- Haskell-Cafe - Haskell.org

[Pipes] Can pipes solve this problem? How?
by Daniel Hlynskyi 16 Aug '12

16 Aug '12

Hello Cafe. Consider code, that takes input from handle until special substring matched: > matchInf a res s | a `isPrefixOf` s = reverse res > matchInf a res (c:cs) = matchInf a (c:res) cs > hTakeWhileNotFound str hdl = hGetContents hdl >>= return.matchInf str [] It is simple, but the handle is closed after running. That is not good, because I want to reuse this function. Code can be rewritten without hGetContent, but it is much less comprehensible: hTakeWhileNotFound str hdl = fmap reverse$ findStr str hdl [0] [] where findStr str hdl indeces acc = do c <- hGetChar hdl let newIndeces = [ i+1 | i <- indeces, i < length str, str!!i == c] if length str `elem` newIndeces then return (c : acc) else findStr str hdl (0 : newIndeces) (c : acc) So, the question is - can pipes (any package of them) be the Holy Grail in this situation, to both keep simple code and better deal with handles (do not close them specifically)? How?

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linking Haskell app with Curl on Windows
by Eugene Dzhurinsky 16 Aug '12

16 Aug '12

Hi! I'm facing strange issue with linking my application against Curl (using Haskell Curl binding curl-1.3.7): the application compiles well, but fails on linking stage: ===================================================================================== C:\haskell\bin\ghc.exe --make -o dist\build\imgpaste\imgpaste.exe -hide-all-packages -fbuilding-cabal-package -package-conf dist\package.conf.inplace -i -idist\build\imgpaste\imgpaste-tmp -i. -idist\build\autogen -Idist\build\autogen -Idist\build\imgpaste\imgpaste-tmp -optP-include -optPdist\build\autogen\cabal_macros.h -odir dist\build\imgpaste\imgpaste-tmp -hidir dist\build\imgpaste\imgpaste-tmp -stubdir dist\build\imgpaste\imgpaste-tmp -package-id base-4.5.0.0-597748f6f53a7442bcae283373264bb6 -package-id bytestring-0.9.2.1-df82064cddbf74693df4e042927e015e -package-id curl-1.3.7-ed08f87bd8c487f1e11a8c3b67bf4e51 -package-id directory-1.1.0.2-0270278088d4b2588b52cbec49af4cb7 -package-id hxt-9.2.2-e687550fbbb6ff367ee9c95584c3f0a0 -package-id hxt-xpath-9.1.2-4a15d34a0b66fa21832bb4bb0f68477f -package-id regex-pcre-0.94.4-f2f06ed579a684904354d97b04a74d9e -O -XHaskell98 .\Main.hs -llibcrypto -lssh2 -lssl -lz -lidn -LC:\curl\lib Linking dist\build\imgpaste\imgpaste.exe ... C:\Program Files\Haskell\curl-1.3.7\ghc-7.4.1/libHScurl-1.3.7.a(curlc.o):curlc.c:(.text+0xd2): undefined reference to `_imp__curl_easy_getinfo' C:\Program Files\Haskell\curl-1.3.7\ghc-7.4.1/libHScurl-1.3.7.a(curlc.o):curlc.c:(.text+0xee): undefined reference to `_imp__curl_easy_getinfo' C:\Program Files\Haskell\curl-1.3.7\ghc-7.4.1/libHScurl-1.3.7.a(curlc.o):curlc.c:(.text+0x10a): undefined reference to `_imp__curl_easy_getinfo' [ lots of error messages skipped ] C:\curl\lib/libcurl.a(md5.o):(.text+0x3b): undefined reference to `MD5_Update' C:\curl\lib/libcurl.a(md5.o):(.text+0x4e): undefined reference to `MD5_Final' C:\curl\lib/libcurl.a(md5.o):(.rdata+0x0): undefined reference to `MD5_Init' C:\curl\lib/libcurl.a(md5.o):(.rdata+0x4): undefined reference to `MD5_Update' C:\curl\lib/libcurl.a(md5.o):(.rdata+0x8): undefined reference to `MD5_Final' C:\curl\lib/libcurl.a(md5.o):(.rdata+0x14): undefined reference to `MD5_Init' C:\curl\lib/libcurl.a(md5.o):(.rdata+0x18): undefined reference to `MD5_Update' C:\curl\lib/libcurl.a(md5.o):(.rdata+0x1c): undefined reference to `MD5_Final' cabal.EXE: Error: some packages failed to install: imgpaste-0.2 failed during the building phase. The exception was: ExitFailure 1 ===================================================================================== What may be wrong here? Curl itself was installed without errors. Looking for symbols 'MD5_Final' in directory C:\curl\lib results in 'libcrypto.a', 'libcrypto.dll.a' and 'libcurl.a' -- Eugene N Dzhurinsky

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Custom QuickCheck Gens without custom shrinks
by Niklas Hambüchen 15 Aug '12

15 Aug '12

I wrote this Gen to generate lines of texts without \NUL and \n: fullLinesProp = forAll linesGen ... linesGen = listOf . listOf $ arbitrary `suchThat` (`notElem` ['\NUL', '\n']) -- alternatively: linesGen = arbitrary `suchThat` (all (all (`notElem` ['\NUL', '\n']))) However, I just realized that QuickCheck disables shrinking when I use this instead of (linesGen = arbitrary :: Gen [String]). Why is that? Is there a way to get what I want + shrinking without defining a custom shrink (e.g. forAllShrink)? Thanks

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Haskell Weekly News: Issue 240
by Daniel Santa Cruz 15 Aug '12

15 Aug '12

Welcome to issue 240 of the HWN, an issue covering crowd-sourced bits of information about Haskell from around the web. This issue covers the week of August 05 to 11, 2012. Quotes of the Week * johnw: Monads are an interface, all bets are off until you see what the interface does for a given Type * Evbn: I heard that Untyped and Well Typed tried to set up a corporate softball league, but they couldn't agree on a ruleset to use. * wuttf: i think i have to learn this language, the type systems i know just dont feel right Top Reddit Stories * Studying protein structures in Haskell Domain: haskellforall.com, Score: 53, Comments: 6 On Reddit: [1] http://goo.gl/94PA4 Original: [2] http://goo.gl/VJJD0 * Haskell Live Episode 2: Time To Refactor is up! Domain: youtube.com, Score: 52, Comments: 14 On Reddit: [3] http://goo.gl/BOmK7 Original: [4] http://goo.gl/5wTVu * Announcing Raskell - user ratings for Hackage Domain: ocharles.org.uk, Score: 43, Comments: 29 On Reddit: [5] http://goo.gl/wgK4E Original: [6] http://goo.gl/7q4RP * Yesod 1.1 Released Domain: yesodweb.com, Score: 38, Comments: 14 On Reddit: [7] http://goo.gl/jiwLx Original: [8] http://goo.gl/B5czq * Running Haskell on Raspberry Pi Domain: alenribic.com, Score: 37, Comments: 5 On Reddit: [9] http://goo.gl/zPcDA Original: [10] http://goo.gl/FsESS * Koka - a "function"-oriented language with side-effect inteference Domain: rise4fun.com, Score: 36, Comments: 18 On Reddit: [11] http://goo.gl/lyKhA Original: [12] http://goo.gl/n35n1 * Is Haskell liberal or conservative? (Response post to Yegge) Domain: blog.ezyang.com, Score: 34, Comments: 51 On Reddit: [13] http://goo.gl/AJ5Wp Original: [14] http://goo.gl/Juis3 * ANNOUNCE: basic-prelude Domain: haskell.org, Score: 34, Comments: 8 On Reddit: [15] http://goo.gl/iiDLq Original: [16] http://goo.gl/4Taz0 * ANNOUNCE: tardis Domain: haskell.org, Score: 31, Comments: 3 On Reddit: [17] http://goo.gl/e6yi7 Original: [18] http://goo.gl/590QR * Any Hackage mirrors? How do you deal with Hackage outages? Domain: self.haskell, Score: 30, Comments: 27 On Reddit: [19] http://goo.gl/1BOMF Original: [20] http://goo.gl/1BOMF * Is there a standard Haskell development setup for Vim? Domain: self.haskell, Score: 29, Comments: 44 On Reddit: [21] http://goo.gl/gSRWp Original: [22] http://goo.gl/gSRWp * O'Reilly Webinar this Thursday: Designing Type-Safe Haskell APIs Domain: yesodweb.com, Score: 28, Comments: 8 On Reddit: [23] http://goo.gl/GNogN Original: [24] http://goo.gl/ZRkrH * acid-state with Yesod Domain: meadowstalk.com, Score: 25, Comments: 13 On Reddit: [25] http://goo.gl/NM4Bc Original: [26] http://goo.gl/8MDXo * Philip Wadler: Faith, Evolution, and Programming Languages [InfoQ] Domain: infoq.com, Score: 25, Comments: 6 On Reddit: [27] http://goo.gl/WFxLq Original: [28] http://goo.gl/fBqx7 * Hiring Haskell Developers (Singapore) Domain: cufp.org, Score: 22, Comments: 13 On Reddit: [29] http://goo.gl/bhqrb Original: [30] http://goo.gl/umhh4 * Verifying Software Transactional Memory: bisimulation in Agda [pdf] Domain: cs.nott.ac.uk, Score: 22, Comments: On Reddit: [31] http://goo.gl/X1zvj Original: [32] http://goo.gl/vJ1gA * iterate (*2) 1 Domain: postimage.org, Score: 17, Comments: 13 On Reddit: [33] http://goo.gl/lwLv1 Original: [34] http://goo.gl/lfIab * Error Handling: How would you solve this? Domain: self.haskell, Score: 16, Comments: 11 On Reddit: [35] http://goo.gl/jHLZ8 Original: [36] http://goo.gl/jHLZ8 Top StackOverflow Questions * Advice defining a data structure in Haskell votes: 13, answers: 4 Read on SO: [37] http://goo.gl/xVxlx * What is the preferred way to combine two sinks? votes: 13, answers: 2 Read on SO: [38] http://goo.gl/QUczW * Why is numCapabilities a pure function? votes: 12, answers: 1 Read on SO: [39] http://goo.gl/4HU27 * Using generics to convert between types of the same “shape” votes: 10, answers: 1 Read on SO: [40] http://goo.gl/gx8ZL * Controlling parallel execution votes: 9, answers: 2 Read on SO: [41] http://goo.gl/zzvtU * Lists of lists of lists votes: 9, answers: 5 Read on SO: [42] http://goo.gl/HEicW * Positive integer type votes: 8, answers: 5 Read on SO: [43] http://goo.gl/xXY49 * Haskell bit arrays votes: 7, answers: 1 Read on SO: [44] http://goo.gl/g9TDQ * How to keep track of number of guesses in a simple guessing game (Haskell) votes: 6, answers: 2 Read on SO: [45] http://goo.gl/VQaWn * A haskell program that controls the mouse votes: 5, answers: 1 Read on SO: [46] http://goo.gl/rtveO Until next time, Daniel Santa Cruz References 1. http://www.haskellforall.com/2012/08/code-example-1.html 2. http://www.reddit.com/r/haskell/comments/y0wlw/studying_protein_structures_… 3. http://www.youtube.com/watch?v=6KkF5-_erns 4. http://www.reddit.com/r/haskell/comments/xy6gt/haskell_live_episode_2_time_… 5. http://ocharles.org.uk/blog/posts/2012-08-05-announcing-raskell.html 6. http://www.reddit.com/r/haskell/comments/xq5ap/announcing_raskell_user_rati… 7. http://www.yesodweb.com/blog/2012/08/announcing-yesod-1-1 8. http://www.reddit.com/r/haskell/comments/xujq6/yesod_11_released/ 9. http://alenribic.com/writings/post/running-haskell-on-raspberry-pi 10. http://www.reddit.com/r/haskell/comments/xs5hn/running_haskell_on_raspberry… 11. http://www.rise4fun.com/koka/tutorial 12. http://www.reddit.com/r/haskell/comments/xwe10/koka_a_functionoriented_lang… 13. http://blog.ezyang.com/2012/08/is-haskell-liberal-or-conservative/ 14. http://www.reddit.com/r/haskell/comments/xzukd/is_haskell_liberal_or_conser… 15. http://www.haskell.org/pipermail/haskell/2012-August/023461.html 16. http://www.reddit.com/r/haskell/comments/y0kld/announce_basicprelude/ 17. http://www.haskell.org/pipermail/haskell/2012-August/023455.html 18. http://www.reddit.com/r/haskell/comments/xt7yg/announce_tardis/ 19. http://www.reddit.com/r/haskell/comments/y1tgc/any_hackage_mirrors_how_do_y… 20. http://www.reddit.com/r/haskell/comments/y1tgc/any_hackage_mirrors_how_do_y… 21. http://www.reddit.com/r/haskell/comments/xxxyi/is_there_a_standard_haskell_… 22. http://www.reddit.com/r/haskell/comments/xxxyi/is_there_a_standard_haskell_… 23. http://www.yesodweb.com/blog/2012/08/webinar-oreilly 24. http://www.reddit.com/r/haskell/comments/xrebo/oreilly_webinar_this_thursda… 25. http://meadowstalk.com/post/migration-to-acid-state 26. http://www.reddit.com/r/haskell/comments/xs0t2/acidstate_with_yesod/ 27. http://www.infoq.com/presentations/Faith-Evolution-Programming-Languages 28. http://www.reddit.com/r/haskell/comments/xtusf/philip_wadler_faith_evolutio… 29. http://cufp.org/jobs/haskell-development-role-within-quant-development-team… 30. http://www.reddit.com/r/haskell/comments/xrpl4/hiring_haskell_developers_si… 31. http://www.cs.nott.ac.uk/~gmh/hu-thesis.pdf 32. http://www.reddit.com/r/haskell/comments/xw1p5/verifying_software_transacti… 33. http://postimage.org/image/ucqiynz17/ 34. http://www.reddit.com/r/haskell/comments/xwfbm/iterate_2_1/ 35. http://www.reddit.com/r/haskell/comments/y1gg0/error_handling_how_would_you… 36. http://www.reddit.com/r/haskell/comments/y1gg0/error_handling_how_would_you… 37. http://stackoverflow.com/questions/11833920/advice-defining-a-data-structur… 38. http://stackoverflow.com/questions/11844523/what-is-the-preferred-way-to-co… 39. http://stackoverflow.com/questions/11851005/why-is-numcapabilities-a-pure-f… 40. http://stackoverflow.com/questions/11887666/using-generics-to-convert-betwe… 41. http://stackoverflow.com/questions/11828654/controlling-parallel-execution 42. http://stackoverflow.com/questions/11850821/lists-of-lists-of-lists 43. http://stackoverflow.com/questions/11910143/positive-integer-type 44. http://stackoverflow.com/questions/11853306/haskell-bit-arrays 45. http://stackoverflow.com/questions/11856135/how-to-keep-track-of-number-of-… 46. http://stackoverflow.com/questions/11896870/a-haskell-program-that-controls…

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Improvement suggestions
by José Lopes 15 Aug '12

15 Aug '12

Hello everyone, I am quite new to monadic code so I would like to ask for improvement suggestions on the last line of the code below. I know I could do something like "do strs <- mapM ...; intercalate ..." etc, but I would like to avoid the use of "<-". Thank you, José data XmlState = XmlState Int type XmlM a = State XmlState a loop :: Document -> XmlM String someFn :: [Document] -> XmlM String someFn docs = return concat `ap` (sequence $ intersperse (return "\n") (map loop docs)) <--- improve this line -- José António Branquinho de Oliveira Lopes 58612 - MEIC-A Instituto Superior Técnico (IST), Universidade Técnica de Lisboa (UTL) jose.lopes(a)ist.utl.pt

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Upcoming resourcet 0.4
by Michael Snoyman 15 Aug '12

15 Aug '12

Hi all, I've been working with Aristid on an enhancement to resourcet[1]. Please see the issue for more details, this email isn't about that change. Instead, now that we're looking at a new breaking release, I was wondering if anyone had ideas of something they thought should be changed in resourcet. Thanks, Michael [1] https://github.com/snoyberg/conduit/issues/61

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For consistency; it would be better if the import statement matched the cabal install statement or :m form.
by KC 15 Aug '12

15 Aug '12

:m +Data.Array.Repa.Algorithms.Randomish cabal install repa.algrothms would be more consistent. -- -- Regards, KC

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Debian 6.0.5: 'cabal install curl' problem
by dokondr 14 Aug '12

14 Aug '12

Please help to solve a problem installing curl package ( http://hackage.haskell.org/package/curl/) on Debian 6.0.5. I am running the most recent Debian Haskell platform with GHC 6.12.1. I did: -> cabal update -> cabal install cabal-install It is interesting that in case you do again 'cabal update" you again get a suggestion from cabal to upgrade cabal-install, and this process never ends: """ -> cabal update Downloading the latest package list from hackage.haskell.org Note: there is a new version of cabal-install available. To upgrade, run: cabal install cabal-install """ Anyway, then I did: -> apt-get install curl -> cabal install curl Cabal fails to install 'curl' because it can not find curl library. Please see detailed cabal output at the end of this message. So my questions: 1) What is missing to install curl package? 2) Should I upgrade Debian GHC 6.12.1 to the latest GHC 7.4.2? Maybe this should solve the problem with 'cabal install'? Thanks! ---------- cabal install output ---------- -> cabal install curl Resolving dependencies... Configuring curl-1.3.7... checking for gcc... gcc checking for C compiler default output file name... a.out checking whether the C compiler works... yes checking whether we are cross compiling... no checking for suffix of executables... checking for suffix of object files... o checking whether we are using the GNU C compiler... yes checking whether gcc accepts -g... yes checking for gcc option to accept ANSI C... none needed checking how to run the C preprocessor... gcc -E configure: error: curl libraries not found, so curl package cannot be built See `config.log' for more details. cabal: Error: some packages failed to install: curl-1.3.7 failed during the configure step. The exception was: ExitFailure 1

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I use "cabal install repa" but then WinGHCi says module Data.Array.Rep.Algorithms.Ramdomish not found.
by KC 14 Aug '12

14 Aug '12

-- -- Regards, KC

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Fixity declaration extension
by Евгений Пермяков 14 Aug '12

14 Aug '12

fixity declaration has form *infix(l|r)? [Digit]* in haskell. I'm pretty sure, that this is not enough for complicated cases. Ideally, fixity declarations should have form *infix(l|r)? [Digit](\.(+|-)[Digit])** , with implied infinitely long repeated (.0) tail. This will allow fine tuning of operator priorities and much easier priority selection. For example, it may be assumed, that bit operations like (.&.) operator have hightest priority and have priorities like 9.0.1 or 9.0.2, anti-lisps like ($) have lowest priority like 0.0.1, control operators have base priority 1.* and logic operations like (&&) have priority of 2.* and it will be possibly to add new operators between or above all (for example) control operators without moving fixity of other ones. Agda2 language supports wide priority range, but still without 'tails' to my knowledge. Is there any haskell-influenced language or experimental syntactic extension that address the issue?

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