- Haskell-Cafe - Haskell.org

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

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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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Reaching Max Bolingbroke
by Roman Cheplyaka 18 Nov '12

18 Nov '12

For the last two months I've been trying to reach Max Bolingbroke via his hotmail address, github and linkedin, but did not succeed. Does anyone know if he's well? If someone could help by telling him that I'd like to get in touch, I'd appreciate that. Roman

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Re: [Haskell-cafe] List all multiply/add combinations
by Rune Harder Bak 18 Nov '12

18 Nov '12

On Sun, Nov 18, 2012 at 2:04 PM, Stefan Klinger <all-lista(a)stefan-klinger.de> wrote: > Sounds like you would want to enumerate all possible *abstract* syntax > trees, these implicitly have exactly the necessary parentheses. I'd do > this recursively, splitting the sequence of numbers in two at all > possible places, and then combine the corresponding results with all > possible operators. That was my second idea, but just doing it naively resulted in many equivalent calculations, so I thought there might be a better way to view the problem. But as Artyom showed On Sat, Nov 17, 2012 at 11:37 PM, Artyom Kazak <artyom.kazak(a)gmail.com> wrote: > Indentation messed up… I have pasted the code here: http://hpaste.org/77864 enumerating the abstract syntax tree is actually (or at least could be) the way to go! Thanks a lot! What I need is a little bit different, but now I feel I'm on the right track! This is my first question to the café and it makes me a lot more certain using Haskell for production, when you can get this kind of quick and thorough help when in doubt. Great community! -Rune

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Re: [Haskell-cafe] Automation of external library installation in haskell package.
by Maksymilian Owsianny 18 Nov '12

18 Nov '12

Hi Johan, Originally, that was my intention, to have the user install the library himself, and I have specified the extra-libraries field in the .cabal file. However, the problem with hackage not being able to build the package, and therefore generate documentation, remains. So conversely my question would be if there is any way to get around this? Best regards, Max. On Sun, Nov 18, 2012 at 8:21 PM, Johan Tibell <johan.tibell(a)gmail.com>wrote: > Hi Maksymilian, > > Generally I don't recommend that you bundle C libraries with your > Cabal package. On Linux users should get C libraries through their > distribution's package manager. The people who package Cabal packages > for Debian (as Debian packages) can then have the Debian package they > create depend on the C library's package, making sure it gets > installed automatically. > > You can list the library name in an extra-libraries field in your > .cabal file to communicate to users that they need this library > installed. There's a little bit of documentation on the > extra-libraries field in the Cabal User Guide > (http://www.haskell.org/cabal/users-guide/developing-packages.html#library > ). > > Cheers, > Johan >

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Automation of external library installation in haskell package.
by Maksymilian Owsianny 18 Nov '12

18 Nov '12

Hello Haskell-Cafe, I have created a package that requires an external library to be present on the machine. Because of that, obviously, hackage fails to build it, and subsequently fails to generate documentation. So my question is, how should I go about configuring Cabal/Setup.hs to automatize the process to allow hackage to build it properly and also simplify the package installation for the user. The packages that I'm talking about are bindings to Awesomium<http://awesomium.com/> : awesomium-raw <http://hackage.haskell.org/package/awesomium-raw> and subsequently, the higher level ones that depend on it awesomium <http://hackage.haskell.org/package/awesomium> awesomium-glut <http://hackage.haskell.org/package/awesomium-glut> Specifically, the installation process for linux is described as follows: To install Awesomium, you'll need to add the shared library to your > system's library search path. On Ubuntu, you can use the following > commands: > > cd awesomium_v1.6.5_sdk_linux32 > sudo mkdir /usr/lib/awesomium-1.6.5 > sudo cp -r build/bin/release/* /usr/lib/awesomium-1.6.5 > sudo ldconfig /usr/lib/awesomium-1.6.5 > > So if anyone could give me some hints, or point me to package that have a similar, external-library-copying-and-registering installation process i would be grateful.

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Parsing different types, same typeclass
by José Lopes 18 Nov '12

18 Nov '12

Hello everyone, I was wondering if you could help me! So, I have a typeclass "Action" which defines method "run": class Action a where run :: a -> Int and two data types that are instances of this typeclass: data A = A Int deriving (Read, Show) instance Action A where run (A n) = n data B = B Int deriving (Read, Show) instance Action B where run (B n) = n Now, I want to parse either "A" or "B" from a String. I was thinking about something like this... parseAction :: (Action a, Read a) => String -> a parseAction str | "(A " `isPrefixOf` str = (read :: String -> A) str | "(B " `isPrefixOf` str = (read :: String -> B) str The problem is that when calling "parseAction" I get "ambiguous type constraints". How to implement a parse function for two distinct types that share the same typeclass "Action". Because after calling "parseAction" I don't whether "A" or "B" was returned: I only care that they are "Action" instances so I can call "run". Best regards, José

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A small step towards solving cabal hell.
by timothyhobbs＠seznam.cz 18 Nov '12

18 Nov '12

I've read a lot of negative regarding the problems with cabal and hackage. I've written quite a few of them myself. I want to propose a simple change in philosophy of packages. Haskell has inherited a philosophy from the imperative world, that there are two types of packages: Libraries and applications. Libraries are big collections of modules. Applications are big collections of modules. There is a difference from the perspective of the build system. Applications are big collections of modules that belong together and mutually rely upon each other for the application to work. Such that if one module is missing, the application cannot build and thus cannot do useful tasks. If an application doesn't build, then the maintainer has to go and fix that problem. This isn't perfect, I do not solve this problem in this email. Libraries don't always have this property. For example, XMonad.Layout.Column (http://hackage.haskell.org/packages/archive/xmonad-contrib/0.10/doc/html/XM…) has no mutual dependency on XMonad.Layout.Circle (http://hackage.haskell.org/packages/archive/xmonad-contrib/0.10/doc/html/XM…) . This is a feature of libraries that can and should be taken advantage of wherever possible :) We can and should, break up libraries into "books". I hold this opinion, because libraries are hard to maintain. If xmonad-contrib refuses to build, I open up it's source code, and see some hundred modules. I cannot, as a non-xmonad developer, imagine myself fixing such a large library. But if it was just one small module from that library I wanted, and it refused to build, and I opened it up, and there were just 3 files there. I wouldn't feel so overwhelmed. I would fix the problem myself. What I'm trying to say, is that "books" (small packages containing 3 modules or less) are so easy to maintain, that they really need no maintainer at all. Any idiot can fix one. But libraries, with their hundreds of modules, and seemingly endless dependencies, Can be much harder to maintain, and require a knowledgeable maintainer. So lets stop publishing libraries, and maintaining libraries, and listening to people crying when libraries don't build, and lets start writing books, and publishing really small packages, that are so simple anyone can fix them when they break even when they have no in depth knowledge of the package. Lets make a new guideline for "libraries" that if it is possible to split a library into two or more, non-mutually dependent parts, than we *should* split them such. Timothy PS, I noticed that yesod is already a collection of "books", but it appears to me, that these packages are STILL mutually dependent :(

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