- Haskell-Cafe - Haskell.org

Better versions of this code
by Tyson Whitehead 24 Oct '13

24 Oct '13

Hey All, I wrote some quick code to change mediawiki preformatted text (adjacent lines begining with a ' ') to nowiki blocks (first line with a ' ' and rest enclosed in <nowiki>...</nowiki> quotes). http://lpaste.net/94688 I frequently find myself pretty unsatisfied with this type of code though. Anyone have any rewrites that would help teach me how to do this more elegantly in the future. Thanks! -Tyson PS: The mediawiki text I was using the above on has no existing <nowiki>...</nowiki> blocks.

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Why do I need UndecidableInstances?
by Alejandro Serrano Mena 24 Oct '13

24 Oct '13

Dear café, I'm trying to compile a set of simple examples using Functional Dependencies. One of the first ones is the case of natural numbers, which I've defined along with some operations as: data Zero data Succ a class Plus x y z | x y -> z instance Plus Zero x x instance Plus x y z => Plus (Succ x) y (Succ z) class Max x y z | x y -> z instance Max Zero y y instance Max (Succ x) Zero (Succ x) instance Max x y z => Max (Succ x) (Succ y) (Succ z) I thought the compiler would accept this only with the extensions EmptyDataDecls, MultiParamTypeClasses, FunctionalDependencies and FlexibleInstances. But, to my surprise, GHC is also asking me for UndecidableInstances. Why is this the case? Thanks in advance :)

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mongoDB performance problem
by 陈灿华 24 Oct '13

24 Oct '13

hi, any also find that mongoDB package is too slow. I have two programs that are almost the same, which one dumps document to stdout, the other one insert into mongodb, and the first one is hundreds times faster than the mongodb one. any one has ideas to tune the second one ? Thanks.

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Stackage with GHC 7.8 has started
by Michael Snoyman 24 Oct '13

24 Oct '13

Hi everyone, I wanted to announce that FP Complete is now running a Jenkins job to build Stackage with GHC 7.8. You can see the current results in the relevant Github issue[1]. Essentially, we're still trying to get version bounds updated so that a build can commence. I'd like to ask two things from the community: * If you have a package with a restrictive upper bound, now's a good time to start testing that package with GHC 7.8 and relaxing those upper bounds. It would be great if, when GHC 7.8 is released, a large percentage of Hackage already compiled with it. * If you have a package on Hackage that is not yet on Stackage, now's a great time to add it. We're going to be doing daily builds against three versions of GHC (7.4.2, 7.6.3, and 7.8), which will help ensure your packages continue to build consistently. Michael [1] https://github.com/fpco/stackage/issues/128

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Re: [Haskell-cafe] [ANN] IHaskell -- Haskell for Interactive Computing (via IPython)
by Andrew Gibiansky 24 Oct '13

24 Oct '13

Thank you for the correction, Ivan. I've pushed that change to IHaskell.cabal so that this doesn't trip anyone up in the future. IHaskell assumes that when you run 'cabal install', your IHaskell executable will be on the $PATH. (In order to run 'IHaskell setup', both your shell and IHaskell itself must be able to detect where the IHaskell executable is, because it needs to put that information into the IPython configuration it generates.) -- Andrew On Wed, Oct 23, 2013 at 2:18 AM, Triwanto Simanjuntak < simanjuntak.triwanto(a)gmail.com> wrote: > Andrew, > > The solution from Ivan made the installation of IHaskell successful. > However when creating IPython profile by invoking, "IHaskell setup", > gave error, "IHaskell: command not found". Is it because the > installation didn't make IHaskell on $Path ? > > Triwanto > simanjuntak.triwanto(a)gmail.com > > > On Wed, Oct 23, 2013 at 2:39 PM, Ivan Lazar Miljenovic > <ivan.miljenovic(a)gmail.com> wrote: > > On 23 October 2013 16:53, Andrew Gibiansky <andrew.gibiansky(a)gmail.com> > wrote: > >> Triwanto, > >> > >> IHaskell depends on the 'uuid' package and requires version 1.2.*. > Check to > >> make sure you have uuid installed. I build it with 1.2.13, and it looks > like > >> the most recent one is 1.2.14, which should also have that module [1]. > So, > >> before building, make sure you have uuid==1.2.* installed - I'm sort of > new > >> to cabal packaging, so perhaps my dependencies are not specified quite > >> correctly, but that is the issue that message seems to point to. > >> > >> Let me know how it goes. The full list of dependencies from the *.cabal > file > >> is as follows, in case you have other problems: > >> build-depends: base ==4.6.*, > >> zeromq3-haskell ==0.5.*, > >> aeson ==0.6.*, > >> MissingH ==1.2.*, > >> basic-prelude ==0.3.*, > >> classy-prelude ==0.6.*, > >> bytestring ==0.10.*, > >> uuid ==1.2.*, > >> containers ==0.5.*, > >> haskell-src-exts ==1.14.*, > >> ghc ==7.6.*, > >> ghc-paths ==0.1.*, > >> random ==1.0.*, > >> strict ==0.3.*, > >> shelly ==1.3.*, > >> text ==0.11.* > >> > >> Note that zeromq3-haskell will require zmq3 installed, and in saucy > that is > >> provided via 'apt-get install libzmq3-dev', I think. > > > > The .V4 module only seems to have appeared in version 1.2.6; as such > > you'll need to change the appropriate line to "uuid >= 1.2.6 && < 1.3" > > (assuming you have indeed tested and found that your code won't work > > with the 1.3.x versions). > > > >> > >> Andrew > >> > >> [1] > >> > http://haddocks.fpcomplete.com/fp/7.4.2/20130922-179/uuid/Data-UUID-V4.html > >> > >> > >> On Tue, Oct 22, 2013 at 10:11 PM, Triwanto Simanjuntak > >> <simanjuntak.triwanto(a)gmail.com> wrote: > >>> > >>> Andrew, > >>> > >>> I tried to install IHaskell on Ubuntu 13.10 (Saucy 64 bit) and recieved > >>> the following error > >>> > >>> Resolving dependencies... > >>> Configuring IHaskell-0.1.0.0... > >>> Building IHaskell-0.1.0.0... > >>> Preprocessing executable 'IHaskell' for IHaskell-0.1.0.0... > >>> > >>> IHaskell/Message/UUID.hs:10:8: > >>> Could not find module `Data.UUID.V4' > >>> Perhaps you meant > >>> Data.UUID.V1 (from uuid-1.2.3) > >>> Data.UUID.V3 (from uuid-1.2.3) > >>> Data.UUID.V5 (from uuid-1.2.3) > >>> Use -v to see a list of the files searched for. > >>> Failed to install IHaskell-0.1.0.0 > >>> cabal: Error: some packages failed to install: > >>> IHaskell-0.1.0.0 failed during the building phase. The exception was: > >>> ExitFailure 1 > >>> > >>> Any idea how to solve it? > >>> > >>> Thanks, > >>> > >>> Triwanto > >>> > >>> > >>> On Tuesday, October 22, 2013 4:32:10 AM UTC+7, Andrew Gibiansky wrote: > >>>> > >>>> Hey everyone! > >>>> > >>>> I'm excited to announce the initial release of IHaskell, a Haskell > >>>> language kernel for IPython: > >>>> > >>>> http://gibiansky.github.io/IHaskell > >>>> > >>>> IHaskell allows IPython to communicate with the kernel and evaluate > >>>> Haskell code. This enables using IPython interfaces such as console, > >>>> qtconsole, and most importantly, IPython notebook with Haskell. The > IPython > >>>> Notebook supports image, HTML, and LaTeX output, which enables things > such > >>>> as Javascript viewers for complex data structures or embedded graphs > and > >>>> makes it a great platform for interactive computing. > >>>> > >>>> You can take a look at the code and install instructions here: > >>>> > >>>> https://github.com/gibiansky/IHaskell > >>>> > >>>> A general overview of the architecture is available as well: > >>>> > >>>> http://andrew.gibiansky.com/blog/ipython/ipython-kernels/ > >>>> > >>>> Contributing: IHaskell is a very young project, but one that I think > >>>> would make a great contribution to the Haskell community. There's > still tons > >>>> and tons left to do before it's on par with what IPython notebook is > capable > >>>> of, so if you're at all interested in contributing, please get in > touch! > >>>> I've tried to keep everything well-documented and readable, but I > will also > >>>> be happy to answer questions about the code myself. > >>>> > >>>> If you find any bugs or edge cases or installation difficulties, > please > >>>> send me an email or create a Github issue for it! > >>>> > >>>> Thanks, > >>>> -- Andrew Gibiansky > >>>> > >>>> > >> > >> > >> _______________________________________________ > >> Haskell-Cafe mailing list > >> Haskell-Cafe(a)haskell.org > >> http://www.haskell.org/mailman/listinfo/haskell-cafe > >> > > > > > > > > -- > > Ivan Lazar Miljenovic > > Ivan.Miljenovic(a)gmail.com > > http://IvanMiljenovic.wordpress.com >

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What's wrong with Hackage lately?
by Nikita Volkov 23 Oct '13

23 Oct '13

Recently two bugs settled on Hackage: 1. Page not found<http://hackage.haskell.org/package/base-4.6.0.1/docs/GHC-IO-Exception.html> for definitely existing pages. 2. Links starting with "file:///". Try any link on this page<http://hackage.haskell.org/package/pipes-network-0.6.0/docs/Pipes-Network-T…>, for example. Since it hasn't gotten fixed in at least a week, I am now wondering: why and where to report this?

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HackChi #1 - Nov 9 @ 1PM
by Jeremy Shaw 23 Oct '13

23 Oct '13

Hello, We are pleased to announce the first ever(?) Chicago Haskell Hackathon. There is a G+ invite here: https://plus.google.com/u/0/events/cc4njkf8kh5aho6soboisv6c7rc?authkey=CJD9… Hopefully I have the permissions set correctly. The contents of the invite are duplicated below. - jeremy Sat, November 9, 1:00 PM 1834 Ridge Ave #124, Evanston, IL 60201 We are please to announce the first Chicago Area Haskell Hackathon. What is as Hackathon? A Hackathon is basically just a bunch of people getting together and hacking on the Haskell code of their choice. It’s a great chance to meet other local Haskell hackers, discuss ideas, or just hack on code without other distractions. The Hackathon is open to people of all ages, experience, genders, races, orientations, etc. Never used Haskell before? We are going to kick things off with a ‘Get Started with Haskell’ session. Bring your laptop, and we’ll help you get Haskell installed and working and get your started on ‘Learn You a Haskell’ and other Haskell learning resources. Jeremy Shaw has volunteered to host this Hackathon at his place. This means we can bring our own food and drink and not have to worry about staying at a coffee house or other business for too long. You are highly encouraged to bring food, drinks, beer, etc. You can use the stove, oven, fridge, and propane grill if needed. The address is: 1834 Ridge Ave #124 Evanston, IL 60201 Dial 124 on the callbox to get in. You can also send email to jeremy(a)n-heptane.com or call 619-301-7429. The callbox sometimes fails to get through on the first try, so call more than once if you get sent to voicemail. Easily accessible via public transportation. Take the Purple Line or Metra and get off at the Davis stop. Head west towards Ridge. Cross over ridge and then head north 2-3 blocks on Ridge.

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Re: [Haskell-cafe] [ANN] IHaskell -- Haskell for Interactive Computing (via IPython)
by Andrew Gibiansky 23 Oct '13

23 Oct '13

Triwanto, IHaskell depends on the 'uuid' package and requires version 1.2.*. Check to make sure you have uuid installed. I build it with 1.2.13, and it looks like the most recent one is 1.2.14, which should also have that module [1]. So, before building, make sure you have uuid==1.2.* installed - I'm sort of new to cabal packaging, so perhaps my dependencies are not specified quite correctly, but that is the issue that message seems to point to. Let me know how it goes. The full list of dependencies from the *.cabal file is as follows, in case you have other problems: build-depends: base ==4.6.*, zeromq3-haskell ==0.5.*, aeson ==0.6.*, MissingH ==1.2.*, basic-prelude ==0.3.*, classy-prelude ==0.6.*, bytestring ==0.10.*, uuid ==1.2.*, containers ==0.5.*, haskell-src-exts ==1.14.*, ghc ==7.6.*, ghc-paths ==0.1.*, random ==1.0.*, strict ==0.3.*, shelly ==1.3.*, text ==0.11.* Note that zeromq3-haskell will require zmq3 installed, and in saucy that is provided via 'apt-get install libzmq3-dev', I think. Andrew [1] http://haddocks.fpcomplete.com/fp/7.4.2/20130922-179/uuid/Data-UUID-V4.html On Tue, Oct 22, 2013 at 10:11 PM, Triwanto Simanjuntak < simanjuntak.triwanto(a)gmail.com> wrote: > Andrew, > > I tried to install IHaskell on Ubuntu 13.10 (Saucy 64 bit) and recieved > the following error > > Resolving dependencies... > Configuring IHaskell-0.1.0.0... > Building IHaskell-0.1.0.0... > Preprocessing executable 'IHaskell' for IHaskell-0.1.0.0... > > IHaskell/Message/UUID.hs:10:8: > Could not find module `Data.UUID.V4' > Perhaps you meant > Data.UUID.V1 (from uuid-1.2.3) > Data.UUID.V3 (from uuid-1.2.3) > Data.UUID.V5 (from uuid-1.2.3) > Use -v to see a list of the files searched for. > Failed to install IHaskell-0.1.0.0 > cabal: Error: some packages failed to install: > IHaskell-0.1.0.0 failed during the building phase. The exception was: > ExitFailure 1 > > Any idea how to solve it? > > Thanks, > > Triwanto > > > On Tuesday, October 22, 2013 4:32:10 AM UTC+7, Andrew Gibiansky wrote: >> >> Hey everyone! >> >> I'm excited to announce the initial release of IHaskell, a Haskell >> language kernel for IPython: >> >> http://gibiansky.github.io/**IHaskell<http://gibiansky.github.io/IHaskell> >> >> IHaskell allows IPython to communicate with the kernel and evaluate >> Haskell code. This enables using IPython interfaces such as console, >> qtconsole, and most importantly, IPython notebook with Haskell. The IPython >> Notebook supports image, HTML, and LaTeX output, which enables things such >> as Javascript viewers for complex data structures or embedded graphs and >> makes it a great platform for interactive computing. >> >> You can take a look at the code and install instructions here: >> >> https://github.com/gibiansky/**IHaskell<https://github.com/gibiansky/IHaskell> >> >> A general overview of the architecture is available as well: >> >> http://andrew.gibiansky.com/**blog/ipython/ipython-kernels/<http://andrew.gibiansky.com/blog/ipython/ipython-kernels/> >> >> Contributing: IHaskell is a very young project, but one that I think >> would make a great contribution to the Haskell community. There's still >> tons and tons left to do before it's on par with what IPython notebook is >> capable of, so if you're at all interested in contributing, please get in >> touch! I've tried to keep everything well-documented and readable, but I >> will also be happy to answer questions about the code myself. >> >> If you find any bugs or edge cases or installation difficulties, please >> send me an email or create a Github issue for it! >> >> Thanks, >> -- Andrew Gibiansky >> >> >>

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[ANN] IHaskell -- Haskell for Interactive Computing (via IPython)
by Andrew Gibiansky 22 Oct '13

22 Oct '13

Hey everyone! I'm excited to announce the initial release of IHaskell, a Haskell language kernel for IPython: http://gibiansky.github.io/IHaskell IHaskell allows IPython to communicate with the kernel and evaluate Haskell code. This enables using IPython interfaces such as console, qtconsole, and most importantly, IPython notebook with Haskell. The IPython Notebook supports image, HTML, and LaTeX output, which enables things such as Javascript viewers for complex data structures or embedded graphs and makes it a great platform for interactive computing. You can take a look at the code and install instructions here: https://github.com/gibiansky/IHaskell A general overview of the architecture is available as well: http://andrew.gibiansky.com/blog/ipython/ipython-kernels/ Contributing: IHaskell is a very young project, but one that I think would make a great contribution to the Haskell community. There's still tons and tons left to do before it's on par with what IPython notebook is capable of, so if you're at all interested in contributing, please get in touch! I've tried to keep everything well-documented and readable, but I will also be happy to answer questions about the code myself. If you find any bugs or edge cases or installation difficulties, please send me an email or create a Github issue for it! Thanks, -- Andrew Gibiansky

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Extract text from PDF file: need testers
by Yuras Shumovich 21 Oct '13

21 Oct '13

Hello, I just uploaded new version of pdf-toolbox suite. Now it supports text extraction, see http://hackage.haskell.org/package/pdf-toolbox-document-0.0.2.0/docs/Pdf-To… New library, pdf-toolbox-content, contains low level tools for text extraction. For example, one can extract glyphs with exact positions. It can be used e.g. to implement text selection in PDF viewer (see screenshots). Is anybody interested in that functionality? I tested it on all PDF files in my ~/Downloads, but there is a number of corner cases that are not handled because I never saw them in the wild. So, if you are interested, please try it out and report any issue. The easiest way is to install pdf-toolbox-viewer (not on Hackage, see https://github.com/Yuras/pdf-toolbox/tree/master/viewer , it depends on gtk2hs) and run it with path to PDF file as an argument. Or you can just use pageExtractText function directly: import System.IO import Pdf.Toolbox.Document main = withBinaryFile "input.pdf" ReadMode $ \handle -> runPdfWithHandle handle knownFilters $ do pdf <- document catalog <- documentCatalog pdf rootNode <- catalogPageNode catalog count <- pageNodeNKids rootNode liftIO $ print count -- the first page of the document page <- pageNodePageByNum rootNode 0 txt <- pageExtractText page liftIO $ print txt Few screenshots (please let me know if you can't access them): - render via ImageMagick: https://docs.google.com/file/d/0B0K_fl2fc1ZgcnVtZXhFTUx5ekE/edit?usp=sharing - render extracted text with correct positions: https://docs.google.com/file/d/0B0K_fl2fc1ZgZE52X0hMcVNnaG8/edit?usp=sharing - combined image: https://docs.google.com/file/d/0B0K_fl2fc1ZgaUE5Qkt6S19VQlE/edit?usp=sharing On Hackage: - pdf-toolbox-document: http://hackage.haskell.org/package/pdf-toolbox-document - pdf-toolbox-core: http://hackage.haskell.org/package/pdf-toolbox-core - pdf-toolbox-content: http://hackage.haskell.org/package/pdf-toolbox-content Thanks, Yuras

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