- Haskell-Cafe - Haskell.org

05 Mar '09

Is there a way to do binary serialization of Haskell values (in GHC, at least)? If you propose a method, what are its type safety and portability properties?

3 2

ANN: Happstack 0.2 Released
by Matthew Elder 05 Mar '09

05 Mar '09

Happstack 0.2 has been released; it is available on Hackage. A lot of community effort has gone into it! For details, please see this post: http://blog.happstack.com/2009/03/04/happstack-02-released Regards, Matthew Elder -- Need somewhere to put your code? http://patch-tag.com Want to build a webapp? http://happstack.com

1 0

Optimizing array operation?
by Xiao-Yong Jin 05 Mar '09

05 Mar '09

Dear list, I decided to extract some common code I use in my data analysis code and end up with some interesting pattern. > -- | Confined array operation. The type Arr here is actually used as > -- a C-like array with index runs from 0 to n-1. > type Arr = Array Int > > -- | Element fetching function, no bounds checking. Works with array > -- with index [0..n-1] > (!>) :: Arr e -> Int -> e > (!>) = unsafeAt > {-# INLINE (!>) #-} > > -- | Length of the array. > arrLength :: Arr e -> Int > arrLength = numElements > {-# INLINE arrLength #-} > > -- | Sequentially loop over all elements in an array. > loopArrM :: (Monad m) => > (e -> m a) -- ^ function to apply to elements > -> Arr e -- ^ the array > -> m () > loopArrM = loopArrMp (\ _ -> True) > {-# INLINE loopArrM #-} > > -- | Same as loopArrM but only to those with index satisfies predicate. > loopArrMp :: (Monad m) => > (Int -> Bool) -- ^ predicate > -> (e -> m a) -- ^ function to apply to elements > -> Arr e -- ^ the array > -> m () > loopArrMp p f arr = loopArrMG 0 end p f arr > where > end = arrLength arr > {-# INLINE loopArrMp #-} > > -- | Same as loopArrM but only to indices within a range. > loopArrMr :: (Monad m) => > Int -- ^ start index > -> Int -- ^ end index > -> (e -> m a) -- ^ function to apply to elements > -> Arr e -- ^ the array > -> m () > loopArrMr start end = loopArrMG start end (\ _ -> True) > {-# INLINE loopArrMr #-} > > -- | Generic loopArrM for indices with in a range [start, end-1] and > -- satisfy predicate. > loopArrMG :: (Monad m) => > Int -- ^ start index > -> Int -- ^ end index > -> (Int -> Bool) -- ^ predicate > -> (e -> m a) -- ^ function to apply to elements > -> Arr e -- ^ the array > -> m () > loopArrMG start end p f arr = go start > where > go !j | j == end = return () > | p j = f (arr !> j) >> go (j + 1) > | otherwise = go (j + 1) > {-# INLINE loopArrMG #-} It is quite frequently to loop over Arr with various conditions, so I wrote loopArrMG to do it. I know a list comprehension would just do the trick, but the extra time and heap allocation is not what I want. My question here is that whether there is a better data structure available to accomplish such task? If not, is there a better way to write the above code? Thanks, Xiao-Yong -- c/* __o/* <\ * (__ */\ <

1 0

(no subject)
by R J 05 Mar '09

05 Mar '09

Could someone provide an elegant solution to Bird problem 4.2.13? Here are the problem and my inelegant solution: Problem ------- Since concatenation seems such a basic operation on lists, we can try to construct a data type that captures concatenation as a primitive. For example, data (CatList a) = CatNil | Wrap a | Cat (CatList a) (CatList a) The intention is that CatNil represents [], Wrap x represents [x], and Cat x y represents x ++ y. However, since "++" is associative, the expressions "Cat xs (Cat ys zs)" and "Cat (Cat xs ys) zs" should be regarded as equal. Define appropriate instances of "Eq" and "Ord" for "CatList". Inelegant Solution ------------------ The following solution works: instance (Eq a) => Eq (CatList a) where CatNil == CatNil = True CatNil == Wrap z = False CatNil == Cat z w = ( z == CatNil && w == CatNil ) Wrap x == CatNil = False Wrap x == Wrap z = x == z Wrap x == Cat z w = ( Wrap x == z && w == CatNil ) || ( Wrap x == w && z == CatNil ) Cat x y == CatNil = x == CatNil && y == CatNil Cat x y == Wrap z = ( x == Wrap z && y == CatNil ) || ( x == CatNil && y == Wrap z ) Cat x y == Cat z w = unwrap (Cat x y) == unwrap (Cat z w) unwrap :: CatList a -> [a] unwrap CatNil = [] unwrap (Wrap x) = [x] unwrap (Cat x y) = unwrap x ++ unwrap y instance (Eq a, Ord a) => Ord (CatList a) where x < y = unwrap x < unwrap y This solution correctly recognizes the equality of the following, including nested lists(represented, for example, by Wrap (Wrap 1), which corresponds to [[1]]): Wrap 1 == Cat (Wrap 1) CatNil Cat (Wrap 1) (Cat (Wrap 2) (Wrap 3)) == Cat (Wrap 1) (Cat (Wrap 2) (Wrap 3)) Wrap (Wrap 1) == Wrap (Cat (Wrap 1) CatNil) Although this solution works, it's a hack, because unwrap converts CatLists to lists. The question clearly seeks a pure solution that does not rely on Haskell's built-in lists. What's the pure solution that uses cases and recursion on CatList, not Haskell's built-in lists, to capture the equality of nested CatLists? _________________________________________________________________ Windows Live™: Life without walls. http://windowslive.com/explore?ocid=TXT_TAGLM_WL_allup_1a_explore_032009

2 1

Optimization by cafe
by ChrisK 05 Mar '09

05 Mar '09

I have a performance glitch in regex-tdfa related to GHC-6.10.1 (on a PPC G4 with -O2). I have okay code that runs in 0.2 seconds. I simplify this code to run faster and it takes 4.0 seconds (it allocates something in the loop, I think) I turn on -prof for the simpler code and it runs in 0.25 seconds. I can't profile my way out of it, due to above paradox. Has anyone else seen this sort of paradox? The simpler code's loop is just a bunch of pattern matching and lookups, multi: > matchTest :: Regex -> S.ByteString -> Bool > matchTest !r !input = ... > > multi (Simple' {dt_win=w,dt_trans=CharMap t, dt_other=o}) !off = > if IMap.null w > then if off > endOff > then False > else case IMap.findWithDefault o (fromEnum (input `S.unsafeIndex` off)) t of > Transition {trans_many=DFA {d_dt=dt'}} -> > multi dt' (succ off) > else True All the above regex search does is look for a match. It is a tester, returning Bool. The "w" is checked for winning, if it wins it returns True. If not winning, the offset is checked against the end (cached in endOff). If the end has been reach it returns False. Otherwise it looks up the Word8 at offset "off" in "input" , looks up this Word8 as an Int in the t::IntMap Transition , defaulting to Transition "o" The next DT is followed with the (succ off), note that !off is strict. I cannot think of how to reduce the code any further. It should not be doing any allocation. The Regex is being compiled once, cached, and run 10^6 times against a short piece of text. I know it can run fast because I have huge module running in ST.Strict that does all kinds of extra computation and runs in 0.2 seconds. It should be possible to cut this down and win. So I also applied my delete key to most of the code in the complicated ST.Strict module, keeping the runST. The end result was not unlike the above code, and ran in 4.0 seconds instead of 0.2 seconds. I have looked hard at the core output. I am at a loss. So I have turned to haskell-cafe for insight and moral support. -- Chris

1 0

environment variables for runghc?
by Erik de Castro Lopo 05 Mar '09

05 Mar '09

Hi all, Is there some environment variable I can set so that runghc can be told to always use -Wall? Cheers, Erik -- ----------------------------------------------------------------- Erik de Castro Lopo ----------------------------------------------------------------- "... a discussion of C++'s strengths and flaws always sounds like an argument about whether one should face north or east when one is sacrificing one's goat to the rain god." -- Thant Tessman

3 4

Re: Left fold enumerator - a real pearl overlooked?
by John Lato 05 Mar '09

05 Mar '09

Hello Günther, I think the largest reason Haskellers don't use left-fold enumerators is that there isn't a ready-to-use package on Hackage. Oleg's code is extremely well commented and easy to follow, but it's not cabalized. In addition to Takusen, Johan Tibbe's hyena application server uses enumerators for IO: http://github.com/tibbe/hyena/tree/master There is a darcs repo of a cabalized iteratee package available at http://inmachina.net/~jwlato/haskell/iteratee/ This is essentially Oleg's code, slightly modified and reorganized. If anyone is interested in using left-fold enumerators for IO, please give it a look and let me know what you think. I'd like to put this on hackage in about a week or so, if possible. I would especially appreciate build reports. There are a few iteratee/enumerator design questions that remain, which Oleg and others would like to explore more fully. The results of that research will likely find there way into this library. Sincerely, John Lato > Hi all, > > in the last few months I was looking for haskell database library, > eventually settling for HDBC (thanks John btw). > > Takusen also caught my eye although I even failed installing it. > > Nevertheless a particular property of takusen, left-fold-enumerator, > also sparked my interest and I tried to follow it up. > > I had the impression this is something of relevance but something that > is not mentioned or made use of often. There are actually only a few > references on the net and most of those by one person only, Oleg. > > There was one post from John Goerzen about Haskell HTTP libraries in > which he hinted using left-fold enumerators. > > Anyway what I'm saying is that the whole topic is somewhat off the radar > of the larger haskell community, how come, or am I merely overestimating > its relevance and usefulness? > > Günther

12 19

*almost* composition in writer monad
by Edsko de Vries 05 Mar '09

05 Mar '09

Hi, Does this function remind anybody of anything? It seems like I'm missing an obvious abstraction: composeWriter :: [a -> (a, b)] -> a -> (a, [b]) composeWriter [] a = (a, []) composeWriter (f:fs) a = let (a', b) = f a (final_a, bs) = composeWriter fs a' in (final_a, b:bs) It's almost but not quite composition for functions in the Writer monad; the difference is that every function has exactly one b result, rather than a list of them. Edsko

2 2

Stacking State on State.....
by Phil 05 Mar '09

05 Mar '09

Hi, I¹ve been teaching myself Monads recently with some success, but I¹ve hit a snag when I tried to look at transformers. I¹m not sure if the problem is my understanding of transformer use at a theoretical level or if I¹m just getting the syntax wrong. If I stick a (hopefully) fairly simple example below, I was wondering if people could comment: Bit of background I have no problem using the State Monad and find it very useful for holding the state or say a homemade random number generator. I written several little bits of code like this: VanDerCorput :: Int-> ( Double, Int ) VanDerCorput state = ( output, state+1 ) where output = reflect state getVanDC :: State Int Double getVanFC = State VanDerCorput This is just holding an incremental state and each time it is evaluated the next number in the Van Der Corput sequence in generated this is just a quasi random sequence the implementation details of the sequence are irrelevant safe to say that the sequence is generated from N=1,2,3,4.....Infinity. The above example is so trivial it can of course be implemented easily in purely functional code by threading the state as a parameter to a pure function and then mapping that function to an ³iterate (+1) 1² statement, but that is not the point of the exercise! The next step of the program is to wrap the above example up in another function which takes the Van Der Corput sequence as input and provides output depending on*it¹s own* state. I¹m passing it to a Box-Muller transform. Very quickly the Box-Muller transform requires TWO inputs from VanDerCourput to produce TWO outputs itself, however we only ever need one at a time, so the Box-Muller transform itself must hold state saying weather it has already saved the 2nd output from a previous call, and thus doesn¹t need to call Van Der Corput this time to produce output it just returns its own state. (P.S. If you know what I¹m doing from a maths point of view please ignore the fact using a 1D Van Der Corput with Box Muller is a very bad idea I know this; I¹m keeping the example simple and Haskell orientated!) In C-like imperative code you¹d could do something like the below not that this is massively elegant, but it shows the case-in-point: Boxmuller() { // The ³outer² states of Box Muller static bool myState = False; static double storedNormal = 0.; // Local copy of current state bool currentState = myState; // State always flips each run myState = not myState; // If we don¹t have a stored value from a previous run if currentState == False { // Generate two new Van Der Corputs this would increment a state in getNextVanDerCorput() twice producing different output each time double rand1 = getNextVanDerCorput(); double rand2 = getNextVanDerCorput(); // Store one result for the NEXT run of Boxmuller() storedNormal = SOME_TRANSFORM(rand2); // Return the other return SOME_TRANSFORM(rand1); } // We have a leftover value from a previous run get a local copy double currentNormal = storedNormal; // Reset the stored value to zero storedNormal = 0.; // Return the local copy of the stored value return currentNormal; } getNextVanDerCorput() { // Starting state state int n = 1; int currentState = n; // Incremented each time we call the function ++n; // Value computed on the internal state of this function return SOME_OTHER_TRANSFORM(currentState); } Right, hopefully that explains explicitly what I¹m trying to do apologies for dropping into C, it¹s easier to explain in code than in words. It struck me that this could be done using a plain and simple State Monad in Haskell carrying ALL states for both functions around in a tuple. This is pretty ugly tho, and I figure both BoxMuller and VanDerCorput should have their own internal states so they can be used as building blocks in other functionality too so one big ugly Monad is bad code design, even if it would work for this specific example. Let¹s not go there. The VanDerCorput building block is just the Monad at the start of this post. The problem is HOW DO I WRAP ANOTHER INDEPENDENT STATE AROUND THIS? After some googling it looked like the answer may be Monad Transformers. Specifically we could add a StateT transform for our Box Muller state to our VanDerCorput State Monad. Google didn¹t yield a direct answer here so I¹m not even sure if my thinking is correct, people describe the process of using a transform as wrapping one monad in another¹ or threading one monad into another¹. What we want to do is have some internal state controlled by an independent outer state - this sounds about right to me? So I started playing around with the code, and got the below to compile. test :: StateT (Bool,Double) (State Int) Double test = do (isStored,normal) <- get let (retNorm,storeNorm) = if isStored then (normal,0) else (n1,n2) where n1 = 2 n2 = 3 put (not isStored, storeNorm) return retNorm Now this is incomplete and may be even wrong! I¹ll Explain my thinking: (Bool,Double) is equivalent to myState and storedNormal in the C example The last Double is the return value of the BoxMuller Monad The (State Int) is supposed to represent the VanDerCorput monad but the compiler (GHC 6.10) will only let me specify one parameter with it so I¹ve put the state and left the return type to the gods!!.... As I said this isn¹t quite right any ideas how to specify the type? The next few lines get and test the BoxMuller state, this seems to work OK to me, the problem is when I try to look at the STATE OF THE INTERNAL monad. n1 and n2 should evaluate and increment the state of VanDerCorput monad but I can¹t get anything to compile here. 2 and 3 are just dummy values to make the thing compile so I could debug. My last gripe is how to actually call this from a pure function do I need to use both evalStateT and evalState I can¹t see how to initialize both the inner and outer state ? OK I think that¹s more than enough typing, apologies for the war&peace sized post. Any help muchly muchly appreciated, Many Thanks, Phil.

4 17

OpenVG: Linker errors with ghc --make, but not with ghci?
by Peter Verswyvelen 04 Mar '09

04 Mar '09

I followed the instructions on how to build OpenVG on Windows. It works fine when I run the examples using "GHCi -lopenvg32", but when compiling it with "GHC --make -lopenvg32" I get a bunch of linker errors, like C:\Program Files\Haskell\OpenVG-0.1\ghc-6.10.1/libHSOpenVG-0.1.a(Paths.o):fake:(.text+0x82): undefined reference to `vgInterpolatePath' C:\Program Files\Haskell\OpenVG-0.1\ghc-6.10.1/libHSOpenVG-0.1.a(Paths.o):fake:(.text+0x40d): undefined reference to `vgModifyPathCoords' etc However it does seem that the libopenvg32.a file contains all these undefined references, and it is in the gcc-lib directory of GHC. I'm a stuck. Any hints? Thanks, Peter

2 2

Data.Binary stack overflow with Data.Sequence String
by Gwern Branwen 04 Mar '09

04 Mar '09

So recently I've been having issues with Data.Binary & Data.Sequence; I serialize a 'Seq String' You can see the file here: http://code.haskell.org/yi/Yi/IReader.hs The relevant function seems to be: -- | Read in database from 'dbLocation' and then parse it into an 'ArticleDB'. readDB :: YiM ArticleDB readDB = io $ (dbLocation >>= r) `catch` (\_ -> return empty) where r x = fmap (decode . BL.fromChunks . return) $ B.readFile x -- We read in with strict bytestrings to guarantee the file is closed, -- and then we convert it to the lazy bytestring data.binary expects. -- This is inefficient, but alas... My current serialized file is about 9.4M. I originally thought that the issue might be the recent upgrade in Yi to binary 0.5, but I unpulled patches back to past that, and the problem still manifested. Whenever yi tries to read the articles.db file, it stack overflows. It actually stack-overflowed on even smaller files, but I managed to bump the size upwards, it seems, by the strict-Bytestring trick. Unfortunately, my personal file has since passed whatever that limit was. I've read carefully the previous threads on Data.Binary and Data.Map stack-overflows, but none of them seem to help; hacking some $!s or seqs into readDB seems to make no difference, and Seq is supposed to be a strict datastructure already! Doing things in GHCi has been tedious, and hasn't enlightened me much: sometimes things overflow and sometimes they don't. It's all very frustrating and I'm seriously considering going back to using the original read/show code unless anyone knows how to fix this - that approach may be many times slower, but I know it will work. -- gwern

2 1

Status of Haskell under OsX
by Cristiano Paris 04 Mar '09

04 Mar '09

Hi, I'm planning to purchase a MacBookPro so I'm wondering how well Haskell is supported under this platform. Thanks, Cristiano

10 16

Memory usage when passing arrays in state
by Tobias Olausson 04 Mar '09

04 Mar '09

Hello all. I am currently implementing an emulation of a CPU, in which the CPU's RAM is part of the internal state that is passed around in the program using a state monad. However, the program performs unexpectingly bad, and some profiling information makes us believe that the problem is the high memory usage of the program. The program below is similar to our main program used when testing a sorting algorithm in this CPU: module Main where import Control.Monad.State.Lazy import Data.Word import Data.Array.Diff import Control.Concurrent (threadDelay) data LoopState = LoopState { intVal :: Integer , diff :: DiffUArray Word8 Word8 } initState :: LoopState initState = LoopState 0 (array (0x00,0xFF) [(idx,0)|idx<-[0x00..0xFF]]) main :: IO () main = do execStateT looper initState >>= putStrLn . show . intVal looper :: StateT LoopState IO () looper = do st <- get let res = intVal st + 1 idx = fromIntegral res put $ st { intVal = res, diff = (diff st) // [(idx,idx)] } if res == 13000000 then return () else looper Of course our program does more than updating a counter ;-) Compiling and running this program yields the following result: [~]:[olaussot] >> ghc --make -O2 -o array ArrayPlay.hs [~]:[olaussot] >> ./array +RTS -sstderr ./array +RTS -sstderr 13000000 313,219,740 bytes allocated in the heap 1,009,986,984 bytes copied during GC 200,014,828 bytes maximum residency (8 sample(s)) 4,946,648 bytes maximum slop 393 MB total memory in use (3 MB lost due to fragmentation) Generation 0: 590 collections, 0 parallel, 3.06s, 3.09s elapsed Generation 1: 8 collections, 0 parallel, 3.56s, 4.21s elapsed INIT time 0.00s ( 0.00s elapsed) MUT time 0.27s ( 0.27s elapsed) GC time 6.62s ( 7.30s elapsed) EXIT time 0.00s ( 0.00s elapsed) Total time 6.89s ( 7.57s elapsed) %GC time 96.1% (96.4% elapsed) Alloc rate 1,155,958,754 bytes per MUT second Productivity 3.9% of total user, 3.6% of total elapsed Why does the program spend 96.1% of its total running time collecting garbage? Any tips to make this program perform better are appreciated. Please do tell if anything is unclear. -- Tobias Olausson tobsan(a)gmail.com

4 5

How to build sourceview depend for gtk2hs?
by Andy Stewart 04 Mar '09

04 Mar '09

Hi all, I use Debian testing. I have install GHC 6.10.1 binary package. When i use "autoreconf && ./configure --enable-docs" to config gtk2hs ************************************************** * Configuration completed successfully. * * The following packages will be built: * * glib : yes * gtk : yes * gio : yes * glade : yes * cairo : yes * svgcairo : yes * gtkglext : yes * gconf : yes * sourceview : no * gtksourceview2 : yes * mozembed : yes * soegtk : yes * gnomevfs : yes * gstreamer : yes * documentation : yes * * Now do "(g)make" followed by "(g)make install" ************************************************** But "sourceview" is not pass, have anyone successful? I have install below packages: libglade2-dev libgtksourceview-dev libgconf2-dev librsvg2-dev libgstreamer-plugins-base0.10-dev libgstreamer0.10-dev libgtkglext1-dev libgnomevfs2-dev xulrunner-dev So i need install which depend package to fix above problem? Thanks! Below is the detail config information. checking for a BSD-compatible install... /usr/bin/install -c checking whether build environment is sane... yes checking for a thread-safe mkdir -p... /bin/mkdir -p checking for gawk... no checking for mawk... mawk checking whether make sets $(MAKE)... yes checking build system type... i686-pc-linux-gnu checking host system type... i686-pc-linux-gnu checking for style of include used by make... GNU checking for gcc... gcc checking for C compiler default output file name... a.out checking whether the C compiler works... yes checking whether we are cross compiling... no checking for suffix of executables... checking for suffix of object files... o checking whether we are using the GNU C compiler... yes checking whether gcc accepts -g... yes checking for gcc option to accept ISO C89... none needed checking dependency style of gcc... none checking how to run the C preprocessor... gcc -E checking for a BSD-compatible install... /usr/bin/install -c checking whether ln -s works... yes checking for ar... /usr/bin/ar checking for ld... /usr/bin/ld checking for basename... /usr/bin/basename checking for grep that handles long lines and -e... /bin/grep checking for gzip... /bin/gzip checking for a sed that does not truncate output... /bin/sed checking for cut... /usr/bin/cut checking for tar... /bin/tar checking for touch... /usr/bin/touch checking for ranlib... ranlib checking for xargs... /usr/bin/xargs checking for ghc... /usr/local/bin/ghc checking version of GHC... 6.10.1 checking for ghc-pkg... /usr/local/bin/ghc-pkg checking whether to build deprecated bindings... yes checking whether to build deprecated packages (gnomevfs, sourceview)... yes checking for the GHC package "base"... yes, version 4.0.0.0 checking for the GHC package "haskell98"... yes, version 1.0.1.0 checking for the GHC package "mtl"... yes, version 1.1.0.2 checking for the GHC package "bytestring"... yes, version 0.9.1.4 checking for the GHC package "containers"... yes, version 0.2.0.0 checking for the GHC package "array"... yes, version 0.2.0.0 checking for the GHC package "old-time"... yes, version 1.0.0.1 checking for the GHC package "pretty"... yes, version 1.0.1.0 checking for pkg-config... /usr/bin/pkg-config checking pkg-config is at least version 0.9.0... yes checking for GLIB... yes checking for GTK... yes checking whether to build gtk package... yes checking for GIO... yes checking whether to build gio package... yes checking for LIBGLADE... yes checking whether to build glade package... yes checking for GCONF... yes checking whether to build gconf package... yes checking for GTKSOURCEVIEW2... yes checking whether to build gtksourceview2 package... yes checking whether to build sourceview package... no checking for MOZILLA_MOZEMBED... yes checking whether to build mozembed package... yes checking for SEAMONKEY_MOZEMBED... no checking whether to build mozembed package... no checking for FIREFOX_MOZEMBED... no checking whether to build mozembed package... no checking for XULRUNNER_MOZEMBED... no checking whether to build mozembed package... no checking for CAIRO... yes checking whether to build cairo package... yes checking for SVGCAIRO... yes checking whether to build svgcairo package... yes checking for GTKGLEXT... yes checking whether to build gtkglext package... yes checking for GNOMEVFS... yes checking whether to build gnomevfs package... yes checking for GSTREAMER... yes checking whether to build gstreamer package... yes checking for hsc2hs... /usr/local/bin/hsc2hs checking for happy... /usr/local/bin/happy checking version of happy... 1.18.2 checking for alex... /usr/local/bin/alex checking for haddock... /usr/local/bin/haddock checking version of haddock... 2.4.1 configure: creating ./config.status config.status: creating Makefile config.status: creating gtk2hs.spec config.status: creating mk/chsDepend config.status: creating mk/link-splitobjs.sh config.status: creating mk/fix-package-conf.sh config.status: creating docs/prologue.txt config.status: creating glib/glib.package.conf config.status: creating glib/glib.cabal config.status: creating gtk/gtk.package.conf config.status: creating gtk/gtk.cabal config.status: creating gio/gio.package.conf config.status: creating gio/gio.cabal config.status: creating glade/glade.package.conf config.status: creating glade/glade.cabal config.status: creating gconf/gconf.package.conf config.status: creating gconf/gconf.cabal config.status: creating sourceview/sourceview.package.conf config.status: creating sourceview/sourceview.cabal config.status: creating gtksourceview2/gtksourceview2.package.conf config.status: creating gtksourceview2/gtksourceview2.cabal config.status: creating mozembed/mozembed.package.conf config.status: creating mozembed/mozembed.cabal config.status: creating cairo/cairo.package.conf config.status: creating cairo/cairo.cabal config.status: creating svgcairo/svgcairo.package.conf config.status: creating svgcairo/svgcairo.cabal config.status: creating gtkglext/gtkglext.package.conf config.status: creating gtkglext/gtkglext.cabal config.status: creating soegtk/soegtk.package.conf config.status: creating soegtk/soegtk.cabal config.status: creating gnomevfs/gnomevfs.package.conf config.status: creating gnomevfs/gnomevfs.cabal config.status: creating gstreamer/gstreamer.package.conf config.status: creating gstreamer/gstreamer.cabal config.status: creating gtk2hs-config.h config.status: gtk2hs-config.h is unchanged config.status: executing depfiles commands config.status: executing default commands ************************************************** * Configuration completed successfully. * * The following packages will be built: * * glib : yes * gtk : yes * gio : yes * glade : yes * cairo : yes * svgcairo : yes * gtkglext : yes * gconf : yes * sourceview : no * gtksourceview2 : yes * mozembed : yes * soegtk : yes * gnomevfs : yes * gstreamer : yes * documentation : yes * * Now do "(g)make" followed by "(g)make install" ************************************************** -- Andy

2 3

Relying on GCC as the hsc2hs C compiler
by John Van Enk 04 Mar '09

04 Mar '09

While working on my new bindings project (using hsc2hs) I came across the __alignof__() statement available in GNU's C compiler. As it turns out, having this computed for me in Storable instances using something like this would be great: instance Storable Foo where .... sizeOf _ = #{const sizeof(CFoo)} alignment _ = #{const __alignof__(CFoo)} .... Can I rely on hsc2hs using GCC? How many people will hate me if I depend on GCC-specific extensions? Legal? Acceptable? Infuriating? /jve

1 0

Threading and Mullticore Computation
by mwinter＠brocku.ca 04 Mar '09

04 Mar '09

Hi, I tried a get into concurrent Haskell using multiple cores. The program below creates 2 task in different threads, executes them, synchronizes the threads using MVar () and calculates the time needed. import System.CPUTime import Control.Concurrent import Control.Concurrent.MVar myTask1 = do return $! fac 60000 print "Task1 done!" where fac 0 = 1 fac n = n * fac (n-1) myTask2 = do return $! fac' 60000 1 1 print "Task2 done!" where fac' n m p = if m>n then p else fac' n (m+1) (m*p) main = do mvar <- newEmptyMVar pico1 <- getCPUTime forkIO (myTask1 >> putMVar mvar ()) myTask2 takeMVar mvar pico2 <- getCPUTime print (pico2 - pico1) I compiled the code using $ ghc FirstFork.hs -threaded and executed it by $ main +RTS -N1 resp. $ main +RTS -N2 I use GHC 6.8.3 on Vista with an Intel Dual Core processor. Instead of getting a speed up when using 2 cores I get as significant slow down, even though there is no sharing in my code above (at least none I am aware of. BTW, that was reason that I use 2 different local factorial functions). On my computer the 1-core version takes about 8.3sec and the 2-core version 12.8sec. When I increase the numbers from 60000 to 100000 the time difference gets even worse (30sec vs 51 sec). Can anybody give me an idea what I am doing wrong? Thanks, Michael

8 20

interaction between ghci and cudaBLAS library
by Simon Beaumont 03 Mar '09

03 Mar '09

In my efforts to integrate this library into Haskell (I am working on OS X 10.5.6 with ghc-6.10.1 and CUDA 2.0) I am getting a bad interaction between the threads in ghci - when I call the library init function via the FFI, ghci will block in __semwait_signal. Of course if I build an executable which I guess has only one thread then all is well. AFAIK the CUDA library is re-entrant (or threadsafe) in that it will initialize a device context for each thread that calls it. I guess that might be part of the problem. Certainly there is a call to _pthread_getspecific in that library. This is show stopper for me as I want to use GHCI to call blas routines on the device (this lends itself very nicely to a monadic approach - leaving the matrices on the device until we are done applying sequential computations - and only then bringing them back into the "real" world). Since there is this association between the device context and the calling thread - is there a way to get a handle on the threading in ghci? (or just have a single thread) But why are we blocking? I would have expected completion or is ghci smart enough to prevent any non-deterministic behaviour that the current setup would entail? Any ideas or suggestions of how to proceed with this? The final work should it be successful will be offered to the community as a basis for doing high performance linear algebra on CUDA devices as well as get my haskell up to speed as a side effect :) -- View this message in context: http://www.nabble.com/interaction-between-ghci-and-cudaBLAS-library-tp22300… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

3 6

ANNOUNCE: Extensible and Modular Generics for the Masses: emgm-0.3
by Sean Leather 03 Mar '09

03 Mar '09

============================================== Extensible and Modular Generics for the Masses ============================================== Extensible and Modular Generics for the Masses (EMGM) is a library for generic programming in Haskell using type classes and a sum-of-products view. ------- Updates ------- emgm-0.3 is the third major release, and it arrives a little over a month after emgm-0.2. Deriving is now greatly improved! Due to recent reports from users, we realized the current implementation just wasn't going to cut it. EMGM already supports a wide range of datatypes, so why not make the deriving code support just as many. Hopefully, it works well for you. Please let us know if your datatype is not supported. There are several new functions in the EMGM family. These include: cast (a type-safe, configurable, generic cast) and everywhere and everywhere' (functions similar to those of the same name in SYB that apply a transformation everywhere a certain type is found). ------- Changes ------- Changes from emgm-0.2 include: * Improved deriving can now handle datatype collections like this one: http://www.haskell.org/pipermail/generics/2009-February/000429.html * cast function > cast :: Rep (Map a) b => a -> b * everywhere and everywhere' > everywhere :: Rep (Everywhere a) b => (a -> a) -> b -> b > everywhere' :: Rep (Everywhere' a) b => (a -> a) -> b -> b They both perform transformations on a-values in a b-value. The former does them bottom-up, the latter top-down. The names come from similar functions in SYB that use rank-2 types. Note the difference. > everywhere :: (forall a. Data a => a -> a) -> forall a. Data a => a -> a > everywhere' :: (forall a. Data a => a -> a) -> forall a. Data a => a -> a ------------ Known Issues ------------ Due to a problem with the template-haskell package and Cabal, you cannot cabal-install the emgm package with GHC 6.8. However, take heart! EMGM works very well with GHC 6.8. You merely have to download the tar.gz package from Hackage yourself, build it, and install it. Since it doesn't require any dependencies beyond what comes with GHC, installation is a breeze! ------------------- General Information ------------------- Visit the home page: http://www.cs.uu.nl/wiki/GenericProgramming/EMGM ---------------- General Features ---------------- The primary features of EMGM include: * Datatype-generic programming using sum-of-product views * Large collection of ready-to-use generic functions * Included support for standard datatypes: lists, Maybe, tuples * Easy to add support for new datatypes * Type classes make writing new functions straightforward in a structurally inductive style * Generic functions are extensible with ad-hoc cases for arbitrary datatypes * Good performance of generic functions The features of this distribution include: * The API is thoroughly documented with Haddock * Fully tested with QuickCheck and HUnit * Program coverage ensures that all useful code has been touched by tests * Tested on both Mac and Windows systems ------------ Requirements ------------ EMGM has the following requirements: * GHC 6.8.1 - It has been tested with versions 6.8.3 and 6.10.1 * Cabal library 1.2.1 - It has been tested with versions 1.2.4.0 and 1.6.0.1. ----------------- Download & Source ----------------- Use caball-install: cabal install emgm Get the package: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/emgm Check out the current source with Subversion: svn checkout https://svn.cs.uu.nl:12443/repos/dgp-haskell/EMGM/trunk Or view it online: https://svn.cs.uu.nl:12443/viewvc/dgp-haskell/EMGM/trunk/ -------- Examples -------- Check out the examples: https://svn.cs.uu.nl:12443/viewvc/dgp-haskell/EMGM/trunk/examples/ -------------- Bugs & Support -------------- Report issues or request features: http://code.google.com/p/emgm/issues/list Discuss EMGM with the authors, maintainers, and other interested persons: http://www.haskell.org/mailman/listinfo/generics ------- Credits ------- The research for EMGM originated with Ralf Hinze. It was extended with work by Bruno Oliveira and Andres Löh. More details of the library functionality were explored by Alexey Rodriguez. We are very grateful to all of these people for the foundation on which this library was built. The current authors and maintainers of EMGM are: * Sean Leather * José Pedro Magalhães * Alexey Rodriguez * Andres Löh

2 2

Hidden module?
by Cristiano Paris 03 Mar '09

03 Mar '09

Cabalising hsc2hc I get (this is actually from manually building the package): --- [paris@bagend hsc2hs-0.67.20061107]$ runghc Setup.hs build Preprocessing executables for hsc2hs-0.67.20061107... Building hsc2hs-0.67.20061107... Main.hs:32:7: Could not find module `System.Process': it is a member of package process-1.0.1.0, which is hidden [paris@bagend hsc2hs-0.67.20061107]$ which I cannot understand. Please help! --- Cristiano

5 7

Cabal and `main-is` field
by Manlio Perillo 03 Mar '09

03 Mar '09

Hi. I have started to use Cabal for a small project where I have to build several executables. The project layout is something like this: / bin/ a.hs b.hs src/ X.hs Y.hs The Cabal configuration file is something like: executable a build-depends: haskell98, base, ... main-is: a.hs hs-source-dirs: src bin other-modules: X This is perfectly reasonable, but it is odd, IMHO. I don't understand why `main-is` is relative to `hs-source-dirs`. What is the rationale? After all, there is only one executable that can be specified in the `executable` block. The configuration file should be, instead (IMHO, of course): executable a build-depends: haskell98, base, ... main-is: bin/a.hs hs-source-dirs: src other-modules: X Another "problem" I have noted, is that if I specify `main-is` field two times, no error is reported. Simply, Cabal uses the last directive. One last thing: is it possible to define "macros" in Cabal? In my package, I have n executables, that have many dependencies in common. I would like to avoid having to repeat the same dependencies for each executable block. Thanks Manlio Perillo

4 7

ANNOUNCE: text and text-icu, fast and comprehensive Unicode support using stream fusion
by Bryan O'Sullivan 03 Mar '09

03 Mar '09

On behalf of the Data.Text team, I am delighted to announce the release of preview versions of two new packages: text 0.1 Fast, packed Unicode text support, using a modern stream fusion framework. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/text text-icu 0.1 Augments text with comprehensive character set conversion support and normalization (and soon more), via bindings to the ICU library. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/text-icu These packages fill out critical pieces of functionality for the Haskell platform, without compromising on either performance or safety. We are referring to these as *preview* releases because although the text package in particular has been quite heavily tested, it has not been thoroughly tuned, and we have not yet implemented a chunked lazy text representation suitable for streaming gigabytes of data. The APIs are pretty conventional, but are still subject to change. If you want to contribute, please get copies of the source trees from here: darcs get http://code.haskell.org/text darcs get http://darcs.serpentine.com/text-icu Please send bug reports and patches to your friendly Data.Text team: Tom Harper <rtharper(a)aftereternity.co.uk> Duncan Coutts <duncan.coutts(a)worc.ox.ac.uk> Bryan O'Sullivan <bos(a)serpentine.com>

4 9

Left fold enumerator - a real pearl overlooked?
by Gü?nther Schmidt 03 Mar '09

03 Mar '09

Hi all, in the last few months I was looking for haskell database library, eventually settling for HDBC (thanks John btw). Takusen also caught my eye although I even failed installing it. Nevertheless a particular property of takusen, left-fold-enumerator, also sparked my interest and I tried to follow it up. I had the impression this is something of relevance but something that is not mentioned or made use of often. There are actually only a few references on the net and most of those by one person only, Oleg. There was one post from John Goerzen about Haskell HTTP libraries in which he hinted using left-fold enumerators. Anyway what I'm saying is that the whole topic is somewhat off the radar of the larger haskell community, how come, or am I merely overestimating its relevance and usefulness? Günther

4 4

Basic problem in Haskell language design?
by Nicu Ionita 03 Mar '09

03 Mar '09

Hi, Today I found the following problem when writing a simple function: > -- Whole info from a word8 list to moves > movesFromWord8s :: [Word8] -> [Move] > movesFromWord8s (f:t:ws) = (f, t) : movesFromWord8s ws > moverFromWord8s _ = [] Here I made a small typo in the second equation, writing "mover..." instead of "moves..." for the name of the declared function. Of course this is an error, because I have non-exhaustive patterns in the function movesFromWord8s. But the compiler (here GHC 6.8.2 on WinXP) has in principle no chance to detect this mistake, I saw it only in QuickCheck (aka at run-time). I think this is a basic problem with the language design. In small programs it's not so bad, but in large ones this could be. What do you think about it? Are there possible solutions or workarounds? Nicu Ionita

6 6

ANNOUNCE: tar 0.3.0.0
by Duncan Coutts 03 Mar '09

03 Mar '09

All, I'm pleased to announce a major new release of the tar package for handling ".tar" archive files. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/tar This release has a completely new and much improved API. See the hackage page for the API documentation. There are high level "all in one" functions for extracting or creating .tar files. More interestingly, it is easy to make variants by composing a pipeline. For example extracting a ".tar.gz" file is just: > Tar.unpack dir . Tar.read . GZip.decompress =<< BS.readFile tar Or creating a ".tar.bz2" file: > BS.writeFile tar . BZip.compress . Tar.write =<< Tar.pack base dir In addition it provides a full api for inspecting and constructing tar files without having to pack or unpack to local files. The functions are lazy which allows large archives to be processed in constant space. It is based on the tar handling code that has been in use in the cabal-install program for the last year or so. It has been tested on a large number of real world .tar.gz files so compatibility should be pretty good. There is also an 'htar' tool which is essentially a demo program for the tar library. It implements the common subset of the command line interface of the standard tar program, including gzip and bzip compression. Thanks to Christian Maeder for feedback on pre-release versions. Duncan

2 2

shuffle error
by friggin friggin 03 Mar '09

03 Mar '09

http://hpaste.org/fastcgi/hpaste.fcgi/view?id=1989#a1990 Is the algorithm wrong ar am I using it wrong? Also, is the second argument to shuffle supposed to eb random numbers, ie the function should be used in the IO Monad?

4 3

ANNOUNCE: The Industrial Haskell Group
by Duncan Coutts 02 Mar '09

02 Mar '09

We are pleased to announce the creation of the Industrial Haskell Group (IHG). The IHG is an organisation to support the needs of commercial users of the Haskell programming language. For more information, please see http://industry.haskell.org/ Currently, the main activity of the IHG is a collaborative development scheme, in which multiple companies fund work on the Haskell development platform to their mutual benefit. The scheme has started with three partners of the IHG, including Galois and Amgen. More details are available at http://industry.haskell.org/collab If your company is interested in joining then please e-mail info(a)industry.haskell.org -- Duncan Coutts, Haskell Consultant Well-Typed LLP, http://www.well-typed.com/

1 0

How to work with date?
by Magicloud Magiclouds 02 Mar '09

02 Mar '09

Hi, I am working on some calendar GUI thing. And I cannot find a library to operate the "date". Like, when `now <- getZonedTime`, how could I get all the dates of the week. Or when I got `today`, how to get the date of 10 days ago? Thanks. -- 竹密岂妨流水过山高哪阻野云飞

3 3

Assignment of grayCode
by Anonymous Anonymous 02 Mar '09

02 Mar '09

Hello, I'm working on a project for my university. But I do not understand the assignment. It asks me to write a function that does the following: grayCode :: Int -> ([Char] -> Int, Int -> [Char]) well in my opinion this assignment tells me to write some function that gets one input (an integer) and result two functions in one tuple. One function goes from [Char] to Int and the other one goes from Int to [Char]. But in my opinion this function will stay the same forever... am I mistaken? The assignment should be: Write an efficient code grayCode :: Int -> ([Char] -> Int, Int -> [Char]) that, for values between 2 and 36 (included), creates a Gray Code. That is, a tuple of two functions. Thanks!

3 2

major speed improvement: regex-tdfa reaches 1.0.0
by ChrisK 02 Mar '09

02 Mar '09

Announcing the version 1.0.0 release of regex-tdfa. I am proud of this release. This is not just a bug fix release. It is a serious improvement in the asymptotic running time. The previous versions allowed bad combinations of pattern and searched text length to scale badly in the length of the text. Previously the worst case for text of length N was O(N^3). The new worst case asymptotic runtime scaled as O(N). There is never any backtracking. And the worst case storage space is independent of N. The package is on hackage at http://hackage.haskell.org/cgi-bin/hackage-scripts/package/regex-tdfa The darcs repository is at http://darcs.haskell.org/packages/regex-unstable/regex-tdfa/ All non-overlapping matches are found and returned, along with all captured (parenthesized) subexpressions. The result is precisely what Posix extended regular expressions are supposed to return. To be concrete, consider example text with length of N of (2^n)+2: > longInput = replicate (2^n) 'a' ++ "bc" And define 4 worst-case-scenario patterns. I wrote the code and I know how to kill it: > wcs0 = "a*b" > wcs1 = "a*c" > wcs2 = "(a|aa)*b" > wcs3 = "(a|aa)*c" wcs0 is easy. wcs1 causes the old code to backtrack. wcs2 causes the old code's storage to scale as O(N). wcs3 causes both backtracking and O(N) storage with the old code. The old code's time scales as O(N) for wcs0, O(N^2) for wcs1 and wcs2, and O(N^3) for wcs3. The new code is always O(N). The actual timings for the old code on my G4 laptop for wcs on 2^8 and 2^9 and 2^10 are: Reason:compare-tdfa chrisk$ time ./Test-TDFA-np wcs3 8 +RTS -sstderr 2>&1 | head -4 ./Test-TDFA-np wcs3 8 +RTS -sstderr Test for [Char] Right [array (0,1) [(0,(257,1)),(1,(-1,0))]] 263,776,756 bytes allocated in the heap user 0m1.017s sys 0m0.058s Reason:compare-tdfa chrisk$ time ./Test-TDFA-np wcs3 9 +RTS -sstderr 2>&1 | head -4 ./Test-TDFA-np wcs3 9 +RTS -sstderr Test for [Char] Right [array (0,1) [(0,(513,1)),(1,(-1,0))]] 1,998,647,452 bytes allocated in the heap user 0m7.083s sys 0m0.289s Reason:compare-tdfa chrisk$ time ./Test-TDFA-np wcs3 10 +RTS -sstderr 2>&1 | head -4 ./Test-TDFA-np wcs3 10 +RTS -sstderr Test for [Char] Right [array (0,1) [(0,(1025,1)),(1,(-1,0))]] 15,653,277,200 bytes allocated in the heap user 0m53.350s sys 0m2.056s The doubling of length is causing a nearly eight-fold time increase. The heap allocation is also increasing nearly eight-fold. The new code with the same input pattern and texts gives: Reason:compare-tdfa chrisk$ time ./Test-TDFA2-0.99.19-np2 wcs3 8 +RTS -sstderr 2>&1 | head -4 ./Test-TDFA2-0.99.19-np2 wcs3 8 +RTS -sstderr Test for [Char] Right [array (0,1) [(0,(257,1)),(1,(-1,0))]] 2,135,324 bytes allocated in the heap user 0m0.017s sys 0m0.017s Reason:compare-tdfa chrisk$ time ./Test-TDFA2-0.99.19-np2 wcs3 9 +RTS -sstderr 2>&1 | head -4 ./Test-TDFA2-0.99.19-np2 wcs3 9 +RTS -sstderr Test for [Char] Right [array (0,1) [(0,(513,1)),(1,(-1,0))]] 3,588,656 bytes allocated in the heap user 0m0.024s sys 0m0.017s Reason:compare-tdfa chrisk$ time ./Test-TDFA2-0.99.19-np2 wcs3 10 +RTS -sstderr 2>&1 | head -4 ./Test-TDFA2-0.99.19-np2 wcs3 10 +RTS -sstderr Test for [Char] Right [array (0,1) [(0,(1025,1)),(1,(-1,0))]] 6,345,436 bytes allocated in the heap user 0m0.038s sys 0m0.018s Note that the heap allocation for the 1026 character example above is 2466 times less than the old code. That was too fast to prove the scaling, so take more input: Reason:compare-tdfa chrisk$ time ./Test-TDFA2-0.99.19-np2 wcs3 20 +RTS -sstderr 2>&1 | head -4 ./Test-TDFA2-0.99.19-np2 wcs3 20 +RTS -sstderr Test for [Char] Right [array (0,1) [(0,(1048577,1)),(1,(-1,0))]] 5,708,574,848 bytes allocated in the heap user 0m26.023s sys 0m0.985s Reason:compare-tdfa chrisk$ time ./Test-TDFA2-0.99.19-np2 wcs3 21 +RTS -sstderr 2>&1 | head -4 ./Test-TDFA2-0.99.19-np2 wcs3 21 +RTS -sstderr Test for [Char] Right [array (0,1) [(0,(2097153,1)),(1,(-1,0))]] 11,416,354,056 bytes allocated in the heap user 0m52.656s sys 0m1.985s The length and time both doubled, as did the heap allocation. And the new code has searched two million characters in the time the old code searched one thousand. How about away from the worst case scenario? On the testing suite the new code is running slightly slower: Reason:compare-tdfa chrisk$ time ./Test-TDFA-np -r 1 100 > /dev/null user 0m4.841s sys 0m3.019s Reason:compare-tdfa chrisk$ time ./Test-TDFA2-0.99.19-np2 -r 1 100 > /dev/null user 0m5.970s sys 0m3.012s So that is an increase of execution time of 14%. This small dip in performance might be reclaimable with more optimization. I think the gain in worst case performance already offsets the slight cost. The code for String is complete. The strict and lazy bytestrings and the (Seq Char) are currently using the String code for matching. This will be improved in a future release. Cheers, Chris The small print: regex-tdfa will still behave badly in space and time if given a pathological pattern, e.g. "(((a|aa){0,100}){0,100}){0,100}". But, I am hopeful than I can improve regex-tdfa to behave well with the patterns like this one. That is my vague goal for a future version 2.0.0 release. The very small print: I have been using ghc-6.10.1, and I think I have carried over cabal switches to make ghc-6.8.3 also work. The library probably can work with ghc-6.6, but the cabal file will need editing first as well as fixes to "Text.Regex.TDFA.NewDFA.copySTU".

3 2

A foray into type-level programming, and getting stuck
by George Pollard 02 Mar '09

02 Mar '09

Okay, so I've written a small library to generalize 'fst' and 'snd' to arbitrary tuples, but I'd like to extend it a bit. I'm using the type-level library to do the thinking :) Imports and defines first: > {-# LANGUAGE UnicodeSyntax, MultiParamTypeClasses, > FunctionalDependencies, FlexibleInstances, FlexibleContexts, > UndecidableInstances, DeriveDataTypeable, OverlappingInstances, > ScopedTypeVariables #-} > import Prelude hiding ((-),Eq) > import qualified Prelude as P > import Data.TypeLevel.Num.Sets > import Data.TypeLevel.Num.Reps > import Data.TypeLevel.Num.Aliases > import Data.TypeLevel.Bool > import Data.TypeLevel.Num.Ops > import Data.Typeable I start by requiring that if you can access element 'n', you should be able to access element 'n-1'. > class (ImplementsPrev t n a) ⇒ Nthable t n a | t n → a where > nth ∷ n → t → a > > class (Pos n) ⇒ ImplementsPrev t n a > instance (Pred n n', Nthable t n' a') ⇒ ImplementsPrev t n a > instance ImplementsPrev t D1 a So, this is a simple induction. Testing it with the nthable instances confirms that it works; removing either of the first two lines stops the code from compiling, hurrah! > instance Nthable (a,b,c) D1 a where nth _ (a,_,_) = a > instance Nthable (a,b,c) D2 b where nth _ (_,b,_) = b > instance Nthable (a,b,c) D3 c where nth _ (_,_,c) = c Now, I have heard talk/suggestions of revamping tuples in Haskell to a more flexible system. Perhaps we would like to do it like this (modulo strictness annotations): > data (Nat n) ⇒ Tuple n a b = Tuple a b > deriving (Show,Read,Typeable,P.Eq,Ord) > infixr 0 `comma` > -- comma :: a -> (b ~> c) -> (a ~> (b ~> c)) -- to investigate > comma ∷ (Succ n n') ⇒ a → Tuple n b c → Tuple n' a (Tuple n b c) > x `comma` y = Tuple x y > empty ∷ Tuple D0 () undefined > empty = Tuple () undefined Thus, we can create, e.g. (1 `comma` 2 `comma` empty). Now, I'd like to be able to write Nthable instances, so I start with the base case: > instance (n :>=: D1) ⇒ Nthable (Tuple n a b) D1 a where > nth _ (Tuple a _) = a This works well. However, I am really stuck on the instance for the inductive case. My first idea was this: > instance (Pred x x', Nthable b x' r) ⇒ Nthable (Tuple n a b) x r where > nth _ (Tuple _ b) = nth (undefined ∷ x') b But this doesn't work, muttering about IncoherentInstances and hidden datatypes from the type-level library. So, I turn to Haskell café for help :)

3 3

Re: [Haskell-cafe] Basic problem in Haskell language design?
by Daniel Schüssler 02 Mar '09

02 Mar '09

Hi, On Sunday 01 March 2009 14:26:42 Nicu Ionita wrote: > [...] > movesFromWord8s (f:t:ws) = (f, t) : movesFromWord8s ws > moverFromWord8s _ = [] > [...] > Are there possible solutions or workarounds? for the particular problem of having to repeat the function name, you could use "case": movesFromWord8s x = case x of f:t:ws -> (f, t) : movesFromWord8s ws _ -> [] (at the cost of one extra variable name :)) Greetings, Daniel

1 0

Take a break: write an essay for Onward! Essays
by Simon Peyton-Jones 02 Mar '09

02 Mar '09

Friends Writing papers is fun, we mostly only get to write one *kind* of paper. Here is an opportunity to write something in a totally different style: Submit an essay to Onward! Essays Deadline: 20 April 2009 http://onward-conference.org/calls/foressays An Onward! essay is a thoughtful reflection upon software-related technology. Its goal is to help the reader to share a new insight, engage with an argument, or wrestle with a dilemma. A successful essay is a clear and compelling piece of writing that explores a topic important to the software community. The subject area should be interpreted broadly, including the relationship of software to human endeavours, or its philosophical, sociological, psychological, historical, or anthropological underpinnings. An essay can be an exploration of its topic, its impact, or the circumstances of its creation; it can present a personal view of what is, explore a terrain, or lead the reader in an act of discovery; it can be a philosophical digression or a deep analysis. It can describe a personal journey, perhaps that by which the author reached an understanding of such a topic. I'm the program chair, and I'd love to get submissions from the POPL/ICFP/types community. Reflections on programming languages, types, testing, verification, software engineering, compilers, society, ... you name it. Anything to do with software. NB: Onward! is co-located with OOPSLA, but they are otherwise unrelated. OO is fine, but not required. Don't forget: 20th April. Simon PS: To get your imagination going, here are a couple of (strongly-contrasting) past essays: * Dan Grossman "The transactional memory / garbage collection analogy" http://www.cs.washington.edu/homes/djg/papers/analogy_oopsla07.pdf * Dick Gabriel "Designed as designer" http://dreamsongs.org/DesignedAsDesigner.html

2 1

Hint & Cabal Install weirdness.
by Joseph Fredette 02 Mar '09

02 Mar '09

I'm attempting to install hint, I started by doing: cabal install hint and it gives me the following error: cabal: dependencies conflict: ghc-6.10.1 requires process ==1.0.1.1 however process-1.0.1.1 was excluded because ghc-6.10.1 requires process ==1.0.1.0 So I decided to try installing it via darcs, expecting to either have it work, or boil it down to one or two dependencies that were causing the problem, my hunch was right, it boils down to the ghc-mtl package, leading to the same error as above. My question is, how can I fix this? Doing a ghc-pkg hide on either process package breaks Cabal and Haddock (among others) according to the error message, and even after that happens, cabal complains about needing ghc >= 6.6 (or 6.8, depending on which package I disable), even though I have ghc 6.10. Detailed system info follows, help me haskell-cafe-kenobi(s), you're (all) my only hope(s)! Sysinfo: Arch Linux: uname -a gives: Linux Erdos 2.6.28-ARCH #1 SMP PREEMPT Mon Feb 2 22:22:59 UTC 2009 i686 Intel(R) Celeron(R) CPU 3.06GHz GenuineIntel GNU/Linux ghc --version gives: The Glorious Glasgow Haskell Compilation System, version 6.10.1 cabal --version: cabal-install version 0.6.0 using version 1.6.0.1 of the Cabal library Thanks again, /Joe

2 2

Supplying a default implementation for a typeclass based on another class
by Svein Ove Aas 02 Mar '09

02 Mar '09

I'm in the process of writing a distributed filesystem (in haskell, yay), which of course means I'm using Binary for de/serialization. Now, that's fine enough, but for simplicity (and for wireshark), I'd like to be able to have Binary fall back on an instance based on Show/Read for any type that lacks any other Binary instance.. Well, I understand why this would be somewhere between extremely hard and impossible in haskell '98, but I'm not entirely up on all the extensions, so I thought I'd ask - given every extension implemented in ghc 6.10.1, is there any reasonable way to do this?

6 7

Re: a newbies confusion with repositories - darcs or git
by trentbuck＠gmail.com 02 Mar '09

02 Mar '09

Max Battcher <me(a)worldmaker.net> writes: > +1. For the most part this was a great email. It probably belongs > immortalized on the darcs blog and elsewhere. It could even go in the manual! I think the first two chapters of the manual should be 1. Why Darcs? 2. Quick Start ...and the stuff about compiling darcs and migrating from other VCSs moved either to the end (as appendices) or simply onto the wiki.

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nubBy changed?
by Tim Newsham 02 Mar '09

02 Mar '09

Did nubBy change recently? In 6.8.2 I could generate primes as: nubBy (\a b -> b `mod` a == 0) [2..] but in 6.10.1 I have to use nubBy (\a b -> a `mod` b == 0) [2..] Is this change intentional? If so, what is the reason? Tim Newsham http://www.thenewsh.com/~newsham/

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Re: [Haskell-cafe] Re: memory issues
by Martin Huschenbett 02 Mar '09

02 Mar '09

ChrisK schrieb: > Bulat is right about making Block's fields strict. > >> >> -- | Get the offsets between entries in a list >> getSizes :: [Integer] -> [Integer] >> getSizes (x:y:[]) = [y - x] >> getSizes (x:y:ys) = (y - x):(getSizes (y:ys)) > > You should change the first part to add maxSize: > > > getSizes :: [Integer] -> [Integer] > > getSizes (x:y:[]) = [y - x,maxSize] > > getSizes (x:y:ys) = (y - x):(getSizes (y:ys)) > > This avoids the ugly use of (++) below. Note that appending to a singly > linked list is a bad "code smell": But Chris' version changed semantics. It should be > getSizes :: [Integer] -> [Integer] > getSizes (x:y:[]) = [y-x,maxSize-y] > getSizes (x:y:ys) = (y-x):getSizes (y:ys) instead. But > getSizes :: [Integer] -> [Integer] > getSizes [x] = [maxSize-x] > getSizes (x:y:ys) = (y-x):getSizes (y:ys) is even better as it doesn't repeat the y-x term. Regards, Martin.

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differences between Data.Array and Data.Vector
by Manlio Perillo 02 Mar '09

02 Mar '09

Hi. In Hackage there are some packages named "*array*", and others named "*vector*". What are the differences? Is available a guide to the various data structures available in Haskell? Thanks Manlio Perillo

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odd problem with export list of System.IO
by Manlio Perillo 01 Mar '09

01 Mar '09

Hi. Maybe I'm missing something, but I don't understand why the following program: module Main where import System.IO (Handle, withFile, ReadMode) main = do return fails to compile, with a Module `System.IO' does not export `ReadMode' Thanks Manlio Perillo

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memory-efficient data type for Netflix data - UArray Int Int vs UArray Int Word8
by Kenneth Hoste 01 Mar '09

01 Mar '09

Hello, I'm having a go at the Netflix Prize using Haskell. Yes, I'm brave. I kind of have an algorithm in mind that I want to implement using Haskell, but up until now, the main issue has been to find a way to efficiently represent the data... For people who are not familiar with the Netflix data, in short, it consist of roughly 100M (1e8) user ratings (1-5, integer) for 17,770 different movies, coming from 480,109 different users. The idea I have in mind requires fast access to all the ratings for a particular user, so I was thinking about an IntMap in terms of user ids, which maps to movie id/rating pairs somehow. To see if I could efficiently represent the data set in this way, I wrote a small Haskell program (attached) which uses the following data type: type data = IntMap (UArray Int Word8) -- map of user IDs to ratings (lacks movie IDs) For convenience, and because I've been discussing this with various people in #haskell @ IRC, the code is also available here: http://hpaste.org/fastcgi/hpaste.fcgi/view?id=1671#a1671 . I'm aware that the way in which the UArray's are constructed (i.e. by adding a single element each time), is far from efficient performance-wise, but that's not the point here... By reformatting the raw data, I can easily read in the data more efficiently. The issue I ran into is that changing the data type to the following, doesn't yield any significant different in memory usage. type data = IntMap (UArray Int Int) -- use Int instead of Word8 for a user rating Someone (dolio) @ #haskell suggested that maybe UArray is not byte packed for Word8, which would cause little difference with a UArray containing Int's, but someone else (dons @ #ghc) was able to tell me it _is_ byte packed. Does anyone know why the Word8 version is not significantly better in terms of memory usage? greetings, Kenneth PS: My adventures on trying to tackle the Netflix Prize problem with Haskell can be followed at http://boegel.kejo.be. -- Kenneth Hoste ELIS - Ghent University email: kenneth.hoste(a)elis.ugent.be blog: http://www.elis.ugent.be/~kehoste/blog website: http://www.elis.ugent.be/~kehoste

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Problem with haddock - it dislikes my comments
by Colin Paul Adams 01 Mar '09

01 Mar '09

Having just read the Haddock manual , I am haddocking (may I copyleft that verb?) my code. But half-way through this data type, I discover that haddock rejects my non-haddock comments, although GHC is fine: -- | Non-interactive representation of a Chu Shogi move data Move = Pass Piece Coordinate -- ^ Double move to empty square and back to origin | Igui Piece Coordinate -- ^Capture without moving Piece Coordinate -- Captured piece | Double_move Piece -- ^ Other double moves Coordinate -- Initial location Coordinate -- First destination (Maybe Piece) -- Capture? Coordinate -- Second destination (Maybe Piece) -- Capture? | Capture Piece Coordinate Piece Coordinate Bool -- Promote? Bool -- Declined to promote | Move Piece Coordinate Coordinate Bool Bool How can I document the components of each constructor? -- Colin Adams Preston Lancashire

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Can't install mkcabal because of pcre-lite
by Colin Paul Adams 01 Mar '09

01 Mar '09

cabal: Error: some packages failed to install: mkcabal-0.4.2 depends on pcre-light-0.3.1 which failed to install. pcre-light-0.3.1 failed during the configure step. The exception was: exit: ExitFailure 1 Downloading pcre-light-0.3.1... Configuring pcre-light-0.3.1... cabal: Missing dependency on a foreign library: * Missing C library: pcre This problem can usually be solved by installing the system package that provides this library (you may need the "-dev" version). If the library is already installed but in a non-standard location then you can use the flags --extra-include-dirs= and --extra-lib-dirs= to specify where it is. I'm on fedora 10. I have package pcre installed. But yum install pcre-dev so no such package. Anyone know the anser? -- Colin Adams Preston Lancashire

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MPTC inheritance
by Derek Gladding 01 Mar '09

01 Mar '09

Please forgive me if I'm still mentally contaminated by the OO way of seeing (and discussing) the universe, but I'm trying to figure out how to "inherit an interface" from a multi-parameter type class. I have a Graph class that's parameterisable by Node and Edge type: class (Node a, Edge b) => Graph a b where (lots of stuff that you can do with Graph a b) Now, I'd like to build a FooGraph on top of this that adds additional capabilities: class (Graph a b) => FooGraph a b where (lots of additional stuff) but this isn't allowed (kind mismatch). Of couse, I can do: class (Node a, Edge b) => FooGraph a b but this means that I have to manually replicate the Graph a b operations in the FooGraph a b class definition, which is (a) work that the machine should (?) be able to do for me, and (b) fragile. Any pointers / wisdom would be very much appreciated. - Derek

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missing support for NFData in uvector package
by Manlio Perillo 01 Mar '09

01 Mar '09

Today I noticed that there is no instance declaration for NFData, in the uvector package. The definition is quite simple: instance NFData a => NFData (UArr a) where -- NOTE: UArr is already strict rnf array = array `seq` () but it is important. In a my program I was using a tuple of two arrays, and plain `seq` did not worked. Regards Manlio Perillo

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Bug in HLint or haskell-src-exts?
by Martin Huschenbett 01 Mar '09

01 Mar '09

Hello Haskellers, I've got the following piece of code type Memory addr value = Map.Map addr value type Stack item = [item] data MachineState addr value item = MachineState { memory :: Memory addr value , stack :: Stack item } deriving (Show) newtype Machine addr value item m a = Machine { unMachine :: StateT (MachineState addr value item) m a } deriving (Monad, MonadState (MachineState addr value item), MonadTrans, MonadIO) and HLint complains: Machine.hs:20:31: Parse failure, Parse error This is exactly the position of the opening bracket after MonadState. Why can GHC parse this and HLint cannot? Regards, Martin.

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Re: [Haskell-cafe] Performance question
by haskell＠kudling.de 01 Mar '09

01 Mar '09

Hi, thanks for your input. >You can get reasonable numeric performance out of GHC, but you need to >work at it. There is some advice in the GHC manual at >http://www.haskell.org/ghc/docs/latest/html/users_guide/faster.html I am using -O2 and strictness already. Currently i can only imagine to define a data type in order to use unboxed Ints instead of the accumulator tuple. The thing is that i don't see in the profile output yet what to improve. There are some allocations going on in "main", but i don't know what causes it. >The first thing I would do is replace your >isInCircle :: (Floating a, Ord a) => (a,a) -> Bool >with >isInCircle :: (Double, Double) -> Bool Can you point me to why that matters? > >Ben. > > > >On 26/02/2009, at 8:53 PM, haskell(a)kudling.de wrote: > >> Hi, >> >> i have compared a C++ implementation with a Haskell implementation >> of the Monte Carlo Pi approximation: >> >> http://lennart.kudling.de/haskellPi/ >> >> The Haskell version is 100 times slower and i wonder whether i do >> something obvious wrong. >> >> Profiling says that the majority of the time is spend in "main". But >> i have no idea where. >> >> Can someone give me a hint? >> >> Thanks, >> Lenny >> >> >

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Coming up with a better API for Network.Socket.recv
by Johan Tibell 01 Mar '09

01 Mar '09

Hi all, I find it quite inconvenient to use the `recv` function in Network.Socket as it throws an exception when reaching EOF and there's no way to check whether EOF has been reached before calling `recv`. This means that all calls to `recv` needs to be wrapped in an exception handler. I've been thinking about changing the version of `recv` that's included in the network-bytestring library [1] so it behaves differently from the one in the network library. Before I do so I thought I should see if we can reach a consensus on what a nicer definition of `recv` would look like. My current thinking is that it would mimic what C/Python/Java does and return a zero length ByteString when EOF is reached. I'm also interested in understanding the reasons behind the design of the `recv` function in the network library. More generally, I'm interested in discussing the pros and cons of the current Haskell I/O library design where the different read functions throw EOF exceptions and you have to call e.g. hIsEOF before reading from a Handle. 1. http://github.com/tibbe/network-bytestring Cheers, Johan

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controlling timeout for Network.Socket.connect - how?
by Belka 01 Mar '09

01 Mar '09

Hello, communion people! I have a problem and ask for an advice. I'm dealing with sockets on *Linux* platform (Network.Socket). The problem is that I can't fully control timeout for (connect :: Socket -> SockAddr -> IO ()) operation. On my system the timeout is - 3 seconds - I want to be able to change that in run-time. Well I managed to find out how to make it LESS THAN 3 seconds - using System.Timeout. But how to make timeout bigger (for example 9 seconds) is a mystery. (Notice: in order to achieve 9 seconds timeout - just repeating *connect* 3 times won't be effective for long-slow-way-connections. So it's not a solution.) The source code of Network.Socket.connect, taken from darcs: --------------------------------- -- Connecting a socket -- -- Make a connection to an already opened socket on a given machine -- and port. assumes that we have already called createSocket, -- otherwise it will fail. -- -- This is the dual to $bindSocket$. The {\em server} process will -- usually bind to a port number, the {\em client} will then connect -- to the same port number. Port numbers of user applications are -- normally agreed in advance, otherwise we must rely on some meta -- protocol for telling the other side what port number we have been -- allocated. connect :: Socket -- Unconnected Socket -> SockAddr -- Socket address stuff -> IO () connect sock@(MkSocket s _family _stype _protocol socketStatus) addr = do modifyMVar_ socketStatus $ \currentStatus -> do if currentStatus /= NotConnected then ioError (userError ("connect: can't peform connect on socket in status " ++ show currentStatus)) else do withSockAddr addr $ \p_addr sz -> do let connectLoop = do r <- c_connect s p_addr (fromIntegral sz) if r == -1 then do rc <- c_getLastError case rc of 10093 -> do -- WSANOTINITIALISED withSocketsDo (return ()) r <- c_connect s p_addr (fromIntegral sz) if r == -1 then (c_getLastError >>= throwSocketError "connect") else return r _ -> throwSocketError "connect" rc else return r connectBlocked = do #if !defined(__HUGS__) threadWaitWrite (fromIntegral s) #endif err <- getSocketOption sock SoError if (err == 0) then return 0 else do ioError (errnoToIOError "connect" (Errno (fromIntegral err)) Nothing Nothing) connectLoop return Connected --------------------------------- I know that controlling timeout is somehow connected to select(2) (I'm currently investigating this matter...), but it's not in the Network or Network.Socket libs (but in the libs that they FFI with). Hope I won't have to rewrite these low-level functions.... >__< Could anybody, please share some experience on how to adjust timeout for *connect*? Thanks in advance, Best regards, Belka -- View this message in context: http://www.nabble.com/controlling-timeout-for-Network.Socket.connect---how-… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Haskell Weekly News: Issue 107 - February 28, 2009
by Brent Yorgey 01 Mar '09

01 Mar '09

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20090228 Issue 107 - February 28, 2009 --------------------------------------------------------------------------- Welcome to issue 107 of HWN, a newsletter covering developments in the [1]Haskell community. Announcements Google Summer of Code 2009 - mentors wanted!. Eric Kow [2]reminded everyone that darcs will be applying to be a mentoring organisation for the Google Summer of Code project 2009, and is seeking people to serve as mentors. You need not be a darcs expert to serve as a mentor! c2hs 0.16.0. Duncan Coutts [3]announced the release of [4]c2hs version 0.16.0, a tool which assists in the development of Haskell bindings to C libraries by extracts interface information from C header files and generating Haskell code with foreign imports and marshaling. The major change in this release is that it now uses the [5]Language.C library. X Haskell Bindings 0.2. Antoine Latter [6]announced the 0.2.* series release of the [7]X Haskell Bindings, mostly aimed at making the API prettier. The goal of XHB is to provide a Haskell implementation of the X11 wire protocol, similar in spirit to the [8]X protocol C-language Binding (XCB). text and text-icu, fast and comprehensive Unicode support using stream fusion. Bryan O'Sullivan , on behalf of the Data.Text team, [9]announced the release of preview versions of two new packages: [10]text 0.1, providing fast, packed Unicode text support with modern stream fusion, and [11]text-icu 0.1, which augments text with comprehensive character set conversion support and normalization (and soon more), via bindings to the ICU library. Boston Area Haskell User's Group, first meeting on Saturday February 28th. Shae Matijs Erisson [12]announced the first meeting of the [13]Boston Area Haskell User's Group this Saturday, February 28, at 2pm. Directions are on the web page; you can also check out the [14]mailing list. New version of Hieroglyph released: Hieroglyph 1.1 is on hackage. Jeff Heard [15]announced the release of a new version of [16]Hieroglyph; the biggest change is that it now uses Russell O'Connor's excellent [17]Data.Colour library. bug fix for regex-tdfa, version 0.97.4 (and "regex-ast"). ChrisK [18]announced another bug fix release for the [19]regex-tdfa package, which fixes another tricksy bug. This is now the only known regex library that passes the entire test suite. Hac5: April 17-19, Utrecht -- Book Now!. Sean Leather [20]announced some updated information regarding the [21]5th Haskell Hackathon. The executive summary: hotel or hostel accommodation may be hard to come by, so book your room now, and check out the website for lots of useful information. pkgenv - disposable, isolated pkg environments. Paolo Losi [22]announced a tool, [23]pkgenv, which facilitates setting up isolated, disposable package environments. Blog noise [24]Haskell news from the [25]blogosphere. * JP Moresmau: [26]A high-level GUI library for Haskell. * Magnus Therning: [27]More fun with Cabal, visualising dependencies. Giant graphs are fun! * Magnus Therning: [28]A no-no in my book (found in Cabal). * Bryan O'Sullivan: [29]Finally! Fast Unicode support for Haskell. Data.Text is here! * happstack.com: [30]Happstack now outputs Apache Combined Logs. * GHC / OpenSPARC Project: [31]Benchmarking. * Christophe Poucet (vincenz): [32]Fibonacci in the Type System. * Eric Kow (kowey): [33]inkscape layers. * Magnus Therning: [34]Another reason to create distro-specific packages for Haskell modules. * boegel: [35]Using Haskell to win the Netflix Prize. * Magnus Therning: [36]Simple Cabal parsing. * GHC / OpenSPARC Project: [37]Bugfixes and pretty graphs. * Jeff Heard: [38]New version of Hieroglyph released.. * Chris Done: [39]Vgrabbj hacking. * Conal Elliott: [40]Paper: Beautiful differentiation. Another draft paper from Conal. * happstack.com: [41]Momentum builds as we approach Happstack 0.2. * Luke Palmer: [42]RTS Research. * GHC / OpenSPARC Project: [43]Sanity. * Darcs: [44]darcs weekly news #18. * Don Stewart (dons): [45]Can Haskell give me a pony?. The answer is: Yes! Haskell can do that. * Neil Mitchell: [46]Hoogle package search. * Alex Mason: [47]AVar changes. * Xmonad: [48]Using gimp under xmonad. It can actually be quite nice, despite what you might think. * FP-Syd: [49]Sydney FP Group: FP-Syd #12.. * Eric Kow (kowey): [50]implementing join in terms of (>>=). * GHC / OpenSPARC Project: [51]Triage. * Benjamin L. Russell: [52]Learning Haskell through Category Theory, and Adventuring in Category Land: Like Flatterland, Only About Categories. Quotes of the Week * lilac: haskell's learning curve is like this: | * cowardlydragon: [from a reddit comment thread] Don't get me started on monad. What is that, a man with a single testicle? About the Haskell Weekly News New editions are posted to [53]the Haskell mailing list as well as to [54]the Haskell Sequence and [55]Planet Haskell. [56]RSS is also available, and headlines appear on [57]haskell.org. To help create new editions of this newsletter, please see the information on [58]how to contribute. Send stories to byorgey at cis dot upenn dot edu. The darcs repository is available at darcs get [59]http://code.haskell.org/~byorgey/code/hwn/ . References 1. http://haskell.org/ 2. http://www.haskell.org//pipermail/haskell-cafe/2009-February/056798.html 3. http://www.haskell.org//pipermail/haskell/2009-February/021052.html 4. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/c2hs 5. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/language%2Dc 6. http://article.gmane.org/gmane.comp.lang.haskell.general/16888 7. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/xhb 8. http://xcb.freedesktop.org/ 9. http://article.gmane.org/gmane.comp.lang.haskell.cafe/53780 10. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/text 11. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/text-icu 12. http://article.gmane.org/gmane.comp.lang.haskell.cafe/53761 13. http://www.haskell.org/haskellwiki/Boston_Area_Haskell_Users%27_Group 14. http://groups.google.com/group/bostonhaskell 15. http://article.gmane.org/gmane.comp.lang.haskell.cafe/53549 16. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Hieroglyph 17. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/colour 18. http://article.gmane.org/gmane.comp.lang.haskell.cafe/53525 19. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/regex%2Dtdfa 20. http://article.gmane.org/gmane.comp.lang.haskell.cafe/53510 21. http://haskell.org/haskellwiki/Hac5 22. http://article.gmane.org/gmane.comp.lang.haskell.cafe/53448 23. http://bitbucket.org/pao/pkgenv/raw/488bfe8e58dd/pkgenv 24. http://planet.haskell.org/ 25. http://haskell.org/haskellwiki/Blog_articles 26. http://jpmoresmau.blogspot.com/2009/02/high-level-gui-library-for-haskell.h… 27. http://therning.org/magnus/archives/534 28. http://therning.org/magnus/archives/523 29. http://www.serpentine.com/blog/2009/02/27/finally-fast-unicode-support-for-… 30. http://blog.happstack.com/2009/02/26/happstack-now-outputs-apache-combined-… 31. http://ghcsparc.blogspot.com/2009/02/benchmarking.html 32. http://cpoucet.wordpress.com/2009/02/26/fibonacci-in-the-type-system/ 33. http://koweycode.blogspot.com/2009/02/inkscape-layers.html 34. http://therning.org/magnus/archives/522 35. http://boegel.kejo.be/?q=node%2F8 36. http://therning.org/magnus/archives/514 37. http://ghcsparc.blogspot.com/2009/02/bugfixes-and-pretty-graphs.html 38. http://vis.renci.org/jeff/2009/02/24/new-version-of-hieroglyph-released/ 39. http://chrisdone.com/blog/html/2009-02-25-vgrabbj.html 40. http://conal.net/blog/posts/paper-beautiful-differentiation/ 41. http://blog.happstack.com/2009/02/23/momentum-builds-as-we-approach-happsta… 42. http://lukepalmer.wordpress.com/2009/02/24/rts-research/ 43. http://ghcsparc.blogspot.com/2009/02/sanity.html 44. http://blog.darcs.net/2009/02/darcs-weekly-news-18.html 45. http://donsbot.wordpress.com/2009/02/22/can-haskell-give-me-a-pony/ 46. http://neilmitchell.blogspot.com/2009/02/hoogle-package-search.html 47. http://axman6.homeip.net/blog/2009/02/avar-changes.html 48. http://xmonad.wordpress.com/2009/02/21/using-gimp-under-xmonad/ 49. http://www.mega-nerd.com/erikd/Blog/FP-Syd/fp-syd-12.html 50. http://koweycode.blogspot.com/2009/02/implementing-join-in-terms-of.html 51. http://ghcsparc.blogspot.com/2009/02/triage.html 52. http://dekudekuplex.wordpress.com/2009/01/16/learning-haskell-through-categ… 53. http://www.haskell.org/mailman/listinfo/haskell 54. http://sequence.complete.org/ 55. http://planet.haskell.org/ 56. http://sequence.complete.org/node/feed 57. http://haskell.org/ 58. http://haskell.org/haskellwiki/HWN 59. http://code.haskell.org/~byorgey/code/hwn/

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And another request on how to get started - JSON package
by Gü?nther Schmidt 28 Feb '09

28 Feb '09

Hi, Sigbjorn has contributed tons of very useful packages and particularly quite a few package that are especially useful for the handful of us haskell-windows users. Right now though I could do with an example for how to actually use his JSON package. Since it's actively maintained and already there I'd like to avoid starting from scratch and re-implement the whole thing by using the samples from RWH. I had hoped that RWH and his package are 1:1 alas they are not. Günther

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