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Request for code review - Knuth Morris Pratt for Data.Sequence
by Justin Bailey 05 Sep '07

05 Sep '07

Using the code developed for ByteStrings by myself, Christ Kuklewicz and Daniel Fischer, I've implemented Knuth-Morris-Pratt substring searching on Data.Sequence "Seq" values. Attached you'll find the library in kmp.zip.safe. The algorithm is implemented in the module Data.Sequence.KMP. At the root, SpeedTest.hs can be compiled on Windows with the "prof_compile.bat" file included (you'll need to install the "regex-dfa" and "regex-base" packages from Hackage to build). SpeedTest searches for a known value in the 7 MB file "endo.dna" (which can be downloaded from http://www.icfpcontest.org/endo.zip) using several different algorithms and methods: strict and lazy bytestrings, regular expressions, and the KMP algorithm for "Seq" values. SpeedTest is pretty fast but I worry about its space usage. It may just be the nature of Seq values, but I cannot get it to run in constant space when I think it should be. I'm especially interested in help here. All comments and feedback are welcome. Since the zip file includes a darcs context file, feel free to send patches. Justin

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FFI and DLLs
by Lewis-Sandy, Darrell 04 Sep '07

04 Sep '07

An early proposal for the FFI supported importing functions directly from dynamic link libraries: www. <http://www.haskell.org/hdirect/ffi-a4.ps.gz> haskell.org/hdirect/ffi-a4.ps.gz This looks like it was dropped from the final version of the addendum in favor of C header files as the sole form of import entities. Not being a C programmer, how would one go about importing a foreign function (e.g. void Foo(void) ) from a dynamic link library (e.g. foo.dll)?? Would someone be willing to provide an explicit example?

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Re: [Haskell-cafe] [Off topic] Proving an impossibility
by Miguel 04 Sep '07

04 Sep '07

>On 9/3/07,Vimal<j.vimal(a)gmail.com> wrote: >>while E do >>S >>if F then >>break >>end >>T >>end >> >>He then asked us to *prove* that the above programming fragment cannot >> >>be implemented just using if and while statement, even if S and T can >>be duplicated a finite number of times >But it IS possible. Just add a boolean flag: Possibly, you are not allowed to change the sequence of machine operations at all. See, if you change "while(A){B}" to "if(A){B};while(A){B}", the sequence is exactly the same; but it's not possible in this case. It reminds me of a paper by Knuth, where he states that "goto" statement is necessary; don't remember the title, however.

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Are type synonym families really equivalent to fundeps?
by Chris Smith 04 Sep '07

04 Sep '07

The following code builds and appears to work great (assuming one allows undecidable instances). I have tried both a natural translation into type synonym families, and also the mechanical transformation in http://www.cse.unsw.edu.au/~chak/papers/tyfuns.pdf -- but I can't get either to work. The two fishy things are: 1. There is a functional dependency (a -> t) in the original. Actually, this isn't always true since t is sometimes not uniquely determined by a; but GHC always seems to do the right thing anyway. There doesn't seem to be any way to "cheat" like this with type families. 2. In the second and fourth instances, the type variable x appears twice in the parameters of the type function built from the fundep (a b -> c). This causes an error. If I try adding (x ~ x') to the context and making one of them x' instead of x, I get different errors. I'm starting to this this is an example of using functional dependencies that has no translation to type families. Can anyone free me of such thoughts? Code with fundeps is: data Var a = Var Int (Maybe String) data RHS a b = RHS a b class Action t a b c | a -> t, a b -> c, a c -> b instance Action t () y y instance Action t (Var x) (x -> y) y instance Action t [t] y y instance (Action t a b c) => Action t (RHS (Var x) a) (x -> b) c instance (Action t a b c) => Action t (RHS [t] a) b c -- Chris Smith

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Hawiki articles
by Henning Thielemann 04 Sep '07

04 Sep '07

In the current Haskell Wiki (haskell.org/haskellwiki) I found references to articles of the old Hawiki (haskell.org/hawiki) like OnceAndOnlyOnce and SeparationOfConcerns. Are the files still available somewhere?

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Haskell as an extension language
by Yuri D'Elia 04 Sep '07

04 Sep '07

Hello everyone; I've been using haskell for quite some time now, but, as usual, I still find myself resorting to c code too much often due to the performance penalty introduced. FFI is all nice and dandy, yet, the need to compile the code and separate the implementation in two is a mayor development issue I'd like to eliminate along with batch compilation. In the way I like to work, I only use the interpreter (I mainly started with this approach with ocaml); just program interactively; close the whole session and pretend to resume the work next time I reopen the interpreter. Unfortunately, the interpreted performance is, many times, not sufficient for my purposes. In the past I've been coding several programs that would allow the user to extend the functionality at runtime through real c code. The "host" program itself could start an internal editor that accepted c code. The code would then be sent to the system compiler, generating a dynamic object that would be loaded in the current program (and executed) immediately. With some voodoo usage of "unexelf", I could create a simple runtime environment with very good performance (except for the initial compilation delay), interactivity and persistence, but, as you might expect, almost no resilience to errors and difficult debugging issues. I would like to resume this idea. Programming the core (minimal) application in c and then adding an extension mechanism always led to better and faster programs in my experience than trying to use directly an higher-level language and (ab)use the various forms of FFI. UI latency was one of the primary reasons in many cases. The amount of c code needed was always lower too, in the end, as the code was extended beyond the original minimal requirements. The extensions, being wrapped around the core data structures, tended to be more specialized and concise than general all-purpose libraries. Has anyone experienced similar situations? Is there some documentation about integrating an haskell interpreter in host programs that would allow session persistence and some minimal form of debugging? Which interpreter works better in this context? Thanks

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Re: [Haskell-cafe] GHC 6.6.1 and SELinux issues
by Alexander Vodomerov 04 Sep '07

04 Sep '07

On Tue, Aug 28, 2007 at 08:53:05PM -0600, Stuart Jansen wrote: > On Wed, 2007-08-29 at 00:59 +0400, Alexander Vodomerov wrote: > > In what domain do you run GHC? > > Sorry about that, should've dug deeper. And here we have the difference: > > $ ls -Z /usr/lib/ghc-6.6.1/ghc-6.6.1 > -rwxr-xr-x root root > system_u:object_r:unconfined_execmem_exec_t /usr/lib/ghc-6.6.1/ghc-6.6.1 This explains that GHC works fine. unconfined_execmem_exec_t gives permission to map memory with PROT_EXEC and PROT_WRITE simultaneously. I've put GHC in unconfined_execmem_t and it started to work fine. But the problem is not in GHC -- it is in programs compiled by GHC. They also require exec/write memory. Only root can grant unconfined_execmem privileges, so simple user can not run binaries compiled by GHC. How do you solve this problem? Does Fedora GHC package has any additional patches? With best regards, Alexander.

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ANN: HPDF 1.0
by alpheccar 04 Sep '07

04 Sep '07

I am pleased to release the version 1.0 of my PDF library that you can find on hackage: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HPDF-1.0 This email is mainly an opportunity for me to thanks apfelmus who, a very very long time ago when I released HPDF for the first time, gave me very good advices. When you're new to a language, that kind of help from the community is always very appreciated. Christophe.

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Closures and pointfree functions
by Lars Oppermann 04 Sep '07

04 Sep '07

Dear all, In the Haskell Wiki at http://www.haskell.org/haskellwiki/Closure there is an example for a function returning a closure given as f x = (\y -> x + y) Another way to achieve the same effect would be to write f' x = (+) x which to me as a beginner looks somewhat like pointfree style. Would f' be considered to return a closure? Bests, Lars

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Update on monad subexpressions
by Chris Smith 04 Sep '07

04 Sep '07

I know a lot of you are very interested in my planned work on implementing monad subexpressions -- that is, (<- f) notation -- in the GHC compiler. Unfortunately, it's becoming clear that I'm not going to get to it any time soon. Between having a full time job, being a full time student, applying to graduate schools, and some volunteer work that I'm not willing to give up, I simply have no remaining time, and won't until about December or later. If someone else wants to pick up this project, please go for it. Otherwise, I'll get to it when I do. Sorry! -- Chris Smith

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Closures in Haskell and closures in set theory
by Peter Verswyvelen 04 Sep '07

04 Sep '07

If I'm not mistaken, in set theory, a closure of R with respect to some property P is the smallest superset R* that has the property P. To me, intuitively, a closure C in programming languages is a function that has bindings to variables declared in "parent" functions; so the inner function can not exist on its own, it needs a "parent environment". This seems to be related to set theory if we define R as the set of parameters of C, and R* as this set extended with the "parent variables" to which C binds, and P as the property "C can be evaluated". Does this make any sense at all?

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gtk library installation from ubuntu repository
by Vikrant 04 Sep '07

04 Sep '07

Hi, I am using ubuntu 7.04. If I try to install libghc6-gtk-dev package using apt-get (or aptitude) my installation hangs at following stage building GHCi library /usr/lib/haskell-packages/ghc6/lib/gtk- 0.9.10.5/HSgtk.o... it doesn;t move later and machine just slogs! Then I have no other way than killing the process which in turn does not allow me install anything later. In last three days I have installed ubuntu with haskell on three different machines and it seems I have always got this problem whenever I tried to install libghc6-soegtk-dev. does anybody know that the package @ ubuntu repository is faulty or something wrong here? any fix to this problem! (probably I should put this on ubuntu users list... but putting mail here because if it is problem with libghc6-soegtk-dev, then somebody from you must have experienced it!) Thanks N Regards, VIkrant

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Definition of the Haskell standard library
by Chris Smith 03 Sep '07

03 Sep '07

Can someone clarify what's going on with the standard library in Haskell? As of right now, I can download, say, GHC from haskell.org/ghc and get a set of libraries with it. I can visit http://haskell.org/ghc/docs/latest/html/libraries/, linked from the haskell.org home page, and see descriptions of all of those libraries. I can build with --make (or if I'm feeling masochistic, add several lines of -package options) and it works. That's all great. I've seen some stuff lately on -libraries and this list indicating that there's an effort to change this. People asking whether something should be included in the standard library are being told that there is no standard library really. I'm hearing that the only distinction that matters is "used by GHC" or "not used by GHC", and that being on hackage is as official as it gets. Am I misunderstanding? Is there something awesome about Hackage that I'm not seeing? I hope one of those two is the case. Otherwise, there's a serious mistake being made here. Having a web site where people can download any of hundreds of independent libraries is not the same thing as having a good standard library for the language. I don't want to see the day when setting up Haskell involves a day-long effort of figuring out what libraries to download and install from Hackage, and in what order to do it to satisfy all the dependencies, and new Haskellers poring over web sites for the thousandth time before realizing that so-and-so's GUI library hasn't actually been touched since they finished their class project in 1998 and doesn't build with the latest version of Qt or whatever. -- Chris Smith

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APLAS07 - Call for Participation
by Shin-Cheng Mu 03 Sep '07

03 Sep '07

Call for Participation The Fifth Asian Symposium on Programming Languages and Systems November 29 - December 1, 2007 Singapore http://www.comp.nus.edu.sg/~aplas07/ http://flint.cs.yale.edu/aplas2007/ Scope of the Conference ----------------------- APLAS aims at stimulating programming language research by providing a forum for the presentation of recent results and the exchange of ideas and experience in topics concerned with programming languages and systems. APLAS is based in Asia, but is an international forum that serves the worldwide programming languages community. The APLAS series is sponsored by the Asian Association for Foundation of Software (AAFS), which has recently been founded by Asian researchers in cooperation with many researchers from Europe and the USA. The past formal APLAS symposiums were successfully held in Sydney (2006, Australia), Tsukuba (2005, Japan), Taipei (2004, Taiwan) and Beijing (2003, China) after three informal workshops held in Shanghai (2002, China), Daejeon (2001, Korea) and Singapore (2000). Proceedings of the past symposiums were published in Springer-Verlag's LNCS 2895, 3302, 3780, and 4279. Conference Location ------------------- APLAS'07 will be held at Kent Ridge Guild House, National University of Singapore. Singapore is a dynamic city rich in contrast and color where you'll find a harmonious blend of culture, cuisine, arts and architecture. A bridge between the East and the West for centuries, Singapore, located in the heart of fascinating Southeast Asia, continues to embrace tradition and modernity today. Brimming with unbridled energy and bursting with exciting events, the city offers countless unique, memorable experiences waiting to be discovered. Registration ------------ The early registration deadline is set on 28Sept07. The registration fees will cover conference proceeding, banquet dinner, and lunches/teas. Deadline Full Fees Student Fees early 28Sep07 S$600 S$400 online 23Nov07 S$650 S$425 on-site 29Nov07 S$700 S$450 Payment can be made with credit cards. Exchange rate (subject to fluctuation) is approx. US$1 = S$1.53 Online registration can be made at: http://www.comp.nus.edu.sg/~aplas07/local.html#registration Accommodation ------------- A special rate S$155 per nite (excluding taxes but inclusive of daily breakfast) is applicable to attendees of APLAS 2007 at Rendezvous Hotel Singapore: http://www.rendezvoushotels.com/singapore/ The hotel is located in city center. A free daily shuttle bus will be provided between this hotel and the conference site (at NUS) during the conference period. Our block of rooms is guaranteed till 28Sept07, so advanced booking is encouraged as some rooms may be released after this date. For reservation, please use a special form that can be found at: http://www.comp.nus.edu.sg/~aplas07/Hotel.APLAS07.pdf We have also reserved a limited number of cheaper twin/double shared rooms (S$280 for 4-nights) on NUS campus. Priority will be given to students and poster participants. Deadline for application is 20Sep07. Details will be given on our web in early Sept. Poster Session -------------- APLAS07 will include a poster session. Submission deadline is 14 Sept 2007. For details, please see: http://www.comp.nus.edu.sg/~aplas07/posters.html Conference Program ------------------ 29 Nov (Thu) ------------ 915- 930 Opening note 930-1030 Invited Talk X10: Programming Parallel Machines, Productively Vijay Saraswat (IBM TJ Watson Research Lab) 1100-1230 Session 1 The Nuggetizer: Abstracting Away Higher-Orderness for Program Verification Paritosh Shroff (Johns Hopkins University), Christian Skalka (University of Vermont) and Scott F. Smith (Johns Hopkins University) Local Reasoning for Storable Locks and Threads Alexey Gotsman (University of Cambridge), Josh Berdine (Microsoft Research), Byron Cook (Microsoft Research), Noam Rinetzky (Tel Aviv University) and Mooly Sagiv (Tel Aviv University) Monadic, Prompt Lazy Assertions in Haskell Frank Huch (CAU Kiel) and Olaf Chitil (University of Kent) 1345-1515 Session 2 Translation Correctness for First-Order Object-Oriented Pattern Matching Burak Emir (EPFL Lausanne), Qin Ma (OFFIS) and Martin Odersky (EPFL Lausanne) Persistent Oberon: A Programming Language with Integrated Persistence Luc Blaser (ETH Zurich) More Typed Assembly Languages for Confidentiality Dachuan Yu (DoCoMo Communication Laboratories USA) 1515-1630 Poster Session 1630-1730 Session 3 A Novel Test Case Generation Method for Prolog Programs Based on Call Patterns Semantics Lingzhong Zhao (Guilin University of Electronic Technology), Tianlong Gu (Guilin University of Electronic Technology), Junyan Qian (Guilin University of Electronic Technology) and Guoyong Cai (Guilin University of Electronic Technology) On a Tighter Integration of Functional and Logic Programming Frank Huch (CAU Kiel) and Bernd Brassel (CAU Kiel) 1800-2000 Reception 30 Nov (Fri) ------------ 930-1030 Invited Talk Scalable Simulation of Biological Signaling Networks Vincent Danos (University of Paris VII & CNRS) 1100-1230 Session 4 Timed, Distributed, Probabilistic, Typed Processes Martin Berger (Imperial College London) and Nobuko Yoshida (Imperial College London) A Probabilistic Applied Pi-Calculus Jean Goubault-Larrecq (ENS Cachan), Catuscia Palamidessi (Ecole Polytechnique) and Angelo Troina (ENS Cachan & Ecole Polytechnique) Type-Based Verification of Correspondence Assertions for Communication Protocols Daisuke Kikuchi (Tohoku University) and Naoki Kobayashi (Tohoku University) 1400-1530 Session 5 Deriving Compilers and Virtual Machines for a Multi-Level Language Atsushi Igarashi (Kyoto University) and Masashi Iwaki (Kyoto University) Finally Tagless, Partially Evaluated (Tagless Staged Interpreters for Simpler Typed Languages) Jacques Carette (McMaster University), Oleg Kiselyov (FNMOC) and Chung-chieh Shan (Rutgers University) Polymorphic Delimited Continuations Kenichi Asai (Ochanomizu University) and Yukiyoshi Kameyama (University of Tsukuba) 1600-1730 Session 6 Adjunct Elimination in Context Logic for Trees Cristiano Calcagno (Imperial College London), Thomas Dinsdale-Young (Imperial College London) and Philippa Gardner (Imperial College London) Positive Arithmetic without Exchange is a Subclassical Logic Stefano Berardi (University of Torino) and Makoto Tatsuta (National Institute of Informatics, Japan) Mixed Inductive/Coinductive Types and Strong Normalization Andreas Abel (University of Munich) 1900-2100 Banquet 1 Dec (Sat) ------------ 930-1030 Invited Talk Static and Dynamic Analysis : Better Together Sriram Rajamani (Microsoft Research India) 1100-1230 Session 7 The Semantics of "Semantic Patches" in Coccinelle: Program Transformation for the Working Programmer Neil Jones (University of Copenhagen) and Rene Rydhof Hansen (University of Copenhagen) An Efficient SSA-based Algorithm for Complete Global Value Numbering Jiu-Tao Nie (Peking University) and Xu Cheng (Peking University) A Systematic Approach to Probabilistic Pointer Analysis Alessandra Di Pierro (University of Verona), Chris Hankin (Imperial College London) and Herbert Wiklicky (Imperial College London) 1400-1530 Session 8 Complete Lattices and Up-to Techniques Damien Pous (ENS Lyon) A Trace Based Bisimulation for the Spi Calculus: An Extended Abstract Alwen Tiu (Australian National University) CCS with Replication in the Chomsky Hierarchy: The Expressive Power of Divergence Frank Valencia (Ecole Polytechnique), Cinzia Di Giusto (University of Bologna), Jesus Aranda (Ecole Polytechnique) and Mogens Nielsen (University of Aarhus) 1600-1700 Session 9 Call-by-Name and Call-by-Value in Normal Modal Logic Yoshihiko Kakutani (University of Tokyo) Call-by-Value is Dual to Call-by-Name, Extended Daisuke Kimura (National Institute of Informatics, Japan) 1700-1715 Closing note Organization ------------- GENERAL CHAIR Joxan Jaffar (National University of Singapore, Singapore) PROGRAM CHAIR Zhong Shao (Yale University, USA) PROGRAM COMMITTEE Lars Birkedal (IT University of Copenhagen, Denmark) Martin Hofmann (Univ of Munich, Germany) Kohei Honda (Queen Mary, University of London, UK) Atsushi Igarashi (Kyoto University, Japan) Suresh Jagannathan (Purdue University, USA) Annie Liu (State University of New York at Stony Brook, USA) Shin-Cheng Mu (Academia Sinica, Taiwan) Henrik Nilsson (University of Nottingham, UK) Michael Norrish (NICTA, Australia) Jens Palsberg (University of California, Los Angeles, USA) G. Ramalingam (Microsoft Research, India) Zhendong Su (University of California, Davis, USA) Martin Sulzmann (National University of Singapore, Singapore) Eijiro Sumii (Tohoku University, Japan) Jerome Vouillon (CNRS, France) Kwangkeun Yi (Seoul National University, Korea) Jian Zhang (Chinese Academy of Sciences, China) POSTER SESSION CHAIR Eijiro Sumii (Tohoku University, Japan) LOCAL ARRANGEMENT CHAIR Wei-Ngan Chin (National University of Singapore, Singapore)

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Bi-directional Maps
by Andrew Wagner 03 Sep '07

03 Sep '07

Hi folks! So, in writing my chess engine, I've been trying to maintain 2 Map objects. One maps squares on the board to Ints, the other maps Ints to actual Pieces. It occurred to me that it would be useful to explicitly have a Bi-directional Map, which does the maintenance of keeping the Maps synchronized behind the scenes. Thus, Bimap was born! I've taken the API for Data.Map (which you can find at ), and cannibalized it for Bimap. The new API is at http://hpaste.org/2344 . The idea is that if you have a Bimap k a, and you want to treat the k's as keys, and use a function like Data.Map.foo, it will be called Data.Map.left_foo in Bimap. And if they want to do the same thing, but using the a's as keys, then they simply use right_foo. The metaphor is that we can view it as a Map in 2 directions, manipulating it from the left (on the k's), or from the right (on the a's). Is this useful? Is there a better way? Is the API too big, and if so, how can it be pared down?

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GHC-API: a few questions
by Andrea Rossato 03 Sep '07

03 Sep '07

Hi, I'm trying to acquire some confidence with the GHC-API and I'm having some problems, related to error handling, I seem not be able to solve. Basically there are 3 functions to (interactively) compile/run Haskell expressions: compileExpr, dyCompileExpr and runStmt. The first 2 will return the value of the compiled expression, as a Maybe HValue the first, and a Maybe Dynamic the second, while the third can bind names and report them, or report exceptions. But my problem is related to the first two. I run expressions (string_expression) wrapped around some let x = string_expression in take 2048 (show x) to avoid infinite list or loops. According to the documentation one should be able to control how error messages are dealt with, by manipulation the GHC session's state. One component of the session state, indeed, is the log_action which, by default, prints errors and warnings to the standard error (compiler/main/DynFlags.hs). Now, no matter what I do, I seem not to be able to change the log_action to collect error messages and warnings. In any case everything seem to be printed to standard error. This way I can only collect exceptions raised by the compiler. For instance: "Prelude.last: empty list" for string_expression = "last []" But if my expression raises a type error, this is printed to stderr. Like in the case of string_expression = "last" which would produce a "No instance for (Show ([a] -> a))" What am I doing wrong? Thanks for your kind attentions. Andrea ps: there are quite a lot of other questions I'd like to ask about some programming techniques I've seen applied in GHC. For instance, sometime a list of actions is given as a string, to be compiled to a HValue which is written to a IORef. Running those actions is just a matter of reading the IORef (you can see this in compiler/ghci/InteractiveUIhs, when it comes to buffer management. For instance: flushInterpBuffers). I ask to myself: Why? Just to amaze the reader? ;-)

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Ideas
by Andrew Coppin 03 Sep '07

03 Sep '07

How easy would it be to make / would anybody care / has somebody already made ... in Haskell? - Blogging software. (Because there isn't enough of it in the world yet.) - A wiki program. (Ditto.) - A general CMS. - An interactive function plotter. (GNUplot is nice, but it can't plot recursive functions...) - A "graphical programming tool". (You add boxes and put in lines, it constructs a "program" that you can run.)

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Array.Diff, strange oversight or myopia ?
by Chaddaï Fouché 02 Sep '07

02 Sep '07

Data.Array.Diff don't have an instance for DiffUArray Bool, which is strange by itself since IOUArray Bool exists and it's the only IOUArray that is not mirrored in Diff. But ok, why not, I guess it might be a small oversight, so I go on to create the missing instance IArray (IOToDiffArray IOUArray) Bool on the model of the instances in the source of Array.Diff. Ok, Diff exports readDiffArray, newDiffArray and replaceDiffArray for this exact purpose, seems it will be straightforward... except that boundsDiffArray is not exported and you can't rewrite it since it needs to take apart the DiffArrayData type which is not exported either ! So how can I do this (short of copying and renaming an alternative Array.Diff or changing the library in my installation of GHC) ? And is there something obvious I missed due to a sudden case of myopia ? -- Jedaï

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Re: [Haskell-cafe] Learn Prolog...
by Peter Verswyvelen 02 Sep '07

02 Sep '07

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HApps API Documentation?
by James Britt 02 Sep '07

02 Sep '07

Are there alternative sites for HAppS API docs? There are two links on http://happs.org/#documentation but both give "File not found!" messages. Thanks, James

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Looking for suggestions to improve my algorithm
by David Frey 02 Sep '07

02 Sep '07

Hello Haskellers, I have been trying to learn a bit about Haskell by solving Project Euler problems. For those of you who don't know what Project Euler is, see http://projecteuler.net After solving problem 21, which is related to amicable pairs, I decided to attempt problem 95 since it is an extension of the same topic. The full description of problem 95 is here: http://projecteuler.net/index.php?section=problems&id=95 This is the summary: "Find the smallest member of the longest amicable chain with no element exceeding one million." I have attempted to solve this problem, but my solution is too resource hungry to search the full set of 1000000 numbers. I am hoping someone reading this list can suggest : - How I can improve my algorithm - An alternative algorithm that will be more efficient - Ways to profile a Haskell program to help me understand why my implementation is performing poorly. In addition to the question above, I would also be interested in comments on the style of the code. If there is a more idiomatic way to write portions of the code, I would like to see what it is. My solution is at the bottom of this e-mail. The program will probably run obscenely slow or die from stack overflow unless you replace [1..999999] with [1..somethingSmaller] in main. Thanks, David Frey --- BEGIN Main.hs --- module Main where import ProjectEuler (takeUntil, divisors) import qualified Data.Map as M import qualified Data.IntSet as I main = let initialContext = Context (I.fromList []) 0 0 in print $ cycleStart $ foldl checkForChain initialContext [1..999999] {- Idea: * Put all the numbers that have been visited into a map regardless of whether they are a part of a chain or not. * Store the min element in the cycle and the number of elements in the cycle * As you process, from 1->n if the stopping conditions for a sumOfDivisors result are: * has already been seen before * number is less than the start of this chain attempt * >= 1,000,000 -} data Context = Context {seenNum::I.IntSet, cycleStart::Int, cycleLength::Int} hasBeenSeen :: Int -> Context -> Bool hasBeenSeen n context = I.member n (seenNum context) markSeen :: Int -> Context -> Context markSeen n context = context { seenNum = (I.insert n (seenNum context)) } deleteFromSeen :: Int -> Context -> Context deleteFromSeen n context = context { seenNum = (I.delete n (seenNum context)) } {- - Examines the context to see if the input has potential to be a chain or not - based on whether the input number has been visited before. If it could be a - chain, an attempt is made to build the chain. -} checkForChain :: Context -> Int -> Context checkForChain context n = if hasBeenSeen n context then deleteFromSeen n context else buildChain context (sum $ divisors n) n [n] {- - Builds a chain until ones of the 3 stopping conditions are met or a chain is - found. If a chain is found the context will be updated with the new chain if - it is the longest. - - Stopping Conditions: - * Number has already been seen before - * Number is less than the start of this chain attempt - * Number >= 1,000,000 -} buildChain :: Context -> Int -> Int -> [Int] -> Context buildChain context candidate first cycleList = if elem candidate cycleList then foundChain (takeUntil ((==) candidate) cycleList) context else if candidate < first || candidate >= 1000000 || hasBeenSeen candidate context then context else buildChain (markSeen candidate context) (sum $ divisors candidate) first (candidate : cycleList) {- - Updates the context with the new longest chain and the start value if the - chain input parameter is longer than the one currently in the context. -} foundChain :: [Int] -> Context -> Context foundChain ls context = let l = length ls m = minimum ls in if l > (cycleLength context) then context { cycleLength = l, cycleStart = m } else if l == (cycleLength context) then let m = minimum ls in if m < (cycleStart context) then context { cycleStart = m } else context else context --- END Main.hs --- I put a bunch of common functions in ProjectEuler.hs. Here are the relevant functions for this problem: {- - Gets all of the proper divisors of a number. That is all divisors starting - from 1, but not including itself. -} divisors :: (Integral a) => a -> [a] divisors n = let p1 = [x | x <- [1 .. floor $ sqrt $ fromIntegral n], n `mod` x == 0] p2 = map (div n) (tail p1) in p1 `concatNoDupe` (reverse p2) where {- - Concatenate two lists. If the last element in the first list and the - first element in the second list are ==, produce only the value from - the first list in the output. -} concatNoDupe :: (Eq a) => [a] -> [a] -> [a] concatNoDupe [] ys = ys concatNoDupe [x] (y:ys) = if x == y then (y : ys) else (x : y : ys) concatNoDupe (x:xs) ys = x : (concatNoDupe xs ys) {- - Similar to takeWhile, but also takes the first element that fails the - predicate. -} takeUntil :: (a -> Bool) -> [a] -> [a] takeUntil pred (x:xs) = (x : if pred x then [] else takeUntil pred xs) takeUntil _ [] = []

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defining mapPairs function
by Alexteslin 01 Sep '07

01 Sep '07

Hello, I just came across with this question on the exam and can not think of implementing it. mapPair :: (a -> a -> a) -> [a] -> [a] such that mapPairs f [x1, x2, x3, x4...] = [f x1 x2, f x3 x4,...] and if the list contains an odd number of elements, the last one is kept unchanged, for example mapPairs f [x1, x2, x3] = [f x1 x2, x3] Any ideas will be appreciated, thanks -- View this message in context: http://www.nabble.com/defining-mapPairs-function-tf4350356.html#a12395628 Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

7 11

Data.Unique not "safe" in concurrent environments (or brain burned)?
by Neil Davies 01 Sep '07

01 Sep '07

Hi, I was looking over the libraries for bits of GHC (no doubt a standard form of relaxation for readers of this list), and noticed the following statement (in Data.Unique): -- | Creates a new object of type 'Unique'. The value returned will -- not compare equal to any other value of type 'Unique' returned by -- previous calls to 'newUnique'. This set me thinking - so I looked at the code newUnique :: IO Unique newUnique = do val <- takeMVar uniqSource let next = val+1 putMVar uniqSource next return (Unique next) In the concurrent execution world in which we live - I don't think that the implementation supports the "uniqueness" statement above - or am I not understanding something? Cheers Neil

1 1

GHC 6.6.1 binary package for Ubuntu available?
by Sukit Tretriluxana 01 Sep '07

01 Sep '07

Hi, I am wondering if there is the binary package for GHC 6.6.1 for Ubuntu. I searched in the package manager and I only see the version 6.6. Thanks, Ed

3 4

Re: trouble compiling regex posix head (I think >0.92) on ghc 6.7
by Thomas Hartman 01 Sep '07

01 Sep '07

I darcs pulled cabal head to get latest cabal, removed -Werror from GHC-Options in the cabal file, removed HsRegexPosixConfig.h and tried again with the same result. It seems to really want that file. With, it installs, without, no install. $ darcs whatsnew { hunk ./regex-posix.cabal 16 -Build-Depends: regex-base >= 0.80, base >= 2.0 +Build-Depends: regex-base >= 0.80, base >= 2.0, array, containers, byt estring hunk ./regex-posix.cabal 32 -GHC-Options: -Wall -Werror -O2 +GHC-Options: -Wall -O2 hunk ./regex-posix.cabal 43 -Include-Dirs: include +Include-Dirs: include/regex } Chris Kuklewicz <haskell(a)list.mightyreason.com> 08/30/2007 12:34 PM To Thomas Hartman/ext/dbcom@DBAmericas cc haskell-cafe(a)haskell.org, "cvs-ghc(a)haskell.org" <cvs-ghc(a)haskell.org> Subject Re: trouble compiling regex posix head (I think >0.92) on ghc 6.7 Thomas Hartman wrote: > > I'm trying to compile regex-posix on ghc 6.7. (Ultimate goal: happs on > 6.7). I have not explored ghc 6.7. You should also try posting on the <glasgow-haskell-users(a)haskell.org> mailing list. > > First, I patched by changing the cabal file to be compatible with the > new libraries broken out of base. I also had to add HsRegexPosixConfig.h > to include/regex (I just copied it from somewhere else on my hard drive > where I guess it had been put by an earlier regex-posix install, I don't > know if it's compatible here but at least it permitted things to compile > further.) I had no idea what HsRegexPosixConfig was, and I have no such file at all. So I looked in Wrap.hsc and found: > #ifdef HAVE_REGEX_H > #define HAVE_REGCOMP 1 > #else > #ifndef __NHC__ > #include "HsRegexPosixConfig.h" > #else > #define HAVE_REGEX_H 1 > #define HAVE_REGCOMP 1 > #endif > #endif Note that I did not write that section -- that was added by someone else. So HsRegexPosixConfig.h should only matter if HAVE_REGEX_H is undefined. The regex-base.cabal file says: "CC-Options: -DHAVE_REGEX_H" So unless Cabal is having a very very bad day, I assume that HsRegexPosixConfig.h is never needed. That it matters to your build to have that file seems _wrong_ to me. The only header file it should need is "regex.h" > Setup.hs build -v3 had a lot of warnings but didn't seem to fail. > However, Setup.hs install -v3 didn't work. You might try to change the cabal file. Currently I think it is "GHC-Options: -Wall -Werror -O2" and remove -Werror "GHC-Options: -Wall -O2" And you can change the cabal "Include-Dirs" to point to wherever it will find "regex.h" > the problem in build seems to occur around "upsweep partially failed or > main not exported"... That means nothing to me. > > [6 of 6] Compiling Text.Regex.Posix ( Text/Regex/Posix.hs, > dist/build/Text/Regex/Posix.o ) > *** Parser: > *** Renamer/typechecker: > > Text/Regex/Posix.hs:57:2: > Warning: The export item `module Text.Regex.Posix.String' exports > nothing > > Text/Regex/Posix.hs:59:2: > Warning: The export item `module Text.Regex.Posix.Sequence' exports > nothing > > Text/Regex/Posix.hs:61:2: > Warning: The export item `module Text.Regex.Posix.ByteString' > exports nothing > > Text/Regex/Posix.hs:63:2: > Warning: The export item `module Text.Regex.Posix.ByteString.Lazy' > exports nothing Those warning are slightly bogus. Including the module should export the instances. > *** Deleting temp files: > Deleting: /tmp/ghc9618_0/ghc9618_0.s > Warning: deleting non-existent /tmp/ghc9618_0/ghc9618_0.s > Upsweep partially successful. > *** Deleting temp files: > Deleting: > link(batch): upsweep (partially) failed OR > Main.main not exported; not linking. > *** Deleting temp files: > Deleting: > *** Deleting temp dirs: > Deleting: /tmp/ghc9618_0 > > complete output (along with patch) is attached. > > I'd appreciate any advice. > > best, thomas. > > --- This e-mail may contain confidential and/or privileged information. If you are not the intended recipient (or have received this e-mail in error) please notify the sender immediately and destroy this e-mail. Any unauthorized copying, disclosure or distribution of the material in this e-mail is strictly forbidden.

2 1

trying to install gutsy's libghc6-mtl-dev from source on feisty
by Anatoly Yakovenko 01 Sep '07

01 Sep '07

i have ghc6_6.6.1-2ubuntu2_i386.deb and ghc6-prof_6.6.1-2ubuntu2_i386.deb installed, but i cant seem to get mtl to install, can someone tell me what this output means? i just switched to a debian based system from gentoo, so i dont grok dpkg yet: aeyakovenko@snowcrash:~$ sudo dpkg -i libghc6-mtl-dev_1.0.1-2_i386.deb (Reading database ... 129709 files and directories currently installed.) Preparing to replace libghc6-mtl-dev 1.0-3 (using libghc6-mtl-dev_1.0.1-2_i386.deb) ... ghc-pkg: cannot find package mtl-1.0 dpkg: warning - old pre-removal script returned error exit status 1 dpkg - trying script from the new package instead ... ghc-pkg: cannot find package mtl-1.0 dpkg: error processing libghc6-mtl-dev_1.0.1-2_i386.deb (--install): subprocess new pre-removal script returned error exit status 1 Reading package info from stdin ... done. ghc-pkg: dependency base-2.0 doesn't exist (use --force to override) dpkg: error while cleaning up: subprocess post-installation script returned error exit status 1 Errors were encountered while processing: libghc6-mtl-dev_1.0.1-2_i386.deb

2 4

Haskell on the Playstation 3? :-)
by Peter Verswyvelen 31 Aug '07

31 Aug '07

Game developers are really struggling to get performance out of the Playstation 3 console. This console has a single PowerPC CPU with 6 Cell SPU coprocessors, all running at 3.3GHz. These SPUs have 256KB very high speed local RAM, and data from the 512MB main memory can stream in and out via DMA into these SPUs. The problem is that with imperative approaches this is a nightmare to manage.. It would be a very cool project to show that Haskell could run on such a platform, making it easier to take advance of its awesome power J Oh well, I'm just brainstorming here. Cheers, Peter BTW: This Cell platform also seemed to be offered for scientific computing in standard workstation PCs, so it would not just be for the Playstation 3.

10 19

Newbie question: Why gfoldl has this strange type?
by Rodrigo Geraldo 31 Aug '07

31 Aug '07

Hi! I am a novice in Haskell, and particularly I have interested in generic programming. This interest motivated me to read paper Scrap your boilerplate: A practical design pattern for generic programming, but I didn't understand the type of the function gfoldl, that was present in class Term (Data). Somebody could help me to understand the type of this function? Thanks... Rodrigo

2 2

darcs behind firewall
by Sukit Tretriluxana 31 Aug '07

31 Aug '07

Hi all, Does anyone know how to specify proxy server and port for darcs to use when it connects to servers? I am behind firewall most of the time and all requests have to go through a proxy. Thanks, Ed

2 2

Re: [Haskell-cafe] let and fixed point operator
by Dan Piponi 31 Aug '07

31 Aug '07

On 8/30/07, jerzy.karczmarczuk(a)info.unicaen.fr <jerzy.karczmarczuk(a)info.unicaen.fr> wrote: > Dan Piponi writes: > > In Haskell, there is no box. > > Well, there are boxes... > But there also thunks and latent, yet-unevaluated graphs... But the point of Haskell is to provide an abstraction that hides these details from you. (Though ultimately it's a leaky abstraction and there comes a point where you do need to know about these things.) > Anyway, I believe strongly that ALL people who have problems with the > Haskell protocole, and they are numerous, I teach a good sample of them, > should be encouraged to learn Prolog. I'd second that. It's hard to see the difference between declarative and imperative programming when you only have one instance of a declarative language from which to generalise. -- Dan

1 0

happs on ghc 6.7 won't work because of dependency on Data.Binary (everything that depends on Data.Binary broken at present) ( unknown symbol `stg_uncheckedShiftRL64' )
by Thomas Hartman 31 Aug '07

31 Aug '07

happs on ghc 6.7 won't work because of dependency on Data.Binary, since everything that depends on Data.Binary is broken at present. This is for Data.Binary installed via cabal from darcs get --partial http://darcs.haskell.org/binary . Cabal installed without any errors, but perhaps there should have been one since it appears broke. So I think my project of using the ghc debugger to help understand happs is on ice until this gets resolved. Unless this has been fixed since August 16. (Anyone out there got a more recent version?) $ cat UseDataBinary.hs import Data.Binary main = putStrLn "hello world" $ /usr/local/bin/ghc-6.6.1 -e 'main' UseDataBinary.hs hello world $ /usr/local/bin/ghc-6.7.20070816 -e 'main' UseDataBinary.hs <interactive>: /usr/local/lib/binary-0.3/ghc-6.7.20070816/HSbinary-0.3.o: unknown symbol `stg_uncheckedShiftRL64' ghc-6.7.20070816: unable to load package `binary-0.3' $ /usr/local/bin/ghc-6.7.20070816 -e '' UseDataBinary.hs --- This e-mail may contain confidential and/or privileged information. If you are not the intended recipient (or have received this e-mail in error) please notify the sender immediately and destroy this e-mail. Any unauthorized copying, disclosure or distribution of the material in this e-mail is strictly forbidden.

1 0

redirecting stdout
by Chad Scherrer 31 Aug '07

31 Aug '07

Is it possible to write a function redirect :: Handle -> IO () -> IO () so that "redirect h action" is just like action, except that all the output written to stdout now gets sent to h instead? Thanks, Chad

2 1

cabal install of HDBC-odbc fails on ghc 6.7, -I flag causes problems
by Thomas Hartman 31 Aug '07

31 Aug '07

problemw with the -I flag to ghc are causing cabal install to fail for hdbc-odbc (darcs head). man ghc still reports that -I is a valid flag after installing ghc 6.7 from darcs head a couple days ago. I think the problem might be the space after the -I flag (which is bad for both 6.6.1 and 6.7) hartthoma@linuxpt:~/installs/HDBC-odbc-head/hdbc-odbc>/usr/local/bin/ghc-6.7.20070816 -I. -e '' Setup.hs hartthoma@linuxpt:~/installs/HDBC-odbc-head/hdbc-odbc>/usr/local/bin/ghc-6.7.20070816 -I/ -e '' Setup.hs hartthoma@linuxpt:~/installs/HDBC-odbc-head/hdbc-odbc>/usr/local/bin/ghc-6.7.20070816 -I / -e '' Setup.hs ghc-6.7.20070816: unrecognised flags: -I just a guess... anothing thing is it seems like there's a new INCLUDE pragma in 6.7. perhaps this should be used in one of the source files to get it to compile. but which one? I couldn't figure out what was causing ghc -c -I dist/build/Database/HDBC/ODBC/Connection_hsc_make.c -o dist/build/Database/HDBC/ODBC/Connection_hsc_make.o to be run. (I did try grepping on ghc but no luck, below.) Any tips on debugging this cabal install would be appreciated. thanks, thomas ************* $ runghc Setup.hs configure; runghc Setup.hs build ..... configure: Using tar found on system at: /bin/tar Reading parameters from /home/hartthoma/installs/HDBC-odbc-head/hdbc-odbc/HDBC-odbc.buildinfo Preprocessing library HDBC-odbc-1.1.2hartthoma@linuxpt:~/installs/HDBC-odbc-head/hdbc-odbc>darcs whatsnew.0... ghc-6.7.20070816: unrecognised flags: -I Usage: For basic information, try the `--help' option. compiling dist/build/Database/HDBC/ODBC/Connection_hsc_make.c failed command was: ghc -c -I dist/build/Database/HDBC/ODBC/Connection_hsc_make.c -o dist/build/Database/HDBC/ODBC/Connection_hsc_make.o ........ hartthoma@linuxpt:~/installs/HDBC-odbc-head/hdbc-odbc>darcs whatsnew { hunk ./Setup.hs 8 -main = defaultMainWithHooks defaultUserHooks{preConf = conf, postConf = ok} - where ok _ _ _ _ = return ExitSuccess +--main = defaultMainWithHooks defaultUserHooks{preConf = conf, postConf = ok} +-- where ok _ _ _ _ = return ExitSuccess +main = do + let ok _ _ _ _ = do return ExitSuccess + return () + in defaultMainWithHooks defaultUserHooks{preConf = conf, postConf = ok} + return () + } ..... hartthoma@linuxpt:~/installs/HDBC-odbc-head/hdbc-odbc>grep -i ghc * HDBC-odbc.buildinfo:ghc-prof-options: HDBC-odbc.buildinfo:ghc-options: HDBC-odbc.cabal:GHC-Options: -O2 Makefile:GHCPARMS := -fglasgow-exts Makefile:all: setup # GHC build Makefile: ghc -package Cabal Setup.hs -o setup Makefile: cd testsrc && ghc --make -package mtl -package HUnit -package MissingH -package HDBC -lodbc $(GHCPARMS) -o runtests -i../dist/build:.. ../d\ ist/build/hdbc-odbc-helper.o runtests.hs Makefile:test-ghc6: testsrc/runtests Makefile:interact-ghci: all Makefile: ghci -idist/build -Ldist/build $(GHCPARMS) Makefile:test: test-ghc6 test-hugs README.txt:You'll need either GHC 6.4.1 or above, or Hugs 2005xx or above. If README.txt:2) ghc --make -o setup Setup.lhs README.txt:To use with GHC, you'll want to use: --- This e-mail may contain confidential and/or privileged information. If you are not the intended recipient (or have received this e-mail in error) please notify the sender immediately and destroy this e-mail. Any unauthorized copying, disclosure or distribution of the material in this e-mail is strictly forbidden.

2 5

2D game graphics library for Haskell?
by peterv 30 Aug '07

30 Aug '07

I’m currently playing around with SOE to make some simple interactive math exercises for students. This worked fine, although I could have done this much faster using C# (which I know very well), but since I’m addicted to Haskell now, I used the latter language ;) Furthermore, I hope that one day, I will know enough Haskell to learn it to the students, because I feel that functional programming should not be given in the last bachelor or master years, since most software engineering students then know OO programming extremely well and have a horrible time with FP (I currently did not meet anyone in my sector of game development that liked FP, and many of those people had a masters degree and some were PhDs) Anyway, SOE is great for learning Haskell, but it lacks a couple of fundamental functions to make it really attractive, like: - Support for images - Support for rendering to an “offscreen graphics surface” and reading the pixels from that surface (for pixel-wise collision detection) - Support for detecting non-ASCII key presses (cursor keys, etc) - Support for joysticks Concurrent Clean seems to have a nice 2D game library and PLT/DrScheme also has nice support for basic 2D graphics, but somehow I feel Haskell is more mature and more elegant. So before digging into “advanced” APIs (like GTK itself, which I know nothing about, I’m a Win32 GDI/XNA/WPF expert), I should ask the question if something similar exists? It has to be as simple as SOE. Would it be possible to extend the GTK SOE with support for the features mentioned above? Is this insanely difficult for someone like me who knows a lot about Win32 but little Haskell? Thanks, Peter Verswyvelen No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.5.484 / Virus Database: 269.12.4/969 - Release Date: 23/08/2007 16:04

2 1

Re: [Haskell-cafe] Haskell on the Playstation 3? :-)
by Miguel 30 Aug '07

30 Aug '07

> Hmmm, random thought along similar lines, I mean I know the answer to > this thought is no, but I'm curious: could we get Haskell to run on a > graphics card??? I mean, I'm guessing the answer is no (not a > difficult guess ;-) ), but curious what it would take to make a > graphics card able to run Haskell? What about running Haskell on a PostScript printer? PostScript IS Turing-complete.

5 4

Bug in Gtk2HS 0.9.12/SOE on WinXP? Or is it just me?
by Peter Verswyvelen 30 Aug '07

30 Aug '07

First of all, I'm really excited that GTK2HS 0.9.12 now allows launching SOE apps using GHCI. However, in the code below the blue and green triangle should render on top of each other, but the green triangle is rendered incorrectly. Being a newbie, I hesitate to file a bug report... Can anyone reproduce this? Maybe it works fine on unix? Thanks, Peter module Main where import Graphics.SOE.Gtk shape = [(200,100), (200,200), (100,200), (200,100)] main = runGraphics $ do w <- openWindow "Buggy polgon fill?" (300,300) setGraphic w $ (withColor Red $ polyline shape) `overGraphic` (withColor Green $ drawRegion $ createPolygon shape) drawInWindow w $ (withColor Red $ polyline shape) `overGraphic` (withColor Blue $ polygon shape) waitForClose w closeWindow w waitForClose w = do e <- getWindowEvent w case e of Closed -> return () otherwise -> waitForClose w

3 2

GHC optimisations
by Andrew Coppin 30 Aug '07

30 Aug '07

Does GHC do stuff like converting (2*) into (shift 1) or converting x + x into 2*x? If I do x * sin 12, is GHC likely to compute sin 12 at compile-time?

17 42

compiling happs under 6.7 (unbound implicit parameter error)
by Thomas Hartman 30 Aug '07

30 Aug '07

After much progress and learning, I'm stuck again trying to get happs to compile under ghc 6.7. (Hoping that running happs under the new ghc debugger will help me understand it better.) I was trying to compile from the "stable" 8.8 version, unzipped and with just a few modifications. (see attached zip). The problem has to do with an "unbound implicit parameter" [53 of 72] Compiling HAppS.Protocols.MessageWrap.W ( src/HAppS/Protocols/MessageWrap/W.hs, dist/build/HAppS/Protocols/MessageWrap/W.o ) src/HAppS/Protocols/MessageWrap/W.hs:209:63: Unbound implicit parameter (?style::Element -> XML Element) arising from a use of `xmlWrapM' at src/HAppS/Protocols/MessageWrap/W.hs:209:63-72 In the expression: xmlWrapM v In the definition of `ehShow'': ehShow' (DynException e) | Just (DynErr' v) <- fromDynamic e = xmlWrapM v I'd appreciate any advice. thomas. --- This e-mail may contain confidential and/or privileged information. If you are not the intended recipient (or have received this e-mail in error) please notify the sender immediately and destroy this e-mail. Any unauthorized copying, disclosure or distribution of the material in this e-mail is strictly forbidden.

1 0

trouble compiling regex posix head (I think >0.92) on ghc 6.7
by Thomas Hartman 30 Aug '07

30 Aug '07

I'm trying to compile regex-posix on ghc 6.7. (Ultimate goal: happs on 6.7). First, I patched by changing the cabal file to be compatible with the new libraries broken out of base. I also had to add HsRegexPosixConfig.h to include/regex (I just copied it from somewhere else on my hard drive where I guess it had been put by an earlier regex-posix install, I don't know if it's compatible here but at least it permitted things to compile further.) Setup.hs build -v3 had a lot of warnigs but didn't seem to fail. However, Setup.hs install -v3 didn't work. the problem in build seems to occur around "upsweep partially failed or main not exported"... [6 of 6] Compiling Text.Regex.Posix ( Text/Regex/Posix.hs, dist/build/Text/Regex/Posix.o ) *** Parser: *** Renamer/typechecker: Text/Regex/Posix.hs:57:2: Warning: The export item `module Text.Regex.Posix.String' exports nothing Text/Regex/Posix.hs:59:2: Warning: The export item `module Text.Regex.Posix.Sequence' exports nothing Text/Regex/Posix.hs:61:2: Warning: The export item `module Text.Regex.Posix.ByteString' exports nothing Text/Regex/Posix.hs:63:2: Warning: The export item `module Text.Regex.Posix.ByteString.Lazy' exports nothing *** Deleting temp files: Deleting: /tmp/ghc9618_0/ghc9618_0.s Warning: deleting non-existent /tmp/ghc9618_0/ghc9618_0.s Upsweep partially successful. *** Deleting temp files: Deleting: link(batch): upsweep (partially) failed OR Main.main not exported; not linking. *** Deleting temp files: Deleting: *** Deleting temp dirs: Deleting: /tmp/ghc9618_0 complete output (along with patch) is attached. I'd appreciate any advice. best, thomas. --- This e-mail may contain confidential and/or privileged information. If you are not the intended recipient (or have received this e-mail in error) please notify the sender immediately and destroy this e-mail. Any unauthorized copying, disclosure or distribution of the material in this e-mail is strictly forbidden.

1 0

runInteractiveCommand behaves differently on linux and windows
by Thomas Hartman 29 Aug '07

29 Aug '07

Maybe this is by design, but I just thought I would point this behavior out and ask for comment. test1 merely shows that runInteractiveCommand reacts differently to perl warnings than perl errors. Okay, maybe the inconsistency in that case is due to perl and not haskell. test2 behaves the same on win and nix. This is "pipe like" in that the ouptut of a command (which could be the result of a shell call, but just as easily be the return of a haskell function) gets fed into a shell command. In this case, if the shell command is simply "tail" the behavior is consistent from win to nix. test3 shows that the behavior stops being consistent if ssh enters the picture. (piping to tail via ssh). again, maybe this is due to ssh and not haskell. however... note however that on windows ghc -e 'mapM_ ( putStrLn . show ) [1..1000] ' | ssh `whoami`@localhost 'tail -n2' works fine. so it's not *just* ssh, but ssh in conjuction with runInteractiveCommand which seems to cause problems FWIW, using 10 lines instead of 1000 still hangs on windows. Is there a way to code up shell pipelike behavior in a more portable way? curious what the cafe thinks... thomas. import Test.HUnit import Misc ( (>>=^) ) import System.Process import System.IO import System.Exit -- works on linux, error on windows test1 = do res1 <- test_shellrunStderrOk runTestTT $ TestCase ( assertEqual "test1" "made it" res1 ) where test_shellrunStderrOk = do runprocessStdErrAllowed' "" cmdPerlwarn return "made it" cmdPerldie = " perl -e 'die \"error\"' " cmdPerlwarn = " perl -e 'warn \"blee\"' " -- works on linux, windows test2 = pipeTo "tail -n2" -- works on linux, hangs on windows test3 = pipeTo "ssh `whoami`@localhost 'tail -n2'" pipeTo cmd = do res2 <- test_shellrunPipeinLike runTestTT $ TestCase ( assertEqual ( "pipe to, cmd: " ++ cmd) (show l) res2 ) where test_shellrunPipeinLike = do runprocessStdErrAllowed' (unlines $ map show [1..l]) ( cmd ) >>=^ filter (not . ( == '\n') ) l = 1000 runprocessStdErrAllowed' inp s = do (ih,oh,eh,pid) <- runInteractiveCommand s so <- hGetContents oh se <- hGetContents eh hPutStrLn ih inp hClose ih ex <- waitForProcess pid case ex of ExitFailure e -> fail $ "shell command " ++ s ++ "\nFailed with status: " ++ show e _ | otherwise -> return so --- This e-mail may contain confidential and/or privileged information. If you are not the intended recipient (or have received this e-mail in error) please notify the sender immediately and destroy this e-mail. Any unauthorized copying, disclosure or distribution of the material in this e-mail is strictly forbidden.

1 1

Re: [Haskell-cafe] Norvig's Sudoku Solver in Haskell
by manu 29 Aug '07

29 Aug '07

Daniel Fischer's modifications to my original program lead to a 400 % speed boost !!! (It now runs in 22 seconds on my machine) He avoided unecessary calls to 'length', uses Array instead of Map, refactored 'search' function (details below) I've put up his version on hpaste : http://hpaste.org/2452#a1 Manu On Aug 26, 2007, at 10:56 PM, Daniel Fischer wrote: > Without much thinking I can spped it up by a factor of 4 (from 280s > to 60s). > The most important things are: > - don't use length unless you need it > instead of > newV2 <- case length newCell of > 0 -> Nothing > ... > and > case length dPlaces of > 0 -> ... > use > case newCell of > [] -> Nothing > [d'] -> ... > and > case dPlaces of > [] -> Nothing > [s'] -> ... > > - let dPlaces = [ s' | u <- lookup s units, s' <- u, elem d (lookup > s' newV2)] > is bad > let dPlaces = [s' | s' <- lookup s peers, elem d (lookup s' newV2)] > scans each peer only once > > - search is really bad, you lookup all squares several times, > potentially > compute all lengths multiple times... > much better is > > search :: Grid -> Maybe Grid > search g = case [(l,a) | a@(_,xs) <- M.assocs g, let l = length xs, > l /= 1] of > [] -> return g > ls -> do let (_,(s,ds)) = minimum ls > msum [assign g (s,d) >>= search | d <- ds] > > (I also changed the type, and instead of foldl' you should use > foldr, since > "some" is lazy in the second argument, further, since Maybe is a > MonadPlus, > it's "mplus" and 'foldr mplus Nothing' is msum) > > - Maps aren't good here, too slow lookup and you know the keys, so > use arrays >

5 7

Searching for a subsequence in Data.Sequence structure?
by Justin Bailey 29 Aug '07

29 Aug '07

Does anyone have code for finding a subsequence within a Data.Sequence.Seq value, or is there a way to do it with the already defined instances that I am missing? A quick search didn't turn up much. Thanks in advance! Justin

1 0

GHC 6.6.1 and SELinux issues
by Alexander Vodomerov 29 Aug '07

29 Aug '07

Hello! Does anybody here uses GHC on Linux with SELinux turned on? I've just installed SELinux and run into GHC/SELinux incompatibility. It seems that the similar problem was reported some time ago and was fixed in 6.4.3. However, I use 6.6.1 and the problem is still here. $ ghc ghc-6.6.1: internal error: getMBlock: mmap: Permission denied (GHC version 6.6.1 for i386_unknown_linux) Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug Exactly the same bug is appearing on x86_64 architecture. Much more details is available at http://hackage.haskell.org/trac/ghc/ticket/738 Any ideas? With best regards, Alexander. PS. Is it possible to turn on global allow_execmem boolean in SELinux policy, thus enabling executable memory mapping. This solves the problem. However, this is major drawback for system security and should be avoided at any cost.

2 2

Wildly off-topic
by Andrew Coppin 29 Aug '07

29 Aug '07

http://importantshock.wordpress.com/2007/08/21/haskell-curry-yes-i-dated-hi… (Actually, you hardly need to click that. The URL says it all...)

1 0

[Off Topic Amusement] Lylle Lovett lyrics
by David Pollak 29 Aug '07

29 Aug '07

http://www.lyricsdepot.com/lyle-lovett/west-texas-highway.html -- lift, the fast, powerful, easy web framework http://liftweb.net

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[ANN] An efficient lazy suffix tree library
by Bryan O'Sullivan 28 Aug '07

28 Aug '07

I just posted a library named suffixtree to Hackage. http://www.serpentine.com/software/suffixtree/ It implements Giegerich and Kurtz's lazy construction algorithm, with a few tweaks for better performance and resource usage. API docs: http://darcs.serpentine.com/suffixtree/dist/doc/html/Data-SuffixTree.html I've tested it on multi-megabyte input strings. <b

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"quoting" in Haskell
by Peter Verswyvelen 28 Aug '07

28 Aug '07

In Scheme, on can "quote" code, so that it becomes data. Microsoft's F# and C# 3.0 also have something similar that turns code into "expression trees". The latter is used extensively in LINQ which translates plain C# code into SQL code or any other code at runtime (this idea came from FP I heared) I can't find something similar for Haskell? Maybe I am looking at the wrong places? In Haskell, I know one can use a data constructor as a function (as in (map Just [1..3])), but a function cannot be turned into a data constructor (= "quoting"), can it? Now this is all really fuzzy for a newbie like me, because aren't all functions initially just data constructors waiting to be evaluated in a lazy language? I'm actually looking for something like (loose terminilogy follows) "context-based-semi-quoting". The idea is to only quote a set of functions, while evaluating all the others. For example, in the code 1 `add` 2 `mul` 3 where add = (+) mul = (*) I want to write something like selectiveQuote [add] (1 `add` 2 `mul` 3) which would result in an expression tree like add / \ 1 6 So the `mul` is not quoted because it is not part of the "context" = [add] Maybe this is just impossible, I did not dig deep into this. Thanks, Peter

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No Enum nor Ix instance on Graphics.UI.GLUT.Key
by Peter Verswyvelen 28 Aug '07

28 Aug '07

I want to make an array using GLUT.Key as an index, but it is not an instance of Enum nor Ix Of course, I can make it an instance myself, but I guess it would be easier to do so in the library? Cheers, Peter

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Geometry
by Tony Morris 28 Aug '07

28 Aug '07

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 I went camping on the weekend and a friend of mine who is a builder asked me many questions on geometry as they apply to his every day work - - most of which I could answer. However, there was one that I couldn't and I am having trouble googling a solution (for lack of keywords?). I'm hoping a fellow Haskeller could help me out (in Haskell of course). The problem is finding the unknown x from the two knowns a and b in the given image below (excuse my Microsoft Paintbrush skills). I may have misunderstood his problem (we were drawing in dirt) and actually, it is the straight line between the two points on the circumference that are known and not the specified 'b', but I figure I could derive one solution from another if I have misunderstood him. Here is my image: http://tinyurl.com/2kgsjy Thanks for any tips or keywords with which to google! - -- Tony Morris http://tmorris.net/ -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.6 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iD8DBQFG0iM6mnpgrYe6r60RAqfDAJ4gFAdr7zP1ehLl8H2MaCzCNfAvhQCgmL8D 4nrxrK13O9EBNv/ojPIMJXI= =eaxX -----END PGP SIGNATURE-----

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[ANN] pcap 0.3.1, for user-level network packet capture
by Bryan O'Sullivan 28 Aug '07

28 Aug '07

I've taken over maintenance of the pcap library (an interface to libpcap, for user-level network packet capture), and released a new version. Home page: http://www.serpentine.com/software/pcap/ API docs: http://darcs.serpentine.com/pcap/dist/doc/html/pcap/ Download: http://hackage.haskell.org/packages/archive/pcap/ darcs repo: darcs get http://darcs.serpentine.com/pcap/ Thanks are due to Gregory Wright for originally writing the package, and Dominic Steinitz and Nick Burlett for their respective maintenance efforts. <b

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