December 2006 - Glasgow-haskell-users

partially applied type synonyms
by Arie Peterson 05 Mar '12

05 Mar '12

Dear list, Is there a good reason that partially applied type synonyms cannot be made instances of classes? - A simple example would be making the identity type 'Id' ("type Id x = x") instance of 'Monad'. This would eliminate the need for some silly occurrences of 'runIdentity', and perhaps narrow the gap between monads and monad transformers. - The reason I complain about this now is a more involved example, where introducing a newtype to work around the restriction is not an option. Well, not as far as I can see now, anyway. Partially applied type synonyms are, in a sense, the anonymous functions at the type level, and one might argue that they deserve the same 'first-class member status' as the lambda at the value level. Kind regards, Arie Peterson

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Replacement for GMP: Update
by Peter Tanski 23 Jan '07

23 Jan '07

Simon PJ, Simon, Esa and John, Here is an update on what I have been doing so far in making a grand attempt to replace GMP. (1) evaluate replacement libraries LibTomMath: Pros- * has all the operators GMP offered Cons- * slow; about half as fast as OpenSSL in my tests for simple mathematical operations, much slower if you account for time to write or resize memory. (There is another MP library, which LibTomMath is based on, that is also very slow--student work) * not even reentrant; needs significant modification * beta-release; needs a bit of work to get it to production level * configuration needs to be written (not really portable, messy) ARPREC: Pros- * very fast (essentially does everything through the Floating Point Unit of a CPU) * complex mathematical operations * very precise * already thread safe (through C++ thread-safe statics) Cons- * no bitwise operations (not even left and right-shifts) * difficult configuration (everything runs by setting a precision level; ("precision level" ~= number of words (doubles) in array) it does not automatically resize memory; conversion from MP Real to Integer relies specially on careful precision-level) * memory inefficient (underestimates the number of real digits you can fit into a double, i.e., a 64-bit double has 48 bits of precision, holding about 9.6 digits per byte, resulting in an 848-byte array to hold an MP number with 1000 digits). OpenSSL: Crypto++ (http://www.eskimo.com/~weidai/cryptlib.html) Botan (http://botan.randombit.net/) Pros- * all of these are fast, since all use Integers to support cryptography; (Crypto++ and Botan are C++ crypto-libraries, all licenses good) * all of these provide most basic mathematical operations Cons- * none of these provide &, |, ^(xor) bitwise operators * Botan has least mathematical operators of the three * none provide lcm operator * all would realistically have to have the Integer libraries stripped out of the distribution and repackaged for GHC Summary: I finally settled on modifying OpenSSL, since that would be the easiest to work with under GHC's hood (plain C code, not C++). I have to: a. make OpenSSL's BN thread-safe (add thread local storage, at least) b. optimally add configure-conditional parallelism to BN (through PVM) c. add &, |, ^, lcm and a few other operations d. separate the BN from the rest of OpenSSL and rename the symbols to avoid conflicts (necessary because I have to modify the library anyway) (2) work on GHC: * finally understand C--; know what I need to modify * work through Makefiles: touch and go; I haven't mapped out all the variable settings from configure.in on down when it comes to DLLs Comment: for the Makefile in ghc/rts, in lines 300-346, GC_HC_OPTS += -optc-O3 --isn't this problematic? gcc, from -O2 on includes -fgcse which may *reduce* runtime performance in programs using computed gotos; -fgcse is actually run twice, because -frerun-cse-after-loop is also set at -O2. Would it be better to pass individual flags, such as -funroll-loops and -falign-loops=16 (ppc, Intel setting)? (3) I have been looking at how to implement a dual-constructor-in-a- pointer for Integer (i.e., merge constructors of small Integers and big Integers into the Int#). Would that solution be workable or might it break current Haskell programs? Just a thought. -Peter

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Unpacking polymorphic fields
by Takano Akio 05 Jan '07

05 Jan '07

Hi, Suppose I have the following two datatypes. data B = B {-# UNPACK #-} !Int data C a = C {-# UNPACK #-} !Char !a If I have a strict function: test :: C B -> IO () I want it to be worker-wrapper-transformed into: $wtest :: Char# -> Int# -> State# RealWorld -> (# State# RealWorld, () #) but GHC actually generates something like: $wtest :: Char# -> B -> State# RealWorld -> (# State# RealWorld, () #) The question is: is there any way to ask GHC to produce the former? If the field is not polymorphic, UNPACK pragma can be used for this, but it does not work in this case. If there is no such way, would it be a reasonable "feature request" to add one? Regards, Takano Akio

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ghci attempts to link entire package
by Bayley, Alistair 04 Jan '07

04 Jan '07

Related to some of the problems Takusen users have had, I have a question about ghci's linker/loader: why does it appear to try to link an entire package archive, rather than just the modules that are used? This is in contrast to the GNU ld program which the compiler uses, which only tries to link modules which are actually used. Is this a feature or a bug? Alistair ***************************************************************** Confidentiality Note: The information contained in this message, and any attachments, may contain confidential and/or privileged material. It is intended solely for the person(s) or entity to which it is addressed. Any review, retransmission, dissemination, or taking of any action in reliance upon this information by persons or entities other than the intended recipient(s) is prohibited. If you received this in error, please contact the sender and delete the material from any computer. *****************************************************************

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Running GHC on the IBM Cell
by Suter, Jaap 04 Jan '07

04 Jan '07

Hello, I'm trying to get GHC to run on the Cell processor. That is, just on the PPU PowerPC side. The SPUs will continue to run C programs, managed and driven by a Haskell manager on the PPU. I'm mostly interested in GHC for its concurrency features (STM in particular). Not knowing much about GHC yet, here's what I would expect in the ideal situation. 1. The RTS is largely cross-platform already. I might have to make some minor tweaks, but for the most part it should compile out of the box. 2. I setup GHC to compile my .hs files to .hc files; the C intermediates. 3. These are hopefully cross-platform as well, instead of being tied to my GHC distribution's platform. 4. I compile the RTS and .hc files and link them all together. 5. Done. This raises a few questions... * Are the .hc files cross-platform? Or does a GHC compiled for PowerPC generate different intermediate C code than a GHC compiled for X86? Ideally the platform specifics are hidden inside the RTS and two different GHC builds will output identical .hc files. * How cross-platform is the RTS? I downloaded the source tarball and dropped it on top of my XP installation of GHC. I then generated a simple Hello World haskell .hc intermediate and tried to compile that and the RTS. Unfortunately I ran into problems because things like HAVE_WINDOWS_H and HAVE_SIGNALS_H were defined. I started manually editing the code to tweak the configuration but ran into more problems (signal_set_t doesn't exist on my platform, but can't be conditionally compiled. static arrays of unknown size (StgWordArray) make my compiler unhappy. Etcetera). At this point I figured I would stop and ask for some help first, before I invest a lot of energy in a dead-end path. There must be a simpler way. I read parts of the "porting GHC to your platform" documentation, but I believe it addresses a different problem. I don't want to recompile GHC itself. I want to run my existing GHC on my XP machine and output intermediate .hc files. I then feed these plus a cross-platform RTS to my Cell compiler to get a workable program. I suppose I need to regenerate the ghautoconf for my particular platform (rather than hand-tweaking the existing one). Unfortunately I'm not much of a Linux or Gnu toolset expert. I see a bunch of config.* and configure.* file in the root folder. I suppose I should read up on those a little more. I'll do my homework first. In the meanwhile, if anybody has any quick and simple advice to make this process smoother that would be greatly appreciated. Kind regards, Jaap Suter - http://www.jaapsuter.com Some more random questions... * ghautoconf.h and HsBaseConfig.h have similar #defines (like HAVE_WINDOWS_H). Is there a reason for that? I always need to update them in two places now. * After downloading the source tarball and unzipping over my XP GHC installation, I got both an 'include' and an 'includes' directory. This is somewhat confusing.

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LLVM back end
by Michael T. Richter 04 Jan '07

04 Jan '07

I've been eyeing LLVM[1] as interesting technology -- brief executive summary: a virtual machine suited as the back end of compiler output with optimised native code then coming from it as either JIT-based execution of the LLVM bytecode or as a further compilation step -- and couldn't help but immediately think of the possibility of one of the Haskell compiler projects providing an LLVM code generator. I think this would help in several areas: * it could make porting the compiler to other architectures -- including oddball ones that would be too small to otherwise support -- easier; * it could help remove the nigh-ubiquitous reliance upon GCC as a back-end (while I think that GCC is a pretty good piece of software, I'm not sure it's really suited to its current role as the "do-everything" back end); * it could leverage some of the really interesting work that's going on in optimisation technology by letting one VM's optimiser do the work for any number of languages; * it could improve interaction between source code written in multiple languages. Is this me opening up a Pandora's Box of ignorance here? Or is LLVM potentially interesting? (And were someone motivated into perhaps trying to make an LLVM back-end, where would one start to poke around in, say, the GHC codebase to even begin to implement this? And how insane would they be driven by the process?) [1]http://llvm.org -- Michael T. Richter Email: ttmrichter(a)gmail.com, mtr1966(a)hotpop.com MSN: ttmrichter(a)hotmail.com, mtr1966(a)hotmail.com; YIM: michael_richter_1966; AIM: YanJiahua1966; ICQ: 241960658; Jabber: mtr1966(a)jabber.cn "I have never seen the poor people being so familiar with their heads of state as they were with [Michele Duvalier]. It was a beautiful lesson for me. I've learned something from it." --Mother Theresa

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importing "in place" and packages
by Ashley Yakeley 04 Jan '07

04 Jan '07

I'm compiling the files for package "javavm" with GHC 6.6 (using "-package-name javavm"). As part of the compilation process, I need a runnable program that uses the modules I've compiled "in place": import JVMBoot But I get this error when compiling my "Main" module (ShowClasses.hs): ShowClasses.hs:23:1: Bad interface file: JVMBoot.hi Something is amiss; requested module main:JVMBoot differs from name found in the interface file javavm:JVMBoot Really I want to import javavm:JVMBoot, not main:JVMBoot. I tried this, but GHC doesn't like it (because it's not Haskell): import javavm:JVMBoot I tried compiling ShowClasses.hs with "-package-name javavm". This let me compile, but then I get this on link: /usr/bin/ld: Undefined symbols: _ZCMain_main_closure ___stginit_ZCMain collect2: ld returned 1 exit status I tried adding a -main-is in the compile step, but this didn't help. Is there any way to create a main function that calls files imported "in place" that are in some package? I have the same issue when writing tests for my "time" package. -- Ashley Yakeley

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Coverage Condition fails
by Adrian Hey 02 Jan '07

02 Jan '07

Hello folks, Could somebody explain what a coverage condition is and what this error message means.. "Illegal instance declaration for 'GT (GT2 map1 map2) (k1,k2)' (the Coverage Condition fails for one of the functional dependencies) In the instance declaration for 'GT (GT2 map1 map2) (k1,k2)'" The offending code looks like this.. > -- Generalsed Trie map class > class Ord k => GT map k | map -> k , k -> map where > -- Map type for pairs > newtype (GT2 map1 map2 a) = GT2 (map1 (map2 a)) > -- Which is an instance of GT > instance (GT map1 k1, GT map2 k2) => GT (GT2 map1 map2) (k1,k2) where This is with ghc 6.6. The strange thing is this code used to compile fine with earlier versions (but I don't know if it actually worked because I never tested it). Thanks -- Adrian Hey

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Second Call for Papers: TFP 2007, New York, USA
by TFP 2007 31 Dec '06

31 Dec '06

CALL FOR PAPERS Trends in Functional Programming 2007 New York, USA April 2-4, 2007 http://cs.shu.edu/tfp2007/ 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. A formal post-symposium refereeing process then selects the best articles presented at the symposium for publication in a high-profile volume. TFP 2007 is co-hosted by Seton Hall University and The City College of New York (CCNY) and will be held in New York, USA, April 2-4, 2007 at the CCNY campus. The TFP symposium is the successor to the successful series of Scottish Functional Programming Workshops. Previous TFP symposia were held in Edinburgh, Scotland in 2003 (co-located with IFL), in Munich, Germany in 2004, in Tallinn, Estonia in 2005 (co-located with ICFP and GPCE), and in Nottingham, UK in 2006 (co-located with Types). For further general information about TFP please see the TFP homepage at http://cs.shu.edu/tfp2007/ . 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 Articles leading-edge, previously unpublished research work Position Articles on what new trends should or should not be Project Articles descriptions of recently started new projects Evaluation Articles what lessons can be drawn from a finished project Overview Articles 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. Articles on the following subject areas are particularly welcomed: o Dependently Typed Functional Programming o Validation and Verification of Functional Programs o Debugging for Functional Languages o Functional Programming and Security o Functional Programming and Mobility o Functional Programming to Animate/Prototype/Implement Systems from Formal or Semi-Formal Specifications o Functional Languages for Telecommunications Applications o Functional Languages for Embedded Systems o Functional Programming Applied to Global Computing o Functional GRIDs o Functional Programming Ideas in Imperative or Object-Oriented Settings (and the converse) o Interoperability with Imperative Programming Languages o Novel Memory Management Techniques o Parallel/Concurrent Functional Languages o Program Transformation Techniques o Empirical Performance Studies o Abstract/Virtual Machines and Compilers for Functional Languages o New Implementation Strategies o 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 2007 program chair, Marco T. Morazan, at tfp2007(a)shu.edu. BEST STUDENT PAPER AWARD TFP traditionally pays special attention to research students, acknowledging that students are almost by definition part of new subject trends. A prize for the best student paper is awarded each year. SUBMISSION AND DRAFT PROCEEDINGS Acceptance of articles for presentation at the symposium is based on the review of extended abstracts (6 to 10 pages in length) by the program committee. Accepted abstracts are to be completed to full papers before the symposium for publication in the draft proceedings and on-line. The submission must clearly indicate to which category it belongs to: research, position, project, evaluation, or overview paper. It should also indicate whether the main author or authors are research students. Formatting details can be found at the TFP 2007 website. Submission procedures will be posted on the TFP 2007 website as the submission deadline is reached. The papers in the draft proceedings will also be made available on-line under the following conditions, with which all authors are asked to agree: The documents distributed by this server have been provided by the contributing authors as a means to ensure timely dissemination of scholarly and technical work on a noncommercial basis. Copyright and all rights therein are maintained by the authors or by other copyright holders, notwithstanding that they have offered their works here electronically. It is understood that all persons copying this information will adhere to the terms and constraints invoked by each author's copyright. These works may not be reposted without the explicit permission of the copyright holder. POST-SYMPOSIUM REFEREEING AND PUBLICATION In addition to the draft symposium proceedings, we intend to continue the TFP tradition of publishing a high-quality subset of contributions in the Intellect series on Trends in Functional Programming. All TFP authors will be invited to submit revised papers after the symposium. These will be refereed using normal conference standards and a subset of the best papers, over all categories, will be selected for publication. Papers will be judged on their contribution to the research area with appropriate criteria applied to each category of paper. Student papers will be given extra feedback by the Program Committee in order to assist those unfamiliar with the publication process. IMPORTANT DATES Abstract Submission: February 1, 2007 Notification of Acceptance: February 20, 2007 Registration Deadline: March 2, 2007 Camera Ready Full Paper Due: March 9, 2007 TFP Symposium: April 2-4, 2007 PROGRAMME COMMITTEE John Clements California Polytechnic State University, USA Marko van Eekelen Radboud Universiteit Nijmegen, The Netherlands Benjamin Goldberg New York University, USA Kevin Hammond University of St. Andrews, UK Patricia Johann Rutgers University, USA Hans-Wolfgang Loidl Ludwig-Maximilians Universität München, Germany Rita Loogen Philipps-Universität Marburg, Germany Greg Michaelson Heriot-Watt University, UK Marco T. Morazán (Chair) Seton Hall University, USA Henrik Nilsson University of Nottingham, UK Chris Okasaki United States Military Academy at West Point, USA Rex Page University of Oklahoma, USA Ricardo Pena Universidad Complutense de Madrid, Spain Benjamin C. Pierce University of Pennsylvania, USA John Reppy University of Chicago, USA Ulrik P. Schultz University of Southern Denmark, Denmark Clara Segura Universidad Complutense de Madrid, Spain Jocelyn Sérot Université Blaise Pascal, France Zhong Shao Yale University, USA Olin Shivers Georgia Institute of Technology, USA Phil Trinder Heriot-Watt University, UK David Walker Princeton University, USA ORGANIZATION Symposium Chair: Henrik Nilsson, University of Nottingham, UK Programme Chair: Marco T. Morazan, Seton Hall University, USA Treasurer: Greg Michaelson, Heriot-Watt University, UK Local Arrangements: Marco T. Morazan, Seton Hall University, USA SPONSORS The Department of Mathematics and Computer Science, Seton Hall University The Department of Computer Science, The City College of New York The Center for Algorithms and Interactive Scientific Software of The City College of New York The Grove School of Engineering of The City College of New York We are actively looking for additional TFP sponsors, who may, for example, help to subsidise attendance by research students. If you or your organisation might be willing to sponsor TFP, or if you know someone who might be willing to do so, please do not hesitate to contact the Program Chair, Marco T. Morazan, or the Symposium Chair, Henrik Nilsson. Your students will be grateful! ************************************************************************************ Dr. Marco T. Morazan TFP 2007 Program Committee Chair http://cs.shu.edu/tfp2007/

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Building GHC on Mac OS 10.2.1
by Kirsten Chevalier 30 Dec '06

30 Dec '06

Hi all, I'm trying to build the HEAD on a somewhat old PowerBook G4 running Mac OS 10.2.1. It would seem that I don't have a new enough version of gcc: % gcc --version gcc (GCC) 3.1 20020420 (prerelease) and I can't seem to build a newer version of gcc (3.3) due to missing system include files which I assume (though that assumption may be wrong) are due to running 10.2 instead of 10.4. (For the full tale of woe, see http://hackage.haskell.org/trac/ghc/wiki/KirstenSandbox) Am I right in thinking that building GHC on Mac OS 10.2.1 is more or less impossible, or has anyone managed to do it? I'm pretty close to just giving up and buying a PC (various things make it difficult for me to upgrade to Tiger). Thanks, Kirsten -- Kirsten Chevalier* chevalier(a)alum.wellesley.edu *Often in error, never in doubt "Are you aware that rushing toward a goal is a sublimated death wish? It's no coincidence we call them 'deadlines'." -- Tom Robbins

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