let x = Just 1 Just y1 <- return $ fmap f_plain x Just y2 <- return $ mapMaybe f_lazy x Just y3 <- return $ mapMaybe f_strict x let results = (y1,y2,y3) buildHeapTree 10 (asBox results) >>= putStrLn . ppHeapTree and here the result: (_thunk _fun{0} (I# 1),_thunk (I# 1),I# 2) as expected and desired, fmap and mapMaybe with the lazy f left a thunk in the Just constructor, while the strict f had a chance to evaluate its result. Of course (#..#) has it downsides, e.g. you cannot make a newtype for it (newtype Box a = (# x #)) does not work... but it might be an interesting design pattern if you need it – imagine a "mapTuple10", which takes 10 function arguments – you can’t have '-variants for every 2^10 possible strictness combinations. Greetings, Joachim -- Joachim “nomeata” Breitner mail(a)joachim-breitner.de • http://www.joachim-breitner.de/ Jabber: nomeata(a)joachim-breitner.de • GPG-Key: 0x4743206C Debian Developer: nomeata(a)debian.org

2 1

Haskell on Heroku (improved)
by Joe Nelson 06 Dec '13

06 Dec '13

Hey all, I just created a buildpack to deploy Haskell apps to Heroku. If you use Yesod or Snap or whatever give it a try. It uses GHC 7.6.3 and Cabal 1.18 so it should support all the modern goodies you like to use. https://github.com/begriffs/heroku-buildpack-ghc Also some people have reported an issue with cabal-install choosing the wrong versions of packages. Anyone run into this kind of thing before? https://github.com/begriffs/heroku-buildpack-ghc/issues/7 Regards, Joe Nelson

1 0

hash tables, judy arrays, and more
by Ketil Malde 06 Dec '13

06 Dec '13

Hi, As some of you may know¹, I've been playing around with associative data structures, and in particular Judy arrays, using the "judy" package by Don S. Now, I find these to be fast and (more importantly) frugal concerning memory - but now I see what I can only interpret as memory corruption - a bit depending on the ordering of the code and/or insertion of print statements, output is truncated or contaminated. The strange thing is that this only occurs when I also use Data.Vector or Data.HashTable.IO in the same program - if it's all Judy, then things work as expected - as far as I have seen, anyway. First I thought it was my dubious "insertWith" function, but when I reverted to separate "insert" and "lookup", I can still provoke the behavior. Has anybody else seen anything similar? Any idea how to debug something like this? Then I thought I'd look at hash tables, using the 'hashtables' package. I haven't tested it much yet, but it appears to be a lot slower than Judy (maybe as much as 10x), and uses a lot more memory (also perhaps a factor of 10). I guess I might be able to improve things a bit by judiciously applying strictness, but it seems to be storing both keys and values unboxed, so I don't expect to come close to Judy - I guess there isn't any unboxed hash table implementations around? Anyway - I seem to have programmed myself into a corner here, so suggestions welcome! -k ¹ http://blog.malde.org/posts/frequency-counting.html and http://blog.malde.org/posts/k-mer-counting.html -- If I haven't seen further, it is by standing in the footprints of giants

2 1

Return of the revenge of the revisit of the extensible records, reiterated
by Atze van der Ploeg 06 Dec '13

06 Dec '13

Dear all, Extensible records have been a long outstanding feature request for GHC. Using the new closed type families and type literals, it is actually possible to implement Daan Leijen's "`Extensible Records with Scoped Labels" system as a library. I have implemented this library at https://github.com/atzeus/openrec (the documentation is at http://homepages.cwi.nl/~ploeg/openrecvardocs/) The only thing it requires is the availability of a closed type family that compares two type level symbols (i.e. the ordering on strings): type family (m :: Symbol) <=.? (n :: Symbol) :: Bool patches to GHC that implement this built-in closed type family are also at the github site. I would like to generate some discussion about: * Is this the interface we would like for open records and variants? * Would it be worthwhile to invest in syntactic sugar for open record operations? * Any comments on the interface and or its implementation? Cheers! Atze van der Ploeg

6 20

Help with profiling
by Uri Braun 06 Dec '13

06 Dec '13

Hi Café, I'm attempting to profile my rather large (~18K LOC) Haskell program that primarily manipulates graph structures based on Data.IntMap. The program is chewing up _lots_ of memory (approx. 4G for 2.5K nodes & 2.5K edges) and I have profiled it in an attempt to figure out why. It appears that the .prof and .hp (which I visualize with hp2ps -c) files do not agree on the source of the problem. The hp results are located at: http://www.eecs.harvard.edu/~uribraun/sybil.ps and the top of the .prof file looks like this: COST CENTRE MODULE %time %alloc compare Policy.Edge 21.7 50.0 eqPartition.edges Policy.EdgeQuad 6.5 3.7 toConstructedSet Types.TaggedIntMultimap 6.1 3.6 elems Types.TaggedIntMap 6.0 6.8 elems Types.TaggedIntSet 5.7 3.8 toPairs Types.TaggedIntMultimap 3.9 5.2 assocs Types.TaggedIntMap 3.2 4.1 eqIsValid Policy.EdgeQuad 2.9 0.5 rIsValid Policy.Relations 2.2 0.2 assocs.\ Types.TaggedIntMap 1.8 0.0 keysSet Types.TaggedIntMap 1.5 1.7 mergeIdenticalNodesT.exactMap Minimize.MergeIdentical 1.4 1.2 fromList Types.TaggedIntSet 1.3 1.6 tePartitionSrc Policy.TaggedEdge 1.2 0.9 null Types.TaggedIntSet 1.2 0.0 scc.comps Policy.Scc 1.2 0.9 tePartitionTgt Policy.TaggedEdge 1.1 0.8 member Types.TaggedIntSet 1.1 0.8 alter Types.TaggedIntMap 1.0 1.1 Also, the line in the .prof that corresponds to the anormUnion.name (what the hprof image claims is taking up space) looks like (some spaces removed): anormUnion.name Anormalize.Anormalize 2914 60 0.0 0.0 0.0 0.0 My main questions at this point are: 1. What are the chances the hprof image is just wrong? 2. What would you suggest I try next in debugging my space issue? This is my first big Haskell program, please do inform me of any big war tools I dont know about. Many thanks in advance! +Uri

2 2

Re: [Haskell-cafe] free vs. operational vs. free-operational
by oleg＠okmij.org 06 Dec '13

06 Dec '13

Alejandro Serrano Mena wrote: > I really like the separation between providing a data type and then a > interpretation that operational embodies... Then perhaps you may like extensible effects then. They are designed around the separation of requestors and their interpreters. However, the set of requests is open (and can be extended at any time without recompiling the program). Likewise the interpreters can be extended incrementally. One can add an interpreter for an effect without caring what other effects are there -- unless one has some reason for caring about other effects (e.g.,m for finalization). One may then snoop on other effects while interpreting. Moreover, the handlers may be scattered around program; they don't have to be all at the very top. Crucially, unlike data types a la carte, extensible effects provide effect encapsulation: one can not only add effects but subtract them, by completely handling the effects. The type system ensures that all effects must be completely handled at the end.

7 13

Cannot find HS*.o linked object for loading into ghci after last update
by Thiago Padilha 05 Dec '13

05 Dec '13

Hi After last update, cabal-install stopped generating an HSfoo-VERSION.o(assuming the package name is 'foo') in the dist/build directory. How can I force cabal to generate this file again?

2 2

Simple script to make existing GHC or HP installation work with Xcode 5
by Mark Lentczner 05 Dec '13

05 Dec '13

Friends - I've developed a simple shell script that should enable your existing GHC 7. or HP installation work with Xcode 5. https://gist.github.com/mzero/7245290 Place that script somewhere, make it executable, and run it. *Then follow the instructions it tells you!* You will end up having to run it more than once: First time it will tell you where to install a copy of the script Second time it will patch your GHC settings file(s) The script is safe to install and setup before you upgrade to Xcode 5, as it reverts to "getting out of the way" if it detects Xcode 4 based installation. It has been tested on two machines: - OS X 10.8 and Xcode 4 - OS X 10.9 and Xcode 5 If a few more intrepid souls test it and it works, I'll post instructions in more prominent places! I'll be testing OS X 10.9 and Xcode 4, tomorrow, and expect it should work fine on OS X10.8 with Xcode 5. But looking for reports that it all works. - Mark "Mac Packager" Lentczner

3 2

Re: [Haskell-cafe] Writer + log each computation to stdout
by oleg＠okmij.org 05 Dec '13

05 Dec '13

Bryan Vicknair wrote: > I have a bunch of little database IO functions. Each does something to the > database, and returns a log string describing what it did, and possibly a > meaningful result from the database. > ...and a few functions that orchestrate all the little functions into doing > useful work. > > I don't want the individual functions to know what is done with the log string > describing what they did. Top-level orchestrating functions should make that > decision, which can be one of: > > 1) Collect and print all to a log once all computations are done. > 2) Print to stdout *as each computation is run*. > 3) Ignore them. What an excellent case for extensible effects! Many thanks to Ben Foppa for making the package available on hackage, as extensible-effects. Extensible Effects designed specifically to separate a client (the requestor of an action) from a handler, the executor of an action. A logging client merely requests a string to be logged. It has no idea what happens when that request is executed. Therefore, the same client can be used with several handlers, even within the same expression. One can also build various interceptors, such as logIntercept, which is similar to Unix' tee. The following file illustrates how to solve the problem with all three scenarios. http://okmij.org/ftp/ The extensible effects package actually defines a very similar function, calls trace. For illustration and clarity, the file develops the Logging effect from scratch. After all, Extensible Effects encourages developing effects to suit the problem at hand. Defining a new effect is as simple as -- The request to log a string -- The request carries the String to log. It seems no particular -- reply is needed for the request (other than the simple acknowledgment), -- so we set the reply to be unit. data Log v = Log String (() -> v) deriving (Typeable, Functor) Clients use the function logit :: Member Log r => [Char] -> Eff r () (this signature, as all signatures in the code, are inferred). The signature says that the function request Log effect to be done. It does not concern itself how this effect its to be done. The file shows three handlers: runLogCollect, runLogTrace, runLogIgnore. There is also another handler, logIntercept, that like Unix 'tee', prints out the log message immediately while still propagating it. It can be used with any of the three handlers.

2 2

PhD at age 45?
by Dennis Raddle 05 Dec '13

05 Dec '13

A more specific question than my last post. I guess I'm wondering if it's a good idea to begin a PhD in CS at age 45 (currently having a BS in CS). My goal is to obtain work that interests me, work that really draws on the skills one develops in a PhD program. Work in academia is hard to obtain, I understand, but I could take an industry job. I'm wondering if I'll just be postponing a job with no financial gain afterward and poor prospects for work. Or if there is ageism that will work against a guy coming out of school at age 52. Or, if it will truly lead to an interesting job with good pay. Dennis

18 25

Need help: Cabal rejecting stringsearch, conflict in base
by Thiago Negri 04 Dec '13

04 Dec '13

I don't know what to do. :-( I can't install scotty or yesod. $ cabal install scotty cabal: Could not resolve dependencies: trying: scotty-0.5.0 (user goal) trying: base-4.7.0.0/installed-dc1... (dependency of scotty-0.5.0) trying: wai-extra-1.3.4.6 (dependency of scotty-0.5.0) trying: stringsearch-0.3.6.4 (dependency of wai-extra-1.3.4.6) rejecting: stringsearch-0.3.6.4:-base3 (conflict: base==4.7.0.0/installed-dc1..., stringsearch-0.3.6.4:base3 => base>=2 && <3) rejecting: stringsearch-0.3.6.4:+base3 (conflict: base==4.7.0.0/installed-dc1..., stringsearch-0.3.6.4:base3 => base>=3 && <4) Backjump limit reached (change with --max-backjumps).

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Trouble cabal installing uniplate?
by David Banas 04 Dec '13

04 Dec '13

Has anyone else bumped into this error, when cabal installing uniplate? Data/Generics/Uniplate/Direct.hs:78:4: error: invalid preprocessing directive #-} ^ 1 error generated. Failed to install uniplate-1.6.11 Thanks, -db

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Writer + log each computation to stdout
by Bryan Vicknair 04 Dec '13

04 Dec '13

Hello, I have a bunch of little database IO functions. Each does something to the database, and returns a log string describing what it did, and possibly a meaningful result from the database. query :: IO (String, a) update :: a -> IO (String, ()) ...and a few functions that orchestrate all the little functions into doing useful work. syncWeek :: Week -> IO () syncAll : : IO () I don't want the individual functions to know what is done with the log string describing what they did. Top-level orchestrating functions should make that decision, which can be one of: 1) Collect and print all to a log once all computations are done. 2) Print to stdout *as each computation is run*. 3) Ignore them. Here is my understanding of how common monads would handle these requirements: Writer: 1 and 3 are easy. This is what I originally attempted to use, but I couldn't figure out how to accomplish #2. Reader: 2 and 3 can be accomplished if each function reads a shouldLog config variable from the reader and does a putStrLn depending on the value. Very ugly, as now each function has to know how to log output. State: Not sure, but the Writer docs in the transformers package points to this monad as maybe solving requirement #2 above. The use case is that when I call the top-level functions from a command line script, I want to see logging happening in real-time to stdout, but I may call the same top-level functions from a larger application that may be logging to somewhere other than stdout, and may call the top-level functions from yet another larger application which doesn't want anything to be logged. How can I glue together a bunch of smaller computations, which may call each other, and decide at a higher level what to do with the logging result of each computation? Seems like a perfect fit for Writer, except for the requirement to be able to print to stdout at each step. Bryan Vicknair

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[TFP 2014] 1st Call For Papers
by Peter Achten 03 Dec '13

03 Dec '13

Dear reader, Please find included the first call for papers for next year's Trends In Functional Programming event, organized by Jurriaan Hage from Utrecht University, The Netherlands. With kind regards, Peter Achten Communication chair TFP ----------------------------- C A L L F O R P A P E R S ----------------------------- ======== TFP 2014 =========== 15th Symposium on Trends in Functional Programming May 26-28, 2014 Utrecht University Soesterberg, The Netherlands http://www.cs.uu.nl/wiki/TFP2014/WebHome The symposium on Trends in Functional Programming (TFP) is an international forum for researchers with interests in all aspects of functional programming, taking a broad view of current and future trends in the area. It aspires to be a lively environment for presenting the latest research results, and other contributions (see below), described in draft papers submitted prior to the symposium. A formal post-symposium refereeing process then selects a subset of the articles presented at the symposium and submitted for formal publication. Selected papers will be published as a Springer Lecture Notes in Computer Science (LNCS) volume. TFP 2014 will be the main event of a pair of functional programming events. The other is the International Workshop on Trends in Functional Programming in Education (TFPIE). TFPIE will take place on May 25th. The TFP symposium is the heir of the successful series of Scottish Functional Programming Workshops. Previous TFP symposia were held in Edinburgh (Scotland) in 2003, in Munich (Germany) in 2004, in Tallinn (Estonia) in 2005, in Nottingham (UK) in 2006, in New York (USA) in 2007, in Nijmegen (The Netherlands) in 2008, in Komarno (Slovakia) in 2009, in Oklahoma (USA) in 2010, in Madrid (Spain) in 2011, St. Andrews (UK) in 2012 and Provo (Utah, USA) in 2013. For further general information about TFP please see the TFP homepage. INVITED SPEAKERS TFP is pleased to announce talks by the following two invited speakers: John Hughes of Chalmers, Goteborg, Sweden, is well-known as author of Why Functional Programming Matters, and as one of the designers of QuickCheck (together with Koen Claessen); the paper on QuickCheck won the ICFP Most Influential Paper Award in 2010. Currently he divides his time between his professorship and Quviq, a company that performs property-based testing of software with a tool implemented in Erlang. Dr. Geoffrey Mainland received his PhD from Harvard University where he was advised by Greg Morrisett and Matt Welsh. After a two year postdoc with the Programming Principles and Tools group at Microsoft Research Cambridge, he is now an assistant professor at Drexel University. His research focuses on high-level programming language and runtime support for non-general purpose computation. SCOPE The symposium recognizes that new trends may arise through various routes. As part of the Symposium's focus on trends we therefore identify the following five article categories. High-quality articles are solicited in any of these categories: Research Articles: leading-edge, previously unpublished research work Position Articles: on what new trends should or should not be Project Articles: descriptions of recently started new projects Evaluation Articles: what lessons can be drawn from a finished project Overview Articles: summarizing work with respect to a trendy subject Articles must be original and not submitted for simultaneous publication to any other forum. They may consider any aspect of functional programming: theoretical, implementation-oriented, or more experience-oriented. Applications of functional programming techniques to other languages are also within the scope of the symposium. Topics suitable for the symposium include: Functional programming and multicore/manycore computing Functional programming in the cloud High performance functional computing Extra-functional (behavioural) properties of functional programs Dependently typed functional programming Validation and verification of functional programs Using functional techniques to reason about imperative/object-oriented programs Debugging for functional languages Functional programming in different application areas: security, mobility, telecommunications applications, embedded systems, global computing, grids, etc. Interoperability with imperative programming languages Novel memory management techniques Program analysis and transformation techniques Empirical performance studies Abstract/virtual machines and compilers for functional languages (Embedded) domain specific languages New implementation strategies Any new emerging trend in the functional programming area If you are in doubt on whether your article is within the scope of TFP, please contact the TFP 2014 program chair, Jurriaan Hage at J.Hage(a)uu.nl. BEST PAPER AWARDS To reward excellent contributions, TFP awards a prize for the best paper accepted for the formal proceedings. TFP traditionally pays special attention to research students, acknowledging that students are almost by definition part of new subject trends. A student paper is one for which the authors state that the paper is mainly the work of students, the students are listed as first authors, and a student would present the paper. A prize for the best student paper is awarded each year. In both cases, it is the PC of TFP that awards the prize. In case the best paper happens to be a student paper, that paper will then receive both prizes. SPONSORS TFP is financially supported by NWO (Netherlands Organisation for Scientific Research), Well-Typed and Erlang Solutions. PAPER SUBMISSIONS Acceptance of articles for presentation at the symposium is based on a lightweight peer review process of extended abstracts (4 to 10 pages in length) or full papers (16 pages). The submission must clearly indicate which category it belongs to: research, position, project, evaluation, or overview paper. It should also indicate whether the main author or authors are research students. In the case of a full student paper, the paper will receive additional feedback by one of the PC members shortly after the symposium has taken place. We shall use EasyChair for the refereeing process. IMPORTANT DATES Submission of draft papers: March 17, 2014 Notification: March 24, 2014 Registration: April 7, 2014 TFP Symposium: May 26-28, 2014 Student papers feedback: June 9th, 2014 Submission for formal review: July 1st, 2014 Notification of acceptance: September 8th, 2014 Camera ready paper: October 8th, 2014 PROGRAM COMMITTEE Peter Achten Radboud University Nijmegen Emil Axelsson Chalmers Lucilia Camarao de Figueiredo Universidade Federal de Ouro Preto Laura Castro University of A Coruna Frank Huch Christian-Albrechts-University of Kiel Matthew Fluet Rochester Institute of Technology Jurriaan Hage (chair) University of Utrecht Yukiyoshi Kameyama University of Tsukuba Andrew Kennedy Microsoft Research Tamas Kozsik Eotvos Lorand University Ben Lippmeier University of New South Wales Luc Maranget INRIA Jay McCarthy Brigham Young University Marco T. Morazan Seton Hall University Ricardo Pena Universidad Complutense de Madrid Alexey Rodriguez madvertise Sven-Bodo Scholz Heriot-Watt University Manuel Serrano INRIA Sophia Antipolis Simon Thompson University of Kent Tarmo Uustalu Inst of Cybernetics David Van Horn Maryland University Janis Voigtlaender University of Bonn

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Re: [Haskell-cafe] Constraint-folding
by oleg＠okmij.org 03 Dec '13

03 Dec '13

Andras Slemmer wrote: > I stumbled upon something pretty neat, and although I'm 95% sure Oleg did > this already 10 years ago in Haskell98 You're quite right about this: Chung-chieh Shan and I did this reification of constraint in December 2003, and almost in Haskell 98 (we needed Rank2 types though). It was described in the following paper http://okmij.org/ftp/Haskell/types.html#Prepose We called this transformation reflection/reification. I'm writing though to show a dual formulation to your development of using singletons. It gets by without GADTs and uses very few extensions: essentially Haskell98 with Rank2 types. {-# LANGUAGE RankNTypes #-} data Zero data Succ a class Class n instance Class Zero instance (Class m) => Class (Succ m) -- Tagless final class Sym repr where z :: repr Zero s :: repr n -> repr (Succ n) newtype R x = R{unR:: x} -- the identity interpreter instance Sym R where z = R undefined s _ = R undefined newtype S x = S Integer -- for show instance Sym S where z = S 0 s (S x) = S (x + 1) newtype Reify n = Reify (forall a. (Class n => n -> a) -> a) instance Sym Reify where z = Reify (\f -> f (unR z)) s (Reify f) = Reify (\g -> f (g . unR . s . R)) genericClass :: (forall repr. Sym repr => repr n) -> (Class n => a) -> a genericClass m f = case m of Reify k -> k (const f)

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