September 2007 - Haskell

Re: [Haskell] (no subject)
by Chaddaï Fouché 05 Sep '07

05 Sep '07

2007/9/5, Tomi Owens <t.owens(a)hautlieu.sch.je>: > So now I try to apply the function to the list: > > Prelude> map (f) [(a2+b2,a)| a <- [1..4] , b<- [1..4], a2+b2<20, b<=a] > > and I get this result: > > <interactive>:1:5: > Ambiguous type variable `t' in the constraints: > `Integral t' arising from use of `f' at <interactive>:1:5 > `RealFrac t' arising from use of `f' at <interactive>:1:5 > Probable fix: add a type signature that fixes these type variable(s) > > > I'm sorry, but I don't quite get how to set the type signature and how it > will apply to my function... > It's because f need a real, not an integer as the second element of its parameter (since it use (/) in (10000/b)), and as it also needs an integer as it's first, the type checker don't know what the type of a should be (it can't be both an integer and a floating value at the same time). The easiest IMO is to keep a as an integer, but use "fromIntegral" to convert it to a real in the second part of the tuple : map f [( a^2+b^2, fromIntegral a) | a <- [1..4] , b<- [1..4], a^2+b^2<20, b<=a] You would get more help and faster from an IRC channel like %23haskell(a)irc.freenode.net though. -- Jedaï

1 0

ICFP07 Reminder: registration deadline
by Matthew Fluet (ICFP Publicity Chair) 05 Sep '07

05 Sep '07

===================================================================== Final Call for Participation The 12th ACM SIGPLAN International Conference on Functional Programming (ICFP 2007) http://www.informatik.uni-bonn.de/~ralf/icfp07.html http://proglang.informatik.uni-freiburg.de/ICFP2007 Freiburg, Germany, 1-3 October 2007 ===================================================================== ***** Early Registration Deadline: September 7, 2007 ***** ICFP 2007 provides a forum for researchers and developers to hear about the latest work on the design, implementations, principles, and uses of functional programming. The conference covers the entire spectrum of work, from practice to theory, including its peripheries. Schedule including related workshops: * 30 Sep: ACM SIGPLAN Haskell Workshop * 30 Sep: ACM SIGPLAN Workshop on Scheme and Functional Programming * 1-3 Oct: ICFP07 * 4 Oct: ACM SIGPLAN Commercial Users of Functional Programming * 4 Oct: ACM SIGPLAN Workshop on Mechanizing Metatheory * 5 Oct: ACM SIGPLAN Erlang Workshop * 5 Oct: ACM SIGPLAN Workshop on ML * 5 Oct: ACM SIGPLAN Programming Languages meets Program Verification

1 0

ANNOUNCE: xmonad 0.3
by dons＠cse.unsw.edu.au 05 Sep '07

05 Sep '07

The xmonad dev team is pleased to announce the 0.3 release of xmonad. xmonad: a tiling window manager http://xmonad.org About: xmonad is a tiling window manager for X. Windows are arranged automatically to tile the screen without gaps or overlap, maximising screen use. All features of the window manager are accessible from the keyboard: a mouse is strictly optional. xmonad is written and extensible in Haskell. Custom layout algorithms, and other extensions, may be written by the user in config files. Layouts are applied dynamically, and different layouts may be used on each workspace. Xinerama is fully supported, allowing windows to be tiled on several screens. Features: * Very stable, fast, small and simple. * Automatic window tiling and management * First class keyboard support: a mouse is unnecessary * Full support for tiling windows on multi-head displays * Full support for floating windows * XRandR support to rotate, add or remove monitors * Per-workspace layout algorithms * Per-screens custom status bars * Easy, powerful customisation and reconfiguration * Large extension library * Extensive documentation and support for hacking Since xmonad 0.2, the following notable features and bug fixes have appeared: New features: * floating layer support: transients windows are not tiled by default, and windows may be dragged to and from a traditional floating layer (which allows mouse-resizing, and overlapping windows). * improved Xinerama support: workspace switching reuses multiple displays more effectively. * huge new extension library. Over 50 extensions to xmonad have been contributed by users, and are available all in a standard library, with documentation. More information, screenshots, documentation and community resources are available from: http://xmonad.org Xmonad is available from hackage, and via darcs. Happy hacking! The Xmonad Team: Spencer Janssen Don Stewart Jason Creighton Xmonad has also received contributions from at least: Alec Berryman Andrea Rossato Chris Mears Daniel Wagner David Glasser David Lazar David Roundy Hans Philipp Annen Joachim Fasting Joe Thornber Kai Grossjohann Karsten Schoelzel Michael Sloan Miikka Koskinen Neil Mitchell Nelson Elhage Nick Burlett Peter De Wachter Robert Marlow Sam Hughes Shachaf Ben-Kiki Shae Erisson Simon Peyton Jones Stefan O'Rear as well as many others on the IRC channel and mailing list. Thanks to everyone!

2 1

functional dependencies not satisfactory?
by Wolfgang Jeltsch 05 Sep '07

05 Sep '07

Hello, I came across the following problem: I define a class with a functional dependency like so: class C a b | a -> b Then I want to define a datatype using the fact that the second argument of C is dependent on the first: data C a b => T a = MkT a b But unfortunately, this doesn’t work, at least not in GHC. I can try this: data T a = forall b. C a b => MkT a b But if I do pattern matching on a value of T a, GHC doesn’t recognize that the type of MkT’s second argument is determined by the type of the first. For example, the following function definition is not accepted: useB :: C a b => T a -> (b -> ()) -> () useB (MkT a b) f = f b In my opinion, the problem is that GHC doesn’t see that because of the functional dependency the type exists b. C a b => b is at least as general as the type forall b. C a b => b. Is there a solution to this problem? Best wishes, Wolfgang

3 4

ISMM'07: call for participation
by Greg Morrisett 04 Sep '07

04 Sep '07

ISMM'07 CALL FOR PARTICIPATION and Accepted Papers 2007 ACM International Symposium on Memory Management co-located with OOPSLA 2007 Sponsored by ACM SIGPLAN 21-22 October 2007, Montreal http://www.eecs.harvard.edu/~greg/ismm07/ To register for the symposium, see the OOPSLA registration page at http://www.oopsla.org/oopsla2007. Note that the deadline for early registration and reduced rates is Thursday, 13 September. ISMM is a forum for research in management of dynamically allocated memory. Areas of interest include but are not limited to: explicit storage allocation and deallocation; garbage collection algorithms and implementations; compiler analyses to aid memory management; interactions with languages, operating systems, and hardware, especially the memory system; and empirical studies of allocation and referencing behavior in programs that make significant use of dynamic memory. This year's symposium is being held in conjunction with OOPSLA in Montreal on October 21st and 22nd. Invited speakers include Peter O'Hearn (Queen Mary, University of London) and David Kirk (Chief Scientist NVIDIA). In addition to presentation of the papers listed below, there will be an exciting "wild and crazy" ideas session where participants will have a chance to discuss half-baked and interesting ideas. All are welcome! Invited talks and papers to be presented at the symposium: Keynote: Separation Logic and Concurrent Resource Management Peter O'Hearn Safe Manual Memory Management David Gay, Robert Ennals, & Eric Brewer Detecting and Eliminating Memory Leaks Using Cyclic Memory Allocation Huu Hai Nguyen & Martin Rinard Page Access Tracking to Improve Memory Management Reza Azimi, Livio Soares, Michael Stumm, Angela Demke Brown, & Tom Walsh Effective Prefetch for Mark-Sweep Garbage Collection Robin Garner, Stephen Blackburn, & Daniel Frampton Accordion Arrays: Selective Compression of Unicode Arrays in Java Craig Zilles Decrypting the Java Gene Pool: Predicting Object Lifetimes with Micro- Patterns Sebastien Marion, Richard Jones, & Chris Ryder Allocation-Phase Aware Scheduling Policies to Improve Garbage Collection Performance Feng Xian, Witawas Srisa-an, & Hong Jiang Intelligent Selection of Application-Specific Garbage Collectors Jeremy Singer, Gavin Brown, Ian Watson, & John Cavazos Keynote: NVIDIA CUDA Software and GPU Parallel Computing Architecture David Kirk Heap Space Analysis for Java Bytecode Elvira Albert, Samir Genaim, & Miguel Gomez-Zamalloa Uniqueness Inference for Compile-Time Object Deallocation Sigmund Cherem & Radu Rugina A Correct and Useful Incremental Copying Garbage Collector Martin Kero, Johan Nordlander, & Per Lindgren Overlooking Roots: A Framework for Making Nondeferred Reference- Counting Garbage Collection Fast Pramod Joisha Stopless: A Real-Time Garbage Collector for Modern Platforms Filip Pizlo, Daniel Frampton, Erez Petrank, & Bjarne Steensgaard Mark-Sweep or Copying? A "Best of Both Worlds" Algorithm and a Hardware-Supported Real-Time Implementation Sylvain Stanchina & Matthias Meyer

1 0