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HaL4: Haskell-Treffen in Halle/Saale, 12. Juni 2009 - Programm und Anmeldung
by unknown＠example.com 20 May '09

20 May '09

Kindly excuse the German noise, please ... Liebe Haskell-Freunde! Das Programm fuer unser Haskell-Treffen steht jetzt so gut wie fest und man kann sich online anmelden. --------------------------------------------- HaL4 : Haskell - Tutorial + Workshop + Party am Freitag, dem 12. Juni 2009, in Halle/Saale --------------------------------------------- Das traditionsreiche HaL-Treffen bietet eine gute Mischung von Haskell-bezogenen Themen aus Forschung, Anwendung und Lehre mit vielen Möglichkeiten zu Diskussion und Unterhaltung bei der anschließenden Party. Der Workshop wird in diesem Jahr ergänzt durch Tutorien für Haskell-Ein- und Umsteiger. Diesmal findet das Treffen in Halle/Saale im Institut für Informatik der Martin-Luther-Universität Halle-Wittenberg statt. Wir bieten: 10 Uhr: Entwurfsmuster vom Kopf auf die Fuesse gestellt: data, fold und laziness statt Kompositum, Visitor, Iterator. Johannes Waldmann, HTWK Leipzig. 11 Uhr: CAL/openquark: (openquark.org) Haskell + Java => CAL, eine praktische Einfuehrung (Eclipse als CAL-IDE, Excel lesen, typsicheres SQL = LINQ fuer Java?) Alf Richter, iba Consulting, Leipzig 12 Uhr: Wie man das Semikolon ueberlaedt: Code-Strukturierung und -Wiederverwendung durch Monaden 15 Uhr: Hayoo! Haskell API Search Timo Huebel, FH Wedel 16 Uhr: Haskell als reine Spezifikationssprache Baltasar Trancon y Widemann, Universit Bayreuth 17 Uhr: Funktional-logische Programmierung mit Curry Jan Christiansen, Universitaet Kiel 19 - 22 Uhr: Grillparty Wir freuen uns auf rege Teilnahme sowie spannende Vorträge mit heißen Diskussionen und bitten um Anmeldung bis zum 31. Mai. Weitere Informationen auf http://www.iba-cg.de/hal4.html Beste Gruesse Henning Thielemann

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"computation", "action"
by Michael P Mossey 19 May '09

19 May '09

I've seen the following language used: - "computations" - "actions" - "effects" - "context" (For example, a functor is a context, and fmap applies a function to an object in that context without changing the context.) One words that seem to come up in Haskell are "algorithm" and "procedure." For example, a monad is sometimes called a "computation" or an "effect", but I've not seen it called an "algorithm." Can someone elaborate on these terms and why they are used? What is the difference between a computation and an algorithm? The word "effect" has a fairly obvious meaning (like an IO side-effect) but I suspect there's more to it. Why is the word "context" important, and when it is more appropriate than "container"? thanks, Mike

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Intervals?
by Nathan Holden 19 May '09

19 May '09

I have been trying to optimize some research I was doing in my spare time. To spare complexity, it involves music-- I have a class, defining each note in an octave, and I want to write a function that will convert between two notes and an interval-- so, for instance: Foo As {- A sharp-- can't use # -} B = 1 because in the standard scale, A# and B are one semitone apart. My question, however, boils primarily down to this: Is there a way to make Foo :: Note -> Note -> Int Foo a b = a-b work?

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Re: [Haskell-beginners] Intervals?
by Nathan Holden 19 May '09

19 May '09

Yeah, it would. But I always write code like that, it feels ungainly... writing super-long, case-by-case instance declarations (So that I can add in one little caveat at the end, or something), and stuff. Makes me feel like I must be dumb! On Tue, May 19, 2009 at 2:54 PM, Derek Gladding <derek(a)ebollocks.net> wrote: > Nathan Holden wrote: > >> [snip] >> My question, however, boils primarily down to this: Is there a way to make >> >> Foo :: Note -> Note -> Int >> Foo a b = a-b >> >> work? >> > > Would a function > > Bar :: Note -> Int > > make writing Foo easier? > > - Derek >

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Haskell vs Clean (speed)
by Daniel Carrera 19 May '09

19 May '09

Hi, I can't subscribe to Haskell-Cafe, so I'll post here. I found something interesting. "General wisdom" is that Clean (or OCaml) is faster than Haskell. The claim is often followed by a link to the Debian shootout. But on closer inspection, I question this conclusion. The Debian shoot out actually has four sets of benchmarks: 1) Intel 32-bit one core. 2) Intel 32-bit quad-core. 3) Intel 64-bit one core. 4) Intel 64-bit quad-core. It turns out that Clean is only faster for (1). For the others, Haskell is faster. Here I compare Haskell, Clean, OCaml, Lisp SBCL, C# Mono and Fortran because they are all in the same ball mark: 32-bit sing core [1]: Lisp, Fortran, Clean, Haskell, C# Mono. 32-bit quad-core [2]: Haskell, C# Mono, Lisp, Clean, Fortran. 64-bit sing core [3]: Fortran, OCaml, Haskell, Clean, C# Mono, Lisp. 64-bit quad-core [4]: Haskell, OCaml, Lisp, C# Mono, Fortran, Clean. Notes: * The order is "fast language first". * There are no results for OCaml for 32-bit. * "Lisp" is "List SCBL" whatever that is. Tentative conclusions: 1) Haskell makes very good use of multiple cores. It smokes Clean. 2) For single core, they are neck and neck. Whether Clean is faster depends non the architecture. What do you think? Daniel. P.S. [1]http://shootout.alioth.debian.org/u32/benchmark.php?test=all&lang=all&d=d… [2]http://shootout.alioth.debian.org/u32q/benchmark.php?test=all&lang=all&d=… [3]http://shootout.alioth.debian.org/u64/benchmark.php?test=all&lang=all&d=d… [4]http://shootout.alioth.debian.org/u64q/benchmark.php?test=all&lang=all&d=…

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Unable to Cabal Upgrade
by aditya siram 15 May '09

15 May '09

Hi all, I'm unable to cabal upgrade with the following error: Resolving dependencies... cabal: dependencies conflict: ghc-6.10.1 requires process ==1.0.1.1 however process-1.0.1.1 was excluded because ghc-6.10.1 requires process ==1.0.1.0 I am currently running ghc 6.10.1 and process 1.0.1.1. thanks ... deech

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Gtk2Hs + Sourceview on Windows
by mwinter＠brocku.ca 13 May '09

13 May '09

Hi, I have ghc 6.10.1 and gtk2hs 0.10.0 installed on my windows vista computer. Both were installed using the installer on the webpages. I am able to use gtk, glade etc but not sourceview or cairo. In a forum I found that those have to be enabled using ./configure --enable-sourceview (similar for cairo). But my windows installation does not seem to have a script configure. What am I supposed to do? Thanks, Michael

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International Summer School on Advances in Programming Languages (precedes ICFP'09)
by Janis Voigtlaender 13 May '09

13 May '09

Potential participants of the below summer school should pre-register their interest now. The organizers need that information to go ahead with the planning. ===================================================================== International Summer School on Advances in Programming Languages 25th-28th August, 2009 Heriot-Watt University, Edinburgh, Scotland http://www.macs.hw.ac.uk/~greg/ISS-AiPL Overview ~~~~~~~~ This four-day residential International Summer School on Advances in Programming Languages has a major theme of Concurrency, Distribution, and Multicore. Intended primarily for postgraduate research students, the School offers lectures and practical sessions on an engaging blend of cutting edge theoretical and practical techniques from international experts. The Summer School is supported by the Scottish Informatics and Computer Science Alliance (http://www.sicsa.ac.uk/) a Scottish Funding Council Research Pool. Participants from SICSA member institutions may attend at no cost. Confirmed Topics/Speakers * Static and dynamic languages, Prof Philip Wadler, University of Edinburgh * Compiler technology for data-parallel languages, Dr Sven-Bodo Scholz, University of Hertfordshire * New applications of parametricity, Dr Janis Voigtlaender, Technical University of Dresden * Automatic vectorising compilation, Dr Paul Cockshott, University of Glasgow * Foundational aspects of size analysis, Prof Marko van Eekelen / Dr Olha Shakaravska, Radboud University Nijmegen * Context oriented programming, Dr Pascal Costanza, Vrije Universiteit Brussels * Multi-core programming, Dr Phil Trinder, Heriot-Watt University * Multi-core compilation, Dr Alastair Donaldson, Codeplay Software Ltd * Principles and Applications of Refinement Types, Dr Andrew D. Gordon, Microsoft Research, Cambridge * Resource aware programming in Hume, Prof Greg Michaelson, Heriot-Watt University / Prof Kevin Hammond, University of St Andrews * Haskell concurrency & parallelism, Dr Satnam Singh, Microsoft Research, Cambridge Location ~~~~~~~~ The Summer School is at Heriot-Watt University's Riccarton campus, set in pleasant parkland to the west of Edinburgh, with easy access to the airport, city and central Scotland (http://www.hw.ac.uk/welcome/directions.htm) The Summer School immediately precedes the 2009 International Conference on Functional Programming (http://www.cs.nott.ac.uk/~gmh/icfp09.html) and takes place during the Edinburgh International Festival (http://www.eif.co.uk/) , and the associated Edinburgh Festival Fringe (http://www.edfringe.com/) and Edinburgh International Book Festival (http://www.edbookfest.co.uk/) Steering Committee ~~~~~~~~~~~~~~~~~~ Prof Prof Greg Michaelson, Heriot-Watt University (Convenor), <G.Michaelson(a)hw.ac.uk> Prof Kevin Hammond, University of St Andrews Dr Patricia Johann, University of Strathclyde Prof Philip Wadler, University of Edinburgh Fee ~~~ Full rate: £400; (free for SICSA students) Includes: four nights single room, en-suite accommodation with breakfast, lunch and dinner, plus coffee breaks and session materials. Day rate: £200; (free for SICSA students) Includes: lunch, coffee breaks, session materials Registration of Interest ~~~~~~~~~~~~~~~~~~~~~~~~ If you are interested in attending the International Summer School, please complete the form available from (http://www.macs.hw.ac.uk/~greg/ISS-AiPL/ISS-AiPL%20register.doc) or below, and return it to: <ISS-AiPL-register(a)macs.hw.ac.uk> ********** International Summer School on Advances in Programming Languages 25th-28th August, 2009 Heriot-Watt University, Edinburgh, Scotland Registration of Interest Name: Address: Email: Phone: SICSA Uni: Yes / No Rate: Full / Day Accessibility requirements: Dietary requirements: Return to: ISS-AiPL-register(a)macs.hw.ac.uk **********

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The main thread and waiting for other threads
by Thomas Friedrich 13 May '09

13 May '09

Hi everyone, I have a problem with the following example in the Real World Haskell book, which aims to develop a module for controlling different threads. See, http://book.realworldhaskell.org/read/concurrent-and-multicore-programming.… in the chapter "The main thread and waiting for other threads". -- file: ch24/NiceFork.hs import Control.Concurrent import Control.Exception (Exception, try) import qualified Data.Map as M data ThreadStatus = Running | Finished -- terminated normally | Threw Exception -- killed by uncaught exception deriving (Eq, Show) -- | Create a new thread manager. newManager :: IO ThreadManager -- | Create a new managed thread. forkManaged :: ThreadManager -> IO () -> IO ThreadId -- | Immediately return the status of a managed thread. getStatus :: ThreadManager -> ThreadId -> IO (Maybe ThreadStatus) -- | Block until a specific managed thread terminates. waitFor :: ThreadManager -> ThreadId -> IO (Maybe ThreadStatus) -- | Block until all managed threads terminate. waitAll :: ThreadManager -> IO () When I run this through ghci I get the following failure: [1 of 1] Compiling NiceFork ( NiceFork.hs, interpreted ) NiceFork.hs:17:26: Class `Exception' used as a type In the type `Exception' In the data type declaration for `ThreadStatus' Failed, modules loaded: none. Any idea on how to solve this? Exception is a class not a type, so what to put there instead? Cheers, Thomas

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defining 'init' in terms of 'foldr'
by Michael Mossey 12 May '09

12 May '09

In S. Thompson's book, problem 9.13 asks us to define 'init' in terms of foldr. I was baffled at first because I didn't see a natural way to do this. It would look something like init xs = foldr f initialValue xs where f would cons on each character except the rightmost. f <when passed rightmost char> b = [] f <when passed any other char a> b = a : b How does f "know" when it is passed the first character? initialValue has to signal this somehow. On #haskell, one person suggested doing it with some post-processing: init xs = snd $ foldr f (True,[]) xs where f _ (True,_) = (False,[]) f a (False,b) = (False,a:b) I had an idea. If the initial value is the entire list, then its length can function as the "signal" that we are dealing with the rightmost char. This requires no post-processing: init xs = foldr f xs xs where f a b | length b == length xs = [] | otherwise = a:b These seem contrived. I wonder if there is a more natural solution that Thompson had in mind. Any comments? -Mike

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