February 2008 - Glasgow-haskell-users

Deforesting edtiInt
by Robin Houston 03 Feb '08

03 Feb '08

Recently I wrote a short program that builds an array containing the number of divisors of the first 10^7 natural numbers. (Some of you can guess why I did this, but I won't say explicitly lest this post become a Googleable spoiler.) Here's the relevant part of the code. incElem a i = readArray a i >>= \n -> writeArray a i $! n+1 do -- Create an array with elements initialised to 0 a <- newArray (1,n) 0 :: ST s (STUArray s Int Word16) -- Populate the array forM_ [2..n] $ \i -> forM_ [i, i+i .. n] (incElem a) Of course there are more efficient algorithms for this, but this one has the merit of being extremely simple without being unreasonably slow. Except that it is a lot slower than it needs to be. After digging around a bit, I suspected that the reason for this is that the general form of enumeration [from, then .. to] does not benefit from the deforestation optimisation. When I added some deforestation rules to GHC/Enum.lhs and rebuilt the library, I found my suspicion confirmed: after the change, my code runs roughly twice as fast. Is there any reason not to do this? I attach a diff of the change I made, though I expect it could be done better by someone with experience of this sort of thing. Robin

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Re: [Haskell-cafe] strange GHC assembler failure
by Tim Chevalier 03 Feb '08

03 Feb '08

On 2/2/08, Tim Newsham <newsham(a)lava.net> wrote: > I'm getting a weird build error: > [ 9 of 95] Compiling Plugin.Pl.Common ( Plugin/Pl/Common.hs, > dist/build/lambdabot/lambdabot-tmp/Plugin/Pl/Common.o ) > /tmp/ghc52608_0/ghc52608_0.s: Assembler messages: > > /tmp/ghc52608_0/ghc52608_0.s:36:0: Error: unassigned file number 1 > [... more of these ...] > > I narrowed this down -- this happens when I add my new library > "silc-client" to the "Build-depends:" line in the cabal file even > if none of its code is referenced. Removing the dependency makes > the error go away. The module I'm referencing is a new one I'm > still working on and it makes use of FFI and references external > headers and libraries. > (I put a copy at http://www.thenewsh.com/~newsham/silc-client.tgz > if it helps anyone debug.. this is not release-quality code > though). > > Any idea what is going on here? > This would probably be a better question for ghc-users, since that's a lower-traffic list for GHC-specific questions. Redirected there. Cheers, Tim -- Tim Chevalier * http://cs.pdx.edu/~tjc * Often in error, never in doubt "Now, don't bother to flame me, because by the time you read this post I will be a different person from the one who wrote it. You cannot step in the same river twice." -- Sarah Barton

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Read instance of StdGen returns no parse
by Denis Bueno 02 Feb '08

02 Feb '08

Hi all, According to http://haskell.org/ghc/docs/latest/html/libraries/random/System-Random.html… the Read StdGen instance should never fail. However, in GHC 6.8.2, it appears to: > ghci GHCi, version 6.8.2: http://www.haskell.org/ghc/ :? for help Loading package base ... linking ... done. Prelude> :m System.Random Prelude System.Random> read "exsqueeze me" :: StdGen Loading package old-locale-1.0.0.0 ... linking ... done. Loading package old-time-1.0.0.0 ... linking ... done. Loading package random-1.0.0.0 ... linking ... done. *** Exception: Prelude.read: no parse Prelude System.Random> Leaving GHCi. It first fails for me on strings of length seven. Is this a bug, or have I done something wrong? -- Denis

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Second Call for Papers TFP 2008, The Netherlands
by Peter Achten 01 Feb '08

01 Feb '08

2ND CALL FOR PAPERS TRENDS IN FUNCTIONAL PROGRAMMING 2008 RADBOUD UNIVERSITY NIJMEGEN, THE NETHERLANDS MAY 26-28, 2008 INVITED SPEAKER: PROF. HENK BARENDREGT http://www.st.cs.ru.nl/AFP_TFP_2008/ The symposium on Trends in Functional Programming (TFP) is an international forum for researchers with interests in all aspects of functional programming languages, focusing on providing a broad view of current and future trends in Functional Programming. It aspires to be a lively environment for presenting the latest research results through acceptance by extended abstracts and full papers. A formal post-symposium refereeing process selects the best articles presented at the symposium for publication in a high-profile volume. TFP 2008 is hosted by the Radboud University Nijmegen, The Netherlands, and will be held in the rural setting of Center Parcs “Het Heijderbos”, Heijen (in the vicinity of Nijmegen), The Netherlands. TFP 2008 is co-located with the 6th Int’l. Summer School on Advanced Functional Programming (AFP’08), which is held immediately before TFP’08. SCOPE OF THE SYMPOSIUM The symposium recognizes that new trends may arise through various routes. As part of the Symposium's focus on trends we therefore identify the following five article categories. High-quality articles are solicited in any of these categories: Research: leading-edge, previously unpublished research. Position: on what new trends should or should not be. Project: descriptions of recently started new projects. Evaluation: what lessons can be drawn from a finished project. Overview: summarizing work with respect to a trendy subject. Articles must be original and not submitted for simultaneous publication to any other forum. They may consider any aspect of functional programming: theoretical, implementation-oriented, or more experience-oriented. Applications of functional programming techniques to other languages are also within the scope of the symposium. Contributions on the following subject areas are particularly welcomed: * Dependently Typed Functional Programming * Validation and Verification of Functional Programs * Debugging for Functional Languages * Functional Programming and Security * Functional Programming and Mobility * Functional Programming to Animate/Prototype/Implement Systems from Formal or Semi-Formal Specifications * Functional Languages for Telecommunications Applications * Functional Languages for Embedded Systems * Functional Programming Applied to Global Computing * Functional GRIDs * Functional Programming Ideas in Imperative or Object-Oriented Settings (and the converse) * Interoperability with Imperative Programming Languages * Novel Memory Management Techniques * Parallel/Concurrent Functional Languages * Program Transformation Techniques * Empirical Performance Studies * Abstract/Virtual Machines and Compilers for Functional Languages * New Implementation Strategies * Any new emerging trend in the functional programming area If you are in doubt on whether your article is within the scope of TFP, please contact the TFP 2008 program chairs, Peter Achten and Pieter Koopman, at afp_tfp_2008(a)cs.ru.nl. SUBMISSION AND DRAFT PROCEEDINGS Acceptance of articles for presentation at the symposium is based on the review of full papers (15 pages) and extended abstracts (at least 3 pages) by the program committee. TFP encourages PhD students to submit papers. PhD students may request the program committee to provide extensive feedback on their full papers at the time of submission. Full papers describing work accepted for presentation must be completed before the symposium for publication in the draft proceedings and on-line. Further details can be found at the TFP 2008 website http://www.st.cs.ru.nl/AFP_TFP_2008/. POST-SYMPOSIUM REFEREEING AND PUBLICATION In addition to the draft symposium proceedings, we continue the TFP tradition of publishing a high-quality subset of contributions in the Intellect series on Trends in Functional Programming. IMPORTANT DATES (ALL 2008) Paper Submission: March 3 Notification of Acceptance: March 31 Early Registration Deadline: April 14 Late Registration Deadline: May 5 Camera Ready Symposium: May 5 TFP Symposium: May 26-28 Post Symposium Paper Submission: June 20 Notification of Acceptance: September 7 Camera Ready Revised Paper: September 21 PROGRAMME COMMITTEE Peter Achten (co-chair) Radboud Univ. Nijmegen, NL Andrew Butterfield Trinity College, IE Manuel Chakravarty Univ. of New South Wales, AU John Clements Cal Poly State Univ., USA Matthias Felleisen Northeastern Univ., USA Jurriaan Hage Utrecht Univ., NL Michael Hanus Christian-Albrechts Univ. zu Kiel, DE Ralf Hinze Univ. of Oxford, UK Graham Hutton Univ. of Nottingham, UK Johan Jeuring Utrecht Univ., NL Pieter Koopman (co-chair) Radboud Univ. Nijmegen, NL Shriram Krishnamurthi Brown Univ., USA Hans-Wolfgang Loidl Ludwig-Maximilians Univ.München, DE Rita Loogen Philipps-Univ. Marburg, DE Greg Michaelson Heriot-Watt Univ., UK Marco T. Morazán (symp. chair) Seton Hall Univ., USA Sven-Bodo Scholz Univ. of Hertfordshire, UK Ulrik Schultz Univ. of Southern Denmark, DK Clara Segura Univ. Complutense de Madrid, ES Olin Shivers Northeastern Univ., USA Phil Trinder Heriot-Watt Univ., UK Varmo Vene Univ. of Tartu, EE Viktória Zsók Eötvös Loránd Univ., HU ORGANIZATION Symposium Chair: Marco T. Morazán, Seton Hall University, USA Programme Chair: Peter Achten, Pieter Koopman, Radboud University Nijmegen, NL Treasurer: Greg Michaelson, Heriot-Watt University, UK

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Using "GHC as a library" with own functions makes runStmt return RunBreak
by Mads Lindstrøm 01 Feb '08

01 Feb '08

Hi I am trying to use "GHC as a library". From runStmt, I want to load and run functions from a home-grown module. Lets call my home-grown module HomeGrown.hs. I have tried to model my application after http://haskell.org/sitewiki/images/1/17/Interactive-6.8.hs / http://haskell.org/sitewiki/images/f/f9/MyPrelude.hs from http://haskell.org/haskellwiki/GHC/As_a_library . This library loads MyPrelude.hs and runs myPutStrLn & myGetLine + more. However, when I try to run code from HomeGrown.hs like: runStmt session "HomeGrown.foo" GHC.SingleStep runStmt keeps returning RunBreak (of type RunResult). From what I can read of the WWW, RunBreak is related to some debugger and indicate that GHC encountered some breakpoint. However, I did not set any break points. Comparing Interactive-6.8 and MyPrelude.hs to my own code, the largest difference seemed to be that Interactive-6.8 do not only use MyPrelude.hs by calling `addTarget` and `setContext`, it also imports MyPrelude.hs as a regular Haskell import (import MyPrelude). Thus I tried to remove this import to see what would happen. Interactive-6.8 compiled and started just fine. However, whenever it needed to use any functions in MyPrelude, runStmt also returned RunBreak. So is it only possible to load home-grown/non-standard modules when also doing a regular import? Greetings, Mads Lindstrøm

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