December 2011 - Beginners

Parallel Matrix Multiplication
by mukesh tiwari 10 Dec '11

10 Dec '11

Hello all I am trying to learn parallel Haskell and I have gone through couple of resources ( Real world Haskell and http://research.microsoft.com/en-us/um/people/simonpj/papers/parallel/AFP08… ). I understood par and pseq and I wrote matrix multiplication using these two function but it does not look. Although I did not get all these details from ( ./Matpar +RTS -N2 -s ) but none of the sparks converted which is really important for parallel programming. Could some one please tell me how to improve this. Also kindly recommend me some literature for parallel programming in Haskell. Regards Mukesh Tiwari import Data.List import Control.Parallel parHelp :: ( Num a ) => [ a ] -> [ a ] -> a parHelp [] [] = 0 parHelp ( x : xs ) ( y : ys ) = ret where ret = par a ( pseq a ( a + parHelp xs ys ) ) where a = x * y helpMult :: ( Num a ) => [ a ] -> [ [ a ] ] -> [ a ] helpMult _ [] = [] helpMult x ( y : ys ) = ret where ret = par a ( pseq a ( a : helpMult x ys ) ) where a = parHelp x y mult :: ( Num a ) => [ [ a ] ] -> [ [ a ] ] -> [ [ a ] ] mult [] _ = [] mult ( x : xs ) ys = ret where ret = par a ( pseq a ( a : mult xs ys ) ) where a = helpMult x ys main = print $ mult [[1 .. 4 ] , [ 1 .. 4 ] , [ 1 .. 4 ] , [ 1 .. 4] ] ( transpose [[1 .. 4 ] , [ 1 .. 4 ] , [ 1 .. 4 ] , [ 1 .. 4] ]) [user@haskell Programming]$ ghc -O2 -threaded -rtsopts Matpar.hs [1 of 1] Compiling Main ( Matpar.hs, Matpar.o ) Linking Matpar ... [user@haskell Programming]$ ./Matpar +RTS -N2 -s ./Matpar +RTS -N2 -s [[10,20,30,40],[10,20,30,40],[10,20,30,40],[10,20,30,40]] 85,480 bytes allocated in the heap 5,216 bytes copied during GC 47,328 bytes maximum residency (1 sample(s)) 22,304 bytes maximum slop 2 MB total memory in use (0 MB lost due to fragmentation) Generation 0: 0 collections, 0 parallel, 0.00s, 0.00s elapsed Generation 1: 1 collections, 0 parallel, 0.00s, 0.00s elapsed Parallel GC work balance: -nan (0 / 0, ideal 2) MUT time (elapsed) GC time (elapsed) Task 0 (worker) : 0.00s ( 0.00s) 0.00s ( 0.00s) Task 1 (worker) : 0.00s ( 0.00s) 0.00s ( 0.00s) Task 2 (bound) : 0.00s ( 0.00s) 0.00s ( 0.00s) Task 3 (worker) : 0.00s ( 0.00s) 0.00s ( 0.00s) * SPARKS: 84 (0 converted, 0 pruned)* INIT time 0.00s ( 0.00s elapsed) MUT time 0.00s ( 0.00s elapsed) GC time 0.00s ( 0.00s elapsed) EXIT time 0.00s ( 0.00s elapsed) Total time 0.00s ( 0.00s elapsed) %GC time 33.3% (13.5% elapsed) Alloc rate 42,761,380 bytes per MUT second Productivity 33.3% of total user, 45.0% of total elapsed gc_alloc_block_sync: 0 whitehole_spin: 0 gen[0].sync_large_objects: 0 gen[1].sync_large_objects: 0 [user@haskell Programming]$

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comments requested
by rickmurphy 09 Dec '11

09 Dec '11

Hey All: A few months ago I got some help here starting up some RDF and JSON work. Special thanks to David McBride for getting me on the right path. http://osdir.com/ml/beginners@haskell.org/2011-10/msg00348.html Since then I've been exercising some skill building. I've moved this work to github with the hope that folks here can comment and offer suggestions for improvement. You can find the files here: https://github.com/rickmurphy/hafr and a bit of a write up here. http://phaneron.rickmurphy.org/ I welcome your feedback on refactoring, style, performance tuning, etc. -- Rick

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Installing regex-pcre
by MJ Williams 08 Dec '11

08 Dec '11

Dear all, I'm trying to install regex-pcre on my XP Pro machine. I have the latest version of GHC. Do any of you recognise and understand the following error message? install regex-pcre Resolving dependencies... Configuring regex-pcre-0.94.2... cabal: Missing dependency on a foreign library: * Missing C library: pcre This problem can usually be solved by installing the system package that provides this library (you may need the "-dev" version). If the library is already installed but in a non-standard location then you can use the flags --extra-include-dirs= and --extra-lib-dirs= to specify where it is. cabal: Error: some packages failed to install: regex-pcre-0.94.2 failed during the configure step. The exception was: ExitFailure 1 Apologies if the query is a little offtopic. Regards Matthew

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Matrix / Matrix Addition
by Paul Monday 08 Dec '11

08 Dec '11

I'm working on simple matrix / matrix addition for a short project. Doing this with lists (not worrying about matrix sizes and such) is relatively easy and makes quite a bit of sense to me: basically: madd :: Num a => [[a]] -> [[a]] -> [[a]] I could read this as: - with a as a Numeric type, take two lists of lists of Numerics and return a list of lists of Numerics And then to do the job simple madd m n = zipWith (zipWith (+)) m n And I can read that easily enough: -- madd has two inputs, m and n and it will do the function "zipWith (+)" across its inputs of the inner lists from m and n (the rows, basically) Ok, so madd [[1,2,3], [4,5,6], [7,8,9]] [[10,11,12], [13,14,5], [16,17,18]] yields [[11,13,15],[17,19,11],[23,25,27]] Cool I can get a little nicer (possibly) if I use a Matrix type: data Matrix a = Matrix [[a]] deriving (Show, Eq) madd :: Num a => [[a]] -> [[a]] -> [[a]] madd m n = zipWith (zipWith (+)) m n madd2 :: (Num a) => Matrix a -> Matrix a -> Matrix a madd2 (Matrix m) (Matrix n) = Matrix $ zipWith (zipWith (+)) m n The only real change in terms of the code is in the madd2 definition where I have to construct a Matrix to return from the results of the zipWiths … and some better type safety of course. *Main> madd2 (Matrix [[1,2,3], [4,5,6], [7,8,9]]) (Matrix [[10,11,12], [13,14,5], [16,17,18]]) Matrix [[11,13,15],[17,19,11],[23,25,27]] Cool' Now, I really want to use Unboxed Vectors. As I look around the web and poke around through various resources, I believe that I need the rows to be unboxed but the columns can be boxed … the actual operations on the rows will give me the speed up I desire. So, here it is: import qualified Data.Vector as V import qualified Data.Vector.Unboxed as U data UMatrix a = UMatrix (V.Vector (U.Vector a)) deriving (Show, Eq) madd3 :: (U.Unbox a, Num a) => UMatrix a -> UMatrix a -> UMatrix a madd3 (UMatrix m) (UMatrix n) = UMatrix $ V.zipWith (U.zipWith (+)) m n And it works … (really, when I started writing this note, I was completely lost … welcome to the power of sitting and walking through Haskell) madd3 (UMatrix (Data.Vector.fromList [Data.Vector.Unboxed.fromList [1,2,3], Data.Vector.Unboxed.fromList [4,5,6], Data.Vector.Unboxed.fromList [7,8,9]])) (UMatrix (Data.Vector.fromList [Data.Vector.Unboxed.fromList [10,11,12], Data.Vector.Unboxed.fromList [13,14,5], Data.Vector.Unboxed.fromList [16,17,18]])) I have ONE thing that I can't really explain … Why does the declaration of madd3 REQUIRE the use of U.Unbox a as a data type? madd3 :: (U.Unbox a, Num a) => UMatrix a -> UMatrix a -> UMatrix a I would have thought that my declaration of UMatrix would have done this? Cheers. Paul Monday Parallel Scientific, LLC. paul.monday(a)parsci.com

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Compiling shared (dll) library
by Alexander.Vladislav.Popov 05 Dec '11

05 Dec '11

Hi, Haskellers. I'm trying to compile following program (where Regex.Genex is a package what I need to produce all possible expresions by the given pattern and `adder' is just FFI sample): -- genexlib.hs {-# LANGUAGE BangPatterns, ForeignFunctionInterface #-} module GenexLib where import Regex.Genex import System.IO import System.Environment adder :: Int -> Int -> IO Int -- gratuitous use of IO adder x y = return (x+y) foreign export stdcall adder :: Int -> Int -> IO Int -- genexlib.hs end // start.c #include <Rts.h> void HsStart() { int argc = 1; char* argv[] = {"ghcDll", NULL}; // argv must end with NULL // Initialize Haskell runtime char** args = argv; hs_init(&argc, &args); } void HsEnd() { hs_exit(); } // start.c end I'm using ghc >ghc --version The Glorious Glasgow Haskell Compilation System, version 7.0.2 compiling: >ghc -c genexlib.hs >ghc -c start.c >ghc -shared -o genexlib.dll genexlib.o genexlib_stub.o start.o genexlib.o:fake:(.text+0xd1): undefined reference to `__stginit_regexzmgenexzm0zi3zi2_RegexziGenex_' Creating library file: genexlib.dll.a collect2: ld returned 1 exit status and get undefined reference. But If I try to compile the executable from similar code: -- genexlib.hs {-# LANGUAGE BangPatterns, ForeignFunctionInterface #-} -- module GenexLib where import Regex.Genex import System.IO import System.Environment defaultRegex :: String defaultRegex = "a(b|c)d{2,3}e*" main :: IO () main = do hSetBuffering stdout NoBuffering args <- getArgs case args of [] -> do prog <- getProgName if prog == "<interactive>" then run [defaultRegex] else do fail $ "Usage: " ++ prog ++ " regex [regex...]" rx -> run rx run :: [String] -> IO () run regex = do let s = genexPure regex mapM_ print s -- genexlib.hs end >ghc --make genexlib.hs -O2 it's ok, no errors, and you can see in GHCi: *Main> :main "abdd" "acdd" "abddd" "acddd" "abddeee" "acddeee" "abdddeee" "acdddeee" "abddee" "acddee" "abdddee" "acdddee" "abdde" "acdde" "abddde" "acddde" Where is my mistake? What am I doing wrong? In first case, when compiling shared dll, I tried to link libraries what I've found in `cabal' directory (like `libHSregex-genex-0.3.2.a') to work around errors but all in vain. -- Alexander Popov

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Diagnosing : Large memory usage + low CPU
by Hugo Ferreira 05 Dec '11

05 Dec '11

Hello, I am testing a simple algorithm and find that during part of the execution this is fast and uses acceptable memory. However, when it gets to a certain point the memory climbs to 75-80 % of the OS's memory and CPU plummets to a mere 5% at most. In the part of the application that executes ok I have calls as follows: let r9' = evalTagger'' (tagFun suffixCapsFreq) $ test let a9' = tagginAccuracy r9' putStrLn ("Suffix(3) + Caps + Freq tag result done = " ++ (show a9')) The slow one has: let r12' = evalTagger'' ruleSuffixCapsFreq $ test let a12' = tagginAccuracy r12' putStrLn ("Rules + Suffix(3) + Caps + Freq tag result done = " ++ (show a12')) The difference lies in the following functions: ruleApplication :: TransformationRule -> POSTags -> Maybe Tag ruleApplication (NextTagRule (Replacement old new) next) z = do (_, _, proposed) <- Z.safeCursor z (_, _, nextProposed) <- rightCursor z if proposed == old && nextProposed == next then Just new else Nothing .... updateState :: (TransformationRule,Int) -> POSTags -> POSTags updateState r = Z.fromList . reverse . Z.foldlz' (update r) [] where update (r,_) !xs z = case ruleApplication r z of Just tag -> (token, correct, tag):xs Nothing -> e:xs where e@(token, correct, _proposed) = Z.cursor z rulesT :: [(TransformationRule, Int)] -> POSTags -> POSTags rulesT rs state = L.foldl' tag state rs where tag !s rule = updateState rule s (.>) :: (POSTags -> Tag) -> (POSTags -> Tag) -> POSTags -> Tag f .> g = \ x -> case (g x) of "" -> f x t -> t (|>) :: (POSTags -> POSTags) -> (POSTags -> Tag) -> POSTags -> POSTags f |> g = \ x -> f $ tagFun g x let ruleT = rulesT top10Rules let suffixCapsFreq = suffixT .> capitalizeT .> freqT let ruleSuffixCapsFreq = ruleT |> suffixCapsFreq where top10Rules is a list. Note that suffixCapsFreq and tagFun are common to both calls. I have placed bangs in many places and used eager evaluation in the folds. However nothing seems to help. Can anyone tell me how I should diagnose this problem. Any suggestions are welcome. TIA, Hugo F.

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ANNOUNCE: Haskell Communities and Activities Report (21st ed., November 2011)
by Janis Voigtländer 04 Dec '11

04 Dec '11

On behalf of all the contributors, I am pleased to announce that the Haskell Communities and Activities Report (21st edition, November 2011) is now available in PDF and HTML formats: http://haskell.org/communities/11-2011/report.pdf http://haskell.org/communities/11-2011/html/report.html Many thanks go to all the people that contributed to this report, both directly, by sending in descriptions, and indirectly, by doing all the interesting things that are reported. I hope you will find it as interesting a read as I did. If you have not encountered the Haskell Communities and Activities Reports before, you may like to know that the first of these reports was published in November 2001. Their goal is to improve the communication between the increasingly diverse groups, projects, and individuals working on, with, or inspired by Haskell. The idea behind these reports is simple: Every six months, a call goes out to all of you enjoying Haskell to contribute brief summaries of your own area of work. Many of you respond (eagerly, unprompted, and sometimes in time for the actual deadline to the call. The editor collects all the contributions into a single report and feeds that back to the community. When I try for the next update, six months from now, you might want to report on your own work, project, research area or group as well. So, please put the following into your diaries now: ========================================= End of April 2012: target deadline for contributions to the May 2012 edition of the HC&A Report ========================================= Unfortunately, many Haskellers working on interesting projects are so busy with their work that they seem to have lost the time to follow the Haskell related mailing lists and newsgroups, and have trouble even finding time to report on their work. If you are a member, user or friend of a project so burdened, please find someone willing to make time to report and ask them to "register" with the editor for a simple e-mail reminder in April (you could point me to them as well, and I can then politely ask if they want to contribute, but it might work better if you do the initial asking). Of course, they will still have to find the ten to fifteen minutes to draw up their report, but maybe we can increase our coverage of all that is going on in the community. Feel free to circulate this announcement further in order to reach people who might otherwise not see it. Enjoy! Janis Voigtlaender <hcar at haskell.org>

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Question about Interpreter
by Song Zhang 03 Dec '11

03 Dec '11

Hi I am a beginner of Haskell. I want to know why the interpreter was designed in a way that one function or a part fails the whole program fails. why we don't keep the parts that is correct functioning and also give error message for the wrong parts?

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emacs setup for haskell
by Rustom Mody 02 Dec '11

02 Dec '11

I am using haskell inside emacs with the usual setup ie .hs file in one window, ghci in another. Now the most usual workflow one would do is to load the file into ghci (C-c C-l) and try out something in ghci. A small niggle is that after the C-c C-l Ive to manually switch to the other window (current window does not switch to ghci automatically) This seems to be a strange default More importantly the state of the workspace in ghci seems to get messed up unless I do: 0. Prepare some code in .hs 2. Switch to ghci 3. Clear the ghci workspace with :m <nothing> 4. switch back to .hs 5. C-c C-l 6. Switch to ghci to try out new code Is there something I am missing?

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Parallelism?
by Michael Craig 02 Dec '11

02 Dec '11

I was writing some parallel code (asynchronous database writes for an event logger, but that's besides the point), and it seemed like the parallelized version (i.e. compiled with -threaded -with-rtsopts=-N2) wasn't running fast enough. I boiled it down to a dead-simple test: import Control.Concurrent import Data.Time.Clock.POSIX import System.Environment main :: IO () main = do n <- getArgs >>= return . read . head t1 <- getPOSIXTime work n t2 <- getPOSIXTime putStrLn $ show $ t2 - t1 putStrLn $ show $ (fromIntegral n :: Double) / (fromRational . toRational $ t2 - t1) work :: Integer -> IO () work n = do forkIO $ putStrLn $ seq (fact n) "Done" putStrLn $ seq (fact n) "Done" fact :: Integer -> Integer fact 1 = 1 fact n = n * fact (n - 1) (I know this is not the best way to time things but I think it suffices for this test.) Compiled with ghc --make -O3 test.hs, ./test 500000 runs for 74 seconds. Compiling with ghc --make -O3 -threaded -with-rtsopts=-N, ./test 500000 runs for 82 seconds (and seems to be using 2 cpu cores instead of just 1, on a 4-core machine). What gives? Mike S Craig

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