- Haskell-Cafe - Haskell.org

An alternative break
by Pieter Laeremans 28 May '08

28 May '08

Hello, I need a break function that splits the list one element further than the ordinary break. This is the simplest solution I could imagine: breakI :: (a -> Bool) -> [a] -> ([a], [a]) breakI p s = case break p s of ([], []) -> ([], []) (x, []) -> (x, []) (x, l) -> (x ++ [head l], tail l ) Is there a better way to write this ? thanks in advance, Pieter -- Pieter Laeremans <pieter(a)laeremans.org>

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Type Coercion
by PR Stanley 28 May '08

28 May '08

Hi (16 :: Float) is a perfectly legitimate statement although I'm surprised that it's allowed in a type strong language such as Haskell. It's a bit like casting in good old C. What's going on here? Paul

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Benchmarking Framework
by Tom Harper 28 May '08

28 May '08

I am in the process of writing a library for my MSc dissertation and would like to do some benchmarking. In doing so I need to compare the time and space of my library with some other code. Is there a framework for doing so in Haskell, aside from the Profiling tools in GHC? Basically I'm looking for something like QuickCheck, but that helps with generating repeatable tests to measure performance. Is there anything out there that anyone would recommend? -- Tom Harper MSc Computer Science '08 University of Oxford Mobile: +44 (0)7533 998 591 Skype: +1 949 273 4627 (harpertom)

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Examples of using Haskell for mathematics
by Brent Yorgey 28 May '08

28 May '08

Hi all! In a couple weeks I will be giving a short (15-min.) talk to an audience of mostly mathematicians, entitled "Executable Mathematics: A Whirlwind Introduction to Haskell". The idea will be to give a flavor of Haskell, its uniquenesses, and why it is a great language for playing around with mathematics, by way of some well-chosen examples. There are definitely plenty of such examples out there, and I've already found quite a few that I might use, but I thought I would send an email to the cafe to ask whether anyone has any code which you think particularly exemplifies some aspect of why Haskell is a great language for mathematics. I'm looking to include a wide range of examples, so any length (from a few to hundreds of lines of code) and any level (from simple number theory to things only a few people in the world understand) are fair game. Thanks in advance! And yes, I will definitely make the slides available after the talk. I don't know if I can promise a video, I kind of doubt the sessions will be videotaped. I guess we'll see. -Brent

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Re: static linking
by Peter Gammie 28 May '08

28 May '08

Hello, Further on my static linking woes: debian ~$ ghc --version The Glorious Glasgow Haskell Compilation System, version 6.8.2 -debian ~$ cat T.hs main :: IO () main = putStrLn "Hello world" -debian ~$ ghc -optl-static -static --make T.hs Linking T ... /usr/lib/gcc/i486-linux-gnu/4.2.3/../../../../lib/ librt.a(timer_create.o): In function `timer_create': (.text+0x107): undefined reference to `pthread_once' ... < references to missing pthread symbols > Does anyone have static linking working for GHC 6.8.2 and can inform me of the magic incantation? "Get the latest development version from darcs", perhaps? BTW when I said "move to the end", I meant "move to the end of -l flags". cheers peter On 27/05/2008, at 10:37 AM, Peter Gammie wrote: > Hello, > > I am having a bit of trouble static linking my program using GHC > 6.8.2. > > In brief: "rt" uses "pthread", but -lrt is the final thing on the > command line passed to the linker, and so the pthread symbols are > not resolved. Manually moving -lpthread to the end of the collect2 > command line does the trick. > > The question is how to do this using ghc. > > This is on Debian, using the 6.8.2-5 from unstable. > > I can provide the command lines if that is helpful. > > Note the same setup worked fine under GHC 6.6.1. > > cheers > peter

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Re: the Network.URI parser
by Neil Mitchell 28 May '08

28 May '08

Moving to haskell-cafe, as this almost certainly isn't a library issue. Hi > It most certainly is a security flaw. In the src of an img, yes, probably. In the href of a link, its a completely valid thing to do - and one that I've done loads of times. The URI is fine, its just the particular location that is dodgy. > whole pile of dodgy URIs. Most get culled (in my case) by the HaXml parser > and/or XHTML 1.0 Strict validation, and now I hope to eliminate the rest by > carefully handling the URIs. I don't think that's possible. A URI can validly have javascript, and can validly be a lot of things which are unsafe. > On that topic, does anyone have any good advice for handling these things? My advice is that you are targeting security at the wrong level. You shouldn't be cleaning the HTML to get a secure page, you should be having the level that interprets the HTML be secure regardless of the input. > If anyone knows of the state-of-the-art in this area, I'd appreciate a > pointer. > > http://htmlpurifier.org/live/smoketests/printDefinition.php > > doesn't seem to think the style attribute is unsafe. Have they not been > following the MySpace fiascos? Safety is a property of the HTML viewer, not of the HTML or CSS. Thanks Neil

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What's NaN?
by PR Stanley 28 May '08

28 May '08

Hello Why does sqrt (-16) return NaN? What is NaN? Thanks Paul

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re: a build problem
by Galchin, Vasili 28 May '08

28 May '08

Hi Duncan, In response to your below, I am running "runhaskell Setup.hs configure -v3 --prefix=$HOME". Is v3 the current highest Cabal highest verbosity level? FYI basically I am running ghc that I just built a couple of days ago from the ghc source distribution. Vasili (I. Galchin) ;^) On Tue, 2008-05-27 at 15:33 -0700, Thomas Hartman wrote: > I think dist gets populated when you do build. Actually we also stash the configuration in ./dist/setup-config so that gets created at configure time. Galchin's problem is that something goes wrong during the configure and so nothing gets created in dist. From the log it looks like ghc or ld are failing during one of the early tests we do when configuring ghc. To make debugging this kind of thing a bit less mysterious in future Cabal now logs in greater detail what happens when it calls external programs (when invoked at the highest verbosity level). Duncan

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Re: [Haskell-cafe] a build problem ....
by Thomas Hartman 28 May '08

28 May '08

I think dist gets populated when you do build. > > 2008/5/27 Galchin, Vasili <vigalchin(a)gmail.com>: >> when I do a "clean" followed by "configure" then dist is empty >> >> vasili >> >> On Tue, May 27, 2008 at 4:37 PM, Thomas Hartman <tphyahoo(a)gmail.com> wrote: >>> >>> maybe try >>> >>> runghc Setup.hs clean >>> >>> or fresh darcs checkout and try build again from scratch. it's helped >>> me in the past. >>> >>> thomas. >>> >>> >>> Am 26. Mai 2008 21:32 schrieb Galchin, Vasili <vigalchin(a)gmail.com>: >>> > Hello, >>> > >>> > One of my test cases will not build. I am running: >>> > >>> > vigalchin@ubuntu:~$ ghc -v >>> > Glasgow Haskell Compiler, Version 6.8.2, for Haskell 98, stage 2 booted >>> > by >>> > GHC version 6.8.2 >>> > Using package config file: /usr/local/lib/ghc-6.8.2/package.conf >>> > wired-in package base mapped to base-3.0.1.0 >>> > wired-in package rts mapped to rts-1.0 >>> > wired-in package haskell98 mapped to haskell98-1.0.1.0 >>> > wired-in package template-haskell mapped to template-haskell-2.2.0.0 >>> > wired-in package ndp not found. >>> > Hsc static flags: -static >>> > *** Deleting temp files: >>> > Deleting: >>> > *** Deleting temp dirs: >>> > Deleting: >>> > ghc-6.8.2: no input files >>> > Usage: For basic information, try the `--help' option. >>> > vigalchin@ubuntu:~$ >>> > >>> > Here is the build: >>> > >>> > vigalchin@ubuntu:~/FTP/Haskell/unix-2.2.0.0/tests/mlock$ runhaskell >>> > Setup.lhs configure --prefix=$HOME >>> > Configuring mlock-1.0... >>> > vigalchin@ubuntu:~/FTP/Haskell/unix-2.2.0.0/tests/mlock$ runhaskell >>> > Setup.lhs build >>> > Preprocessing executables for mlock-1.0... >>> > Building mlock-1.0... >>> > vigalchin@ubuntu:~/FTP/Haskell/unix-2.2.0.0/tests/mlock$ runhaskell >>> > Setup.lhs install >>> > Installing: /home/vigalchin/bin >>> > Setup.lhs: dist/build/mlock/mlock: copyFile: does not exist (No such >>> > file or >>> > directory) >>> > >>> > The install step fails. I guess "copyFile" is used to copy the >>> > executable to >>> > the install directory?? >>> > >>> > Regards, vasili >>> > >>> > >>> > >>> > >>> > _______________________________________________ >>> > Haskell-Cafe mailing list >>> > Haskell-Cafe(a)haskell.org >>> > http://www.haskell.org/mailman/listinfo/haskell-cafe >>> > >>> > >> >> >

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ANN: HSmugMug 0.1 - a haskell wrapper to the photo site smugmug's api
by Daniel Patterson 27 May '08

27 May '08

Released May 27th, 2008. I've been working for a little while on a haskell wrapper to the photo hosting site Smugmug's api. As of now, the library is pretty simple - it is 'read-only' - ie, you can't use it to upload to or create galleries, but I still think it is potentially useful to haskell/smugmug users. I created it primarily so I could integrate my photos at smugmug into my website, which you can see in the 'photos' section of my website - a very primitive but proof of concept-esque demonstration. I have deliberately not included much glue between the actual api and the use of it, because I think that is something that can more cleanly evolve out of use - if people find themselves repeating certain patterns when using the api, those would logically become part of the api wrapper. So, let me know what you think! Full release notes, brief tutorial, install instructions, etc, at http://dbpatterson.com/articles/10 . Feedback welcome! (this is the first thing longer than a 5 liner that I've written in haskell, so be gentle) Daniel

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