August 2008 - Haskell-Cafe

Lambdabot
by Thomas Davie 11 Aug '08

11 Aug '08

I've been trying to lambdabot running properly recently, and have consistently hit an error "fd:6: hClose: resource vanished (Broken pipe)" whenever I try to run anything that involves executing haskell (including but not limited to evaluating arbitrary expressions, the brainfuck module, unlambda). A quick google revealed that it's a very common error, but not potential solutions. Any ideas on what's up would be very useful. Bob

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I want to upgrade to ghc 6.8.3
by Galchin, Vasili 11 Aug '08

11 Aug '08

Hello, I am building 6.8.3 from my "local" 6.8.2. However, I am getting errors in compiling one of the Main.hs. E.g. Main.hs:76:23: Ambiguous occurrence `flags' It could refer to either `Main.flags', defined at Main.hs:118:0 or `System.Posix.flags', imported from System.Posix at Main.hs:59:0-18 ...... I did a "find . -name Main.hs" and there are several Main.hs. I am not sure which one is causing trouble or why. ?? Kind regards, Vasili

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help
by shoulders 11 Aug '08

11 Aug '08

--------------------------------- 雅虎邮箱，您的终生邮箱！

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please help me to find errors from my first app
by Changying Li 10 Aug '08

10 Aug '08

Hi. I want to write a reverse proxy like perlbal to practive haskell. Now I just write a very simple script to forward any request to www.google.com. but it dosn't work. I run command ' runhaskell Proxy.hs' and 'wget http://localhost:8080/'. but wget just wait forever and runhaskkell can get request. when I break wget, the 'runhaskell' can print response returned from www.google.com. why? module Main where import System.Posix.Process import Network import Prelude hiding (putStr) import System.IO hiding (hGetContents, putStr) import Control.Concurrent import System.Posix.Signals import Data.ByteString.Lazy.Char8 (hGetContents, hPut, putStr,hGet,cons) listenPort = PortNumber 8080 connectToHost = "208.67.219.230" connectToPort = PortNumber 80 main :: IO () main = do hSetBuffering stdout NoBuffering socket <- listenOn listenPort let doLoop = do (hdl, _, _) <- accept socket forkIO $ processRequest hdl doLoop doLoop processRequest :: Handle -> IO () processRequest hRequest = do installHandler sigPIPE Ignore Nothing; hSetBuffering hRequest NoBuffering hSetBuffering stdout NoBuffering request <- hGetContents hRequest putStr $ '>' `cons` (' ' `cons` request) hResponse <- connectTo connectToHost connectToPort hSetBuffering hResponse NoBuffering hPut hResponse request response <- hGetContents hResponse putStr $ '<' `cons` (' ' `cons` response) hPut hRequest response hClose hRequest hClose hResponse -- Thanks & Regards Changying Li

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heap lifetime question
by Galchin, Vasili 10 Aug '08

10 Aug '08

Hello, What is the lifetime of various heap objects ... e.g. created by allocaBytes, alloca, etc? Regards, Vasili

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Re: ANN: interval and polynomial enclosure arithmetics
by Michal Konecny 10 Aug '08

10 Aug '08

Roman Cheplyaka <roma <at> ro-che.info> writes: > * Michal Konecny <mik <at> konecny.aow.cz> [2008-08-08 13:38:56+0100] > > and members of the KEG research group at Aston > > University have used it for reliably solving differential equations > > and numerical constraint satisfaction problems. > > This's very interesting. Do you have any published papers (or other > sources of information) about it? Unfortunately, there isn't much yet but more is on the way. Only the following two papers are available at the moment: http://www-users.aston.ac.uk/~konecnym/papers/cfv08.html is about using our polynomial enclosures to prove NCSPs that arise from floating-point software verification problems. http://www-users.aston.ac.uk/~konecnym/papers/wollic08.html analyses the convergence rate of an ODE solver that uses piecewise constant enclosures (which is rather inefficient). Best regards, Michal -- |o| Michal Konecny |o| http://www-users.aston.ac.uk/~konecnym/ |o| office: (+42) (0)121 204 3462 |o| PGP key http://www-users.aston.ac.uk/~konecnym/ki.aow

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Last Reminder: The Italian Haskellers Summer Meeting takes place tomorrow at Monterosso, 5 Terre
by Titto Assini 10 Aug '08

10 Aug '08

Il titolo dice tutto, maggiori dettagli ad: http://www.haskell.org/haskellwiki/?title=ItaloHaskell/Summer_2008 A domani, titto -- Pasqualino "Titto" Assini, Ph.D. 25 Heath Road - CO79PT Wivenhoe - Colchester - U.K.

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Future of Darcs: Thanks for the poll responses and increase in contributors
by Jason Dagit 09 Aug '08

09 Aug '08

Hello, I just wanted to thank everyone that has shown their support for darcs recently by either stopping by #darcs on freenode or joining in discussions on the darcs-user mailing list. I'm cross posting to haskell-cafe because I suspect many of you came from there. There has been a lot of enthusiasm from people, a lot of discussion about patch theory and excitement about fixing bugs and performance issues. Several people have taken an interest in making darcs work flawlessly on the GHC repository (yes, I know they have already commited to switching, but it gives a great test case to improve on). Eric Kow and myself have been working on a roadmap for future darcs improvements, and we plan to annouce an official version soon. The tentative one can be found here: http://wiki.darcs.net/DarcsWiki/Roadmap Mainly I just wanted to say, Thanks! We're considering the feedback we received from the poll and the future of darcs is not uncertain and we'll do a better job of communicating that message in the future. Now, back to hacking on darcs! Thanks, Jason

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ANN: Haskore tutorial (programming music using Haskell)
by jinjing 09 Aug '08

09 Aug '08

Hi there, Here's the project link: http://github.com/nfjinjing/haskore-guide/tree/master/doc/index.markdown I found Haskore pretty fun :) so I'm documenting it while learning it. Please don't hesitate to give suggestions / corrections. Questions: * How much music theory should be there ? ( I'm gonna learn those anyway ) * What kind of examples would be cool ? regards, jinjing

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ANN: interval and polynomial enclosure arithmetics
by Michal Konecny 09 Aug '08

09 Aug '08

Hello, I have recently released the following two Haskell packages, which model and reasonably efficiently implement exact real arithmetic: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/AERN-Real implements arbitrary-precision interval arithmetic for approximating real numbers http://hackage.haskell.org/cgi-bin/hackage-scripts/package/AERN-RnToRm implements arbitrary-precision arithmetic of bounded-degree piecewise-polynomial enclosures for approximating functions of type R^n -> R^m The libraries are fairly stable and complete (AERN-Real more so than AERN-RnToRm) and members of the KEG research group at Aston University have used it for reliably solving differential equations and numerical constraint satisfaction problems. Also, the libraries are designed in multiple levels of abstraction that are clearly separated by type classes. Thanks to this it is very easy to switch between different implementations of the lower-levels, eg using a different floating point type or different representation of polynomials. There are many similarities between AERN-Real and Augustsson's numbers package. The main difference is in how the bit-size of arbitrary precision floating point numbers is determined. In numbers, the bit size is determined statically via types using a type-level encoding of natural numbers. In AERN-Real, the bit-size is part of the floating-point number, which slows the arithmetic down a bit but one can change precision dynamically. Best regards, Michal -- |-| Dr. Michal Konecny, Computer Science, Aston University |-| Room MB212D | Tel +44 121 204 3462 | Fax +44 121 204 3681 |-| http://www.aston.ac.uk/~konecnym |-| OpenPGP key http://www.aston.ac.uk/~konecnym/ki.aston

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