November 2007 - Haskell-Cafe

Polymorphic dynamic typing
by Paulo Silva 23 Nov '07

23 Nov '07

Hello, Type representations using GADTs are being used to achieve dynamic typing in Haskell. However, representing polymorphic types is problematic. Does anyone know any work about including polymorphism in dynamic typing? Best regards, Paulo

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very elementary "import" problem .. help
by Galchin Vasili 23 Nov '07

23 Nov '07

Hello, import System.Posix --import Network import System.Process --import Directory import STM I am loading the above script in ghci. However, System.Posix, System.Processand STM cannot be found. Network and Directory are found. I assume when ghc is installed on Windows that the Windows registry get populated with paths to GHC 'library" directory paths. Please someone tell me why I am having trouble importing these modules/libraries. Kind regards, vasya

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Interrupting threads and ualarm
by ROBERT DOUGLAS HOELZ 23 Nov '07

23 Nov '07

Hello Haskellers, I have two questions for you: * Is there a Haskell binding to the ualarm() function in unistd.h? I looked in System.Posix.Signals, but there's just a binding for alarm(). * Is there a way to interrupt a blocking operation on another thread? I thought about throwTo, but that seems like overkill. Here's some example code: import Control.Concurrent main :: IO () main = do tid <- myThreadId forkIO $ interruptMain tid getChar interruptMain :: ThreadId -> IO () interruptMain mainThreadId = do threadDelay 5000000 interrupt mainThreadId -- This is probably going to end up being throwTo, isn't it?

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c2hs on Windows?
by Alex Young 23 Nov '07

23 Nov '07

Hi all, Does anyone know if c2hs should be working on Windows? I'm trying to build it under ghc 6.8.0, but this happens: C:\Users\Alex\Documents\Plugins\c2hs\c2hs-0.15.0>runghc Setup.hs configure Configuring c2hs-0.15.0... Setup.hs: Error: Non-empty library, but empty exposed modules list. Cabal may not build this library correctly C:\Users\Alex\Documents\Plugins\c2hs\c2hs-0.15.0>runghc Setup.hs build Setup.hs: error reading dist\setup-config; run "setup configure" command? Apologies if I'm being dense... Thanks, -- Alex

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http/ftp library
by Bulat Ziganshin 23 Nov '07

23 Nov '07

Hello Haskell-Cafe, i write a file-processing utility and want to allow users open URLs like the usual files. for this, i need a library with minimum the following http functionality: getFileSize url readBuf url bufPtr offset size ideally, it should also support ftp and allow to create ftp files: h <- create url writeBuf h bufPtr size close h what libraries can i use? ghc 6.6.1, if it's important -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com

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ANN: Dimensional 0.7.1 (GHC 6.8.1 compatibility)
by Bjorn Buckwalter 23 Nov '07

23 Nov '07

Dear all, The Dimensional library has been ported to GHC 6.8.1 (it remains backwards-compatible with GHC 6.6.1, and also with Cabal 1.1.6 I believe). The new version number is 0.7.1. Due to a GHC 6.8.1 bug (#1919) the CGS module will not compile and has been disabled. Thanks, Bjorn Buckwalter http://dimensional.googlecode.com http://hackage.haskell.org/cgi-bin/hackage-scripts/package/dimensional http://hackage.haskell.org/trac/ghc/ticket/1919

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Digest size
by Simon Marlow 23 Nov '07

23 Nov '07

[ with mailing list maintainer's hat on ] Someone asked me if they could get fewer digests per day from haskell-cafe. The threshold for sending out a digest is currently 30k, which is probably the default, but seems a bit small to me. Any objections to bumping it, to say 100k? Cheers, Simon

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Source code for Visual Haskell
by Felix Martini 23 Nov '07

23 Nov '07

Hi all, The documentation of Visual Haskell mentions that the source code is available under a BSD license. The code is not available from the download page (http://www.haskell.org/visualhaskell/downloads.html) Does anone know where to get it?

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Tetris
by Andrew Coppin 23 Nov '07

23 Nov '07

If you were going to implement Tetris in Haskell, how would you do it? (For that matter, has anybody already *done* it? It would probably make a nice example program...) I'm particularly interested to know 1. How exactly would you do the graphical components? (Presumably there's some deep trickery with Gtk2hs that can draw free-form stuff like this.) 2. How do you implement a program that is fundamentally about state mutation in a programming language which abhors state mutation?

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expanded standard lib
by brad clawsie 23 Nov '07

23 Nov '07

i would categorize myself as a purely practical programmer. i enjoy using haskell for various practical tasks and it has served me reliably. one issue i have with the library support for practical problem domains is the half-finished state of many fundamental codebases such as networking and database support. in the perl world, support for these domains is provided through cpan, and this model is viable due to the (once) massive number of perl coders out there. in the java, c# etc world, a "batteries included" approach implies a narrowing of options, but also an immediate delivery of functionality. so far the haskell community has taken the cpan route for most practical libs but i wonder if a "batteries included" approach might help get some key libraries to a more complete state. in particular, i would like to see support for basic internet protocols, database connectivity, and potentially xml parser support rolled into the ghc standard libs. there is always a strong debate on where the line is drawn, but this functionality at least shows up in a plurality of practical projects. the "batteries included" approach does imply choosing preferred solutions when more than one library is available, this can also be difficult. that said, i think haskell would pick up a lot of new coders if it was obvious that the functionality they were looking for came out of the base libs. i know that people will say they don't use a database or xml, but there will always be parts of a standard library that any particular coder will never touch...but still see value in the inclusion for others. comments?

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