July 2007 - Haskell-Cafe

ANN: Finance.Quote.Yahoo 0.1 on hackage
by brad clawsie 29 Jul '07

29 Jul '07

http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Finance-Quote-Ya… this is a simple module to get stock quote information from yahoo finance, considered alpha quality

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Text.XHtml Documentation
by David F. Place 29 Jul '07

29 Jul '07

Hello: I was just looking into using Text.XHtml for a project. The Haddock documentation points to an introduction by Andy Gill, but the link is broken. Can anyone point me to the correct location of the introduction? Thanks. Cheers, David ___________________ (---o-------o-o-o---o-o-o----( David F. Place mailto:d@vidplace.com

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problems installing Takusen-0.6
by Rahul Kapoor 29 Jul '07

29 Jul '07

I am having problems installing Takusen-0.6 (ghc 6.6.1 on FreeBSD) The configure and build works fine. running ./setup install fails with: Installing: /usr/local/lib/Takusen-0.6/ghc-6.6.1 & /usr/local/bin Takusen-0.6... setup: Error: Could not find module: Database.Oracle.Enumerator with any suffix: ["hi"] I only have sqlite3 installed (no Oracle or Postgres). I followed the usual steps for the install ghc --make -o setup Setup.hs ./setup configure ./setup build ./setup install Any Ideas? Rahul

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Videos of Haskell talks
by dons＠cse.unsw.edu.au 29 Jul '07

29 Jul '07

A new wiki page collecting tutorials and presentations about Haskell, is on the wiki: http://haskell.org/haskellwiki/Video_presentations Highlights include: Transactional Memory for Concurrent Programming Parametric Polymorphism and the Girard-Reynolds Isomorphism Programming in the Age of Concurrency Nested Data Parallelism in Haskell If you know of other online video material, please add it! -- Don

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Using Gtk2Hs version 0.9.12 on a PPC Mac
by Thorkil Naur 28 Jul '07

28 Jul '07

Hello, (From the archives:) > [Haskell] ANNOUNCE: Gtk2Hs version 0.9.12 released > Duncan Coutts duncan.coutts at worc.ox.ac.uk > Fri Jul 27 15:20:57 EDT 2007 > Gtk2Hs - A GUI Library for Haskell based on Gtk+ > Version 0.9.12 is now available from: > ... > Duncan > (on behalf of the Gtk2Hs team) Following the advice of nominolo_ from #haskell yesterday, I added -L/opt/local/lib to my ghc command and then the helloworld demo of Gtk2Hs worked. The problem seems to be the order in which the two library directories /usr/X11R6/lib and /opt/local/lib appear on the link command: For the GTK+ example that worked, /opt/local/lib comes first. For the Gtk2Hs demo that failed, /usr/X11R6/lib comes first. I compared these two directories and found these common files: X11 libXft.2.dylib libXft.a libXft.dylib libXrender.1.dylib libXrender.a libXrender.dylib libexpat.0.dylib libexpat.a libexpat.dylib libfontconfig.1.dylib libfontconfig.a libfontconfig.dylib libfreetype.6.dylib libfreetype.a libfreetype.dylib pkgconfig Since some of these (Xrender, fontconfig, and freetype) are actually used in GTK+ (and therefore also Gtk2Hs) applications, there is clearly a potential for conflict here. In any case, adding -L/opt/local/lib to the ghc command makes this library appear before /usr/X11R6/lib on the link command and this seems to solve the problem. Subsequently, I have tried a handful of the other demos, and as far as they didn't require something that wasn't available (glade, for example), they seemed to work. Thanks and best regards Thorkil

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Frag
by Jon Harrop 28 Jul '07

28 Jul '07

I just stumbled upon this fast action 3D shooter written entirely in Haskell: http://haskell.org/haskellwiki/Frag After 15 minutes trying to build it I find that it segfaults. Can anyone else get this to work? -- Dr Jon D Harrop, Flying Frog Consultancy Ltd. The OCaml Journal http://www.ffconsultancy.com/products/ocaml_journal/?e

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Handling custom types in Takusen
by Salvatore Insalaco 27 Jul '07

27 Jul '07

Disclaimer: I don't know Takusen very well, and I'm talking of Sqlite backend. I noticed that in Takusen there're just two instances to implement to make any Haskell type db-serializable: DBBind / SqliteBind for serialization and DBType for deserialization. I wanted to implement blob serialization for PackedStrings, but I noticed that both DBBind and DBType classes are not public. Defining custom serialization (not just Show / Read string serialization) is very useful in applicative code, and not just in Takusen backend code. There's any way to do it without modifying Takusen Sqlite backend? Salvatore Insalaco

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Memory profiler
by Jon Harrop 27 Jul '07

27 Jul '07

Is there a memory profiler for Haskell? -- Dr Jon D Harrop, Flying Frog Consultancy Ltd. OCaml for Scientists http://www.ffconsultancy.com/products/ocaml_for_scientists/?e

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Avoiding boilerplate retrieving GetOpt cmd line args
by Dave Bayer 27 Jul '07

27 Jul '07

Ok, I'm writing a command line tool, using System.Console.GetOpt to handle command line arguments. My Flags structure so far is > data Flag > = Filter String > | DateFormat String > | DocStart String > | DocEnd String ... and I want to write accessor functions that return the strings if specified, otherwise returning a default. The best I've been able to do is this: > getFilter = getString f "Markdown.pl" > where f (Filter s) = Just s > f _ = Nothing > > getDateFormat = getString f "%B %e, %Y" > where f (DateFormat s) = Just s > f _ = Nothing > > getDocStart = getString f "^{-$" > where f (DocStart s) = Just s > f _ = Nothing > > getDocEnd = getString f "^-}$" > where f (DocEnd s) = Just s > f _ = Nothing using a generic accessor function `getString`. There are eight (and growing) needless lines here, where what I really want to do is to pass the constructors `Filter`, `DateFormat`, `DocStart`, or `DocEnd` to the function `getString`. ghci types each of these as `String -> Flag`, so one at least knows how to type such a `getString`, but using a constructor-passed-as-an-argument in a pattern match is of course a "Parse error in pattern". (I expected as much, but I had to try... `String -> Flag` is not enough information to make it clear we're passing a constructor, rather than some hairy arbitrary function, so such a pattern match would be undecidable in general.) So what's the right idiom for avoiding this boilerplate? Thanks, Dave

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Re: Re: Avoiding boilerplate retrieving GetOpt
by Eric Kow 27 Jul '07

27 Jul '07

> For starters, you could squish these down into something like > > flagToString :: Flag -> Maybe String > > flagToString (Filter s) = Just s > > flagToString (DateFormat s) = Just s > > ... > > flagToString _ = Nothing What am I saying?! This wouldn't work! Sorry for the noise. -- Eric Kow http://www.loria.fr/~kow PGP Key ID: 08AC04F9 Merci de corriger mon français.

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