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Haskell Weekly News: Issue 252
by Daniel Santa Cruz 29 Nov '12

29 Nov '12

Welcome to issue 252 of the HWN, an issue covering crowd-sourced bits of information about Haskell from around the web. This issue covers the week of November 18 to 24, 2012. Quotes of the Week * rwbarton: edwardk now has Lens under Control * atriq: My son looks a bit like me, he can put away the plates after dinner now thanks to edwardk! * mgsloan: Lens got 99 operators, but a (|>) ain't one. * hiptobecubic: I feel like this program is just a bunch of glue and duct tape holding a bottle of nitroglycerine off of the ground. * xplat: Some software is worth trying; most is just plain trying. * edwardk: Control.Lens is my secret ploy to get everyone to give up on Haskell and just move on to Agda as they find the Haskell types too complicated by comparison. * rwbarton: alpha reduction is what happens when you let edwardk maintain your module * edwardk: er that was a tongue sticking out, not an operator suggestion Top Reddit Stories * [Haskell] Leaving Microsoft Domain: haskell.org, Score: 139, Comments: 24 On Reddit: [1] http://goo.gl/DnzZF Original: [2] http://goo.gl/eVcXi * Help Nikki (Game written in Haskell) jump on Steam! Domain: joyridelabs.de, Score: 77, Comments: 8 On Reddit: [3] http://goo.gl/EzLh8 Original: [4] http://goo.gl/H84Nl * Gaussian distributions are monoids Domain: izbicki.me, Score: 46, Comments: 24 On Reddit: [5] http://goo.gl/i4keo Original: [6] http://goo.gl/C0gnN * Getting Started with Lenses Domain: newartisans.com, Score: 42, Comments: 32 On Reddit: [7] http://goo.gl/nv4ab Original: [8] http://goo.gl/h2zCa * Designing the Haskell IDE Domain: fpcomplete.com, Score: 41, Comments: 112 On Reddit: [9] http://goo.gl/yz1Rf Original: [10] http://goo.gl/gpJd7 * Putting haskell down Domain: b7j0c.org, Score: 33, Comments: 279 On Reddit: [11] http://goo.gl/8JWmr Original: [12] http://goo.gl/tZcbj * London Haskell Video (24-Oct-2012) – Why Do Monads Matter? Domain: youtube.com, Score: 33, Comments: 5 On Reddit: [13] http://goo.gl/uWH6w Original: [14] http://goo.gl/KqDji * Combinatorial species definition (Brent Yorgey) Domain: byorgey.wordpress.com, Score: 31, Comments: On Reddit: [15] http://goo.gl/0llrA Original: [16] http://goo.gl/PWIep * PhD Positions in Functional Programming at Chalmers (appl. deadline 2012-12-12) Domain: chalmers.se, Score: 28, Comments: On Reddit: [17] http://goo.gl/WAmYP Original: [18] http://goo.gl/JenYO * Video of the presentations at the first NYC Haskell User's Group meetup. Domain: vimeo.com, Score: 25, Comments: 10 On Reddit: [19] http://goo.gl/rxN75 Original: [20] http://goo.gl/uV4wc Top StackOverflow Questions * Where to start with dependent type programming? votes: 16, answers: 1 Read on SO: [21] http://goo.gl/HXdOu * What other ways can state be handled in a pure functional language besides with Monads? votes: 13, answers: 3 Read on SO: [22] http://goo.gl/D86hV * Why are some Prelude functions defined in terms of foldl? votes: 8, answers: 3 Read on SO: [23] http://goo.gl/wewrb * cabal FFI dependency votes: 8, answers: 1 Read on SO: [24] http://goo.gl/JFtJM * How to write Ctrl-C handler in Haskell? votes: 7, answers: 1 Read on SO: [25] http://goo.gl/pS651 * Why does the 2-tuple Functor instance only apply the function to the second element? votes: 5, answers: 2 Read on SO: [26] http://goo.gl/qGgSv * Type Families with GHC.Generics or Data.Data votes: 5, answers: 0 Read on SO: [27] http://goo.gl/mERdP * Haskell Programmatically/Dynamically Define Functions votes: 5, answers: 6 Read on SO: [28] http://goo.gl/22Wf0 * is this implementation of merge sort good? votes: 5, answers: 1 Read on SO: [29] http://goo.gl/Skznl * Railroad diagrams for Haskell? votes: 5, answers: 1 Read on SO: [30] http://goo.gl/ZeJa9 * Is FRP a proper way to implement most “event-driven” things? votes: 5, answers: 1 Read on SO: [31] http://goo.gl/QglPp * Stack overflow in very simple code votes: 5, answers: 1 Read on SO: [32] http://goo.gl/wB0kg * Mapping over Either's Left votes: 5, answers: 3 Read on SO: [33] http://goo.gl/oJX4v * Haskell - strict vs non-strict with foldl votes: 5, answers: 2 Read on SO: [34] http://goo.gl/3ElzK Until next time, Daniel Santa Cruz References 1. http://www.haskell.org/pipermail/haskell/2012-November/023566.html 2. http://www.reddit.com/r/haskell/comments/13m8eu/haskell_leaving_microsoft/ 3. http://joyridelabs.de/blog/?p=1548 4. http://www.reddit.com/r/haskell/comments/13muex/help_nikki_game_written_in_… 5. http://izbicki.me/blog/gausian-distributions-are-monoids 6. http://www.reddit.com/r/haskell/comments/13qyg2/gaussian_distributions_are_… 7. http://newartisans.com/2012/11/getting-started-with-lenses/ 8. http://www.reddit.com/r/haskell/comments/13l9vj/getting_started_with_lenses/ 9. http://fpcomplete.com/designing-the-haskell-ide/ 10. http://www.reddit.com/r/haskell/comments/13gn8k/designing_the_haskell_ide/ 11. https://www.b7j0c.org/blog/putting_haskell_down.html 12. http://www.reddit.com/r/haskell/comments/13g0ul/putting_haskell_down/ 13. http://www.youtube.com/watch?v=3q8xYFDYLeI 14. http://www.reddit.com/r/haskell/comments/13nwxu/london_haskell_video_24oct2… 15. http://byorgey.wordpress.com/2012/11/20/combinatorial-species-definition/ 16. http://www.reddit.com/r/haskell/comments/13iz3p/combinatorial_species_defin… 17. http://www.chalmers.se/en/about-chalmers/vacancies/Pages/default.aspx?rmpag… 18. http://www.reddit.com/r/haskell/comments/13nxtx/phd_positions_in_functional… 19. http://vimeo.com/53906049 20. http://www.reddit.com/r/haskell/comments/13hyjt/video_of_the_presentations_… 21. http://stackoverflow.com/questions/13497865/where-to-start-with-dependent-t… 22. http://stackoverflow.com/questions/13536761/what-other-ways-can-state-be-ha… 23. http://stackoverflow.com/questions/13474932/why-are-some-prelude-functions-… 24. http://stackoverflow.com/questions/13544642/cabal-ffi-dependency 25. http://stackoverflow.com/questions/13441676/how-to-write-ctrl-c-handler-in-… 26. http://stackoverflow.com/questions/13442544/why-does-the-2-tuple-functor-in… 27. http://stackoverflow.com/questions/13448361/type-families-with-ghc-generics… 28. http://stackoverflow.com/questions/13452907/haskell-programmatically-dynami… 29. http://stackoverflow.com/questions/13455849/is-this-implementation-of-merge… 30. http://stackoverflow.com/questions/13485374/railroad-diagrams-for-haskell 31. http://stackoverflow.com/questions/13486293/is-frp-a-proper-way-to-implemen… 32. http://stackoverflow.com/questions/13489676/stack-overflow-in-very-simple-c… 33. http://stackoverflow.com/questions/13503965/mapping-over-eithers-left 34. http://stackoverflow.com/questions/13533586/haskell-strict-vs-non-strict-wi…

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OpenAL - compiling problem
by Gary Klindt 28 Nov '12

28 Nov '12

Dear Haskell Cafe, I tried installing the haskell openal library via cabal install openal I get the following error: ... [ 7 of 30] Compiling Sound.OpenAL.ALC.QueryUtils ( Sound/OpenAL/ALC/QueryUtils.hs, dist/build/Sound/OpenAL/ALC/QueryUtils.o ) Sound/OpenAL/ALC/QueryUtils.hs:66:1: Unacceptable argument type in foreign declaration: ALCdevice When checking declaration: foreign import ccall unsafe "static alcGetString" alcGetString :: ALCdevice -> ALCenum -> IO (Ptr ALCchar) Sound/OpenAL/ALC/QueryUtils.hs:102:1: Unacceptable argument type in foreign declaration: ALCdevice When checking declaration: foreign import ccall unsafe "static alcGetIntegerv" alcGetIntegerv :: ALCdevice -> ALCenum -> ALCsizei -> Ptr ALCint -> IO () Sound/OpenAL/ALC/QueryUtils.hs:120:1: Unacceptable argument type in foreign declaration: ALCdevice When checking declaration: foreign import ccall unsafe "static alcIsExtensionPresent" alcIsExtensionPresent_ :: ALCdevice -> Ptr ALCchar -> IO ALCboolean Failed to install OpenAL-1.4.0.1 cabal: Error: some packages failed to install: OpenAL-1.4.0.1 failed during the building phase. The exception was: ExitFailure 1 The version of my openal installation is 1.14-1. I also tried to install via darcs, but the error is the same. Any ideas? Greets Gary

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Equality test between types that returns type-level Bool ?
by Takayuki Muranushi 28 Nov '12

28 Nov '12

Is it possible to write type family SameType a b :: Bool which returns True if a and b are the same type, and False otherwise? I encountered this problem when I was practicing promoted lists and tuples in ghc-7.6.1. One of my goal for practice is to write more "modular" version of extensible-dimensional calculations, and to understand whether ghc-7.6.1 is capable of it. http://hackage.haskell.org/packages/archive/dimensional/0.10.2/doc/html/Num… Some of my attempts: https://github.com/nushio3/dimensional-tf/blob/master/attic/list-02.hs This fails because :==: is not an equality test between a and b, but is a equality test within a (promoted) kind. https://github.com/nushio3/dimensional-tf/blob/master/attic/list-03.hs This fails because type instance declarations are not read from top to bottom. (not like function declarations.) https://github.com/nushio3/dimensional-tf/blob/master/attic/map-03.hs I could define a lookup using class constraints, but when I use it, results in overlapping instances. So, will somebody teach me which of the following is correct? * We can write a type family SameType a b :: Bool * We cannot do that because of theoretical reason (that leads to non-termination etc.) * We cannot write SameType, but there are ways to write functions like 'filter' and 'merge' , over type-level lists, without using SameType. Always grateful to your help, -- Takayuki MURANUSHI The Hakubi Center for Advanced Research, Kyoto University http://www.hakubi.kyoto-u.ac.jp/02_mem/h22/muranushi.html

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Conduit and pipelined protocol processing using a threadpool
by Nicolas Trangez 28 Nov '12

28 Nov '12

All, I've written a library to implement servers for some protocol using Conduit (I'll announce more details later). The protocol supports pipelining, i.e. a client can send a 'command' which contains some opaque 'handle' chosen by the client, the server processes this command, then returns some reply which contains this handle. The client is free to send other commands before receiving a reply for any previous request, and the server can process these commands in any order, sequential or concurrently. The library is based on network-conduit's "Application" style [1], as such now I write code like (OTOH) > application :: AppData IO -> IO () > application client = appSource client $= handler $$ appSink client > where > handler = do > negotiateResult <- MyLib.negotiate > liftIO $ validateNegotiateResult negotiateResult > MyLib.sendInformation 123 > loop > > loop = do > command <- MyLib.getCommand > case command of > CommandA handle arg -> do > result <- liftIO $ doComplexProcessingA arg > MyLib.sendReply handle result > loop > Disconnect -> return () This approach handles commands in-order, sequentially. Since command processing can involve quite some IO operations to disk or network, I've been trying to support pipelining on the server-side, but as of now I was unable to get things working. The idea would be to have a pool of worker threads, which receive work items from some channel, then return any result on some other channel, which should then be returned to the client. This means inside "loop" I would have 2 sources: commands coming from the client (using 'MyLib.getCommand :: MonadIO m => Pipe ByteString ByteString o u m Command'), as well as command results coming from the worker threads through the result channel. Whenever the first source produces something, it should be pushed onto the work queue, and whenever the second on yields some result it should be sent to the client using 'MyLib.sendReply :: Monad m => Handle -> Result -> Pipe l i ByteString u m ()' I've been fighting this for a while and haven't managed to get something sensible working. Maybe the design of my library is flawed, or maybe I'm approaching the problem incorrectly, or ... Has this ever been done before, or would anyone have some pointers how to tackle this? Thanks, Nicolas [1] http://hackage.haskell.org/packages/archive/network-conduit/0.6.1.1/doc/htm…

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ANNOUNCE: language-java 0.2.0
by Vincent Hanquez 27 Nov '12

27 Nov '12

Hi Cafe, with the approval of Niklas, the original author and maintainer, i'll be maintaining language-java for now. I've uploaded a new version on hackage [1] with some minor improvements and the repository is now hosted on github [2]. Thanks Niklas for language-java ! [1] http://hackage.haskell.org/package/language-java [2] http://github.com/vincenthz/language-java/ -- Vincent

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Real-time code in Haskell (Was: Can a GC delay TCP connection formation?)
by Mike Meyer 27 Nov '12

27 Nov '12

On Tue, Nov 27, 2012 at 3:45 AM, Gregory Collins <greg(a)gregorycollins.net> wrote: > If you have a hard real-time requirement then a garbage-collected > language may not be appropriate for you. This is a common meme, but frankly, it isn't true. When writing real-time code, you just need to make sure that everything that happens takes a known maximum amount of time. Then, you can sum up the maximums and verify that you do indeed finish in the real-time window of the task. GC is a problem because it's not predictable, and may not have a maximum. However, it's no worse than a modern version of the C function malloc. Some of those even do garbage collection internally before doing an OS call if they're out of memory. The solution is the same in both cases - make sure you don't do GC (or call malloc) in the critical region. Both require knowing implementation details of everything you call, but it isn't impossible, or even particularly difficult. Lazyness, on the other hand ... I haven't thought about. I suspect you need to force the evaluation of everything you're going to need before you start the critical region, but I wonder if that's enough? Has anyone out there investigated this? Thanks, <mike

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Re: [Haskell-cafe] Portability of Safe Haskell packages
by Roman Cheplyaka 27 Nov '12

27 Nov '12

* Herbert Valerio Riedel <hvr(a)gnu.org> [2012-11-24 00:06:44+0100] > Roman Cheplyaka <roma(a)ro-che.info> writes: > > It has been pointed out before that in order for Safe Haskell to be > > useful, libraries (especially core libraries) should be annotated > > properly with Safe Haskell LANGUAGE pragmas. > > > > However, that would make these libraries unusable with alternative > > Haskell implementations, even if otherwise they these libraries are > > Haskell2010. > > > > To quote the standard: > > > > If a Haskell implementation does not recognize or support a particular > > language feature that a source file requests (or cannot support the > > combination of language features requested), any attempt to compile or > > otherwise use that file with that Haskell implementation must fail > > with an error. > > > > Should it be advised to surround safe annotations with CPP #ifs? > > Or does anyone see a better way out of this contradiction? > > ...but IIRC CPP isn't part of Haskell2010, or is it? It isn't indeed. But: 1) it's a very basic extension which is supported by (almost?) all existing implementations; or 2) if you want to be 100% Haskell2010, you can name your file *.cpphs and let Cabal do preprocessing. 1) is a compromise and 2) is not very practical, so I'm eager to hear other alternatives. Roman

2 1

Problem with benchmarking FFI calls with Criterion
by Janek S. 27 Nov '12

27 Nov '12

I am using Criterion library to benchmark C code called via FFI bindings and I've ran into a problem that looks like a bug. The first benchmark that uses FFI runs correctly, but subsequent benchmarks run much longer. I created demo code (about 50 lines, available at github: https://gist.github.com/4135698 ) in which C function copies a vector of doubles. I benchmark that function a couple of times. First run results in avarage time of about 17us, subsequent runs take about 45us. In my real code additional time was about 15us and it seemed to be a constant factor, not relative to "correct" run time. The surprising thing is that if my C function only allocates memory and does no copying: double* c_copy( double* inArr, int arrLen ) { double* outArr = malloc( arrLen * sizeof( double ) ); return outArr; } then all is well - all runs take similar amount of time. I also noticed that sometimes in my demo code all runs take about 45us, but this does not seem to happen in my real code - first run is always shorter. Does anyone have an idea what is going on? Janek

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1st São Paulo Haskell Meeting [1° Encontro de Haskellers em São Paulo]
by Felipe Almeida Lessa 27 Nov '12

27 Nov '12

Hey! I'd like to invite you to the 1st São Paulo Haskell Meeting! It's going to be something simple, we just want to meet each other and talk about Haskell =). We already have 9 people confirmed on the Google+ event [1], so come join us already! Cheers, PS: We still didn't set the place yet. [1] https://plus.google.com/events/cng3rcv1tjl84g2juddk1i36icg -- Felipe.

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Re: [Haskell-cafe] Executables got bigger using dynamic link.
by Magicloud Magiclouds 27 Nov '12

27 Nov '12

Sorry, I left the profiling option on, which seems to suppress the dynamic options. On Mon, Oct 29, 2012 at 1:29 PM, Magicloud Magiclouds <magicloud.magiclouds(a)gmail.com> wrote: > Hi, > I set "shared: True" in ~/.cabal/config, and using ghc 7.6.1. Then > clear user space hackages and reinstall them. > First of all, I think comparing to static link, dynamic linked > executables file should be smaller. And the libraries (.so) could > benefits from caching to save memory usage. > > Well, I installed cabal-install and alex. I got this: > cabal 9.9M -> 24M > alex 2.7M -> 5.1M > Is this correct? > -- > 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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Compilers: Why do we need a core language?
by citb＠lavabit.com 26 Nov '12

26 Nov '12

Hello, I know nothing about compilers and interpreters. I checked several books, but none of them explained why we have to translate a high-level language into a small (core) language. Is it impossible (very hard) to directly translate high-level language into machine code?

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Is there a tool like ri from ruby?
by Magicloud Magiclouds 26 Nov '12

26 Nov '12

RI is a very easy using tool that search and show the documents of ruby modules/functions, etc. Using RI, I could get help when programming with a few commands. Quick and simple. And with RI backend (libs), I could also simply integrate ri to my IDE (like one hotkey to show function summary). So I am wondering if there is such thing in Haskell world. I know haddock saves the .haddock files in document folder. But I do not know if there is any existing tools to index and view them. -- 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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Quasiquotation page on HaskellWiki needs updating
by Erik de Castro Lopo 26 Nov '12

26 Nov '12

Hi all, It seems the Quasiquotation page on HaskellWiki http://www.haskell.org/haskellwiki/Quasiquotation has fallen behind the actually Quasiquotation implementation that is in ghc-7.4.2 and later. Specifically, the QuasiQuoter constructor that the Wiki takes two parameters: data QuasiQuoter = QuasiQuoter { quoteExp :: String -> Q Exp , quotePat :: String -> Q Pat } while the one in ghc-7.4 and later takes four: data QuasiQuoter = QuasiQuoter { quoteExp :: String -> Q Exp , quotePat :: String -> Q Pat , quoteType :: String -> Q Type , quoteDec :: String -> Q [Dec] } I'm just starting out with quasquotation and am not yet qualified to update this page myself. Erik -- ---------------------------------------------------------------------- Erik de Castro Lopo http://www.mega-nerd.com/

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Munich Haskell Meeting
by Heinrich Hördegen 25 Nov '12

25 Nov '12

Dear all, next Tuesday, 27. November 2012, will be our Haskell Meeting in Munich at 19h30 at Cafe Puck. Please go to http://www.haskell-munich.de/dates and hit the button, if you intend to join. Have a good start into your week, Heinrich -- -- Funktionale Programmierung Dr. Heinrich Hördegen Gutenbergstr. 26 80638 München FON: +49 (89) 12 59 79 49 FAX: +49 (89) 12 59 79 50 hoerdegen(a)funktional.info www.funktional.info --

1 0

GHC 7.4.1 hangs and memory usage shoots ups to 100% when compiling with -O2
by magesh b 25 Nov '12

25 Nov '12

I'm facing this problem only when I compiled the code using -O2 Flag. I tried the following, * Compiled with -O1 Flag (7.4.1), It compiled fine * Compiled with ghc-7.0.4 with -O2, it's getting compiled successfully but with the Warning, SpecConstr Function `$wa{v s27vx} [lid]' has one call pattern, but the limit is ... [Module that is getting stuck is using heavy quasiquotation] Env: OS: Ubuntu 12.04 [x86_64] GHC: 7.4.1 Is this a bug? Anything else should I need to try?

1 0

need help with understanding expression
by Daryoush Mehrtash 25 Nov '12

25 Nov '12

I am having hard time understanding how removing the outer parenthesis in (max.(+1)) 2 2 to max.(+1) 2 2 changes the meaning of expression. My expectation was that "max.(+1) takes two numbers and returns the max as defined in the type: :t max.(+1) max.(+1) :: (Ord b, Num b) => b -> b -> b With parenthesis it does what I expect it to: Prelude> :t (max.(+1)) 2 2 (max.(+1)) 2 2 :: (Ord b, Num b) => b Prelude> (max.(+1)) 2 2 3 But if I remove the parenthesis I get a beast that I have no idea what its type signature mean any more Prelude> :t (max.(+1)) 2 2 (max.(+1)) 2 2 :: (Ord b, Num b) => b Prelude> :t max.(+1) 2 2 max.(+1) 2 2 :: (Ord b, Num a1, Num (a1 -> a -> b)) => a -> b -> b How did removal of parenthesis changed the meaning? How do you interpret the type: "(Ord b, Num a1, Num (a1 -> a -> b)) => a -> b -> b"? Thanks -- Daryoush Weblog: http://onfp.blogspot.com/

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cabal isn't updating local doc index after local package upgrade
by Richard Cobbe 24 Nov '12

24 Nov '12

Haskell Platform 2012 v2.0.0, MacOS 64-bit. (MacOS 10.8.2.) I just used cabal to upgrade the installation of a local package I'm writing, and I'm still seeing the old version of the documentation in ~/Library/Haskell/doc/index.html. How can I fix this? In more detail: this machine had greek-1.0.1 installed, but I was working on another package that needed greek-1.1.0. So I went into the directory where I keep the source for the greek package, made sure it was up-to-date, and ran cabal clean && cabal configure && cabal build && cabal install as my normal user, not as root. As far as I can tell, the rebuild was successful; cabal's output finished with Installing library in /Users/cobbe/Library/Haskell/ghc-7.4.1/lib/greek-1.1.0/lib Registering greek-1.1.0... Updating documentation index /Users/cobbe/Library/Haskell/doc/index.html However, when I open ~/Library/Haskell/doc/index.html in my browser, I still see the documentation for greek-1.0. The docs for the new version are present, in ~/Library/Haskell/ghc-7.4.1/lib/greek-1.1.0/doc, but they don't appear in the main index. Am I missing a step in the process, or is this a bug in cabal? Is there a workaround? I do have a couple of older versions of the greek package insatlled, because there doesn't seem to be an easy way to remove obsolete packages. Could they be causing problems? If so, what's the best way to delete them? (I don't particularly mind having the older versions hanging around, as long as they're actually harmless.) Thanks much, Richard

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Survey: What are the more common Haskell IDEs in use ?
by Dan 24 Nov '12

24 Nov '12

Because I see there are many preferences on what IDE to use for Haskell I've created a quick survey on this topic. Please click here and select your choices from the lists. http://kwiksurveys.com/s.asp?sid=oqr42h4jc8h0nbc53652 Any comments/suggestions are welcome. (if any is missing, etc) Apologies for the add they show after you select the preferences - it is a free survey tool - i guess they have to live somehow too :)

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class Bytestringable or ToBytestring
by Vincent Hanquez 24 Nov '12

24 Nov '12

Hi cafe, I've been adding lots of types recently that looks more or less like: newtype A = A ByteString data B = B ByteString This is great for extra type safety and letting the compiler do its job, however getting the bytestring back requires boiler plate. At the moment either you give access to the constructor, which is not always wanted, or you use the record syntax to create a function to extract just the bytestring. The latter is fine for 1 or 2 types, but the scheme fall apart when having many of those types and do pollute namespace. I'm basically after something that looks like this: class ToByteString a where toByteString :: a -> ByteString Before anyone suggest the Serialize interface from cereal or the Binary interface from binary which both looks quite similar (from far away): - serialize work in the put monad, and you have to define a get instance: which is something that is not required or possible sometime. - binary works with lazy bytestrings and got the same problem as cereal. - a serialize instance that just do a single putByteString is really slow: 12 ns to 329 ns (26x time slower) on the same exact data on one isolated bench) - neither of those packages are in the platform. If that doesn't exists, could it be a worthy addition to bytestring ? is this a good idea in general ? is there any other way ? Thanks, -- Vincent

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ANN: hledger-web 0.19.3
by Simon Michael 24 Nov '12

24 Nov '12

hledger-web now supports GHC 7.6 properly (no more "Prelude.read: no parse" error). Release notes: * fix "Prelude.read: no parse" errors with GHC >= 7.6 * web & lib refactoring, easier scripting/developing Thanks! -Simon hledger is a command-line tool and haskell library for tracking financial transactions, which are stored in a human-readable plain text format. In addition to reporting, it can also help you record new transactions, or convert CSV data from your bank. Add-on packages include hledger-web, a web interface. hledger is inspired by and compatible with John Wiegley's Ledger. For more, see http://hledger.org . Install it: cabal update; cabal install hledger-web For more installation help, see http://hledger.org/MANUAL.html#installing . Or, sponsor a ready-to-run binary for your platform: http://hledger.org/DOWNLOAD.html .

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Re: [Haskell-cafe] Cabal failures...
by Gregory Guthrie 24 Nov '12

24 Nov '12

No; the first sentence says that someone else had reported that testing on Windows was hard to do because of (a perceived) lack of access to Windows by Haskell developers... The implication is that Haskell developers (only/mainly) use *nix. I commented that if true this lack of Windows testing could limit the availability of Haskell to the largest market share of users. ------------------------------------------- > Subject: Re: [Haskell-cafe] Cabal failures... > To: haskell-cafe(a)haskell.org > On 12-11-20 08:48 AM, Gregory Guthrie wrote: > > It was also interesting to note a comment that most developers don't > > have access to a Windows machine for testing. With Windows at >90% of > > the computing market (Linux = 1.6%), this seems like a problem which > > might limit growth of Haskell usage. Just an observation. :-) > > There is a paradox in that sentence. > > The first sentence says, most developers don't have access to Windows machines for > testing. But they have access to Linux machines. Then Windows machines must be a scarcity > compared to Linux machines, no? So scarce, you even have difficulty borrowing or renting. > > Then the next sentence says, the scarcity is the other way round, Linux machines are scarce, > Windows machines are abundant. OK, so why is it so hard to access something abundant, and > so easy to access something scarce? > ------------------------------

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isLetter vs. isAlpha
by Artyom Kazak 24 Nov '12

24 Nov '12

Hello! I saw a question on StackOverflow about the difference between isAlpha and isLetter today. One of the answers stated that the two functions are interchangeable, even though they are implemented differently. I decided to find out whether the difference in implementation influences performance, and look what I found: > import Criterion.Main > import Data.Char >fTest name f list = bgroup name $ map (\(n,c) -> bench n $ whnf f c) list >tests = [("latin", 'e'), ("digit", '8'), ("symbol", '…'), ("greek", 'λ')] >main = defaultMain [fTest "isAlpha" isAlpha tests, > fTest "isLetter" isLetter tests] produces this table (times are in nanoseconds): latin digit symbol greek ----- ----- ------ ----- isAlpha | 156 212 368 310 isLetter | 349 344 383 310 isAlpha is twice as fast on latin inputs! Does it mean that isAlpha should be preferred? Why isn’t isLetter defined in terms of isAlpha in Data.Char?

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ANNOUNCE: rethinkdb 0.1.0
by Etienne Laurin 24 Nov '12

24 Nov '12

Greetings, I am pleased to announce a Haskell client library for RethinkDB[1]. RethinkDB[2] is a newly released, open source, distributed database. Its simple yet powerful API seemed well suited to be accessed from a language like Haskell. This haskell library is modelled upon the existing Javascript and Python API and adds static type checking. Here is an example from the RethinkDB javascript tutorial[3] ported to Haskell: run h $ orderBy ["reduction"] . groupedMapReduce (! "Stname") mapF (0 :: NumberExpr) (R.+) . filter' filterF . pluck ["Stname", "POPESTIMATE2011", "Dem", "GOP"] . zip' $ eqJoin (table "county_stats") "Stname" (table "polls") where mapF doc = ((doc ! "POPESTIMATE2011") R.* ((doc ! "GOP") R.- (doc ! "Dem"))) R./ (100 :: Int) filterF doc = let dem = doc ! "Dem" :: NumberExpr; gop = doc ! "GOP" in (dem R.< gop) `and'` ((gop R.- dem) R.< (15::Int)) What is the advantage of RethinkDB? [4] "What's really special about all RethinkDB queries is that the program you wrote gets sent to the server, broken up into chunks, sent to relevant shards, executed completely in parallel (to the degree that the query makes possible -- complex queries often have multiple parallelization and recombination stages), but as a user you don't have to care about that at all. You just get the results. [...] Of course the visceral experience you get from using RethinkDB isn't just about the query language, or parallelization, or pleasant client libraries. It's about hundreds upon hundreds of examples like it, some large, some small, that add up to a completely different product. The team is fastidious about every command, every pixel, every algorithm, sometimes even every assembly instruction, so that people can use the product and at every step say `Wow, I can't believe how easy this was, how do they do that?!!' " I hope this library can help other Haskell programmers use this new database. Etienne Laurin [1] http://hackage.haskell.org/package/rethinkdb [2] http://www.rethinkdb.com [3] http://www.rethinkdb.com/docs/tutorials/elections/ [4] http://www.quora.com/RethinkDB/What-is-the-advantage-of-RethinkDB-over-Mong…

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Portability of Safe Haskell packages
by Roman Cheplyaka 23 Nov '12

23 Nov '12

It has been pointed out before that in order for Safe Haskell to be useful, libraries (especially core libraries) should be annotated properly with Safe Haskell LANGUAGE pragmas. However, that would make these libraries unusable with alternative Haskell implementations, even if otherwise they these libraries are Haskell2010. To quote the standard: If a Haskell implementation does not recognize or support a particular language feature that a source file requests (or cannot support the combination of language features requested), any attempt to compile or otherwise use that file with that Haskell implementation must fail with an error. Should it be advised to surround safe annotations with CPP #ifs? Or does anyone see a better way out of this contradiction? Roman

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Re: [Haskell-cafe] Compilers: Why do we need a core language?
by citb＠lavabit.com 23 Nov '12

23 Nov '12

> What would be the point in doing so? Well, I don't know. Would it save some time? Why bother with a core language?

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Re: [Haskell-cafe] Compilers: Why do we need a core language?
by Richard O'Keefe 23 Nov '12

23 Nov '12

On 23/11/2012, at 1:56 AM, Jacques Carette wrote: > On 20/11/2012 6:08 PM, Richard O'Keefe wrote: >> On 21/11/2012, at 4:49 AM, <citb(a)lavabit.com> wrote: >> >>> Well, I don't know. Would it save some time? Why bother with a core language? >> For a high level language (and for this purpose, even Fortran 66 counts as >> "high level") you really don't _want_ a direct translation from source code >> to object code. You want to eliminate unused code and you want to do all >> sorts of analyses and improvements. It is *much* easier to do all that to >> a small core language than to the full source language. > > Actually, here I disagree. It might be much 'easier' for the programmers to do it for a small core language, but it may turn out to be much, much less effective. I 'discovered' this when (co-)writing a partial evaluator for Maple: we actually made our internal language *larger*, so that we could encode more invariants syntactically. This ended up making our jobs considerably easier, because we did not have to work so hard on doing fancy analyses to recover information that would otherwise have been completely obvious. Yes, there were a lot more cases, but each case was relatively easy; the alternative was a small number of extremely difficult cases. I don't think we do disagree. We are talking about the same thing: ``not hav[ing] to work so hard on doing fancy analyses''. The key point is that an (abstract) syntax *designed for the compiler* and a syntax *designed for programmers* have to satisfy different design goals and constraints; there's no reason they should be the same. As a very very crude example of this, with its user-defined operators, Prolog lets you write rules using lots of (unquoted) operators to express yourself in an quasi-English sort of way, e.g., if Block must move and top of Block is not clear then clear top of Block. Readable. But lousy for processing. You'd want to change it to something like action(clear_top(Block), [ must_move(Block), \+ top_is_clear(Block)]).

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To "cabal install cabal-install" on Windows ...
by KC 23 Nov '12

23 Nov '12

- completely remove the earlier Haskell Platform - reboot - defragment the partition/hard drive - reboot - install the newer Haskell Platform - reboot - defragment the partition/hard drive (recommended) - reboot - cabal update - cabal install cabal-install It seems like what is slowing down the install process (or hanging it) is the thrashing of your hard drive to find all the little file fragments it needs during the install Casey -- -- Regards, KC

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Call for Seattle Area Haskell Users Group
by Eli Frey 22 Nov '12

22 Nov '12

Greetings, (x-posted from /r/haskell) I am calling for any interested parties to come together and help me get a SEA HUG going. My boss has offered to provide facilities and foods. I don't think he's expecting much, maybe we can make him second guess the offer :P. I have put together a meetup <http://www.meetup.com/SEAHUG> group. I don't know what all Seattle area Haskellers are wanting from this kind of thing, so I thought our first meeting would be low key. Some time to shoot the bull and introduce ourselves. Some time to help each other on our stumbling blocks. Then talking about what we would want from further meetups. We'll need a central place for discussion and coordination, so aside from voicing your support, it would be great if you could take further commentary over to the meetup page. If that doesn't work for some, let me know. Hope to hear from y'all soon. - Eli

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QuickCheck Generators
by graham＠fatlazycat.com 22 Nov '12

22 Nov '12

I have data Tweet = Tweet { user :: String, text :: String, retweets :: Double } deriving (Show) data TweetSet = NoTweets | SomeTweets Tweet TweetSet TweetSet and trying to create some generators for testing, with instance Arbitrary Tweet where arbitrary = liftM3 Tweet arbitrary arbitrary arbitrary instance Arbitrary TweetSet where arbitrary = sized set' where set' 0 = return NoTweets set' n | n>0 = oneof[return NoTweets, liftM3 SomeTweets arbitrary subTweets subTweets] where subTweets = set' (n `div` 2) but wondering how I would go about generating a random TweetSet that contains a known random Tweet I later have reference to and I would also assume the known Tweet to be placed randomly. Then I could test a contains function. Thanks

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fixed-length bit-vectors
by Greg Fitzgerald 22 Nov '12

22 Nov '12

Hi all, My goal, eliminate the failure case in 'byte': https://gist.github.com/4128503 I don't want my 'byte' function to fail at runtime or return $ Left "vector not 8 bits". I want it to return a Word8 for an 8-bit bit-vector or not compile. Is there an existing library that offers fixed-length vectors as a thin veneer over the 'vector' package? I see 'vector-static', but it is unmaintained and hasn't been touched in years. Alternatively, there's 'VecN', but having already learned 'vector', I'd like to know if there is an existing solution that uses it. Thanks, Greg

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naming and packaging things
by Rico Moorman 22 Nov '12

22 Nov '12

Hi everyone, As anyone following this mailinglist surely noticed, there are a few issues regarding haskell packaging. Lot of discussion is going on about how cabal contributes to the problems and how things could be fixed by making our tools smarter (which is a great thing to do IMHO). I think though, that there might be other ways to deal with or at least reduce the problems. One of those ways would be expressing the influence of changes in a package's public API, using the name of a package instead of just version numbers. I mean, in case a major backwards incompatible/breaking change happens, one would change the name of the package/namespaces a.s.o. And with breaking I really mean that kind of "oh my ... now I have to rewrite this part of my application because of this". Simple additions to the API do not count as breaking because existing functionality is left alone. This way, incompatible versions of the "same" library can coexist without any problems right within the same program if one chose to do so even allowing for improved transition processes for larger application I presume. It would easily be possible to safely install newer versions of the same package without breaking things. There are more open source libraries/projects as it seems, which use this approach (version number in the package name) such as the kdelibs, gtk, beautifulsoup, apache and bind. One example: take an application which needs two libraries A and B which both depend on library C. Now lets assume that A uses a slightly older version of C and B uses a version with a major incompatibility. In the current versioning scheme, there could be major problems causing development delays or custom forks to emerge a.s.o. But following the other naming method, in case library C chooses to introduce a major breaking change in the public API, a new package C2 is born, which can be used alongside C (and effectively is a different library anyway I think). The choice for the new version of C (C2) is explicit within the name and all related things. I am aware of the fact that this would take more forethought on library design, but I do not think that this alone would be a bad idea anyway. Also it would be difficult to enforce this, but well, a good maintainer would be aware of this anyway, taking care of not introducing breaking changes to the public API I guess. Furthermore we would end up with more packages with different names (but probably the same idea behind it) which would be on hackage. Likely it would be nice to add some grouping or tagging features which would bind them together for everyone browsing the packages. But I think this is probably not a real problem but more a cosmetic one. I really would like to see this discussed here. What would be the good and the bad of promoting this kind of versioning. I am looking forward to hear what you think. Best regards, Rico Moorman

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Haskell Weekly News: Issue 251
by Daniel Santa Cruz 22 Nov '12

22 Nov '12

Welcome to issue 251 of the HWN, an issue covering crowd-sourced bits of information about Haskell from around the web. This issue covers the week of November 4 to 17, 2012. Quotes of the Week * Ralith: [why some people don't use conduits/pipes] also, I think at least some people are waiting for edwardk to write his version. * edwardk: f -| g means that f a -> b is isomorphic to a -> g b (for arrows in the appropriate categories) * edwardk: @type (^.) lambdabot: s -> Getting a s t a b -> a byorgey: I would not like to be getting a stab, thank you * edwardk: I mean we're so oop even our member accessors have diagrams explaining their member accessors. * shapr: hylo! That's the category theorist greeting. * shachaf: type AbstractAlgebra a = Abstract a -> a * nicoo: Yet many Writers concern themselves with issues of State, imaginary or real * rwbarton: when you learn C, watch out for the keyword "return", it doesn't do what you'd expect * Oleg: We show how to program with the law of excluded middle. We specifically avoid call/cc, which is overrated. Top Reddit Stories * Haskell Platform 2012.4.0.0 is out Domain: self.haskell, Score: 89, Comments: 21 On Reddit: [1] http://goo.gl/BPno4 Original: [2] http://goo.gl/BPno4 * A Khan Academy style tutorial on generalized algebraic data types Domain: apfelmus.nfshost.com, Score: 56, Comments: 7 On Reddit: [3] http://goo.gl/kXQ0a Original: [4] http://goo.gl/NWn3B * Cartesian Closed Comic #17: Typing Domain: ro-che.info, Score: 53, Comments: 24 On Reddit: [5] http://goo.gl/6c4Uy Original: [6] http://goo.gl/dZeDx * Cartesian Closed Comic #18: Equality Domain: ro-che.info, Score: 53, Comments: 8 On Reddit: [7] http://goo.gl/8Qf9d Original: [8] http://goo.gl/XCyuB * Natural Language Processing for the Working Programmer (in Haskell!) Domain: nlpwp.org, Score: 50, Comments: 17 On Reddit: [9] http://goo.gl/3yLTZ Original: [10] http://goo.gl/BleWX * Waiting for garbage collection can kill parallelism? Domain: ics.p.lodz.pl, Score: 50, Comments: 7 On Reddit: [11] http://goo.gl/iUPlD Original: [12] http://goo.gl/N0kiV * foldr is made of monoids Domain: byorgey.wordpress.com, Score: 47, Comments: 12 On Reddit: [13] http://goo.gl/Y0mz5 Original: [14] http://goo.gl/IxKov * Solving Cabal Hell: vetted packages, multiple hackages Domain: yesodweb.com, Score: 46, Comments: 67 On Reddit: [15] http://goo.gl/dkzMz Original: [16] http://goo.gl/lDjuj * Parallel falling sand game with Repa Domain: github.com, Score: 45, Comments: 16 On Reddit: [17] http://goo.gl/G6MGG Original: [18] http://goo.gl/cP1zH * Agda, Epigram or Idris. Which one to learn Domain: self.haskell, Score: 38, Comments: 61 On Reddit: [19] http://goo.gl/3PGVo Original: [20] http://goo.gl/3PGVo * Fun with Fay - A ring oscillator Domain: skybluetrades.net, Score: 38, Comments: 6 On Reddit: [21] http://goo.gl/mGvcZ Original: [22] http://goo.gl/bJxCI * Introduction to Category Theory 1: Course Overview Domain: youtube.com, Score: 37, Comments: 6 On Reddit: [23] http://goo.gl/fbfYR Original: [24] http://goo.gl/Nx5SH * HALO: Haskell to Logic through Denotational Semantics [PDF] Domain: research.microsoft.com, Score: 35, Comments: 6 On Reddit: [25] http://goo.gl/V0RWs Original: [26] http://goo.gl/oCzUw * How to write Python in Haskell: State and Either Domain: stackoverflow.com, Score: 34, Comments: 25 On Reddit: [27] http://goo.gl/Z80yb Original: [28] http://goo.gl/W933i * What is foldr made of? Domain: web.jaguarpaw.co.uk, Score: 30, Comments: 22 On Reddit: [29] http://goo.gl/LdS9X Original: [30] http://goo.gl/I2uzX * How to shoot yourself in the foot with Haskell Domain: ics.p.lodz.pl, Score: 29, Comments: 34 On Reddit: [31] http://goo.gl/CcvZB Original: [32] http://goo.gl/SJYvd * Happstack, Fay, & Acid-State: Shared Datatypes are Awesome Domain: happstack.com, Score: 29, Comments: 8 On Reddit: [33] http://goo.gl/AUtj6 Original: [34] http://goo.gl/cYQr1 * ANN: OpenGL packages update Domain: haskell.org, Score: 28, Comments: 7 On Reddit: [35] http://goo.gl/0SN7O Original: [36] http://goo.gl/PbtlT * How can I cleanly/consistently work with 3 different Exception-raising schemes? Domain: self.haskell, Score: 28, Comments: 22 On Reddit: [37] http://goo.gl/Xf4sq Original: [38] http://goo.gl/Xf4sq Top StackOverflow Questions * What are paramorphisms? votes: 39, answers: 1 Read on SO: [39] http://goo.gl/V6rXq * In pure functional languages, is there an algorithm to get the inverse function? votes: 35, answers: 9 Read on SO: [40] http://goo.gl/wBtqv * What are free monads? votes: 26, answers: 5 Read on SO: [41] http://goo.gl/NAx8n * What's the status of current Functional Reactive Programming implementations? votes: 23, answers: 3 Read on SO: [42] http://goo.gl/FmRYF * What does the “world” mean in functional programming world? votes: 22, answers: 7 Read on SO: [43] http://goo.gl/dyM8c * Type-safe difference lists votes: 20, answers: 1 Read on SO: [44] http://goo.gl/TlvF4 * Is it possible to annotate a function's special properties (e.g. surjectivity)? votes: 12, answers: 3 Read on SO: [45] http://goo.gl/uzanF * Under what circumstances are monadic computations tail-recursive? votes: 12, answers: 2 Read on SO: [46] http://goo.gl/lPJef * Should I use new Haskell language extensions in favour of the old ones? votes: 12, answers: 2 Read on SO: [47] http://goo.gl/xkc78 Until next time, Daniel Santa Cruz References 1. http://www.reddit.com/r/haskell/comments/12pxiq/haskell_platform_2012400_is… 2. http://www.reddit.com/r/haskell/comments/12pxiq/haskell_platform_2012400_is… 3. http://apfelmus.nfshost.com/blog/2010/06/01-gadts-video.html 4. http://www.reddit.com/r/haskell/comments/12ou1p/a_khan_academy_style_tutori… 5. http://ro-che.info/ccc/17.html 6. http://www.reddit.com/r/haskell/comments/12nm3w/cartesian_closed_comic_17_t… 7. http://ro-che.info/ccc/18.html 8. http://www.reddit.com/r/haskell/comments/138crz/cartesian_closed_comic_18_e… 9. http://nlpwp.org/book/ 10. http://www.reddit.com/r/haskell/comments/13a0ut/natural_language_processing… 11. http://ics.p.lodz.pl/~stolarek/blog/2012/11/waiting-for-garbage-collection-… 12. http://www.reddit.com/r/haskell/comments/13cpm3/waiting_for_garbage_collect… 13. http://byorgey.wordpress.com/2012/11/05/foldr-is-made-of-monoids/ 14. http://www.reddit.com/r/haskell/comments/12prpr/foldr_is_made_of_monoids/ 15. http://www.yesodweb.com/blog/2012/11/solving-cabal-hell 16. http://www.reddit.com/r/haskell/comments/1306wn/solving_cabal_hell_vetted_p… 17. https://github.com/tranma/falling-turnip 18. http://www.reddit.com/r/haskell/comments/133nja/parallel_falling_sand_game_… 19. http://www.reddit.com/r/haskell/comments/132kg0/agda_epigram_or_idris_which… 20. http://www.reddit.com/r/haskell/comments/132kg0/agda_epigram_or_idris_which… 21. http://www.skybluetrades.net/blog/posts/2012/11/13/fay-ring-oscillator/inde… 22. http://www.reddit.com/r/haskell/comments/134tr6/fun_with_fay_a_ring_oscilla… 23. http://www.youtube.com/watch?v=eu0rj5C2Otg 24. http://www.reddit.com/r/haskell/comments/12vvn2/introduction_to_category_th… 25. http://research.microsoft.com/en-us/people/dimitris/hcc-popl.pdf 26. http://www.reddit.com/r/haskell/comments/12wovt/halo_haskell_to_logic_throu… 27. http://stackoverflow.com/a/13432926/208257 28. http://www.reddit.com/r/haskell/comments/13cz6b/how_to_write_python_in_hask… 29. http://web.jaguarpaw.co.uk/~tom/blog/posts/2012-11-04-what-is-foldr-made-of… 30. http://www.reddit.com/r/haskell/comments/12mnhu/what_is_foldr_made_of/ 31. http://ics.p.lodz.pl/~stolarek/blog/2012/11/how-to-shoot-yourself-in-the-fo… 32. http://www.reddit.com/r/haskell/comments/12rlgt/how_to_shoot_yourself_in_th… 33. http://www.happstack.com/c/view-page-slug/15/happstack-fay-acid-state-share… 34. http://www.reddit.com/r/haskell/comments/1375q0/happstack_fay_acidstate_sha… 35. http://www.haskell.org/pipermail/haskell-cafe/2012-November/104329.html 36. http://www.reddit.com/r/haskell/comments/12mk7h/ann_opengl_packages_update/ 37. http://www.reddit.com/r/haskell/comments/12relk/how_can_i_cleanlyconsistent… 38. http://www.reddit.com/r/haskell/comments/12relk/how_can_i_cleanlyconsistent… 39. http://stackoverflow.com/questions/13317242/what-are-paramorphisms 40. http://stackoverflow.com/questions/13404208/in-pure-functional-languages-is… 41. http://stackoverflow.com/questions/13352205/what-are-free-monads 42. http://stackoverflow.com/questions/13341937/whats-the-status-of-current-fun… 43. http://stackoverflow.com/questions/13340458/what-does-the-world-mean-in-fun… 44. http://stackoverflow.com/questions/13346200/type-safe-difference-lists 45. http://stackoverflow.com/questions/13281316/is-it-possible-to-annotate-a-fu… 46. http://stackoverflow.com/questions/13379060/under-what-circumstances-are-mo… 47. http://stackoverflow.com/questions/13422610/should-i-use-new-haskell-langua…

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Common function names for '(.) . (.)', '(.) . (.) . (.)' ...?
by Thomas Bereknyei 21 Nov '12

21 Nov '12

I use .@. (sometimes ...) .#. .$. for the two three and four dot variations.

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Re: [Haskell-cafe] [Haskell] [ANN] gtk2hs-0.12.4
by Roman Cheplyaka 21 Nov '12

21 Nov '12

* wagnerdm(a)seas.upenn.edu <wagnerdm(a)seas.upenn.edu> [2012-11-21 13:48:35-0500] > Today, we welcome into the world version 0.12.4 of Gtk2Hs[1], a set > of Haskell bindings to many of the libraries included in the > Gtk+/Gnome platform. Gtk+ is an extensive and mature multi-platform > toolkit for creating graphical user interfaces. Great — thanks to you and John for keeping it alive. Roman

1 0

AST Rewriting
by Steve Severance 21 Nov '12

21 Nov '12

Hi Everyone, I am trying to build a function to rewrite and AST. I have and AST which is designed to represent a computation graph. I will present a simplified version here designed to illustrate the problem. I have tried numerous ways of rewriting it including uniplate, recursion and Edward Kmett's implementation of plate in his lens package. My AST is defined using GADTs as follows: class (ReflectDescriptor a, Typeable a, Wire a) => ProtoBuf a data Expression a b where OpenTable :: (ProtoBuf b) => Int -> Table -> Expression () b OpenFile :: (ProtoBuf b) => Int -> String -> Expression () b WriteFile :: (Typeable a, ProtoBuf b) => Int -> String -> Expression a b -> Expression b () WriteTable :: (Typeable a, ProtoBuf b) => Int -> Table -> Expression a b -> Expression b () Map :: (ProtoBuf a, ProtoBuf b, ProtoBuf c) => Int -> (a -> b) -> Expression c a -> Expression a b LocalMerge :: (ProtoBuf a) => Int -> [Expression c a] -> Expression c a The user can create code inside a Monad Transformer like so: q <- query $ do table <- openTable myTable transform <- map someFunc table writeTable otherTable transform As part of this language the compiler I am building would need to for instance transform OpenTable into a series OpenFile nodes with a LocalMerge to merge the results together. So uniplate cannot work over GADTs if I recall correctly. I exchanged emails with Edward and he explained that for the lens case I would need something like an indexed lens family from his indexed package which is not implemented yet but which may be in the future. The issue with recursion is that as you recurse through the AST the a b on the Expression change and GHC cannot compile it because it wants the a b to be the same on each recursive call. My question to the Haskell community is how might one develop AST rewriting functionality. One possible solution is stripping the types away from GHC and doing all the type checking myself. That doesn't seem very good. Another possibility that I have looked at was using hoopl. It seems very compatible given that it is built for describing and optimizing data flow which I am doing however the learning curve looks quite steep. I have been reluctant so far to invest the time in it. Has anyone developed something similar? What recommendations do you have? Thanks. Steve

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Common function names for '(.) . (.)', '(.) . (.) . (.)' ...?
by Daniel Trstenjak 21 Nov '12

21 Nov '12

Greetings, Daniel

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Re: [Haskell-cafe] cabal install... Trying to recover
by Gregory Guthrie 21 Nov '12

21 Nov '12

Thanks for the suggestion, I’ll do that. Here goes: I deleted the ../user/appdata/roaming/ghc and ../cabal files, an uninstalled Haskell-platform. (No trace of anything "ghc" on the disk.) Then reinstalled Haskell, and ran “cabal update”, it said there was a new cabal-install, but trying to install it fails (below), so I went ahead with the current version. The error seems odd to me (cabal-install-1.16.0.2 depends on Cabal-1.16.0.3 which failed to install.), that an older version depends on a newer one? So now I have; (from Windows - Haskell-platform 2012.4.0.0) GHCi = The Glorious Glasgow Haskell Compilation System, version 7.4.2 Cabal = cabal-install version 0.14.0, using version 1.14.0 of the Cabal library I then tried to reload all my previous packages, (all at once?!), but it fails, "out of memory" (w/8GB of memory!) So I split it into sections, and tried the first one; it lists a lot of new installs, and then fails (full list at http://pastebin.com/5ywdUjgX) The first chunk of installs gives this: ... cabal: The following packages are likely to be broken by the reinstalls: QuickCheck-2.4.2 haskell-platform-2012.4.0.0 Use --force-reinstalls if you want to install anyway. I don't understand how it can want to break the Haskell-platform, sounds dangerous! And the second this: G:\Cabal>cabal install Boolean Craft3e Craft3e GLFW GLURaw GLUT HTTP IORefCAS Me moTrie MonadCatchIO-mtl NumInstances ObjectName OpenGL OpenGLRaw QuickCheck SDL SHA StateVar Tensor abstract-deque abstract-par active aeson alex ansi-terminal array asn1-data attoparsec attoparsec-conduit base-unicode-symbols base64-bytest ring bits-atomic blaze-builder blaze-builder-conduit blaze-html blaze-markup bla ze-svg bmp buildwrapper byteorder cabal-dev case-insensitive cereal certificate clientsession cmdargs colour comonad conduit contravariant cookie cpphs cprng-ae s cpu criterion crypto-api crypto-conduit crypto-pubkey-types cryptocipher crypt ohash css-text data-default date-cache diagrams-core diagrams-lib diagrams-svg d list email-validate entropy erf failure fast-logger file-embed filepath filesyst em-conduit ghc-paths gloss gtk2hs-buildtools Resolving dependencies... In order, the following would be installed: Boolean-0.1.1 (new package) ... cabal: The following packages are likely to be broken by the reinstalls: regex-posix-0.95.1 regex-compat-0.95.1 regex-posix-0.94.4 regex-compat-0.93.1 parsec-3.1.1 fgl-5.4.2.4 fgl-5.4.2.3 QuickCheck-2.4.0.1 network-2.3.1.0 haskell-platform-2012.4.0.0 cgi-3001.1.7.4 HTTP-4000.2.5 regex-posix-0.95.2 regex-compat-0.95.1 regex-posix-0.95.1 regex-compat-0.95.1 Use --force-reinstalls if you want to install anyway. So I have a typical situation where it won't install, and gives an option to –force, but that seems to lead to more problems? Do I just have some packages which are intrinsically incompatible, and I have to choose between them? Not sure how to proceed. Any help or hints appreciated! :-) –––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––- > Cabal install cabal-install Configuring Cabal-1.16.0.3... Warning: This package indirectly depends on multiple versions of the same package. This is highly likely to cause a compile failure. package process-1.1.0.1 requires base-4.5.0.0 package pretty-1.1.1.0 requires base-4.5.0.0 package old-time-1.1.0.0 requires base-4.5.0.0 package old-locale-1.0.0.4 requires base-4.5.0.0 package filepath-1.3.0.0 requires base-4.5.0.0 package directory-1.1.0.2 requires base-4.5.0.0 package deepseq-1.3.0.0 requires base-4.5.0.0 package containers-0.4.2.1 requires base-4.5.0.0 package bytestring-0.9.2.1 requires base-4.5.0.0 package array-0.4.0.0 requires base-4.5.0.0 package Win32-2.2.2.0 requires base-4.5.0.0 package filepath-1.3.0.0 requires base-4.5.1.0 package Cabal-1.16.0.3 requires base-4.5.1.0 package Cabal-1.16.0.3 requires filepath-1.3.0.0 package process-1.1.0.1 requires filepath-1.3.0.0 package directory-1.1.0.2 requires filepath-1.3.0.0 package integer-gmp-0.4.0.0 requires ghc-prim-0.2.0.0 package bytestring-0.9.2.1 requires ghc-prim-0.2.0.0 package base-4.5.0.0 requires ghc-prim-0.2.0.0 package integer-gmp-0.4.0.0 requires ghc-prim-0.2.0.0 package base-4.5.1.0 requires ghc-prim-0.2.0.0 package base-4.5.1.0 requires integer-gmp-0.4.0.0 package base-4.5.0.0 requires integer-gmp-0.4.0.0 Building Cabal-1.16.0.3... Preprocessing library Cabal-1.16.0.3... <command line>: cannot satisfy -package-id array-0.4.0.0-3cf1bc3f5cd0078adea24752c18081b9 (use -v for more information) cabal: Error: some packages failed to install: Cabal-1.16.0.3 failed during the building phase. The exception was: ExitFailure 1 cabal-install-1.16.0.2 depends on Cabal-1.16.0.3 which failed to install. (more -v details at: http://pastebin.com/Y2BuMjBP ) ------------------------------------------- From this email and some of the previous emails it seems that your package DB is in a pretty bad state, most likely from using --force-reinstalls. When Cabal warns you that this will break stuff it actually means it. :) My suggestion is that you rm -rf ~/.ghc/x86_64-linux-7.6.1 # or equivalent on your system. Then reinstall all the packages you want by listing them all at once cabal install pkg1 pkg2 pk3 By listing them all together cabal-install tries to come up with an install plan that is globally consistent for all of them. -- Johan

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Re: [Haskell-cafe] cabal install... Trying to recover
by Niklas Larsson 21 Nov '12

21 Nov '12

You should have a ghc directory under appdata, with i386-mingw32-7.4.2\package.conf.d under it. There GHC tracks what packages it knows about. Niklas From: Gregory Guthrie Sent: 2012-11-21 15:11 To: Johan Tibell Cc: haskell-cafe(a)haskell.org Subject: Re: [Haskell-cafe] cabal install... Trying to recover Thanks for the suggestion, I’ll do that. Here goes: I deleted the ../user/appdata/roaming/ghc and ../cabal files, an uninstalled Haskell-platform. (No trace of anything "ghc" on the disk.) Then reinstalled Haskell, and ran “cabal update”, it said there was a new cabal-install, but trying to install it fails (below), so I went ahead with the current version. The error seems odd to me (cabal-install-1.16.0.2 depends on Cabal-1.16.0.3 which failed to install.), that an older version depends on a newer one? So now I have; (from Windows - Haskell-platform 2012.4.0.0) GHCi = The Glorious Glasgow Haskell Compilation System, version 7.4.2 Cabal = cabal-install version 0.14.0, using version 1.14.0 of the Cabal library I then tried to reload all my previous packages, (all at once?!), but it fails, "out of memory" (w/8GB of memory!) So I split it into sections, and tried the first one; it lists a lot of new installs, and then fails (full list at http://pastebin.com/5ywdUjgX) The first chunk of installs gives this: ... cabal: The following packages are likely to be broken by the reinstalls: QuickCheck-2.4.2 haskell-platform-2012.4.0.0 Use --force-reinstalls if you want to install anyway. I don't understand how it can want to break the Haskell-platform, sounds dangerous! And the second this: G:\Cabal>cabal install Boolean Craft3e Craft3e GLFW GLURaw GLUT HTTP IORefCAS Me moTrie MonadCatchIO-mtl NumInstances ObjectName OpenGL OpenGLRaw QuickCheck SDL SHA StateVar Tensor abstract-deque abstract-par active aeson alex ansi-terminal array asn1-data attoparsec attoparsec-conduit base-unicode-symbols base64-bytest ring bits-atomic blaze-builder blaze-builder-conduit blaze-html blaze-markup bla ze-svg bmp buildwrapper byteorder cabal-dev case-insensitive cereal certificate clientsession cmdargs colour comonad conduit contravariant cookie cpphs cprng-ae s cpu criterion crypto-api crypto-conduit crypto-pubkey-types cryptocipher crypt ohash css-text data-default date-cache diagrams-core diagrams-lib diagrams-svg d list email-validate entropy erf failure fast-logger file-embed filepath filesyst em-conduit ghc-paths gloss gtk2hs-buildtools Resolving dependencies... In order, the following would be installed: Boolean-0.1.1 (new package) ... cabal: The following packages are likely to be broken by the reinstalls: regex-posix-0.95.1 regex-compat-0.95.1 regex-posix-0.94.4 regex-compat-0.93.1 parsec-3.1.1 fgl-5.4.2.4 fgl-5.4.2.3 QuickCheck-2.4.0.1 network-2.3.1.0 haskell-platform-2012.4.0.0 cgi-3001.1.7.4 HTTP-4000.2.5 regex-posix-0.95.2 regex-compat-0.95.1 regex-posix-0.95.1 regex-compat-0.95.1 Use --force-reinstalls if you want to install anyway. So I have a typical situation where it won't install, and gives an option to –force, but that seems to lead to more problems? Do I just have some packages which are intrinsically incompatible, and I have to choose between them? Not sure how to proceed. Any help or hints appreciated! :-) –––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––- > Cabal install cabal-install Configuring Cabal-1.16.0.3... Warning: This package indirectly depends on multiple versions of the same package. This is highly likely to cause a compile failure. package process-1.1.0.1 requires base-4.5.0.0 package pretty-1.1.1.0 requires base-4.5.0.0 package old-time-1.1.0.0 requires base-4.5.0.0 package old-locale-1.0.0.4 requires base-4.5.0.0 package filepath-1.3.0.0 requires base-4.5.0.0 package directory-1.1.0.2 requires base-4.5.0.0 package deepseq-1.3.0.0 requires base-4.5.0.0 package containers-0.4.2.1 requires base-4.5.0.0 package bytestring-0.9.2.1 requires base-4.5.0.0 package array-0.4.0.0 requires base-4.5.0.0 package Win32-2.2.2.0 requires base-4.5.0.0 package filepath-1.3.0.0 requires base-4.5.1.0 package Cabal-1.16.0.3 requires base-4.5.1.0 package Cabal-1.16.0.3 requires filepath-1.3.0.0 package process-1.1.0.1 requires filepath-1.3.0.0 package directory-1.1.0.2 requires filepath-1.3.0.0 package integer-gmp-0.4.0.0 requires ghc-prim-0.2.0.0 package bytestring-0.9.2.1 requires ghc-prim-0.2.0.0 package base-4.5.0.0 requires ghc-prim-0.2.0.0 package integer-gmp-0.4.0.0 requires ghc-prim-0.2.0.0 package base-4.5.1.0 requires ghc-prim-0.2.0.0 package base-4.5.1.0 requires integer-gmp-0.4.0.0 package base-4.5.0.0 requires integer-gmp-0.4.0.0 Building Cabal-1.16.0.3... Preprocessing library Cabal-1.16.0.3... <command line>: cannot satisfy -package-id array-0.4.0.0-3cf1bc3f5cd0078adea24752c18081b9 (use -v for more information) cabal: Error: some packages failed to install: Cabal-1.16.0.3 failed during the building phase. The exception was: ExitFailure 1 cabal-install-1.16.0.2 depends on Cabal-1.16.0.3 which failed to install. (more -v details at: http://pastebin.com/Y2BuMjBP ) ------------------------------------------- >From this email and some of the previous emails it seems that your package DB is in a pretty bad state, most likely from using --force-reinstalls. When Cabal warns you that this will break stuff it actually means it. :) My suggestion is that you rm -rf ~/.ghc/x86_64-linux-7.6.1 # or equivalent on your system. Then reinstall all the packages you want by listing them all at once cabal install pkg1 pkg2 pk3 By listing them all together cabal-install tries to come up with an install plan that is globally consistent for all of them. -- Johan _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

1 0

cabal install...
by Gregory Guthrie 21 Nov '12

21 Nov '12

Hmm, Now when I tried to run Leksah, I get not only some broken packages (which I can avoid for my current project), but: <command line>: cannot satisfy -package-id base-4.5.1.0-7c83b96f47f23db63c42a56351dcb917: base-4.5.1.0-7c83b96f47f23db63c42a56351dcb917 is unusable due to missing or recursive dependencies: integer-gmp-0.4.0.0-c15e185526893c3119f809251aac8c5b (use -v for more information) So I tried to install base, then re-install it, but both fail; Any hints? ------------------------------- C:\Users\guthrie>cabal install base Resolving dependencies... All the requested packages are already installed: base-4.5.1.0 Use --reinstall if you want to reinstall anyway. C:\Users\guthrie>cabal install --reinstall base Resolving dependencies... cabal: Could not resolve dependencies: next goal: base (user goal) rejecting: base-3.0.3.2 (conflict: base => base>=4.0 && <4.3) rejecting: base-3.0.3.1 (conflict: base => base>=4.0 && <4.2) rejecting: base-4.6.0.0, 4.5.1.0, 4.5.0.0, 4.4.1.0, 4.4.0.0, 4.3.1.0, 4.3.0.0, 4.2.0.2, 4.2.0.1, 4.2.0.0, 4.1.0.0, 4.0.0.0 (only already installed instances can be used) C:\Users\guthrie>ghc-pkg list base WARNING: there are broken packages. Run 'ghc-pkg check' for more details. e:/Plang/Haskell Platform\lib\package.conf.d: base-4.3.1.0 base-4.5.0.0 base-4.5.1.0 The following packages are broken, either because they have a problem listed above, or because they depend on a broken package. HTTP-4000.2.3 haskell-platform-2012.2.0.0 Can I just unregister the old Haskell platform, I now use a newer one? Ghc-pkg list : ... {haskell-platform-2012.2.0.0} haskell-platform-2012.4.0.0 haskell-src-1.0.1.4 haskell-src-1.0.1.4 haskell-src-1.0.1.5 haskell-src-1.0.1.5 (haskell2010-1.0.0.0) (haskell2010-1.1.0.1) (haskell2010-1.1.0.1) haskell98-1.1.0.1 (haskell98-2.0.0.1) (haskell98-2.0.0.1) -------------------------------------------

5 4

Hackage dependencies problem.
by Magicloud Magiclouds 21 Nov '12

21 Nov '12

Hi, I am having ghc 7.6.1 working here. But anytime I installed something with cabal-install, I got prompts like: Warning: The following packages are likely to be broken by the reinstalls: haskell98-2.0.0.2 ghc-7.6.1 Cabal-1.16.0 bin-package-db-0.0.0.0 directory-1.2.0.0 hpc-0.6.0.0 Continuing even though the plan contains dangerous reinstalls. And even worse, then I got: <command line>: cannot satisfy -package Cabal-1.16.0: Cabal-1.16.0-dd0ce1db6fea670a788547ee85411486 is unusable due to missing or recursive dependencies: directory-1.2.0.0-8edf300597b0da609c8eccc9aa6d0cc3 process-1.1.0.2-03ae5757aa509ffbe497f42660cba52c unix-2.6.0.0-4bc27fc415f60036a88211de7cde3e9a (use -v for more information) What should I do? Why user space directory and process would interrupt Cabal in global space? -- 竹密岂妨流水过山高哪阻野云飞 And for G+, please use magiclouds#gmail.com.

3 5

Instead of Haskell running on the JVM is there a way for Haskell to call a JVM language ...
by KC 20 Nov '12

20 Nov '12

Instead of Haskell running on the JVM is there a way for Haskell to call a JVM language (or generate bytecode) to access the Java class libraries when needed? Or Is there a way for a JVM language or bytecode to call Haskell when needed? -- -- Regards, KC

8 7

code length in Haskell, a comparison
by Gregory Guthrie 20 Nov '12

20 Nov '12

There is some interesting data in the article at: Code Length Measured in 14 Languages http://blog.wolfram.com/2012/11/14/code-length-measured-in-14-languages/ basically comparing program lengths in various languages, and some ensuing discussion of how this relates to language expressiveness, etc. (He does all of his analysis in Mathematica, which is the goal of the article.) It is interesting to see how well Haskell showed in the data; and it would also be interesting to see how well it could replicate the analysis example which was a nice example of web data scraping! The data is the length of a series of programs written in a number of languages (data from: http://rosettacode.org/wiki/Rosetta_Code) (The columns don't map well to text only, Haskell column marked with ≡≡≡≡ (Why doesn't this list support HTML?)). See nicer version at: http://pastehtml.com/view/ciy7woohv.rtxt The average for Haskell of 1.89 means that on the average the same program in Haskell takes ~2x in the other languages. Given the correlation of size to clarity, complexity, effort, and errors, this is a good thing! :-) Code Size relative to Mathematica Larger numbers indicate that the language on top needs more code. C C++ Fortran Java CLisp Python C# JavaScript R MATLAB Clojure Pascal Haskell Ruby Average ??????????? ???? ???? ???? ???? ???? ???? ???? ???? ???? ???? ???? ???? ≡≡≡≡ ???? Mathematica 17.0 9.1 8.1 6.4 6.3 7.2 6.4 5.0 3.2 3.2 1.6 5.8 3.5 5.2 6.29 Ruby 2.7 1.8 1.9 1.3 1.1 1.1 1.5 1.0 0.7 0.9 0.4 1.4 0.7 1.27 Haskell 3.6 2.7 2.5 2.0 1.6 1.7 2.2 1.5 1.1 1.5 0.7 2.1 1.4 1.89 Pascal 2.2 1.5 1.2 0.8 0.8 0.8 1.0 0.8 0.5 0.6 0.2 0.5 0.7 0.89 Clojure 8.8 5.3 5.2 3.6 3.7 3.3 3.8 2.5 1.9 2.9 5.0 1.5 2.6 3.85 MATLAB 3.6 2.4 1.8 1.1 1.4 1.1 1.7 0.9 0.8 0.3 1.6 0.7 1.1 1.42 R 4.7 3.3 2.4 1.9 1.8 1.7 2.1 1.5 1.3 0.5 2.2 0.9 1.4 1.98 JavaScript 2.8 2.1 1.9 1.2 1.2 1.1 1.6 0.7 1.1 0.4 1.3 0.7 1.0 1.31 C# 2.0 1.4 1.3 0.9 0.8 0.8 0.6 0.5 0.6 0.3 1.0 0.5 0.7 0.87 Python 2.2 1.6 1.5 1.1 0.9 1.2 0.9 0.6 0.9 0.3 1.3 0.6 0.9 1.07 Common Lisp 2.8 1.8 1.6 1.3 1.1 1.3 0.8 0.6 0.7 0.3 1.3 0.6 0.9 1.16 Java 2.1 1.4 1.5 0.8 0.9 1.1 0.8 0.5 0.9 0.3 1.2 0.5 0.8 0.98 Fortran 1.4 1.0 0.7 0.6 0.7 0.8 0.5 0.4 0.6 0.2 0.8 0.4 0.5 0.66 C++ 1.4 1.0 0.7 0.6 0.6 0.7 0.5 0.3 0.4 0.2 0.7 0.4 0.6 0.61 C 0.7 0.7 0.5 0.4 0.5 0.5 0.4 0.2 0.3 0.1 0.5 0.3 0.4 0.41 ???????????? ???? ???? ???? ???? ???? ???? ???? ???? ???? ???? ???? ???? ≡≡≡≡ ???? Overall: 4.1 2.58 2.3 1.68 1.56 1.61 1.85 1.27 0.85 1.14 0.41 1.86 0.83 1.29 Overall Ranking: Clojure 0.41 Haskell 0.83 R 0.85 MATLAB 1.14 JavaScript 1.27 Ruby 1.36 Common Lisp 1.56 Python 1.61 C++ 1.68 C# 1.85 Pascal 1.86 Fortran 2.33 C++ 2.58 C 4.09 -------------------------------------------

6 5

ANN: NY Haskell presents Edward Kmett on Lenses, Folds, and Traversals -- Wed., December 12
by Gershom B 20 Nov '12

20 Nov '12

The first NY Haskell Users Group meetup was a great success -- with roughly sixty attendees and conversations that stretched far too late for a weekday night. Video and slides are available for both the Practical Data Processing and Cloud Haskell talks: Video: http://vimeo.com/53906049 Slides on Practical Data Processing: http://gbaz.github.com/slides/PracticalData-11-2012.pdf Slides on Cloud Haskell: http://gbaz.github.com/slides/cloud-11-2012.html Source for Cloud Haskell: https://github.com/gbaz/slides/blob/gh-pages/cloud-11-2012.lhs We expect our next meetup will be equally exciting, at a bare minimum. We're actively seeking cool talks and presentations. If you're not a New York local, but may be passing through or are in the tri-state area or thereabouts, and would like to present some code or research with even tangentially real-world implications to an informed and appreciated audience, please do get in touch :-) Also, there will be a NY tech holiday party on December 11th, which we are organizing along with other NY technology and PL groups. Details are available at the on the meetup site: http://www.meetup.com/NY-Haskell/. Finally, at some point, we will probably cease to spam -cafe with announcements of all our events, so even if you can't make it to the next few ones, registering at the meetup site is the best way to stay on top of what we will have planned. - - - - Lenses, Folds, and Traversals presented by Edward Kmett Wednesday, December 12, 2012 7:00 PM To 9:00 PM Pivotal Labs, 841 Broadway New York, NY (8th Floor) RSVP: http://www.meetup.com/NY-Haskell/ Edward Kmett will introduce his lens library, which provides a highly composable toolbox for accessing and modifying multiple parts of data structures. >From simple beginnings, starting with building blocks such as fmap and (.), we will build up combinators suitable for working with a wide array of data structures. These generalize the notions you already know how to use into a form that is easier to compose, and simultaneously allow them to be used for monomorphic containers such as Data.Text. All without compromising on your ability to reason about them using laws! Once we've built up some foundations, we'll do a bit of a deep dive, exploring consequences of this design. We will discuss the efficient generic programming programming framework exported by lens, and type-safe Traversal-based zippers. Familiarity with the Applicative and Traversable classes from the Haskell base libraries will be helpful (links provided below), but a basic understanding of the concepts will be introduced we go along. Attendees should expect to be gobsmacked with a newfound appreciation for the power of a little (or a lot of) abstraction. Useful (but not mandatory) references: The lens library and documentation: http://hackage.haskell.org/package/lens A previous, more introductory talk on how to use the lenses Edward Kmett wrote for the scalaz in the Scala programming language: https://www.youtube.com/watch?v=efv0SQNde5Q The original Applicative paper: http://www.soi.city.ac.uk/~ross/papers/Applicative.pdf Lots of information on Traversable: http://www.cs.ox.ac.uk/jeremy.gibbons/publications/iterator.pdf A write-up of this talk, as presented at the Bay Area Haskell Users Group: http://google-opensource.blogspot.com/2012/10/lenses-folds-and-traversals-h…

1 0

Re: [Haskell-cafe] Cabal failures...
by Gregory Guthrie 20 Nov '12

20 Nov '12

Thanks to all for the comparisons between apt & cabal. Your reply basically explains why it is broken, and gives a rationale (cost and trouble to do it), but no prognosis for repair. My interest is in using Haskell for teaching, and so far the package system failures often present problems that I can't solve for all but the simplest examples, so I couldn't much pass this onto students! My libraries may have gotten corrupted, so when I get time I will try to reset and clean out everything and start over, but that will of course break a lot of things and take a lot of time for some re-installs, most particularly things depending on underlying C libraries. Any hints for a simple way to do this are welcome. I look forward to the outcomes from the current cabal discussions. It was also interesting to note a comment that most developers don't have access to a Windows machine for testing. With Windows at >90% of the computing market (Linux = 1.6%), this seems like a problem which might limit growth of Haskell usage. Just an observation. :-) Thanks for your article on the topic of Cabal - interesting! ---------------------------------------------- Date: Tue, 20 Nov 2012 01:03:20 -0500 From: "Albert Y. C. Lai" <trebla(a)vex.net> Subject: Re: [Haskell-cafe] Cabal failures... At least I paid my 3 hours to explain some cabal stuff at http://www.vex.net/~trebla/haskell/sicp.xhtml ----------------------------------------------

3 2

Re: [Haskell-cafe] code length in Haskell, a comparison
by Gregory Guthrie 20 Nov '12

20 Nov '12

They also have other comparisons at the referenced site, including for different sizes of programs, and for counting characters or tokens instead of lines over each of these program example groups. The data source does include APL & REBOL (& 483 different languages!), so one could run this analysis with most any languages you liked. Analysis from: http://blog.wolfram.com/2012/11/14/code-length-measured-in-14-languages/ Data from: http://rosettacode.org/wiki/Rosetta_Code ---------------------------------------------------------------- Re: [Haskell-cafe] code length in Haskell, a comparison > I find myself wondering where Rebol would stand in this. Or APL. Greets, Ertugrul -------------------------------------------

1 0

Cabal failures...
by Gregory Guthrie 20 Nov '12

20 Nov '12

I follow the Cabal-messes threads with some interest, since that is the hardest area for me since starting to use Haskell. Probably 40-60% of all package install fail for some mysterious reason, with threats that trying to fix them will break more things, which generally is true. :-) I am not exert in the area, but I wonder how /why/ this is different than other package managers, like apt in Linux, I have never had any problems with it, and I would think that their dependencies are of at least similar complexities. In any case; Trying to do a cabal update" I was told to try to update "cabal-install", which I think means actually updating cabal (since I actually run installs via cabal install...), but that fails with this message below, and I don't know how to proceed. Linking C:\Users\guthrie\AppData\Local\Temp\Cabal-1.16.0.3-13880\Cabal-1.16.0.3\dist\setup\setup.exe ... Configuring Cabal-1.16.0.3... Warning: This package indirectly depends on multiple versions of the same package. This is highly likely to cause a compile failure. package process-1.1.0.1 requires base-4.5.0.0 package pretty-1.1.1.0 requires base-4.5.0.0 package old-time-1.1.0.0 requires base-4.5.0.0 package old-locale-1.0.0.4 requires base-4.5.0.0 package filepath-1.3.0.0 requires base-4.5.0.0 package directory-1.1.0.2 requires base-4.5.0.0 package deepseq-1.3.0.0 requires base-4.5.0.0 package containers-0.4.2.1 requires base-4.5.0.0 package bytestring-0.9.2.1 requires base-4.5.0.0 package array-0.4.0.0 requires base-4.5.0.0 package Win32-2.2.2.0 requires base-4.5.0.0 package filepath-1.3.0.0 requires base-4.5.1.0 package Cabal-1.16.0.3 requires base-4.5.1.0 package Cabal-1.16.0.3 requires filepath-1.3.0.0 package process-1.1.0.1 requires filepath-1.3.0.0 package directory-1.1.0.2 requires filepath-1.3.0.0 package integer-gmp-0.4.0.0 requires ghc-prim-0.2.0.0 package bytestring-0.9.2.1 requires ghc-prim-0.2.0.0 package base-4.5.0.0 requires ghc-prim-0.2.0.0 package integer-gmp-0.4.0.0 requires ghc-prim-0.2.0.0 package base-4.5.1.0 requires ghc-prim-0.2.0.0 package base-4.5.1.0 requires integer-gmp-0.4.0.0 package base-4.5.0.0 requires integer-gmp-0.4.0.0 Building Cabal-1.16.0.3... Preprocessing library Cabal-1.16.0.3... <command line>: cannot satisfy -package-id array-0.4.0.0-3cf1bc3f5cd0078adea24752c18081b9 (use -v for more information) cabal: Error: some packages failed to install: Cabal-1.16.0.3 failed during the building phase. The exception was: ExitFailure 1 cabal-install-1.16.0.2 depends on Cabal-1.16.0.3 which failed to install. -------------------------------------------

5 8

On Windows defragment (Defraggler'ize, etc) the hard drive and turn off your A/V before installing cabal-install :)
by KC 20 Nov '12

20 Nov '12

:) Casey -- -- Regards, KC

1 0

cabal errors
by Gregory Guthrie 20 Nov '12

20 Nov '12

I did a package check, and I always get a ton of these things: Warning: haddock-html: E:\Plang\Haskell Platform\lib\extralibs\doc\haskell-src-1.0.1.4\html doesn't exist or isn't a directory Which I think is just missing documentation, so I ignore them. But this time I also got this: The following packages are broken, either because they have a problem listed above, or because they depend on a broken package. HTTP-4000.2.3 haskell-platform-2012.2.0.0 ghc-pkg list shows: Cabal-1.10.1.0 Cabal-1.10.2.0 Cabal-1.14.0 Cabal-1.14.0 GLUT-2.1.2.1 GLUT-2.1.2.1 GLUT-2.1.2.1 {HTTP-4000.2.3} HTTP-4000.2.5 ... {haskell-platform-2012.2.0.0} haskell-platform-2012.4.0.0 haskell-src-1.0.1.4 haskell-src-1.0.1.4 haskell-src-1.0.1.5 haskell-src-1.0.1.5 (haskell2010-1.0.0.0) (haskell2010-1.1.0.1) (haskell2010-1.1.0.1) haskell98-1.1.0.1 (haskell98-2.0.0.1) (haskell98-2.0.0.1) Not sure what it all means, but looks somewhat goofy to me. I always just do "cabal installs", and an occasional "-force-reinstalls" when told that it is the only option, but recently when they might fail tried a "cabal-dev install" a few times, I assume that is what the "{}" entries are, but am not sure if they can all peacefully coexist. Do I need to do a reset and start over? I hope not, as it took me many hours of fiddling to install some packages like glut, wxcore, and a few others. Argh. -------------------------------------------

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Reactive-Banana-Wx Install Trouble
by Ian 19 Nov '12

19 Nov '12

Hi Everyone, I'm currently trying to install reactive-banana-wx on OSX. Whenever I try to cabal install it though, I get this error back: [1 of 1] Compiling Main ( /var/folders/yy/k1kyw7252q1f_01xv4q5nnj40000gn/T/reactive-banana-wx-0.7.1.0-91555/reactive-banana-wx-0.7.1.0/Setup.hs, /var/folders/yy/k1kyw7252q1f_01xv4q5nnj40000gn/T/reactive-banana-wx-0.7.1.0-91555/reactive-banana-wx-0.7.1.0/dist/setup/Main.o ) /var/folders/yy/k1kyw7252q1f_01xv4q5nnj40000gn/T/reactive-banana-wx-0.7.1.0-91555/reactive-banana-wx-0.7.1.0/Setup.hs:10:22: Couldn't match expected type `Distribution.Simple.Setup.BuildFlags' with actual type `Cabal-1.16.0.3:Distribution.Simple.Setup.BuildFlags' Expected type: Args -> Distribution.Simple.Setup.BuildFlags -> Distribution.PackageDescription.PackageDescription -> Distribution.Simple.LocalBuildInfo.LocalBuildInfo -> IO () Actual type: Cabal-1.16.0.3:Distribution.Simple.UserHooks.Args -> Cabal-1.16.0.3:Distribution.Simple.Setup.BuildFlags -> Cabal-1.16.0.3:Distribution.PackageDescription.PackageDescription -> Cabal-1.16.0.3:Distribution.Simple.LocalBuildInfo.LocalBuildInfo -> IO () In the return type of a call of `appBundleBuildHook' In the `postBuild' field of a record cabal: Error: some packages failed to install: reactive-banana-wx-0.7.1.0 failed during the configure step. The exception was: ExitFailure 1 A couple of things; The version of cabal installed is: cabal-install version 0.14.0 using version 1.14.0 of the Cabal library The version of GHC that I'm using is: The Glorious Glasgow Haskell Compilation System, version 7.4.2 One other thing I should probably note is that I have cabal-macosx installed, but whenever I try to just call it by saying "cabal-macosx" it doesn't work, I have to tunnel down into the actual macosx-app to build any wx stuff. I'm not sure if I'm just using it wrong (I'm quite new to the wx stuff) or if it's a problem with the installation. Any help on these two (possibly related) problems would be fantastic. Cheers, Ian

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[repa] beginner questions
by Dmitry Malikov 19 Nov '12

19 Nov '12

Playing around with repa arrays and got some questions. 1) How I can get list of indexes of array that suffice some predicate? > a1 AUnboxed (Z :. 3) (fromList [False,False,True]) it :: Array U (Z :. Int) Bool Indexes of element that satisfying specific predicate could be obtained like that: > (\a p → Data.List.map (subtract 1 . snd) $ filter (p . fst) $ zip (toList a) [1..]) a1 (== False) [0,1] Looks ugly. How REPA users used to do filtering like that without converting to list? 2) How can I apply some function `f' to each row of 2D array `a' and collect results in single value? f ∷ (Shape sh, Source r Bool) ⇒ Array r sh Bool → Bool f a = (== toList a) $ foldl1 (Prelude.zipWith (||)) $ Prelude.map toList $ foldl (\l k -> filter (\x -> x ! (Z :. k) == False) l) [b1,b2,b3,b4] $ findWhich (== False) a and ∷ [Bool] → Bool [a1,a2] :: [Array U (Z :. Int) Bool] Having all that I could find what I want like that: and $ map f [a1,a2] > True All going on ridiculous and ugly because: - 2D arrays are not 2D arrays but lists of 1D arrays b1,b2,b3,b4,a1,a2 ∷ Array U (Z :. Int) Bool b1 = fromListUnboxed (Z :. (3::Int)) [False, True, False] b2 = fromListUnboxed (Z :. (3::Int)) [False, False, False] b3 = fromListUnboxed (Z :. (3::Int)) [False, False, True] b4 = fromListUnboxed (Z :. (3::Int)) [True, False, False] a1 = fromListUnboxed (Z :. (3::Int)) [False, False, True] a2 = fromListUnboxed (Z :. (3::Int)) [True, True, True] How 2D array could be split to list of 1D arrays? - redundant usage of `toList'; all operations are list-specified. How `f' could be rewritten in REPA terms? -- Best regards, dmitry malikov !

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