- Haskell-Cafe - Haskell.org

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%2Bunsubscribe(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%2Bunsubscribe(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%2Bunsubscribe(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%2Bunsubscribe(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.

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