January 2010 - Haskell-Cafe

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 18 Jan '10

18 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 18 Jan '10

18 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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unexpected behavior / bug in try . System.FilePath.Find.findWithHandler
by Thomas Hartman 18 Jan '10

18 Jan '10

say you want to execute a find function, but abort the computation if it hits any snags, such as an unreadable directory (eg chmod -R a-r dir). Currently try . System.FilePath.Find.findWithHandler will return an exception wrapped in Right, which seems Wrong. For sure it will just get ignored if wrapped in an ErrorT computation and I suspect this could lead to other glitchy/unexpected behavior when used in sysadmin scripts. You do get the expected exception wrapped in Left for certain errors (such as a missing directory), which adds to the confusion. Probable fix: you get the expected behavior if you remove unsafeInterleaveIO from findWithHandler. Does this seem like a reasonable thing to suggest to libraries@haskell? Hacky fix: I haven't actually done this, but I suppose you could trap stdout or stderr, since the exception does get printed although it's not reflected in the result type of the computation. demo of problem: import qualified System.FilePath.Find as F import System.FilePath.Find import System.IO.Error abort path err = fail $ path ++ " , " ++ (show err) prot = "/home/thartman/protected" -- a protected (unreadable) dir {- want result => Left user error (/home/thartman/protected , user error (/home/thartman/protected , /home/thartman/protected: getDirectoryContents: permission denied (Permission denied))) but get result Right *** Exception: user error (/home/thartman/protected , /home/thartman/protected: getDirectoryContents: permission denied (Permission denied)) which means, for example, you would miss the error if you wrapped this in an ErrorT there is probably a workaround from reading stderr, since it does get printed out, but this is awkward compared to just catching the error the right way and certainly feels like unexpected behavior Possible fix: you get the expected behavior if you remove unsafeInterleaveIO from System.FilePath.Find.findWithHandlers don't know why this fixes the problem, I was just messing around I don't know if this breaks anything else, but I was unable to find any breakage when I did a simple test on an unprotected directory What is the gain from unsafeInterleaveIO, and can it be nixed? -} tprot = try . findWithHandler abort (return True) (return True) $ prot tunprot = return . either (error . show) (length) =<< ( try $ findWithHandler abort (return True) (return True) unprot ) unprot = "/home/thartman/unprot" -- Need somewhere to put your code? http://patch-tag.com Want to build a webapp? http://happstack.com

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ghc "make install" question
by Johannes Waldmann 18 Jan '10

18 Jan '10

Hi. How can I get "make install" from a ghc (snapshot) source dir to install binaries $prefix/bin/ghc{,i,-pkg}-$version but *not* overwrite the un-versioned symlinks? Thanks - J.W.

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ANN: atom-0.1.3
by Tom Hawkins 18 Jan '10

18 Jan '10

This release of Atom slightly changes the semantics of assertions and coverage. Assertion and coverage are now checked between the execution of every rule, instead of only when the rules containing assertions are fired. They are still subject to parental guard conditions, but not period or phase constraints. This means... period 20 $ atom "checkSomeStuff" $ do cond ok assert "A" a assert "B" b cover "C" c ... A, B, and C are checked all the time "ok" is true, not just every 20th cycle. Checking between every rule execution obviously impacts simulation time, but the increased testing rigor is worth it. I also added 'linear' to Common, which does linear interpolation and extrapolation on a line given two points. (I found I was replicating this function everywhere for sensor calibrations, control limits, etc.) http://hackage.haskell.org/package/atom

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