August 2008 - Haskell-Cafe

ANN: logfloat
by wren ng thornton 17 Aug '08

17 Aug '08

-------------------------------------------- -- Announcing: logfloat 0.8.2 -------------------------------------------- I just released a new package, logfloat, for manipulating log-domain floating numbers. The main reason for casting numbers into the log-domain is to prevent underflow when multiplying many small probabilities as is done in Hidden Markov Models and other statistical models often used for natural language processing. The log-domain also helps prevent overflow when multiplying many large numbers. In rare cases it can speed up numerical computation (since addition is faster than multiplication, though logarithms are exceptionally slow), but the primary goal is to improve accuracy of results. A secondary goal has been to maximize efficiency since these computations are frequently done within a /O(n^3)/ loop. The Data.Numeric.LogFloat module provides a new data type LogFloat which handles all the conversions and optimizations and can be treated as any other number thanks to type classes. -------------------------------------------- -- Links -------------------------------------------- Homepage: http://code.haskell.org/~wren/ Hackage: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/logfloat Darcs: http://code.haskell.org/~wren/logfloat -------------------------------------------- -- Details -------------------------------------------- The package's version numbers start from 0.8 since this began as a port of my Perl module for doing the same thing. The code is very heavily documented, largely for pedagogical reasons. Since Haddock doesn't play very nicely with literate Haskell, there's also a small lhs2hs converter script which gets run when you call: runhaskell Setup.hs haddock. This converter requires the bytestring package. The library proper does not, so I didn't include this dependency for the package itself. The package uses GHC's rewrite rules to do log/exp fusion. In general, since a newtype is used, the module shouldn't add overhead (beyond crossing the log/exp boundary). In the future I'll be experimenting with strictness as well to try to ensure that everything stays in registers for those /O(n^3)/ loops. I'm not sure whether it'd be helpful to keep a lazy version around as well... The LogFloat type is restricted to non-negative numbers. In the future I'll also add a signed variant for those who aren't just doing statistical work. -- Live well, ~wren

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What's in a name?
by Andrew Coppin 16 Aug '08

16 Aug '08

The naming of cats is a difficult matter... Ahem. So as you may have noticed, we seem to have a profusion of packages all called "binary" or something dangeriously similar. There's also several "MD5" packages. I could point out a few others. So what I'm wondering is... Do we have a formal convention for the naming of packages and/or the naming of the modules they contain? How are name collisions supposed to be avoided? (E.g., Java uses domain names for this. If I write a package named Foo, I put all the classes in orphi.me.uk.Foo.*)

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why isn't the thread blocked?
by Changying Li 16 Aug '08

16 Aug '08

I writed a little program to test forkIO. in fact, I want to know how to implement the 'select' system call in haskell: module Main where import Control.Concurrent.Chan import Control.Concurrent import System.IO main = do chan <- newChan handles <- mapM ((flip openFile) ReadMode) ["/tmp/a","/tmp/b","/tmp/c"] let readF h = do myID <- myThreadId chan' <- dupChan chan char <- hGetChar h writeChan chan' $ show myID putStrLn [char] threads <- mapM (\h -> forkIO $ readF h) handles nr <- readChan chan mapM killThread $ filter (\x -> show x == nr ) threads putStrLn nr I first mkfifo /tmp/{a,b,c} , then run 'echo "hello" >/tmp/a', then 'runhaskell thisProgram.hs' but I got an error: test.hs: /tmp/b: hGetChar: end of file test.hs: /tmp/c: hGetChar: end of file I think the thread will be blocked when /tmp/b has nothing. but it get EOF, why ? -- Thanks & Regards Changying Li

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GHC 6.8.3 package for ArchLinux x86_64
by Dusan Kolar 15 Aug '08

15 Aug '08

Hello all, Is there any plan to make a package for archlinux x86_64 with (more or less) complete GHC 6.8.3 binaries? I know I can download and install myself, usually I do so myself, but the reason is to prepare a list of packages for others. So far, the 6.8.2 is available. Is there any possibility I could help with it? Some guidelines, how to prepare such a package, submit to a right place, etc. Thanks, Dusan

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whatever happened to sendFile?
by Jason Dusek 15 Aug '08

15 Aug '08

I found an old lib for it: http://www.haskell.org/ghc/docs/6.0/html/unix/System.Sendfile.html Hoogle turns up nothing, though. -- _jsn

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Pretty Print, text or ++?
by Paul Keir 15 Aug '08

15 Aug '08

Hi there, I'm writing a pretty printer using the Text.PrettyPrint library, and there's a pattern I'm coming across quite often. Does anyone know whether, text (a ++ b ++ c ++ d) or text a <+> text b <+> text c <+> text d runs quicker? Cheers, Paul

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"Prompt" Monad
by Martin Hofmann 15 Aug '08

15 Aug '08

I just came across last year's thread about Ryan Ingram's "Prompt" monad ( http://www.mail-archive.com/haskell-cafe@haskell.org/msg33040.html ) and wondered if it might be useful for debugging and program analysis purposes. In particular, I thought about enforcing program decisions interactively. Consider for example modifying the heuristic function of a search algorithm at specific breakpoints. Is this possible with the "Prompt" monad? Furthermore, could somebody post the full code of it (and maybe a short example how to use it if at hand)? I was not able to run the code from the previous posts and the referring links are dead. Thanks a lot, Martin

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Re: [Haskell-cafe] Re: Is www.haskell.org down?
by Donn Cave 14 Aug '08

14 Aug '08

Quoth "Thomas Schilling" <nominolo(a)googlemail.com>: | ... Haskell can learn from | O'Caml, O'Caml can learn from Haskell. I also think that most users | of either language actually know that. I'd like to start with a name for it. - Objective CAML (name of the language) - ocaml (name of the compiler) - OCaml (expedient name for language) I'm always a little piqued by "O'Caml", since I was so fond of O'Haskell. Now, there was a real Irishman. Donn

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Re: [Haskell-cafe] GHC Error: "FATAL:Symbol _XJv_srt already defined."
by Ron Alford 14 Aug '08

14 Aug '08

I reopened the bug, since I found slight changes to the file were able to reproduce the bug in recent versions of ghc-6.9. I also can't get the -S compilation step to work with the new file, unless I'm missing a step. -Ron Alford On Mon, Jul 21, 2008 at 3:32 AM, Ron Alford <ronwalf(a)volus.net> wrote: > Oops, already posted the bug: > http://hackage.haskell.org/trac/ghc/ticket/2456 > > On Mon, Jul 21, 2008 at 3:29 AM, Austin Seipp <mad.one(a)gmail.com> wrote: >> Status update: after checking out the latest HEAD and building it, the >> above error does not occur: >> >> $ ~/ghc-head/bin/ghc --version >> The Glorious Glasgow Haskell Compilation System, version 6.9.20080720 >> $ ~/ghc-head/bin/ghc --make DerivingError.hs >> >> <no location info>: >> Warning: -fallow-overlapping-instances is deprecated: Use the >> OverlappingInstances language instead >> [1 of 1] Compiling DerivingError ( DerivingError.hs, DerivingError.o ) >> $ >> >> However, this doesn't exactly help your immediate problem, and it >> likely won't until 6.10.1 is released, as 6.8.3 is going to be the >> last release of the 6.8 branch. >> >> Truly sorry I couldn't have helped you more. >> >> Austin >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> >

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cabal on ubuntu
by Martin DeMello 14 Aug '08

14 Aug '08

I'm running Ubuntu 8 (Hardy Heron), and while trying to install cabal ran into this bug: https://bugs.launchpad.net/ubuntu/+source/haskell-cabal/+bug/231099 I finally had to install cabal manually, but it took me a lot of googling to be sure that was the right thing to do. Could someone who knows more than me put a howto in the ubuntu wiki https://wiki.ubuntu.com/MOTU/Teams/UncommonProgrammingLanguages/Haskell and/or the haskell one http://www.haskell.org/haskellwiki/GNU/Linux#Ubuntu ? martin

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