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Haskell is a declarative language? Let's see how easy it is to declare types of things.
by Johannes Waldmann 05 Apr '13

05 Apr '13

I absolutely love to use Haskell when teaching (and I have several years of experience doing it). And I absolutely dislike it when I have to jump through hoops to declare types in the most correct way, and in the most natural places. This is hard to sell to the students. - Examples: 1. for explicit declaration of type variables, as in reverse :: forall (a :: *) . [a] -> [a] I have to switch on RankNTypes and/or KindSignatures (ghc suggests). C'mon, this has nothing to do with ranks per se. It's a type of a very simple function! IMHO even Java/C# do this better (with slightly strange syntax, but at least you get to declare the type variable). 2. for declaring types of local variables, as in \ (xs :: [Bool]) -> ... I have to enable PatternSignatures (actually ghc suggests ScopedTypeVariables but again there is no type variable in sight) I need to do this often, to disambiguate properties for Smallcheck. All of this just because it seemed, at some time, a clever idea to allow the programmer to omit quantifiers? (I know, mathematicians do this all over the place, but it is never helpful, and especially not when teaching.) I think that (1) implies (2): there could be no ambiguity about scopes (of typevars in patterns) if each typevar had to be introduced by explicit quantification. Then (in a pattern signature) a use could be distinguished from a declaration. Yes, the above is a rant. I can achieve what I want with some ghc options, and perhaps my point is that these should be on by default - or have better names, because presently, they are unintelligible to the (beginner) student.

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Haskell and WinRT
by Mark Flamer 05 Apr '13

05 Apr '13

There was a short thread on this in the beginners section a while back. I think it is an exciting subject and would like to hear what others thoughts are on it. The Windows 8 metro style apps are built using a new API that is designed to be exposed to other languages using "language projections" which are a thin wrapper around the windows runtime. Microsoft has provided these for C#, C++, Javascript & HTML and is encouraging language developers to create them for other languages. This seems like it might be the easiest rout to getting Haskell apps on tablets etc. with a modern UI. Simon Marlow discusses it briefly on this <https://plus.google.com/107890464054636586545/posts/PuFPongpyR4> page and there is a video on the topic here <http://channel9.msdn.com/Events/Lang-NEXT/Lang-NEXT-2012/The-Windows-Runtime> . Might even be a good summer of code project for someone. -- View this message in context: http://haskell.1045720.n5.nabble.com/Haskell-and-WinRT-tp5728106.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Functional Programming Internship @ Intel
by Levent Erkok 05 Apr '13

05 Apr '13

[I'm posting on behalf of my colleague Jesse Bingham. While Jesse and I work for different groups at Intel, we collaborate quite often, and I do expect to work with the intern to an extent as well. To that end, I'm happy to answer any questions you might have. Otherwise, direct all correspondence to Jesse as indicated below. -Levent.] ================================================================= Hi, we are looking to hire an intern to fill the below position. If interested, please send your resume to jesse.d.bingham(a)intel.com. Thanks Intern SW Engr. Formal Verification - 708053 Description Design and Technology Solutions (DTS) creates the software that caters to Intel's insatiable appetite for innovating silicon technology. Through our CAD solutions and engineering services, we enable Intel's process engineers to achieve the technical breakthroughs required to deliver tomorrows technology, and we help Intel's architects and chip designers develop products that change the world. To us, Moore's law is the imperative that drives our work to continuously improve the ways we explore technology options, so we can deliver better products, faster. As a software engineer in DTS, you will work as part of a multi-disciplinary team to create software tools that meet Intel's specific, rapidly evolving requirements for designing, manufacturing, testing, and packaging silicon products. We work very closely with process engineers and chip designers (our internal customers) around the world, to understand their technical challenges, and to create proprietary CAD solutions. We help them apply our software to answer critical questions, and to address their design and manufacturing objectives. The daily work in DTS spans the complete software life cycle, from early research to mature production code with industrial robustness and quality. To deliver critical new features in our established solutions, or to create new CAD capabilities beyond the state of art in the industry, our teams frequently go through all steps in software development - problem analysis, requirements definition, design, coding, test, and deployment. As a member of our team, you are expected to participate actively in all these steps. Success in this fast-paced, results-oriented environment requires strong analytical skills and the ability to perform productive teamwork, which depends on very good communication skills. In this particular job opening, you will join DTS's Formal Verification Center of Expertise (FVCoE) for a three month placement in Hillsboro, Oregon, in the timeframe of fall 2013. A primary responsibility of FVCoE is the maintenance of a large code base used for formal verification of Intel's core datapath designs; you will help rework several key aspects of this code to make it more robust and user-friendly. This will involve strict software engineering discipline to deliver robust, quality code that must perform reliably and predictably, The code is written in an in-house functional language called reflect. Reflect is similar to the popular functional languages Ocaml and Haskell; hence you should have considerable experience with one of these. Experience with formal verification is preferred but not necessarily required. Applicants will ideally be working towards a graduate degree in Computer Science or a related discipline. Qualifications Minimum Requirements Skills: Functional programming coding skills; experience with one or more scripting languages; analytical skills for problem abstraction; broad theoretical knowledge in computer science, including algorithms and data structures; familiarity with standard software engineering practices. Experience: acquired through coursework, internships, or personal projects. Experience in applied computer programming in a functional language. Education: working toward an MS or Ph.D. degree in Computer Science, Applied Mathematics, or in an Engineering field related to silicon technology. Strong senior undergraduates will also be considered. Preferred Requirements Skills: Familiarity with: hardware formal verification techniques (especially symbolic simulation, binary decision diagrams, parametric substitutions, case splitting), arithmetic/floating point computer hardware designs, IEEE 754 floating point standard, Intel x86 instruction set.

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Possible GSoC project
by Ketil Malde 04 Apr '13

04 Apr '13

Hi, I proposed a bioinformatics GSoC project involving Haskell using OSC as the mentoring organization. Typically, haskell.org projects concern infrastructure rather than applications, and I don't know if I'm allowed to submit both places :-) Anyway, as this is a likely place to find prospective students and (co-)mentors, I thought I'd mention it here. But if anybody is interested, I think it makes for a quite focused, solvable problem, which I belive would be quite useful. It could also likely result in a scientific publication of some sort. A quick writeup (that I'll probably update) is here: http://biohaskell.org/Google_Summer_of_Code#optimizing-transalign -k -- If I haven't seen further, it is by standing in the footprints of giants

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Re: [Haskell-cafe] [Haskell] ANN: adobe-swatch-exchange-0.1.0.0
by Brent Yorgey 04 Apr '13

04 Apr '13

(Redirecting follow-up to haskell-cafe) Very cool! I have been hoping someone will find a way to integrate kuler.adobe.com with diagrams, and this will help a lot. =) https://github.com/diagrams/diagrams-lib/issues/77 -Brent On Wed, Apr 03, 2013 at 06:49:34PM -0500, Jeremy Shaw wrote: > I am pleased to annouce the release of adobe-swatch-exchange 0.1.0.0. > > My primary motivation in writing this is to make it easier to download > color swatches from http://kuler.adobe.com/ and test them on my site. > Though, perhaps there is already a great way of doing this and I > didn't look hard enough. > > But, the end result is we can now read and write .ASE files in Haskell > and convert them to .css. So that probably opens up some new > possibilities. > > I have provided both a library and an executable. > > I have also used this as a way to test the waters with github, > > https://github.com/stepcut/ase2css > > I heard putting things on github will get me all sorts of > contributors. I suggest someone start with haddock comments. ;) > > Cheers! > - jeremy > > _______________________________________________ > Haskell mailing list > Haskell(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell

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Resource Limits for Haskell
by Edward Z. Yang 04 Apr '13

04 Apr '13

Hey folks, Have you ever wanted to implement this function in Haskell? -- | Forks a thread, but kills it if it has more than 'limit' -- bytes resident on the heap. forkIOWithSpaceLimit :: IO () -> {- limit -} Int -> IO ThreadId Well, now you can! I have a proposal and set of patches here: http://hackage.haskell.org/trac/ghc/wiki/Commentary/ResourceLimits http://hackage.haskell.org/trac/ghc/ticket/7763 There is a lot of subtlety in this space, largely derived from the complexity of interpreting GHC's current profiling information. Your questions, comments and suggestions are greatly appreciated! Cheers, Edward

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Type level natural numbers
by Mateusz Kowalczyk 04 Apr '13

04 Apr '13

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 About two weeks ago we got an email (at ghc-users) mentioning that comparing to 7.6, 7.7.x snapshot would contain (amongst other things), type level natural numbers. I believe the package used is at [1]. Can someone explain what use is such package in Haskell? I understand uses in a language such as Agda where we can provide proofs about a type and then use that to perform computations using the type system (such as guaranteeing that concatenating two vectors together will give a new one with the length of the two initial vectors combine) however as far as I can tell, this is not the case in Haskell (although I don't want to say ?impossible? and have Oleg jump me). - -- Mateusz K. -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.19 (GNU/Linux) iQIcBAEBAgAGBQJRXIYYAAoJEM1mucMq2pqXT00P/imTf/Wd7UZ0T0ZPUbM6i3Nj P5ffEUvUGf5V1jmXub/ibVFv6QHkTigsF/K9VPo13ChtA7u4qnxH7pd+zbTCp6c4 +A4dgKLVvlB+tGSvKzmsJxEtRh/rtv0UMP2RtvKoB7DH2mMv99EDkKmndWaxOI2z VjAvYFqdi//3O0P9bN9/93KZNUZviHh/5IP8f6HcpCWVDu+Z5CKbzUM6roxsBNM1 a1y6RjQp2SnUFMlJnKbWepRbn2p12dzmMrXzF2UINkTkDTytP+ZIK1ZpS8/qh6i6 q44GUBa2doHxhX9H+Vo3Vims3S0otyVmTQX/b2J1R7FoBl6fsPa+XUeE8RJwfSzm 0Ho75AX39rynO9AJ+/hZQdk6G6VkED/JszWBSnfC56VNB0vdYI4e2mBGny4uL9MU PnVb+fYk0xuSw7wAqLnVo2ZQqyvN79uNDT4x0uf/6zvkQ8LoSzMr99YwjWI5jo2X 8dqphjPPArX9MV0xCPdkpU6wPHSvEK4fOxJcqDq104+ssJdNr8PXbhtIifa/KE/C B2jhmwRllbtbg1HGXQ8zWlY+VbE+sc5O2AvhrV14fKF8xkNtLRzvhAWR/cOTXLZ0 hA7r6Jjf4mzQnUBgb/BW8pH6N+UnjkV/JgJ45WHB3PSADU3JspyuG7uJUOCod75e D/849dOCHHrkYsYEPdJq =JCfK -----END PGP SIGNATURE-----

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Re: [Haskell-cafe] Threadscope 0.2.2 goes in segmentation fault on Mac Os X 10.8.3
by Dominic Steinitz 04 Apr '13

04 Apr '13

Alfredo Di Napoli <alfredo.dinapoli <at> gmail.com> writes: > > Said that,has someone had any luck in running Threadscope on Mac OS X 10.8 at all? > > Thanks, > A. > I think I have encountered the same problem: https://groups.google.com/d/msg/parallel-haskell/-lhrgNN8elw/KzqLM9BzoJwJ In my experience, anything that uses gtk is a problem on a MAC. I still intend to do some analysis *not* using threadscope but using event-logs directly but that is at least a few weeks away. Dominic.

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install cuda
by Peter Caspers 04 Apr '13

04 Apr '13

Hi, I am trying to install the cuda package on a Windows 7 enviroment. However I run into an error and can not figure out, what it is. Can someone help ? Thanks a lot Peter C:\Users\Peter\_dev\haskell>cabal install cuda Resolving dependencies... [1 of 1] Compiling Main ( C:\Users\Peter\AppData\Local\Temp\cuda-0.5.0.1-11856\cuda-0.5.0.1\Setup.hs, C:\Users\Peter\AppData\Local\Temp\cuda-0.5.0.1 -11856\cuda-0.5.0.1\dist\setup\Main.o ) Linking C:\Users\Peter\AppData\Local\Temp\cuda-0.5.0.1-11856\cuda-0.5.0.1\dist\setup\setup.exe ... Configuring cuda-0.5.0.1... cygwin warning: MS-DOS style path detected: C:\Users\Peter\AppData\Roaming\cabal/share/config.site Preferred POSIX equivalent is: /cygdrive/c/Users/Peter/AppData/Roaming/cabal/share/config.site CYGWIN environment variable option "nodosfilewarning" turns off this warning. Consult the user's guide for more details about POSIX paths: http://cygwin.com/cygwin-ug-net/using.html#using-pathnames checking for gcc... C:\Program Files (x86)\Haskell Platform\2012.4.0.0\mingw\bin\gcc.exe checking whether the C compiler works... no configure: error: in `/cygdrive/c/Users/Peter/AppData/Local/Temp/cuda-0.5.0.1-11856/cuda-0.5.0.1': configure: error: C compiler cannot create executables See `config.log' for more details cabal: Error: some packages failed to install: cuda-0.5.0.1 failed during the configure step. The exception was: ExitFailure 77

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Haskell Weekly News: Issue 264
by Daniel Santa Cruz 04 Apr '13

04 Apr '13

Welcome to issue 264 of the HWN, an issue covering crowd-sourced bits of information about Haskell from around the web. This issue covers the week of March 17 to 30, 2013. Quotes of the Week * ddarius: (f x) is a partial application iff f x == (curry (uncurry f) x) * flebron: "Hey, I am Haskell; and this is lazy; so here's a function; I'll call it, maybe." * WinstonChurchill: It is a good thing for an uneducated man to read books of quotations. * ab9rf: (on duck typing) if you want a duck-submarine-employee-tomato, you can do that * johnw: Stealing lens from the gods, and then having my liver eaten out daily. * dibblego: scala puts road blocks in your way proportional to how effective you want to be * hiptobecubic: I want my programs to either be correct or violently explode * shachaf: edwardk will try to get you addicted to monoids. The first one is always free. * merijn: So apparently there's a footballer named lens, who played some important part in the match against the Netherlands... Which would explain the fact that twitter is telling me "lens" is trending, I was starting to think haskell had won the PL revolution with edwardk as our glorious leader ;) * elliott: all I want for christmas is a boring lambdabot. Top Reddit Stories * What’s good for C++ is good for … Haskell!? Domain: serpentine.com, Score: 101, Comments: 20 On Reddit: [1] http://goo.gl/B8Km5 Original: [2] http://goo.gl/tCB0a * Anatomy of Programming Languages (in Haskell) Domain: self.haskell, Score: 72, Comments: 29 On Reddit: [3] http://goo.gl/YmO5M Original: [4] http://goo.gl/YmO5M * Programming and Reasoning with Algebraic Effects and Dependent Types Domain: edwinb.wordpress.com, Score: 58, Comments: 28 On Reddit: [5] http://goo.gl/xfH0Z Original: [6] http://goo.gl/AdGEJ * School of Haskell—Basic Lensing Domain: fpcomplete.com, Score: 57, Comments: 39 On Reddit: [7] http://goo.gl/JIowk Original: [8] http://goo.gl/NX1ak * Haskell for all: mmorph-1.0.0: Monad morphisms Domain: haskellforall.com, Score: 56, Comments: 18 On Reddit: [9] http://goo.gl/nlHfN Original: [10] http://goo.gl/6aHZt * Haskell News Domain: haskellnews.org, Score: 43, Comments: 12 On Reddit: [11] http://goo.gl/fNzzI Original: [12] http://goo.gl/4K1tD * pipes-3.2: ListT, Codensity, ArrowChoice, and performance Domain: haskellforall.com, Score: 43, Comments: 19 On Reddit: [13] http://goo.gl/a0xm8 Original: [14] http://goo.gl/RFLdw * Introducing diagrams-haddock Domain: byorgey.wordpress.com, Score: 41, Comments: 13 On Reddit: [15] http://goo.gl/d5Vl5 Original: [16] http://goo.gl/PmUFs * Optimising Purely Functional GPU Programs Domain: justtesting.org, Score: 41, Comments: 2 On Reddit: [17] http://goo.gl/ZgiXt Original: [18] http://goo.gl/M5fop * Creating board games in Haskell in 100 lines of code Domain: keera.co.uk, Score: 38, Comments: 30 On Reddit: [19] http://goo.gl/lbZke Original: [20] http://goo.gl/epwqQ * What is the logarithm or root operation in type-space? (x-post from r/compsci) Domain: cstheory.stackexchange.com, Score: 38, Comments: 17 On Reddit: [21] http://goo.gl/1z3a9 Original: [22] http://goo.gl/JXAlC * New GHC Extension - Nullary Type Classes (apparently not an April Fool's joke) Domain: hackage.haskell.org, Score: 37, Comments: 24 On Reddit: [23] http://goo.gl/rD5KC Original: [24] http://goo.gl/drfb7 * The Monad.Reader issue 21 Domain: themonadreader.files.wordpress.com, Score: 30, Comments: 2 On Reddit: [25] http://goo.gl/R1dke Original: [26] http://goo.gl/nGHjP * Dependently Typed Functional Programming with Idris 4 (last lecture) Domain: vimeo.com, Score: 28, Comments: 4 On Reddit: [27] http://goo.gl/ozbtK Original: [28] http://goo.gl/2xsaB * Conal Elliot: Folds and Unfolds Domain: conal.net, Score: 28, Comments: 5 On Reddit: [29] http://goo.gl/ZzFZ1 Original: [30] http://goo.gl/JVQK4 * Mihai-Radu Popescu's book in progress: "Speeding Through Haskell" Domain: sthaskell.com, Score: 26, Comments: 15 On Reddit: [31] http://goo.gl/d1wZF Original: [32] http://goo.gl/oB0e8 * hchip - a Haskell emulator for Chip16 Domain: self.haskell, Score: 25, Comments: 1 On Reddit: [33] http://goo.gl/mtHhg Original: [34] http://goo.gl/mtHhg * Introduction to Haskell, Lecture 8 is Live (Monads) Domain: shuklan.com, Score: 25, Comments: 22 On Reddit: [35] http://goo.gl/nCV1q Original: [36] http://goo.gl/D4VGn * School of Haskell: Learning Haskell Through Koans Domain: fpcomplete.com, Score: 22, Comments: 2 On Reddit: [37] http://goo.gl/sKxmz Original: [38] http://goo.gl/2n9aF * Arrow Notation in Functional Reactive Programming demonstrated with a simple OpenGL demo (Yampa) Domain: youtube.com, Score: 22, Comments: 9 On Reddit: [39] http://goo.gl/NN8nr Original: [40] http://goo.gl/m5XEb Top StackOverflow Questions * Maintaining complex state in Haskell votes: 23, answers: 1 Read on SO: [41] http://goo.gl/XbFtx * Is using mapM/sequence considered good practice? votes: 14, answers: 3 Read on SO: [42] http://goo.gl/juA3q * Can I model a list of successes with short circuiting failure via the composition of applicative functors? votes: 12, answers: 2 Read on SO: [43] http://goo.gl/biKxw * Understanding Polytypes in Hindley-Milner Type Inference votes: 12, answers: 2 Read on SO: [44] http://goo.gl/sjzJJ * Why add “Eq” type constraint without using “==”? votes: 11, answers: 1 Read on SO: [45] http://goo.gl/hljhA * :: a -> (a -> b) -> b operator (Haskell) votes: 11, answers: 3 Read on SO: [46] http://goo.gl/O643o * What's the most efficient way to represent finite (non-recursive) algebraic type values? votes: 10, answers: 2 Read on SO: [47] http://goo.gl/ikN78 * What's the “easier way” that deprecates the need for Data.Conduit.Util's zip? votes: 10, answers: 1 Read on SO: [48] http://goo.gl/kk6jq * Haskell equivalent of scala collect votes: 10, answers: 1 Read on SO: [49] http://goo.gl/wjKTR * Scheduling a Timeout in Haskell votes: 10, answers: 1 Read on SO: [50] http://goo.gl/Pya8z Until next time, +Daniel Santa Cruz References 1. http://www.serpentine.com/blog/2013/03/20/whats-good-for-c-is-good-for-hask… 2. http://www.reddit.com/r/haskell/comments/1aok5k/whats_good_for_c_is_good_fo… 3. http://www.reddit.com/r/haskell/comments/1b4m75/anatomy_of_programming_lang… 4. http://www.reddit.com/r/haskell/comments/1b4m75/anatomy_of_programming_lang… 5. https://edwinb.wordpress.com/2013/03/28/programming-and-reasoning-with-alge… 6. http://www.reddit.com/r/haskell/comments/1b64xh/programming_and_reasoning_w… 7. https://www.fpcomplete.com/user/tel/basic-lensing 8. http://www.reddit.com/r/haskell/comments/1anf0n/school_of_haskellbasic_lens… 9. http://www.haskellforall.com/2013/03/mmorph-100-monad-morphisms.html 10. http://www.reddit.com/r/haskell/comments/1ahyzu/haskell_for_all_mmorph100_m… 11. http://haskellnews.org/ 12. http://www.reddit.com/r/haskell/comments/1ahgrn/haskell_news/ 13. http://www.haskellforall.com/2013/03/pipes-32-listt-codensity-arrowchoice.h… 14. http://www.reddit.com/r/haskell/comments/1av2gi/pipes32_listt_codensity_arr… 15. http://byorgey.wordpress.com/2013/03/23/introducing-diagrams-haddock/ 16. http://www.reddit.com/r/haskell/comments/1aw33e/introducing_diagramshaddock/ 17. http://justtesting.org/optimising-purely-functional-gpu-programs 18. http://www.reddit.com/r/haskell/comments/1bapa5/optimising_purely_functiona… 19. http://keera.co.uk/blog/2013/03/19/creating-board-games-in-haskell/ 20. http://www.reddit.com/r/haskell/comments/1ani3n/creating_board_games_in_has… 21. http://cstheory.stackexchange.com/questions/17006/what-is-the-logarithm-or-… 22. http://www.reddit.com/r/haskell/comments/1aynxj/what_is_the_logarithm_or_ro… 23. http://hackage.haskell.org/trac/ghc/ticket/7642 24. http://www.reddit.com/r/haskell/comments/1atlvu/new_ghc_extension_nullary_t… 25. http://themonadreader.files.wordpress.com/2013/03/issue21.pdf 26. http://www.reddit.com/r/haskell/comments/1ahrii/the_monadreader_issue_21/ 27. http://vimeo.com/62059837 28. http://www.reddit.com/r/haskell/comments/1aisv0/dependently_typed_functiona… 29. http://conal.net/talks/folds-and-unfolds.pdf 30. http://www.reddit.com/r/haskell/comments/1asxuf/conal_elliot_folds_and_unfo… 31. http://www.sthaskell.com/ 32. http://www.reddit.com/r/haskell/comments/1azvcy/mihairadu_popescus_book_in_… 33. http://www.reddit.com/r/haskell/comments/1akhgi/hchip_a_haskell_emulator_fo… 34. http://www.reddit.com/r/haskell/comments/1akhgi/hchip_a_haskell_emulator_fo… 35. http://shuklan.com/haskell/lec09.html 36. http://www.reddit.com/r/haskell/comments/1alqjq/introduction_to_haskell_lec… 37. https://www.fpcomplete.com/blog/2013/03/learning-through-koans 38. http://www.reddit.com/r/haskell/comments/1amuuz/school_of_haskell_learning_… 39. http://www.youtube.com/watch?v=T3xXebIr8AM#t=17m58s 40. http://www.reddit.com/r/haskell/comments/1ao4nx/arrow_notation_in_functiona… 41. http://stackoverflow.com/questions/15467925/maintaining-complex-state-in-ha… 42. http://stackoverflow.com/questions/15546216/is-using-mapm-sequence-consider… 43. http://stackoverflow.com/questions/15460794/can-i-model-a-list-of-successes… 44. http://stackoverflow.com/questions/15497315/understanding-polytypes-in-hind… 45. http://stackoverflow.com/questions/15512541/why-add-eq-type-constraint-with… 46. http://stackoverflow.com/questions/15604290/a-a-b-b-operator-haskell 47. http://stackoverflow.com/questions/15572996/whats-the-most-efficient-way-to… 48. http://stackoverflow.com/questions/15627359/whats-the-easier-way-that-depre… 49. http://stackoverflow.com/questions/15634549/haskell-equivalent-of-scala-col… 50. http://stackoverflow.com/questions/15671328/scheduling-a-timeout-in-haskell 51. https://plus.google.com/105107667630152149014/about

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What happened to http://hackage.haskell.org/platform/2010.2.0.0/cabal/haskell-platform-2010.2.0.0.tar.gz?
by Peter Simons 03 Apr '13

03 Apr '13

Is it just me or have some of the old Haskell Platform releases disappeared from haskell.org? The 2010.x links from http://www.haskell.org/platform/prior.html also point to non-existent pages.

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Re: [Haskell-cafe] User group in Stockholm?
by Vincent Ambo 03 Apr '13

03 Apr '13

Hej! I live in Stockholm but don't know of any user group here. How long are you going to stay? Cheers! 2013/4/2 Vincent Ambo <tazjin(a)gmail.com> > Hej! > > I live in Stockholm but don't know of any user group here. How long are > you going to stay? > > Cheers! > > Vincent > > > 2013/4/1 Sergey Bushnyak <sergey.bushnyak(a)sigrlami.eu> > >> I'll be in Stockholm next month, so I'm curious about haskellers in >> Stockholm. >> >> I saw attempts to organize regular meetings in old mailing threads, but >> can't find *up to date* information to correct my schedule and see fellow >> haskellers. >> >> Sorry, if this offtopic >> >> -- >> Best regards, >> Sergey Bushnyak >> >> >> ______________________________**_________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://www.haskell.org/**mailman/listinfo/haskell-cafe<http://www.haskell.org/mailman/listinfo/haskell-cafe> >> > >

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Layout section of Haskell 2010 Language Report -- Notes 1&2
by Seth Lastname 03 Apr '13

03 Apr '13

I'm sure I'm missing something, but I'm having difficulty parsing or reconciling Note 1 and Note 2 of Section 10.3 ("Layout") of the Haskell 2010 Language Report. http://www.haskell.org/onlinereport/haskell2010/haskellch10.html#x17-178000… Can somebody point me in the right direction? To be clear, I'm not concerned with GHC behavior or best programming practices here, only with the specification of the language given in the Report. Note 1 says, "A nested context must be further indented than the enclosing context ('n' > 'm'). If not, 'L' fails, and the compiler should indicate a layout error." Note 2 says, "If the first token after a 'where' (say) is not indented more than the enclosing layout context, then the block must be empty, so empty braces are inserted." It seems that, in Note 2, the "first token" necessarily refers to a lexeme other than '{' (else it would not make sense), in which case a '{n}' token will have been inserted after 'where' (in the example given in the note), yielding a nested context which is "not indented more than the enclosing layout context", and thus failing the test in the first sentence of Note 1. So, in the places where Note 2 would apply, it seems Note 1 would yield a "layout error". For example, in the following code (replace '.' with space), f x = let ......g y = 2 * y ..........where ..g x it seems that Note 1 would "layout error", yet this seems precisely the case addressed by Note 2 wherein "{}" would be inserted after the 'where' yielding syntactically correct (albeit strange) code. Any insight would be appreciated. Thanks, Seth

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Fwd: [Yesod] Type issue when migrating to new yesod
by Magicloud Magiclouds 03 Apr '13

03 Apr '13

Hi, I have a yesod project that used to be compilable. Now when I migrate it to latest yesod, it failed compiling. ---------- Forwarded message ---------- From: Magicloud Magiclouds <magicloud.magiclouds(a)gmail.com> Date: Tue, Apr 2, 2013 at 9:32 PM Subject: Re: [Yesod] Type issue in new yesod To: "yesodweb(a)googlegroups.com" <yesodweb(a)googlegroups.com> Sure. The error message is as following. And the new code is here: http://pastebin.com/sqCkeY2q [12 of 13] Compiling Handler.FetchProcessPathRollup ( Handler/FetchProcessPathRollup.hs, dist/build/Handler/FetchProcessPathRollup.o ) Handler/FetchProcessPathRollup.hs:43:16: No instance for (PersistUnique (Data.Conduit.Internal.ConduitM (containers-0.5.0.0:Data.Map.Base.Map Text Text) ProcessPathRollup (ResourceT (Database.Persist.GenericSql.Raw.SqlPersist (GHandler App App))))) arising from a use of `getKey' Possible fix: add an instance declaration for (PersistUnique (Data.Conduit.Internal.ConduitM (containers-0.5.0.0:Data.Map.Base.Map Text Text) ProcessPathRollup (ResourceT (Database.Persist.GenericSql.Raw.SqlPersist (GHandler App App))))) In a stmt of a 'do' block: reportKey <- getKey (UniqueReport (t "Report")) (Report (t "Report")) In the expression: do { let t = (!) r d = liftM fst . double . t ....; reportKey <- getKey (UniqueReport (t "Report")) (Report (t "Report")); lineitemKey <- getKey (UniqueLineitem (t "LineItem Name") (t "LineItem Id")) (Lineitem (t "LineItem Id") (t "LineItem Name")); mainProcessKey <- getKey (UniqueMainProcess (t "Main Process")) (MainProcess (t "Main Process")); .... } In the second argument of `($)', namely `\ r -> do { let ...; reportKey <- getKey (UniqueReport (t "Report")) (Report (t "Report")); .... }' On Tue, Apr 2, 2013 at 7:32 PM, Michael Snoyman <michael(a)snoyman.com> wrote: > Can you provide the new source code and the new compiler error message? > > > On Tue, Apr 2, 2013 at 11:18 AM, Magicloud Magiclouds < > magicloud.magiclouds(a)gmail.com> wrote: > >> Sorry, the first error about CSV was due to parsePPR's type. If I set it >> type, then CSV error was gone. And the error of PersistUnique reported on >> first getKey call, instead of processPPR call. >> >> >> On Tue, Apr 2, 2013 at 2:50 PM, Michael Snoyman <michael(a)snoyman.com>wrote: >> >>> This doesn't look like it's anything to do with Yesod; it looks like a >>> problem with the usage of conduit and csv-conduit. Did you try following >>> the GHC recommendation and adding a type signature to parsePPR? >>> >>> >>> On Tue, Apr 2, 2013 at 8:09 AM, Magicloud Magiclouds < >>> magicloud.magiclouds(a)gmail.com> wrote: >>> >>>> Hi, >>>> I have a yesod project that used to be compilable. Now when I migrate >>>> it to latest yesod, it failed compiling. >>>> >>>> The failed part is here: http://pastebin.com/pWn5FdeS . >>>> And the error message is: >>>> >>>> Handler/FetchProcessPathRollup.hs:27:30: >>>> No instance for (Data.CSV.Conduit.CSV >>>> Data.ByteString.Internal.ByteString >>>> (containers-0.5.0.0:Data.Map.Base.Map a0 Text)) >>>> arising from a use of `intoCSV' >>>> The type variable `a0' is ambiguous >>>> Possible fix: add a type signature that fixes these type variable(s) >>>> Note: there is a potential instance available: >>>> instance (Data.CSV.Conduit.CSV >>>> s (csv-conduit-0.5.1:Data.CSV.Conduit.Types.Row s'), >>>> Ord s', Data.String.IsString s) => >>>> Data.CSV.Conduit.CSV s (MapRow s') >>>> -- Defined in `Data.CSV.Conduit' >>>> Possible fix: >>>> add an instance declaration for >>>> (Data.CSV.Conduit.CSV >>>> Data.ByteString.Internal.ByteString >>>> (containers-0.5.0.0:Data.Map.Base.Map a0 Text)) >>>> In the first argument of `(=$=)', namely `intoCSV defCSVSettings' >>>> In the second argument of `($$+-)', namely >>>> `(intoCSV defCSVSettings >>>> =$= parsePPR (zonedTimeToUTC day) k =$ sinkPersist)' >>>> In a stmt of a 'do' block: >>>> responseBody src >>>> $$+- >>>> (intoCSV defCSVSettings >>>> =$= parsePPR (zonedTimeToUTC day) k =$ sinkPersist) >>>> >>>> Handler/FetchProcessPathRollup.hs:27:57: >>>> No instance for (PersistUnique >>>> (Data.Conduit.Internal.ConduitM >>>> (containers-0.5.0.0:Data.Map.Base.Map a0 Text) >>>> ProcessPathRollup >>>> (ResourceT >>>> >>>> (Database.Persist.GenericSql.Raw.SqlPersist (GHandler App App))))) >>>> arising from a use of `parsePPR' >>>> Possible fix: >>>> add an instance declaration for >>>> (PersistUnique >>>> (Data.Conduit.Internal.ConduitM >>>> (containers-0.5.0.0:Data.Map.Base.Map a0 Text) >>>> ProcessPathRollup >>>> (ResourceT >>>> (Database.Persist.GenericSql.Raw.SqlPersist (GHandler >>>> App App))))) >>>> In the first argument of `(=$)', namely >>>> `parsePPR (zonedTimeToUTC day) k' >>>> In the second argument of `(=$=)', namely >>>> `parsePPR (zonedTimeToUTC day) k =$ sinkPersist' >>>> In the second argument of `($$+-)', namely >>>> `(intoCSV defCSVSettings >>>> =$= parsePPR (zonedTimeToUTC day) k =$ sinkPersist)' >>>> >>>> -- >>>> 竹密岂妨流水过 >>>> 山高哪阻野云飞 >>>> >>>> And for G+, please use magiclouds#gmail.com. >>>> >>>> -- >>>> You received this message because you are subscribed to the Google >>>> Groups "Yesod Web Framework" group. >>>> To unsubscribe from this group and stop receiving emails from it, send >>>> an email to yesodweb+unsubscribe(a)googlegroups.com. >>>> For more options, visit https://groups.google.com/groups/opt_out. >>>> >>>> >>>> >>> >>> -- >>> You received this message because you are subscribed to the Google >>> Groups "Yesod Web Framework" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to yesodweb+unsubscribe(a)googlegroups.com. >>> For more options, visit https://groups.google.com/groups/opt_out. >>> >>> >>> >> >> >> >> -- >> 竹密岂妨流水过 >> 山高哪阻野云飞 >> >> And for G+, please use magiclouds#gmail.com. >> >> -- >> You received this message because you are subscribed to the Google Groups >> "Yesod Web Framework" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to yesodweb+unsubscribe(a)googlegroups.com. >> For more options, visit https://groups.google.com/groups/opt_out. >> >> >> > > -- > You received this message because you are subscribed to the Google Groups > "Yesod Web Framework" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to yesodweb+unsubscribe(a)googlegroups.com. > For more options, visit https://groups.google.com/groups/opt_out. > > > -- 竹密岂妨流水过山高哪阻野云飞 And for G+, please use magiclouds#gmail.com. -- 竹密岂妨流水过山高哪阻野云飞 And for G+, please use magiclouds#gmail.com.

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Re: [Haskell-cafe] closed world instances, closed type families
by oleg＠okmij.org 03 Apr '13

03 Apr '13

Henning Thielemann wrote: > However the interesting part of a complete case analysis on type level > peano numbers was only sketched in section "8.4 Closed type > families". Thus I tried again and finally found a solution that works > with existing GHC extensions: You might like the following message posted in January 2005 http://www.haskell.org/pipermail/haskell-cafe/2005-January/008239.html (the whole discussion thread is relevant). In particular, the following excerpt -- data OpenExpression env r where -- Lambda :: OpenExpression (a,env) r -> OpenExpression env (a -> r); -- Symbol :: Sym env r -> OpenExpression env r; -- Constant :: r -> OpenExpression env r; -- Application :: OpenExpression env (a -> r) -> OpenExpression env a -> -- OpenExpression env r -- Note that the types of the efold alternatives are essentially -- the "inversion of arrows" in the GADT declaration above class OpenExpression t env r | t env -> r where efold :: t -> env -> (forall r. r -> c r) -- Constant -> (forall r. r -> c r) -- Symbol -> (forall a r. (a -> c r) -> c (a->r)) -- Lambda -> (forall a r. c (a->r) -> c a -> c r) -- Application -> c r shows the idea of the switch, but on more complex example (using higher-order rather than first-order language). That message has anticipated the tagless-final approach.

1 0

Why is "Cont" out of scope?
by Daryoush Mehrtash 03 Apr '13

03 Apr '13

I am trying to use the Cont in Control.Monad.Cont but it seems to be missing Prelude> import Control.Monad.Cont Prelude Control.Monad.Cont> :t Cont <interactive>:1:1: Not in scope: data constructor `Cont' Perhaps you meant `ContT' (imported from Control.Monad.Cont) Prelude Control.Monad.Cont> :t runCont runCont :: Cont r a -> (a -> r) -> r Prelude Control.Monad.Cont> :t ContT ContT :: ((a -> m r) -> m r) -> ContT r m a Prelude Control.Monad.Cont> Any ideas? Thanks -- Daryoush Weblog: http://onfp.blogspot.com/

2 1

closed world instances, closed type families
by Henning Thielemann 03 Apr '13

03 Apr '13

Recently I needed to define a class with a restricted set of instances. After some failed attempts I looked into the DataKinds extension and in "Giving Haskell a Promotion" I found the example of a new kind Nat for type level peano numbers. However the interesting part of a complete case analysis on type level peano numbers was only sketched in section "8.4 Closed type families". Thus I tried again and finally found a solution that works with existing GHC extensions: data Zero data Succ n class Nat n where switch :: f Zero -> (forall m. Nat m => f (Succ m)) -> f n instance Nat Zero where switch x _ = x instance Nat n => Nat (Succ n) where switch _ x = x That's all. I do not need more methods in Nat, since I can express everything by the type case analysis provided by "switch". I can implement any method on Nat types using a newtype around the method which instantiates the f. E.g. newtype Append m a n = Append {runAppend :: Vec n a -> Vec m a -> Vec (Add n m) a} type family Add n m :: * type instance Add Zero m = m type instance Add (Succ n) m = Succ (Add n m) append :: Nat n => Vec n a -> Vec m a -> Vec (Add n m) a append = runAppend $ switch (Append $ \_empty x -> x) (Append $ \x y -> case decons x of (a,as) -> cons a (append as y)) decons :: Vec (Succ n) a -> (a, Vec n a) cons :: a -> Vec n a -> Vec (Succ n) a The technique reminds me on GADTless programming. Has it already a name?

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ANNOUNCE: Ajhc 0.8.0.3 Release
by Kiwamu Okabe 02 Apr '13

02 Apr '13

We are happy to announce Ajhc 0.8.0.3. Major change on this release is supporting Windows MinGW32 platform. And you can cabal install ajhc. http://hackage.haskell.org/package/ajhc Perhaps changes on the announce will be merged to jhc. Ajhc's project web site is found at http://ajhc.masterq.net/. You can get the source code from https://github.com/ajhc/ajhc/tags. ## Changes * Support Windows MinGW32 platform * You can cabal install Ajhc. * Use DrIFT-cabalized command also to generate DrIFT deriving * Dump Haskell heap with gdb script (utils/gdb_jhc.py) * Use haskeline package to replace readline or editline * No more depend on haskell98 package - - - Metasepi team

1 0

APLAS 2013 call for papers
by Chung-chieh Shan 02 Apr '13

02 Apr '13

=============================================================== APLAS 2013 11th Asian Symposium on Programming Languages and Systems 9-11 December 2013 Melbourne, Australia (colocated with CPP 2013) CALL FOR PAPERS =============================================================== ========== BACKGROUND ========== APLAS aims to stimulate programming language research by providing a forum for the presentation of latest results and the exchange of ideas in programming languages and systems. APLAS is based in Asia, but is an international forum that serves the worldwide programming language community. APLAS is sponsored by the Asian Association for Foundation of Software (AAFS) founded by Asian researchers in cooperation with many researchers from Europe and the USA. Past APLAS symposiums were successfully held in Kyoto ('12), Kenting ('11), Shanghai ('10), Seoul ('09), Bangalore ('08), Singapore ('07), Sydney ('06), Tsukuba ('05), Taipei ('04) and Beijing ('03) after three informal workshops. Proceedings of the past symposiums were published in Springer's LNCS. ====== TOPICS ====== The symposium is devoted to foundational and practical issues in programming languages and systems. Papers are solicited on topics such as * semantics, logics, foundational theory; * design of languages, type systems and foundational calculi; * domain-specific languages; * compilers, interpreters, abstract machines; * program derivation, synthesis and transformation; * program analysis, verification, model-checking; * logic, constraint, probabilistic and quantum programming; * software security; * concurrency and parallelism; * tools and environments for programming and implementation. Topics are not limited to those discussed in previous symposiums. Papers identifying future directions of programming and those addressing the rapid changes of the underlying computing platforms are especially welcome. Demonstration of systems and tools in the scope of APLAS are welcome to the System and Tool presentations category. Authors concerned about the appropriateness of a topic are welcome to consult with program chair prior to submission. ========== SUBMISSION ========== We solicit submissions in two categories: *Regular research papers* describing original scientific research results, including tool development and case studies. Regular research papers should not exceed 16 pages in the Springer LNCS format, including bibliography and figures. They should clearly identify what has been accomplished and why it is significant. Submissions will be judged on the basis of significance, relevance, correctness, originality, and clarity. In case of lack of space, proofs, experimental results, or any information supporting the technical results of the paper could be provided as an appendix or a link to a web page, but reviewers are not obliged to read them. *System and Tool presentations* describing systems or tools that support theory, program construction, reasoning, or program execution in the scope of APLAS. System and Tool presentations are expected to be centered around a demonstration. The paper and the demonstration should identify the novelties of the tools and use motivating examples. System and Tool papers should not exceed 8 pages in the Springer LNCS format, including bibliography and figures. Submissions will be judged based on both the papers and the described systems or tools. It is highly desirable that the tools are available on the web. Papers should be submitted electronically via the submission web page: https://www.easychair.org/conferences/?conf=aplas2013 Acceptable formats are PostScript or PDF. Submitted papers must be unpublished and not submitted for publication elsewhere. Papers must be written in English. The proceedings will be published as a volume in Springer's LNCS series. Accepted papers must be presented at the conference. (While the general chair and the program chair cannot submit papers, other members of the program committee can.) ===== DATES ===== Abstract due: 10 June 2013 (Monday), 23:59 UTC Submission due: 14 June 2013 (Friday), 23:59 UTC Notification: 26 August 2013 (Monday) Final paper due: 19 September 2013 (Thursday) Conference: 9-11 December 2013 (Monday-Wednesday) ========== ORGANIZERS ========== General chair: Peter Schachte (University of Melbourne) Program chair: Chung-chieh Shan (Indiana University) Program committee: Filippo Bonchi (CNRS, ENS-Lyon, France) Yu-Fang Chen (Academia Sinica, Taiwan) Shigeru Chiba (The University of Tokyo, Japan) Jacques Garrigue (Nagoya University, Japan) Robert Glück (University of Copenhagen, Denmark) R. Govindarajan (Indian Institute of Science, India) Kazuhiro Inaba (Google, Inc., Japan) Jie-Hong Roland Jiang (National Taiwan University, Taiwan) Shin-ya Katsumata (Kyoto University, Japan) Gabriele Keller (University of New South Wales, Australia) Ana Milanova (Rensselaer Polytechnic Institute, USA) Keisuke Nakano (The University of Electro-Communications, Japan) Hakjoo Oh (Seoul National University, Korea) Bruno C. d. S. Oliveira (National University of Singapore, Singapore) Kaushik Rajan (Microsoft Research, India) Max Schäfer (Nanyang Technological University, Singapore) Ulrich Schöpp (Ludwig-Maximilians-Universität München, Germany) Paula Severi (University of Leicester, UK) Gang Tan (Lehigh University, USA) Hiroshi Unno (University of Tsukuba, Japan) Meng Wang (Chalmers University of Technology, Sweden) Jingling Xue (University of New South Wales, Australia) Mingsheng Ying (University of Technology, Sydney, Australia) Kenny Q. Zhu (Shanghai Jiao Tong University, China) ======= CONTACT ======= http://aplas2013.soic.indiana.edu/ aplas2013(a)easychair.org

1 0

mueval, interpreter options
by Johannes Waldmann 02 Apr '13

02 Apr '13

What am I missing? I want to use mueval to read a file that contains "instance Serial m a => Serial m (Tree a)" (as in http://hackage.haskell.org/packages/archive/smallcheck/1.0.2/doc/html/Test-…) so I put in my call of mueval: let Right opts = M.interpreterOpts [] keepCurrentDir $ do System.Directory.setCurrentDirectory d I.runInterpreter $ Mueval.Interpreter.interpreter $ opts { M.timeLimit = 10 -- seconds? , M.modules = Just [ "Prelude" , "Test.SmallCheck.Drivers", "Test.SmallCheck.Series" , "GHC.Generics" ] , M.namedExtensions = [ "MultiParamTypeClasses" , "FlexibleInstances", "DeriveGeneric" ] but it gives me "MultiParamTypeClasses is not enabled" on inputs like {-# language MultiParamTypeClasses #-} import Test.SmallCheck.Series import GHC.Generics data Tree a = Null | Fork (Tree a) a (Tree a) deriving Generic instance Serial m a => Serial m (Tree a) where I don't understand mueval's design anyway here: do the interpreter options mean that these are automatically on, or just that the source text will be allowed to switch then on? (I'd prefer the latter.) Thanks - J.W.

2 1

Optimizing Fold Expressions
by J. J. W. 02 Apr '13

02 Apr '13

Dear all, I was wondering whether it was possible to write fold expressions more elegantly. Suppose I have the following datastructure: data Expr = Add Expr Expr | Sub Expr Expr | Mul Expr Expr | Eq Expr Expr | B Bool | I Int deriving Show type ExprAlgebra r = (r -> r -> r, -- Add r -> r -> r, -- Sub r -> r -> r, -- Mul r -> r -> r, -- Eq Bool -> r, -- Bool Int -> r -- Int ) foldAlgebra :: ExprAlgebra r -> Expr -> r foldAlgebra alg@(a, b, c ,d, e, f) (Add x y) = a (foldAlgebra alg x) (foldAlgebra alg y) foldAlgebra alg@(a, b, c ,d, e, f) (Sub x y) = b (foldAlgebra alg x) (foldAlgebra alg y) foldAlgebra alg@(a, b, c ,d, e, f) (Mul x y) = c (foldAlgebra alg x) (foldAlgebra alg y) foldAlgebra alg@(a, b, c ,d, e, f) (Eq x y) = d (foldAlgebra alg x) (foldAlgebra alg y) foldAlgebra alg@(a, b, c ,d, e, f) (B b') = e b' foldAlgebra alg@(a, b, c ,d, e, f) (I i) = f i If I am correct, this works, however if we for example would like to replace all Int's by booleans (note: this is to illustrate my problem): replaceIntByBool = foldAlgebra (Add, Sub, Mul, Eq, B, \x -> if x == 0 then B False else B True) As you can see, a lot of "useless" identity code. Can I somehow optimize this? Can someone give me some pointers how I can write this more clearly (or with less code?) So I constantly don't have to write Add, Sub, Mul, for those things that I just want an "identity function"? Thanks in advance! Jun Jie

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Announcement - HGamer3D - 0.2.1 - why netwire
by Peter Althainz 02 Apr '13

02 Apr '13

Peter Althainz wrote: > Dear All, > > I'm happy to announce release 0.2.1 of HGamer3D, the game engine with > Haskell API, featuring FRP based API and FRP based GUI. The new FRP API > is based on the netwire package. Currently only available on Windows: > http://www.hgamer3d.org. Nice work! Of course, I have to ask: what influenced your choice of FRP library in favor of netwire instead of reactive-banana ? Best regards, Heinrich Apfelmus -- http://apfelmus.nfshost.com Hi Heinrich good question, actually I need to thank you for your excellent tutorials on FRP and GUI on the WEB. I tried the version of reactive-banana without switches as the first FRP framework to have contact with and I liked its simplicity and the cool introduction around Excel cells you gave on the Web. HGamer3D is my personal way to get more insight into FP and Haskell especially and from the beginning I wanted to have a FRP API to try it with game examples. So your intro on FRP and the examples were very helpful with that. After reading a lot on the web it became clear, that currently reactive-banana and netwire are good candidates to start with. So why in the end I decided to use netwire for the binding? It's some personal things and I do not claim to have done a proper evaluation or comparison. I also cannot judge on performance or other relevant topics. Having said that, I can give you some points why I choosed netwire: - The cool simplicity of reactive-banana API seems to have suffered a little bit after the introduction of the switch functionality. - After getting around Monads and Applicative by great help of "Learning a Haskell for great good" I was shocked to see, there is even more to learn, when I detected Arrows. So I started to look at it and discovered some nice tutorials for Arrows. - What struck me was introduction of netwire author Ertugrul Söylemez on Arrows and the explanations of local state, which can be kept into an arrow. Since I was also curious on OOP and FP and game state handling, actually this raised some interest. So I think this "Arrows keep local state" argument was the killer feature. But also behaviours keep local state and maybe I got misguided here. - I then did some trials with netwire and I felt it's a quite comprehensive and nice API, so I got started with that. regards Peter

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Re: [Haskell-cafe] Cabal install pandoc
by Roger Mason 02 Apr '13

02 Apr '13

Hello Albert, On 04/01/2013 11:41 PM, Albert Y. C. Lai wrote: > On 13-04-01 06:26 AM, Roger Mason wrote: >> It turned out that there was a stale version of 'array' lurking in the >> ghc package db. In spite of reinstalling ghc it did not go away until I >> unregistered it. I think it was persisting because re-installing ghc >> simply unpacked over the old directory leaving that pre-existing file >> intact. > > See my http://www.vex.net/~trebla/haskell/sicp.xhtml for how does GHC > know or not know what libs you have. In particular, it has very little > to do with files, and clearing GHC is only half the story. > > And how to have the same kind of problems recur in the future. Thank you. I have read and filed away the article for future reference. I guess the best (least error prone) method of installing ghc and packages is to obtain a binary ghc (outside one's package manager), build haskell platform and then maintain ghc and packages outside the distro package manager. Comments welcome. Roger This electronic communication is governed by the terms and conditions at http://www.mun.ca/cc/policies/electronic_communications_disclaimer_2012.php

1 0

N-ANN: HBlog-0.1
by Tom Murphy 02 Apr '13

02 Apr '13

Hi All, Not particularly happy to announce the non-release of my latest library, HBlog 0.1. I've been working on it steadily for a long time now, but it's still not ready. The library -- when it's finished -- will be a 100% Haskell representation of blogs, from authors and posts up to the most abstract notion of an entire blog as a Haskell data type. I'd like to finish the library sometime, but I've been so busy! Any spare time I've had, I've just ended up watching TV. I've been so caught up with the final season of The Office, I didn't realize how much time had passed since I originally had the idea! (2 years.) Didn't it seem like Jim and Pam were going to break up a couple weeks ago?! Anyway, here's the code I've definitely settled on so far: data Author = Author { name :: String } deriving (Show, Eq) data Post = Post { title :: String , body :: String , authors :: [Author] } deriving (Show) data Blog = Blog [Post] hasSingleAuthor :: Post -> Bool hasSingleAuthor post = 1 == (length $ authors post) Feel free to use portions of this code in your own projects! Just be sure to put at the top of all your source files: "Portions of this code (c) 2013 Tom Murphy. All rights reserved." ROADMAP: -- Lenses sound pretty cool, so I've started writing lenses for the Author type, as well as finding out what a lens is. Maybe one day there'll be lenses for the Post type, too -- keep your fingers crossed! -- One time when I was walking home from work, I had the idea for blogs being modeled as monads. Wouldn't that be awesome?: "The Blog Monad." I haven't done it yet, though, because I haven't figured out what bind would do. If you figure out how to model blogs as monads, just be sure to include this in all of your sourcefiles: "Idea for blog monad (c) 2013 Tom Murphy. All rights reserved." Happy hacking! Tom

2 2

cabal install pandoc
by Roger Mason 02 Apr '13

02 Apr '13

Hello, I installed ghc (7.6.2) on an Arch Linux machine. I'm trying to install pandoc via cabal but it fails: ... Configuring text-0.11.2.3... Warning: This package indirectly depends on multiple versions of the same package. This is highly likely to cause a compile failure. package deepseq-1.3.0.1 requires array-0.4.0.1 package text-0.11.2.3 requires array-0.4.0.1 Building text-0.11.2.3... Preprocessing library text-0.11.2.3... <command line>: cannot satisfy -package-id array-0.4.0.1-db49bb8b0087ae85b5875d4c0cc12874 (use -v for more information) Failed to install text-0.11.2.3 ... There are then errors for other packages that depend on 'text' or 'array'. I will be grateful for any help. Thanks, Roger This electronic communication is governed by the terms and conditions at http://www.mun.ca/cc/policies/electronic_communications_disclaimer_2012.php

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User group in Stockholm?
by Sergey Bushnyak 01 Apr '13

01 Apr '13

I'll be in Stockholm next month, so I'm curious about haskellers in Stockholm. I saw attempts to organize regular meetings in old mailing threads, but can't find *up to date* information to correct my schedule and see fellow haskellers. Sorry, if this offtopic -- Best regards, Sergey Bushnyak

1 0

Haskel let
by A Smith 01 Apr '13

01 Apr '13

Hi I think I've mastered much of functional programming with Haskell, or at least I can write programs which process as desired. However the existence of the "let" statement evades me apart from a quick way to define a function. Then there is the "in" and "where" parts. Its been suggested its to do with scope and is obvious. I think I need to understand it in a C/C++/Perl style of code to have a Eureka moment when it will be obvious. Can someone refer me to something which will assist me ? Andrew

3 2

Assembly EDSL in Haskell
by C K Kashyap 01 Apr '13

01 Apr '13

Hi Cafe, I am trying to embed x86 assembly in Haskell. I'd like the EDSL to not allow invalid movements into registers - for example, should not allow moving into RIP. I was not able to get it to work. I ended up using DataTypeContexts - which is considered misfeature anyway. I was wondering if I could get some suggestions. {-# LANGUAGE DatatypeContexts #-} data SREG = RIP data DREG = RBX data SNDREG = RAX data (Source s, Destination d) => Instruction s d = MOV s d class Source a class Destination a instance Source SREG instance Source SNDREG instance Destination DREG instance Destination SNDREG move :: (Source s, Destination d) => s -> d -> Instruction s d move s d = MOV s d hello = [move RAX RAX, move RAX RAX] hello = [move RAX RAX, move RAX RBX] -- this is still not allowed. Regards, Kashyap

2 2

graphical editor links ?
by Luc TAESCH 01 Apr '13

01 Apr '13

I am designing some graphical editor ( visio - dia like) and would be interested to hear any pointer to help me think on the architecture of this, in term of data structure/ EDSL/ persistence/ paradigm (FP/ FRP/...) for the different "layers of abstraction " I may see , like rendering libraries ( gtk/wx..)<-> model of the diagram<-> semantics ( this is a state diag/ archimate / mind mapping , i.e. what the glyph and lines means ) <-> persistence Any help & pointers welcomed ! ( and which place is best to discuss this ?) Luc

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Haskell SBV Package with Z3
by J. J. W. 01 Apr '13

01 Apr '13

Dear all, I have a small question regarding the installation of the SBV package. I first installed the SBV 2.10 package with cabal with the following instructions: cabal install sbv Next I installed the Z3 theorem prover and adding the path to my system variables (Windows 7 x64). Next I tested whether I could find it by opening cmd.exe and then typing z3, I get an error message of Z3, so I can safely assume the system can find it. (I added the path to the bin of Z3, I have not included the include directory, I see no reason why I should add a path to this directory, but maybe I am wrong). I ran the program: SBVUnitTests. However it had some errors in the beginning and afterwards a few failures. Having no idea how to fix this, I continued to check whether I can get the SBV to work. So I started to execute the SBV package: ghci -XScopedTypeVariables ghci> :m Data.SBV ghci> prove $ \(x::SWord8) -> x `shiftL` 2 .== 4*x Now this should return Q.E.D., however it returned the following: An error occured. Failed to complete the call to z3 Executable: "C:\\Program Files\\z3-4.3.0-x64\\bin\\z3.exe Options: /in /smt2 Exit code: 0 Solver output: =========================================================== ; :smt.mbqi ; :pp.decimal_precision =========================================================== Giving up.. It does seems like that the Z3 has a normal output, however not a result. Can someone help me to figure out what I actually did wrong? I am using Z3 version 4.3.0, SBV 2.10 and GHCi 7.4.2 Thank you for your help! Yours sincerely, Jun Jie

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Organising code in FRP
by luc taesch 31 Mar '13

31 Mar '13

I am just learning FRP ( via reactive-banana) . so possibly opening a topic already mentionned , apologises in advance, and pointers welcomed. I am wondering about "code structuration" ? ie spagetti code for the network 1/ in a non trivial FRP applicaiton, how to manage "modulatity" or structuration of the Network ? ( most of the example I scanned are toy-size). I ca imagine it may not be trvial to find its way around in a large setup ... 2/ what about the separation of "layers". I mean fine, we extract the reactive ness from the GUI, and separate the layout of widgets from the behaviors of these great, but is it to then mingle the UI with the "business part" ( say in banking), and the infrastructure side ( say persistence, comms, transactionnality, etc) in other words, how tdoes the nice abstraction developped ( module/ interface / categoty patterns, monad, etc) coexsit with a netork of FRP event and behaviors ? Any prior art on this ? ( and which place si best to discuss this ?)

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Specialized Computer Architecture - A Question
by OWP 31 Mar '13

31 Mar '13

Hi, I was reading the paper "A History of Haskell: being lazy with class" ( http://www.haskell.org/haskellwiki/History_of_Haskel) and came on a section (I 2.1) which briefly explained the work people did on making non-von Neumann architectures. It concluded by saying "Much (but not all) of this architecturally oriented work turned out to be a dead end, when it was later dis- covered that good compilers for stock architecture could outper- form specialised architecture. But at the time it was all radical and exciting." These "stock architectures", were they really so good that they out performed the specialized ones on it's own merits or was this mainly due to Moore's Law on transistors? In other words, suppose we separate Moore's Law from the stock architecture, would it still outperform the specialized ones? Thank you for any response

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Threadscope 0.2.2 goes in segmentation fault on Mac Os X 10.8.3
by Alfredo Di Napoli 31 Mar '13

31 Mar '13

Hi Cafè, I've tried installing threadscope, but when I run it from console with "threadscope" I get a laconic segmentation fault. Some info to help the debugging: * Installed gtk via brew * gtk-demo runs correctly * I'm using Mac Os X 10.8.3 * Running gtk and threadscope through a virtual environment (provided by hsenv) * Using XQuartz 2.7.4 I know it's a bit difficult to debug this way, I can try debugging with gdb if it can help. Cheers, A.

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[ANN] hoodle-0.2
by Ian-Woo Kim 30 Mar '13

30 Mar '13

Hi, all, Pen note-taking program hoodle, which is being developed entirely in haskell, is updated to version 0.2. The previous version was 0.1.1. About what is hoodle, please refer to http://ianwookim.org/hoodle The changes in this version are - hoodle data format updated. now hoodle document has a unique id. - linking between documents implemented - vertical space inserting tool implemented - a widget introduced for panning and zooming - drag and drop linking implemented - drag and drop image embedding implemented - poppler pdf support is mandatory - pdf can be embedded in a file - toolbox ui reflects current hoodle state more correctly - slimmer select box design - several rendering glitches fixed Note that poppler is mandatory for hoodle (in the previous versions, poppler support was optional). One needs to install poppler-glib before installing hoodle. After gtk2hs and poppler installed, installing hoodle should be simply > cabal install hoodle As for the detail information about wacom tablet support, please read installation page on the webpage. If you were using the previous versions of hoodle, you will find this version gives you much smoother experience and many interesting improvements. (especially adding vertical space tool and pan-zoom widget ) Enjoy~ best, Ian-Woo Kim

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Idea: Source maps for GHC's -pgmF
by Christopher Done 30 Mar '13

30 Mar '13

Here's an idea. For the -pgmF flag, because compile errors become really obscure and line numbers rendered unhelpful, why don't we use source maps as recently done for JavaScript in the browser? Info: https://wiki.mozilla.org/DevTools/Features/SourceMap https://docs.google.com/document/d/1U1RGAehQwRypUTovF1KRlpiOFze0b-_2gc6fAH0… Here is an example I experimented with the Fay (Haskell→JS compiler): https://dl.dropbox.com/u/62227452/Screenshots/Screenshot%20from%202012-09-2… This shows the original source code and a backtrace of an exception thrown in JavaScript. We can use Mozilla/Google's format: http://hackage.haskell.org/package/sourcemap Though it's kind of an obscure format because it's aimed at being small, but if it's already been done, why not? Otherwise a simple JSON format is probably sufficient. It could be used both in GHC's compilation, pattern match exceptions, and even in debugger stepping, if desired. Provided with, e.g. -pgmFsm foo.map. This would make things like the XML mode or other syntactical extensions feel quite natural and not awkward in GHC's error messages. What say you, -pgmF users and GHC hackers? Ciao!

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Monad.Reader #22 call for copy
by Edward Z. Yang 29 Mar '13

29 Mar '13

Call for Copy: The Monad.Reader - Issue 22 -------------------------------------------- Another ICFP submission deadline has come and gone: why not celebrate by submitting something to The Monad.Reader? Whether you're an established academic or have only just started learning Haskell, if you have something to say, please consider writing an article for The Monad.Reader! The submission deadline for Issue 22 will be: **Saturday, June 1** The Monad.Reader ~~~~~~~~~~~~~~~~ The Monad.Reader is a electronic magazine about all things Haskell. It is less formal than journal, but somehow more enduring than a wiki- page. There have been a wide variety of articles: exciting code fragments, intriguing puzzles, book reviews, tutorials, and even half-baked research ideas. Submission Details ~~~~~~~~~~~~~~~~~~ Get in touch with me if you intend to submit something -- the sooner you let me know what you're up to, the better. Please submit articles for the next issue to me by e-mail (ezyang(a)mit.edu) Articles should be written according to the guidelines available from http://themonadreader.wordpress.com/contributing/ Please submit your article in PDF, together with any source files you used. The sources will be released together with the magazine under a BSD license. If you would like to submit an article, but have trouble with LaTeX please let me know and we'll work something out.

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my knucleotide fast on 64 bit but extremely slow on 32 bit?
by Branimir Maksimovic 29 Mar '13

29 Mar '13

I have posted previous knucleotide program, it is fast on 64 bit butvery slow on 32 bit.I cannot install 32 bit ghc to test it so I can only guess is thatcause is use of Int64 for hash and HashMap array indexing.What bothers me is that it that much slower , and I guessthat array indexing of 64 bit int where native index is 32 bitis culprit.Am I right? If I make Int index of array it will be fast on32 bit platform too?I cannot imagine that hashing to 64 bit int is culprit ratherarray indexing as I guess that every array accessrequires indirect access on 32 bit platform? 64 bit :http://benchmarksgame.alioth.debian.org/u64q/program.php?test=knucleotide&lang=ghc&id=119.80 secs32 bit:http://benchmarksgame.alioth.debian.org/u32q/program.php?test=knucleoti… secs ;( I really like Haskell, but Im frustrated as how inpredictable it is.Im programming from 1983' but found Haskell as much more difficultto program efficiently than C++.In C++ whatever lousy program I write it performs decently,but not so in Haskell. It requires much deeper knowledge thanc++.

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introducing Maybe at managing level
by luc taesch 29 Mar '13

29 Mar '13

I was looking for some link introducing the way FP/ Haskell handles errors and Exceptions. This is for a non FP Guy, and ideally withought scaring them with Monads and category theory :-). for the background : the guy said : As I mentioned in another thread in banking (in particular) it is the exception processing that often dominates the functionality of a system - as the core concept is generally very straightforward. Developing for "exception handling" (not in a Java/C++ sense) is a tricky thing - as the exception don't necessarily shout themselves out - and are often why we have large misunderstood legacy systems which are hard to replace.

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Re: [Haskell-cafe] warp and http-conduit on concurrent threads on windows
by Lars Kuhtz 29 Mar '13

29 Mar '13

That resolved the issue. Thanks for the hint. Lars On 2013-03-28 18:17, Joey Adams wrote: > Try upgrading to the latest network package. There's a bug prior to > version 2.4.1.0 where 'connect' blocks other threads from running, > because the underlying FFI call was marked "unsafe". > > Somewhat unrelated, but if your program needs to run for long periods > of time (e.g. a server), you're in for a nasty surprise: GHC > currently > doesn't support interrupting network I/O on Windows. After about a > thousand hung connections, the program will run out of address space > and hang. A partial workaround is to use socket timeouts; see > setHandleTimeouts in the network-socket-options package.

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Remove redundancy with Template Haskell
by Corentin Dupont 29 Mar '13

29 Mar '13

Hi Café, I have a function that looks like this: call :: SomeFunction -> String -> SomeState The string is actually the representation of the function passed in parameter. It is stored in the state for documentation. So a call looks like that: call (\a -> putStrLn a) "\a -> putStrLn a" There is a clear redundancy here, how could I remove it with Template Haskell? I cannot figure out... Thanks! Corentin

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warp and http-conduit on concurrent threads on windows
by Lars Kuhtz 28 Mar '13

28 Mar '13

Hi, I'd like to know what is wrong with the following program on windows8 (GHC 7.4.2, 32bit): {-# LANGUAGE OverloadedStrings #-} {-# LANGUAGE ScopedTypeVariables #-} module Main where import Control.Concurrent.Async import qualified Control.Exception as E import Network.HTTP.Conduit import Network.HTTP.Types import Network.Wai import Network.Wai.Handler.Warp query port = E.catch (simpleHttp ("http://haskell.org:" ++ show port) >>= print . take 10 . show) (\(e :: HttpException) -> print $ "caught: " ++ show e) listen = run 8080 $ \_ -> return $ responseLBS ok200 [] "abc" main = do withAsync (query 12345) $ \a -> do withAsync listen $ \b -> do wait a wait b I compile the program with "ghc --make -threaded Main.hs" and run it as "./Main +RTS -N". On POSIX systems this works as expected. Even if the failing "query" runs in a forever loop the "listen" thread responds promptly to requests. On windows the "listen" thread seems blocked by the failing "query" thread. Sometimes the query returns (relatively) prompt. But sometimes (about a third of all runs) it takes very long (about 20 sec). Also, sometimes it returns with "Connection timed out (WSAETIMEDOUT)", sometimes with "getAddrInfo: does not exist (error 11003)", and sometimes just with "FailedConnectionException". The fact that the "listen" thread is blocked seems to contradict the following quote form the documentation of Control.Concurrent: -- Quote from Control.Concurrent -- Using forkOS instead of forkIO makes no difference at all to the scheduling behaviour of the Haskell runtime system. It is a common misconception that you need to use forkOS instead of forkIO to avoid blocking all the Haskell threads when making a foreign call; this isn't the case. To allow foreign calls to be made without blocking all the Haskell threads (with GHC), it is only necessary to use the -threaded option when linking your program, and to make sure the foreign import is not marked unsafe. -- End Quote -- By the way: using withAsyncBound instead of withAsync seems to improve (but not completely solve) the issue. Thanks, Lars

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nice pattern from simple converging series
by Christopher Howard 28 Mar '13

28 Mar '13

I made a nice little pattern from just a few lines of Haskell (mostly code comments) using gloss. It is very kindergarten in terms of mathematical art, but the idea was to illustrate that in a pretty short amount of time, and a small amount code, you could easily translate simple math concepts into geometry on your screen. http://frigidcode.com/code/haskell-series-circles/ -- frigidcode.com

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Parallel Data.Vector.generate?
by Myles C. Maxfield 28 Mar '13

28 Mar '13

Hello all. I'm using the Data.Vector.generate function with a complicated creation function to create a long vector. Is it possible to parallelize the creation of each element? Alternatively, if there was something like parMap for vectors, I suppose I could pass id to Data.Vector.generate and use parMap. Does something like this exist? Thanks, Myles C. Maxfield

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duplicate type signatures
by Heinrich Hördegen 28 Mar '13

28 Mar '13

Dear all, why is this allowed (GHCi, version 7.4.1): main :: IO () main = do let a, a :: Int a = 5 print a but this not: main :: IO () main = do let a :: Int a :: Int a = 5 print a Is there a deeper sens or is it just a little bit inconsistent? Heinrich

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Re: [Haskell-cafe] [extension]syntactic sugar for maps
by Eli Frey 28 Mar '13

28 Mar '13

> Sorry, I forgot to explain (probably because I'm too used to it). I am referring to a syntax for easy creation of maps. Something equivalent to lists: > > to build a list: [ 1, 2, 3] > to build a map; { 1, "one", 2, "two", 3, "three"} > > Without it I am always forced to use fromList. This looks like something to use records for, or in any case something where association list performance is not an issue. If you just want to store some configuration-like structure and pass it around, a record is great for this. You might find where in other languages you would simply leave a key "null", in Haskell you can just fill it with a Nothing. Maps (hash or binary-tree) really pay off when they are filled dynamically with massive numbers of associations. I find when I am ending up in this scenario, I am generating my map programatically, not writing it as a literal. Sometimes people even write maps simply as functions and not even as a data-structure. > myMap char = case char of > 'a' -> 1 > 'b' -> 2 > 'c' -> 3 Perhaps you could describe a situation you are in where you are wanting this, and we could see if there is something you can do already that is satisfying and solves your problem. On Wed, Mar 27, 2013 at 12:59 PM, Eli Frey <eli.lee.frey(a)gmail.com> wrote: > > http://hackage.haskell.org/trac/ghc/wiki/OverloadedLists comes to mind. > > This assumes you can turn ANY list into a thing. Maps only make sense to > be constructed from association list. If I've got a [Char], how do I make > a map form it? > > > On Wed, Mar 27, 2013 at 12:56 PM, Nicolas Trangez <nicolas(a)incubaid.com>wrote: > >> On Wed, 2013-03-27 at 21:30 +0200, Răzvan Rotaru wrote: >> > I am terribly missing some syntactic sugar for maps (associative data >> > structures) in Haskell. I find myself using them more than any other >> > data >> > structure, and I think there is no big deal in adding some sugar for >> > this >> > to the language. I could not find out whether such an extension is >> > beeing >> > discussed. If not, I would like to propose and extension. Any help and >> > suggestions are very welcome here. Thanks. >> >> http://hackage.haskell.org/trac/ghc/wiki/OverloadedLists comes to mind. >> >> Nicolas >> >> >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> > >

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[extension]syntactic sugar for maps
by Răzvan Rotaru 27 Mar '13

27 Mar '13

Hi, I am terribly missing some syntactic sugar for maps (associative data structures) in Haskell. I find myself using them more than any other data structure, and I think there is no big deal in adding some sugar for this to the language. I could not find out whether such an extension is beeing discussed. If not, I would like to propose and extension. Any help and suggestions are very welcome here. Thanks. Also related to the topic: 1/ Is there a list of proposals for extensions to Haskell that has currently been accepted in the new standard? I have not found one on Haskell' ( http://hackage.haskell.org/trac/haskell-prime/query?status=new&status=assig…) but it looks outdated. No mentions to the new standard! 2/ I have seen somewhere a statement that a new language standard will be published yearly. Didn't happen until now. Is there even a new standard on the way? Cheers, Răzvan

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Re: [Haskell-cafe] Pattern matching with singletons
by Richard Eisenberg 27 Mar '13

27 Mar '13

Hello Paul, > ----- Forwarded message from Paul Brauner <polux2001(a)gmail.com> ----- <snip> > - is a ~ ('CC ('Left 'CA)) a consequence of the definitions of SCC, > SLeft, ... (in which case GHC could infer it but for some reason can't) > - or are these pattern + definitions not sufficient to prove that a > ~ ('CC ('Left 'CA)) no matter what? The first one. GHC can deduce that (a ~ ('CC ('Left b))), for some fresh variable (b :: TA), but it can't yet take the next step and decide that, because TA has only one constructor, b must in fact be 'CA. In type-theory lingo, this deduction is called eta-expansion. There have been on-and-off debates about how best to add this sort of eta-expansion into GHC, but all seem to agree that it's not totally straightforward. For example, see GHC bug #7259. There's a non-negligible chance I will be taking a closer look into this at some point, but not for a few months, so don't hold your breath. I'm not aware of anyone else currently focusing on this problem either, I'm afraid. I'm glad you're finding use in the singletons package! Let me know if I can be of further help. Richard

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my take at knucleotide
by Branimir Maksimovic 27 Mar '13

27 Mar '13

Hi, I have tried to implement knucleotide benchmark program this time:http://benchmarksgame.alioth.debian.org/u64q/performance.php?test=knuc… Implementation is shorter (uses hashtable from hashtables package),but two time slower then current Haskell entry ( which is too low levelfor my taste :)).What is interesting is that if I try to place Int64 as a key tohash table, performance is even slower.Strange that dropping and taking from bytestring would befaster than packing string in 64 bit int and directly indexing. If someone can see something that can bring performance on parwith current haskell entry , I would post it , otherwise no point,except that program is shorter and not low level. {-# Language BangPatterns #-}---- The Computer Language Benchmarks Game-- http://benchmarksgame.alioth.debian.org/---- Contributed by Branimir Maksimovic--import Data.Charimport Data.Listimport Data.IORefimport qualified Data.HashTable.IO as Himport qualified Data.ByteString.Char8 as Simport Control.Concurrentimport Text.Printf main = do s <- S.getContents let content = (S.map toUpper . S.concat . tail . dropWhile (\l->not $ S.isPrefixOf (S.pack ">THREE") l) . S.lines) s mapM_ (execute content) actions data Actions = I Int | S Stringactions = [I 1,I 2, S "GGT",S "GGTA",S "GGTATT",S "GGTATTTTAATT",S "GGTATTTTAATTTATAGT"]execute content (I i) = writeFrequencies content iexecute content (S s) = writeCount content s writeFrequencies input size = do ht <- tcalculate input size lst <- H.foldM (\lst (k,v)->do v' <- readIORef v return $ insertBy (\(_,x) (_,y)->y `compare` x) (k,v') lst) [] ht let sum = fromIntegral ((S.length input) + 1 - size) mapM_ (\(k,v)-> do printf "%s %.3f\n" (S.unpack k) ((100 * (fromIntegral v)/sum)::Double)) lst putChar '\n' writeCount input string = do let size = length string ht <- tcalculate input size res <- H.lookup ht (S.pack string) case res of Nothing -> putStrLn $ string ++ " not found..." Just v -> do r <- readIORef v printf "%d\t%s\n" r (string::String) tcalculate input size = do let l = [0..7] actions = map (\i -> (calculate input i size (length l))) l vars <- mapM (\action -> do var <- newEmptyMVar forkIO $ do answer <- action putMVar var answer return var) actions result <- newTable results <- mapM takeMVar vars mapM_ (\ht -> H.foldM (\lst (k,v) -> do res <- H.lookup lst k case res of Nothing -> do r1 <- readIORef v r2 <- newIORef r1 H.insert lst k r2 Just v1 -> do r1 <- readIORef v1 r2 <- readIORef v writeIORef v1 (r1+r2) return lst) result ht) results return result calculate input beg size incr = do ht <- newTable let calculate' :: S.ByteString -> Int -> IO HashTable calculate' str i | i >= ((S.length input)+1 - size) = return ht | otherwise = do res <- H.lookup ht k case res of Nothing -> do !r <- newIORef 1 H.insert ht k r Just v -> do !r <- readIORef v writeIORef v (r+1) calculate' (S.drop incr str) (i+incr) where k = S.take size str calculate' (S.drop beg input) beg type HashTable = H.BasicHashTable S.ByteString (IORef Int) newTable :: IO HashTablenewTable = H.new

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Word8 literals in ByteString haddock?
by Niklas Hambüchen 27 Mar '13

27 Mar '13

Hey, according to http://hackage.haskell.org/packages/archive/bytestring/0.10.2.0/doc/html/Da… I can write: split '\n' "a\nb\nd\ne" Can I really do that? I don't know of a way to make a '\n' literal be a Word8, so maybe these Haddocks are wrong? I guess they would apply for Data.ByteString.Char8, but this is Data.ByteString. Or is there a way? Niklas

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Future of MonadCatchIO
by Arie Peterson 26 Mar '13

26 Mar '13

Hi all, The function 'block' and 'unblock' (from Control.Exception) have been deprecated for some time, and are apparantly now being removed (in favour of 'mask'). Generalisations of these functions are (part of) the interface of MonadCatchIO-transformers (the 'MonadCatchIO' class has methods 'block' and 'unblock'). So, the interface would have to change to keep up with base. I'm inclined to deprecate MonadCatchIO-transformers itself, in favour of monad-control. I suspect that most clients do not use 'block' or 'unblock' directly, but use only derived functions, like 'bracket'. (I have partly confirmed this, by inspecting some reverse dependencies on hackage.) This allow an easy transition to monad-control: in many cases, only imports will need to be changed. In the minority of cases where 'block' and 'unblock' are used and/or instances of MonadCatchIO are defined, code will need to be updated. There is a difference in functionality between MonadCatchIO and monad-control. In the former, 'bracket' will not perform the final action if the main action is an ErrorT that throws an error (in contrast with exceptions in the underlying IO monad). In monad-control, 'bracket' will perform the final action in this case. (See this discussion for background: <http://www.haskell.org/pipermail/haskell-cafe/2010-October/084890.html>.) Probably, in most use cases the behaviour of monad-control is preferred. This seems to be the case also for snap, which uses MonadCatchIO-transformers, but defines its own variant of 'bracket' to get the right behaviour. Would anyone have a problem with a deprecation of MonadCatchIO-transformers, and a failure to update it to work with a base without 'block' and 'unblock'? Regards, Arie

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