- Haskell-Cafe - Haskell.org

Re: [Haskell-cafe] ANNOUNCE: hfann-01
by Olivier Boudry 10 Jun '08

10 Jun '08

On Mon, Jun 9, 2008 at 11:29 AM, Don Stewart <dons(a)galois.com> wrote: > Excellent. Would you like to upload it to hackage.haskell.org, so it can > be easily installed with the 'cabal install' tool? > > Hi all, As suggested by Don, I just uploaded the hfann package to hackage.haskell.org. It's available here: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hfann Best regards, Olivier.

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"sum" in hmatrix and blas?
by Xiao-Yong Jin 10 Jun '08

10 Jun '08

Hi, probably I am just being dumb, but what is the most efficient way to do a sum of every elements in a Vector of either hmatrix or blas? I know there is sum of absolute values from BLAS. So what about I want a plain "sum"? I can only think of the following two ways. 1. Using Data.List.foldl', so it is > sum' = foldl' (+) 0 . toList in hmatrix or > sum' = foldl' (+) 0 . elems in blas. 2. Using <.>, so it is > sum' v = constant 1 (dim v) <.> v in hmatrix or > sum' v = constant (dim v) 1 <.> v in blas. Which one is better? I guess it probably depends on the internal implementation of BLAS, but I am actually thinking in some thing similar to > t += *v++; Any delightful idea to convert my mind from a C shaped one to a Haskell shaped one? Best, Xiao-Yong -- c/* __o/* <\ * (__ */\ <

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ANNOUNCE: hfann-01
by Olivier Boudry 09 Jun '08

09 Jun '08

Hi all, I'm pleased to announce the first release of the hfann module ( http://code.haskell.org/~oboudry/hfann/) This module is an interface to the "Fast Artificial Neural Network (FANN)" library (see http://leenissen.dk/fann/) This is an early release. At the moment the hfann module does not cover all the functions found in the FANN library but it should be useable to train and use simple Neural Networks. At least is can be used to run an equivalent of the "Getting Started" example found in http://leenissen.dk/fann/html/files2/gettingstarted-txt.html. The module was developped on Windows XP with GHC-6.8.2. The README should provide you with all required information to install this module. The haddock documentation should give enough information to get started using it. == Installation == Download version 2.0 of the FANN library from: http://leenissen.dk/fann/download.php and build it according to the instruction found on: http://leenissen.dk/fann/html/files2/installation-txt.html Get the hfann module darcs get http://code.haskell.org/~oboudry/hfann/ Build it using Cabal runghc Setup.lhs configure runghc Setup.lhs build runghc Setup.lhs haddock runghc Setup.lhs install == Examples == Training an ANN to the xor function: > import HFANN > main = do > withStandardFann [2,3,1] $ \fann -> do > setActivationFunctionHidden fann fannSigmoidSymetric > setActivationFunctionOutput fann fannSigmoidSymetric > trainOnFile fann "xor.data" -- train data > 20000 -- max epochs > 100 -- epochs between reports > 0.001 -- desired error > saveFann fann "xor.ann" C:\Temp\Haskell\hfann\examples\xor>Train.exe Max epochs 20000. Desired error: 0.0010000000. Epochs 1. Current error: 0.2503675520. Bit fail 4. Epochs 100. Current error: 0.0181358512. Bit fail 0. Epochs 169. Current error: 0.0009599295. Bit fail 0. Using the trained ANN on the 4 possible input values to the xor function (-1 = False, 1 = True). > import HFANN > main = do > withSavedFann "xor.ann" $ \fann -> do > mapM_ (\x -> runFann fann x >>= print) [[-1,-1],[-1,1],[1,-1],[1,1]] C:\Temp\Haskell\hfann\examples\xor>Use.exe [-0.950566361876292] [0.9178714756661263] [0.9457588340834527] [-0.9482816646878051] The "xor.data" training data content: 4 2 1 -1 -1 -1 -1 1 1 1 -1 1 1 1 -1 The files for this example can be found in the "examples/xor" directory == Bug reports, suggestions and comments are welcome. You can send them directly to my e-mail address. Olivier.

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Moving "forall" over type constructors
by Klaus Ostermann 09 Jun '08

09 Jun '08

At first I'd like to thank Claus, Ryan, Edsko, Luke and Derek for their quite helpful replies to my previous thread. In the course of following their advice I encountered the problem of moving a "forall" quantifier over a wrapper type constructor. If I have > newtype Wrapper a = Wrapper a and I instantiate Wrapper with a polymorphic type, then it is possible to move the quantifier outside: > outside :: Wrapper (forall a. (t a)) -> (forall a. Wrapper (t a)) > outside(Wrapper x) = Wrapper x (surprisingly the code does not work with the implementation 'outside x = x'; I guess this is a ghc bug) However, the other way around does not work: > inside :: (forall a. Wrapper (t a))-> Wrapper (forall a. (t a)) > inside x= x results in the following error: Couldn't match expected type `forall a. t a' against inferred type `t a' Expected type: Wrapper (forall a1. t a1) Inferred type: Wrapper (t a) In the expression: x In the definition of `inside': inside x = x Any ideas on how to make this work? Klaus

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Quick question for a slow program
by Slavomir Kaslev 09 Jun '08

09 Jun '08

Hello, I was just brushing my haskell-fu skills writing a solution for Google Treasure Hunt Problem 4. Hers is what it looks like: > primes = sieve [2..] > where > sieve (p:xs) = p : sieve [x | x <- xs, x `mod` p /= 0] > > sumOf n l = sum (take n l) : sumOf n (tail l) > > find l = foldl1 aux l > where > aux (x:xs) (y:ys) | x == y = x : aux xs ys > | x < y = aux xs (y:ys) > | x > y = aux (x:xs) ys > > puzzle = find (reverse [primes, p7, p17, p41, p541]) > where > p7 = sumOf 7 primes > p17 = sumOf 17 primes > p41 = sumOf 41 primes > p541 = sumOf 541 primes > > main = do mapM (\x -> putStrLn $ show x) puzzle While the code is quite readable and straight forward it is as slow as tortoise with four legs broken. What optimizations would you suggest, while still keeping the code clear and highlevel? Thank you in advance. Cheers. -- Slavomir Kaslev

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Package updates on haskell.org
by Don Stewart 09 Jun '08

09 Jun '08

The HWN, which I'm sadly too busy to maintain now, had a useful function of generating recent package releases and getting them on the wiki, and to people's inboxes. This facility has been replaced by two processes: 1) Users can subscribe to recent package updates via RSS: http://hackage.haskell.org/packages/archive/recent.rss 2) The 'hackage2hwn' script now runs to keep the http://haskell.org 'Recent Package Updates' section fresh, listing the latest updates. So you can always find the newest 20 packages by looking at haskell.org Cheers, Don

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Fwd: [Haskell-cafe] FunPtr error?
by Galchin, Vasili 09 Jun '08

09 Jun '08

So Luke .. how do I go from (Sigval -> ()), i..e notifyFunc, to FunPtr using the suggested data constructors? On Sun, Jun 8, 2008 at 10:01 PM, Luke Palmer <lrpalmer(a)gmail.com> wrote: > 2008/6/8 Galchin, Vasili <vigalchin(a)gmail.com>: > > Hello, > > > > I am getting what is to me a mysterious error in a test case that I > am > > writing: > > vigalchin@ubuntu:~/FTP/Haskell/unix-2.2.0.0/tests/timer$ runhaskell > > Setup.lhs build > > Preprocessing executables for Test-1.0... > > Building Test-1.0... > > [1 of 1] Compiling Main ( ./timer.hs, > > dist/build/timer/timer-tmp/Main.o ) > > > > ./timer.hs:11:45: Not in scope: data constructor `FunPtr' > > There is a *type* called FunPtr in scope, but not a data constructor > as you are using it. That is, you could say: > > foo :: FunPtr (Int -> IO ()) > > That is, use the type called FunPtr, but you may not use a *function* > called FunPtr, because it doesn't exist. You need to use functions > like nullFunPtr, castPtrToFunPtr, etc. to construct FunPtrs. > > Luke >

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Vancouver Haskell users meeting
by Jon Strait 09 Jun '08

09 Jun '08

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Printing a random list
by Bryan Catanzaro 09 Jun '08

09 Jun '08

I'm just starting out with Haskell, and I could use some help. I'm trying to create a random list and print it out, which seems simple enough, but has been giving me problems. Here's what I have: module Main where import IO import Random randomList :: Random a => a -> a-> [IO a] randomList lbound ubound = randomRIO(lbound, ubound) : randomList lbound ubound main = do myRandomList <- sequence(randomList(0::Int 255)) putStrLn(show(take(10 myRandomList))) ----- So, I have tried to make a randomList action which defines an infinite random list, bounded by lbound and ubound. It seems that to print this, I need to convert between randomList, which is of type [IO a] to something like IO [a], which is what sequence should do for me. Then I just want to print out the first 10 elements. I'm currently getting the error "Only unit numeric type pattern is valid", pointing to 0::Int 255 in the code. I'm not sure what this means. I'm sure I'm looking at this the wrong way, since I'm new to Haskell and haven't quite wrapped my head around it yet. Maybe you can fix the problem by showing me a more Haskell approach to creating a random list and printing it... =) Thanks! - bryan catanzaro

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Patrick Perry's BLAS package
by Alberto Ruiz 09 Jun '08

09 Jun '08

Hello all, I have just noticed that yesterday this fantastic package has been uploaded to hackage: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/blas-0.4 We finally have a high quality library for numeric linear algebra. This is very good news for the Haskell community. Patrick, many thanks for your excellent work. Do you have similar plans for LAPACK? Alberto

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Issues of the "mailto" link on the list archive page
by Xiao-Yong Jin 08 Jun '08

08 Jun '08

Hi, I had private conversation with Andrzej Jaworski about the fact that his reply to Alberto Ruiz's post is off thread. What he did was clicking on the "mailto" link beside the author's name on the list archive web page [1]. [1] http://www.haskell.org/pipermail/haskell-cafe/2008-June/044023.html I am not quite sure about what this link is supposed to do. But, if it is meant for people to click and reply to the thread, it is not doing this correctly, as the "Subject" and "In-Reply-To" fields in the link are obtained from these fields in the head of current email. It would be useful if the link shows "Subject" with an added "Re: " if there is not already one, and fill in the "in-Reply-To" field with the value from the "Message-Id" field of current email head. An optional "Reference" field is informative for most of the email client, too. Sorry if this topic has the least connection to the glorious Haskell. Best, Xiao-Yong -- c/* __o/* <\ * (__ */\ <

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Data.Map traversal.
by Serguey Zefirov 08 Jun '08

08 Jun '08

I found that I often need predecessor and successor of some key in Data.Map.Map. Just like that: predKey, succKey :: Ord k => Data.Map.Map k a -> k -> Maybe k predKeyElem, succKeyElem :: Ord k => Data.Map.Map k a -> k -> Maybe (k,a) Data.Map has operations like that on key indexes, but it is slightly unnatural to work with three entities (index, key and element) where two suffices. So I propose to include those operations into next version of Data.Map. If anyone could point me in the right direction I could do any necessary modifications myself (just because I need it).

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Mersenne Build Problem
by Dominic Steinitz 08 Jun '08

08 Jun '08

I'm getting errors (see below) trying to build the tests in http://hackage.haskell.org/cgi-bin/hackage-scripts/package/mersenne-random-… I built the package itself using ./Setup configure -f use_sse2 I thought I had an intel core duo (also see below). I think I may be missing a library but I'm not sure which one. Thanks, Dominic. > dom@lagrange:~/mersenne-random-0.1.1> cat /proc/cpuinfo > processor : 0 > vendor_id : GenuineIntel > cpu family : 6 > model : 15 > model name : Intel(R) Core(TM)2 Duo CPU E4500 @ 2.20GHz > stepping : 13 > cpu MHz : 1200.000 > cache size : 2048 KB > physical id : 0 > siblings : 2 > core id : 0 > cpu cores : 2 > fdiv_bug : no > hlt_bug : no > f00f_bug : no > coma_bug : no > fpu : yes > fpu_exception : yes > cpuid level : 10 > wp : yes > flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe lm constant_tsc pni monitor ds_cpl est tm2 ssse3 cx16 xtpr lahf_lm > bogomips : 4392.14 > clflush size : 64 > > processor : 1 > vendor_id : GenuineIntel > cpu family : 6 > model : 15 > model name : Intel(R) Core(TM)2 Duo CPU E4500 @ 2.20GHz > stepping : 13 > cpu MHz : 1200.000 > cache size : 2048 KB > physical id : 0 > siblings : 2 > core id : 1 > cpu cores : 2 > fdiv_bug : no > hlt_bug : no > f00f_bug : no > coma_bug : no > fpu : yes > fpu_exception : yes > cpuid level : 10 > wp : yes > flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe lm constant_tsc pni monitor ds_cpl est tm2 ssse3 cx16 xtpr lahf_lm > bogomips : 4388.99 > clflush size : 64 > dom@lagrange:~/mersenne-random-0.1.1/tests> make > ghc -O2 -ddump-simpl-stats -no-recomp Unit.hs --make > [1 of 1] Compiling Main ( Unit.hs, Unit.o ) > > ==================== FloatOut stats: ==================== > 154 Lets floated to top level; 35 Lets floated elsewhere; from 40 Lambda groups > > > > ==================== FloatOut stats: ==================== > 133 Lets floated to top level; 14 Lets floated elsewhere; from 34 Lambda groups > > > > ==================== Grand total simplifier statistics ==================== > Total ticks: 8378 > > 2022 PreInlineUnconditionally > 1760 PostInlineUnconditionally > 991 UnfoldingDone > 132 RuleFired > 1 *# > 15 +# > 25 ++ > 1 <# > 3 ==#->case > 2 SC:a0 > 1 SC:a_s2sW0 > 1 SPEC GHC.Num.- > 2 SPEC GHC.Real.$p1Integral > 2 SPEC GHC.Real.$p1Real > 2 SPEC GHC.Real.$p2Real > 3 SPEC Main.speed > 3 SPEC System.Random.random > 1 eftInt > 9 fold/build > 14 foldr/app > 1 fromIntegral/Word->Int > 1 int2Double# > 1 int2Word# > 3 map > 2 mapList > 1 minimumInt > 2 remInt# > 2 take > 2 takeList > 17 unpack > 6 unpack-append > 9 unpack-list > 212 LetFloatFromLet > 1 EtaReduction > 2874 BetaReduction > 27 CaseOfCase > 341 KnownBranch > 3 CaseElim > 2 CaseIdentity > 13 FillInCaseDefault > 22 SimplifierDone > > > Linking Unit ... > Unit.o: In function `s4Da_info': > (.text+0x1b21): undefined reference to `genrand_real2' > Unit.o: In function `s4RA_info': > (.text+0x3e75): undefined reference to `genrand_real2' > Unit.o: In function `s4S4_info': > (.text+0x3f61): undefined reference to `genrand_real2' > Unit.o: In function `s5su_info': > (.text+0x40bc): undefined reference to `genrand_real2' > /usr/local/lib/mersenne-random-0.1.1/ghc-6.9.20080517/libHSmersenne-random-0.1.1.a(Mersenne.o): In function `mersennezmrandomzm0zi1zi1_SystemziRandomziMersenne_zdwa2_info': > ghc13223_0.hc:(.text+0x1a3): undefined reference to `gen_rand64_mix' > /usr/local/lib/mersenne-random-0.1.1/ghc-6.9.20080517/libHSmersenne-random-0.1.1.a(Mersenne.o): In function `s2J1_info': > ghc13223_0.hc:(.text+0x91d): undefined reference to `gen_rand64_mix' > /usr/local/lib/mersenne-random-0.1.1/ghc-6.9.20080517/libHSmersenne-random-0.1.1.a(Mersenne.o): In function `s2JZ_info': > ghc13223_0.hc:(.text+0xb3d): undefined reference to `genrand_real2' > /usr/local/lib/mersenne-random-0.1.1/ghc-6.9.20080517/libHSmersenne-random-0.1.1.a(Mersenne.o): In function `s2LJ_info': > ghc13223_0.hc:(.text+0xf8d): undefined reference to `gen_rand64_mix' > /usr/local/lib/mersenne-random-0.1.1/ghc-6.9.20080517/libHSmersenne-random-0.1.1.a(Mersenne.o): In function `s35i_info': > ghc13223_0.hc:(.text+0x1397): undefined reference to `genrand_real2' > /usr/local/lib/mersenne-random-0.1.1/ghc-6.9.20080517/libHSmersenne-random-0.1.1.a(Mersenne.o): In function `s36A_info': > ghc13223_0.hc:(.text+0x1517): undefined reference to `gen_rand64_mix' > collect2: ld returned 1 exit status > make: *** [all] Error 1

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Newbie Q: Overloading and type classes
by Dmitri O.Kondratiev 08 Jun '08

08 Jun '08

{-- I try to define class Store that will group types implmenting different storage mechanisms . All types should support two functions: 1) put (key, value) pair into storage 2) get value from storage corresponding to the given key As an example I start with the following storage types: --} -- simple memory cell data OneCell k v = Cell(k, v) -- list of cells data CellList k v = CLst [(k, v)] {-- First, without grouping these types into any class, just to illustrate what these types should do, I define the following functions: --} {-- put::(k, v) -> OneCell k v -> OneCell k v put (k1, v1) (Cell(k, v)) = Cell(k1, v1) get :: Eq k => k -> OneCell k v -> Maybe v get k (Cell (_, v)) = Just v c1 ::OneCell String Int c1 = Cell("one", 1) putLst :: (k,v) -> CellList k v -> CellList k v putLst (k,v) (CLst xs) = CLst ((k,v) : xs) getLst :: Eq k => k -> CellList k v -> Maybe v getLst k (CLst xs) = lookup k xs cl1 = CLst [("one",1),("two",2),("three",3)] --} {-- These work as expected. Now I try to define Store class that should allow me to overload put & get functions: --} class Store s where put :: Eq k => (k, v) -> s -> s get :: k s -> Maybe v {-- instance Store OneCell where put (k1, v1) (Cell(k, v)) = Cell(k1, v1) get k (Cell (_, v)) = Just v --} {-- I get the following error: `OneCell' is not applied to enough type arguments Expected kind `*', but `OneCell' has kind `* -> * -> *' In the instance declaration for `Store OneCell' --} instance Store CellList where put (k,v) (CLst xs) = CLst ((k,v) : xs) get k (CLst xs) = lookup k xs {-- I get the following error: `CellList' is not applied to enough type arguments Expected kind `*', but `CellList' has kind `* -> * -> *' In the instance declaration for `Store CellList' --} What should I do to create Store class? Thanks! -- Dmitri O. Kondratiev dokondr(a)gmail.com http://www.geocities.com/dkondr

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[ANN] Bindings to Xen Control (xenctrl.h)
by Thomas M. DuBuisson 08 Jun '08

08 Jun '08

All, I'm just getting started with hsXenCtrl [1] as both a fun way to play with Xen and become proficient with Haskell FFI. Once I get my community.haskell.org account squared away I'll likely setup a public darcs repo (and a homepage somewhere). As for modules: I intend to expand on the trival FFI bindings in System.Xen.CBindings and there'll be a higher level interface in System.Xen (functions will standardize on returning Either or throwing exceptions, hiding the xc_handle open/close, etc). Typical Disclaimers: The _only_ thing I've actually done with this, just tonight, is pause / unpause domains. API is subject to change! Only my exact build of Xen is sure to work, and no promise even then. TomMD [1] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hsXenCtrl

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Re: Fwd: installing happy 1.17
by Duncan Coutts 08 Jun '08

08 Jun '08

On Sat, 2008-06-07 at 09:36 -0700, Thomas Hartman wrote: > cabal issue? Yes and no. What is happening is that there are several versions of the Cabal library installed. In particular Cabal-1.3.12 and Cabal-1.5.2. The happy package uses build-type Custom so cabal-install compiles the Setup.lhs script. The question is what version of the Cabal library should it use? The happy.cabal file specifies cabal-version: >= 1.2 so we'd better respect that. But even then we have several choices. Currently it just picks the highest one of the remaining choices. In this case that meant Cabal-1.5.2 -- the latest development version. This version turns out to have API changes that means that we get a type error when compiling Setup.lhs. As it happens, if cabal-install had picked one of the other choices then it would have compiled ok because the 1.2.x and upcoming 1.4.x series do not have those api changes. The immediate workarounds are: * unregister Cabal-1.5.2 * cabal install happy --cabal-lib-version 1.3.12 Perhaps a better solution is for cabal-install to choose the version of the Cabal library differently. Of course it has to be within the hard constraints specified in the .cabal file and on the command line. But after that perhaps it should prefer the version of the Cabal library that it itself was built with and at second preference the latest version in the same major series. The last preference would be as now, the latest version available. Sound sensible? Duncan > ---------- Forwarded message ---------- > From: Thomas Hartman <tphyahoo(a)gmail.com> > Date: 2008/6/7 > Subject: installing happy 1.17 > To: haskell <haskell-cafe(a)haskell.org> > > > I had a problem installing happy 1.17 (same result with happy head). > This appears to be required for installing happs-hsp-template via > cabal install. > > thanks for any advice! > > Thomas. > > ***** > > thartman@thartman-laptop:~/haskellInstalls/smallInstalls>darcs get > --partial http://darcs.haskell.org/happy/ > ********************** > Copying patch 87 of 87... done. > Applying patch 86 of 86... done. > Finished getting. > > thartman@thartman-laptop:~/haskellInstalls/smallInstalls>cd happy > > thartman@thartman-laptop:~/haskellInstalls/smallInstalls/happy>runghc > Setup.lhs configure > > Setup.lhs:30:43: Not in scope: `buildVerbose' > thartman@thartman-laptop:~/haskellInstalls/smallInstalls/happy>cabal --version > cabal-install version 0.4.9 > using version 1.3.12 of the Cabal library > thartman@thartman-laptop:~/haskellInstalls/smallInstalls/happy>ghc-pkg > list | grep -i cabal > Cabal-1.2.3.0, Cabal-1.3.11, Cabal-1.3.12, Cabal-1.5.2,

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Re: [Haskell-cafe] example of FFI FunPtr
by Galchin, Vasili 08 Jun '08

08 Jun '08

Hi Claude, I want to do an incremental "experiment". I want just want to pass a C function to "callback" to a Haskell function. ??? Thanks, Vasili On Thu, Jun 5, 2008 at 4:21 AM, Claude Heiland-Allen < claudiusmaximus(a)goto10.org> wrote: > Galchin, Vasili wrote: > >> Hello, >> >> I want to model a Haskell function that is a callback from C. I have >> only found one example in the unix package's Semaphore.hsc, which >> apparently >> is not used. I want to be able to marshall a Haskell function that is a >> first class citizen residing in a Haskell data type and pass to a C >> function >> via FFI. Are there examples of this? >> > > Attached is a simple example. > > The main thing to note is 'foreign import ccall "wrapper"' which gives you > a factory for turning Haskell functions into foreign function pointers. > > More information: > > http://www.cse.unsw.edu.au/~chak/haskell/ffi/<http://www.cse.unsw.edu.au/%7Echak/haskell/ffi/> > > > Claude > -- > http://claudiusmaximus.goto10.org > > > CallBacker: CallBacker.hs callerback.c callerback.h > ghc -O2 -Wall -fffi -o CallBacker CallBacker.hs callerback.c > >

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Patrick Perry's BLAS package
by Andrzej Jaworski 08 Jun '08

08 Jun '08

Hi, Indeed, this has been long awaited. Long live Patrick!!! And continue the good work:-) However, such essential work shouldn't be dependent on heroic effort of an individual. If Haskell is to remain non-commercial a disciplined community effort should be taken akin to Pythonian. Perhaps also thouse of you who teach Haskell could better use cheap labour of students, after all Haskell's module system is not all that weak;-) Cheers, -A.J.

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Dynamic curiosity
by Gökhan San 08 Jun '08

08 Jun '08

Hello All, I've recently modified my existing project to support dynamic data (using 'Data.Dynamic'), and despite my earlier benchmarks on 'Dynamic', the program slowed down by a factor of 10. Profiler says that 'fromDynamic' is consuming 60% of the CPU time (with -O2). Using the below function instead of 'fromDynamic' seems to make coercion 20 times faster (thereby solving my problem): > {-# OPTIONS -fglasgow-exts #-} > import GHC.Prim > data Dynamic' = Dynamic' TypeRep Any > fromDynamic' :: forall a. Typeable a => Dynamic -> Maybe a > fromDynamic' d = > let Dynamic' t v = unsafeCoerce# d > in if t == typeOf (undefined :: a) > then Just (unsafeCoerce# v) > else Nothing I was able to reproduce the same result from scratch. The only difference with the standard implementation (I put it below for reference), other than the first ugly unsafeCoerce#, seems to be existential quantification (i.e. When I replace "if t == typeOf (undefined :: a) ..." with the "case ..." below, performance goes down again.). > fromDynamic :: Typeable a => Dynamic -> Maybe a > fromDynamic (Dynamic t v) = > case unsafeCoerce v of > r | t == typeOf r -> Just r > | otherwise -> Nothing So what is causing the improvement, or am I missing something? Thanks. -- Gokhan

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Teaching Monads
by Ronald Guida 08 Jun '08

08 Jun '08

Monads in Haskell are a topic that I, like most beginners, find difficult and "mind-twisting". Now that I think I understand monads, they seem to be very simple; I've read that this is a common experience. So I wonder, what would it take to help beginners catch on with a minimum of fuss or frustration? The plethora of monad tutorials out there is clear evidence that plenty of others have wondered the same thing. What made monads "click" for me is when I understood the following things: 1. When monads are being used, closures are almost always involved. 2. These closures naturally arise when desugaring do-syntax. do x1 <- m1 m1 >>= (\x1 -> x2 <- m2 m2 >>= (\x2 -> [Eq1] x3 <- m3 m3 >>= (\x3 -> return (f x1 x2 x3) return (f x1 x2 x3)))) 3. These closures are extremely similar to the closures that arise when desugaring let-syntax. let x1 = f1 in f1 -$ (\x1 -> Where: let x2 = f2 in f2 -$ (\x2 -> (-$) :: a -> (a -> b) -> b let x3 = f3 in f3 -$ (\x3 -> x -$ f = f x f x1 x2 x3 f x1 x2 x3))) 4. While I can think of a monad as a fancy container that holds an element of type "t", it might be more accurate to think of a monad as a container that merely displays the type "t" as a label for its contents. The container might hold one object of type "t", or it might hold several. It might not be holding any at all. Perhaps the container /never/ holds an object of type "t", but instead it holds a set of instructions to produce such an object. (e.g. Reader, State). Naturally, it's hard to illustrate nested closures, higher-order functions, and objects that aren't really there. It's easy to illustrate a sequential scheme where a single "thing" passes through a series of operations, while some related data travels in parallel. m1 >>= f1 >>= f2 >>= f3 [Eq2] In any case, the extreme similarity between desugared "do" and desugared "let" leads me to think of the concepts of a manual plumbing system and a monadic plumbing system. Basically, a manual plumbing system is what I have if I'm threading information down through a series of nested function calls in a certain stereotypical way. A monadic plumbing system is what I get when I introduce the appropriate monad to encapsulate my threading. In fact, if I look at Wadler [*], there are three examples of an evaluator that use what I'm calling "manual plumbing". In section 2.5, the operations required of a monad (return, bind) pretty much just drop right out. Wadler even points out the similarity between "bind" and "let". Now that I finally "get it", I feel that the Wadler paper, section 2.5 in particular, is probably a better introduction than many of the monad tutorials out there. Moreover, I feel that for /some/ of the tutorials out there, they spend too much time and too many illustrations explaining things like [Eq2], and then they quickly present do-notation and gloss over [Eq1]. For me, I found that that the concepts of "manual plumbing" and "monadic plumbing" were key to actually grasping the Wadler paper and understanding what monads are. In particular, I feel that these two concepts might be a way to help other beginners catch on as well. OK, so before I attempt to write a monad tutorial based on "manual plumbing" and "monadic plumbing", I would like to know, does anyone else think this is a good idea? [*] "Monads for Functional Programming". (http://homepages.inf.ed.ac.uk/wadler/papers/marktoberdorf/baastad.pdf)

4 3

ANNOUNCE: Cabal-1.4 release candidate
by Duncan Coutts 08 Jun '08

08 Jun '08

Hi everyone, == Cabal-1.4 release candidate == The second release candidate of Cabal-1.4 is out: http://haskell.org/cabal/download.html Please test and report bugs: http://hackage.haskell.org/trac/hackage/ The aim for the Cabal-1.4 release is to get various fixes and improvements into the hands of developers and to support a release of cabal-install. == cabal-install == A snapshot of cabal-install is also available: http://haskell.org/cabal/download.html It requires the zlib and HTTP packages (both are available from hackage). Bug reports should go in the same trac as above. cabal-install is intended to be the standard command line interface to the whole Cabal/Hackage system. It replaces the "runhaskell Setup.hs" interface and a few other tools you may or may not have heard of (cabal-setup, cabal-upload, cabal-get). cabal-install is usable now and we will be making a proper release some time after the Cabal-1.4 release. == Testing == We are particularly interested in finding regressions from Cabal-1.2.x or any important fixes that will require API changes since once we release 1.4 we have to maintain API compatibility for the rest of the 1.4.x series. This is also an excellent opportunity to make sure your favourite bug or feature request is properly described in our bug tracker: http://hackage.haskell.org/trac/hackage/ To help us guide development priorities please add yourself to the ticket's cc list and describe why that bug or feature is important to you. == Compatibility == We have tried to preserve compatibility with all packages that worked with the Cabal-1.2.x series. That is, packages that can be built using Cabal (including custom Setup.hs scripts) but not packages that directly import and use the Cabal API. Packages that directly import and use the Cabal api will need updating. This affects packages that build distro packages for example, rpm debs etc. Currently we know of only one package on hackage which has a Setup.hs script that compiles with 1.2 but fail to compile with 1.4. Takusen, will require an update to be able to work with both Cabal-1.2.x and 1.4.x. A patch has been sent to the maintainers of Takusen. == Credits == On behalf of the Cabal hackers and the community generally I'd like to thank the large number of people who have contributed patches during this development series. Previously I was rather worried that we were not getting enough contributors to fix bugs and do new feature development, but now I'm very pleased. :-) == Get involved == Of course there's still a lot to do! We have big plans for Cabal-2.0, cabal-install and the Hackage website. So if you're interested in helping out with this core infrastructure project then: * subscribe to the cabal-devel mailing list: http://www.haskell.org/mailman/listinfo/cabal-devel * grab the source: http://haskell.org/cabal/code.html * read the guide to the source code: http://hackage.haskell.org/trac/hackage/wiki/SourceGuide * take a look at our list of bugs and feature requests: http://hackage.haskell.org/trac/hackage/report/12 especially the easy tickets: http://hackage.haskell.org/trac/hackage/report/13 Duncan (wearing his Cabal release manager hat)

2 1

installing happy 1.17
by Thomas Hartman 08 Jun '08

08 Jun '08

I had a problem installing happy 1.17 (same result with happy head). This appears to be required for installing happs-hsp-template via cabal install. thanks for any advice! Thomas. ***** thartman@thartman-laptop:~/haskellInstalls/smallInstalls>darcs get --partial http://darcs.haskell.org/happy/ ********************** Copying patch 87 of 87... done. Applying patch 86 of 86... done. Finished getting. thartman@thartman-laptop:~/haskellInstalls/smallInstalls>cd happy thartman@thartman-laptop:~/haskellInstalls/smallInstalls/happy>runghc Setup.lhs configure Setup.lhs:30:43: Not in scope: `buildVerbose' thartman@thartman-laptop:~/haskellInstalls/smallInstalls/happy>cabal --version cabal-install version 0.4.9 using version 1.3.12 of the Cabal library thartman@thartman-laptop:~/haskellInstalls/smallInstalls/happy>ghc-pkg list | grep -i cabal Cabal-1.2.3.0, Cabal-1.3.11, Cabal-1.3.12, Cabal-1.5.2,

1 0

Question about kinds
by Klaus Ostermann 07 Jun '08

07 Jun '08

Why does the code below not pass the type checker? If I could explictly parameterize y with the type constructor Id (as e.g. in System F), then 'y Id' should have the type Int -> Int and hence "y Id x" should be OK, but with Haskell's implicit type parameters it does not work. So, how can I make this work? Klaus ------------ type Id a = a x :: Id Int x = undefined y :: (a Int) -> (a Int) y = undefined test = y x Error: Couldn't match expected type `a Int' against inferred type `Id Int' In the first argument of `y', namely `x' In the expression: y x In the definition of `test': test = y x -- View this message in context: http://www.nabble.com/Question-about-kinds-tp17701553p17701553.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

6 5

What is the maturity of Haskell Web Frameworks
by Aditya Siram 06 Jun '08

06 Jun '08

I am building a web-app that, in broad strokes, allows a leader to assign tasks to team members and allows team members to accept/reject/pick tasks that they want to do. I really like Haskell and I would like to use it to implement the solution. Are frameworks like Happs ready? Not so much in terms of documentation, but in functionality and stability. -Deech _________________________________________________________________ Give to a good cause with every e-mail. Join the i’m Initiative from Microsoft. http://im.live.com/Messenger/IM/Join/Default.aspx?souce=EML_WL_ GoodCause

15 20

Analysing music
by Achim Schneider 06 Jun '08

06 Jun '08

The recent discussion about Markoff chains inspired me to try to train one with all the Bach midi's I have on my disk, collecting statistics on what intervals tend to get played simultaneously, which follow others and in which way the pitch offsets from its mean, so that melodies fall and raise "naturally". The rationale is that if it's Bach, it's harmonious but not respecting any kind of usual chord progression. So far, I got (a bit confused around the edges): getMid mf = do mid <- MidiLoad.fromFile mf return $ MidiRead.retrieveTracks mid toMelody :: MidiMusic.T -> StdMelody.T toMelody = Music.mapNote f where f note = let body = MidiMusic.body note in Melody.Note StdMelody.na (MidiMusic.pitch body) main = do args <- Env.getArgs let mf:[] = args m <- getMid mf putStr $ Format.prettyMelody $ Optimise.all $ Music.chord $ map (\m -> Music.line $ map toMelody m) m which results in chord [e 3 bn na, chord [b 2 wn na, line [hnr, d 3 wn na, hnr, cs 3 hn na, a 2 hn na, chord [cs 3 hn na, line [b 2 hn na, c 3 hn na]]]]] , for a set of random clicks in rosegarden's matrix editor. Right now, I'm desperately searching for functions that can help me analyse this beast, which afaict right now works best by having a multitude of transformations (e.g. one big top-level chord with maximum polyphony and a hell a lot of rests) that provide easy access to whatever information is needed. Does anyone of you know about previous work in this area? I don't want to break cultural imperatives by not being as lazy as possible. -- (c) this sig last receiving data processing entity. Inspect headers for past copyright information. All rights reserved. Unauthorised copying, hiring, renting, public performance and/or broadcasting of this signature prohibited.

6 7

How would you hack it?
by Andrew Coppin 06 Jun '08

06 Jun '08

So anyway, today I found myself wanting to build a program that generates some test data. I managed to make it *work* without too much difficulty, but it wasn't exactly "elegant". I'm curios to know how higher-order minds would approach this problem. It's not an especially "hard" problem, and I'm sure there are several good solutions possible. I have a file that contains several thousand words, seperated by white space. [I gather that on Unix there's a standard location for this file?] I want to end up with a file that contains a randomly-chosen selection of words. Actually, I'd like the end result to be a LaTeX file, containing sections, subsections, paragraphs and sentences. (Although obviously the actual sentences will be gibberish.) I'd like to be able to select how big the file should be, to within a few dozen characters anyway. Exact precision is not required. How would you do this? The approach I came up with is to slurp up the words like so: raw <- readFile "words.txt" let ws = words raw let n = length ws let wa = listArray (1,n) ws (I actually used lazy ByteStrings of characters.) So now I have an array of packed ByteStrings, and I can pick array indexes at random and use "unwords" to build my gibberish "sentences". The fun part is making a sentence come out the right size. There are two obvious possibilities: - Assume that all words are approximately N characters long, and estimate how many words a sentence therefore needs to contain to have the required length. - Start with an empty list and *actually count* the characters as you add each word. (You can prepend them rather than append them for extra efficiency.) I ended up taking the latter approach - at least at the sentence level. What I actually did was to write a function that builds lists of words. There is then another function that builds several sublists of approximately the prescribed lengths, inserts some commas, capitalises the first letter and appends a fullstop. This therefore generates a "sentence". After that, there's a function that builds several sentences of random size with random numbers of commas and makes a "paragraph" out of them. Next a function gathers several paragraphs and inserts a randomly-generated subsection heading. A similar function takes several subsections and adds a random section heading. In my current implementation, all of this is in the IO monad (so I can pick things randomly). Also, the whole thing looks very repetative and really if I thought about it harder, it ought to be possible to factor it out into something smaller and more ellegant. The clause function builds clauses of "approximately" the right size, and each function above that (sentence, paragraph, subsection, section) becomes progressively less accurate in its sizing. On the other hand, the final generated text always for example has 4 subsections to each section, and they always look visually the same size. I'd like to make it more random, but all the code works by estimating "roughly" how big a particular construct is, and therefore how many of then are required to full N characters. For larger and larger N, actually counting this stuff would seem somewhat inefficient, so I'm estimating. But that makes it hard to add more randomness without losing overall size control. The final file can end up being a fair way different in size to what I requested, and has an annoyingly regular internal structure. But essentially, it works. It would be nice to modify the code to generate HTML - but since it's coded so simple-mindedly, that would be a copy & paste job. Clearly, what I *should* have done is think more about a good abstraction before writing miles of code. ;-) So how would you guys do this?

11 23

getting set up in ubuntu
by Martin DeMello 06 Jun '08

06 Jun '08

I finally ditched sabayon for ubuntu (one wireless problem too many), and now I'm slowly getting stuff set up on it. Any Ubuntu people care to share their experiences? I'm especially looking for guidelines on what to install via apt-get and what to install independently. Also, while I'm making Major Life Changes I might as well check out xmonad :) If anyone has made the switch from fluxbox, do share how it went. martin

3 4

automatically deriving Map and Filter on datatypes etc.
by Cetin Sert 06 Jun '08

06 Jun '08

Hi ^_^, Let's say we have the following data type and functions: data Tab a = (:↺:) | a :↓: Tab a | Tab a :↙↘: (Tab a,Tab a) deriving (Eq, Show, Read) map f (:↺:) = (:↺:) map f (a :↓: t) = f a :↓: map f t map f (h :↙↘: (l,r)) = map f h :↙↘: (map f l, map f r) filter p (:↺:) = (:↺:) filter p (a :↓: t) | p a = filter p t | otherwise = a :↓: filter p t filter p (h :↙↘: (l,r)) = filter p h :↙↘: (filter p l, filter p r) is it possible to automatically derive map and filter? data Tab a = (:↺:) | a :↓: Tab a | Tab a :↙↘: (Tab a,Tab a) deriving (Eq, Show, Read, Map, Filter) If not, do you think it might be nice to have something like this in the future? Best Regards, Cetin Sert

8 8

hmatrix
by Anatoly Yakovenko 06 Jun '08

06 Jun '08

What is the most efficient way to update a position in a matrix or a vector? I came up with this: updateVector :: Vector Double -> Int -> Double -> Vector Double updateVector vec pos val = vec `add` v2 where v2 = fromList $ (replicate (pos) 0.0) ++ ((val - (vec @> pos)):(replicate ((dim vec)- pos - 1) 0.0)) but this seems pretty inefficient to me. thanks, Anatoly

4 12

More on performance
by Don Stewart 06 Jun '08

06 Jun '08

I wrote up the second part of the tour of understanding low level performance in GHC here, http://reddit.com/r/programming/info/6lx36/comments/ Follows on from the discussion last week about various performance related things. Enjoy. -- Don

12 13

Ubuntu and ghc
by Galchin, Vasili 06 Jun '08

06 Jun '08

Hello, https://bugs.launchpad.net/ubuntu/+source/gtk2hs/+bug/229489 .... this is almost identical to my problem. I am just trying to help others on this list who are using Ubuntu Linux to avoid my predicament! Kind regards, Vasili

11 27

re: very hard to build darcs with win32 ghc-6.8.2!
by Tim Newsham 06 Jun '08

06 Jun '08

Here's the wrapup, thanks to those who replied: - the haskell zlib package on hackage no longer requires that zlib (the C library) be prebuilt. It includes sources itself and builds and installs them using Cabal. - the haskell zlib package is not used by darcs. It links against libz.a directly. You do need to have libz.a somehow to build darcs. - the darcs link error with "SleepEx" is caused because it uses "foreign import ccall" when it should use "foreign import stdcall". Fixing the decl in src/win32/System/Posix.hs to stdcall fixes this issue. I still think its odd that ghc's "gcc" is not very useable outside of Cabal, but in this case it has no bearing on the zlib package. If you choose to build "libz.a" (the C library) from sources using this gcc it will be hard, but you could also get it from an external source (such as the prebuilt libcurl library package). Tim Newsham http://www.thenewsh.com/~newsham/

1 0

Laziness leaks
by Ronald Guida 06 Jun '08

06 Jun '08

I was looking at the real time queues in [1] and I wanted to see what would happen if I tried to write one in Haskell. The easy part was translating the real time queue from [1], p43 into Haskell. The hard part is testing to see if the rotations really happen what they should. Basically, I decided to use Debug.Trace.trace to see when rotations were actually occurring. I pushed the numbers 1 to 10 into the queue, and then I popped the queue ten times. What I found is that none of the rotations would actually take place until the first time I actually tried to /display the value/ of a popped element. What I realized is that my test driver is lazy. I figured out that I could put a bunch of 'seq' functions in the test driver to get the rotations to happen. My demonstration code is in: http://hpaste.org/8080 This leads to two questions: 1. If I find a laziness leak, is 'seq' the appropriate way to plug it? 2. Is there any way to systematically search for or detect laziness leaks?

12 17

GHCi gives type signature that won't compile.
by A A 06 Jun '08

06 Jun '08

Hi All I can successfully compile the following code using ghci import Data.Array.IArray makeArray (lower, upper) f = listArray (lower, upper) [(f i) | i <- [lower..upper] tridiagonal_solve (a, b, c, d, (lower, upper)) = x where gen_array f = (makeArray (lower, upper) f) x = gen_array x_f where x_f i | i == upper = (d_dash ! upper) | otherwise = (d_dash ! i) - (c_dash ! i) * (x ! (i + 1)) d_dash = gen_array d_dash_f where d_dash_f i | i == lower = (d ! lower) / (b ! lower) | otherwise = ((d ! i) - (d_dash ! (i - 1)) * (a ! i)) / ((b ! i) - (c_dash ! (i - 1)) * (a ! i)) c_dash = gen_array c_dash_f where c_dash_f i | i == lower = (c ! lower) / (b ! lower) | otherwise = (c ! i) / ((b ! i) - (c_dash ! (i - 1)) * (a ! i)) I then attempted to write a type signature for tridiagonal_solve. I didn't succeed at this however, all of my type signatures gave compile errors when attempting to load them in ghci. I asked in the #haskell channel, and they suggested that I try the type signature from ghci :type function. So I removed any type signatures, and reloaded the file in ghci, and typed ":type tridiagonal_solve" which produced the following output: tridiagonal_solve :: (IArray a3 e, IArray a6 e, IArray a7 e, Fractional e, Ix a, Num a, IArray a4 e, IArray a2 e, IArray a5 e, IArray a1 e, Enum a) => (a4 a e, a2 a e, a1 a e, a5 a e, (a, a)) -> a7 a e I then attempted to paste this into my code, the resulting code looking like this: import Data.Array.IArray makeArray (lower, upper) f = listArray (lower, upper) [(f i) | i <- [lower..upper]] tridiagonal_solve :: (IArray a3 e, IArray a6 e, IArray a7 e, Fractional e, Ix a, Num a, IArray a4 e, IArray a2 e, IArray a5 e, IArray a1 e, Enum a) => (a4 a e, a2 a e, a1 a e, a5 a e, (a, a)) -> a7 a e tridiagonal_solve (a, b, c, d, (lower, upper)) = x where gen_array f = (makeArray (lower, upper) f) x = gen_array x_f where x_f i | i == upper = (d_dash ! upper) | otherwise = (d_dash ! i) - (c_dash ! i) * (x ! (i + 1)) d_dash = gen_array d_dash_f where d_dash_f i | i == lower = (d ! lower) / (b ! lower) | otherwise = ((d ! i) - (d_dash ! (i - 1)) * (a ! i)) / ((b ! i) - (c_dash ! (i - 1)) * (a ! i)) c_dash = gen_array c_dash_f where c_dash_f i | i == lower = (c ! lower) / (b ! lower) | otherwise = (c ! i) / ((b ! i) - (c_dash ! (i - 1)) * (a ! i)) When I attempt to load this into ghci, I recieve the following error: [1 of 1] Compiling Main ( main.lhs, interpreted ) main.lhs:29:11: Could not deduce (IArray a1 e) from the context (IArray a3 e, IArray a6 e, IArray a7 e, Fractional e, Ix a2, Num a2, IArray a4 e, IArray a21 e, IArray a5 e, IArray a11 e, Enum a2) arising from a use of `gen_array' at main.lhs:29:11-28 Possible fix: add (IArray a1 e) to the context of the type signature for `tridiagonal_solve' In the expression: gen_array d_dash_f In the definition of `d_dash': d_dash = gen_array d_dash_f where d_dash_f i | i == lower = (d ! lower) / (b ! lower) | otherwise = ((d ! i) - (d_dash ! (i - 1)) * (a ! i)) / ((b ! i) - (c_dash ! (i - 1)) * (a ! i)) In the definition of `tridiagonal_solve': tridiagonal_solve (a, b, c, d, (lower, upper)) = x where gen_array f = (makeArray (lower, upper) f) x = gen_array x_f where x_f i | i == upper = (d_dash ! upper) | otherwise = (d_dash ! i) - (c_dash ! i) * (x ! (i + 1)) d_dash = gen_array d_dash_f where d_dash_f i | i == lower = (d ! lower) / (b ! lower) | otherwise = ((d ! i) - (d_dash ! (i - 1)) * (a ! i)) / ((b ! i) - (c_dash ! (i - 1)) * (a ! i)) c_dash = gen_array c_dash_f where c_dash_f i | i == lower = (c ! lower) / (b ! lower) | otherwise = (c ! i) / ((b ! i) - (c_dash ! (i - 1)) * (a ! i)) main.lhs:35:11: Could not deduce (IArray a e) from the context (IArray a3 e, IArray a6 e, IArray a7 e, Fractional e, Ix a2, Num a2, IArray a4 e, IArray a21 e, IArray a5 e, IArray a11 e, Enum a2) arising from a use of `gen_array' at main.lhs:35:11-28 Possible fix: add (IArray a e) to the context of the type signature for `tridiagonal_solve' In the expression: gen_array c_dash_f In the definition of `c_dash': c_dash = gen_array c_dash_f where c_dash_f i | i == lower = (c ! lower) / (b ! lower) | otherwise = (c ! i) / ((b ! i) - (c_dash ! (i - 1)) * (a ! i)) In the definition of `tridiagonal_solve': tridiagonal_solve (a, b, c, d, (lower, upper)) = x where gen_array f = (makeArray (lower, upper) f) x = gen_array x_f where x_f i | i == upper = (d_dash ! upper) | otherwise = (d_dash ! i) - (c_dash ! i) * (x ! (i + 1)) d_dash = gen_array d_dash_f where d_dash_f i | i == lower = (d ! lower) / (b ! lower) | otherwise = ((d ! i) - (d_dash ! (i - 1)) * (a ! i)) / ((b ! i) - (c_dash ! (i - 1)) * (a ! i)) c_dash = gen_array c_dash_f where c_dash_f i | i == lower = (c ! lower) / (b ! lower) | otherwise = (c ! i) / ((b ! i) - (c_dash ! (i - 1)) * (a ! i)) My question is, what should the type signature for tridiagonal_solve actually be? I would like one that doesn't limit the generality of tridiagonal_solve because I would like to pass different array types in the one function invocation, as long as they have the same index and element types. I'm happy if other functions need type signatures as well. I'm using ghc 6.8.2 on windows, though I get a similar issue with ghc 6.4.1. Thanks. Clinton

3 2

example of FFI FunPtr
by Galchin, Vasili 05 Jun '08

05 Jun '08

Hello, I want to model a Haskell function that is a callback from C. I have only found one example in the unix package's Semaphore.hsc, which apparently is not used. I want to be able to marshall a Haskell function that is a first class citizen residing in a Haskell data type and pass to a C function via FFI. Are there examples of this? Thanks, Vasili

2 2

HDBC-odbc 1.1.4.4 fixes Windows linking problems
by John Goerzen 05 Jun '08

05 Jun '08

Hi, HDBC-odbc version 1.1.4.4 has been uploaded to Hackage. It fixes the problems some here have encountered regarding ODBC crashes or other similar odd behavior on Windows. Thanks to Andrew Appleyard for tracking down the problem and sending me a patch. The detailed explanation, if you're interested, is a ccall vs. stdcall issue in FFI. Details here: http://git.complete.org/hdbc-odbc?a=commit;h=cca312d9891d227094494dcee518f4… People that are not using HDBC-odbc on Windows will not find any difference or other changes in this version. -- John Goerzen Author, Foundations of Python Network Programming http://www.amazon.com/exec/obidos/tg/detail/-/1590593715

3 5

library for drawing charts
by Peter Gammie 05 Jun '08

05 Jun '08

Hello, Has anyone got some code for drawing charts? I don't mean graphs of functions, ala http://dockerz.net/twd/HaskellCharts and I don't mean calls to the Google Charts API ala http://community.livejournal.com/evan_tech/241080.html I would like something that can generate PNGs in memory, i.e. not directly to a file. This is close to what I have in mind: http://www.fred.net/brv/chart/ I'd like 2D pie charts, bar charts and something like a google-o-meter. Any pointers? cheers peter

4 5

Re: Having trouble with parallel Haskell
by Donnie Jones 05 Jun '08

05 Jun '08

Hello Bryan, 2008/6/4 Bryan O'Sullivan <bos(a)serpentine.com>: > I intended to write a half chapter or so about parallel programming in > Haskell for the book I'm working on, but I've been coming to the > conclusion that the time is not yet ripe for this. I hope it will be > helpful if I share my experiences here. > > Specifically, I was planning to write about parallel programming in pure > code: use of "par" and programming with strategies. > > The most substantial problem is that the threaded RTS in GHC 6.8.2 is > very crashy in the face of "par": about 90% of my runs fail with a > segfault or an assertion failure. Simon Marlow mentioned that this bug > is fixed, but I've been unsuccessful in building a GHC 6.8.3 release > candidate snapshot so far, so I can't verify this. > > When a run does go through, I have found it surprisingly difficult to > actually get both cores of a dual-core system to show activity. As > there are no tools I can use to see what is happening, I am stumped. It > is of course quite likely that I am doing something wrong that results > in unexpected dependencies, but I cannot find a means to gaining insight > into the problem. Although my Google Summer of Code project was not selected, I decided to go ahead and work on the Parallel Profiling Tools for GHC this Summer, with the help of Simon Marlow of course, for my Master's thesis. The work is nowhere near complete, as I just began working on it a couple of weeks ago. I was able to run the ParSort.hs program in your original post with my modified version of GHC HEAD that now supports parallel profiling. Hopefully, by the end of the Summer, Haskell's support for parallel profiling will be vastly improved. This is the example test I performed: ghc -parprof -threaded -o ParSort --make ParSort.hs time ./ParSort 1000000 +RTS -pN -N6 -RTS We have 1000000 elements to sort. Sorted all 1000000 elements. 28.04362s elapsed. real 0m36.060s user 0m44.107s sys 0m0.708s I have attached an Postscript file containing a graph that visualizes the parallel profiling data from the above test. A lot of work still needs to be done, but I just wanted to let you know that improvements are expected soon. Btw, ParSort.hs was taking advantage of both cores on my machine. Thank you. __ Donnie Jones

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very hard to build darcs with win32 ghc-6.8.2!
by Tim Newsham 05 Jun '08

05 Jun '08

I built darcs for win32 recently and it was much more difficult than it should be. Probably most of the blame goes to ghc-6.8.2 binary release for win32. Half of the effort is getting the zlib prereq working. Previously to build zlib for win32 ghc I did the following: http://www.haskell.org/pipermail/haskell-cafe/2007-March/023059.html However, now, the gcc binary for ghc-6.8.2 does not work as well as I would like which requires a bit more effort: - It did not automatically add mingw headers during compilation, and to fix this I had to force some extra flags. I built a shell script "xcc": #!/bin/sh GHC=/ghc/ghc-6.8.2 PATH=/c$GHC/gcc-lib:$PATH export PATH /c$GHC/gcc -I $GHC/include -I $GHC/include/mingw \ -I $GHC/gcc-lib/include -L $GHC/gcc-lib "$@" - During linking it did not find crt2.o and adding it to PATH and -L did not help, so I just copied wholesale all of /c/ghc/ghc-6.8.2/gcc-lib into my zlib source directory. - At this point I was able to build with: CC=./xcc ./configure --prefix=/c/ghc/ghc-6.8.2 \ --libdir=/c/ghc/ghc-6.8.2 make make install Why is the gcc in ghc's directory so non-functional? Ok, so with zlib (the C library) installed, the zlib haskell package installs properly. Dependency resolved. Next, to build darcs I had to configure it without libcurl support (or alternately spend time chasing down that dep, pass for now). Using cygwin I ran "./configure" which falsely uses the cygwin gcc for configuration checks, but since gcc is never used directly during the compilation process, that doesn't matter that much. I could have tried the "xcc" trick here again, but didn't bother. I ran into two problems during the build: - -Werror is specified in the GNUMakefile and there are many warnings. I just removed -Werror for now. - During linking it was not able to resolve "SleepEx" from src/win32/System/Posix.hs. I could not figure out what is going on here. I tried adding "-lkernel32" and "-L /ghc/ghc-6.8.2/gcc-lib -Lkernel32" to the Makefile and it still did not work even though /ghc/ghc-6.8.2/gcc-lib/libkernel32.a has SleepEx@8 defined(!) Finally I bit the bullet and hacked around this by noticing that mingw headers have _sleep() defined. I replaced the code in Posix.hs with: foreign import ccall "_sleep" c_sleep :: CULong -> IO () sleep :: Integer -> IO CInt sleep n = c_sleep (fromIntegral n) >> return (toEnum $ fromIntegral n) At this point darcs builds and the binary seems to work (so far). I don't know the implication of my sleep hack (which doesn't return the actual time slept). Here's a small test program which uses FFI to SleepEx which I was not able to get working with win32 ghc-6.8.2. ------ {-# OPTIONS -fglasgow-exts -fffi #-} module Main where import Foreign.C.Types foreign import ccall "SleepEx" c_SleepEx :: CUInt -> CInt -> IO CInt main = do putStrLn "start" n <- c_SleepEx (2*1000) 1 print n ------- So, what is going on with ghc-6.8.2? Why is the gcc so hard to use now? Why can't I get FFI working with standard win32 functions? Why aren't there prebuilt win32 darcs binaries anymore? Tim Newsham http://www.thenewsh.com/~newsham/

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[ANN] hs-pgms 0.1 -- Programmer's Minesweeper in Haskell
by Bertram Felgenhauer 05 Jun '08

05 Jun '08

Hi, I've just uploaded hs-pgms to hackage. It is a Haskell implementation of Programmer's Minesweeper [1], which allows programmers to implement minesweeper strategies and run them. (Note: ghc >= 6.8 is required.) hs-pgms uses MonadPrompt to achieve a clean separation between strategies, game logic, and presentation. There are two frontends, one command line frontend which is mainly useful for collecting statistics, and a GUI frontend, using gtk2hs, for watching the strategies in action. There's a git repo, see http://repo.or.cz/w/hs-pgms.git . enjoy, Bertram [1] http://www.ccs.neu.edu/home/ramsdell/pgms/index.html

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ICFP2008 Call for Poster proposals
by Matthew Fluet (ICFP Publicity Chair) 05 Jun '08

05 Jun '08

ICFP 2008 poster session September 21, 2008 Call for presentation proposals ICFP 2008 will feature a poster session for researchers and practitioners, including students. The session will provide friendly feedback for work that is in gestation or ongoing, as well as opportunities to meet each other and exchange ideas. We welcome poster submissions on all ICFP topics, especially presentations of - applications of and to functional programming; - recent work presented at more distant venues; and - ongoing work, whether or not submitted to ICFP. There will be no formal proceedings, but presenters will be invited to submit working notes, demo code, and other materials to supplement their abstract and poster. These materials will be released informally on a Web page dedicated to the poster session. An accepted submission is not intended to replace conference or journal publication. Persons interested in presenting a poster are invited to submit a one-page abstract in SIGPLAN conference style http://www.acm.org/sigs/sigplan/authorInformation.htm to the Web site https://www.softconf.com/s08/icfp08-posters/submit.html by June 30, 2008. The program committee will review the submissions for relevance and interest, and notify the authors by July 14, 2008. Accepted posters must be presented by the authors in person on Sunday, September 21, 2008. Important dates: Submission: Monday, June 30, 2008 Notification: Monday, July 14, 2008 Presentation: Sunday, September 21, 2008 Program committee: Benjamin Pierce (University of Pennsylvania) Colin Runciman (University of York) Chung-chieh Shan (Rutgers University)

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[ANNOUNCE] git-darcs-import 0.1
by Bertram Felgenhauer 05 Jun '08

05 Jun '08

Hi, I'm pleased to announce yet another tool for importing darcs repositories to git. Unlike darcs2git [1] and darcs-to-git [2], it's written in Haskell, on top of the darcs2 source code. The result is a much faster program - it can convert the complete ghc 6.9 branch (without libraries) in less than 15 minutes on my slightly dated machine (Athlon XP 2500+), which is quite fast [3]. Incremental updates work, too. The program is still rough around the edges, and there's some cosmetical work to do, especially with respect to converting author names. The program should recover from most errors, as long as nobody else modifies the destination repository. Nevertheless, it seems quite useable already. I hope somebody finds this useful. You can grab the source at http://int-e.home.tlink.de/haskell/git-darcs-import-0.1.tar.bz2 Look at the README for further information. Credits go to: David Roundy and all contributors for darcs2. The code base is surprisingly pleasant to work with. And of course, Linus Torvalds, Junio Hamano and all other git contributors. Enjoy, Bertram [1] http://repo.or.cz/w/darcs2git.git?a=shortlog [2] http://git.sanityinc.com/?p=darcs-to-git.git [3] http://nominolo.blogspot.com/2008/05/thing-that-should-not-be-or-how-to.html

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Installing Haskore under Windows
by David 04 Jun '08

04 Jun '08

Hi! I'm currently running ghc under Windows XP and want to play around with Haskore, but I'm a little confused about how to install it, or if it's even possible to use it with ghc. The 'readme' file contains this note: "Note that the file ghc_add/IOExtensions.hs is a partial replacement of a library file of the same name under Hugs. It does not work yet on Windows/GHC (where one has to distinguish between binary and text IO)." Does this mean I have to use Hugs rather than ghc? I have both Hugs and ghc installed, but I'd prefer to use ghc if possible. In either case, I find the install instructions (for Haskore, that is) a little confusing, probably because I'm also new to Haskell. Any help would be greatly appreciated. Thanks.

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problems with derive/TH
by Thomas Hartman 04 Jun '08

04 Jun '08

Haskellers/Chris, As part of my quest to better understand STM and eventually build a concurrent haskell server app, I checked out an embryonic haskell mud demo from Chris Smith's repo. It seemed like a great sample app. But I ran into a build issue that seems to have to do with derive/TH. I am assuming this used to work, but something changed, either in TH itself or switching from ghc6.6 to ghc6.8. From the error message (below) I surmise either a) M.Map based values used to automagically work with derive/TH, but no longer do... in which case I need to create this instance manually or b) this should still work, more or less... but I have to import the map instance via an additional module, or something like that. Any advice? Thomas. ***** This is the error I am getting: thartman@thartman-laptop:~/mud>cat _darcs/prefs/defaultrepo http://cdsmith.twu.net/demos/mud thartman@thartman-laptop:~/mud>ghc --version The Glorious Glasgow Haskell Compilation System, version 6.8.2 thartman@thartman-laptop:~/mud>runghc Setup.lhs configure; runghc Setup.lhs build Configuring mud-0.1... Preprocessing executables for mud-0.1... Building mud-0.1... [2 of 5] Compiling World ( World.hs, dist/build/mud/mud-tmp/World.o ) World.hs:42:0: No instances for (Eq (a (M.Map String Player)), Eq (a (M.Map ItemId Item)), Eq (a (M.Map PlayerId Player)), Eq (a (M.Map RoomId Room)), Eq (a RoomId)) arising from the 'deriving' clause of a data type declaration at World.hs:(42,0)-(50,14) Possible fix: add an instance declaration for (Eq (a (M.Map String Player)), Eq (a (M.Map ItemId Item)), Eq (a (M.Map PlayerId Player)), Eq (a (M.Map RoomId Room)), Eq (a RoomId)) When deriving the instance for (Eq (World a))

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A simple beginner question
by Adam Smyczek 04 Jun '08

04 Jun '08

Example: data SampleType = A | B Int | C String | D -- .... etc. sampleTypes = [A, B 5, C "test"] :: [SampleType] How do I find for example element A in the sampleTypes list? Do I have to create e.g.: isA :: SampleType -> Bool isA A = True isA _ = False for every constructor and use find? It feels like this is not the quicker method. Thanks, Adam

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Wouter-style expressions
by Ron Alford 04 Jun '08

04 Jun '08

Here's something that should be an easy extension of Wouter's approach to extensible datatypes, but I'm failing (possibly since it's 2:20am). I several classes of expressions I'm trying to represent (thus, Wouter's approach), and my first operation to implement over them is printing. Attached is a simplified version of what I'm doing. Expressions are composed of conjunctives (and) and atoms. Atoms are composed of a predicate string and a list of fillers (taken from 'Const' and 'Var'). For example (in a lisp like syntax): (and (pred c ?var1) (pred ?var1 ?var2)) To do this, I defined a 'Printable' class: class Functor f => Printable f where exprDoc :: f t -> Doc I think the 't' here will get me into trouble later. Combinations of printable types are also printable: instance (Printable f, Printable g) => Printable (f :+: g) where exprDoc (Inr x) = exprDoc x exprDoc (Inl y) = exprDoc y Constants, variables, and atoms are defined to be printable: instance Printable Var where exprDoc (Var name) = text ('?':name) instance Printable Const where exprDoc (Const name) = text name instance Printable f => Printable (Atomic (Expr f)) where exprDoc (Atomic p tl) = parens $ hsep $ (text p) : (map (\ (In t) -> exprDoc t) tl) But the obvious definition for conjunction doesn't work: instance Printable And where exprDoc (And el) = sep (map exprDoc el) GHC barfs, throwing: Couldn't match expected type `f t' against inferred type `t1' `t1' is a rigid type variable bound by the type signature for `exprDoc' at WouterTest.hs:62:17 Expected type: [f t] Inferred type: [t1] In the second argument of `map', namely `el' In the first argument of `sep', namely `(map exprDoc el)' I've attached the code. Compile and inspect with: $ ghci -fglasgow-exts -fallow-overlapping-instances WouterTest.hs test1 works great (other than needing some redundant typing, any hints?). test2 needs the definition of 'Printable And' to print, but I haven't gotten that to work yet. It also needs the redundant typing. -Ron However, I tried making more complex expression (conjunction, in this case), but I can't get the types to align. In particular, if I uncomment the obvious definition

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[ANN] bloomfilter 1.0 - Fast immutable and mutable Bloom filters
by Bryan O'Sullivan 04 Jun '08

04 Jun '08

I'm pleased to announce the availability of a fast Bloom filter library for Haskell. A Bloom filter is a probabilistic data structure that provides a fast set membership querying capability. It does not give false negatives, but has a tunable false positive rate. (A false positive arises when the filter claims that an element is present, but in fact it is not.) The library is easy to use. As an example, here's a reimplementation of the Unix "spell" command. import Data.BloomFilter.Easy (easyList, elemB) main = do filt <- (easyList 0.01 . words) `fmap` readFile "dictionary.txt" let check word | word `elemB` filt = "" | otherwise = word ++ "\n" interact (concat . map check . lines) It is also carefully tuned for performance. On my laptop, I can sustain a construction or query rate well in excess of a million ByteStrings per second. Source code: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/bloomfilter Latest bits: darcs get http://darcs.serpentine.com/bloomfilter <b

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ghc 6.8.2 issue
by Galchin, Vasili 04 Jun '08

04 Jun '08

Hello, I have been developing new code for the "unix" package. I have run into what I think are ghc 6.8.2 anomalies but couldn't see a pattern. Possibly now I do. I have been using the 32-bit x86 ghc binary that I downloaded from http://www.haskell.org and running on Ubuntu Linux. I am pretty I can repeat now. Everything is ok until I do "sudo runhaskell Setup.hs install" which installs a new "unix" package that I just built. Of course the "intall" installs into /usr/local/lib/unix-2.3.0.0/ghc-6.8.2. The "install" seems to destroy some ghc compiler state under /usr/local ... This is of course just a theory. However, once I re-install ghc et. al. from the binary download then things are ok again. I have tried the ghc re-install at least 4 times. Hope I am not misleading anybody .. just trying to help! Kind regards, Vasili

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hs-plugins compile error
by Edsko de Vries 04 Jun '08

04 Jun '08

Hi, I'm getting the compilation error that is actually logged on Hackage: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/plugins Below is a small diff file that resolves these problems; I don't know what the proper protocol is for submitting these diffs but it may be useful to someone. - E diff -ur plugins-1.2-orig/src/System/Plugins/Env.hs plugins-1.2/src/System/Plugins/Env.hs --- plugins-1.2-orig/src/System/Plugins/Env.hs 2008-06-02 14:57:59.000000000 +0100 +++ plugins-1.2/src/System/Plugins/Env.hs 2008-06-02 15:00:25.000000000 +0100 @@ -73,7 +73,7 @@ import Control.Concurrent.MVar ( MVar(), newMVar, withMVar ) -import Distribution.Package +import Distribution.Package hiding (packageName) import Text.ParserCombinators.ReadP import qualified Data.Map as M diff -ur plugins-1.2-orig/src/System/Plugins/PackageAPI.hs plugins-1.2/src/System/Plugins/PackageAPI.hs --- plugins-1.2-orig/src/System/Plugins/PackageAPI.hs 2008-06-02 14:57:59.000000000 +0100 +++ plugins-1.2/src/System/Plugins/PackageAPI.hs 2008-06-02 14:59:49.000000000 +0100 @@ -40,7 +40,7 @@ #if CABAL == 1 || __GLASGOW_HASKELL__ >= 604 import Distribution.InstalledPackageInfo -import Distribution.Package +import Distribution.Package hiding (depends, packageName) #else import System.Plugins.Package #endif diff -ur plugins-1.2-orig/src/System/Plugins/ParsePkgConfCabal.hs plugins-1.2/src/System/Plugins/ParsePkgConfCabal.hs --- plugins-1.2-orig/src/System/Plugins/ParsePkgConfCabal.hs 2008-06-02 14:57:59.000000000 +0100 +++ plugins-1.2/src/System/Plugins/ParsePkgConfCabal.hs 2008-06-02 14:58:56.000000000 +0100 @@ -6,7 +6,7 @@ ) where import Distribution.InstalledPackageInfo -import Distribution.Package +import Distribution.Package hiding (depends) import Distribution.Version import Data.Char ( isSpace, isAlpha, isAlphaNum, isUpper, isDigit )

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Rewrite class with fundeps in pure h98?
by Darrin Thompson 04 Jun '08

04 Jun '08

I thought that I should be able to write something like the toHtml function below with pure H98, but when I went to write it I ended up needing fundeps. Is there a way to express this without using any extensions? The idea was to take a remotely Dom-like tree and flatten it into a string, but not require any particular string type. Mostly I'm ripping off HStringTemplate for the fun of it. {-# OPTIONS -fglasgow-exts #-} module Control.WebWidget where import Data.Monoid import Data.String data (IsString s, Monoid s) => Dom s = Element s [Attr s] [Dom s] | Text s data (IsString s, Monoid s) => Attr s = Attr s s class (Monoid s, IsString s) => HTML d s | d -> s where toHtml :: d -> s instance (Monoid s, IsString s) => HTML (Dom s) s where toHtml (Element name attrs children) = mconcat [ fromString "<", name, mconcat $ map toHtml attrs, fromString ">", mconcat $ map toHtml children, fromString "</", name, fromString ">" ] toHtml (Text s) = s instance (Monoid s, IsString s) => HTML (Attr s) s where toHtml (Attr key value) = mconcat [ fromString " '", key, fromString "'='", value, fromString "' " ] -- Darrin

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