November 2002 - Haskell

Announce: Update of the Haskell Bibliography
by Benderjgdefault＠aol.com 28 Nov '02

28 Nov '02

I have just finished a major update of the Haskell bibliography: http://haskell.readscheme.org/ This update includes 135 new citations (a 40% increase in the size of the bibliography). Jim Bender

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RE: "cartesian classes"
by David Bergman 27 Nov '02

27 Nov '02

Frank, Then we do mean the same thing, because a relation is indeed a subset of a cartesian product ;-) That is what I meant with "cartesian classes". Sorry for any confusion that might have caused. And, I am fully aware that most people in this mail group are quite familiar with simple set-theoretic concepts, but since the question was raised, and I know that there are a few more pragmatic programmers aboard, I assumed it would not hurt to explain that a bit. I still think "multi-parameter classes" is bad terminology, though, since the subconstruct "C a b" in the class declaration "class C a b where ..." does not denote a class (template), but the "C" does... This is in contrast to "multi-parameter types", such as "data Tree a b = Leaf a | Branch b (Tree a b) (Tree a b)" where the subconstruct "Tree a b" does denote a type (template). Maybe I am the only one with this view... Thanks for the concrete usage info for functional dependencies restricting these "class relations". David -----Original Message----- From: Frank Atanassow [mailto:franka@cs.uu.nl] Sent: Wednesday, November 27, 2002 10:15 AM To: David Bergman Subject: Re: "cartesian classes" David Bergman wrote (on 26-11-02 13:18 -0500): > > What do you mean by "cartesian classes"? Do you mean multi-parameter > > type classes? > > > They're supported by GHC and Hugs, but not NHC98 or HBC. The same goes > > for functional dependencies. > > Yes, I meant what is commonly known as multi-parameter type classes, > although that name IMHO does not make much sense, since only the > explicitly parameterized type class should qualify as a any-parameter > type class, with the (non-Haskell syntax) "b in C a", where "a" is the > parameter, "C a" the resulting type class, and, finally, "b" the (type) > element of the class. > > In a regular class declaration, "C a", I would argue that "C" is the > class, not being single-parameter, but zero-parameter. It is sometimes > unfortunate that the syntax of Haskell makes this look like a > constructor... I'm afraid I don't understand this. If it helps, the way I think of classes is that they are predicates/relations at the type level; a multi-parameter class gives an n-ary predicate for n>1. So, in: class C a b c where ... C is a ternary predicate and instance C Int Char Int where ... says that (Int, Char, Int) is a member of C regarded as a subset of a product of sets. > What I meant by cartesian is that using several variables, you would get > (also in non-Haskell syntax) "(a, b, c) in C", i.e., the class actually > being a subclass of the third cartesian power of the universal > (implicit) type class. Yes, I know what cartesian products, categories and coordinate systems are, but I've never heard multi-parameter type classes referred to that way before. > If both GHC and Hugs support functional dependencies, I would probably > dare to wander off into the mysterious land of Haskell 2. > > A very concrete, but naïve, question: what is the syntax for defining > functional dependencies in Hugs and GHC? Since Mark Jones' syntax was > abstract in his paper, it is kind of hard to deduce an ASCII equivalence > (I have tried to figure out how to create a curly arrow from the > keyboard ;-) The syntax is, for example: class Class a b c d | a c -> b d where ... meaning that a and c determine b and d, so if the declaration instance Class A B C D is in scope, then, for all B', D' s.t. B'/=B or D'/=D, it is illegal for there to be a declaration of the form instance Class A B' C D' also in scope. There is an account of the syntax and semantics in the Hugs manual, 7.1.1.3: http://cvs.haskell.org/Hugs/pages/hugsman/exts.html -- Frank

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IEEE/ACM MEMOCODE'03: Call for papers
by Miroslav Velev 27 Nov '02

27 Nov '02

Call for Papers: IEEE/ACM METHODS and MODELS for CODESIGN (MEMOCODE 2003) Homepage: http://www.irisa.fr/manifestations/2003/MEMOCODE/ Sponsors: IEEE Circuits and System Society ACM Special Interest Group on Digital Automation IEEE Computer Society, Digital Automation Technical Committee Organized at the Relais du Mont Saint-Michel in cooperation with INRIA and IRISA. High-level design and modeling of hardware and embedded hardware-software systems has gained prominence in the face of rising technological complexities and performances, as well as shortened time to market demands for complex electronic equipments. Numerous programming languages, tools and frameworks have been proposed in the past to design, simulate and validate heterogeneous systems within an abstract and rigorously defined mathematical model. Recently, attention has shifted to modeling frameworks based on variants of general purpose programming languages, in response to the growing industry demand for use of higher levels of abstraction in the system design process. Meanwhile, the installed base of existing IP adds further requirements for the adaptation of existing IPs with new services within complex integrated architectures, calling for appropriate methodological approaches. Whereas abstract frameworks are ways to unambiguously model the essence of hardware software systems, help understand the design, implement formal correctness proofs, predict performances and other metrics; general-purpose languages facilitate programming, reuse and gain from the popularity of C, C++ like languages. Still, important gaps need to be filled and bridges to be built between the theory of modeling and the practice of programming. Languages shall benefit the rigorousness of models and models the experience of programming practice. This calls for finding a convergence between both approaches. A focus on formal methods (programming and concurrency models, analysis and verification techniques) for hardware/software codesign is necessary, because language in which system designers work are general-purpose ones, because the only way provably correct systems can be constructed are by technology transfer of research in formal methods. Opening speaker Jose Meseguer (SRI) Invited speakers Ahmed Jerraya (IMAG) Nancy Lynch (MIT) Ken McMillan (Cadence) Program co-chairs Sandeep K. Shukla (Virginia Tech) Jean-Pierre Talpin (INRIA) Program committee Gul Agha (University of Illinois at Urbana-Champaign) Arvind (Massachussets Institute of Technology) Brian Bailey (Mentor Graphics) François Bodin (University of Rennes-IRISA) Forrest Brewer (University of California at Santa Barbara) Stephen Edwards (Columbia University) Hans Eveking (University of Darmstadt) Harry Foster (Verplex Systems) Franco Fummi (University of Verona) Vijay Kumar Garg (University of Texas at Austin) Rajesh Gupta (University of California at San Diego) Connie Heitmeyer (Naval Research Laboratory) James Hoe (Carnegie Mellon University) Alan Hu (University of British Columbia) Marta Kwiatkowska (University of Birmingham) Kim Larsen (Aalborg University) Paul Le Guernic (INRIA-IRISA) Stan Liao (Synopsys) Grant Martin (Cadence) Hillel Miller (Motorola) Zebo Peng (Linköping University) Carl Pixley (Synopsys) Rob Slater (Motorola) Sandeep Kumar Shukla (Virginia Tech) Jean-Pierre Talpin (INRIA-IRISA) Marten Van Hulst (Philips Research) Miroslav Velev (Georgia Tech) Wayne Wolf (Princeton University) Steering committee Masahiro Fujita (University of Tokyo) Vijay Kumar Garg (University of Texas at Austin) Paul Le Guernic (INRIA-IRISA) Rajesh Gupta (University of California at Irvine) Nancy Lynch (Massachussets Institute of Technology)

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Linking ghc .o files with MSVC++
by Mauricio Carvalho 26 Nov '02

26 Nov '02

Hi I need help specifically building Haskell functions that I can call from C++ (or C). I looked at the Foreign Function Interface explanation at GHC user's guide, but I didn't understand itt well, and I'm not succeeding at doing it. I'm using GCH 5.04.1 in Win32 environment, and Microsoft Visual C++ That is as far as I got: I compiled a simple MyModule.hs file with ghc -c -fffi MyModule.hs It was just a test module that conatined a factorial function called fac. Here is the source: module MyModule where foreign export ccall "fac" fac :: Int -> Int fac :: Int -> Int fac n | n <= 0 = 1 | otherwise = n * fac(n-1) It gave me 4 files: MyModule_stub.h, MyModule_stub.c, MyModule_stub.o, MyModule.o (and a MyModule.hi, but I think not relevant for linking with C) I was thinking that a .o and a .h file would be sufficient for the linking; anyway, I copied those 4 files to my c++ program directory, included the .h file at my c++ main program, add the file MyModule_stub.o to the linking process and tried to compile. That is my c++ program: #include <iostream> #include "MyModule_stub.h" int main(){ std::cout << fac(10) << std::endl; return 0; } The linker complains that some function calls are unresolved: Compiling... principal.cpp Linking... MyModule_stub.o : error LNK2001: unresolved external symbol _MyModule_zdffac_closure MyModule_stub.o : error LNK2001: unresolved external symbol _GHCziTopHandler_runNonIO_closure MyModule_stub.o : error LNK2001: unresolved external symbol _rts_getInt MyModule_stub.o : error LNK2001: unresolved external symbol _rts_checkSchedStatus MyModule_stub.o : error LNK2001: unresolved external symbol _rts_mkInt MyModule_stub.o : error LNK2001: unresolved external symbol _rts_apply MyModule_stub.o : error LNK2001: unresolved external symbol _rts_evalIO Debug/templates.exe : fatal error LNK1120: 7 unresolved externals Error executing link.exe. I tried to use the file MyModule.o, instead of MyModule_stub.o, and got mor unresolved symbols. What was worse, the function symbol itself was unresolved: Linking... MyModule.o : error LNK2001: unresolved external symbol _getStablePtr MyModule.o : error LNK2001: unresolved external symbol _GHCziNum_Szh_con_info MyModule.o : error LNK2001: unresolved external symbol _stg_upd_frame_info MyModule.o : error LNK2001: unresolved external symbol _GHCziBase_ZMZN_closure MyModule.o : error LNK2001: unresolved external symbol _stg_ap_2_upd_info MyModule.o : error LNK2001: unresolved external symbol _GHCziBase_ZC_con_info MyModule.o : error LNK2001: unresolved external symbol _stg_sel_0_upd_info MyModule.o : error LNK2001: unresolved external symbol _GHCziBase_Izh_static_info MyModule.o : error LNK2001: unresolved external symbol _GHCziReal_zdfIntegralInt_closure MyModule.o : error LNK2001: unresolved external symbol _stg_CAF_BLACKHOLE_info MyModule.o : error LNK2001: unresolved external symbol _newCAF MyModule.o : error LNK2001: unresolved external symbol _stg_IND_STATIC_info MyModule.o : error LNK2001: unresolved external symbol _stg_INTLIKE_closure principal.obj : error LNK2001: unresolved external symbol _fac Debug/templates.exe : fatal error LNK1120: 14 unresolved externals Error executing link.exe. Even trying to include both .o modules to the linking process didn't help If I link this module to a Haskel program, it works out fine... So, it seems that when I create an object file from a Haskell module, I must link with other object files, that ghc probably links automatically. Is it true? An being the case, how can one know which object files to link? Please, understand that I'm quite a newbie using haskell when answering. Thanks for any help, Mauricio

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Best recursion choice for "penultimax"
by Dr Mark H Phillips 26 Nov '02

26 Nov '02

Hi, I have just implemented the function "penultimax" which takes a list of positive integers and produces the "penultimate maximum", that is, the next biggest integer in the list after the maximum. Eg: penultimax [15,7,3,11,5] = 11 One implementation is: penultimax :: [Int] -> Int penultimax ms = foldr max 0 (filter (<msMax) ms) where msMax = foldr max 0 ms But I can think of two variations which might be more efficient: penultimax2 :: [Int] -> Int penultimax2 ms = penultimax2' ms 0 0 where penultimax2' :: [Int] -> Int -> Int -> Int penultimax2' [] p q = q penultimax2' (m:ms) p q | m>p = penultimax2' ms m p | m>q = penultimax2' ms p m | otherwise = penultimax2' ms p q penultimax3 :: [Int] -> Int penultimax3 ms = snd (maxpenmax ms) where maxpenmax :: [Int] -> (Int,Int) maxpenmax [] = (0,0) maxpenmax [m] = (m,0) maxpenmax (m:ms) | m>p = (m,p) | m>q = (p,m) | otherwise = (p,q) where (p,q) = maxpenmax ms How do I work out which is best to use? Is there one clear "winner", or will they each have pros and cons? Thanks, Mark. -- Dr Mark H Phillips Research Analyst (Mathematician) AUSTRICS - smarter scheduling solutions - www.austrics.com Level 2, 50 Pirie Street, Adelaide SA 5000, Australia Phone +61 8 8226 9850 Fax +61 8 8231 4821 Email mark(a)austrics.com.au

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EACL03 Last call for Research Notes and Demos
by Claire Gardent 26 Nov '02

26 Nov '02

+---------------------------------------------------+ EACL 2003 10th Conference of the European Chapter of the Association for Computational Linguistics April 12-17, 2003 Budapest, Hungary http://www.conferences.hu/EACL03/ +---------------------------------------------------+ Last Call for Research Notes and Demos Important dates: ---------------- . Paper Registration deadline: 01 December . Paper Submission deadline: 06 December Important URLs: --------------- Main conference: http://www.conferences.hu/EACL03/ Research notes and Demos: http://tcc.itc.it/people/lavelli/eacl2003/

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Re: diff in Haskell: clarification
by Yoann Padioleau 25 Nov '02

25 Nov '02

there is the perl version of the diff algorithm on CPAN that may be a better starting point than the C version. -- Yoann Padioleau, INSA de Rennes, France, Opinions expressed here are only mine. Je n'écris qu'à titre personnel. **____ Get Free. Be Smart. Simply use Linux and Free Software. ____**

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RE: Best recursion choice for "penultimax"
by Simon Marlow 25 Nov '02

25 Nov '02

> Some quick tests with Hugs +s on a example list that I constructed > with 576 elements give food for thought: > > reductions cells > my one liner 4035 11483 > tournament 7053 12288 > your penultimax 16715 20180 > your penultimax2 7466 10344 > your penultimax3 8605 13782 And with GHC -O, the results are quite different: Mark's one liner 0.60s tournament 0.25s your penultimax 0.26s your penultimax2 0.25s your penultimax3 0.25s the tests were with random numbers (different seed each time), but there was only a little little fluctuation from run to run. I specialised all the algorithms to Int. Hugs doesn't do much optimisation, so the reductions/cells counts tend to vary quite a bit between programs which GHC will optimise to the same or similar code. The moral, as usual, is YMMV... Cheers, Simon

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Web Demonstration of Type Error Slicing
by Christian Haack 25 Nov '02

25 Nov '02

Previous methods have generally identified the location of a type error as a particular program point or the program subtree rooted at that point. In the paper "Type Error Slicing in Implicitly Typed Higher-Order Languages" by two of us (Haack and Wells), we present a new approach that treats the location of a type error as a minimal set of program points which are necessary for the type error and presents this "location" as a slice of the program. Connected to this paper, we have implemented type error slicing for a subset of core Standard ML. We have prepared a web interface that allows you to experiment with our implementation using just your web browser. This interface is now available at: http://www.cee.hw.ac.uk/ultra/compositional-analysis/type-error-slicing/ -- Sebastien Carlier, Christian Haack, and Joe Wells Members of the ULTRA group and the Church Project

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Re: how to convert IO String to string---- still have questions
by Lu Mudong 25 Nov '02

25 Nov '02

Thanks a lot for you guys' help. I am very new to haskell and tried some methods you guys advised, doesn't seem to work, i think i didn't do it properly, here's my code and result, hope you can point out what's wrong. thanks! my code: myReadFile :: IO String myReadFile = readFile "d:/hugs98/input.txt" theString :: String theString = do s <- myReadFile putStrLn s the error message i got in hugs98 ERROR "D:\hugs98\parser.hs":16 - Type error in explicitly typed binding *** Term : theString *** Type : IO () *** Does not match : String >From: Ashley Yakeley <ashley(a)semantic.org> >To: "Ahn Ki-yung" <kyagrd(a)bawi.org>,"Haskell List" <haskell(a)haskell.org> >Subject: Re: how to convert IO String to string >Date: Fri, 22 Nov 2002 15:09:34 -0800 > >At 2002-11-22 14:49, Ahn Ki-yung wrote: > > >'do' is a syntactic sugar of monadic operations. > >The original form can be written as > > > >main = myReadFile >>= \s -> putStrLn s > >That's correct. In this case, the 's' has type String. So the IO String >has been 'converted' into a String, but only within the context of the IO >monad. > >I think ultimately everything is syntactic sugar. > >-- >Ashley Yakeley, Seattle WA > >_______________________________________________ >Haskell mailing list >Haskell(a)haskell.org >http://www.haskell.org/mailman/listinfo/haskell _________________________________________________________________ Add photos to your messages with MSN 8. Get 2 months FREE*. http://join.msn.com/?page=features/featuredemail

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