March 2010 - Haskell-Cafe

Cabal Compiler Flag Problem
by Ben Derrett 24 Mar '10

24 Mar '10

Hi, I'm trying to install the Haskell cgi module, as per here http://passingcuriosity.com/2009/haskell-fastcgi-with-apache/. When I type cabal install cgi, I get the following error (on a Fedora instance): cabal install cgi Resolving dependencies... Configuring MonadCatchIO-mtl-0.3.0.0... Preprocessing library MonadCatchIO-mtl-0.3.0.0... Building MonadCatchIO-mtl-0.3.0.0... [1 of 1] Compiling Control.Monad.CatchIO ( Control/Monad/CatchIO.hs, dist/build/Control/Monad/CatchIO.o ) Control/Monad/CatchIO.hs:146:34: Illegal signature in pattern: E.SomeException Use -XPatternSignatures to permit it cabal: Error: some packages failed to install: MonadCatchIO-mtl-0.3.0.0 failed during the building phase. The exception was: exit: ExitFailure 1 cgi-3001.1.8 depends on MonadCatchIO-mtl-0.3.0.0 which failed to install. So, I modified my /root/.cabal/config with: -- flags: -XPatternSignatures This doesn't seem to resolve the problem. What do I need to do to change the compiler flags? Thanks, Ben

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installing Network on windows
by gladstein＠gladstein.com 24 Mar '10

24 Mar '10

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Timeouts that don't cause data growth.
by David Leimbach 23 Mar '10

23 Mar '10

Trying to understand why the code here: http://moonpatio.com/fastcgi/hpaste.fcgi/view?id=8823#a8823 exhausts memory. I need to have timeouts in a program I'm writing that will run an interactive polling session of some remote resources, and know when to give up and handle that error. Unfortunately this code dies pretty quickly and produces an -hc graph like the one attached. It seems that System.Timeout can't be used for this. I should note that if the code is changed to use an inifnite timeout (-1) that this problem doesn't occur. Is this a bug in System.Timeout, or is there something I should be doing to keep the data size down? Dave

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ANNOUNCE: Bravo-0.1.0
by Matthias Reisner 23 Mar '10

23 Mar '10

Hello, I'm pleased to announce the first release of Bravo, a static text template generation library, on Hackage: http://hackage.haskell.org/package/Bravo. Bravo is a text template library that provides parsing and generation of templates at compile time. Templates can be read from strings or files and for each a new record data type is created, allowing convenient access to all template variables in a type-safe manner. Since all templates are processed at compile time, no extra file access or error handling at runtime is necessary. Bravo is inspired by the PHP template engine Smarty and the Haskell template library chunks. Compared to chunks, Bravo provides additional features like conditional template evaluation, embedding of Haskell expressions and customized data type generation. I'm going to add further information to the HaskellWiki page (http://www.haskell.org/haskellwiki/Bravo) later. Bravo is still highly experimental and not well-tested, so bug reports and additional feedback are very welcome. I'd also like to hear if you feel the package dependencies are to restrictive. Regards, Matthias Reisner

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Bytestrings and [Char]
by Johann Höchtl 23 Mar '10

23 Mar '10

Hello, I was recentyl playing with Haskell (GHC that is) IO and text processing. Bytestrings and Lazy Bytestrings allow for fast and memory eficient string (well, bytestring) handling, yet a lot of libraries do not support them (yet) Given the incredibly inneficient memory representation of [Char] (16 bytes? per cell) I wonder wheather String should default to lazy batestring altogether instead of [Char]. The levenshtein distance as is on hackage uses e.g. String ([Char]) and as such is unneccessarily slow. My question or discussion point: Why not depreciate [Char] altogether and favour of lazy Bytestrings? Regards, Johann

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Fwd: [Haskell-cafe] Bytestrings and [Char]
by Alberto G. Corona 23 Mar '10

23 Mar '10

Just a dream: -separate interface and implementation for all containers, via type classes -develop, by genetic programming techniques + quickcheck, a system that find the best container implementation for a particular program. Is that suitable for a Google Summer of Code project? 2010/3/23 Alberto G. Corona <agocorona(a)gmail.com> The question can be generalized via type classes: Is there any common set of > primitives encapsulated into a single type class that has instances for > Strings (Data.List) ByteStrings, Data.Text, Lazy bytestrings, Arrays, > vectors and wathever container that can store an boxed, unboxed, packed > unpacked sequence of wathever including chars? All of them have folds, > heads, tails and a lot of common functions with the same name, but since > there is not a single type class, the library programmer can not abstract > his code when it is possible, so the library user can chose the particular > instance for his particular problem. > > 2010/3/23 Johann Höchtl <johann.hoechtl(a)gmail.com> > > On 22.03.2010 14:15, Ivan Miljenovic wrote: >> >>> On 23 March 2010 00:10, Johan Tibell<johan.tibell(a)gmail.com> wrote: >>> >>> >>>> A sequence of bytes is not the same thing as a sequence of Unicode >>>> code points. If you want to replace String by something more efficient >>>> have a look at Data.Text. >>>> >>>> >>> Though Data.Text still has the disadvantage of not being as nice to >>> deal with as String, since you can't pattern match on it, etc. >>> >>> Whilst it may degrade performance, treating String as a list of >>> characters rather than an array provides you with greater flexibility >>> of how to deal with it. >>> >>> >>> >> But doesn't this basically mean sacrifice performance / applicability for >> algorithmic beauty? Sure, pattern match comes in handy, but in the case of >> strings at a high price >> >> >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> > >

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Re: [Haskell-cafe] Bytestrings and [Char]
by Iustin Pop 23 Mar '10

23 Mar '10

On Tue, Mar 23, 2010 at 05:53:00PM +0000, Vincent Hanquez wrote: > On 23/03/10 17:11, Iustin Pop wrote: > >Data.ByteString.Lazy (bytestring readFile + length) -< 10 miliseconds, > >incorrect length (as expected). > > > >Data.ByteString.Lazy.UTF8 (system readFile + fromString + length) - 11 > >seconds, correct length. > > Why would you use system readFile and not bytestring readFile in the > second case ? > > using the later i got a ~48x slowdown, not a >1100x slowdown, and > the length is correct too. Hmm… because I didn't think of that :) iustin

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RE: [Haskell-cafe] Cabal source installation
by Chris Dornan 23 Mar '10

23 Mar '10

> Have you tried? > > cabal unpack <package-name> Thanks if I understand rightly, that 'cabal unpack' be used to build the shell script I have in mind. But I really want an option to Cabal to request it to install the source code of a package in a source-tree edition of the installed binary package. Chris -----Original Message----- From: Colin Paul Adams [mailto:colin@colina.demon.co.uk] Sent: 23 March 2010 11:35 AM To: Chris Dornan Subject: Re: [Haskell-cafe] Cabal source installation Have you tried? cabal unpack <package-name> -- Colin Adams Preston Lancashire

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Cabal source installation
by Chris Dornan 23 Mar '10

23 Mar '10

I am using Cabal on Windows and Haskell Platform 2009.2.0.2 and have been trying get it to install the package source code with no success, so I am considering writing a script to unpack the tar archive and install it in my own package source repository. Is there an easier way to do this? Chris

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"Improve Cabal's test support" for Google summer of code
by Mujtaba Boori 23 Mar '10

23 Mar '10

Hello I'm thinking of project for my google proposal . I found "improve Cabal's test support' is really interesting .I have a decent knowledge about Haskell programming and testing methods . I was wondering if this project is suitable for me and what skill I required to have. I would be very thankful if you give me advice for resources to look and understand it. Thank you -- Mujtaba Ali Alboori

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