August 2013 - Haskell-Cafe

ANN: hspec-smallcheck - SmallCheck support for the Hspec testing framework
by Simon Hengel 13 Aug '13

13 Aug '13

Hi, I'm glad to announce SmallCheck support [1] for the Hspec testing framework. A tiny example on how to use it is here: https://github.com/hspec/hspec-smallcheck/blob/master/example/Spec.hs More documentation for Hspec is here: http://hspec.github.io/ Cheers, Simon [1] http://hackage.haskell.org/package/hspec-smallcheck

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Reminder: today is the deadline for HIW talk proposals (Haskell Implementor's Workshop)
by Ryan Newton 13 Aug '13

13 Aug '13

If you would like to give a talk pertaining to Haskell implementation (including libraries). Please submit a short abstract below. See you in Boston! -Ryan * Call for Talks* ACM SIGPLAN Haskell Implementors' Workshop http://haskell.org/haskellwiki/HaskellImplementorsWorkshop/2013 Boston, USA, September 22th, 2013 The workshop will be held in conjunction with ICFP 2013 http://www.icfpconference.org/icfp2013/ Important dates Proposal Deadline: 13th August 2013 (by midnight, any timezone) Notification: 27th August 2013 Workshop: 22th September 2013

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Diagrams and GTK
by Michael Oswald 13 Aug '13

13 Aug '13

Hello, I am currently writing an application which draws the structure of some packets with help of the diagrams library directly to a GTK GUI. Now the packets can have several hundreds of parameters which have to be drawn so it takes some seconds to calculate the diagram itself. Of course this now blocks the GUI thread, so the basic idea was to put the calculation in a separate thread. Unfortunately this doesn't work as lazyness kicks in and the final diagram is calculated when it is rendered and not evaluated before. Using seq didn't help (because of WHNF) and there seems to be no deepseq instance for the diagrams. Does somebody has an idea on how to speed this up / get the diagram evaluated strictly as especially scrolling the DrawingArea is now really a pain? lg, Michael

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ANN: libxkbcommon bindings
by Auke Booij 13 Aug '13

13 Aug '13

There's a lot of work nowadays towards replacing the X11 infrastructure. Notably, wayland intends to replace some of the functionality that X.Org now provides, and it uses libxkbcommon to replace the X11 XKB.h keyboard event parsing code (actually it is not a dependency, but it is the de facto standard). I think it would be great if haskell supports these new libraries as soon as they are being used, which is why I wrote haskell FFI bindings for libxkbcommon. Partly because I am not exactly an experienced haskell developer, and partly because I am unsure how users will use libxkbcommon, at this point haskell-xkbcommon is rather thin. I intend to add a layer of code that makes this look more haskelly based on your feedback. Hence, feedback is MOST welcome in any area, be it code style, documentation, or API preferences. I did not upload haskell-xkbcommon to hackage yet - should I at this stage? https://github.com/tulcod/haskell-xkbcommon PS: If this turns out to be a success, I'd like to develop wayland bindings as well, so if you have anything to say about that feel free to contact me.

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Default query for AcidState?
by Kyle Hanson 12 Aug '13

12 Aug '13

I am looking for something with a type signature like this: grabAcidState :: AcidState as -> IO as basically I just want to return my data from database abstractly or based on a class. The reason for this is because I want to have a class instance of state and then I can implement my library like so: data MyCoolData :: MyCoolData T.Text class HasCoolData a where getCoolDataList :: a -> MyCoolData grabStoredList :: HasCoolData as => AcidState as -> IO [MyCoolData] grabStoredList as = do cs <- grabAcidState as return $ getCoolDataList cs and users could implement it like so: data AppState = AppState { someCoolData :: [MyCoolData] } instance HasCoolData AppState { getCoolDataList = someCoolData } However trying to implement this simple behavior has been proving quite difficult. Maybe I am making this too difficult and I should just have a seperate AcidState datatype for my library. Any help would be appreciated.

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ANN: restricted-workers-0.1
by Daniel F 12 Aug '13

12 Aug '13

Introducing: restricted-workers library, version 0.1.0. This library provides an abstract interface for running various kinds of workers under resource restrictions. It is being developed as part of the interactive-diagrams project and you can read more about the origins of the library in my GSoC report: <http://parenz.wordpress.com/2013/07/15/interactive-diagrams-gsoc-progress-r…> The library provides a convenient way of running worker processes, saving data obtained by the workers at start-up, a simple pool abstraction and a configurable security and resource limitations. Right now there are several kinds of security restrictions that could be applied to the worker process: - RLimits - chroot jail - custom process euid - cgroups - process niceness - SELinux security context You can read more about the library on the wiki: <https://github.com/co-dan/interactive-diagrams/wiki/Restricted-Workers> The library has been uploaded to hackage and you can install it using cabal-install. -- Thanks -- Daniil Frumin

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Value-weak hash tables in Haskell ?
by Aleksey Uymanov 11 Aug '13

11 Aug '13

Hello, haskellers. Is there any package implementing magic hash tables weak in value? I mean when the value is garbage collected, then this key+value authomatically removes from the hash table. -- Aleksey Uymanov <s9gf4ult(a)gmail.com>

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Rank N Kinds
by Wvv 10 Aug '13

10 Aug '13

It was discussed a bit here: http://ghc.haskell.org/trac/ghc/ticket/8090 Rank N Kinds: Main Idea is: If we assume an infinite hierarchy of classifications, we have True :: Bool :: * :: ** :: *** :: **** :: ... Bool = False, True, ... * = Bool, Sting, Maybe Int, ... ** = *, *->Bool, *->(*->*), ... *** = **, **->*, (**->**)->*, ... ... RankNKinds is also a part of lambda-cube. PlyKinds is just type of ** (Rank2Kinds) class Foo (a :: k) where <<==>> class Foo (a :: **) where *** is significant to work with ** data and classes; more general: Rank(N)Kinds is significant to work with Rank(N-1)Kinds First useful use is in Typeable. In GHC 7.8 class Typeable (a::k) where ... <<==>> class Typeable (a ::**) where ... But we can't write data Foo (a::k)->(a::k)->* ... deriving Typeable If we redeclare class Typeable (a ::***) where ... or even class Typeable (a ::******) where ... it becomes far enough for many years I'm asking to find other useful examples -- View this message in context: http://haskell.1045720.n5.nabble.com/Rank-N-Kinds-tp5733482.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Installling Leksah on ghc7.6.3 with haskell-platform 2013?
by Carlo Hamalainen 10 Aug '13

10 Aug '13

Hi, I'm trying to install Leksah from hackage on my Debian testing laptop, which has ghc 7.6.3 and the Haskell Platform 2013. I fixed a bunch of errors about "catch" not being exported from the Prelude, but now I'm stuck on these two errors in leksah-server-0.8.0.5: [10 of 13] Compiling IDE.Utils.GHCUtils ( src/IDE/Utils/GHCUtils.hs, dist/build/IDE/Utils/GHCUtils.o ) src/IDE/Utils/GHCUtils.hs:94:40-62: Not in scope: data constructor `Opt_ReadUserPackageConf' src/IDE/Utils/GHCUtils.hs:161:44-50: Not in scope: data constructor `Opt_Cpp' Perhaps you meant one of these: `Opt_CSE' (imported from GHC), `Opt_Pp' (imported from GHC) Where have Opt_ReadUserPackageConf and Opt_Cpp gone in ghc 7.6.3? Cheers, -- Carlo

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Importing more modules by default
by aditya bhargava 10 Aug '13

10 Aug '13

Hi there, It seems like every Haskell program I write imports the following modules: Control.Monad Control.Applicative Data.Maybe Data.List Is there a good reason why these modules aren't imported by default? When I write a simple script usually a 1/4th of the script is just imports, and my code just looks uglier. Adit

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