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Proposal: add exeExtension to System.Info
by Dimitry Golubovsky 19 Jul '07

19 Jul '07

Hi, While adopting my older program to the newer (GHC 6.6) infrastructure, I came across the issue: OS-dependent functions like exeExtension are missing in the newer version of the FilePath package. I checked with Neil who currently maintains FilePath, and he agreed with me on this idea. I am proposing to add the following to the System.Info module (which seems to be the best place to collect OS-specific things) - the code was found in Distribution.Compat.FilePath and slightly modified (#if directive) in the same way as the current System.FilePath distinguishes between Posix and Windows interfaces: ------------------------------- begin -------------------------------------- -- | Extension for executable files -- (typically @\"\"@ on Unix and @\"exe\"@ on Windows or OS\/2) exeExtension :: String #if defined(mingw32_HOST_OS) || defined(__MINGW32__) exeExtension = "exe" #else exeExtension = "" #endif -- | Extension for object files. For GHC and NHC the extension is @\"o\"@. -- Hugs uses either @\"o\"@ or @\"obj\"@ depending on the used C compiler. objExtension :: String objExtension = "o" -- | Extension for dynamically linked (or shared) libraries -- (typically @\"so\"@ on Unix and @\"dll\"@ on Windows) dllExtension :: String #if defined(mingw32_HOST_OS) || defined(__MINGW32__) dllExtension = "dll" #else dllExtension = "so" #endif ------------------------------- end -------------------------------------- Thanks -- Dimitry Golubovsky Anywhere on the Web

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Data.Map.updateAt problem
by Andriy Palamarchuk 18 Jul '07

18 Jul '07

I'm currently improving Data.Map documentation. Behavior of updateAt in this module differs from what I would expect. The documentation says: updateAt :: (k -> a -> Maybe a) -> Int -> Map k a -> Map k a O(log n). Update the element at index. Calls error when an invalid index is used. So I expected this code: let m = fromList [(3,"b"),(5,"a")] let f k a = Just "x" updateAt f 1 m to return fromList [(3,"b"),(5,"x")] but it returns fromList [(5,"x")] deleting the key 3. I tested this using ghci 6.6. Is this a bug or I missed something here? Thanks, Andriy ____________________________________________________________________________________ Fussy? Opinionated? Impossible to please? Perfect. Join Yahoo!'s user panel and lay it on us. http://surveylink.yahoo.com/gmrs/yahoo_panel_invite.asp?a=7

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Control.Concurrent.Chan: how do i close a channel?
by Claus Reinke 18 Jul '07

18 Jul '07

in principle, Chan looks like a nice way to do pipes within haskell code, or to avoid unsafeInterleaveIO, in combination with getChanContents (which explicitly mentions hGetContents in its API doc). however, i seem to be missing a way to close a channel? am i misinterpreting this library? claus

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ANNOUNCE: Haskell Hackathon 07 II: Freiburg: Oct 5-7
by dons＠cse.unsw.edu.au 17 Jul '07

17 Jul '07

------------------------------------------------------------------------ Hac 2007 II Haskell Hackathon 2007 II October 5-7, 2007 Freiburg, Germany http://haskell.org/haskellwiki/Hac_2007_II ------------------------------------------------------------------------ We are pleased to announce the 2nd Haskell Hackathon for 2007! The event will be held over 3 days, October 5-7 2007, at the University of Freiburg, in Germany, after ICFP. The plan is to hack on serious Haskell infrastructure, tools, libraries and compilers. To attend please register, and get ready to hack those lambdas! Code to hack on: * Hackage * Cabal * Porting foreign libraries * Bug squashing * You decide! At the last Hackathon, in January at Oxford, resulted in: * Cabal, Hackage, Haddock improvements * Data.Binary and DeferedBinary libraries * GHCi debugger improvements * ghc-api interface from Emacs * Crypto lirbary improvments * A native Haskell 'tar' implementation * And more And we hope to be similarly productive this time around. Before you attend, do start thinking and familiarising yourself with 1 or 2 projects you wish to work on, to ensure no wasted effort during the Hackathon. A list of possible projects is available on the website == Registration: We ask that you register you interest. Follow the instructions on the registration page: http://haskell.org/haskellwiki/Hac_2007_II/Register Once you've registered, do add your info to the attendees self-organising page, http://haskell.org/haskellwiki/Hac_2007_II/Attendees if you are looking to share costs, or meet up prior to the hackathon, with other attendees. N.B. if you already expressed interest via the wiki, do confirm by registering `officially' anyway. == Important dates: Hackathon: October 5-7, 2007 == Organisers: Duncan Coutts Ian Lynagh Don Stewart With local arrangements courtesy: Stefan Wehr Phillip Heidegger

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System.Posix.User.getAllUserEntries can be called only once
by Sascha Böhme 16 Jul '07

16 Jul '07

Hello, are there special constraints why the function System.Posix.User.getAllUserEntries of the unix package can be called only once? Beginning with the second call, it only returns the empty list. Thus, this function cannot be used for a long running process which needs to query the user database from time to time, again and again. Thanks, Sascha

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Functor (Either a)
by Conor McBride 16 Jul '07

16 Jul '07

Hi all I read TFM http://haskell.org/ghc/docs/latest/html/libraries/base/ Prelude.html#t%3AFunctor and it does rather suggest that there's an instance of Functor for (Either a). Yet, ___ ___ _ / _ \ /\ /\/ __(_) / /_\// /_/ / / | | GHC Interactive, version 6.6, for Haskell 98. / /_\\/ __ / /___| | http://www.haskell.org/ghc/ \____/\/ /_/\____/|_| Type :? for help. Loading package base ... linking ... done. Prelude> fmap not (Right True) <interactive>:1:0: No instance for (Functor (Either a)) arising from use of `fmap' at <interactive>:1:0-20 Am I being dim? Conor

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darcs patch: s6_addr32 is undefined on darwin. Added an AC check a...
by Thomas Schilling 13 Jul '07

13 Jul '07

Fri Jun 22 18:58:52 CEST 2007 Thomas Schilling <nominolo(a)gmail.com> * s6_addr32 is undefined on darwin. Added an AC check and a definition taken from the NetBSD sources.

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Proposal: Data.Stream
by Wouter Swierstra 13 Jul '07

13 Jul '07

Dear all, I just uploaded a fairly unspectacular package Data.Stream to Hackage. It implements quite a few operations on streams (infinite lists), analogous to those defined in Data.List. Sometimes it is just good to know a list is infinite. * Haddock documentation: http://www.cs.nott.ac.uk/~wss/repos/Stream/ dist/doc/html/ * Hackage homepage: http://hackage.haskell.org/cgi-bin/hackage- scripts/package/Stream-0.1 I know of a few libraries that implement this package themself (Ross Paterson's arrow library and my IOSpec spring to mind). I think it's fairly uncontroversial, and would like to see it added to base (I realize that there are also proposals to clean up base to speed up the build of ghc), or at least, the standard libraries. What's the right way to accomplish this? Send a darcs patch to Ian? Submit a trac ticket? Thanks, Wouter

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Re: Optimising words
by Neil Mitchell 11 Jul '07

11 Jul '07

Hi > > Now we have eliminated an extra isSpace test per character, and as it > > happens, isSpace is very slow. > > Isn't it possible to improve isSpace, too? Yes, most definitely. But unless we improve it to the stage where it takes 0 time, its still worth eliminating useless additional calls. Thanks Neil

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Optimising words
by Neil Mitchell 10 Jul '07

10 Jul '07

Hi While benchmarking a word count program I found that it wasn't running as fast as it could. I traced this back to the original definition of words, which isn't as good as it could be: This is the version in Base: words :: String -> [String] words s = case dropWhile isSpace s of "" -> [] s' -> w : words s'' where (w, s'') = break isSpace s' We can instantiate s' with s:ss, since we already pattern match: words :: String -> [String] words s = case dropWhile isSpace s of "" -> [] s:ss -> w : words s'' where (w, s'') = break isSpace (s:ss) Now we know that s is not a space, since if it was the dropWhile would have removed it. This means that we don't need to test it, and can put it straight on to w: words :: String -> [String] words s = case dropWhile isSpace s of "" -> [] s:ss -> (s:w) : words s'' where (w, s'') = break isSpace ss Now we have eliminated an extra isSpace test per character, and as it happens, isSpace is very slow. Is my reasoning correct? If so, can we make this optimisation? Thanks Neil

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