April 2005 - Haskell - Haskell.org

readline troubles
by Arjan van IJzendoorn 19 Apr '05

19 Apr '05

Hello all, Using GHCi 6.2.2 and HaXml-1.12 gives you the output below on Windows with Cygwin. I've seen this message on several other occasions and I finally managed to fix this using info at: http://www.haskell.org/pipermail/glasgow-haskell-users/2004-November/007370… (thank you, Sigbjorn!) However, this is no trivial job and everyone who wants to compile a project using readline on Windows needs to patch this. My question is: has this been solved in GHC 6.4 and if not, can this easily be solved? Maybe by including some version of readline in the Windows GHC installation? Cheers, Arjan van IJzendoorn ----------------------- GHCi output [...header...] Loading package base ... linking ... done. Loading package lang ... linking ... done. Loading package haskell98 ... linking ... done. Loading package concurrent ... linking ... done. Loading package QuickCheck ... linking ... done. Loading package readline ... linking ... c:/apps/ghc/HSreadline.o: unknown symbol `_rl_redisplay_function' ghc.exe: unable to load package `readline'

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Re: [Haskell] the wonders of lazy IO
by Cale Gibbard 19 Apr '05

19 Apr '05

> Well, not quite. ($!) (like `seq`, out of which it's built) forces > evaluation only to "weak head normal form": essentially enough to > determine the top-level constructor. Here, for String, that means > only the first character need be evaluated, which in practice means > only the first bufferful of the file is read. You need to use ($!!) > or something like it to force evaluation of the entire file contents. > [See http://www.mail-archive.com/haskell@haskell.org/msg15819.html.] > > Dean > Ah, good point, I missed that.

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the wonders of lazy IO
by Johannes Waldmann 19 Apr '05

19 Apr '05

it took me quite a while to isolate the following. what does this program print? certainly "A" (written by the first system call) is different from "B"? import System main = do system "echo A > foo" a <- readFile "foo" system "echo B > foo" b <- readFile "foo" print (a == b) best regards, -- -- Johannes Waldmann -- Tel/Fax (0341) 3076 6479/80 -- ---- http://www.imn.htwk-leipzig.de/~waldmann/ -------

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Y in haskell?
by Lloyd Allison 18 Apr '05

18 Apr '05

Is it possible to define Y in Haskell (pref' H98) -- and get it to pass type checking? -- E.g. As in SML let datatype 'a rt = recrt of ('a rt) -> 'a; fun Y G = let fun Ggg (recrt g) n = G(g (recrt g))n in Ggg (recrt Ggg) end; fun F f n = if n=0 then 1 else n*f(n-1); in Y F 3 end -- I've tried various things, some of which *seem* to put the checker in a loop? -L --

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big integer in haskell
by ting wang 16 Apr '05

16 Apr '05

Hello all, I am a new learner, and i am trying to write a function to calculate factorial of a natural number: (I use ghc 6.4, window xp) fac :: Int -> Int fac n | n == 0 = 1 | n > 0 = fac (n-1) * n | otherwise = 0 this works when n < 14 and result is 1278945280, when n > 14 the answer is not right n = 15 result is 2004310016. I know it is maybe because of overflow. So i calclate 2^32, 2^64, 2^128 the result correct and is much bigger as 14!,Why? 2^n use some big integer or my implementation of n! is not correct, I'm really confused. Someone can help me? Thanks Ting Wang

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Control.Monad.Writer as Python generator
by ChrisK 16 Apr '05

16 Apr '05

Hi, I was thinking to myself: What in Haskell would give me a "yield" command like a Python generator? And the answer was "tell" in Control.Monad.Writer -- and I wrote some simple examples (see below). Most Python code using yield would be translated to something much more idiomatic in Haskell than using Writer, or to something more complicated if it needed IO. I thought this interesting enough to put on the haskell mailing list and wiki since it seemed to be in neither place (I searched, but your searching may be better than mine). If there are no objections then I'll put this example on the wiki; any suggestions where on wiki to place it (e.g. MonadWriter)? === CUT HERE === import Control.Monad.Writer -- Some type signatures would need -fglasgow-exts to compile -- We only care about the Writer output, not the function return value asGenerator :: Writer [a] v -> [a] asGenerator writer = values where (_,values) = runWriter writer --yield :: (MonadWriter [a] m) => a -> m () yield x = tell [x] -- This allows several items to be yielded with one command --yieldMany :: (MonadWriter [a] m) => [a] -> m () yieldMany = tell zeros :: [Integer] zeros = asGenerator (do yield 0 yield 0 yield 0) zerosInf :: [Integer] zerosInf = asGenerator zeros' where zeros' = (yield 0 >>zeros') -- The Collatz sequence function foo :: (Integral a) => a -> a foo x = case (x `mod` 2) of 0 -> x `div` 2 1 -> (3*x+1) -- Uses "return ()" to end the list when 1 is reached --collatzW :: (MonadWriter [a] m, Integral a) => a -> m () collatzW x = do yield x case x of 1 -> return () _ -> collatzW (foo x) -- Keeps going, will repeat "1,4,2,1,.." if 1 is reached --collatzInfW :: (MonadWriter [a] m, Integral a) => a -> m t collatzInfW x = do yield x collatzInfW (foo x) --collatzGen :: (MonadWriter [a] (Writer [a]), Integral a) => a -> [a] collatzGen x = asGenerator (collatzW x) --collatzInfGen :: (MonadWriter [a] (Writer [a]), Integral a) => a -> [a] collatzInfGen x = asGenerator (collatzInfW x) -- And these can be combined collatz1 x = asGenerator (collatzW x >> yield 0 >> collatzW (x+1)) === CUT HERE === *Main> zeros [0,0,0] *Main> take 10 zerosInf [0,0,0,0,0,0,0,0,0,0] *Main> collatzGen 13 [13,40,20,10,5,16,8,4,2,1] *Main> take 100 $ collatzInfGen 13 [13,40,20,10,5,16,8,4,2,1,4,2,1,4,2,1,4,2,1,4,2,1,4,2,1,4,2,1,4,2,1,4,2, 1,4,2,1,4,2,1,4,2,1,4,2,1,4,2,1,4,2,1,4,2,1,4,2,1,4,2,1,4,2,1,4,2,1,4,2, 1,4,2,1,4,2,1,4,2,1,4,2,1,4,2,1,4,2,1,4,2,1,4,2,1,4,2,1,4,2,1] *Main> collatz1 12 [12,6,3,10,5,16,8,4,2,1,0,13,40,20,10,5,16,8,4,2,1]

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FroCoS 2005: Last Call for Papers
by Bernhard Gramlich 15 Apr '05

15 Apr '05

[Apologies for multiple copies] ---------------------------------------------------------------------------- FroCoS 2005: LAST CALL FOR PAPERS ---------------------------------------------------------------------------- NEW: Submission site: http://www.logic.at/frocos05/submit/ Invited speakers (complete list) SUBMISSION DEADLINE APPROACHING: May 2, 2005 (abstracts) May 9, 2005 (papers) ---------------------------------------------------------------------------- 5th International Workshop on Frontiers of Combining Systems (FroCoS 2005) Vienna, Austria, September 19-21, 2005 http://www.logic.at/frocos05/ ---------------------------------------------------------------------------- BACKGROUND In various areas of computer science, such as logic, computation, program development and verification, artificial intelligence, and automated reasoning, there is an obvious need for using specialized formalisms and inference mechanisms for special tasks. In order to be usable in practice, these specialized systems must be combined with each other, and they must be integrated into general purpose systems. The development of general techniques and methods for the combination and integration of special formally defined systems, as well as for the analysis and modularization of complex systems has been initiated in many areas. The International Workshop on Frontiers of Combining Systems (FroCoS) traditionally focuses on this type of research questions and activities and aims at promoting progress in the field. The previous FroCoS workshops were held in Munich (1996), Amsterdam (1998), Nancy (2000) and Santa Margherita Ligure (2002). In 2004, FroCoS joined IJCAR 2004, the 2nd International Joint Conference on Automated Reasoning. Like its predecessors, FroCoS 2005 wants to offer a common forum for research activities in the general area of combination, modularization and integration of systems (with emphasis on logic-based ones), and of their practical use. TOPICS Typical topics of interest include (but are not limited to): * combination of logics (e.g., modal logics, logics in AI, ...); * combination of decision procedures, of satisfiability procedures, and of constraint solving techniques (e.g. unification and matching algorithms, general symbolic constraints, numerical constraints); * combinations and modularity in term rewriting; * integration of equational and other theories into deductive systems (e.g. theory resolution, constraint resolution, constraint paramodulation, ...); * combination of deduction systems and computer algebra; * integration of data structures (e.g., sets, multisets, lists) into CLP formalisms and deduction processes; * model/problem analysis and decomposition (e.g. isolating tractable or loosely connected sub-problems, global constraints design, etc.) * hybrid methods for deduction, resolution and constraint propagation (e.g., combinations of local and global, complete and propagation techniques) * hybrid systems in computational linguistics, knowledge representation, natural language semantics, and human computer interaction; * logical modelling of multi-agent systems; * logical aspects of combining and modularizing programs and specifications. INVITED SPEAKERS * Luca de Alfaro (U California, Santa Cruz) * Silvio Ghilardi (U Milano) * Fausto Giunchiglia (U Trento & ITC-IRST) * Eric Monfroy (U Nantes & UTFSM/Chile) SUBMISSIONS The programme committee seeks high-quality submissions that are original and not submitted for publication elsewhere. Submission is electronic in postscript or PDF format. Submitted papers must conform to the Springer LNCS style, preferably using LaTeX2e and the Springer llncs class files. Submission categories include full papers, for work on foundations, applications, implementation techniques, and problem sets (up to 15 pages), as well as system descriptions (up to 8 pages), for describing publicly available systems. The submission deadline is May 2, 2005 for titles and abstracts, and May 9, 2005 for papers. For further information and submission instructions see the FroCoS 2005 web page: http://www.logic.at/frocos05/. PROCEEDINGS Accepted papers will appear in the proceedings of the conference, published as a volume of the Lecture Notes in Artificial Intelligence (LNAI) series, Springer-Verlag. Proceedings will be available at the time of the conference. IMPORTANT DATES May 2, 2005: Deadline for electronic submission of abstract May 9, 2005: Deadline for electronic submission of papers June 20, 2005: Notification of acceptance/rejection Jul 11, 2005: Deadline for final versions of accepted papers Sep 19-21, 2005: Conference PROGRAM COMMITTEE * Alessandro Armando (U Genova) * Franz Baader (TU Dresden) * Clark W. Barrett (NYU New York) * Frederic Benhamou (LINA, U Nantes) * Michel Bidoit (LSV, CNRS & ENS Cachan) * Jacques Calmet (U Karlsruhe) * Juergen Giesl (RWTH Aachen) * Bernhard Gramlich (chair) (TU Wien) * Deepak Kapur (UNM Albuquerque) * Maarten Marx (U Amsterdam) * Joachim Niehren (INRIA Futurs, U Lille) * Christophe Ringeissen (LORIA-INRIA Nancy) * Manfred Schmidt-Schauss (U Frankfurt) * Cesare Tinelli (U Iowa) * Ashish Tiwari (SRI Menlo Park) * Frank Wolter (U Liverpool) ORGANIZING COMMITTEE * Aneta Binder * Bernhard Gramlich * Franziska Gusel * Gernot Salzer * Jana Srna PROGRAM COMMITTEE AND CONFERENCE CHAIR Bernhard Gramlich TU Wien, Fakultaet fuer Informatik, Theory and Logic Group Favoritenstr. 9 - E185/2, A-1040 Wien, Austria Email: frocos05(a)logic.at FURTHER INFORMATION FroCoS 2005 web page: http://www.logic.at/frocos05/ ----------------------------------------------------------------------------

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Do you use GHC?
by Simon Peyton-Jones 15 Apr '05

15 Apr '05

Dear Haskell folk, PLEASE READ THIS IF YOU USE THE Glasgow Haskell Compiler (GHC). I virtually never send messages to overlapping sets of lists, but I'm doing so this time, because I'd really like to get to everyone who uses GHC. Here at GHC HQ, we are often asked how many people use GHC, and what kind of folk they are. Since GHC is free software, we have no clue. Download stats tell us a bit, but not much, because GHC gets out through a variety of other routes too (e.g. Debian). We also have little idea about which aspects of GHC are most valued, nor of what enhancements would be most sought after, or which platforms are most important to you. We hear quite a bit from the bleeding-edge folk who push the limits, but much less from people who just want to get the job done. Thus motivated, Tomasz Zielonka kindly put together a (WASH-powered) survey for us, which asks you to tell us a bit yourself and how you use GHC. We've had about 230 responses so far; thank you to those 230 folk. But I'm pretty certain there are more than 230 people in the world who use GHC! THIS MESSAGE IS TO ASK YOU TO TAKE 5 MINS TO COMPLETE THE SURVEY http://www.haskell.org/ghc/survey/start.cgi We'd like to hear from *absolutely everyone* who uses GHC: whether you are a first-year undergraduate or a famous professor; whether you use GHC for industrial applications or recreation; whether you use higher-rank polymorphism or have only just learned what functional programming is. Everyone! We'll use the information to guide our future priorities, and we'll publish some kind of summary of what we learn in due course. It's all anonymous, of course, unless you choose to say who you are. If you think it's appropriate, please circulate this announcement locally, e.g. to your students who may not be on the Haskell mailing list Many thanks Simon PJ and Simon Marlow

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ANNOUNCE: Haskell XML Toolbox Version 5.01
by Uwe Schmidt 14 Apr '05

14 Apr '05

Haskell XML Toolbox 5.01 I would like to announce a new version of the Haskell XML Toolbox for processing XML including a validating parser and a new XPath module. new features: * works with ghc-6.4 * more flexible and cleaner arrow interface for XML filter * cabal installation More information and download: http://www.fh-wedel.de/~si/HXmlToolbox/index.html Please email comments, bugs, etc. to hxmltoolbox(a)fh-wedel.de Uwe Schmidt <uwe(a)fh-wedel.de> -- University of Applied Sciences, Wedel, Germany http://www.fh-wedel.de/~si/index.html

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HCAR?
by Ashley Yakeley 14 Apr '05

14 Apr '05

Was there a call for HCAR contributions on this list? Did I miss it? -- Ashley Yakeley, Seattle WA

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