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c2hs and cabal?
by Magnus Therning 28 Nov '06

28 Nov '06

Can I use cabal to build packages that incorporates C libraries and FFI Haskell created using c2hs? Any pointers on how to do that? /M -- Magnus Therning (OpenPGP: 0xAB4DFBA4) magnus(a)therning.org Jabber: magnus.therning(a)gmail.com http://therning.org/magnus Software is not manufactured, it is something you write and publish. Keep Europe free from software patents, we do not want censorship by patent law on written works. If voting could really change things it would be illegal.

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GHCi and HXT
by Alexis Hazell 28 Nov '06

28 Nov '06

Hi all, i'm having a bit of difficulty using GHCi to try out HXT. i brought the Text.XML.HXT.Arrow module into scope using :m. Then i entered: let contact = mkelem "stream:stream" [ sattr "xmlns:stream" "http://etherx.jabber.org/streams", sattr "xmlns" "jabber:client", sattr "to" "livejournal.com" ] [] and got the error message: <interactive>:1:14: Ambiguous type variable `a' in the constraint: `ArrowXml a' arising from use of `mkelem' at <interactive>:1:14-19 Probable fix: add a type signature that fixes these type variable(s) The type signature of mkelem is mkelem :: (ArrowXml a) => String -> [a n XmlTree] -> [a n XmlTree] -> a n XmlTree So then i modified it to: let contact = mkelem "stream:stream" [ sattr "xmlns:stream" "http://etherx.jabber.org/streams", sattr "xmlns" "jabber:client", sattr "to" "livejournal.com" ] [] :: ArrowXml a => a XmlTree XmlTree And got: <interactive>:1:14: Ambiguous type variable `a' in the constraint: `ArrowXml a' arising from instantiating a type signature at <interactive>:1:14-194 Probable fix: add a type signature that fixes these type variable(s) i don't understand why i need to specify type signatures when they should already be in scope? And if i /do/ need to specify the type signatures for some reason, how do i do so in a manner that works? Any help much appreciated! Alexis.

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Binary code
by escafia 28 Nov '06

28 Nov '06

Hi, i've one fuction receiving an int . The objective is return the respective binary code of that int. For example, if i receive 28 the fuction will return 011100. My question is that there is any fuction in libraries that do this? If not, anyone has any suggestion? Thank you. -- View this message in context: http://www.nabble.com/Binary-code-tf2704645.html#a7541561 Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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ANN: NeHe Tutorials in Haskell
by Jason Dagit 27 Nov '06

27 Nov '06

Hello, I was recently reminded by http://haskell.org/haskellwiki/How_to_write_a_Haskell_program that you should announce your haskell projects! About a year ago I started converting the (somewhat) famous NeHe tutorials for OpenGL to HOpenGL. I have created a darcs repository for anyone interested (and I welcome darcs patches). You may find it here: http://codersbase.com/index.php/Nehe-tuts If you're interested in contributing, please observe one requirement, I want the examples to be as much in vanilla Haskell98 as possible to help make it accessible to beginners. Also, if you have feedback that is also very welcome. Thanks Jason

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Optimizing a hash function
by Ivan Tomac 27 Nov '06

27 Nov '06

Hi, Yesterday evening I had a go at porting Bob Jenkins' hash function (http://www.burtleburtle.net/bob/c/lookup3.c) to Haskell. The first version I came up with ran 20 times slower than C. Thanks to Don Stewart's suggestions on IRC, I managed to improve the performance by replacing tuples with a strict type so the current version is about 10 times slower than C code. Is there any way this can be further optimized? To keep things fair I've simplified the C function so it works on one byte at a time as opposed to an int at a time. The code was compiled with GHC-6.6 on a G5 iMac running OS X 10.4. Options used to compile the version using the hash function written in Haskell: ghc -O -funbox-strict-fields -fglasgow-exts -fbang-patterns -cpp -o test hashByteString.hs test.hs Options used to compile the version using the hash function in C: ghc -O -fglasgow-exts -ffi -fbang-patterns -cpp -DCHASH -o ctest ctest.c test.hs Ivan Tomac

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Glade Gtk2Hs Tutorial
by Hans van Thiel 27 Nov '06

27 Nov '06

Hello, The Haskell Gtk2Hs adaptation of the 'Developing Gnome Apps with Glade' tutorial for beginners is now also on http://eddy.writelinux.com/ Note there are translations there of the original version for C in French, Dutch, Spanish, Turkish and Korean. Native speakers of those languages who are interested could use these and check out the Haskell Gtk2Hs listings later. Thanks, Hans van Thiel

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Priority Queue?
by Ken Takusagawa 27 Nov '06

27 Nov '06

Is there a Haskell implementation of an efficient priority queue (probably heap-based) out there that I can use? I do not see it in the GHC libraries.

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Implementations of bit vectors
by Dominic Steinitz 26 Nov '06

26 Nov '06

You could also look at http://darcs.haskell.org/crypto/Data/LargeWord.hs but it would need modifying to produce a 33 bit word. Dominic.

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re: Improving library documentation
by brad clawsie 26 Nov '06

26 Nov '06

don, i am glad you raised this point, i was going to write a note to this list soon with a similar request i would suggest comparing perldoc to haddock and other haskell documentation tools. generally speaking, i find that documentation for perl libraries is written as if the author is enthusiastic about users understanding it. there are typically detailed function descriptions, and often inlined examples. on the other hand i have found most haddock documentation to consist merely of function signatures. as a result i have to employ spotty supplemental references like the haskell ref at zvon.org (which i am sure is a copy of a well-known reference set floating around out there), which includes some examples, or google's code search with haskell support. furthermore, perldoc has querying capabilities (-f etc) which preclude having to surf around references, another great feature. regardless of format, well-written documentation will go a long way to forwarding haskell adoption. brad

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Haddock question
by Luis Cabellos 26 Nov '06

26 Nov '06

Hello, I follow the How to Write a Haskell program from http://www.haskell.org/haskellwiki/How_to_write_a_Haskell_program, but I have a problem with Haddock. I use Windows XP, I when I install GHC + Haddock I have this warning output C:\code\haskell\test> runhaskell Setup.hs haddock Preprocessing executables for Test-0.0... Running Haddock for Test-0.0... Warning: cannot use package Test-0.0: ghc-pkg failed Warning: cannot use package base-2.0: does not exist.y $topdir\html\libraries\base There is something generated in dist\doc\html\test path but only the main function page but it don't has the comments from *.hs file. I use --prefix=c:\programs instead of --prefix=$HOME in configure. Because I am working on Windows. I don't use darcs, but I think that it's not the problem. -- Thanks a lot, Luis Cabellos

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