February 2011 - Beginners

Anyone have problems with cabal and SDL?
by Tom Murphy 17 Jul '11

17 Jul '11

When I use Cabal to get any program which depends on the SDL library, this is the error I get. " checking for sdl-config... no checking for sdl11-config... no configure: error: *** SDL not found! Get SDL from www.libsdl.org. If you already installed it, check it's in the path. If problem remains, please send a mail to the address that appears in ./configure --version indicating your platform, the version of configure script and the problem. cabal: Error: some packages failed to install: Raincat-1.1.1.2 depends on SDL-0.6.2 which failed to install. SDL-0.6.2 failed during the configure step. The exception was: exit: ExitFailure 1 SDL-image-0.6.1 depends on SDL-0.6.2 which failed to install. SDL-mixer-0.6.1 depends on SDL-0.6.2 which failed to install. " I have SDL 1.2.14 (correctly) installed on my system. I'd really appreciate any help with this. Tom

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haskell for FPGAS
by David Blubaugh 09 May '11

09 May '11

To All, Has anyone developed HASKELL FOR FPGA development ?? Thank You, Daid Blubaugh

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dealing with chained functions
by Alec Benzer 20 Apr '11

20 Apr '11

Is there a generally accepted "better" way of dealing with the following: say I have three functions that all rely on output from each other. Ie, we get raw input, which one function processes. another function then requires the output from this function and produces some other output, which a third function then requires. would it be better to implement the functions like this: f1 :: a -> b f2 :: b -> c f3 :: c -> d final :: a -> d or like this: f1 :: a -> b f2 :: a -> c f3 :: a -> d Ie, in the latter set, f2 calls f1 on its input, and then proceeds to process it. f3 calls f2 on its input, etc. In the former case, final would just chain all three functions together itself (or I might just do it in main or somewhere else that's appropriate) Are one of these methods generally considered a better practice than the other, specifically in a functional context? My gut tells me that the former method looks more appropriate, but I'm not sure if it'd really be the accepted practice regardless of context, or if one might use either of these methods depending on the specifics of what they're doing. Or if it's just a matter of taste/opinion?

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HUnit - testing for failed pattern match
by Xavier Shay 25 Feb '11

25 Feb '11

Hello, Given the following contrived function: giveMeThree x | x == 3 = True How do I test with HUnit that 2 is invalid input? giveMeThreeTests = [ "Likes 3" ~: True ~=? giveMeThree 3 , "Dislikes 2" ~: ..... -- what? ] I couldn't find anything mentioned in the HUnit user guide. References to appropriate documentation appreciated. Cheers, Xavier

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Can't reproduce the build failure of my package on hackage
by Daniel Seidel 25 Feb '11

25 Feb '11

Hi, a while ago I uploaded a package to Hackage ( http://hackage.haskell.org/package/SBench ). I checked it with ghc-6.12.3 and it worked well. The uploaded version was tried to compile via ghc-7 and failed with the following log: cabal: dependencies conflict: haskell98-1.1.0.1 requires time ==1.2.0.3 however time-1.2.0.3 was excluded because gnuplot-0.4.1 requires time ==1.1.* Now, on Hackage, the latest haskell98 version is 1.1.0.0 and it does, at least directly, *not* depend on time. To figure out the problem I installed ghc-7.0.1 and tried to install my package. It worked. Can anyone give me a hint why compilation fails on Hackage and where haskell98-1.1.0.1 comes from? I want to upload a new version because I needed to adjust to the '-rtsopts' flag in ghc 7. Before doing so it would be great to ensure the new upload will compile on Hackage. A way might be to restrict haskell98 to be less or equal to 1.1.0.0, but I think it's not a good way. Cheers, Daniel.

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GTK Haskell and Error on Win32, anyone see the issue?
by Berlin Brown 23 Feb '11

23 Feb '11

I am following the steps outlined here but I am still getting errors related to my install of gtk Here is one of the first errors: tup\setup.exe ... Configuring cairo-0.12.0... setup.exe: Missing dependencies on foreign libraries: * Missing C libraries: z, cairo This problem can usually be solved by installing the system packages that provide these libraries (you may need the "-dev" versions). If the libraries are already installed but in a non-standard location then you can use the flags --extra-include-dirs= and --extra-lib-dirs= to specify where they are. http://www.haskell.org/haskellwiki/Gtk2Hs Here is the output: C:\Documents and Settings\Bot User>echo %LIB% C:\Program Files\Gtk+\lib C:\Documents and Settings\Bot User>echo %PKG_CONFIG_PATH% C:\Program Files\Gtk+\lib\pkgconfig;C:\ Program Files\Gtk+\include\libglade-2.0;C:\Program Files\libxml2\libxml2-dev_2.7.7-1_win32\lib\pkgconfig I got the install of GTK and everything worked: http://ftp.gnome.org/pub/GNOME/binaries/win32/glade3/3.6/glade3-3.6.7-with-… Microsoft Windows XP [Version 5.1.2600] C:\Documents and Settings\Bot User>cabal update Downloading the latest package list from hackage.haskell.org Version: C:\Documents and Settings\Bot User>ghc --version The Glorious Glasgow Haskell Compilation System, version 6.12.3 C:\Documents and Settings\Bot User>cabal install gtk2hs-buildtools Resolving dependencies... Configuring gtk2hs-buildtools-0.12.0... Preprocessing executables for gtk2hs-buildtools-0.12.0... ... hs\gtk2hsC2hs-tmp\GenBind.o ) [41 of 41] Compiling Main ( c2hs\toplevel\Main.hs, dist\build\gtk2hs C2hs\gtk2hsC2hs-tmp\Main.o ) Linking dist\build\gtk2hsC2hs\gtk2hsC2hs.exe ... Installing executable(s) in C:\Documents and Settings\Bot User\Application Data\cabal\bin Here is where it fails: C:\Documents and Settings\Bot User>cabal install gtk Resolving dependencies... C:\DOCUME~1\BOTBER~1\LOCALS~1\Temp\cairo-0.12.03164\cairo-0.12.0\Gtk2HsSetup.hs: 25: warning: #warning Setup.hs is guessing the version of Cabal. If compilation of Setup.hs fails use -DCABAL_VERSION_MINOR=x for Cabal version 1.x.0 when build ing (prefixed by --ghc-option= when using the 'cabal' command) [1 of 2] Compiling Gtk2HsSetup ( C:\DOCUME~1\BOTBER~1\LOCALS~1\Temp\cairo-0 .12.03164\cairo-0.12.0\Gtk2HsSetup.hs, C:\DOCUME~1\BOTBER~1\LOCALS~1\Temp\cairo- 0.12.03164\cairo-0.12.0\dist\setup\Gtk2HsSetup.o ) [2 of 2] Compiling Main ( C:\DOCUME~1\BOTBER~1\LOCALS~1\Temp\cairo-0 .12.03164\cairo-0.12.0\Setup.hs, C:\DOCUME~1\BOTBER~1\LOCALS~1\Temp\cairo-0.12.0 3164\cairo-0.12.0\dist\setup\Main.o ) Linking C:\DOCUME~1\BOTBER~1\LOCALS~1\Temp\cairo-0.12.03164\cairo-0.12.0\dist\se tup\setup.exe ... Configuring cairo-0.12.0... setup.exe: Missing dependencies on foreign libraries: * Missing C libraries: z, cairo This problem can usually be solved by installing the system packages that provide these libraries (you may need the "-dev" versions). If the libraries are already installed but in a non-standard location then you can use the flags --extra-include-dirs= and --extra-lib-dirs= to specify where they are. C:\DOCUME~1\BOTBER~1\LOCALS~1\Temp\glib-0.12.03164\glib-0.12.0\Gtk2HsSetup.hs:25 : warning: #warning Setup.hs is guessing the version of Cabal. If compilation of Setup.hs fails use -DCABAL_VERSION_MINOR=x for Cabal version 1.x.0 when buildin g (prefixed by --ghc-option= when using the 'cabal' command) [1 of 2] Compiling Gtk2HsSetup ( C:\DOCUME~1\BOTBER~1\LOCALS~1\Temp\glib-0. 12.03164\glib-0.12.0\Gtk2HsSetup.hs, C:\DOCUME~1\BOTBER~1\LOCALS~1\Temp\glib-0.1 2.03164\glib-0.12.0\dist\setup\Gtk2HsSetup.o ) [2 of 2] Compiling Main ( C:\DOCUME~1\BOTBER~1\LOCALS~1\Temp\glib-0. 12.03164\glib-0.12.0\Setup.hs, C:\DOCUME~1\BOTBER~1\LOCALS~1\Temp\glib-0.12.0316 4\glib-0.12.0\dist\setup\Main.o ) Linking C:\DOCUME~1\BOTBER~1\LOCALS~1\Temp\glib-0.12.03164\glib-0.12.0\dist\setu p\setup.exe ... Configuring glib-0.12.0... setup.exe: Missing dependencies on foreign libraries: * Missing C libraries: gobject-2.0, glib-2.0, intl This problem can usually be solved by installing the system packages that provide these libraries (you may need the "-dev" versions). If the libraries are already installed but in a non-standard location then you can use the flags --extra-include-dirs= and --extra-lib-dirs= to specify where they are. cabal: Error: some packages failed to install: cairo-0.12.0 failed during the configure step. The exception was: ExitFailure 1 gio-0.12.0 depends on glib-0.12.0 which failed to install. glib-0.12.0 failed during the configure step. The exception was: ExitFailure 1 gtk-0.12.0 depends on glib-0.12.0 which failed to install. pango-0.12.0 depends on glib-0.12.0 which failed to install. C:\Documents and Settings\Bot User> -- Berlin Brown (berlin dot brown at gmail.com) http://botnode.com http://berlinbrowndev.blogspot.com/

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Help with GHC Packages Installation on Fedora 14
by Hong Yang 23 Feb '11

23 Feb '11

Hi, I installed a Fedora 14 virtual machine on my home Windows desktop. Then I tried to install GHC packages on Fedora by typing "yum install ghc" as root, and got the following error: "Error: Cannot retrieve repository metadata (repomd.xml) for repository: fedora. Please verify its path and try again." What should I do now to fix this error? Thanks, Hong

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Very basic question on monads
by blackcat＠pro-ns.net 23 Feb '11

23 Feb '11

I'm working through the "Write Yourself a Scheme" wikibook and having trouble with one of the exercises. For the function parseNumber :: Parser LispVal, both parseNumber = liftM (Number . read) $ many1 digit parseNumber' = do digits <- many1 digit return $ (Number . read) digits work. But parseNumber'' = many1 digit >>= liftM read >>= liftM Number complains "couldn't match expected type Char against inferred type [Char]". Is liftM engaging the list monad? How do I fix this?

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Having trouble defining type correctly
by Chris Bolton 22 Feb '11

22 Feb '11

Ok, so here's my current code: http://paste.pocoo.org/show/342949/ My basic problem is I'm not quite sure how to define Command. When a user calls the script they can either call add, remove, update, or query, which all have different type signatures, which is why I need Command so it'll pass through haskell's type checking. If I get rid of query, A definition of { data Command m = Save m | Rem m } seemed to work, from what I can tell, but query screws it up, so I'm trying to define exactly what Save, Rem, etc. should be, which I've taken directly from the MongoDB API, but it just keeps throwing errors, as seen here: http://paste.pocoo.org/show/342924/ Also, I'm very new to haskell and programming in general, so sorry for the possibly messy code / noobish question, but anyone have any ideas here? :P

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Cabal dependencies problem
by Jun HU 22 Feb '11

22 Feb '11

Hello everyone, I've some problems with cabal dependency mechanism. For example, when i try to install package "funsat", :> cabal install funsat it shows ====================== MSG =================== BGN Registering parsec-3.1.1... Installing library in /home/jhu/.cabal/lib/parsec-3.1.1/ghc-6.12.1 Registering parsec-3.1.1... cabal: Error: some packages failed to install: array-0.2.0.0 failed during the building phase. The exception was: ExitFailure 1 bimap-0.2.4 depends on array-0.2.0.0 which failed to install. containers-0.2.0.1 depends on array-0.2.0.0 which failed to install. fgl-5.4.2.2 depends on array-0.2.0.0 which failed to install. funsat-0.6.1 depends on array-0.2.0.0 which failed to install. parse-dimacs-1.2 depends on array-0.2.0.0 which failed to install. ====================== MSG =================== END while the current array package is on version array-0.3.0.2. The package has back compatibility problem. Any advice is appreciated... thank you in advance. Sincerely, Jun

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