November 2004 - Haskell

Haskell-mode 2.0
by Stefan Monnier 02 Feb '09

02 Feb '09

I have recently taken over maintainership of Haskell-mode, and after making a bunch of changes, I figured it would be a good idea to make a new release. You can find this new release at: http://www-perso.iro.umontreal.ca/~monnier/elisp/ If you think it should also be found at http://www.haskell.org/haskell-mode/, then please tell John Peterson to get back to me (my email to him seem to go straight to the bitbucket. John?). This release has several changes that have all been only lightly tested, especially w.r.t compatibility with various Emacsen. See appended the NEWS file that describes some of the notewirthy changes. Stefan Changes since 1.45: * keybindings C-c <char> have been replaced by C-c C-<char> so as not to collide with minor modes. * The following modules are now automatically activated without having to add anything to haskell-mode-hook: haskell-font-lock (just turn on global-font-lock-mode). haskell-decl-scan (just bind `imenu' to some key). * In recent Emacsen, haskell-doc hooks into eldoc-mode. * haskell-hugs and haskell-ghci are superceded by inf-haskell. * Indentation rules have been improved when using layout inside parens/braces. * Symbols like -> and \ can be displayed as actual arrows and lambdas. See haskell-font-lock-symbols. * Tweaks to the font-lock settings. Among other things paren-matching with things like \(x,y) should work correctly now. * New maintainer <monnier(a)gnu.org>.

3 6

Mixing monadic and non-monadic functions
by Sean E. Russell 17 Sep '05

17 Sep '05

Hello, I posted this question to comp.lang.functional, and someone suggested that I try this group instead. I'm struggling with monads. Well, not monads themselves, but mixing them with non-monadic functions. Here's my base case: someFunc :: String -> IO [a] ... ax <- someFunc a bx <- someFunc b assertBool "fail" $ length ax == length bx I don't like the assignments; the typing is redundant, if I have a lot of asserts like this, and the "variables" are temporary. What I'd much rather have is: ... assertBool "fail" $ (length $ someFunc a) == (length $ someFunc b) which is more readable, to my eye. The only solution which has been suggested that may work is liberal use of the liftM variants, but this gets *really* tedious and obtuse. Is there an elegant way to do what I want to do, or am I stuck with procedural-style assignments and bunches of temp vars? Thanks! -- ### SER ### Deutsch|Esperanto|Francaise|Linux|XML|Java|Ruby|Aikido ### http://www.germane-software.com/~ser jabber.com:ser ICQ:83578737 ### GPG: http://www.germane-software.com/~ser/Security/ser_public.gpg

23 37

WS-FM 2004 Call For Participation
by Mario Bravetti 20 Jul '05

20 Jul '05

---------------------------------------------------------------------- We apologize if you receive multiple copies of this announcement. ---------------------------------------------------------------------- ====================================================================== 1st International Workshop on Web Services and Formal Methods (WS-FM 2004) February 23-24, 2004, Pisa, Italy Workshop affiliated to COORDINATION 2004, February 24-27, 2004 WS-FM 2004 homepage: http://www.cs.unibo.it/~lucchi/ws-fm04/ ====================================================================== - The technical program is available at: http://www.cs.unibo.it/~lucchi/ws-fm04/ - Information about registration, travel and accomodation can be found at the COORDINATION 2004 web site: http://www.di.unipi.it/Coordination2004/ If you intend to participate, we recommend you to register and book the hotel as soon as possible. The Coordination 2004 Organizing Committee informed us that hotels are going to be fully booked in short time.

1 1

ICALP'05: Call for Papers
by Luis Caires 13 May '05

13 May '05

___________________________________________________________________ CALL FOR PAPERS - ICALP'05 32nd International Colloquium on Automata, Languages and Programming July 11-15, 2005, Lisboa, Portugal http://icalp05.di.fct.unl.pt/ ___________________________________________________________________ The 32nd International Colloquium on Automata, Languages and Programming, the main conference and annual meeting of the European Association for Theoretical Computer Science EATCS will take place from the 11th to the 15th of July 2005 in Lisboa, Portugal. As a complement to the established Tracks on Algorithms, Automata, Complexity and Games (A), and on Logic, Semantics, and Theory of Programming (B), corresponding to the two main streams of the journal Theoretical Computer Science, ICALP'05 innovates on the structure of its traditional scientific program with the inauguration of a new special Track (C). The aim of Track C is to allow a deeper coverage of a particular topic, to be specifically selected for each year's edition of ICALP on the basis of its timeliness and relevance for the theoretical computer science community. Papers presenting original research on all aspects of theoretical computer science are sought. Typical but not exclusive topics of interest are: Track A (Algorithms, Automata, Complexity and Games): Giuseppe F. Italiano Università di Roma "Tor Vergata", Italy (PC Chair) * Algorithmic Aspects of Networks * Algorithms and Data Structures * Automata Theory and Formal Languages * Combinatorics in Computer Science * Computational Biology * Computational Complexity * Computational Geometry * Internet Algorithmics * Machine Learning * Parallel and Distributed Computing * Quantum Computing Track B (Logic, Semantics, and Theory of Programming): Catuscia Palamidessi INRIA Futurs and LIX, France (PC Chair) * Algebraic and Categorical Models * Databases, Semi-Structured Data and Finite Model Theory * Principles of Programming Languages * Logics, Formal Methods and Model Checking * Models of Concurrent, Distributed, and Mobile Systems * Models of Reactive, Hybrid and Stochastic Systems * Program Analysis and Transformation * Specification, Refinement and Verification * Type Systems and Typed Calculi Track C (Security and Cryptography Foundations): Moti Yung Columbia University, USA (PC Chair) * Cryptographic Notions, Mechanisms, Systems and Protocols * Cryptographic Proof Techniques, Lower bounds, Impossibilities * Foundations of Secure Systems and Architectures * Logic and Semantics of Security Protocols * Number Theory and Algebraic Algorithms in Cryptography * Pseudorandomness, Randomness, and Complexity Issues * Secure Data Structures, Storage, Databases and Content * Security Modeling: Combinatorics, Graphs, Games, Economics * Specifications, Verifications and Secure Programming * Theory of Privacy and Anonymity * Theory of Security in Networks and Distributed Computing * Quantum Cryptography and Information Theory SUBMISSIONS: ************ Authors are invited to submit an extended abstract of no more than 12 pages in LNCS style presenting original research on the theory of Computer Science. Submissions should indicate to which track (A, B, or C) the paper is submitted. No simultaneous submission to other publication outlets (either a conference or a journal) is allowed. The proceedings will be published in the Lecture Notes in Computer Science Series by Springer-Verlag. IMPORTANT DATES: **************** Workshop proposals due: November 28, 2004 Submissions: February 13, 2005 Notification: April 8, 2005 Final version due: April 30, 2005 PROGRAM COMMITTEE: ****************** Track A (Algorithms, Automata, Complexity and Games) * Lars Arge, Duke University, USA * Giorgio Ausiello, University of Rome "La Sapienza", Italy * Surender Baswana, Max-Planck-Institut fur Informatik, Saarbrucken, Germany * Hans Bodlaender, University of Utrecht, The Netherlands * Véronique Bruyère, University of Mons-Hainaut, Belgium * Adam Buchsbaum, AT&T Labs - Research, USA * Josep Diaz, Universitat Politecnica de Catalunya, Spain * David Eppstein, University of Irvine, USA * Andrew Goldberg, Microsoft, USA * Monika Henzinger, ETH Lausanne, Switzerland * Giuseppe F. Italiano, University of Rome "Tor Vergata", Italy (Chair) * Marios Mavronicolas, University of Cyprus, Cyprus * Peter Bro Miltersen, University of Aarhus, Denmark * Mike Paterson, University of Warwick, United Kingdom * Dominique Perrin, Université de Marne la Vallée, France * Seth Pettie, Max-Planck-Institut fur Informatik, Saarbrucken, Germany * Yuval Rabani, Technion, Israel * Antonio Restivo, University of Palermo, Italy * José Rolim, University of Geneva, Switzerland * Dorothea Wagner, University Karlsruhe, Germany * Tandy Warnow, University of Texas at Austin, USA * Christos Zaroliagis, CTI and University of Patras, Greece Track B (Logic, Semantics, and Theory of Programming) * Kenichi Asai, University of Ochanomizu, Japan * Joos Baeten, University of Eindhoven, NL * Peter Buneman, University of Edinburgh, UK * Zoltan Esik, University of Szeged, Hungary * Javier Esparza, University of Stuttgart, Germany * Marcelo Fiore, Christ's College and University of Cambridge, UK * Manuel Hermenegildo, Universidade de Madrid, Spain * Delia Kesner, Universite Paris VII, France * Kim Guldstrand Larsen, University of Aalborg , Denmark * Gopalan Nadathur, University of Minnesota, USA * Uwe Nestmann, EPFL, Switzerland * Catuscia Palamidessi, INRIA, France (Chair) * Amr Sabry, University of Indiana, USA * Davide Sangiorgi, Universita di Bologna, Italy * Roberto Segala, Universita di Verona, Italy * Harald Sondergaard, University of Melbourne, Australia Track C (Security and Cryptography Foundations) * David Basin, ETH Zurich, Switzerland * Christian Cachin, IBM Research, Switzerland * Alfredo De Santis, Universita di Salerno, Italy * Cynthia Dwork, Microsoft Research, USA * Matt Franklin, U.C. Davis, USA * Michael Goodrich, U.C. Irvine, USA * Andrew D. Gordon, Microsoft Research, UK * Roberto Gorrieri, Universita di Bologna, Italy * Yuval Ishai, Technion, Israel * Phil McKenzie, DoCoMo Labs., USA * Tatsuaki Okamoto, NTT Labs., Japan * David Pointcheval, ENS Paris, France * Tal Rabin, IBM Research, USA * Omer Reingold, IAS Princeton, USA * Adi Rosen, Technion, Israel * Amit Sahai, UCLA, USA * Andre Scedrov, University of Pennsylvania, USA * Igor Shparlinsky, Macquarie University, Australia * Nigel Smart, University of Bristol, UK * Moti Yung, Columbia University, USA (Chair) ORGANIZING COMMITTEE: ********************* Luis Monteiro Luis Caires Antonio Ravara Vasco Vasconcelos CONTACT ADDRESSES: ****************** For further information see: http://icalp05.di.fct.unl.pt/

1 2

Better Exception Handling
by John Goerzen 30 Nov '04

30 Nov '04

Hi everyone, I've been using Haskell for 1-2 months now, and feel fairly comfortable with the language. However, my #1 gripe is the difficulty of working with exceptions. I have two main complaints: difficulty of defining custom exceptions, and difficulty of handling exceptions. I've been working on a library of various bits of Haskell code. There are several things that could raise exceptions within that library. There's no real easy way to do it, and make it easy for people using the library to trap only my exceptions. I could just use error("foo: bar") and tell them to look for a string that starts with "foo:". It works, but it's clumsy, and unreliable too ("foo:" is a valid filename, for instance, and could be used in other exceptions.) My other choice is to use Dynamic for my exceptions, but that makes it even more difficulty to catch and handle, and requires the programmer to be ready to deal with a fairly esoteric part of Haskell. In OCaml, there is an exception keyword, that is essentially the same as a data keyword. It defines a new exception, and can use the same constructors, etc. that any other type can. It's very useful. In Python, the situation is even better. There, an object can be thrown as an exception. Moreover, when catching exceptions, you can match an exception by a particular object *or any of its parents*. That means that I can easily extend someone else's work, adding my own exceptions as child objects of the existing ones. When I want to catch exceptions, I can be as specific or as general as I want, and any code designed to catch the more general exceptions will keep working. Java also works this way. Now, on to catching errors. OCaml makes this easy: try (whatever) with End_of_file -> foo | My_custom_error x -> bar x Here, "whatever", "foo", and "bar x" must all be of the same type. If there is no error, whatever is returned. If there is an error that we catch, the given value is returned. Otherwise, the exception is passed on up. Python can work that way, but also adds another feature: try: blah moreblah finally: foo The code "foo" will be executed whenever an exception occurs in the try block, or whenever the block ends normally. In other words, it is *always* executed. This is useful for doing cleanup actions like closing network connections. Haskell's exception catching doesn't really have less functionality than OCaml (some might argue it has more), but it takes a lot more effort to compose, needing to provide a function that returns a function in many cases. The other annoying thing is forcing it to run in the IO monad. I don't really understand this restriction. If we're not dealing with IO code to start with, we have deterministic behavior (if something raises an exception on a given value once, it will do that every time). So why do we have: catchJust :: (Exception -> Maybe b) -> IO a -> (b -> IO a) -> IO a instead of: catchJust :: (Exception -> Maybe b) -> (c -> a) -> c -> (b -> a) -> a This would let us run an arbitrary function (so long as it takes one parameter) and handle the exception completely outside of the IO monad. I can't think of a theoretical reason that this wouldn't work, though I suppose I may be missing something. Thoughts? Flames? :-) -- John

12 29

Network.CGI: <INPUT TYPE="file">?
by Johannes Waldmann 30 Nov '04

30 Nov '04

I am using Network.CGI (with ghc-6.2) How can I use an <INPUT TYPE="file"> element? I guess I know how to produce one: Text.Html.input ! [ Text.Html.name tag , Text.Html.thetype "file" , Text.Html.intAttr "maxlength" 10000 , Text.Html.strAttr "accept" "text/*" ] But to get to the file contents, it seems I should add Text.Html.strAttr "enctype" "multipart/form-data" to the <FORM> element, where I already have Text.Html.method "POST" but then I can't ready any values out of the environment that is provided by Network.CGI.wrapper. The environment then contains , ( "QUERY_STRING", "" ), ( "CONTENT_LENGTH", "1590" ) , ( "CONTENT_TYPE" , "multipart/form-data; boundary=---------------------------1409895718904..." ) Am I doing something wrong, HTML-wise (is it allowed to mix TYPE="file" input with other input elements in one FORM?) or is this a problem with the library? Any help appreciated. -- -- Johannes Waldmann, Tel/Fax: (0341) 3076 6479 / 6480 -- ------ http://www.imn.htwk-leipzig.de/~waldmann/ ---------

3 3

Re: Parameterized Show
by George Russell 30 Nov '04

30 Nov '04

Graham Klyne wrote (snipped): > I like the principle of parameterizing Show to allow for different encoding > environments (indeed, I had wondered as I was writing my earlier message if > the two cases were really sufficient). Indeed, in the application area > that interests me (Semantic Web) it could be beneficial to have different > encoding options corresponding to different serializations of RDF (e.g. > RDF/XML and Notation3). I like the idea too, not just for Show but for any instances. It seems to me that in general you should be able to combine the convenience of the Haskell type system with the power of Standard ML's structures and functors. Something along these lines was done by Kahl & Scheffczyk ("Named Instances for Haskell Type Classes", Haskell Workshop 2001). In general I suspect you can do this without even having to extend the existing Haskell typesystem very far. The following language extensions seem sufficient. (1) for a class declaration, a way of declaring that a certain type represents a dictionary of functions for that class, for example class Show a (ShowDict,appFn) where ... would define the new class "Show" but also the new type (ShowDict a) representing dictionaries for that class. It also declares a value appFn which I shall explain in a moment. (2) for an instance declaration, a way of "naming" the corresponding dictionary. instance Show Int (intShowDict) where would create a value "intShowDict :: ShowDict Int" (3) a way of using the dictionary. For this we need (appFn), declaraed by the type declaration. appFn has the unorthodox type appFn :: ShowDict a -> (forall a . Show a => b) -> b

19 73

Problems with using the memo-function
by Tom Hofte 30 Nov '04

30 Nov '04

Dear all, I have a problem when I use the memo-function to implement a dynamic programming algorithm to traverse a graph. I use the memo-function in the code below: dynamicPropagationUpAlg cname graph = let mh n = memo h n h n = let annotsuccs = (nub (concat (map (memo h) (succs n)))) in -- When the annotation set of the -- current node is empty, then we have to -- perform a if (length (myannots n) == 0) && ((length annotsuccs) > 1)then {- if length (succs n) > 1 then error ("<<Annotation failure>> Interface has to be annotated. "++(show n)) else -} case (trace ("Analyzing in component "++cname++"..\n"++"Before renaming successors annotations\n"++"Check for cycles in: \n"++"Comp: "++(getCompname n)++" Intf: "++(getIntfname n)++" Inst: "++(getFunname n)) (hasCycleInAnnots annotsuccs)) of Nothing -> map (replaceFunname (getCompname n)(getFunname n)) annotsuccs jMessage@(Just a) -> error (fromJust jMessage) else let mergeannots = mergeAnnotSets (annotsuccs++(myannots n)) (myannots n) in case (trace ("Analyzing in component "++cname++"..\n"++"After merging successors annotations\n"++"Check for cycles in: \n"++"Comp: "++(getCompname n)++" Intf: "++(getIntfname n)++" Inst: "++(getFunname n)) (hasCycleInAnnots mergeannots)) of Nothing -> mergeannots jMessage@(Just a) -> error (fromJust jMessage) g n@(InterfaceNode (annots, bo ,tp) names) = (InterfaceNode ((memo h n), bo, tp) names) succs n = (getSuccsOfNode n graph) myannots (InterfaceNode (annots,b,tp) names) = annots nodes = listNodes graph getFunname (InterfaceNode (annots, bo ,tp) (c,t,i)) = i getCompname (InterfaceNode (annots, bo ,tp) (c,t,i)) = c getIntfname (InterfaceNode (annots, bo ,tp) (c,t,i)) = t in map (g) nodes The idea is that the every node in the graph is visited only once, moreover that the function "h" is computed only once for every node. My implementation is not working properly. I don't know the cause for my problem, so can anyone hint me one the right use of the memo-function? Thanks in advance.. Kind regards, Tom

1 0

HaXml
by Dominic Steinitz 28 Nov '04

28 Nov '04

I'd be grateful for some help on using HaXml. 1. I can parse a String into a Document but it's not clear how you operate on it as the combinators all operate on Content. The only function I could find that operated on a Document was "document" in Pretty. 2. I can construct a CFilter but it's not clear how you operate on it. How do I calculate the number of components of an Element? What I would like to do is accept "vname" (with 3 elements) and reject "iname" (with 4 elements). I'd also like to check that the characters in givenName, initial and familyName are in a given range (for example upper case or between ' ' and '~'). Thanks, Dominic. import Text.XML.HaXml import Text.XML.HaXml.Pretty xmlName = "<Name><givenName>John</givenName>" ++ "<initial>P</initial>" ++ "<familyName>Smith</familyName>" ++ "</Name>" d = document $ xmlParse "tmp" xmlName gn = mkElemAttr "givenName" [] [literal "John"] i = mkElemAttr "initial" [] [literal "P"] fn = mkElemAttr "familyName" [] [literal "Smith"] validName = mkElemAttr "Name" [] [gn,i,fn] invalidName = mkElemAttr "Name" [] [gn,i,i,fn] vname = processXmlWith validName iname = processXmlWith invalidName *Main> d <Name ><givenName >John</givenName ><initial >P</initial ><familyName >Smith</familyName></Name> *Main> *Main> vname <?xml version='1.0'?> <Name ><givenName >John</givenName ><initial >P</initial ><familyName >Smith</familyName></Name> *Main>

2 1

RE: ANNOUNCE: Haskell support for Visual Studio .NET 2003 and Assignment Manager tools
by Morris Sim 27 Nov '04

27 Nov '04

Congratulations! Shan and Rogerio, please get in contact with Andre. I would love to see a demo of this. Thanks Morris ________________________________ From: Andre W B Furtado [mailto:andrewilsonfurtado@yahoo.com.br] Sent: Wed 11/24/2004 22:37 To: haskell(a)haskell.org Cc: visualhaskell(a)haskell.org; Morris Sim Subject: ANNOUNCE: Haskell support for Visual Studio .NET 2003 and Assignment Manager tools We are pleased to announce an alpha/preview version of VHS (Visual Haskell), which integrates the Haskell functional language with the Microsoft Visual Studio .NET 2003 IDE, and VHS-AM, which allows the use of VHS with the Microsoft Assignment Manager tools. This preview version supports: - Syntax coloring - Brace matching through CTRL+] (including "module/where", "let/in", etc.)* - Brace highlighting (including "module/where", "let/in", etc.)* - Brace matching text indicated in the status bar - "TODO" comments in code are added to the task list and can be reached by double-clicking it - Quick-info* - Word-completion* - Method tip* - Member-list popup* - Haskell Console Application creation - Haskell Console Application compilation (integrated with GHC) - Haskell Console Application execution - The presence of parse errors is indicated on-the-fly in the task list (specific errors are still not specified) - Error source location can be reached by double-clicking the task list - Haskell Assignment Manager exercise creation and advertisement - Haskell Assignment Manager exercise answering and submission - Compilation checking (via GHC) and output checking of Haskell exercises by Assignment Manager server Please note that this first release of VHS has some known bugs: - A VS.NET session can become unstable if you open a .hs file or create a Haskell Console Application project. - After opening a .hs file, the devenv.exe process is not being killed when VS.NET exits. - The above features marked with * sometimes do not work 100% as expected, mainly if the haskell module under development has errors. - Some features do not work in a "inter-module fashion". - The Visual Haskell logo does not disappear from VS.NET splash screen after uninstall. Note: development of a Visual Studio plugin for Haskell has been proceeding on two fronts. Simon Marlow & Krasimir Angelov have been working on adding complete editor support and a project framework integrated with Cabal, whereas this release is based on a fork of the codebase several months ago, and has a different feature set. We hope to combine these versions and make further releases in the future. Downloads, documentation and screenshots can be found in: http://www.cin.ufpe.br/~haskell/vhs-am/ http://www.cin.ufpe.br/~haskell/vhs/ The VHS/VHS-AM team is: - Simon Marlow - Krasimir Angelov - Andre Santos - Andre Furtado - Mauro La-Salette - Marden Costa This project was partially supported by a MS grant for extending the Assignment Manager tool.

1 0