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Re: [Haskell-cafe] Problems building lambdabot on osx
by John Lato 10 Aug '11

10 Aug '11

> From: Brandon Allbery <allbery.b(a)gmail.com> > > On Mon, Aug 8, 2011 at 21:38, Adam Turoff <adam.turoff(a)gmail.com> wrote: > >> First, there's the issue with linking against libiconv, which is solved >> this >> way: >> >> cabal install --extra-lib-dirs=/usr/lib >> >> That leaves a whole mess of link errors against libHSreadline: >> > > Yes, because now it's finding the system readline, which isn't actually > readline (Apple ships a "readline" which is actually BSD "editline", so you > get missing symbols for things editline doesn't support such as completion). > I think you'll need to temporarily deactivate MacPorts' iconv instead of > using --extra-lib-dirs. > > This can't really be fixed by either GHC or MacPorts; there doesn't seem to > be a good solution as yet, although the MacPorts folks may end up > implementing a hacky solution because Apple has introduced *another* > MacPorts-breaking library conflict in Lion (libnotify). Yep, this is Apple's problem and everyone else just has to put up with it. If you want to mix macports and a non-macports ghc, I think the best solution is to self-compile ghc against the macports libiconv. This is easy, just configure ghc with ./configure --with-iconv-includes=/opt/local/include --with-iconv-libraries=/opt/local/lib I haven't had a problem since I started building ghc this way (10.5 and 10.6). John L.

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Analyzing slow performance of a Haskell program
by Chris Yuen 09 Aug '11

09 Aug '11

Hello Cafe, I was trying to solve ITA Software's "Word Nubmers" puzzle ( http://www.itasoftware.com/careers/puzzle_archive.html) using a brute force approach. Here's a my version of a quick recap of the problem: > A wordNumber is defined as > > wordNumber 1 = "one" > wordNumber 2 = "onetwo" > wordNumber 3 = "onethree" > wordNumber 15 = "onetwothreefourfivesixseveneightnineteneleventwelvethirteenfourteenfifteen" > ... > > Problem: Find the 51-billion-th letter of (wordNumber Infinity); assume that letter is found at 'wordNumber x', also find 'sum [1..x]' >From an imperative perspective, a naive algorithm would be to have 2 counters, keep counting the length of each wordNumber and "break" to return the result. The imperative brute-force approach is implemented in C# here: http://ideone.com/JjCb3. It takes about 1.5 minutes to find the answer on my computer. Then I implemented a brute-force Haskell version: http://ideone.com/ngfFq. It cannot finish the calculation in 5 minutes on my machine. (Irony: it's has more lines than the C# version) Here is the `-p` profile of the Haskell program: http://hpaste.org/49934 The Question: Are there obvious mistakes I am making? (Note: I am fully aware that brute-forcing it is not the correct solution to this problem. I am mainly interested in making the Haskell version perform comparatively to the C# version. Right now it is at least 5x slower so obviously I am missing something obvious) (Note 2: It does not seem to be space leaking. The program runs with constant memory (about 2MB) on my computer) (Note 3: I am compiling with `ghc -O2 WordNumber.hs) Chris

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Snap Riak Extension v0.1
by Edward Tate 09 Aug '11

09 Aug '11

Hi, I released this library a while ago but didn't tell anyone, thought I would let people know. Would be cool to get feedback, suggestions etc. https://github.com/et4te/snap-extension-riak/ PS: There are no recent commits since I'm going to be overhauling the architecture once Snap 6 comes out with 'Snaplets'.

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Problems building lambdabot on osx
by Adam Turoff 09 Aug '11

09 Aug '11

I've tried off and on the last couple of days to build Lambdabot on Mac OS X (before and after the upgrade from 10.6 to 10.7) and I keep running into linker errors with the 64-bit Haskell Platform (ghc 7.0.3). First, there's the issue with linking against libiconv, which is solved this way: cabal install --extra-lib-dirs=/usr/lib That leaves a whole mess of link errors against libHSreadline: Linking dist/build/lambdabot/lambdabot ... ld: warning: could not create compact unwind for _ffi_call_unix64: does not use RBP or RSP based frame Undefined symbols for architecture x86_64: "_rl_insert_completions", referenced from: _readlinezm1zi0zi1zi0_SystemziConsoleziReadline_zdwa5_info in libHSreadline-1.0.1.0.a(Readline.o) "_rl_possible_completions", referenced from: _readlinezm1zi0zi1zi0_SystemziConsoleziReadline_zdwa7_info in libHSreadlin (full error report at http://hpaste.org/50036 ) I did manage to install readline through macports: $ port installed readline The following ports are currently installed: readline @6.2.000_0 (active) $ file /opt/local/lib/libreadline.dylib /opt/local/lib/libreadline.dylib: Mach-O 64-bit dynamically linked shared library x86_64 and I did manage to get readline installed properly by specifying the include/lib dirs from macports: cabal install readline --configure-option=--with-readline-libraries=/opt/local/lib --configure-option=--with-readline-includes=/opt/local/include and readline does work in ghci: $ ghci GHCi, version 7.0.3: http://www.haskell.org/ghc/ :? for help Prelude> :m + System.Console.Readline Prelude System.Console.Readline> readline "testing> " testing> exit exit Just "exit" Prelude System.Console.Readline> The only issue, which has me stumped, is that lambdabot can't seem to find the readline dependency. Adding the --with-readline options when trying to build lambdabot has no effect. Neither does adding --extra-lib-dirs=/opt/local/lib to cabal install. Anyone have a clue where to start to work around this? Would switching to ghc HEAD help here? Thanks, -- Adam

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Second CFP: PADL'12 - Practical Aspects of Declarative Languages 2012
by Claudio Russo 09 Aug '11

09 Aug '11

[Apologies if you receive multiple copies.] Call for Papers =============== 14th International Symposium on Practical Aspects of Declarative Languages (PADL 2012) http://research.microsoft.com/~crusso/padl12 Philadelphia, Pennsylvania, USA, January 23-24, 2012 Co-located with ACM POPL'12 Abstract/Paper submission deadline: September 10th/17th, 2011 Conference Description ====================== Declarative languages build on sound theoretical bases to provide attractive frameworks for application development. These languages have been successfully applied to many different real-world situations, ranging from data base management to active networks to software engineering to decision support systems. New developments in theory and implementation have opened up new application areas. At the same time, applications of declarative languages to novel problems raise numerous interesting research issues. Well-known questions include designing for scalability, language extensions for application deployment, and programming environments. Thus, applications drive the progress in the theory and implementation of declarative systems, and benefit from this progress as well. PADL is a forum for researchers and practitioners to present original work emphasizing novel applications and implementation techniques for all forms of declarative concepts, including, functional, logic, constraints, etc. Topics of interest include, but are not limited to: * Innovative applications of declarative languages * Declarative domain-specific languages and applications * Practical applications of theoretical results * New language developments and their impact on applications * Declarative languages and Software Engineering * Evaluation of implementation techniques on practical applications * Practical experiences and industrial applications * Novel uses of declarative languages in the classroom * Practical extensions such as constraint-based, probabilistic, and reactive languages. PADL'12 welcomes new ideas and approaches pertaining to applications and implementation of declarative languages. In this occasion PADL is co-located, as traditionally, with ACM POPL, which will be held immediately following PADL, January 25-27. The symposium will be held in Philadelphia, Pennsylvania, USA. Important Dates and Submission Guidelines ========================================= Abstract Submission: September 10, 2011 Paper Submission: September 17, 2011 Notification: October 22, 2011 Camera-ready: November 5, 2011 Symposium: January 23-24, 2012 Authors should submit an electronic copy of the full paper in PDF using the Springer LNCS format. The submission will be done through EasyChair conference system. If electronic submission is impossible, please contact the program chairs for information on how to submit hard copies. All submissions must be original work written in English. Submissions must be unpublished and not submitted for publication elsewhere. Work that already appeared in unpublished or informally published workshops proceedings may be submitted. PADL'12 will accept both technical and application papers: * Technical papers must describe original, previously unpublished research results. Technical papers must not exceed 15 pages in Springer LNCS format. * Application papers are a mechanism to present important practical applications of declarative languages that occur in industry or in areas of research other than Computer Science. Application papers will be published in the Springer-Verlag conference proceedings, and will be presented in a separate session. Application papers are expected to describe complex and/or real-world applications that rely on an innovative use of declarative languages. Application descriptions, engineering solutions and real-world experiences (both positive and negative) are solicited. The limit for application papers is 6 pages in Springer LNCS format. Program Committee ================= Marcello Balduccini, Intelligent Systems Department, Kodak Research Labs Edwin Brady, University of St Andrews, Scotland Henning Christiansen, Roskilde University, Denmark Agostino Dovier, University of Udine, Italy Matthew Flatt, University of Utah, USA Gopal Gupta, University of Texas at Dallas, USA John Hughes, Chalmers University of Technology, Sweden; Quviq AB Gabriele Keller, University of New South Wales, Australia Lunjin Lu, Oakland University, USA Marc Pouzet, École normale supérieure, France Ricardo Rocha, University of Porto, Portugal Andreas Rossberg, Google Germany GmbH, Germany Claudio Russo, Microsoft Research Cambridge, UK (co-chair) Kostis Sagonas, Uppsala Univeristy, Sweden Satnam Singh, Microsoft Research Cambridge, UK Zoltan Somogyi, University of Melbourne, Australia Eijiro Sumii, Tohoku University, Japan Terrance Swift, Universidade Nova de Lisboa, Portugal; Johns Hopkins University, USA Andrew Tolmach, Portland State University, USA Jan Wielemaker, University of Amsterdam, The Netherlands Roland Yap, National University of Singapore, Republic of Singapore Kwangkeun Yi, Seoul National University, Korea Neng-Fa Zhou, Brooklyn College, City University of New York, USA (co-chair) Contacts ======== For additional information about papers and submissions, please contact the Program Chairs: Claudio Russo Microsoft Research Cambridge,UK Email: crusso <AT> microsoft <DOT> com Neng-Fa Zhou Brooklyn College, The City University of New York, USA Email: zhou <AT> sci <DOT> brooklyn <DOT> cuny <DOT> edu With the Cooperation of ======================= The Association for Logic Programming (ALP) ACM SIGPLAN Microsoft Research, Cambridge ===================================

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PhD Position available at Strathclyde
by Conor McBride 09 Aug '11

09 Aug '11

[My colleague, Patricia Johann, advertises the following...] PhD Position in Category Theory and Functional Programming Department of Computer and Information Sciences University of Strathclyde, Scotland Applications are invited for one PhD position within the Mathematically Structured Programming group at the University of Strathclyde. The group comprises Prof. Neil Ghani, Dr. Patricia Johann, Dr. Conor McBride, Dr. Peter Hancock, Dr. Robert Atkey, and six PhD students. The PhD project centres around applications of categorical methods to functional programming languages. The project is under the direction of Patricia Johann. The successful applicant will have either a first-class degree or an MSc in Mathematics or Computing Science or a related subject with a strong Mathematics or Computing Science component. Ideally, they will also have a strong, documented interest in doing research. Strong mathematical background and problem-solving skills are essential; good programming skills are a plus. Prior knowledge of category theory and/ or functional programming is an advantage, but is not required. The PhD position is for 3 years; it starts in January 2012. The position is a fully-funded post for a UK or EU student, and includes both coverage of fees and an EPSRC-level stipend for each of the three years. More information about the department is available at http://www.strath.ac.uk/cis The University of Strathclyde (http://www.strath.ac.uk) is located in the heart of Glasgow, which Lonely Planet Travel Guides hail as "one of Britain's largest, liveliest and most interesting cities" (seehttp://www.lonelyplanet.com/worldguide/scotland/glasgow/) . Southern Scotland provides a particularly stimulating environment for researchers in theoretical computer science, with active groups in this area at Heriot-Watt University, the University of Edinburgh, the University of Glasgow, the University of St. Andrews, and the University of Strathclyde. Requests for further information and other informal enquiries can be sent to: Patricia Johann patricia at cis.strath.ac.uk Those interested in the position are asked to send e-mail to the address given above in the next short while.

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Question Formlets, file upload
by "Dr. Heinrich Hördegen" 09 Aug '11

09 Aug '11

Dear all, I am using the library Text.XHtml.Strict.Formlets to build a validating form. I use the function "file" to get a file upload widget. The encoding is set to multipart. I want to check, if the user entered something or left the widget empty. However, when entering nothing, instead of an empty string, I always get a string like "/tmp/12101" which corresponds to an empty file. It would be nice, if I could check for the empty string to see, weather the user entered something or not into the upload widget. I appreciate any hints to achive this and wish you a good day, Heinrich -- -- hoerdegen(a)funktional.info www.funktional.info --

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Declarative configuration languages?
by Richard O'Keefe 09 Aug '11

09 Aug '11

A colleague just asked me I'm trying to kick off some work into middleware for configuration of large-scale, distributed systems. Have you come across any elegant, declarative configuration languages used for this sort of job? I've found a couple of papers, but I've never _used_ any of the systems. Any recommendations?

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Couldn't match expected type `Integer' against inferred type `Int'
by Paul Reiners 09 Aug '11

09 Aug '11

Why am I getting this error: > Couldn't match expected type `Integer' against inferred type `Int' > In the expression: foldl step 0 xs > In the definition of `asInt_foldAux': > asInt_foldAux xs > = foldl step 0 xs > where > step acc '.' = error "cannot handle decimal numbers" > step acc x = acc * 10 + digitToInt x for this code? > import Data.Char (digitToInt) > > asInt_fold :: String -> Integer > asInt_fold ('-':xs) = -(asInt_foldAux xs) > asInt_fold xs = asInt_foldAux xs > > asInt_foldAux :: String -> Integer > asInt_foldAux xs = foldl step 0 xs > where step acc '.' = error "cannot handle decimal numbers" > step acc x = acc * 10 + digitToInt x Note that I'm using Int, rather than Integer, to avoid silent overflow errors.

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For class Monoid; better names than mempty & mappend might have been: mid (mident) & mbinop
by KC 08 Aug '11

08 Aug '11

It would be easier for beginners to "grok". -- -- Regards, KC

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