February 2004 - Haskell

ANNOUNCE: HsUnix 1.0.1 - Haskell for Unix Shell Scripting
by Volker Wysk 10 Feb '04

10 Feb '04

I'm pleased to announce the first release of the HsUnix library. It enables you to do things easily in Haskell which are typically done by the shell. Thus Haskell can be used to write shell scripts. Features -------- Command Line Arguments Parser HsUnix has facilities for managing command line arguments, which are (hopefully) easier to use than the GHC library GetOpt. Command line arguments are described in lists of properties. HsUnix builds on top of GetOpt, but hides it completely. Command line arguments handling has been added because GetOpt was found to be too cumbersome. Shell Like Commands HsUnix has a growing list of front end functions for shell like programming, such as chmod or mkdir. They wrap calls to external programs, system calls or standard Haskell functions. Analyzing Paths Dealing with paths is not as trivial as it sounds. Take, for example ../for///./../bar/. HsUnix has taken care of it thoroughly and provides functions such as splitting a path into (real) path components, or syntactically normalising paths. Dealing with Processes and Calling External Programs There are corresponding functions in the GHC Posix library, but the ones here are simpler. Redirecting Input and Output HsUnix defines operators like ->- and ->>- which work just like redirection operators in shells. Building Pipes Reading the output of an external program, or piping the output of one program into the input of another, is almost as easy as in shells. HsUnix provides corresponding operators. Error Handling Error handling is one thing which is done much more thoroughly in HsUnix than in shells. Failed programs won't be silently ignored. Dynamic exceptions are used for error handling. Non zero exit codes are thrown as exceptions. Quoting of Strings and Building Commands for Shells Taking care of shell metacharacters usually isn't done right. HsUnix provides functions for doing it safely. Homepage -------- http://www.volker-wysk.de/hsunix -- Volker Wysk <post(a)volker-wysk.de> http://www.volker-wysk.de

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Lectureship in Nottingham
by Graham Hutton 10 Feb '04

10 Feb '04

Dear all, We are currently advertising a new lectureship (assistant professorship) in Nottingham, England. There are no particular research areas specified for this position, but applications in the area of the Foundations of Programming research group (http://www.cs.nott.ac.uk/Research/fop/) would be most welcome. Further details are available from: http://www.nottingham.ac.uk/hr/vacancies/academic.html#RUB591S The closing date for applications is 26th February 2004. Graham Hutton +---------------------------------------------------------------------+ | Dr Graham Hutton Email : gmh(a)cs.nott.ac.uk | | School of Computer Science and IT Web : www.cs.nott.ac.uk/~gmh | | University of Nottingham | | Jubilee Campus, Wollaton Road | | Nottingham NG8 1BB Phone : +44 (0)115 951 4220 | | United Kingdom Fax : +44 (0)115 951 4254 | +---------------------------------------------------------------------+

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newbie question
by Lee Render 10 Feb '04

10 Feb '04

is "HaskellScript" still working? I tried mucking around with this lately using the latest version of Hugs but the example scripts seemed broken. __________________________________ Do you Yahoo!? Yahoo! Finance: Get your refund fast by filing online. http://taxes.yahoo.com/filing.html

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vim syntax files for GHC-style .lhs, .hs + cpp
by dons＠cse.unsw.edu.au 09 Feb '04

09 Feb '04

Hey all, ------------------------------------------------------------- Vim syntax highlighting for GHC-style .lhs and .hs + cpp ------------------------------------------------------------- Rather than let this just sit on my hd, I'm making them available. ftp://ftp.cse.unsw.edu.au/pub/users/dons/vim/ These are vim syntax files for the tex-style (not the bird-feet style) literate Haskell used in much of GHC, and for normal Haskell with -cpp preprocessor sprinkles. The directories should go in your ~/.vim/ folder. There is also a preliminary outline of a vim indent file for .hs code. If you'd like to finish this off, then send me diff's please! The .lhs file still has a few minor buglets, so by making this stuff available I'm hoping someone has time to fix them. Cheers, Don

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LDTA 2004 - Call for Participation
by jas＠di.uminho.pt 09 Feb '04

09 Feb '04

Apologies if you receive multiple copies of this message. ********************************************************** *** Fourth Workshop on *** *** Language Descriptions, Tools and Applications *** *** LDTA 2004 *** *** *** *** Satellite event of ETAPS 2004 *** *** *** *** In Co-Operation with ACM SIGPLAN *** *** *** *** APRIL, 3, 2004 *** *** BARCELONA, SPAIN *** *** *** *** http://www.di.uminho.pt/LDTA04 *** ********************************************************** --> Deadline for early registration: February, 15 The ETAPS online registration form is available at http://www.lsi.upc.es/etaps04/Registration/registration-frame.html - The LDTA 2004 Preliminary Program is available at http://www.cs.lth.se/Research/LDTA2004/ - Invited speaker: Jim Cordy, Queen's University, Canada Title of the talk: TXL - A Language for Programming Language Tools and Applications

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behavioral difference between GHC and GHCi
by S. Alexander Jacobson 09 Feb '04

09 Feb '04

This code works echos lines properly under GHCi, but just sucks in input when running the GHC compiled executable. import IO main= do x<-hGetLine stdin putStr x main Am I doing something wrong? -Alex- _________________________________________________________________ S. Alexander Jacobson mailto:me@alexjacobson.com tel:917-770-6565 http://alexjacobson.com

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Making Haskell web development easier
by S. Alexander Jacobson 08 Feb '04

08 Feb '04

I decided to try developing a web app using Haskell/HaskellWebServer/HaXML and found the barriers both very high and perhaps easily lowered. Could someone out there: -- 1. Provide a link to the Haskell web server CODE on <http://www.haskell.org/practice.html> (or, if it has been end of lifed, remove it from the CVS repository) 2. Document anon CVS access to haskell.org in some obvious location? 3. Add a README for the package saying * this the package doesn't build with enclosed Makefile * this the package doesn't buld on win32 because it depends on the posix package * STRONGLY suggest that people use the sourceforge package rather than this one --- Also, what does it take to get posix/HWS working on win32? I suspect that much of posix is easily portable, but that a few functions are not. I don't know if HWS is dependent on these functions? If HWS (and other packages) actually use the portable subset of posix, perhaps it makes sense to create a separate posix_LowestCommonDenominator package. If not, how much effort is involved in making the posix package work on win32? -Alex- _________________________________________________________________ S. Alexander Jacobson mailto:me@alexjacobson.com tel:917-770-6565 http://alexjacobson.com

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[Fwd: Midland Graduate School 2004 / APPSEM Spring School 2004]
by Conor McBride 05 Feb '04

05 Feb '04

Hello all I'm forwarding this announcement on behalf of Thorsten Altenkirch. Conor

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What are possible causes of "C stack overflow" in Hugs?
by Graham Klyne 05 Feb '04

05 Feb '04

I'm getting a "C stack overflow" error from Hugs when processing a moderately large dataset, but not doing anything that looks unreasonably complex or involved. As far as I can tell, the code causing the problem is about here: [[ -- Return list of distinct labels used in a graph graphLabels :: (Label lb) => [Arc lb] -> [lb] graphLabels gs = graphLabels1 gs [] graphLabels1 (t:gs) ls = graphLabels1 gs $ foldl (flip addSetElem) ls (arcLabels t) graphLabels1 [] ls = ls ]] I think the function graphLabels1 is set to call itself recursively to a depth of a little over 1000. Can this kind of recursion blow the Hugs stack? This code has been working quite happily for some time. The called function arcLabels is quite trivial, and addSetElem is pretty simple too: [[ addSetElem :: (Eq a) => a -> [a] -> [a] addSetElem e es = if e `elem` es then es else e:es ]] ... I changed the function 'graphLabels' thus: [[ graphLabels :: (Label lb) => [Arc lb] -> [lb] graphLabels gs = nub $ concat $ map arcLabels gs ]] and the C stack overflow goes away. But I've been burned in the past with serious performance problems using nub, so I'm wary of this. #g ------------ Graham Klyne For email: http://www.ninebynine.org/#Contact

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partition in Data.List bug
by Koji Nakahara 04 Feb '04

04 Feb '04

Hi, I've encountered a bug of partition in Data.List shipped with ghc-6.2 and hugs(Nov 2002) It cannot work with an infinite list. Example: > partition (==0) (cycle [0,1]) does not return and so not conform to the specification in the Haskell 98 and the library document. I found some discussion on this bug in the haskell mailing-list archive, e.g. http://www.mail-archive.com/haskell@haskell.org/msg07789.html Is there some good reason not to change this behaviour? (And if it is, I think that the library document should be fixed.) Patch: --- List.hs.orig Thu Feb 5 04:15:59 2004 +++ List.hs Thu Feb 5 04:16:31 2004 @@ -240,8 +240,8 @@ {-# INLINE partition #-} partition p xs = foldr (select p) ([],[]) xs -select p x (ts,fs) | p x = (x:ts,fs) - | otherwise = (ts, x:fs) +select p x ~(ts,fs) | p x = (x:ts,fs) + | otherwise = (ts, x:fs) -- @mapAccumL@ behaves like a combination -- of @map@ and @foldl@; --- Koji Nakahara

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