April 2002 - Haskell - Haskell.org

text/x-haskell and text/x-literate-haskell added to the GNOME MIME database
by Martin Norbäck 18 Apr '02

18 Apr '02

These MIME types has now been added to the GNOME MIME database: text/x-haskell for *.hs text/x-literate-haskell for *.lhs The default icons that will be used for these files in the GNOME file browser are: http://jimmac.musichall.cz/stuff/gnome-application-x-haskell.png http://jimmac.musichall.cz/stuff/gnome-application-x-literate-haskell.png The icons are covered by the GPL license, so feel free to use them under the terms of this license. Some rationale for the name of the MIME types. text/* indicates that if no suitable viewer for the MIME type is found, displaying the contents as plain text is OK. x-* means that it's not an officially registered MIME type (there is really no need to register it officially.) Our hope is that everyone will use these MIME types where appropriate. Regards, Martin -- Martin Norbäck d95mback(a)dtek.chalmers.se Kapplandsgatan 40 +46 (0)708 26 33 60 S-414 78 GÖTEBORG http://www.dtek.chalmers.se/~d95mback/ SWEDEN OpenPGP ID: 3FA8580B

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Questions concerning hierarchical module system
by Wolfgang Jeltsch 18 Apr '02

18 Apr '02

Hi, I have some questions regarding the hierarchical module system now implemented in Hugs as well as in GHC. Currently it is possible to have a module A1.A2. ... .Am and a module A1.A2. ... .Am. ... .An (n > m) at the same time. The first one's source code would be in file <root>/A1/A2/ ... /Am.hs and the second one's in file <root>/A1/A2/ ... /Am/ ... /An.hs. So there would be both a Am.hs file and a Am directory in the same directory. A1.A2. ... .Am would have two meanings: a module and a "module container". Hugs and GHC doesn't seem to have problems with this. But I want to know if I can rely on this behaviour still beeing present in future implementations and if this kind of module organisation is maybe considered bad practice. Wolfgang

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Haskell Web Publisher --- help wanted
by Wolfgang Jeltsch 18 Apr '02

18 Apr '02

Hello Haskell freaks, I'm developing some software which I call the "Haskell Web Publisher". This software shall allow the implementation of websites in Haskell and will consist mainly of Haskell modules providing the necessary types and variables. By using HWP, website implementors shall be able to write clear and problem-oriented website implementations. In addition, many errors (e.g. "broken links") shall be prevented by compiler checks. This shall be achieved by using Haskell's type system appropriately. I have written some kind of paper about the basic ideas which can, at the moment, be downloaded by using the following URI: http://www.wolfgang.jeltsch.net/ convenient-website-implementation-with-haskell.pdf I decided to exclude all the code from HWP which may also be useful for other software This code will form a separate library called Seaweed. During the last 2 1/2 years I worked on the described kind of software. Last year I decided to revise some of the code and to rewrite the rest of it. In conjunction with this I made the split into Seaweed and HWP and began hosting these projects on Sourceforge (now Sourceforge.net) The respective URI are these: http://sourceforge.net/projects/seaweed/ http://sourceforge.net/projects/hwp/ Because I didn't have the time, I didn't rewrite the existing HWP stuff and didn't write what is missing of HWP until now. I only worked on the Seaweed part. Some of the resulting code is already in the CVS repository, and some code is on my harddisk and will, hopefully, be checked in during April/May. If somebody should be interested, I can also send him/her the code from before the revision/rewrite phase which covers some of the more interesting stuff of HWP, namely code for realising the compiler checks mentioned above. Now let me come to the aim of this e-mail. I'm looking for people who are interested in helping me realising HWP and Seaweed. Because I develop these things only in my free time, finishing them is far away if it's only me who is working on them. So if someone of you is interested in taking part in the development process, please, please write me! Thank you in advance! Okay, I will finish now and I hope for reply. Ciao, Wolfgang

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data structure question
by Hal Daume III 17 Apr '02

17 Apr '02

i need an associative data structure (like finitemap) which will map data elements to Doubles. i don't need to be able to remove elements and don't even need to insert elements once i've built the structure; all i really care about is fast lookup. i have reasonable instances of Eq and Ord and probably any other reasonable comparitive metric you could think of. moreover, when i'm creating the data structure, i *know* the (approximate) relative frequency of each element. that is, i know that on average i will need to get the Double corresponding to element 'a' ten times more frequently than the Double corresponding to element 'b'. does anyone have any suggestions for data structures to solve such a problem. i'm currently using FiniteMap, but would like something faster (btw, there are a LOT of these elements -- around 1million or so). - Hal -- Hal Daume III "Computer science is no more about computers | hdaume(a)isi.edu than astronomy is about telescopes." -Dijkstra | www.isi.edu/~hdaume

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Flocasa: 2nd Call for Paper
by Jean-Marie JACQUET 17 Apr '02

17 Apr '02

[ Our apologies for multiple copies. ] ====================================================================== 1st International Workshop on Foundations of Coordination Languages and Software Architectures (Foclasa 2002) August 24, 2002, Brno, Czech Republic Workshop affiliated to CONCUR'2002, 20 - 23 August 2002. http://www.info.fundp.ac.be/~jmj/Workshops/Concur2002/Foclasa.html ====================================================================== SCOPE AND TOPICS Modern information systems rely more and more on combining concurrent, distributed, mobile and heterogenous components. This move from old systems, typically conceived in isolation, induces the need for new languages and software architectures. In particular, coordination languages have been proposed to cleanly separate computational aspects and communication. On the other hand, software architects face the problem of specifying and reasoning on non-functional requirements. All these issues are widely perceived as fundamental to improve software productivity, enhance maintainability, advocate modularity, promote reusability, and lead to systems more tractable and more amenable to verification and global analysis. The aim of the workshop is to bring together researchers working on the foundations of component-based computing, coordination, and software architectures. Topics of interest include (but are not limited to): o Theoretical models for coordination (component composition, concurrency, dynamic aspects of coordination, semantics, expressiveness); o Specification, refinement, and analysis of software archi- tectures (patterns and styles, verification of functional and non-functional properties); o Coordination, architectural, and interface definition languages (implementation, interoperability, heterogeneity); o Agent-oriented languages (formal models for interacting agents); o Dynamic software architectures (mobile agents, configuration, reconfiguration); o Modeling of information systems (groupware, internet and the web, workflow management, CSCW and multimedia applications) o Coordination patterns (mobile computing, internet computing); o Tools and environments for the development of coordinated applications SUBMISSION GUIDELINES Papers describing original work are solicited as contributions to Foclasa. Submitted papers should be limited to 6 000 words, preferrably formatted according to the Fundamenta Informaticae style (available at http://fi.mimuw.edu.pl/submissions.html) They should be emailed as PostScript (PS) or Portable Document Format (PDF) files to jmj(a)info.fundp.ac.be. PROCEEDINGS The proceedings will be published as a technical report of the Institute of Informatics at the University of Namur, and will be available at the workshop. PUBLICATION Selected papers will be published in a special issue of the Funda- menta Informaticae journal, with February 2003 as expected publi- cation time. IMPORTANT DATES: o May 25, 2002: Submission deadline. o June 30, 2002: Notification of acceptance. o August 1, 2002: Final version. o August 24, 2002: Meeting Date. LOCATION The workshop will be held in Brno in August 2002. It is a satellite workshop of CONCUR 2002. For venue and registration see the CONCUR web page at http://www.fi.muni.cz/concur2002/ WORKSHOP ORGANIZERS o Antonio Brogi (University of Pisa, Italy) o Jean-Marie Jacquet (University of Namur, Belgium) PROGRAMME COMITTEE: o Antonio Brogi (University of Pisa, Italy) - Co-chair o Rocco De Nicola (University of Firenze, Italy) o Jos Luiz Fiadeiro (ATX Software and Univ. of Lisbon, Portugal) o Roberto Gorrieri (Univerity of Bologna, Italy) o Paola Inverardi (Univerity L'Aquila, Italy) o Jean-Marie Jacquet (University of Namur, Belgium) - Co-chair o Joost Kok (University of Leiden, The Netherlands) o Antonio Porto (New University of Lisbon, Portugal)

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Bug?
by Jorge Adriano 17 Apr '02

17 Apr '02

[1] Bug1? This declaration: > A = (,) Int Int is accepted by ghci. Is this behaveour correct, 1. It kind of shadows (,) is defined in PrelTup meaning that you can no longer use (,) prefix to refer to tuples - like (,) 1 2. 2. Seems to me like (,) is not correct syntax for a consym as defined in the H98 Report so we shouldn't be able to redefine it. Note: didn't check any other interpreter/compiler. [2] Bug2? - Step 1 Load this in ghci, ----------------------- module Test where data C = C ((,) Int Int) data A = (,) !Int !Int h :: A h = (,) 1 2 {- f :: C f = C ((,) 3 4) -} ------------------------ - Step 2 Uncomment the f function. (you'll get an error function) - Step 3 To get rid of the error comment out the 'data A' declaration and function 'h'. Now you should get this error message: ------------------------------------------------- Failed to find interface decl for `Teste.A' from module `Teste' ------------------------------------------------- [3] Strict Pairs question I really miss them :-) I know I can do something like data A a b= A !a !b But then you can't use zips fst etc etc... One possible solution would be to add some Class Pair, with default instances for these functions. Is this a bad idea for any particular reason? It would also be nice to be able to generalize the idea syntatic sugar for standar tuples and be able to define constructors like, say (:,:) and (#:, , :#) etc. Is this feasable? J.A.

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ANNOUNCE: Tour of the Haskell Syntax
by Arjan van IJzendoorn 17 Apr '02

17 Apr '02

Hello everybody, Earlier I announced the Tour of the Haskell Prelude, a HTML version of a paper by Bernie Pope: http://www.cs.uu.nl/~afie/haskell/tourofprelude.html Since then it has been overshadowed by the more complete reference at ZVON (great work, guy(s)) http://zvon.org/other/haskell/Outputglobal/index.html Now I've written a new document. It is an overview of the Haskell syntax and can be used alongside Haskell textbooks. They often introduce language constructs by example and the reader may not see the whole picture. Looking at the formal syntax in BNF at the Haskell site is not much fun either. So I thought it was time for "The Tour of the Haskell Syntax": http://www.cs.uu.nl/~afie/haskell/tourofsyntax.html I hope it can be of use to other teachers. Of course, comments are welcome. Good luck, Arjan

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Re: Coding Problems!! Please help
by John Hughes 17 Apr '02

17 Apr '02

I am currently working on an assignment with requires us to write in Haskell. I am having trouble with "pipeline". The required textbook called, "The Craft of Functional Programming" 2nd Edition. There is a pipeline example, which I find it useful in my assignment, but for some reason, there may be a typo in the pipeline syntax, which is ">.>". Coz it doesn't compile. Your problem is that that book defines and uses a non-standard composition operator. The standard Haskell function composition is written just ".", defined by (f . g) x = f (g x) Notice that in f . g, it is *g* which is applied first to the argument, and f which is applied to the result of that. That is, composition is "backwards" in some sense. Here's an example: sqrt . abs takes the absolute value of its argument first, and then the square root of that, not the absolute value of the square root (which would fail for negative arguments). Many people (including mathematicians) prefer to write the arguments of compose in the other order, so that the first function to be applied is the first one you write. To make that possible, Simon Thompson defines (f >.> g) x = g (f x) So now you would write the example above as abs >.> sqrt You take the absolute value first, so you write it first. Regardless of which you prefer, the important thing to understand is that >.> IS NOT PART OF THE HASKELL STANDARD. So if you want to use it, you have to include the definition above in your own program. John Hughes

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Coding Problems!! Please help
by Jack Tsai 17 Apr '02

17 Apr '02

Dear staff, I am currently working on an assignment with requires us to write in Haskell. I am having trouble with "pipeline". The required textbook called, "The Craft of Functional Programming" 2nd Edition. There is a pipeline example, which I find it useful in my assignment, but for some reason, there may be a typo in the pipeline syntax, which is ">.>". Coz it doesn't compile @_@ I have attached a file of the example, I found from the book. There is a website where I could download the entire book. It's got the same stuff as in my textbook. Please help me, coz i've tried even Unix's pipeline syntax which is obviously wrong... I'm not desperate, please reply, thank you very much. Sincerely, Jack This is the output of the compilor... /*********************************************************************/ Haskell 98 mode: Restart with command line option -98 to enable Reading file "C:\PROGRAM FILES\HUGS98\lib\Prelude.hs": Parsing........................................................ Dependency analysis............................................ Type checking.................................................. Compiling...................................................... Reading file "E:\433\CHAPTE~1.LHS": Parsing........................................................ Dependency analysis ERROR "E:\433\CHAPTE~1.LHS" (line 22): Undefined variable ">.>" Prelude> /**********************************************************************/ _________________________________________________________________ Chat with friends online, try MSN Messenger: http://messenger.msn.com

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Coding Problems!! Please help
by Jack Tsai 17 Apr '02

17 Apr '02

Dear staff, I am currently working on an assignment with requires us to write in Haskell. I am having trouble with "pipeline". The required textbook called, "The Craft of Functional Programming" 2nd Edition. There is a pipeline example, which I find it useful in my assignment, but for some reason, there may be a typo in the pipeline syntax, which is ">.>". Coz it doesn't compile @_@ I have attached a file of the example, I found from the book. There is a website where I could download the entire book. It's got the same stuff as in my textbook. Please help me, coz i've tried even Unix's pipeline syntax which is obviously wrong... I'm not desperate, please reply, thank you very much. Sincerely, Jack This is the output of the compilor... /*********************************************************************/ Haskell 98 mode: Restart with command line option -98 to enable Reading file "C:\PROGRAM FILES\HUGS98\lib\Prelude.hs": Parsing........................................................ Dependency analysis............................................ Type checking.................................................. Compiling...................................................... Reading file "E:\433\CHAPTE~1.LHS": Parsing........................................................ Dependency analysis ERROR "E:\433\CHAPTE~1.LHS" (line 22): Undefined variable ">.>" Prelude> /**********************************************************************/ _________________________________________________________________ Send and receive Hotmail on your mobile device: http://mobile.msn.com

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