January 2004 - Haskell

Use of tab characters in indentation-sensitive code
by Graham Klyne 23 Jan '04

23 Jan '04

I have found on a number of occasions that the use of tab characters in indentation-sensitive code is a cause of compilation errors, on occasions where I have opened the file with an editor which ap0plies a convention other than 8 spaces for a tab. I fear that sooner or later, one of these errors is going to manifest as a logic error. I would suggest that, where code uses the indentation-scope feature of Haskell, it would reduce the possibility for errors of all tabs were replaced with a corresponding number of spaces. I think that compilers should issue a warning when indentation that determines the scope of a construct is found to contain tab characters. #g ------------ Graham Klyne For email: http://www.ninebynine.org/#Contact

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[ANN] The Scala programming language
by Martin Odersky 22 Jan '04

22 Jan '04

We'd like to announce availability of the first implementation of the Scala programming language. Scala smoothly integrates object-oriented and functional programming. It is designed to express common programming patterns in a concise, elegant, and type-safe way. Scala introduces several innovative language constructs. For instance: - Abstract types and mixin composition unify ideas from object and module systems. - Pattern matching over class hierarchies unifies functional and object-oriented data access. It greatly simplifies the processing of XML trees. - A flexible syntax and type system enables the construction of advanced libraries and new domain specific languages. At the same time, Scala is compatible with Java. Java libraries and frameworks can be used without glue code or additional declarations. The current implementation of Scala runs on Java VM. It requires JDK 1.4 and can run on Windows, MacOS, Linux, Solaris, and most other operating systems. A .net version of Scala is currently under development. For further information and downloads, please visit: scala.epfl.ch ====================================================================== Martin Odersky and the Scala team, Swiss Federal Institute of Technology, Lausanne (EPFL).

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Hugs/GHC incompatibility
by Wolfgang Jeltsch 22 Jan '04

22 Jan '04

Hello, I have some code which runs fine with GHC/GHCi but signals Program error: undefined array element when run with Hugs. Does anyone know why this difference occurs and where I have to search for the cause of the error in my code? Wolfgang

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Any versions of Fudgets working with GHC-6?
by Henrik Berg 22 Jan '04

22 Jan '04

Hi! I've been trying for a while now to install the Fudget GUI library (http://www.cs.chalmers.se/ComputingScience/Research/Functional/Fudgets/) but with no luck so far. I've tried many different versions, both source and binary, but it seems like there's some kind of dependency or something that I don't know of, the sources won't compile and the binaries won't run... My system is linux (RedHat 7.1), ghc version 6.0.1. Does anyone know how/where I can get a working version of Fudgets, without too many version problems/dependency problems etc etc? -- Henrik

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CFP: Workshop on Constraint Programming and Constraint for Verification (CP+CV'04)
by Giorgio Delzanno 20 Jan '04

20 Jan '04

Apologies for multiple copies ================================================================================ CALL FOR PAPERS Workshop on Constraint Programming and Constraint for Verification (CP+CV'04) March 28, Barcelona, Spain at the European Joint Conferences on Theory and Practice of Software (ETAPS) Home page: http://www.disi.unige.it/person/DelzannoG/CP+CV/ Deadline: January 28, 2004 ================================================================================ OVERVIEW The use of constraints had its scientific and commercial breakthrough in the 1990s. Programming with constraints makes it possible to model and specify problems with uncertain, incomplete information and to solve combinatorial problems, as they are abundant in industry and commerce, such as scheduling, planning, transportation, resource allocation, layout, design, and analysis. Constraint-based programming languages enjoy elegant theoretical properties, conceptual simplicity, and practical success. The aim of the workshop is to provide opportunity for interactions with the other ETAPS'04 events and to be a major meeting point in the research area inbetween the Constraint Programming conferences, which are held each autumn. The workshop will consist of sessions with invited talks that summarize the main challenges and/or application potential for the community, and sessions with short presentations describing ongoing work. Taking inspiration from the CP 02 workshop CFV, we will have a special track dedicated to "formal verification". In recent years there has been an increasing interest for the application of constraint programming and constraint solving technology to the formal verification of hardware and software systems. Constraint solvers for Boolean (SAT) and arithmetic domains (Presburger, polyhedra, linear constraints) are widely used as subprocedures of symbolic model checkers (e.g. nuSMV) and of model checkers for hybrid and real time systems (e.g. HyTech, Uppaal). Constraint solving is also used for computing static analysis of programs with numerical data variables and concurrent systems (e.g. via the Structural Theory of Petri Nets). The aim of this special track is to bring together researchers working in constraints and verification and to investigate the theoretical foundations, new applications, and future developments in this area. SUBMISSION To submit, send an email to Giorgio Delzanno giorgio(a)disi.unige.it containing four consecutive ASCII lines with title, author(s), email(s) and WWW link directly to compressed postscript file (5-15 pages). Accepted papers will be available electronically at the workshop web-page and may be published in hard-copy proceedings (available at the workshop). ORGANISATION AND PROGRAM COMMITTEE Giorgio Delzanno, DISI - University of Genova Thom Fruehwirth, University of Ulm Francois Fages, INRIA Rocquencourt Joao Marques-Silva, Technical University of Lisbon, IST/INESC-ID/CEL Andreas Podelski, MPI - Saarbruecken Peter Stuckey, University of Melbourne IMPORTANT DATES January 28, 2004: Paper/abstract submissions February 25, 2004: Acceptance decisions March 12, 2004: Final version due March 28, 2004: Workshop at ETAPS 2004

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HBase Haddocumentation Available
by Ashley Yakeley 17 Jan '04

17 Jan '04

I now have some haddock for HBase available to browse. There's only one module missing, Org.Org.Semantic.HBase.Category.Constant, due to a kind declaration. Thanks to Simon M. for creating an excellent documentation tool. <http://hbase.sourceforge.net/haddock/> -- Ashley Yakeley, Seattle WA

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OpenBSD/sparc Haskell support
by dons＠cse.unsw.edu.au 16 Jan '04

16 Jan '04

Hello OpenBSD Haskellers, GHC is now distributed for the sparc architecture in the OpenBSD ports tree. This means that happy, haddock, alex, hmake and other Haskell tools already in the tree are now being built for sparc/openbsd too. Just update to the current ports tree to use this stuff. Cheers, Don N.B. this is GHC 6.0.1, port tree builds for sparc, for 6.2 are coming soon

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RE: Haddock and fixity declarations
by Simon Marlow 15 Jan '04

15 Jan '04

> could Haddock be made to document also fixity declarations? Yes, it's on the ToDo list. Cheers, Simon

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GHC source bitten by the ghost of DOS
by Graham Klyne 15 Jan '04

15 Jan '04

I've just been bitten by the ghost of DOS when trying to unpack the source kit for GHC on a Windows (XP) system. It appears that the filename AUX is reserved (still crazy after all these years?). Unfortunately, the GHC source kit contains a file aux.dtd in .\ghc-6.2\src\libraries\HaXml\bugs So, when trying to copy this to my working system, I get strange errors that this file cannot be created. It's not a big deal for me -- I just unpacked the tar file on my Linux server machine, renamed the offending file, and the copy then works fine. But for Windows users without a Linux box to fall back on, this might be problematic. Maybe it's worth using another filename? #g ------------ Graham Klyne For email: http://www.ninebynine.org/#Contact

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overlapping instances and modules
by Iavor S. Diatchki 14 Jan '04

14 Jan '04

hello, i am a bit stuck on the following problem, which seems to be GHC related. consider the following two modules: > {-# OPTIONS -fglasgow-exts -fallow-overlapping-instances #-} > module Test where > > data T m a = T (m a) > > class C m where get :: m a > > instance C (T m) > instance C m => C (t m) > > obs :: T [] Int > obs = get > module Test1 where > > import Test > > obs' :: T [] Int > obs' = get i can load the first one (Test) without problems, but when i load the second one (Test1) a get the error: Test1.hs:6: No instance for (C []) arising from use of `get' at Test1.hs:6 In the definition of `obs'': obs' = get this seems to indicate that the second instance is being used, but i cannot figure out why. am i doing something silly here? -iavor ps: i am not on the GHC users list so please cc me if you replay there -- ================================================== | Iavor S. Diatchki, Ph.D. student | | Department of Computer Science and Engineering | | School of OGI at OHSU | | http://www.cse.ogi.edu/~diatchki | ==================================================

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