- Haskell-Cafe - Haskell.org

memory issues
by Rogan Creswick 28 Feb '09

28 Feb '09

First off, my apologies for breaking etiquette, if/when I do -- I've only just joined Haskell-cafe, and I'm quite new to Haskell. I have recently been trying to process a large data set (the 2.8tb wikipedia data dump), and also replace my scripting needs with haskell (needs that have previously been filled with bash, perl, and bits of Java). Last week I needed to do some quick scanning of the (7zipped) wikipedia dump to get a feel for the size of articles, and from that determine the best way to process the whole enchilada... cutting to the chase, I ended up with a file consisting of byte offsets and lines matched by a grep pattern (a 250mb file). Specifically, 11m lines of: 1405: <page> 14062: <page> 15979: <page> 18665: <page> 920680797: <page> ...... 2807444041476: <page> 2807444043623: <page> I needed to know how large the lagest <page> elements were, so I'd know if they would fit in memory, and some idea of how many would cause swapping, etc. So, I wrote a simple app in haskell (below) to find the sizes of each <page> and sort them. Unfortunately, it consumes an absurd amount of memory (3+gb) and dies with an out-of-memory error. Given the input size, and what it is doing, this seems ridiculously high -- can anyone help me understand what is going on, and how I can prevent this sort of rampant memory use? I can provide a link to the input file if anyone wants it, but it doesn't seem particularly useful, given the simplicity and size. Since I needed to get results fairly quickly, I've re-implemented this in java, so that reference implementation is also available should anyone want it (the approach that is most similar to the haskell requires a 1.4gb heap, but by streaming the string->long parsing, that requirement drops to ~600mb, which seems pretty reasonable, since the *output* is 215mb.) Thanks! Rogan \begin{code} -- Compiled with: -- $ ghc --make offsetSorter.hs -- -- (ghc v. 6.8.2) -- -- Run with: -- $ time ./offsetSorter data/byteOffsets.txt > haskOffsets.txt -- offsetSorter: out of memory (requested 1048576 bytes) -- -- real 4m12.130s -- user 3m4.812s -- sys 0m5.660s --(OOM happened after consuming just over 3000mb of Virt, 2.6gb Res, according to top.) -- import System (getArgs) import Data.Maybe import Monad import Text.Printf (printf) import Data.Function (on) import Data.List (sort) import Data.ByteString (ByteString) import qualified Data.ByteString.Char8 as C8 import qualified Data.ByteString as B -- get the lines -- parse each line to get the offset. -- scan the list of offsets -- | The full file size: maxSize :: Integer maxSize = 2807444044080 -- | Block is a contiguous chunk of data. -- The first entry is the offset, the second is the length. data Block = Block { offset::Integer , size::Integer } deriving (Eq) -- | Ordering of Blocks is based entirely on the block size. instance Ord Block where compare = compare `on` size instance Show Block where show (Block o s) = (show o) ++ " " ++ (show s) -- turn the file into a list of offsets: getOffsets :: ByteString -> [Integer] getOffsets = catMaybes . map parseOffset . C8.lines -- | Pull out the offsets frome a line of the file. parseOffset :: ByteString -> Maybe Integer parseOffset s = do (i, _) <- C8.readInteger (C8.filter (/=':') s) Just i -- | 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)) -- | creates and returns a list of Blocks, given a file's content. blocks :: ByteString -> [Block] blocks s = zipWith (Block) offsets sizes where offsets = getOffsets s sizes = getSizes (offsets ++ [maxSize]) main :: IO () main = do args <- getArgs content <- B.readFile (args!!0) printf "%s" $ unlines $ map (show) (sort $! blocks content) \end{code}

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subscription problems for projects.haskell.org mailing list
by Wolfgang Jeltsch 28 Feb '09

28 Feb '09

Hello, I created a mailing list for Grapefruit on the Haskell Community Server (<grapefruit(a)projects.haskell.org>). If I try to subscribe to it, I receive a confirmation e-mail but my answers to this e-mail seem to get ignored. Does anyone have an idea what’s wrong here? Best wishes, Wolfgang

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Hardware for FRP programming - what should it support?
by Noam Lewis 28 Feb '09

28 Feb '09

Greetings, I've heard about the Reduceron (graph reduction machine in FPGA), and also FRP (functional reactive programming). What sort of features/capabilities/architecture would you expect from a processor that will be designed a-priori for FRP programming? I guess it will need graph-reduction capabilities for the Functional in FRP, but what other tools do we need or can we take advantage of for the Reactive Programming? I haven't thought about this much yet, just a question that came to mind. Any thoughts? - Noam

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Google Summer of Code 2009 - mentors wanted!
by Eric Kow 28 Feb '09

28 Feb '09

Hi everybody, Just a reminder that darcs will be applying to be a mentoring organisation for the Google Summer of Code project 2009. Anybody interested in mentoring a project? Darcs hackers? Haskellers in general? According to the GSoC FAQ, mentoring should take about 5 hours a week <http://code.google.com/opensource/gsoc/2009/faqs.html>. It would be a wonderful way to contribute to the darcs and Haskell communities and a fun learning experience to boot. Haskellers in general, if you've been thinking about contributing to darcs, give mentoring a try! Or if you're already working on a more general project like Grapefruit or Haskeline, you could think about mentoring as a way to turn darcs into one of your customers :-) Eric PS. Students and project ideas wanted too. Also, see you at the Hackathon! 17-19 April, Utrecht Previous discussions -------------------- * http://lists.osuosl.org/pipermail/darcs-users/2009-February/017766.html * http://lists.osuosl.org/pipermail/darcs-users/2009-February/017865.html -- Eric Kow <http://www.nltg.brighton.ac.uk/home/Eric.Kow> PGP Key ID: 08AC04F9

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Re: [Haskell-cafe] HackageDB suggestion [WAS: Re: Hidden module?]
by Cristiano Paris 28 Feb '09

28 Feb '09

On Fri, Feb 27, 2009 at 9:53 PM, Achim Schneider <barsoap(a)web.de> wrote: > ... > In general, just try the maintainer and/or author adresses given on > hsc2hs's hackage page. Ok, thanks. I suggest to add a comment section to every package's area in the HackageDB so as to let users report errors, info and the likes regarding the package. > I'd advice you to switch over to c2hs, which is actively developed, > while hsc2hs's last update date smells like abandonware. I had to use it as it's required by jhc. Thanks for the suggestion though. Cristiano

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ANNOUNCE: pqueue-mtl, stateful-mtl
by Louis Wasserman 28 Feb '09

28 Feb '09

Hello all, I just released two new packages on Hackage, stateful-mtl and pqueue-mtl. Stateful-mtl provides an ST monad transformer, several useful operations on generic monad transformers, and a monad transformer intended to cleanly externally wrap operations on a mutable array (including resizing operations). It provides wrappers to generic MArray instances, an "array" based on an IntMap, and a specialized transformer that completely wraps what is essentially a pared-down STArray into a monadic interface that doesn't mention ST at all. pqueue-mtl provides implementations of several structures supporting a generic 'single-in, single-out' paradigm (encapsulated in a typeclass named Queuelike), including stacks, queues, and several implementations of priority queues, including primarily a PQueue structure (in Data.Queue.PQueue) based on a pairing heap. In addition, the package provides monad transformers encapsulating single-threaded access to a Queuelike structure, and provides a fully encapsulated array-backed heap implementation (using the array transformers from stateful-mtl). The primary motivation for all this was to improve elegance of graph algorithms. The following is an implementation of a shortest-path algorithm based on the fgl library that returns an IntMap mapping each node to its parent in a shortest-path tree: type DijkstraM gr a b = IntMapT (Node, b) (PQueueT (Edge :-> b) (State (gr a b))) expand :: (Num b, Ord b, MonadQueue (Edge :-> b) m) => b -> Context a b -> m () expand d cxt = let x = node' cxt -- node being expanded in queueInsertAll [(y, x) :-> (d + w) | (y, w) <- lsuc' cxt] dijkstraM :: (Graph gr, Num b, Ord b) => DijkstraM gr a b () dijkstraM = execMaybeT $ forever $ do -- this line repeats a monadic operation until a pattern match fails False <- gets isEmpty Just ((v, w) :-> d) <- queueExtract statefully (match v) >>=? \ c -> writeAt v (w, d) >> expand d c -- performs an action if the match does not return Nothing dijkstra :: (Graph gr, Num b, Ord b) => gr a b -> Node -> IntMap (Node, b) dijkstra g v = evalState (runQueueTOn (execIntMapT_ dijkstraM) [(v, v) :-> 0]) g As an imperative programmer for many years, this is pretty much the most intuitive implementation of Dijkstra's algorithm that I've seen. Let me know what you think. Louis Wasserman wasserman.louis(a)gmail.com

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Re: Incremental array updates
by Keith Sheppard 28 Feb '09

28 Feb '09

I'm still learning haskell, so I may be missing something pretty obvious, but isn't this the kind of thing that the diff array types were created for. http://en.wikibooks.org/wiki/Haskell/Hierarchical_libraries/Arrays#DiffArra… -Keith >On Thu, Feb 26, 2009 at 06:45:27PM +0000, Ross Paterson wrote: >> Yes, bucketing problems like this are a common case that the standard >> functions cannot handle. Perhaps the libraries need a canned solution. > >Stratch that -- as Bulat points out, accumArray is such a canned solution.

2 1

Translating an imperative algorithm - negascout
by Colin Paul Adams 28 Feb '09

28 Feb '09

Hello Haskellers, I want to implement the negascout algorithm for the game I'm writing. Wikipedia gives the algorithm in imperative terms: http://en.wikipedia.org/wiki/Negascout I've tried to translate this into Haskell. I'm not sure if I'm going about it the right way, and if I am, if I've done it correctly. Any comments on my effort here, are welcome: module Move (negascout ) where {-# contract negascout Ok -> {depth | depth >= 0} -> Ok -> Ok -> Ok #-} negascout :: Node -> Int -> Int -> Int -> Int negascout node depth alpha beta = case depth == 0 || is_terminal node of True -> evaluate node False -> let child:rest = children node b = beta -- initial window is (-beta, -alpha) in negascout' child (depth-1) (- b) (- alpha) beta rest -- Implementation {-# contract negascout' Ok -> {depth | depth >= 0} -> Ok -> Ok -> Ok -> Ok -> Ok #-} negascout' :: Node -> Int -> Int -> Int -> Int -> [Node] -> Int negascout' node depth beta' alpha beta rest = let a = negate $ negascout child depth beta' alpha in case a > (- alpha) of True -> let alpha' = a in case alpha' >= beta of True -> alpha' -- beta cut-off False -> case alpha' >= (- beta') of -- null window failed high? True -> let alpha'' = negate $ negascout child depth (- beta) (- alpha') -- full re-search in case alpha'' >= beta of True -> alpha'' -- beta cut-off False -> case rest of [] -> alpha'' child':rest' -> let b' = alpha'' + 1 in negascout' child' depth (- b') alpha'' beta rest' False -> case rest of [] -> alpha' child':rest' -> let b' = alpha' + 1 in negascout' child' depth (- b') alpha' beta rest' False -> case rest of [] -> alpha child':rest' -> let b' = alpha + 1 in negascout' child' depth (- b') alpha beta rest' -- Colin Adams Preston Lancashire

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Samples for http package
by Gü?nther Schmidt 28 Feb '09

28 Feb '09

Hi everyone, are there any examples on how to use the current version of the http package? Günther

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How can you effectively manually determine the type?
by Anonymous Anonymous 28 Feb '09

28 Feb '09

Hello, I'm new at haskell and I have the following question: let's say I type the following: function = foldr until Now my first question is what is the type of this function? Well let's see what the type of until and foldr is: until :: (a -> Bool) -> (a -> a) -> a -> a foldr :: (a -> b -> b) -> b -> [a] -> b So I would be thinking: we fill until in the position of (a -> b -> b) so, a correspond with (a -> Bool) and b correspond with (a -> a) and b correspond with a. Hmm a small problem, I think we can divide that as follows: b1 corresponds with (a -> a) and b2 corresponds with a. So I get: foldr until :: b1 -> [a] -> b2 foldr until :: (a -> a) -> [a -> Bool] -> a Is this a correct way of thinking or am I wrong? And another question is: can someone give me an example how this can be executed? All my code that I tried to execute resulted in errors with "foldr until". Thanks!

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Sparse vector operations
by Grzegorz Chrupala 28 Feb '09

28 Feb '09

Hi all, In a couple of my projects I have needed to perform operations on (very) sparse vectors. I came up with the attached simple module which defines a typeclass and implements instances for simple and nested (Int)Maps. Is this the right way to go about it? Am I reinventing some wheels? Comments welcome. Best, -- Grzegorz http://www.nabble.com/file/p22247686/SparseVector.hs SparseVector.hs -- View this message in context: http://www.nabble.com/Sparse-vector-operations-tp22247686p22247686.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Trouble building ArrayRef 0.1.3
by Mads Lindstrøm 28 Feb '09

28 Feb '09

Hi When I try to build ArrayRef 0.1.3 I get: Control/Concurrent/LockingBZ.hs:159:54: Ambiguous type variable `e' in the constraint: `Exception e' arising from a use of `throw' at Control/Concurrent/LockingBZ.hs:159:54-60 Probable fix: add a type signature that fixes these type variable(s) I am compiling with: > runhaskell Setup.hs build I run Debian Linux with GHC 6.10.1. Anybody has a solution for my problem? Greetings, Mads Lindstrøm

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Making the pointfree package work with cabal
by Niemeijer, R.A. 28 Feb '09

28 Feb '09

Today I was very happy to discover the pointfree package, since lambdabot unfortunately doesn't work on Windows. The package works just fine, but the installation process is less than ideal. "cabal install pointfree" doesn't work and to install it manually you have to add containers and array to the build-depends list in the cabal file. To get rid of the warning about the build type you have to add build-type: Simple. I asked in the IRC channel what the best course of action was to fix this and they referred me here. The author of the package is Thomas Jäger, who should go by the IRC name TheHunter. I would hereby like to ask him to make these small changes and upload a new version, or to give me or someone else permission to do so. Regards, Remco Niemeijer

1 0

Data.Binary, strict reading
by Neil Mitchell 28 Feb '09

28 Feb '09

Hi, I want to read a file using Data.Binary, and I want to read the file strictly - i.e. when I leave the read file I want to guarantee the handle is closed. The reason is that (possibly immediately after) I need to write to the file. The following is the magic I need to use - is it all necessary, is it guaranteed correct, should I use something else? src <- decodeFile "_make/_make" Map.size mp `seq` performGC Thanks for all the helpful replies to the last post, I think I've nearly come up with a minimal test case I can give you, or at least characterise where the issue might lie. But I'll post to that thread when I've got the details. Thanks Neil

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Strict version of Data.Map.map
by Edsko de Vries 27 Feb '09

27 Feb '09

Hi, Is it possible to write a strict version of Data.Map.map (so that the Map becomes strict in the elements as well as the keys)? Thanks, Edsko

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darcs and Google Summer of Code
by Eric Kow 27 Feb '09

27 Feb '09

Dear Haskellers, Recently, there has been a suggestion that darcs apply to be a mentoring organisation for Google Summer of Code in its own right. Thanks! I think we will definitely try this out! Ideas: GUI and hashed-storage ----------------------------- So far, we have two active projects, active in the sense that there are interested students and mentors. The first is to work towards a sort of graphical interface for darcs (as has been suggested on this list). I suspect that we what we will likely do with this idea is to refine it into something that may either be part of a GUI (like a patch dependency viewer), or which will make it much easier for third parties to write a GUI in the future. I'll note that last year, we had a few interested students for this year and a potential mentor (Shelarcy from wxHaskell). Hopefully we can call on them again this year? There is also some work by Wolgang Jeltsch and students that we could talk about extending into a GSoC project. The second idea is to continue our performance work. Petr Ročkai has done some very interesting work in optimising the way that darcs stores files for its hashed and darcs-2 format repositories. In one of his tests, he reports having a possible tenfold speed-up in darcs whatsnew times, and a halving of the number of filesystem calls in one his tests. <http://bugs.darcs.net/issue1202>. It would be very interesting to see Petr continue this sort of work and perhaps tie it into of some of the other optimisations the darcs community have in mind. Anyway, you may be interested to know that we have a parallel discussion going on about this on the darcs-users list: http://lists.osuosl.org/pipermail/darcs-users/2009-February/017766.html We are also keeping a summary of this discussion here with our active ideas: http://wiki.darcs.net/index.html/GoogleSummerOfCode Hackathon --------- Finally, darcs will be holding its second hacking sprint within the Haskell Hackathon, April 17-19, Utrecht. There's already at least 5 of us from darcs/camp, and we would love to see more of you. Or if you're already planning on joining Hac5, come hack a little darcs while you're there! http://wiki.darcs.net/index.html/Sprints/2009-04 Hope to see you soon, -- Eric Kow <http://www.nltg.brighton.ac.uk/home/Eric.Kow> PGP Key ID: 08AC04F9

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Incremental array updates
by Daniel Kraft 27 Feb '09

27 Feb '09

Hi, I seem to be a little stuck with incremental array updates... I've got an array of "few" (some thousand) integers, but have to do a calculation where I incrementally build up the array. For sake of simplicity, for now I don't use a State-Monad but simply pass the array as state down the recursive calls. Unfortunatelly, I seem to experience problems with lazyness; when I run my program, memory usage goes up to horrific values! The simple program below reproduces this; when run on my machine, it uses up about 300 MB of real and 300 MB of virtual memory, and the system starts swapping like mad! I compiled with ghc --make -O3, ghc version 6.8.3 if that matters. BTW, I tried to make the array update strict using the `seq` as below, but with no effect... What am I doing wrong here? Many thanks, Daniel import Data.Array; arraySize = 1000 limit = 100000 type MyArray = Array Int Int emptyArray :: MyArray emptyArray = array (0, arraySize - 1) [ (i, 0) | i <- [0 .. arraySize - 1] ] procOne :: Int -> MyArray -> MyArray procOne a cnt | a > limit = cnt | otherwise = let ind = a `mod` arraySize oldcnt = cnt ! ind newarr = cnt // [(ind, oldcnt + 1)] in procOne (a + 1) (newarr `seq` newarr) main :: IO () main = do arr <- return $ procOne 0 emptyArray print $ arr ! 42

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ByteString questions
by Galchin, Vasili 27 Feb '09

27 Feb '09

Hello, 1) I noticed there is no "open" function in Data.ByteString. So when I call writeFile or readFile is there an implicit open? 2) For both readFile and writeFile, the first parameter is of type FilePath (which is of course alliased to just String). In any case, for Windows and POSIX OS's like Linux can read and write to a serial device like RS232 by specfiying the device path, e.g. /dev/tty01? Thanks, Vasili

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Missing documentation for Haddock
by Colin Paul Adams 27 Feb '09

27 Feb '09

On http://haskell.org/haddock/doc/html/module-attributes.html the not-home attribute is missing (it's documentation is present, but the attribute itself is not named). -- Colin Adams Preston Lancashire

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base-4 + gtk2hs-0.10.0 licensing
by Victor Nazarov 27 Feb '09

27 Feb '09

I wonder what software licence I can use to release my application. I've developed some education tool with the following dependencies: % ghci Main.hs GHCi, version 6.10.1: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer ... linking ... done. Loading package base ... linking ... done. Ok, modules loaded: Main, UI, Lambda, Lambda.Eval, Lambda.Zipper, Lambda.Show, Lambda.Parser, Lambda.Common. Prelude Main> main Loading package syb ... linking ... done. Loading package array-0.2.0.0 ... linking ... done. Loading package containers-0.2.0.0 ... linking ... done. Loading package bytestring-0.9.1.4 ... linking ... done. Loading package Win32-2.2.0.0 ... linking ... done. Loading package parsec-2.1.0.1 ... linking ... done. Loading package mtl-1.1.0.2 ... linking ... done. Loading package old-locale-1.0.0.1 ... linking ... done. Loading package time-1.1.2.2 ... linking ... done. Loading package glib-0.10.0 ... linking ... done. Loading package cairo-0.10.0 ... linking ... done. Loading package gtk-0.10.0 ... linking ... done. Loading package glade-0.10.0 ... linking ... done. I just don't know the options and I think licensing is subtle enough to ask for suggestions. Thanks in advance. -- Victor

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Re: Hoogle and Network.Socket
by John Lato 27 Feb '09

27 Feb '09

Achim Schneider wrote: > John Lato <jwlato(a)gmail.com> wrote: >> On Wed, Feb 25, 2009 at 4:45 PM, Brandon S. Allbery KF8NH >> <allbery(a)ece.cmu.edu> wrote: >> > On 2009 Feb 25, at 5:23, John Lato wrote: >> >> >> >> Brandon Allbery wrote: >> >>> >> >>> I have to second this; I'm a Unix sysadmin, 98% of the time if I'm >> >>> writing a program it's for Unix *and* requires POSIX APIxs, and >> >>> even if it could apply to Windows the program needed there would >> >>> be very significantly different. __And we have a Windows group for >> >>> that. >> >> >> >> 2. __As of now, the "Windows Group" seems to be mostly Duncan. __And >> > >> > Wrong Windows group: __Duncan doesn't work for us. >> > >> >> Sorry, I misunderstood you. I thought you meant a Windows group >> within the Haskell community, not within your company. >> >> Honestly, what I wrote wasn't directed at you. As I mentioned before, >> writing code as a Unix sysadmin has very different priorities than >> writing for many other problem domains. Most of your code wouldn't >> make sense outside a Unix context, whereas bytestrings, tries, or >> graph libraries would. >> > I don't think it makes sense to talk about missing support on any > platform: In a strict sense, how well a platform is supported is a > function of how many people care to use it. While there seems to be a > disparity between people developing programs on/for Windoze and people > working on Windoze's cross-platform capabilities wrt. Haskell, this > does not mean that you can rightfully expect people who chose not to use > your favourite platform to give a damn about it. Search for allies > amidst your pals. Somehow I really gave off the wrong impression. Windows is most definitely not my favorite platform. My primary development computer is currently a MacBook, and my secondary system runs Linux. I'm advocating for Windows for two reasons: 1. There are a non-trivial number of Windows Haskellers, and they frequently post about problems on this list. I would like to make their lives a little better.. 2. A substantial portion of computer users are on Windows. If I want them to use my software, or even expose them to the glory of Haskell, I need to speak their language. A possible third reason is that I have used some number of gnu-toolchain-developed programs on Windows (using mingw), and the experience is frequently miserable. Graphics libraries lag, all sorts of configuration errors, missing packages, etc. Compared to that, the GHC compiler chain and libraries are fantastic. It pretty much works, and I think it can be better. I would like to see a wider adoption of Haskell in general, and improving Haskell support for windows is would definitely help. > > I honestly doubt that iff a viable[1] way to support multiple platforms > exists any developer aware of it would choose a platform-locked in > alternative. This is the only thing you can hope for, and the only > thing you need to provide to other developers to get platform support > for free. There's a free lunch, after all, but you gotta bring your own > dishes. Or pay someone to spoon-feed you, but that's another issue. > I think Haskell is a lot closer to this than many other languages. Generally, Haskell packages that don't work on Windows fall into one of three categories: 1. Packages that link to a C library, in which case it depends on the underlying library. 2. Packages that are closely tied to Unix/Posix. 3. Packages that depend on one of the above (or another in this category). It's the third category that's mostly under discussion here. If Package A is posix-dependent, but a cross-platform alternative is available, then by using the cross-platform alternative Package B really can get Windows compatibility for free (assuming equivalent functionality between alternatives). I really don't see anything wrong with using Hoogle to increase awareness (although I would appreciate it if platform-specific packages were searched as an option). Cheers, John

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Boston Area Haskell User's Group, first meeting on Saturday February 28th
by Shae Matijs Erisson 27 Feb '09

27 Feb '09

This weekend the Boston Area Haskell User's Group will have its first meeting. You are invited to the mailing list, and to the first meeting this weekend! If you think you'll show up to the meeting, please send your RSVP to the mailing list, thanks! Mailing list: http://groups.google.com/group/bostonhaskell Agenda: Edward Kmett will talk about either comonads or Kan extensions. Shae Erisson will talk about QuickCheck and relatives. Some attendees will volunteer to talk at the next meeting (I hope). Time: Starts at noon, organized stuff stops at 2pm. Place: BlueSpec in Waltham, MA Wikipage with directions to the venue: http://www.haskell.org/haskellwiki/Boston_Area_Haskell_Users%27_Group If you're in or near Boston and you're interested in Haskell, show up! -- Programming is the Magic Executable Fridge Poetry, | www.ScannedInAvian.com It is machines made of thought, fueled by ideas. | -- Shae Matijs Erisson

1 0

Performance question
by haskell＠kudling.de 27 Feb '09

27 Feb '09

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 individual inherited COST CENTRE MODULE no. entries %time %alloc %time %alloc MAIN MAIN 1 0 0.0 0.0 100.0 100.0 main Main 254 1 88.1 90.8 100.0 100.0 monteCarloPi Main 255 1 0.6 1.1 11.9 9.2 pairs Main 257 10000000 0.7 1.4 0.7 1.4 countHits Main 256 10000001 4.2 2.9 10.6 6.7 accumulateHit Main 258 27852236 3.0 2.3 6.4 3.8 isInCircle Main 259 30000000 3.3 1.5 3.3 1.5 CAF:lit_r1A7 Main 248 1 0.0 0.0 0.0 0.0 isInCircle Main 260 0 0.0 0.0 0.0 0.0

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Performance Issue
by James Swaine 27 Feb '09

27 Feb '09

i'm implementing a benchmark which includes a detailed specification for a random number generator. for any of the kernels outlined in the benchmark, i might have to generate a set of random numbers R, which has a length n, using the following formulas: R[k] = ((2^-46)(X[k])) mod 2^46, where X[k] = (a^k)s where the values of a and s are constant and defined below. many of the kernels in the benchmark require a large number of randoms to be generated (in the tens of millions). when i invoke the following getRandAt function that many times to build up a list, evaluation of the list takes forever (somewhere between 5 and 10 minutes). i've tried optimizing this several different ways, with no luck. i though i might post my code here and see if anyone notices anything i'm doing wrong that might be causing such a large bottleneck: --constants a :: Int64 a = 5^13 divisor :: Int64 divisor = 2^46 multiplier :: Float multiplier = 2**(-46) --gets r[k], which is the value at the kth --position in the overall sequence of --pseudorandom numbers getRandAt :: Int64 -> Int64 -> Float getRandAt 0 seed = multiplier * (fromIntegral seed) getRandAt k seed = multiplier * (fromIntegral x_next) where x_prev = (a^k * seed) `mod` divisor x_next = (a * x_prev) `mod` divisor thanks all in advance for your help! -james

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Memoization local to a function
by Dusan Kolar 27 Feb '09

27 Feb '09

Dear all, I have a function a computation of which is quite expensive, it is recursively dependent on itself with respect to some other function values - we can roughly model its behaviour with fib function (returns n-th number of Fibonacci's sequence). Unfortunately, it is not fib, it is far more complicated. Nevertheless, for demonstration of my question/problem I will use fib, it's quite good. I want to store results in a list (array, with its strong size limit that I do not know prior to computation, is not suitable) and then pick them up using (!!) operator. Well, if the list is "global" function/constant then it works quite well. Unfortunately, this is not, what I would like to have. Nevertheless, local version does not work. Could someone point me to some text that explains it? Memoization text on wiki does not seem to be helpful. Time/operation consumption is deduced from number of reductions reported by hugs and winhugs (tested both on Linux and Windows). Thank you for hints, Dusan P.S. Code I used for testing. module Testmemo ( fibW , fibL , fibM ) where fibW m = allfib !! m where allfib = 0:1:[allfib!!n + allfib!!(n+1) | n <- [0..]] fibL m = let allfib = 0:1:[allfib!!n + allfib!!(n+1) | n <- [0..]] in allfib !! m fibM n = myallfib !! n myallfib = 0:1:[myallfib!!n + myallfib!!(n+1) | n <- [0..]]

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Re: [Haskell-cafe] Performance question
by haskell＠kudling.de 27 Feb '09

27 Feb '09

Do you think it would be feasable to replace the GHC implementation of System.Random with something like System.Random.Mersenne? >Here is a variant that uses mersenne-random-pure64 and works less than >2x slower than C++: > > - You don't need to compute samples count an extra time > - You don't need to assemble double pairs from a list > - Notice the strictness in randomDoublePairs: it doubled performance > >{-# LANGUAGE BangPatterns #-} > >import System.Random.Mersenne.Pure64 >import System( getArgs ) >import Data.List( foldl' ) > >isInCircle :: (Double,Double) -> Bool >isInCircle (!x,!y) = sqrt (x*x + y*y) <= 1.0 > >accumulateHit :: Int -> (Double,Double) -> Int >accumulateHit !hits pair = if isInCircle pair then hits + 1 else hits > >monteCarloPi :: Int -> [(Double,Double)] -> Double >monteCarloPi n xs = 4.0 * fromIntegral hits / fromIntegral n > where hits = foldl' accumulateHit 0 . take n $ xs > >randomDoublePairs g = let > !(!x,!g') = randomDouble g > !(!y,!g'') = randomDouble g' > in (x,y):randomDoublePairs g'' > >main = do > samples <- (read . head) `fmap` getArgs > randomNumbers <- randomDoublePairs `fmap` newPureMT > putStrLn . show $ monteCarloPi samples randomNumbers > >jkff@*****:~/montecarlo$ time ./mc-hs 10000000 >3.1417088 > >real 0m1.141s >user 0m1.140s >sys 0m0.000s >jkff@*****:~/montecarlo$ time ./mc 10000000 >10000000 >3.14113 > >real 0m0.693s >user 0m0.690s >sys 0m0.000s > > > >2009/2/26 Ben Lippmeier <Ben.Lippmeier(a)anu.edu.au>: >> >> On 26/02/2009, at 9:27 PM, haskell(a)kudling.de wrote: >>> >>> Currently i can only imagine to define a data type in order to use unboxed >>> Ints instead of the accumulator tuple. >> >> That would probably help a lot. It would also help to use two separate >> Double# parameters instead of the 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? >> >> At the machine level, GHC treats the (Floating a, Ord a) as an extra >> argument to the function. This argument holds function pointers that tell >it >> how to perform multiplication and <= for the unknown type 'a'. If you use >> Double instead of 'a', then it's more likely to use the actual machine op. >> >> Ben. >> >> >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> > > > >-- >Eugene Kirpichov >Web IR developer, market.yandex.ru

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Re: Hoogle and Network.Socket
by John Lato 26 Feb '09

26 Feb '09

> John Lato <jwlato(a)gmail.com> writes: > >> Brandon Allbery wrote: >>> On 2009 Feb 21, at 20:47, Jonathan Cast wrote: >>>> On Sat, 2009-02-21 at 07:25 -0700, John A. De Goes wrote: > >>>>> Not showing platform-specific packages by default *might* make >>>>> package writers more likely to develop cross-platform >>>>> packages. > > You're saying a developer would think, oh, I need to test this on > windows, or else Hoogle won't index it? > > I think it is way more likely that not showing platform-specific > packages will result in yet another platform-specific library > duplicating (the necessary) part of the functionality. > > On the other hand, displaying platfom-specific libraries might lead to > them being more used, and in turn being ported. I agree with both of these points. I think at least the first would be adequately addressed if Hoogle categorized results by platform compatibility in some way. Then a person looking for, e.g. a BSD-Sockets package should be able to find it more quickly. > >>>>> We've heard many times someone say, "I don't know if it >>>>> works on Windows, never really thought of that." > > I'd say it. I'd be happy to accept patches for Windows compatibility, > but I'm not going to go out and buy an OS, install it, install all the > required software and so on - just to tick a checkbox I'm not sure > anybody - a potential user of software, that is, not a user of > checkboxes - even cares about. I certainly don't expect every developer to run out and buy Windows just to test their stuff. I have access to a Windows box, and I hate testing my code on it because I have to reboot to do so. I'll freely admit it's a pain. That's not the point, though. In my experience, most haskell code works on windows, unless you have a Unix or FFI dependency. In those cases, yes, it's a lot more work to port and test. But if you don't, or could use a cross-platform equivalent, then there's a good chance your code will work on Windows *with no extra effort.* That's what I'm arguing for: making it easier to make cross-platform choices without any extra work on the developer's part. > >> 1. It's often easier (and almost never more difficult) to design for >> cross-platform support from the beginning than to add it later. > > I don't entirely agree. I have no particular experience writing > cross-platform software, and no way to test it - chances are I'd just > mess it up anyway. Better that an expert, with a real need to cater > to, do this later on. I didn't phrase this well. In the context of my argument, "design for cross-platform" meant "avoid platform-limiting choices in the absence of any compelling reasons otherwise", which really isn't the same. In the specific case of Haskell software, I argue that this goes a long way to ensuring ease of porting (if necessary at at all). Again, with very little impact on the actual work that you need to do. Note that "compelling reasons" would include better features, better API, industry standards compliance, etc. I wouldn't say that a half-implemented, poorly documented cross-platform library is functionally equivalent to an alternative well-supported product. > >> 2. As of now, the "Windows Group" seems to be mostly Duncan. And >> while I greatly appreciate all the time and effort he continues to put >> into Windows support, he's got a lot to do and could use some help. >> If you can't help by joining the Windows group, at least you could >> make your own packages cross-platform. > > If you care about Windows support, the least you can do is to install > my stuff, and mail me the required patches to make it work - or let me > know if it works already. I am most definitely not a Windows programmer, so I'm in only a slightly better position than you to make such patches if necessary. I will test your code, though. > > As far as I know, none of those 80% of users even know I exist. > In your case, I suppose that >80% of users don't care about bioinformatics, which seems to be your area of specialization. Fine. Even when coding for a broad audience, as opposed to coding for oneself, it's not true that you're coding for *everyone*. > >> 4. Cross-platform concerns are something that responsible developers >> need to consider, just like localization and i18n. I.e., why >> *shouldn't* you think of that? > > I don't consider those other two either, for about the same reasons. > I don't need it for the software I'm writing, and I have no reason to > believe anybody else does either. > > I suppose that one might think that my views here are quite selfish. > Where's the community spirit? Where is social responsibility? In a > way you'd be right, but I also think that if you start *imposing* this > kind of responsibility and community spirit, you'd start to se less > free software out there. The cost of releasing software is low, but > hell, if I'm going to be flamed for it, the cost of *not* releasing it > is not any higher. I'm really not trying to argue that this should be imposed upon developers, for exactly the reasons you give. One of the great things about hackage is the extremely low barrier to entry. I think that the "publish stuff and see what gets used" model is very effective, and I certainly don't want that to change. I do apologize if you think I'm flaming you (or anyone else). That was certainly not my intent. Honestly, I'm quite surprised that so many experienced Haskellers, all of whom have made far more contributions than I have, responded so strongly to my comments. I'm certainly not saying that I think every developer should go out of their way to actively support OS's they don't even have access to. I'm not even asking anyone to write any more code than they already feel like doing. I'm simply saying that, in the cases in which Windows compatibility can be had *for free*, the community should encourage it. I also thought that most developers would be happy to take advantage of such a situation, but it seems I was mistaken. Sincerely, John Lato

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ANN: gitit 0.5.1
by John MacFarlane 26 Feb '09

26 Feb '09

I've just uploaded gitit 0.5.1 to HackageDb. Gitit is a wiki program that uses git or darcs as a filestore and HAppS as a server. Changes: * Major code reorganization, making gitit more modular. * Gitit can now optionally be built using Happstack instead of HAppS (just use -fhappstack when cabal installing). * Fixed bug with directories that had the same names as pages. * Added code from HAppS-Extra to fix cookie parsing problems. * New command-line options for --port, --debug. * New debug feature prints the date, the raw request, and the processed request data to standard output on each request. * Files with ".page" extension can no longer be uploaded. * Apostrophes and quotation marks now allowed in page names.

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Grapefruit infrastructure
by Wolfgang Jeltsch 26 Feb '09

26 Feb '09

Hello, I just want to mention that the Grapefruit FRP library now has a mailing list and a Trac instance which contains a bug tracker. See: <http://www.haskell.org/haskellwiki/Grapefruit#Community> Please also note that the Grapefruit repositories have moved to code.haskell.org. Best wishes, Wolfgang

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Re: [Haskell-cafe] Performance question
by haskell＠kudling.de 26 Feb '09

26 Feb '09

>accumulateHit because it doesn't need to count to total. That is >already known. Well in theory i agree. But somone could feed a non-infite number of doubles. Then the argument "n" would not necessarily be the same as the number of random number pairs really used.

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Re: [Haskell-cafe] Performance question
by haskell＠kudling.de 26 Feb '09

26 Feb '09

>> But you can remove sqrt from the C++ implementation as well, so it only >> improves the relative performance if the C++ implementation of sqrt is >> worse than its Haskell counterpart. > >Oops, of course I mean, you only improve if Haskell's implementation is >worse than C++'s implementation :) Actually i intend to compare real life performance of comparable algorithms. If sqrt is a problem in GHC/Haskell then this would be a valuable result. I want to know about these problems and not work around them at this point. Thanks, lenny

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popularity context with Cabal
by Manlio Perillo 26 Feb '09

26 Feb '09

Hi. Debian some time ago introduced the popularity context, to find the most installed/used packages: http://popcon.debian.org/ Is it possible to do something similar with Cabal? From popularity-context FAQ: "For each package, popularity-contest looks at the most recently used (based on atime) files, and reports the filename, its last access time (atime) and last change time (ctime). However, some files are not considered, because they have unreliable atime." "A computer 'vote' for a package if according to the data provided in the report, a program provided or depending on the package was used less than thirty days ago. This computation is performed by the popcon server." Manlio Perillo

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Cabal package bug?
by jpaulo＠di.uminho.pt 26 Feb '09

26 Feb '09

hello all, I've used cabal to install package haskell-src-1.0.1.3 under ghc 6.10.1; Apparently, it worked fine! However, function parseModule has been given the type: parseModule :: String -> ParseResult haskell-src-1.0.1.3:Language.Haskell.Syntax.HsModule instead of simply parseModule :: String -> ParseResult HsModule as described in the Language.Haskell.Parser module; This causes conflicting types for all my other modules! Can anyone please help me on this? Any help would be very much appreciated! bests, joao -- João Paulo Fernandes Departamento de Informática Universidade do Minho www.di.uminho.pt/~jpaulo

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Cabal haskell-src-1.0.1.3 package bug?
by jpaulo＠di.uminho.pt 26 Feb '09

26 Feb '09

[now with the name of the package on subject; appologies for multiple emails] hello all, I've used cabal to install package haskell-src-1.0.1.3 under ghc 6.10.1; Apparently, it worked fine! However, function parseModule has been given the type: parseModule :: String -> ParseResult haskell-src-1.0.1.3:Language.Haskell.Syntax.HsModule instead of simply parseModule :: String -> ParseResult HsModule as described in the Language.Haskell.Parser module; This causes conflicting types for all my other modules! Can anyone please help me on this? Any help would be very much appreciated! bests, joao -- João Paulo Fernandes Departamento de Informática Universidade do Minho www.di.uminho.pt/~jpaulo

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Re: Hoogle and Network.Socket
by John Lato 26 Feb '09

26 Feb '09

Brandon Allbery wrote: > On 2009 Feb 21, at 20:47, Jonathan Cast wrote: >> On Sat, 2009-02-21 at 07:25 -0700, John A. De Goes wrote: >>> Not showing platform-specific packages by default *might* make >>> package >>> writers more likely to develop cross-platform packages. We've heard >>> many times someone say, "I don't know if it works on Windows, never >>> really thought of that." >> >> Um, why *should* I think of that? > > I have to second this; I'm a Unix sysadmin, 98% of the time if I'm > writing a program it's for Unix *and* requires POSIX APIxs, and even > if it could apply to Windows the program needed there would be very > significantly different. And we have a Windows group for that. > I completely disagree, for the following reasons: 1. It's often easier (and almost never more difficult) to design for cross-platform support from the beginning than to add it later. 2. As of now, the "Windows Group" seems to be mostly Duncan. And while I greatly appreciate all the time and effort he continues to put into Windows support, he's got a lot to do and could use some help. If you can't help by joining the Windows group, at least you could make your own packages cross-platform. 3. It contributes to the "Avoid success at all costs" mantra often attributed to Haskell. I'm pretty sure that some people prefer this, but many (including myself) consider it at best misguided, and possibly harmful. 4. Cross-platform concerns are something that responsible developers need to consider, just like localization and i18n. I.e., why *shouldn't* you think of that? In some situations, it is true that a project is particularly tied to a Posix (or Windows) feature, and it wouldn't make sense to attempt a cross-platform version. If you're a Unix sysadmin and you use Haskell, that may be true most or all of the time. But for many packages, including most packages on hackage, it should be given consideration. Cheers, John Lato

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speed: ghc vs gcc
by Bulat Ziganshin 26 Feb '09

26 Feb '09

Hello haskell-cafe, since there are no objective tests comparing ghc to gcc, i made my own one. these are 3 programs, calculating sum in c++ and haskell: main = print $ sum[1..10^9::Int] main = print $ sum0 (10^9) 0 sum0 :: Int -> Int -> Int sum0 0 !acc = acc sum0 !x !acc = sum0 (x-1) (acc+x) main() { int sum=0; //for(int j=0; j<100;j++) for(int i=0; i<1000*1000*1000;i++) sum += i; return sum; } execution times: sum: ghc 6.6.1 -O2 : 12.433 secs ghc 6.10.1 -O2 : 12.792 secs sum-fast: ghc 6.6.1 -O2 : 1.919 secs ghc 6.10.1 -O2 : 1.856 secs ghc 6.10.1 -O2 -fvia-C : 1.966 secs C++: gcc 3.4.5 -O3 -funroll-loops: 0.062 secs -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com

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MapReduce reverse engineered
by Galchin, Vasili 26 Feb '09

26 Feb '09

Hello, Here is an interesting paper of Google's MapReduce reverse engineered into Haskell. I apologize if already posted ..... http://www.cs.vu.nl/~ralf/MapReduce/ Kind regards, Vasili

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forall & ST monad
by Peter Verswyvelen 26 Feb '09

26 Feb '09

I'm having trouble understanding the explanation of the meaning of the signature of runST at http://en.wikibooks.org/wiki/Haskell/Existentially_quantified_types I could try to read the article a couple of times again, but are there any other good readings about these existentially quantified types and how the ST monad works? I'm currently only using forall in combination with type classes, as in data MVC m v = forall c. Controller c => MVC m v c However - as the article mentions - forall can also be used to constrain the scope of type variables, but I don't get it yet. Thanks!

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Re: [Haskell-cafe] MapReduce reverse engineered
by Alberto G. Corona 26 Feb '09

26 Feb '09

2009/2/25 Alberto G. Corona <agocorona(a)gmail.com> > And it would solve a lot of problem: scalability, system re-configuraition > and installation: just by adding or removing nodes at runtime.. heavy > numerical computations are also good candidates. > > 2009/2/25 Rick R <rick.richardson(a)gmail.com> > > I agree. A distributed database could be made as usable as a standard >> RDBMS by offering an interface by which you supply a map/reduce pair >> of functions and a list (range?) of keys. >> >> This could be easily implemented with a database such as Scalaris, in >> which the Chord algorithm is responsible for placing and finding the >> data among nodes. >> >> The user would interface with any node in the distributed database, >> supplying a map and reduce function. It would distribute the map >> function to nodes of its choosing (weighted by some metrics such as >> idle cpu), retrieve the intermediate sets and run reduce if supplied. >> >> >> 2009/2/25 Alberto G. Corona <agocorona(a)gmail.com>: >> > Galchin, >> > >> > Maybe you are asking not only about remote execution, but also mobility >> of >> > code. This is a problem that is previous to mapReduce, since mapReduce >> > assumes that all the code (and the data) is in place in the respective >> > nodes. In fact, the distribution of resources in order to efficiently >> use >> > mapReduce is a design problem that the google people has done by hand. >> > But my intuition says that there are a general algorithm for >> distribution >> > of code, data, bandwidth and resources in general that moves around at >> > execution time to achieve better and better performance for a given grid >> of >> > nodes and for any task, for example, a mapReduce task. I would be very >> > interesting to read something about this. >> > I know that some efforts have been carried out the past , for example >> mobile >> > haskell >> > >> http://homepages.inf.ed.ac.uk/stg/workshops/TFP/book/DuBois/duboismhaskell/… >> > which is a first step for this goal but I this has been discontinued and >> the >> > source code is not available. >> > >> > 2009/2/25 Galchin, Vasili <vigalchin(a)gmail.com> >> >> >> >> Hello, >> >> >> >> Here is an interesting paper of Google's MapReduce reverse >> engineered >> >> into Haskell. I apologize if already posted ..... >> >> http://www.cs.vu.nl/~ralf/MapReduce/ >> >> >> >> Kind regards, Vasili >> >> >> >> _______________________________________________ >> >> Haskell-Cafe mailing list >> >> Haskell-Cafe(a)haskell.org >> >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> >> >> > >> > >> > _______________________________________________ >> > Haskell-Cafe mailing list >> > Haskell-Cafe(a)haskell.org >> > http://www.haskell.org/mailman/listinfo/haskell-cafe >> > >> > >> >> >> >> -- >> We can't solve problems by using the same kind of thinking we used >> when we created them. >> - A. Einstein >> > >

1 0

cabal install profiling and documentation
by Ben 26 Feb '09

26 Feb '09

i've gone and cabal installed a lot of packages, but now i want to go back and install their profiling libraries and documentation. is there an easy way of doing this, short of reinstalling all of them (in the proper dependency order)? ben

1 0

package code duplication
by Louis Wasserman 26 Feb '09

26 Feb '09

There was a question recently about being allowed to get into package internals, and I had a question. I want to use uvector's stream internals in ways that the exposed methods don't permit, but I don't especially want to use another package (e.g. vector, which does expose its internals) or reimplement my own stream fusion. Would it make sense to duplicate uvector's internals, copying licensing information and other stuff of course, inside my package? It's a suboptimal solution, but it seems better than the alternative... >< Louis Wasserman wasserman.louis(a)gmail.com

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Re: [Haskell-cafe] base-4 + gtk2hs-0.10.0 licensing
by Robert Greayer 26 Feb '09

26 Feb '09

Colin Paul Adams wrote: > But IF there is no difference between LGPL and GPL for Haskell > programs, then the licensing of gtk2hs as LGPL is just a smokescreen - > it is effectively GPL, so you have to license your program as GPL. > Which I'm all in favour of :-) I actually don't think this is 100% true. With the LGPL, you can distribute your program with under a non-GPL license, as long as you provide *some mechanism* for replacing the library and recreating the program. Normally this means dynamic linking. But it also allows you (I think) to distribute your program with a GPL-incompatible-but-nevertheless-open-source license, because that provides a mechanism for replacing the library (because you can rebuild the program from source). If you license the library under GPL, you cannot even do that. At least this is my understanding...

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[Colin Paul Adams] Re: [Haskell-cafe] base-4 + gtk2hs-0.10.0 licensing
by Colin Paul Adams 25 Feb '09

25 Feb '09

>>>>> "Wolfgang" == Wolfgang Jeltsch <g9ks157k(a)acme.softbase.org> writes: Wolfgang> Am Mittwoch, 25. Februar 2009 14:33 schrieb Duncan Wolfgang> Coutts: >> Note that some people will tell you that by a strict >> interpretation of the LGPL that statically linked Haskell libs >> under that license are a pain in the backside. When we decided >> on that license for gtk2hs that was not our intention. In other >> words nobody is going to sue you if you statically link gtk2hs >> libs. Of course if you need a cast iron legal guarantee then >> that's not good enough and you'd have to ship .a and .o files >> to let users relink if they wanted to. Wolfgang> I’m not sure whether this would be enough. .a and .o Wolfgang> files are not compatible among GHC versions, as far as I Wolfgang> know. Relinking against newer Gtk2Hs versions might not Wolfgang> work. And a program using Gtk2Hs contains code from the Wolfgang> .hi files of Gtk2Hs through inlining. So it’s not pure Wolfgang> linking. However, the LGPL only allows linking, as far Wolfgang> as I understand. Wolfgang> I want to repeat what I’ve said earlier on this list: Wolfgang> For Haskell, there is no real difference between LGPL Wolfgang> and GPL, as far as I understand it. If you don’t want to Wolfgang> force the users of your library to use an open source Wolfgang> license for their work then use BSD3 or a similar Wolfgang> license for your library. But IF there is no difference between LGPL and GPL for Haskell programs, then the licensing of gtk2hs as LGPL is just a smokescreen - it is effectively GPL, so you have to license your program as GPL. Which I'm all in favour of :-) -- Colin Adams Preston Lancashire

1 0

Cabal: local documentation
by Martijn van Steenbergen 25 Feb '09

25 Feb '09

Hello, Can cabal automatically generate local documentation for packages I install? It'd be awesome if it generated a page like [1] for locally installed packages. Thanks, Martijn. [1] http://www.haskell.org/ghc/dist/current/docs/libraries/

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The community is more important than the product
by Don Stewart 25 Feb '09

25 Feb '09

http://haskell.org/haskellwiki/Protect_the_community Random notes on how to maintain tone, focus and productivity in an online community I took a few years ago. Might be some material there if anyone's seeking to help ensure we remain a constructive, effective community. -- Don P.S. release some code on hackage.haskell.org.

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ONeillPrimes.hs - priority queue broken?
by Eugene Kirpichov 25 Feb '09

25 Feb '09

Hi, I've recently tried to use the priority queue from the ONeillPrimes.hs, which is famous for being a very fast prime generator: actually, I translated the code to Scheme and dropped the values, to end up with a key-only heap implementation. However, the code didn't work quite well, and I decided to check the haskell code itself. Turns out that it is broken. module PQ where import Test.QuickCheck data PriorityQ k v = Lf | Br {-# UNPACK #-} !k v !(PriorityQ k v) !(PriorityQ k v) deriving (Eq, Ord, Read, Show) emptyPQ :: PriorityQ k v emptyPQ = Lf isEmptyPQ :: PriorityQ k v -> Bool isEmptyPQ Lf = True isEmptyPQ _ = False minKeyValuePQ :: PriorityQ k v -> (k, v) minKeyValuePQ (Br k v _ _) = (k,v) minKeyValuePQ _ = error "Empty heap!" minKeyPQ :: PriorityQ k v -> k minKeyPQ (Br k v _ _) = k minKeyPQ _ = error "Empty heap!" minValuePQ :: PriorityQ k v -> v minValuePQ (Br k v _ _) = v minValuePQ _ = error "Empty heap!" insertPQ :: Ord k => k -> v -> PriorityQ k v -> PriorityQ k v insertPQ wk wv (Br vk vv t1 t2) | wk <= vk = Br wk wv (insertPQ vk vv t2) t1 | otherwise = Br vk vv (insertPQ wk wv t2) t1 insertPQ wk wv Lf = Br wk wv Lf Lf siftdown :: Ord k => k -> v -> PriorityQ k v -> PriorityQ k v -> PriorityQ k v siftdown wk wv Lf _ = Br wk wv Lf Lf siftdown wk wv (t @ (Br vk vv _ _)) Lf | wk <= vk = Br wk wv t Lf | otherwise = Br vk vv (Br wk wv Lf Lf) Lf siftdown wk wv (t1 @ (Br vk1 vv1 p1 q1)) (t2 @ (Br vk2 vv2 p2 q2)) | wk <= vk1 && wk <= vk2 = Br wk wv t1 t2 | vk1 <= vk2 = Br vk1 vv1 (siftdown wk wv p1 q1) t2 | otherwise = Br vk2 vv2 t1 (siftdown wk wv p2 q2) deleteMinAndInsertPQ :: Ord k => k -> v -> PriorityQ k v -> PriorityQ k v deleteMinAndInsertPQ wk wv Lf = error "Empty PriorityQ" deleteMinAndInsertPQ wk wv (Br _ _ t1 t2) = siftdown wk wv t1 t2 leftrem :: PriorityQ k v -> (k, v, PriorityQ k v) leftrem (Br vk vv Lf Lf) = (vk, vv, Lf) leftrem (Br vk vv t1 t2) = (wk, wv, Br vk vv t t2) where (wk, wv, t) = leftrem t1 leftrem _ = error "Empty heap!" deleteMinPQ :: Ord k => PriorityQ k v -> PriorityQ k v deleteMinPQ (Br vk vv Lf _) = Lf deleteMinPQ (Br vk vv t1 t2) = siftdown wk wv t2 t where (wk,wv,t) = leftrem t1 deleteMinPQ _ = error "Empty heap!" toDescList :: Ord k => PriorityQ k v -> [(k,v)] toDescList q | isEmptyPQ q = [] | otherwise = (minKeyValuePQ q) : toDescList (deleteMinPQ q) fromList :: Ord k => [(k,v)] -> PriorityQ k v fromList = foldr (uncurry insertPQ) emptyPQ Here goes a test: *PQ> let s = map fst . toDescList . fromList . (`zip` (repeat ())) :: [Int]->[Int] *PQ> s [4,3,1,2] [1,2,3,4] Looks fine. *PQ> s [3,1,4,1,5,9,2,6,5,3,5,8] [1,1,2*** Exception: Empty heap! OK, probably it doesn't like duplicates. *PQ> s [3,1,4,5,9,2,6,8,10] [1,2,3,4,5,9,10] Whoops, 6 and 8 are lost. So, the morale is: don't use the priority queue from ONeillPrimes in your projects. It works for primes by a lucky chance. I haven't yet figured out, however, what exactly the bug is. -- Eugene Kirpichov Web IR developer, market.yandex.ru

3 3

Indentation Question.
by Ramaswamy, Vivek 25 Feb '09

25 Feb '09

Hello All~ I have been reading the book "Haskell for real programmers" and am presently on chapter 03. There was a small program demonstrated by the author on "let". The problem is that when I cut and paste authors code into eclipse, the program works fine, where as when I write my own copy of the program I am getting an error. I figured out that when I remove the function any one function lend or bend, the file compiles and runs fine. My question is why does the Haskell compiler complains, in the case 2 functions with the same signature and logic, even though their names are different. module Lending where {-- snippet lend --} lend amount balance = let reserve = 100 newBalance = balance - amount in if balance < reserve then Nothing else Just newBalance {-- /snippet lend --} bend amount balance = let reserver = 100 newBalance=balance-amount in if balance < reserver then Nothing else Just newBalance Regards -Vivek Ramaswamy- ........................................................................ ........................................................................ ............................................ Disclaimer: This e-mail, including any attachment(s) hereto, is intended only for the individual or entity to whom it is addressed. It may contain proprietary, confidential or privileged information or attorney work product belonging to Fidelity Business Services India Pvt. Ltd. (FBS India) or its affiliates. If you are not the intended recipient of this e-mail, or if you have otherwise received this e-mail in error, please immediately notify the sender via return e-mail and permanently delete the original mail, any print outs and any copies, including any attachments. Any dissemination, distribution, alteration or copying of this e-mail is strictly prohibited. The originator of this e-mail does not guarantee the security of this message and will not be responsible for any damages arising from any dissemination, distribution, alteration or copying of this message and/or any attachments to this message by a third party or as a result of any virus being passed on. Any comments or statements made in this are not necessarily those of FBS India or any other Fidelity entity. All e-mails sent from or to FBS India may be subject to our monitoring and recording procedures. ........................................................................ ........................................................................ ..........................................

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IntMap documentation error
by Louis Wasserman 25 Feb '09

25 Feb '09

In the documentation for Data.IntMap updateMin, a piece of example code both communicates incorrect intuition, and fails to even compile. updateMin :: (a -> a) -> IntMap a -> IntMap a updateMin (\ _ -> Nothing) (fromList [(5,"a"), (3,"b")]) -- code straight from the docs <interactive>:1:49: Couldn't match expected type `Maybe a' against inferred type `[Char]' In the expression: "a" In the expression: (5, "a") In the first argument of `fromList', namely `[(5, "a"), (3, "b")]' As a side note, the sort of operation implied by the example code was really what I was looking for in the documentation -- but such a method no longer exists in IntMap. ::sad:: Who do I tell this to / how do I ask to get it fixed? Louis Wasserman wasserman.louis(a)gmail.com

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Data.Binary poor read performance
by Neil Mitchell 25 Feb '09

25 Feb '09

Hi, In an application I'm writing with Data.Binary I'm seeing very fast write performance (instant), but much slower read performance. Can you advise where I might be going wrong? The data type I'm serialising is roughly: Map String [Either (String,[String]) [(String,Int)]] A lot of the String's are likely to be identical, and the end file size is 1Mb. Time taken with ghc -O2 is 0.4 seconds. Various questions/thoughts I've had: 1) Is reading a lot slower than writing by necessity? 2) The storage for String seems to be raw strings, which is nice. Would I get a substantial speedup by moving to bytestrings instead of strings? If I hashed the strings and stored common ones in a hash table is it likely to be a big win? 3) How long might you expect 1Mb to take to read? Thanks for the library, its miles faster than the Read/Show I was using before - but I'm still hoping that reading 1Mb of data can be instant :-) Thanks Neil

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emacs cedet support for haskell?
by Xiao-Yong Jin 25 Feb '09

25 Feb '09

Hi, I've googled around for possible haskell support in emacs cedet, but couldn't find any. From cedet's website, it claims to support the following Language Parsers Parsers that have already been implemented: Emacs Lisp, Java, C/C++, C#, Python, Erlang, awk, Makefile, Scheme, HTML, Texinfo, Javascript, dot. Also: Semantic's own grammar format (.by or .wy) Is there any plan to support haskell in the near future? Best, Xiao-Yong -- c/* __o/* <\ * (__ */\ <

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