August 2003 - Haskell

help!
by Trouble ... 18 Aug '03

18 Aug '03

Hi! I'm new to this whole programming thing, and I was wondering if someone can help me out with the following question: How do I translate a string into an integer. For example, I need to know how to translate "one hundred" into 100, or "fifty thousand ten " into 50 010 etc etc .. I need to know how to do this for single numbers, hundreds, thousands and millions using Haskell. Thanx for your time and help. _________________________________________________________________ Hot chart ringtones and polyphonics. Go to http://ninemsn.com.au/mobilemania/default.asp

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Compositional Verification of UML Models
by M.M. Bonsangue 15 Aug '03

15 Aug '03

(We apologize for the reception of multiple copies) ************** DEADLINE IS APPROACHING: CALL FOR PAPER *************** Call for Papers Compositional Verification of UML Models Workshop of the UML 2003 Conference The definition of UML has been motivated by the need for a standard notation for modelling system architectures and behaviours at functional and implementation level. The main fqocus has been essentially on terminology, notation and syntax without addressing semantic, validation and methodology issues which are important for formal design and verification techniques. This workshop addresses the application of formal methods and techniques that exploit the architectural structure of UML models in a compositional manner. TOPICS The workshop topics include (but are not limited to): * semantic foundations of architectural and component-based design within UML * compositional techniques for the analysis embedded and real-time systems in UML * compositional model checking of UML behavioural models * compositional deductive methods based on OCL * methodologies based on compositional formal techniques FORMAT OF THE WORKSHOP The workshop will consist of presentations of the accepted papers, which will be the basis for an intensive discussion on the workshop topics. Extended abstracts of the presentations will be published after the workshop by Elsevier Science as a volume of the Electronic Notes in Theoretical Computer Science. For an up-to-date program and invited talks see the workshop web-site http://fmco.liacs.nl/compuml.html SUBMISSIONS Authors are invited to submit by August 25th an extended abstract not exceeding 20 pages electronically to F.S.de.Boer(a)cwi.nl. Submissions must be either in Postscript or PDF format and prepared for USLetter or A4 page sizes. Submissions will be evaluated by the program committee for inclusion in the proceedings, which will be published by Electronic Notes in Theoretical Computer Science series. Papers must contain original contributions, be clearly written, and include appropriate reference to and comparison with related work. Simultaneous submissions to other conferences are not allowed. IMPORTANT DATES 25 August Submission deadline 10 September Notification to authors 1 October Deadline for preliminary version 21 October Workshop date 21 November Deadline for final version PROGRAM COMMITTEE Frank de Boer (CWI, NL) Marcello Bonsangue (LIACS, NL) Werner Damm (OFFIS, DE) Susanne Graf (Verimag, France) David Harel (Weizmann Institute, Israel) Jozef Hooman (University of Nijmegen, NL) Bernhard Josko (OFFIS, DE) Amir Pnueli (Weizmann Institute, ISR) Willem-Paul de Roever (Kiel University, DE) Joseph Sifakis (Verimag, FR) ORGANIZERS Frank de Boer (CWI, NL) Marcello Bonsangue (LIACS, NL) Bernhard Josko (OFFIS, DE) SPONSORS This workshop is sponsored by the European R&D project OMEGA - Correct Development of Real-time Embedded Systems (http://www-omega.imag.fr) and the German-Dutch project Mobi-J (main sponsor of FMCO, http://fmco.liacs.nl)

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Type class problem
by Brandon Michael Moore 14 Aug '03

14 Aug '03

To try some of the examples from paper "Recursion Schemes from Comonads", I wanted to define instances of Show and Observable for types defined as the fixed point of a functor. I defined type recursion and naturals as >newtype Mu f = In {unIn :: f (Mu f)} >data N f = S f | Z >type Nat = Mu N An application of Mu should be showable if the functor maps showable types to showable types, so the most natural way to define the instance seemed to be instance (Show a => Show (f a)) => Show (Mu f) where show (In x) = show x Of course that constraint didn't work, so I made a class PShow with a method that witnessed the constraint >class PShow f where > pshow :: (Show a) => f a -> String Now I could define a generic show instance for Mu, and got a Show instance for Nat by defing a PShow instance for N >instance (PShow f) => Show (Mu f) where > show (In x) = pshow x >instance PShow N where > pshow Z = "Z" > pshow (S k) = "S "+show K show (In (S (In (S (In Z))))) -> "S S Z" This works fine, but you need to be able to use the method of P<Class> in the definition of <Class> (Mu f). I couldn't figure out how to do the same thing with Observable (the use of the class methods is a few layers away from the public interface). I tried to define a set of mutaully recursive definitions instance (Observable (f (Mu f))) => Observable (Mu f) where observer (In x) = send "In" (return In << x) instance (Observable a) => Observable (N a) where observer Z = send "Z" (return Z) observer (S x) = send "S" (return S << x) unfortunately, the class constraint solver doesn't doesn't like this. I get an error message like Constraint Stack Overflow: Observable (N (Mu N)) Observable (Mu N) Observable (N (Mu N)) Observable (Mu N) ... I expected that that constraint solver would realize it could construct a dictionary transformer with a type like Observer Nat -> Observer Nat and take the fixed point to get an instance for Nat. I haven't looked at the implementation, but it seems like it would be easy to add the constraint we are trying to derive to the list of assumptions when trying to construct all the anteceedents of an instance declaration. Can anyone tell me how to 1) get around this 2) modify GHC to handle this :) Brandon

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ICFP 2003 / PLI 2003 -- final call for participation
by Olin Shivers 14 Aug '03

14 Aug '03

The following message is a courtesy copy of an article that has been posted to comp.lang.scheme,comp.lang.scheme.scsh,comp.lang.dylan,comp.lang.functional,comp.lang.lisp,comp.lang.lisp.franz,comp.lang.lisp.mcl,comp.lang.lisp.x,comp.lang.apl,comp.lang.clos as well. ICFP 2003, the International Conference on Functional Programming, will be happening two weeks from now, 8/25-27. If you are contemplating registering for the conference, note that on-line/remote registration closes on Friday (8/15) -- although walk-in/on-site registration will be available up to and through the conference. I append the programme of talks to this message. For more information, see the conference web page http://www.cc.gatech.edu/~shivers/icfp03/schedule.html -Olin Shivers ------------------------------------------------------------------------------- ICFP 2003 program ----------------- http://www.cc.gatech.edu/icfp03/schedule.html http://www.cc.gatech.edu/icfp03/schedule.txt Affiliated with PLI 2003 August 25-29, 2003 Uppsala, Sweden =============================================================================== Monday 25 August 2003 Invited talk: 9:00-10:00 ------------------------ Conservation of information: Applications in functional, reversible, and quantum computing Thomas Knight, Jr. (MIT Artificial Intelligence Laboratory) Session I: 10:30-12:30 ---------------------- Scripting the type-inference process Bastiaan Heeren, Jurriaan Hage, Doaitse Swierstra (Universiteit Utrecht) Discriminative sum types locate the source of type errors Matthias Neubauer, Peter Thiemann (Universität Freiburg) MLF: Raising ML to the power of System F Didier Le Botlan, Didier Rémy (INRIA Rocquencourt) An extension of HM(X) with bounded existential and universal data-types Vincent Simonet (INRIA Rocquencourt) Session II: 2:15-3:45 --------------------- CDuce: an XML-centric general-purpose language Véronique Benzaken (LRI, Université Paris Sud, Orsay), Giuseppe Castagna (CNRS, LIENS, École Normale Supérieure), Alain Frisch (LIENS, École Normale Supérieure, Paris) Compiling regular patterns Michael Levin (University of Pennsylvania) Software is discrete mathematics Rex Page (University of Oklahoma) Session III: 4:15-6:00 ---------------------- Global abstraction-safe marshalling with hash types James Leifer (INRIA Rocquencourt), Gilles Peskine(INRIA Rocquencourt), Peter Sewell (University of Cambridge), Keith Wansbrough (University of Cambridge) Dynamic rebinding for marshalling and update, with destruct-time lambda Gavin Bierman (University of Cambridge), Michael Hicks (University of Maryland, College Park), Peter Sewell (University of Cambridge), Gareth Stoyle (University of Cambridge), Keith Wansbrough (University of Cambridge) Iterative-free program analysis Mizuhito Ogawa (Japan Advanced Institute of Science and Technology), Zhenjiang Hu (University of Tokyo), Isao Sasano (Japan Advanced Institute of Technology and Science) Report on ICFP 2003 & 2004 Olin Shivers & Kathleen Fisher =============================================================================== Tuesday 26 August 2003 Invited talk: 9:00-10:00 ------------------------ From Hilbert space to Dilbert space: Context semantics as a language for games and flow analysis Harry Mairson (Brandeis University) Session IV: 10:30-12:30 ----------------------- A theory of aspects David Walker (Princeton University), Steve Zdancewic (University of Pennsylvania), Jay Ligatti (Princeton University) Dependency-style Generic Haskell Andres Löh, Dave Clarke, Johan Jeuring (Universiteit Utrecht) Functional automatic differentiation with Dirac impulses Henrik Nilsson (Yale University) A user-centred approach to functions in Excel Simon Peyton Jones (Microsoft Research), Alan Blackwell (University of Cambridge), Margaret Burnett (Oregon State University) Session V: 2:15-3:45 -------------------- A sound and complete axiomatization of delimited continuations Yukiyoshi Kameyama (University of Tsukuba), Masahito Hasegawa (Kyoto University) Call-by-value is dual to call-by-name Philip Wadler (Avaya Labs) Disjunctive normal forms and local exceptions Emmanuel Beffara (CRNS, Université Paris 7), Vincent Danos (CRNS, Université Paris 7) Session VI: 4:15-6:00 --------------------- An effective theory of type refinements Yitzhak Mandelbaum (Princeton University), David Walker (Princeton University), Robert Harper (Carnegie Mellon University) A static type system for JVM access control Tomoyuki Higuchi, Atsushi Ohori (Japan Advanced Institute of Science and Technology) Parsing polish, step by step (functional pearl) John Hughes (Chalmers University), Doaitse Swierstra (Universiteit Utrecht) Programming contest awards presentation John Hughes et al. (Chalmers University of Technology) =============================================================================== Wednesday 27 August 2003 Session VII: 9:00-10:30 ----------------------- Boxes go bananas: Encoding higher-order abstract syntax with parametric polymorphism Geoffrey Washburn, Stephanie Weirich (University of Pennsylvania) FreshML: Programming with binders made simple Mark Shinwell, Andrew Pitts, Murdoch Gabbay (University of Cambridge) Meta-programming through typeful code representation Chiyan Chen, Hongwei Xi (Boston University) Session VIII: 11:00-11:30 ------------------------- Optimistic evaluation: An adaptive evaluation strategy for non-strict programs Robert Ennals (University of Cambridge), Simon Peyton Jones (Microsoft Research) Invited talk (joint with PPDP'03): 11:30-12:30 ---------------------------------------------- Understanding aspects Mitchell Wand (Northeastern University)

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Announce: release candidate 1 of buddha version 1.0
by Bernard James POPE 14 Aug '03

14 Aug '03

Announcing buddha version 1.0 release candidate 1 ------------------------------------------------- www.cs.mu.oz.au/~bjpop/buddha Buddha is a declarative debugger for Haskell 98. It is based on program transformation and relies on GHC version 5.04 or greater (but not version 6 yet). It also needs GHC's libraries compiled for profiling. This is the first candidate release of buddha version 1.0 New features include: - a more user friendly interface than previous versions, - the ability to show higher-order arguments by name or by value (similar to Hood), - deriving Ix is now supported (all standard deriving statements should work now). This is a release candidate. There will probably be a number of candidates before the final version 1.0 is done. Other candidates will not be announced to this list. This candidate has been tested only on Linux (Debian and Mandrake). Previous versions have worked on OS X and Solaris x86, but I don't have access to those machines at the moment. GHC version 6.0 is still not supported by buddha. If there is a great demand for this then I will sort it out faster. Cheers, Bernie.

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Calling Haskell from Java
by Immanuel Litzroth 13 Aug '03

13 Aug '03

Calling Haskell from java was supposed to be supported by a tool called lambada, but all I can seen to find of that on the net is a paper. Does anyone have any pointers to more information/implementation. I specifically want to call Java->Haskell and not the other way around. thanks in advance Immanuel *************************************************************************** It makes me uncomfortable to see An English spinster of the middle class Describe the amorous effects of `brass', Reveal so frankly and with such sobriety The economic basis of society. W.H. Auden -- Immanuel Litzroth Software Development Engineer Enfocus Software Kleindokkaai 3-5 B-9000 Gent Belgium Voice: +32 9 269 23 90 Fax : +32 9 269 16 91 Email: Immanuell(a)enfocus.be web : www.enfocus.be ***************************************************************************

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RE: Help with Exceptions on I/O
by Hal Daume 13 Aug '03

13 Aug '03

you can write this a bit more simply as: main = do (do do-the-major stuff here putStr "File created...") `catch` (\_ -> show the error) getLine -- look ma, no <- return () now, your problem is almost certainly with buffering. in the main do, put hSetBuffering stdout NoBuffering hSetBuffering stdin NoBuffering you'll need to import System.IO to get these. -- Hal Daume III | hdaume(a)isi.edu "Arrest this man, he talks in maths." | www.isi.edu/~hdaume -----Original Message----- From: haskell-cafe-admin(a)haskell.org [mailto:haskell-cafe-admin@haskell.org] On Behalf Of Alexandre Weffort Thenorio Sent: Tuesday, August 12, 2003 4:17 PM To: haskell(a)haskell.org Cc: haskell-cafe(a)haskell.org Subject: Help with Exceptions on I/O I have a program which creates textfiles out of other files. Since the program is runned from windows I output some text strings (Like "File created succefully") and I need to stop the program before it quits so that the user can read the line outputted to know what went on and then he can press ENTER to quit the program. I managed to do this fine if no error occurs but when a error occurs I am having problems. The code goes like that main :: IO() main =catch (do Do all the needed stuff here putStr "File created Successfully. Press RETURN to quit" dummy <- getLine --Halts the program so the user can read the above line) putStr "Exiting now..." --needed since I can't finish a do function with the "dummy<- getLine" line) (\_ -> do putStr "\nFile not found. Press RETURN (ENTER) to quit." dumb <- getLine putStr "\nExiting...") So when the program runs, if the input file is found the program writes successfull creation of file but if the file doesn't exist, after the user gives the input filename and press enter, the program creates a new line and Halts (Probably because of the getLine function) without writing out anything, then when the user press ENTER again it writes the line at the first putStr (File not...), then writes the next putStr line under it (Exiting...) and exits. I don't know why it doesn't wirte the first line, halts and then when user press enter it writes the second and quits. Can anybody help me as I am not very familiar with exception and catches. Another question I have is: Is there any other function rather than getLine that halts a program and continues when a user press any key (Instead of ENTER) and besides this is an ugly code since getLine wasn't made for that but I couldn't find anything else myself. Thank you in advance. Best Regards Alex

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Help with Exceptions on I/O
by Alexandre Weffort Thenorio 12 Aug '03

12 Aug '03

I have a program which creates textfiles out of other files. Since the program is runned from windows I output some text strings (Like "File created succefully") and I need to stop the program before it quits so that the user can read the line outputted to know what went on and then he can press ENTER to quit the program. I managed to do this fine if no error occurs but when a error occurs I am having problems. The code goes like that main :: IO() main =catch (do Do all the needed stuff here putStr "File created Successfully. Press RETURN to quit" dummy <- getLine --Halts the program so the user can read the above line) putStr "Exiting now..." --needed since I can't finish a do function with the "dummy<- getLine" line) (\_ -> do putStr "\nFile not found. Press RETURN (ENTER) to quit." dumb <- getLine putStr "\nExiting...") So when the program runs, if the input file is found the program writes successfull creation of file but if the file doesn't exist, after the user gives the input filename and press enter, the program creates a new line and Halts (Probably because of the getLine function) without writing out anything, then when the user press ENTER again it writes the line at the first putStr (File not...), then writes the next putStr line under it (Exiting...) and exits. I don't know why it doesn't wirte the first line, halts and then when user press enter it writes the second and quits. Can anybody help me as I am not very familiar with exception and catches. Another question I have is: Is there any other function rather than getLine that halts a program and continues when a user press any key (Instead of ENTER) and besides this is an ugly code since getLine wasn't made for that but I couldn't find anything else myself. Thank you in advance. Best Regards Alex

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Help with Exceptions on I/O
by Alexandre Weffort Thenorio 12 Aug '03

12 Aug '03

I have a program which creates textfiles out of other files. Since the program is runned from windows I output some text strings (Like "File created succefully") and I need to stop the program before it quits so that the user can read the line outputted to know what went on and then he can press ENTER to quit the program. I managed to do this fine if no error occurs but when a error occurs I am having problems. The code goes like that main :: IO() main =catch (do Do all the needed stuff here putStr "File created Successfully. Press RETURN to quit" dummy <- getLine --Halts the program so the user can read the above line) putStr "Exiting now..." --needed since I can't finish a do function with the "dummy<- getLine" line) (\_ -> do putStr "\nFile not found. Press RETURN (ENTER) to quit." dumb <- getLine putStr "\nExiting...") So when the program runs, if the input file is found the program writes successfull creation of file but if the file doesn't exist, after the user gives the input filename and press enter, the program creates a new line and Halts (Probably because of the getLine function) without writing out anything, then when the user press ENTER again it writes the line at the first putStr (File not...), then writes the next putStr line under it (Exiting...) and exits. I don't know why it doesn't wirte the first line, halts and then when user press enter it writes the second and quits. Can anybody help me as I am not very familiar with exception and catches. Another question I have is: Is there any other function rather than getLine that halts a program and continues when a user press any key (Instead of ENTER) and besides this is an ugly code since getLine wasn't made for that but I couldn't find anything else myself. Thank you in advance. Best Regards Alex

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Re: Haskell and algebra
by Gustavo Villavicencio 11 Aug '03

11 Aug '03

Frank Atanassow said: > Gustavo Villavicencio wrote: > > > Hi all, > > > > I am trying to understand the algebraic laws and operators > > behind a functional expression... > > > > f >>= g \equiv g* . f > > > > in the Kleisli Star context. Is this right? > > Yep. > > > If it is so, can I combine g*.f with a fork for example? > > What do you mean by a "fork"? Jeremy Gibbons in "Conditional in distributive categories", among others, calls fork to the operator typed as f /_\ g : A -> B x C where f : A -> B and g : A -> C. In other literature it is also called split operador: <f,g> So, the question is, if i have f : A -> T B and g : A -> T C where T is a monad, i.e. an endofunctor, can i combine f and g as <f,g> : A -> T (BxC) knowing that T involves side effects? > > Regards, > Frank Regards, gustavo

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