September 2012 - Haskell-Cafe

haddock changes between 2.10 and 2.12?
by Edward Kmett 27 Sep '12

27 Sep '12

Was there some significant change/bug introduced to haddock made between 2.10 and 2.12? When I look at the haddocks for kan-extensions 3.1: Data.Functor.Yoneda<http://hackage.haskell.org/packages/archive/kan-extensions/3.1/doc/html/Dat…> which purports to have been built by haddock 2.12 it shows all sorts of spurious superclass constraints on almost every instance that should have simplified out, but going back to kan-extensions-2.7: Data.Functor.Yoneda<http://hackage.haskell.org/packages/archive/kan-extensions/2.7/doc/html/Dat…> none of this extra noise is present -- and the code in question hasn't been changed in the interim, so I'm pretty sure its not on my end. -Edward

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Can not configure haskell platform
by s9gf4ult＠gmail.com 27 Sep '12

27 Sep '12

> 13:53 razor@localhost /home/razor/tmp/haskell-platform-2012.2.0.0 % ./configure --prefix=/home/razor/.haskell > ************************************************** > * > * Haskell Platform Source Installer > * > * For the Haskell Platform 2012.2.0.0 and GHC 7.4.1 > * > ************************************************** > checking build system type... scripts/config.guess: line 156: 34:LIBC=gnu: command not found > Invalid configuration `x86_64-unknown-linux-': machine `x86_64-unknown-linux' not recognized > configure: error: /bin/sh scripts/config.sub x86_64-unknown-linux- failed ghc is available in PATH, google does not google. How to fix ?

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Haskell Weekly News: Issue 245
by Daniel Santa Cruz 26 Sep '12

26 Sep '12

Welcome to issue 245 of the HWN, an issue covering crowd-sourced bits of information about Haskell from around the web. This issue covers the week of September 16 to September 22, 2012. Quotes of the Week * dmwit: You have your intuition correct, despite all the pedantry in the room. * Cale: THIS CODE IS EXCELLENT CODE, I AM AN EXCELLENT ENTERPRISE PROGRAMMER ACCOMPLISHING REAL WORLD TASKS USING PATTERNS LIKE I READ ABOUT IN ALL THE JAVA BLOGS * byorgey: HASKELL is a pure, functional, strongly typed language featuring a name with all capitals, so it is suitable for beginners * ciaranm: a comonad is just a comonoid in the category of endofunctors. what's the coproblem? * dmwit: ISAAC -- ignore success at all costs * merijn: If you're not gonna use the types [by writing them] you might as well just write python * Cale: The real reason for the installed size of GHC being so large is that in the background it secretly downloads a video of SPJ riding a unicycle. Top Reddit Stories * First commercial Haskell-powered (game logic) computer game? (Nikki and the Robots Story Episodes) Domain: buy.joyridelabs.de, Score: 57, Comments: 27 On Reddit: [1] http://goo.gl/hngXz Original: [2] http://goo.gl/Y5Oax * Common misconceptions about Safe Haskell Domain: blog.ezyang.com, Score: 49, Comments: 23 On Reddit: [3] http://goo.gl/NBSx7 Original: [4] http://goo.gl/43i6n * The MonadTrans class is missing a method Domain: haskellforall.com, Score: 44, Comments: 32 On Reddit: [5] http://goo.gl/okxAX Original: [6] http://goo.gl/GnvzB * The Haskell Implementors' Workshop videos and slides available online Domain: haskell.org, Score: 43, Comments: 4 On Reddit: [7] http://goo.gl/LuORg Original: [8] http://goo.gl/pEvww * Writing javascript games in haskell : breakout Domain: jshaskell.blogspot.com, Score: 39, Comments: 10 On Reddit: [9] http://goo.gl/Dv8QK Original: [10] http://goo.gl/lXxsS * HIW 2012. Simon Peyton Jones: GHC Status Update. - YouTube Domain: youtube.com, Score: 37, Comments: 12 On Reddit: [11] http://goo.gl/3GEZK Original: [12] http://goo.gl/j7al9 * Comparing Snap's and Yesod's Template Languages Heist and Hamlet Domain: gist.github.com, Score: 36, Comments: 33 On Reddit: [13] http://goo.gl/AzaVV Original: [14] http://goo.gl/StRaF * Request: Tutorial on debugging using stack trace features of GHC 7.4 Domain: self.haskell, Score: 31, Comments: 6 On Reddit: [15] http://goo.gl/DcR1C Original: [16] http://goo.gl/DcR1C * A kind for regions Domain: monoidal.blogspot.com, Score: 29, Comments: 27 On Reddit: [17] http://goo.gl/4aBe7 Original: [18] http://goo.gl/tBDDW * [screencast] Quick introduction to Haskell using Gtk and the web Domain: vimeo.com, Score: 28, Comments: 4 On Reddit: [19] http://goo.gl/oi2IB Original: [20] http://goo.gl/LOkcf * Warp optimization - Sending header and body at once Domain: yesodweb.com, Score: 27, Comments: 17 On Reddit: [21] http://goo.gl/wstwx Original: [22] http://goo.gl/opsHb * Runtime Codegeneration in Haskell: Harpy vs. LLVM Domain: blog.wien.tomnetworks.com, Score: 24, Comments: 10 On Reddit: [23] http://goo.gl/aD0hE Original: [24] http://goo.gl/jU3nf * Show off your Vim/Emacs config! Domain: self.haskell, Score: 24, Comments: 7 On Reddit: [25] http://goo.gl/jV6Sa Original: [26] http://goo.gl/jV6Sa * Elm 0.4: Graphics Upgrade! Markdown, better for games, new optimizations, minification, ... Domain: elm-lang.org, Score: 22, Comments: 1 On Reddit: [27] http://goo.gl/SJW29 Original: [28] http://goo.gl/2Q5Fg * Making your zipper disappear with Zippo Domain: brandon.si, Score: 22, Comments: 6 On Reddit: [29] http://goo.gl/MQg77 Original: [30] http://goo.gl/Ua8a9 * [ANNOUNCE] Juicy.Pixels 2.0 - With Gif file decoding Domain: hackage.haskell.org, Score: 20, Comments: 12 On Reddit: [31] http://goo.gl/kEKrE Original: [32] http://goo.gl/EVvBh * Videos from this the CUFP 2012 in Copenhagen are now up Domain: cufp.org, Score: 17, Comments: 2 On Reddit: [33] http://goo.gl/mpe8Z Original: [34] http://goo.gl/aCB9I * Haskell developer jobs at StanChart - London, Singapore and Tianjin Domain: haskellers.com, Score: 17, Comments: 6 On Reddit: [35] http://goo.gl/t7axk Original: [36] http://goo.gl/wZrV5 * New GHCJS Hello World (can you find the hidden game?) Domain: ghcjs.github.com, Score: 17, Comments: 10 On Reddit: [37] http://goo.gl/c4BeA Original: [38] http://goo.gl/Aqh1i Top StackOverflow Questions * “What part of Milner-Hindley do you not understand?” votes: 73, answers: 4 Read on SO: [39] http://goo.gl/Nossl * Matching on type level Nat in GHC 7.6 votes: 17, answers: 1 Read on SO: [40] http://goo.gl/YijoA * Threading extra state through a parser in Scala votes: 16, answers: 1 Read on SO: [41] http://goo.gl/8cYMQ * find all types that are instances of a typeclass votes: 13, answers: 1 Read on SO: [42] http://goo.gl/ywHUN * When to use various language pragmas and optimisations? votes: 13, answers: 2 Read on SO: [43] http://goo.gl/qqtID * What are these explicit “forall”s doing? votes: 12, answers: 1 Read on SO: [44] http://goo.gl/fO0kf * How does the ST monad work? votes: 11, answers: 2 Read on SO: [45] http://goo.gl/xxntD * What are the pros and cons of adding additional functions/combinators to a typeclass definition? votes: 10, answers: 2 Read on SO: [46] http://goo.gl/HhDgT * Type parameters constraints for instances of typeclasses with kind * -> * votes: 9, answers: 2 Read on SO: [47] http://goo.gl/bGEQW * Theoretically, is this a valid comonad instance for a list? votes: 9, answers: 2 Read on SO: [48] http://goo.gl/z4DI4 * In haskell how can I uppercase a unicode character with respect to current locale votes: 9, answers: 1 Read on SO: [49] http://goo.gl/enNwK * Does haskell erase types? votes: 8, answers: 2 Read on SO: [50] http://goo.gl/YP8Nn * Is there an Iteratee-like concept which pulls data from multiple sources? votes: 8, answers: 4 Read on SO: [51] http://goo.gl/AOV0Y Until next time, Daniel Santa Cruz References 1. http://buy.joyridelabs.de/ 2. http://www.reddit.com/r/haskell/comments/106ocf/first_commercial_haskellpow… 3. http://blog.ezyang.com/2012/09/common-misconceptions-about-safe-haskell/ 4. http://www.reddit.com/r/haskell/comments/10242c/common_misconceptions_about… 5. http://www.haskellforall.com/2012/09/the-monadtrans-class-is-missing-method… 6. http://www.reddit.com/r/haskell/comments/106xwf/the_monadtrans_class_is_mis… 7. http://www.haskell.org/haskellwiki/HaskellImplementorsWorkshop/2012#Program… 8. http://www.reddit.com/r/haskell/comments/102x4p/the_haskell_implementors_wo… 9. http://jshaskell.blogspot.com/2012/09/breakout.html 10. http://www.reddit.com/r/haskell/comments/109hsb/writing_javascript_games_in… 11. http://www.youtube.com/watch?v=2Pucbf8_hGQ&feature=plcp 12. http://www.reddit.com/r/haskell/comments/102t49/hiw_2012_simon_peyton_jones… 13. https://gist.github.com/3757918 14. http://www.reddit.com/r/haskell/comments/107v79/comparing_snaps_and_yesods_… 15. http://www.reddit.com/r/haskell/comments/104xa2/request_tutorial_on_debuggi… 16. http://www.reddit.com/r/haskell/comments/104xa2/request_tutorial_on_debuggi… 17. http://monoidal.blogspot.com/2012/09/a-kind-for-regions.html 18. http://www.reddit.com/r/haskell/comments/102v1x/a_kind_for_regions/ 19. https://vimeo.com/49918847 20. http://www.reddit.com/r/haskell/comments/10az3o/screencast_quick_introducti… 21. http://www.yesodweb.com/blog/2012/09/header-body 22. http://www.reddit.com/r/haskell/comments/104sx0/warp_optimization_sending_h… 23. http://blog.wien.tomnetworks.com/2012/09/17/runtime-codegeneration-in-haske… 24. http://www.reddit.com/r/haskell/comments/1014ct/runtime_codegeneration_in_h… 25. http://www.reddit.com/r/haskell/comments/10b20f/show_off_your_vimemacs_conf… 26. http://www.reddit.com/r/haskell/comments/10b20f/show_off_your_vimemacs_conf… 27. http://elm-lang.org/blog/announce/version-0.4.0.elm 28. http://www.reddit.com/r/haskell/comments/102zqr/elm_04_graphics_upgrade_mar… 29. http://brandon.si/code/making-your-zipper-disappear-with-zippo/ 30. http://www.reddit.com/r/haskell/comments/103rhu/making_your_zipper_disappea… 31. http://hackage.haskell.org/package/JuicyPixels-2.0 32. http://www.reddit.com/r/haskell/comments/zziwm/announce_juicypixels_20_with… 33. http://cufp.org/videos 34. http://www.reddit.com/r/haskell/comments/102rer/videos_from_this_the_cufp_2… 35. http://www.haskellers.com/jobs/19 36. http://www.reddit.com/r/haskell/comments/106wat/haskell_developer_jobs_at_s… 37. http://ghcjs.github.com/bin/ghcjs-hello.jsexe 38. http://www.reddit.com/r/haskell/comments/10b6h3/new_ghcjs_hello_world_can_y… 39. http://stackoverflow.com/questions/12532552/what-part-of-milner-hindley-do-… 40. http://stackoverflow.com/questions/12463474/matching-on-type-level-nat-in-g… 41. http://stackoverflow.com/questions/12487827/threading-extra-state-through-a… 42. http://stackoverflow.com/questions/12524034/find-all-types-that-are-instanc… 43. http://stackoverflow.com/questions/12534145/when-to-use-various-language-pr… 44. http://stackoverflow.com/questions/12519878/what-are-these-explicit-foralls… 45. http://stackoverflow.com/questions/12468622/how-does-the-st-monad-work 46. http://stackoverflow.com/questions/12515655/what-are-the-pros-and-cons-of-a… 47. http://stackoverflow.com/questions/12497542/type-parameters-constraints-for… 48. http://stackoverflow.com/questions/12537149/theoretically-is-this-a-valid-c… 49. http://stackoverflow.com/questions/12537377/in-haskell-how-can-i-uppercase-… 50. http://stackoverflow.com/questions/12468722/does-haskell-erase-types 51. http://stackoverflow.com/questions/12496654/is-there-an-iteratee-like-conce…

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Haskell Programmers for Distributed Systems
by Richard Lyman 26 Sep '12

26 Sep '12

Hi folks, Parallel Scientific is looking for Haskell developers for distributed systems work. Parallel Scientific, Inc. is a Boulder, CO based funded startup company working in the area of scalable parallelization. We seek experienced Haskell programmers to build a sophisticated, ultra-scalable high availability framework to be used in conjunction with scientific applications, big data applications and I/O systems. We are primarily seeking candidates in Northern England, central France and/or Germany but candidates in other locations will be considered. Relocation to these places can be discussed. Parallel Scientific was founded by Dr Peter Braam in 2010. Peter formerly taught mathematics and computer science at Oxford and Carnegie Mellon. Then he contributed file systems to Linux and invented Lustre (which provides storage to 9 of the top 10 systems in the world). He ran several successful startups, and Parallel Scientific is run by an very experienced management team and board. Successful candidates will work in a modern virtual environment in their homes. Some travel may be required. We provide training in advanced processes for software design and implementation and domain specific knowledge. Required skills: Capability to design and implement sophisticated distributed algorithms (quorum, liveness, lock management, barriers) Very strong background in computer science or mathematics Experience with Haskell, or network and cluster programming in other functional languages (e.g. Erlang) Knowledge of systems programming and operating systems functionality Experience in one or more of the following areas is desirable: Experience in high availability clustering projects Experience with internals of sophisticated distributed I/O and/or database systems To apply, please send a resume to jobs(a)parsci.com. Thanks... Rich -- Rich Lyman richard.lyman(a)parsci.com

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Partial statical linking
by Jason Dusek 26 Sep '12

26 Sep '12

Some time ago, I wrote to this list about making shared libraries with GHC, in such a way that the RTS was linked and ready to go. Recently, I've been looking a similar but, in a sense, opposite problem: linking Haskell executables with some of their non-Haskell dependencies, for distribution. I tried passing a few different sets of options to the linker through GHC, with -optl: -optl'-Wl,-r' -optl'-Wl,-r,-dy' -optl'-Wl,-static,-lffi,-lgmp,-dy' None of these had the desired effect. In the end, running GHC with -v and carefully editing the linker line produced the desired change (I have linked to and provided the diff below). The effect -optl seems to be to introduce options in the linker line just before -lHSrtsmain, which would seem to prevent one from linking libffi and libgmp differently. Is editing and storing away the linker script the best option at present for partially static linking? -- Jason Dusek () ascii ribbon campaign - against html e-mail /\ www.asciiribbon.org - against proprietary attachments https://github.com/solidsnack/arx/commit/90ec5efdb0e991344aa9a4ad29456d466e… #@@ -122,10 +122,8 @@ # -lHSarray-0.3.0.2 \ # -lHSbase-4.3.1.0 \ # -lHSinteger-gmp-0.2.0.3 \ #- -lgmp \ # -lHSghc-prim-0.2.0.0 \ # -lHSrts \ #- -lffi \ # -lm \ # -lrt \ # -ldl \ #@@ -136,4 +134,7 @@ # -lgcc_s --no-as-needed \ # /usr/lib/gcc/x86_64-linux-gnu/4.6.1/crtend.o \ # /usr/lib/gcc/x86_64-linux-gnu/4.6.1/../../../x86_64-linux-gnu/crtn.o \ #+ -static \ #+ -lgmp \ #+ -lffi \

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Re: [Haskell-cafe] Church vs Boehm-Berarducci encoding of Lists
by oleg＠okmij.org 26 Sep '12

26 Sep '12

Dan Doel wrote: > >> P.S. It is actually possible to write zip function using Boehm-Berarducci > >> encoding: > >> http://okmij.org/ftp/Algorithms.html#zip-folds > > If you do, you might want to consider not using the above method, as I > seem to recall it doing an undesirable amount of extra work (repeated > O(n) tail). It is correct. The Boehm-Berarducci web page discusses at some extent the general inefficiency of the encoding, the need for repeated reflections and reifications for some (but not all) operations. That is why arithmetic on Church numerals is generally a bad idea. A much better encoding of numerals is what I call P-numerals http://okmij.org/ftp/Computation/lambda-calc.html#p-numerals It turns out, I have re-discovered them after Michel Parigot (so my name P-numerals is actually meaningful). Not only they are faster; one can _syntactically_ prove that PRED . SUCC is the identity. The general idea of course is Goedel's recursor R. R b a 0 = a R b a (Succ n) = b n (R b a n) which easily generalizes to lists. The enclosed code shows the list encoding that has constant-time cons, head, tail and trivially expressible fold and zip. Kim-Ee Yeoh wrote: > So properly speaking, tail and pred for Church-encoded lists and nats > are trial-and-error affairs. But the point is they need not be if we > use B-B encoding, which looks _exactly_ the same, except one gets a > citation link to a systematic procedure. > > So it looks like you're trying to set the record straight on who actually > did what. Exactly. Incidentally, there is more than one way to build a predecessor of Church numerals. Kleene's solution is not the only one. Many years ago I was thinking on this problem and designed a different predecessor: excerpted from http://okmij.org/ftp/Haskell/LC_neg.lhs One ad hoc way of defining a predecessor of a positive numeral predp cn+1 ==> cn is to represent "predp cn" as "cn f v" where f and v are so chosen that (f z) acts as if z == v then c0 else (succ z) We know that z can be either a numeral cn or a special value v. All Church numerals have a property that (cn combI) is combI: the identity combinator is a fixpoint of every numeral. Therefore, ((cn combI) (succ cn)) reduces to (succ cn). We only need to choose the value v in such a way that ((v I) (succ v)) yields c0. > predp = eval $ > c ^ c > # (z ^ (z # combI # (succ # z))) -- function f(z) > # (a ^ x ^ c0) -- value v {-# LANGUAGE Rank2Types #-} -- List represented with R newtype R x = R{unR :: forall w. -- b (x -> R x -> w -> w) -- a -> w -- result -> w} nil :: R x nil = R (\b a -> a) -- constant type cons :: x -> R x -> R x cons x r = R(\b a -> b x r (unR r b a)) -- constant time rhead :: R x -> x rhead (R fr) = fr (\x _ _ -> x) (error "head of the empty list") -- constant time rtail :: R x -> R x rtail (R fr) = fr (\_ r _ -> r) (error "tail of the empty list") -- fold rfold :: (x -> w -> w) -> w -> R x -> w rfold f z (R fr) = fr (\x _ w -> f x w) z -- zip is expressed via fold rzipWith :: (x -> y -> z) -> R x -> R y -> R z rzipWith f r1 r2 = rfold f' z r1 r2 where f' x tD = \r2 -> cons (f x (rhead r2)) (tD (rtail r2)) z = \_ -> nil -- tests toR :: [a] -> R a toR = foldr cons nil toL :: R a -> [a] toL = rfold (:) [] l1 = toR [1..10] l2 = toR "abcde" t1 = toL $ rtail l2 -- "bcde" t2 = toL $ rzipWith (,) l2 l1 -- [('a',1),('b',2),('c',3),('d',4),('e',5)]

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Help me with space leaks
by Alexey Uimanov 26 Sep '12

26 Sep '12

Hello. I am trying to write some thing in haskell and i need fast storage to store and select this things from storage. https://github.com/s9gf4ult/projs/tree/master/haskell/teststorage I am writing simple testing package to determine my needs and select the fastest storage and i have encountered problems. Firstly i decided to check out postgresql-simple, but when i am doing "executeMany" i see space leaks, here is the picture http://bayimg.com/NAdjHAaeA http://bayimg.com/NADjKAAea I dont fully understand what is happening here, but i belive this is because of lazy consuming of "executeMany" or something. So things im trying to insert do not calculate one by one, but this is creating many thunks for calculate them. I would understand how to narrow the cause of this problem and create more strict function "executeMany" which would work in constant space (or space of data). Here the insertMany from postgresql-simple executeMany :: (ToRow q) => Connection -> Query -> [q] -> IO Int64 executeMany _ _ [] = return 0 executeMany conn q qs = do result <- exec conn =<< formatMany conn q qs finishExecute conn q result And this is not looks like a problem case go to formatMany formatMany :: (ToRow q) => Connection -> Query -> [q] -> IO ByteString formatMany _ q [] = fmtError "no rows supplied" q [] formatMany conn q@(Query template) qs = do case parseTemplate template of Just (before, qbits, after) -> do bs <- mapM (buildQuery conn q qbits . toRow) qs return . toByteString . mconcat $ fromByteString before : intersperse (fromChar ',') bs ++ [fromByteString after] Nothing -> fmtError "syntax error in multi-row template" q [] Here bs is the map of bs and must stay lazy evaluated and here we see mconcat which must be strict i think, and if i am right so problem must disapear whan i replace it with strict mconcat mconcat' :: (Monod a) => [a] -> a mconcat' [] = mempty mconcat' (x:xs) = x `seq` (mappend x $ mconcat' xs) but it doesnt. I assume i must write the same for "deepseq" to realy calculate each parameter up to value. But if so, this must touch several projects such as blaze and maybe bytestring because of the need to make NFData instances. How to solve this problem right - way ? Maybe haskell have elegant solution for this ?

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How to take a minimum sub list that only contain certain number of elements of certain type?
by Magicloud Magiclouds 25 Sep '12

25 Sep '12

Hi, For example, I have an array [0..]. Now I want to take a sub list that starts from index 0, and only contain 4 odds, and is minimum result. The answer should be [0, 1, 2, 3, 4, 5, 6, 7]. How to do that? Combining lazy computing, I cannot figure out an efficient algorithm. -- 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] [Haskell] ANN: HERMIT for GHC 7.6
by Jay Sulzberger 25 Sep '12

25 Sep '12

[Note that original post was on the Haskell list, and not the Haskell-cafe list.] On Tue, 25 Sep 2012, Andrew Farmer <afarmer(a)ittc.ku.edu> wrote: > A new version of HERMIT (0.1.2.0) that is compatible with GHC 7.6 is now > available on hackage. This release has essentially the same functionality > as the 7.4-only pre-alpha release made before ICFP 2012. > > HERMIT (Haskell Equational Reasoning Model-to-Implementation Tunnel) is a > plugin for GHC that provides an interactive interface for applying > transformations directly to GHC's internal intermediate language, Core. > This plugin is part of a larger HERMIT toolkit, which is being developed at > the University of Kansas with the aims of supporting equational reasoning > and allowing custom optimizations to be applied without modifying either > GHC or the Haskell source code. > > Introduction to HERMIT via Neil Sculthorpe's Haskell Symposium 2012 talk: > > http://www.youtube.com/watch?v=x2QH3jJCJso > > Example transformations can be found in the examples folder, contained in > the cabal source package. > > Hackage: http://hackage.haskell.org/package/hermit > Github (for bug reports): https://github.com/ku-fpg/hermit > > Andrew Farmer Thank you and all the HERMIT Team for this! Does the HERMIT system provide an executable Haskell Core, that is, we can get an ordinary text file which can be executed by some version of GHC+HERMIT? oo--JS.

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Re: [Haskell-cafe] [Haskell] Well-Typed and Skills Matter offer Haskell courses in London in October
by Claude Heiland-Allen 25 Sep '12

25 Sep '12

On 19/09/12 08:52, Andres Löh wrote: > Registration for all these events is open. I hope to see many > of you there. Is there an informal hangout without the £225 price-tag > > Cheers, > Andres >

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