- Haskell-Cafe - Haskell.org

category-extras clash with transformers
by Tony Morris 20 Nov '10

20 Nov '10

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 I have installed mtl-1.1.1.0 so that xmonad-contrib-0.9.1 would compile with GHC 6.12.1. http://permalink.gmane.org/gmane.comp.lang.haskell.xmonad/10603 Then I tried to installed category-extras-0.53.5, which clashed with transformers-0.2.2.0 for the Applicative/Monad instances for Either. Is there any way out of this problem? Thanks for any pointers. $ ghc-pkg list | grep mtl mtl-1.1.1.0 mtl-2.0.1.0 $ ghc-pkg list | grep transformers transformers-0.2.2.0 $ cabal install category-extras ... [39 of 99] Compiling Control.Monad.Either ( src/Control/Monad/Either.hs, dist/build/Control/Monad/Either.o ) src/Control/Monad/Either.hs:44:9: Duplicate instance declarations: instance Monad (Either e) -- Defined at src/Control/Monad/Either.hs:44:9-24 instance Monad (Either e) -- Defined in transformers-0.2.2.0:Control.Monad.Trans.Error src/Control/Monad/Either.hs:49:9: Duplicate instance declarations: instance Applicative (Either e) -- Defined at src/Control/Monad/Either.hs:49:9-30 instance Applicative (Either e) -- Defined in transformers-0.2.2.0:Control.Monad.Trans.Error src/Control/Monad/Either.hs:53:9: Duplicate instance declarations: instance MonadFix (Either e) -- Defined at src/Control/Monad/Either.hs:53:9-27 instance MonadFix (Either e) -- Defined in transformers-0.2.2.0:Control.Monad.Trans.Error cabal: Error: some packages failed to install: category-extras-0.53.5 failed during the building phase. The exception was: ExitFailure 1 - -- Tony Morris http://tmorris.net/ -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.10 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iEYEARECAAYFAkznxgQACgkQmnpgrYe6r60dkACfZQkYKbMOQuGfaVpFb2MfhJWD asAAn1/hoX+m/YpUOch3r4NsR99y2htz =IsZc -----END PGP SIGNATURE-----

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RegEx versus (Parsec, TagSoup, others...)
by Michael Litchard 20 Nov '10

20 Nov '10

I've been working on a project that requires me to do screen scraping. When I first started this, I worked off of other people's examples. Not one used regex. By luck I found someone at work to help me along this project. His clues and hints don't use regex either. I was at a point where I had to make a decision concerning design, so I asked the guy sitting next to me at work. He's very experienced, and comes from a Perl perspective. I let him into what I was doing, and he opined I should be using pcre. So now I'm second guessing my choices. Why do people choose not to use regex for uri parsing?

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Re: [Haskell-cafe] Quasi quotation question
by Oscar Finnsson 20 Nov '10

20 Nov '10

Sure. Just use http://hackage.haskell.org/package/haskell-src-meta-0.0.6. You are probably interested in parsePat or parseExp. I've used parseExp in a package. -- Oscar

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Quasi quotation question
by jean-christophe mincke 20 Nov '10

20 Nov '10

Hello, Is it possible for a quasi quoter to have access to information about haskell identifiers declared before the quasi-quotation? I tried the 'reify' function but without success. Just as in the following exemple: a = 6 x = [$expr|a|] Where the generated haskell code is a= 6 x = a Thank you Regards J-C

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GitIt
by Andrew Coppin 19 Nov '10

19 Nov '10

The other day, I did a slightly foolish thing. I uttered the command cabal install gitit Actually, while I was "foolish", it actually worked better than you'd think. It wanted to install several thousand billion packages, but all of them compiled without issue. Well, all except one. You see, for reasons that I have yet to determine, cabal is *convinced* that gitit transitively requires the "unix" package. Astonishingly, this doesn't work on Windows. :-P Question: Why does 90% of the network-related stuff on Hackage require the unix package? What's in there that's so network-related? I don't understand. We've *got* a portable "network" package that works on all platforms, so...? Anyway, on further investigation, it appears that the culprit is "cautious-file". If a certain CPP flag it set, "unix" gets added to the Build-Depends: field. Except... I didn't set any CPP flags! What the hell? So I manually edit the package description (!), and now it builds and installs perfectly happily. So now I tell cabal to install gitit again... and it immediately tries to install unix, even though the only package that (it thinks) requires unix is already installed? Wuh? So I unpack gitit and tell cabal to build it. Building takes about 30 seconds. *Linking* takes about 4 minutes (??!) And then it fails due to some missing symbols. (No, I don't remember off the top of my head what they were.) At this point, I am completely lost. Does anybody have any ideas on how I can make GitIt work, short of installing Linux? I've searched and searched and I can't see a pre-built binary anywhere.

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Impredicative Types
by Gregory Crosswhite 19 Nov '10

19 Nov '10

Hey everyone! I haven't had a chance to try out GHC 7 myself, but I saw in the documentation that Impredicative Types are still supported. Is this true? I thought that they were on their way out because they overcomplicated type checking; has this plan been changed? Cheers, Greg

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a simple question about types
by Jerzy M 19 Nov '10

19 Nov '10

Hallo, let me take this simple function: (2*). If I check its type :t (2*) I'll obtain (2*) :: (Num a) => a -> a But now it suffices to write g = (2*) and check :t g to obtain g :: Integer -> Integer One more combination, now I write h x = (2*) x and check once more :t h to get h :: (Num a) => a -> a So my question is: why (in this second example) Integer is inferred? What makes a difference? Jerz

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Problem with linking HDBC-ODBC
by hanjoosten 19 Nov '10

19 Nov '10

Hi Yesterday I upgraded to the new version of hdbc-odbc (2.2.3.1.). Then I rebuilt my own project, but the linker gives an error: . . . [88 of 90] Compiling CC ( CC.hs, C:\eclipseworkspace_fp1\ampersand\out\CC.o ) [89 of 90] Compiling Parser ( Parser.hs, C:\eclipseworkspace_fp1\ampersand\out\Parser.o ) [90 of 90] Compiling Main ( Main.hs, C:\eclipseworkspace_fp1\ampersand\out\Main.o ) Linking C:\eclipseworkspace_fp1\ampersand\bin\adl.exe ... C:\Documents and Settings\nl22118\Application Data\cabal\HDBC-odbc-2.2.3.1\ghc-6.12.3/libHSHDBC-odbc-2.2.3.1.a(Statement.o):fake:(.text+0x1a3d): undefined reference to `SQLNumParams' C:\Documents and Settings\nl22118\Application Data\cabal\HDBC-odbc-2.2.3.1\ghc-6.12.3/libHSHDBC-odbc-2.2.3.1.a(Statement.o):fake:(.text+0x3961): undefined reference to `SQLNumParams' collect2: ld returned 1 exit status Is there anything I do wrong? My environment is a windows machine. I use the haskell-platform. I upgraded to the current version of hdbc-odbc using cabal install. Any suggestions are welcome. -- View this message in context: http://haskell.1045720.n5.nabble.com/Problem-with-linking-HDBC-ODBC-tp32721… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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borked windows environment, want to start over
by Michael Litchard 19 Nov '10

19 Nov '10

I think I may have borked things good using cygwin. I want to remove it and do a clean install of haskell platform w/out cygwin. What do I need to do to make sure all configuration files have been removed?

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How to generalize executing a series of commands, based on a list?
by Peter Schmitz 19 Nov '10

19 Nov '10

I am able to use System.Cmd (system) to invoke a shell command and interpret the results. Please see the code below that works okay for one such command. (I invoke a program, passing two args.) I am wondering how to generalize this to do likewise for a series of commands, where the varying args (filenames, in this case) are in a list ('inOutLeafs'). I will also want to accumulate some results; probably just a failure count at this time. Any advice or pointers to examples would be much appreciated. Thanks in advance, -- Peter > run :: ... -> IO (Int) -- will return a fail count > run > -- some args to this function here... > = do > -- ... set up: inputLeafs, outputLeafs, etc. > > -- zip two lists of filenames: > let inOutLeafs = zip inputLeafs outputLeafs > > -- the first pair for the first command: > let (inFile1,outFile1) = head inOutLeafs > > -- build 1st command using 1st pair of filenames: > let cmd1 = ... > > exitCode <- system cmd1 > case (exitCode) of > ExitSuccess -> do > putStrLn $ "-- OK." > return 0 > ExitFailure failCnt -> do > putStrLn $ "-- Failed: " ++ show failCnt > return 1

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