- Haskell-Cafe - Haskell.org

Haskell Paralellism
by Dominik Luecke 25 Oct '07

25 Oct '07

Hello, I am trying to use the code rels list = let o1 = (map makeCompEntry) $ head $ splitList list o2 = (map makeCompEntry) $ head $ tail $ splitList list o3 = (map makeCompEntry) $ head $ tail $ tail $ splitList list in case (head $ tail $ tail $ tail $ splitList list) of [] -> o1 `par` o2 `par` o3 `seq` o1 : o2 : o3 : [] _ -> let o4 = rels (head $ tail $ tail $ tail $ splitList list) in o1 `par` o2 `par` o3 `par` o4 `seq` o1 : o2 : o3 : o4 to apply some operation on some lists in parallel. The input list "list" is quite long (about 10^17) entries, and I split it into chunks of 1000 entries each. I am compiling with the options " -O2 --make -smp -threaded" and when running the file with "+RTS -N2 -sstderr -RTS", I see that only one worker thread is really doing anything. I am using a vanilla build of ghc-6.6.1 running on Ubuntu 7.10. I am currently wondering about what I am doing wrong. Regards, Dominik -- Dominik Luecke Phone +49-421-218-64265 Dept. of Computer Science Fax +49-421-218-9864265 University of Bremen luecke(a)informatik.uni-bremen.de P.O.Box 330440, D-28334 Bremen PGP-Key ID 0x2D82571B

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Type vs TypeClass duality
by TJ 25 Oct '07

25 Oct '07

Hi again, Following up on my previous thread, I have figured out why it bothered me that we cannot have a list such as the following: ["abc", 123, (1, 2)] :: Show a => [a] It seems to me that there is an annoying duality in treating simple algebraic data type vs type classes. As it stands, I can only have a list where all the elements are of the same basic, ADT, type. There is no way to express directly a list where all the elements satisfy a given type class constraint. If I am not mistaken, type classes are currently implemented in GHC like so: Given a function "show" of type Show a => a -> string, and the expression "show 10", GHC will pass the Int dictionary for class Show's methods and the integer 10 to the function "show". In other words, for each type class constraint in the function type, there will be a hidden dictionary parameter managed entirely by the compiler. What I find strange is, if we can have functions with hidden parameters, why can't we have the same for, say, elements of a list? Suppose that I have a list of type Show a => [a], I imagine that it would not be particularly difficult to have GHC insert a hidden item along with each value I cons onto the list, in effect making the concrete type of the list [(Dictionary Show, a)]. I'm assuming that it will not be particularly difficult because GHC will know the types of the values I cons onto it, so it will most definitely be able to find the Show dictionary implemented by that type, or report a type mismatch error. No dynamic type information is necessary. I am not an OO programming zealot, but I'd like to note here that this is also how (class based) OO languages would allow the programmer to mix types. e.g. I can have a List<Show> where the elements can be instances of Show, or instances of subclasses of Show. Why does this second rate treatment of type classes exist in Haskell? TJ

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XML parser recommendation?
by Ketil Malde 24 Oct '07

24 Oct '07

Hi, I'm struggling to get my HXT-based parser to parse a largish file (<300MB), even after breaking into reasonably-sized chunks. The culprit appears to be parsing one element comprising 25K lines of text, which apparently requires more memory than the 2Gb my computer is equipped with. I'm wondering what approach others use for non-toy XML data. Is the problem due to some error I have made, or should I just ignore the XML, and just parse it "manually" by dissecting bytestrings, or will another XML library serve better? -k -- If I haven't seen further, it is by standing in the footprints of giants

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Haskell Report??
by Galchin Vasili 24 Oct '07

24 Oct '07

Hello, I am trying to use a Haskell shell (Hsh.hs). I am a little frustrated. There are two modules that are imported: import LibPosix import LibSystem I am running WinHugs (Windows) and hugs/ghci can't find LibSystem. I am confused about 1) what are currently standard libraries, etc. in Haskell, 2) what is deprecated and 3) what are "home grown tomatoes" ;^) How current and definitive is the Haskell Report? Kind regards, Bill Halchin

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ANNOUNCE: dataenc 0.9
by Magnus Therning 24 Oct '07

24 Oct '07

My collection of data encoding functions are now available at http://hackage.haskell.org/cgi-bin/hackage-scripts/package/dataenc-0.9: Dependencies base License LGPL Copyright Magnus Therning, 2007 Author Magnus Therning Maintainer magnus(a)therning.org Exposed modules Codec.Binary.DataEncoding, Codec.Binary.Base16, Codec.Binary.Base32Hex, Codec.Binary.Base32, Codec.Binary.Uu, Codec.Binary.Base64Url, Codec.Binary.Base64 There's a short description of the library on the wiki: http://haskell.org/haskellwiki/Library/Data_encoding The source darcs repo is available on code.haskell.org. Hopefully the haddockuments will be generated on hackage soon-ish. /M -- Magnus Therning (OpenPGP: 0xAB4DFBA4) magnus＠therning．org Jabber: magnus．therning＠gmail．com http://therning.org/magnus

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Re: [Haskell-cafe] will the real quicksort please stand up? (or: sorting a > million element list)
by Brent Yorgey 24 Oct '07

24 Oct '07

On 10/23/07, Thomas Hartman <thomas.hartman(a)db.com> wrote: > > > Actually I can't compile it, with or without -O2. loads fine into ghci, > but when I try to create an executable I get > > ghc quicksort.hs -o quicksort > quicksort.o: In function `r1Nc_info': undefined reference to > `QuickCheckzm1zi0zi1_TestziQuickCheck_vector_closure' > quicksort.o: In function `r1Nc_info': undefined reference to > `QuickCheckzm1zi0zi1_TestziQuickCheck_zdf16_closure' > quicksort.o: In function `s1Ws_info': undefined reference to > `QuickCheckzm1zi0zi1_TestziQuickCheck_generate_closure' > quicksort.o: In function `r1Nc_srt': undefined reference to > `QuickCheckzm1zi0zi1_TestziQuickCheck_vector_closure' > quicksort.o: In function `r1Nc_srt': undefined reference to > `QuickCheckzm1zi0zi1_TestziQuickCheck_zdf16_closure' > quicksort.o: In function `rzC_srt': undefined reference to > `QuickCheckzm1zi0zi1_TestziQuickCheck_generate_closure' > collect2: ld returned 1 exit status hmm, try adding --make to the ghc command line? Unfortunately, GHC doesn't automatically chase down dependencies for linking; you must specify them explicitly with -package, or tell it to auto-chase dependencies with --make. -Brent

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Job: web development in Haskell
by red nucleus 24 Oct '07

24 Oct '07

Anyone who is serious about doing web development in Haskell is welcome to apply for the job outlined below. If we found a good functional programmer, we can ignore the bits about Rails. Web Developer RedNucleus Ltd (rednucleus.co.uk) is seeking a highly motivated programmer for a full or part-time posititon developing social web applications. Initially you will develop and maintain applications using RubyOnRails or a similar framework, but there will be opportunities to explore new web programming paradigms with declarative languages. The successful application will have: -a good degree in computer science or a quantitative topic. -good independent programming and quantitative analysis skills. -some familiarity with HTML, CSS, JavaScript and SQL, and with network programming. -exposure to functional programming methodologies, e.g. in Haskell, Lisp or Erlang. Graduate level qualifications in computer science and expertise in web development including RubyOnRails would be a plus. RedNucleus is based in Beeston, Nottingham. The successful application could work here or mostly from home. Salary depends on experience and qualifications, starting from £22,000 plus performance bonus. To apply, please prepare a single pdf file containing your cover letter and CV, and name the file with your surname, e.g. smith.pdf. Then send the file to: rednucleusltd(a)gmail.com. Informal enquiries can be directed to the same address. The closing date for applications is 22nd November 2007

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ANN: new version of matrix library (GSLHaskell)
by Alberto Ruiz 24 Oct '07

24 Oct '07

Dear Haskellers, I am happy to announce a new version of GSLHaskell, a basic library for matrix computations and other numeric algorithms based on LAPACK, BLAS and GSL. The goal is that simple problems involving singular values, linear systems, etc, can be easily solved using Haskell. The library is horribly incomplete, I don't recommend it for any serious work. But at least I enjoy using it in my projects... Some features of this release are: * Improved internal implementation, most code has been refactored. * It works on Linux, Windows, and MacOS X (see the README of the distribution). * Automatic bindings to 200+ GSL special functions. Source code, documentation, updated tutorial, and more information is available from: http://dis.um.es/~alberto/GSLHaskell I'd like to upload a decent version to hackage, so any kind of feedback is very welcome! Thanks, Alberto

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A possibly stupid doubt about the GHC's overlapping instances flag's
by Rodrigo Geraldo 24 Oct '07

24 Oct '07

Hi! Suppose that the GHC's flag -fallow-incoherent-instances is enabled. In this situation, when a instance will be rejected? And if the flag -fallow-overlapping-instances is enabled. When a instance will be rejected? Thanks! Rodrigo

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string literals and haskell'
by David Roundy 23 Oct '07

23 Oct '07

I've just been annoyed with errors ghc reports when I use a string literal such as ":\/:" (which is a contructor in darcs). Of course, it wants ":\\/:", but I'd rather type the former. Is there any reason why the language couldn't be modified (e.g. in haskell') to make the former legal? i.e. to treat string literals with '\\' followed by a character that doesn't describe an escape as a literal backslash? It makes the rules a bit more complicated, but doesn't modify the meaning of any currently-legal code, and removes a potential error. -- David Roundy Department of Physics Oregon State University

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