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ZuriHac registration deadline on February 14, 2010
by Johan Tibell 19 Jan '10

19 Jan '10

Hi all, Due to budget and security constraints, we need to know the final number of attendees a bit in advance. We've therefore set a registration deadline on February 14, 2010. To register please follow the instructions on the registration page: http://www.haskell.org/haskellwiki/ZuriHac/Register Cheers, Johan & Christophe

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parallel matrix multiply (dph, par/pseq)
by Johannes Waldmann 19 Jan '10

19 Jan '10

Hello. How can I multiply matrices (of Doubles) with dph (-0.4.0)? (ghc-6.12.1) - I was trying type Vector = [:Double:] type Matrix = [:Vector:] times :: Matrix -> Matrix -> Matrix times a b = mapP ( \ row -> mapP ( \ col -> sumP ( zipWithP (*) row col ) ) ( transposeP b ) ) a but there is no such thing as transposeP. When I try any kind of index manipulations, the compiler invariably tells me that it does not want to build [: :] - lists of indices (e.g., there is no enumFromToP) (I guess because I'm using Data.Array.Parallel.Prelude.Double) Puzzled - J.W. PS: what's the recommended way to multiply matrices (better modelled as Array (Int,Int) Double or [[Double]] ?) with the par/pseq approach (if this is recommended at all)? As I said earlier, I just want to have some nice and easy benchmarks for demonstration in a lecture (to be run on 2, 4, or 8 cores). Of course if they work, I'd use them in real life as well...

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Declarative binary protocols
by Antoine Latter 19 Jan '10

19 Jan '10

Cafe, We have some fantastic tools for binary parsing in packages like binary and cereal (and presumably attoparsec, which I've not used). But they don't quite scratch an itch I have when writing implementations of binary communication protocols. A good example of my problem is in my implementation of the memcached binary wire protocol: http://hackage.haskell.org/package/starling What I've tried to do is divide up the library into a declarative protocol description and an imperative machine to sit on a handle and link together a server response with the source request. In the declarative core all of the types which come off of the wire have an associated Data.Binary.Get action - but this isn't quite good enough. Data.Binary works on ByteStrings, but I have a handle. I don't want to use hGetContents because I have trouble working out when lazy IO is and is not correct. I can't use hGet because I don't know how much to get until I'm in the middle of the Get action. How do other folks solve this issue? What I've done is broken down and included (getResponse :: Handle -> IO Response) in my core protocol description module, which gets a fixed-length header from which we can figure out how much else to get to form the complete response. But it would be nice to have something cleaner. One thing I've thought of is generalizing Data.Binary.Get to operate over either ByteStrings or Handles. But then I would be doing reads from the handle every couple of bytes. To avoid that I could extend the monad to include declarations of how many bytes the parser will require, which may be declared mutliple times throughout the parser. This felt a bit weird to me, though. Thanks, Antoine Declarative core module: http://hackage.haskell.org/packages/archive/starling/0.1.1/doc/html/Network… IO-centric module: http://hackage.haskell.org/packages/archive/starling/0.1.1/doc/html/Network…

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sorting and merging in haskell
by jjoshua 19 Jan '10

19 Jan '10

So I defined a type called term which is a coefficient and degree of x. int a int b. I want to write a method/methods in haskell to sort them and combine ones with same degree. I think I need to combine somehow, and then use sortby method? I'm just learning haskell, but I now java and c# pretty well and I'm having a hard term converting to functional thinking. its of type [(Int a Int b)] and if b1< b2 put tuple 1 before tuple2, else if = combine by adding a1 to a2, else place 2 before 1. I know how to do it logically, just not the syntax I guess. Thanks so much guys! -- View this message in context: http://old.nabble.com/sorting-and-merging-in-haskell-tp27222668p27222668.ht… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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ANN: afv-0.0.3
by Tom Hawkins 19 Jan '10

19 Jan '10

This release of AFV adds counter example generation for both concrete bounded violations or for inconclusive results when the induction fails to converge. I also put Linux and Windows binaries here: http://tomahawkins.org/. http://hackage.haskell.org/package/afv -Tom

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Windows emulator for testing purposes
by Gregory Crosswhite 19 Jan '10

19 Jan '10

Hey everyone! I have a Linux machine and a OSX machine, and I am developing packages that I would like to upload to Hackage one day. Do you have any recommendations for a free/open source solution that would let me emulate a Windows environment for testing purposes? Cheers, Greg

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FFI, C/C++ and undefined references
by DNM 19 Jan '10

19 Jan '10

Note: I'm relatively new to Haskell, and my knowledge of C and C++ is basically pretty minimal -- I can read, modify and compile C/C++ programs (usually). I'm trying to interface with some C++ code by writing a little bit of C code that uses that C++ code, and I'm getting "undefined reference" errors when I try to 'ghc --make' a client application to test it. Actually, I'm modifying Nitin Madnani's (freely available) Python SRILM toolkit wrapper code. (SRILM, by the bye, is a C++-based toolkit for training and using statistical n-gram language models. I was surprised that no-one has tried to do this yet -- or at least not that they have shared with the rest of us.) Anyhow, I've verified that my modification of Madnani's C code works by compiling it and running it through a SWIG interface in Madnani's Python code, so I'm pretty confident the C client of SRILM is solid. The culprit is either my Haskell FFI code or the client of that code. Without cooking up a microcosm of my problem with little Foo's and Bar's, I'll just give my actual C, header file and Haskell code (or at least the relevant bits), and then the error. ------------- srilm.h ---------------- #ifdef __cplusplus extern "C" { #else typedef struct Ngram Ngram; /* dummy type to stand in for class */ #endif Ngram* bldLM(int order, const char* filename); void deleteLM(Ngram* ngram); float getSeqProb(Ngram* ngram, const char* ngramstr, unsigned order, unsigned length); #ifdef __cplusplus } #endif ----------------------------------------- ------------- srilm.c ---------------- // Initialize and read in the ngram model Ngram* bldLM(int order, const char* filename) { ... } ... // Delete the ngram model void deleteLM(Ngram* ngram) { delete srilm_vocab; delete ngram; } ... // Get the ngram probability of the given string, given n-gram order 'order' and string length // 'length'. float getSeqProb(Ngram* ngram, const char* ngramstr, unsigned order, unsigned length) { ...} ----------------------------- Next, the Haskell FFI specs and code that marshals data between Haskell and C. ---------------- LM.hs ---------------------- {-# INCLUDE "srilm.h" #-} {-# LANGUAGE ForeignFunctionInterface, EmptyDataDecls #-} ... module decl's, imports, etc. {- | A dummy placeholder for SRILM n-gram model thingies. -} data Ngram data NGModel = NGModel {ng :: !(ForeignPtr Ngram)} foreign import ccall "srilm.h bldLM" c_blm :: CInt -> CString -> Ptr Ngram foreign import ccall "srilm.h deleteLM" c_dlm :: FunPtr ((Ptr Ngram) -> IO ()) foreign import ccall "srilm.h getSeqProb" c_ngramProb :: Ptr Ngram -> CString -> CUInt -> CUInt -> CFloat {- | Given an n-gram model, an Int representing the n-gram order and a list of strings (word sequence), compute the n-gram probability of the sequence. -} scoreSequence :: NGModel -> Int -> [String] -> Float scoreSequence ngram order seq = unsafePerformIO $ do stringSeq <- newCString (unwords seq) let sc = c_ngramProb (unsafeForeignPtrToPtr $ ng ngram) stringSeq (fromIntegral order) (fromIntegral $ length seq) return (realToFrac sc) ... buildLM :: Int -> String -> NGModel buildLM order fname = NGModel $ unsafePerformIO $ do cFName <- newCString fname let ng = c_blm (fromIntegral order) cFName return $ unsafePerformIO $ newForeignPtr c_dlm ng -------------------------------------------- Now, I've defined a simple app that tries to use this: ------------------- Main.hs ------------------------- module Main where import SRILM.LM(scoreSequence, buildLM) main :: IO () main = do let lm = buildLM 5 "eng.kn.5g.lm" putStrLn $ show $ scoreSequence lm 5 ["the", "prime", "minister", "gave", "a", "speech", "."] ----------------------------------------------------------- But when I try to compile it (after having successfully compiled the C code with g++), I get: $ ghc --make Main.hs Linking Main ... LM.o: In function `r18k_info': (.text+0x122): undefined reference to `bldLM' LM.o: In function `r18m_info': (.text+0x14e): undefined reference to `deleteLM' LM.o: In function `r18o_info': (.text+0x28b): undefined reference to `getSeqProb' collect2: ld returned 1 exit status Any ideas? Note that I'm not confident that everything on the Haskell side is correct, but it seems that ghc can't find my C client of SRILM. As I said, I've compiled this code using g++, and it works when I interface with it through Python. Sorry for the long-windedness, but I figured I'd err on the side of TMI so that I don't have to keep posting more and more code snippets and error messages. Any help is greatly appreciated. (And I'd be happy to share my interface to SRILM to anyone who's interested, once I get it working -- and I get permission from Nitin Madnani to distribute a modified version of his code.) Thanks, Dennis -- View this message in context: http://old.nabble.com/FFI%2C-C-C%2B%2B-and-undefined-references-tp27139612p… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Broken registration link on hackage trac
by Andy Gimblett 18 Jan '10

18 Jan '10

Hi all, I want to register an account on hackage's trac instance, but the "register an account" link on the start page: http://hackage.haskell.org/trac/hackage/wiki/WikiStart is broken. I'm guessing someone here knows what it should be and has registered already and thus can fix it. :-) Cheers, -Andy -- Andy Gimblett http://gimbo.org.uk/

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Mini-announce: A few package updates
by Andrew Coppin 18 Jan '10

18 Jan '10

In case somebody else on this planet besides me is using these... I've just updated my handful of packages on Hackage so they should now build with GHC 6.12.1. (In most cases, just tweaks to the package dependancies.) I have also changed the documentation for AC-EasyRaster-GTK, to hopefully make it clearer that all the event-related stuff is ONLY necessary if you want to display your images in a GTK window. Oh, and I discovered that I fail basic linear algebra; the AC-Vector package had a bug in vcross, which is fixed in 1.2.2 (but exists in all prior versions). AC-Vector gets a minor version bump because I renamed some stuff; nothing really "exciting" is different. PS. Apparently AC-VanillaArray causes GHC 6.12.1 to panic during compilation... I'll have to investigate that. Still, it does play with GHC.Prim, so that's probably got something to do with it.

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Newbie question about Parsec
by david fries 18 Jan '10

18 Jan '10

Hey everybody I've been playing around with Parsec a little bit lately. I like it a lot, but now I've hit a bit of a challenge. Suppose I have to parse a variable length string representing a time interval. Depending on how many fields there are, the time is either interpreted as seconds, minutes and seconds or hours, minutes and seconds. For example: "... 31 ..." would be parsed as 31 seconds. "... 05:31 ..." would be parsed as 5 minutes and 31 seconds. "... 01:05:31 ..." would be parsed as 1 hour, 5 minutes and 31 seconds. I've come up with the following solution using optionMaybe to deal with the problem: data ElapsedTime = ElapsedTime { hours :: Int, minutes :: Int, seconds :: Int } deriving (Show, Eq, Ord) p_elapsed_time :: CharParser () ElapsedTime p_elapsed_time = toElapsedTime <$> (optionMaybe p_Int) <*> (optionMaybe (char ':' *> p_Int)) <*> (optionMaybe (char ':' *> p_Int <* skipSpaces)) where toElapsedTime Nothing Nothing Nothing = ElapsedTime 0 0 0 toElapsedTime (Just s) Nothing Nothing = ElapsedTime 0 0 s toElapsedTime (Just m) (Just s) Nothing = ElapsedTime 0 m s toElapsedTime (Just h) (Just m) (Just s) = ElapsedTime h m s Where p_Int simply parses a sequence of digits as an Int and skipSpaces does just that. This works correctly, but it also feels kinda clumsy. For one the compiler rightly complains about non-exhaustive pattern matches in the definition of the toElapsedTime function, although I believe that's negligible in that particular case. Is there a better i.e. more elegant way to tackle such a problem? regards, david

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