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MissingH status and thanks
by John Goerzen 08 Dec '06

08 Dec '06

Since the MissingH discussion took place on this list, I thought I should update you all on the status. First off, MissingH now has a new Trac-based homepage, complete with wiki, Darcs repository information, source browser, bug tracker, etc. It's at http://software.complete.org/missingh Secondly, the MissingH modules have been renamed as we discussed here. And finally, various pieces of MissingH have been split off already into separate packages. (See the announcements on haskell@h.o) The full list of changes -- planned and executed -- is at http://software.complete.org/missingh/wiki/TransitionPlanning Thanks to all for your valuable feedback. I hope that these changes will make this set of code more useful to everyone. -- John

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"computational time" always 0.0 in this example...
by Lennart 08 Dec '06

08 Dec '06

Hi, with the following code, I want to measure the time being needed to execute the algorithm. But the result is always 0.0. import Char (toLower) import Maybe import List ( delete, sort, intersect ) import System.CPUTime import Control.Exception import Debug.Trace fromInt = fromIntegral wordList2 :: [String] wordList2 = ["Sam J Chapman", "Samuel Chapman", "S Chapman", "Samuel John Chapman", "John Smith", "Richard Smith", "aaaa mnop zzzz", "bbbb mnop yyyy", "aa mnop zzzzzz", "a ", "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa", "aaaa bcdefgh mmmmmmmm stuvwx zzzzzz", "jjjj bcdefgh qqqqqqqq stuvx yyyyyy", "aaaaa bcdefgh stuvwx zzzzzz", "aaaaa aaaaa aaaaa zzzzzz", "aaaaa aaaaa"] time :: IO t -> IO t time a = do start <- getCPUTime v <- a end <- getCPUTime let diff = (fromIntegral (end - start)) / (10^12) -- let diff = (fromIntegral (end - start)) putStrLn "Computation time:" print (diff :: Double) return v main = do putStrLn "Starting..." time $ doTest wordList2 wordList2 `seq` return () putStrLn "Done." test3 = let loop = getCPUTime >>= print >> loop in loop doTest :: [String] -> [String] -> [ Double ] doTest [] _ = [] doTest (x:xs) [] = doTest xs xs doTest (x:xs) (y:ys) = result : (doTest (x:xs) (ys)) where result = qGramMetrics2 x y qGramMetrics2:: String -> String -> Double qGramMetrics2 t1 t2 = let i = intersect (qGramList (map toLower t1) 3) (qGramList (map toLower t2) 3) il = fromInt (length i) ml = fromInt ((max (length t1) (length t2)) - 1 ) in (il / ml ) -- list of chars within list of qgrams qGramList :: String -> Int -> [[Char]] qGramList [] _ = [] qGramList (x:[]) _ = [] qGramList (x:xs) i1 = (x: take (i1 - 1) xs):(qGramList xs i1) -- list of chars within list of qgrams numberedQgramListWithStart :: String -> Int -> [(Int, [Char])] numberedQgramListWithStart x i1 = let prefix = replicate (i1-1) '#' suffix = replicate (i1-1) '$' in numberedQgramList (prefix++(x++suffix)) i1 0 numberedQgramList :: String -> Int -> Int -> [(Int, [Char])] numberedQgramList [] _ _ = [] numberedQgramList (x:xs) i1 i2 -- add the dollar-sign | (length xs) < i1 && x=='$'= [] | otherwise = (i2,(x: take (i1 - 1) xs)):(numberedQgramList xs i1 (i2+1)) Am using ghci 6.6 under a Kubuntu 6.10 Linux. time $ product [1..1000] `seq` return () instead of time $ doTest wordList2 wordList2 `seq` return () works fine. things like time $ print (doTest wordList2 wordList2) `seq` return () or time $ length (doTest wordList2 wordList2) `seq` return () or time $ trace (doTest wordList2 wordList2) `seq` return () didn't work. Am desperated... Lennart

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STUArray's newArray_ breaks referential transparency
by Stefan O'Rear 08 Dec '06

08 Dec '06

newArray_ allocates an array full of garbage. > import Control.Monad.ST > import Data.Array.ST > import Data.Array > > tickle :: Int > tickle = runST (do { > x <- newArray_ (0,100) ; > (readArray :: STUArray s Int Int -> Int -> ST s Int) x 3 > })

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Hac 2007 : Haskell Hackathon - extended registration
by dons＠cse.unsw.edu.au 07 Dec '06

07 Dec '06

------------------------------------------------------------------------ Hac 2007 The 2007 Haskell Hackathon January 10-12, 2007 Oxford University Computing Laboratory http://haskell.org/haskellwiki/Hac_2007 ------------------------------------------------------------------------ The deadline for registration for Hac 2007, the Haskell Hackathon, has passed, and some places are still available, on a first-come first-served basis. The current attendee list is up at: http://haskell.org/haskellwiki/Hac_2007/Attendees If you want to attend the hackathon, and hack on Haskell infrastructure, tools, libraries and compilers, please register, and get ready to hack those lambdas! Follow the instructions on the registration page: http://haskell.org/haskellwiki/Hac_2007/Registration Numbers for the hackathon are limited to 20. The organisers, Duncan Coutts Ian Lynagh Don Stewart Attached is the initial announcement: ------------------------------------------------------------------------ Hac 2007 The 2007 Haskell Hackathon January 10-12, 2007 Oxford University Computing Laboratory http://haskell.org/haskellwiki/Hac_2007 ------------------------------------------------------------------------ Following the success of the GHC Hackathon at ICFP, we are pleased to announce the inaugural Haskell Hackathon, Hac 2007! The event will be held over 3 days, January 10-12 2007, at the Oxford University Computing Laboratory, in the UK. The plan is to hack on Haskell infrastructure, tools, libraries and compilers. To attend please register, and get ready to hack those lambdas! Code to hack on: * Hackage * Cabal * Porting foreign libraries * Porting compilers * Bug squashing * Performance improvements to compilers * You decide! Registration: We ask that you register you interest. Follow the instructions on the registration page: http://haskell.org/haskellwiki/Hac_2007/Registration Numbers for the hackathon are limited to 20, due to room size constraints. Should space be available after the registration period ends, additional attendees may register on a first-come first-served basis. Important dates: Registration deadline: December 6th, 2006 Confirmation: December 10th, 2006 Hackathon: January 10-12, 2007 Organisers: Duncan Coutts Ian Lynagh Don Stewart

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How to get subset of a list?
by Huazhi (Hank) Gong 07 Dec '06

07 Dec '06

Like given a string list s="This is the string I want to test", I want to get the substring. In ruby or other language, it's simple like s[2..10], but how to do it in Haskell? -- View this message in context: http://www.nabble.com/How-to-get-subset-of-a-list--tf2735647.html#a7631994 Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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File locked unnecessarily
by Arie Peterson 07 Dec '06

07 Dec '06

Hi, After a partial rewrite of my webserver, it is suffering from locked files: /path/to/file: openBinaryFile: resource busy (file is locked) The file in question really shouldn't be locked: - Only my server knows of the file's existence. - Only one thread accesses the file. - The thread accesses the file multiple times in quick succession, opening and closing it each time, but debugging statements show that it is properly closed before it is reopened. I tried opening, reading/writing and closing a file continuously for some time in an isolated environment, and that works without problems. Also, my server did not have this file locking problem before the rewrite, and the rewrite did not touch the part of the code that accesses the file. This suggests that the locking is somehow triggered by the specific access pattern of my code, if that is even possible. Does anyone know what could cause this locking and/or how to prevent it? I'm using ghc 6.4 on gentoo linux (amd64). Thanks and greetings, Arie

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GADT vs Arrows for parsers/FSMs/etc.
by S. Alexander Jacobson 07 Dec '06

07 Dec '06

It seems like Haskell has two emerging idioms for parsing and fsms: GADTs and Arrows. I am thinking about using one of these idioms to represent server structure in a future version of HAppS but I'm not sure where to start. Why would one choose one or the other? -Alex- ______________________________________________________________ S. Alexander Jacobson tel:917-770-6565 http://alexjacobson.com

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Typeclass question
by Jonathan Tang 07 Dec '06

07 Dec '06

I've got what's probably a beginner's question, but I'm out of ideas for solving it. It looks like it tripped me up in "Write Yourself a Scheme..." too, since the code there seems like it's arranged so I never ran into it... I've got a couple functions: binop :: (AmbrosiaData -> AmbrosiaData -> AmbrosiaM AmbrosiaData) -> AmbrosiaM () binop operator = do second <- popStack first <- popStack result <- operator first second pushStack result numNumOp :: Num a => (a -> a -> a) -> AmbrosiaData -> AmbrosiaData -> AmbrosiaM AmbrosiaData numNumOp op (Number val1) (Number val2) = return $ Number $ op val1 val2 numNumOp op (Float val1) (Float val2) = return $ Float $ op val1 val2 numNumOp op _ _ = throwError . TypeMismatch $ "Number" the intention being that I can define primitive operations for an interpreter with ("+", binop $ numNumOp (+)). In the Number case, val1 & val2 are Integers, while in the Float case, they're Floats. However, when I try to compile, I get: ./Primitives.hs:82: Cannot unify the type-signature variable `a' with the type `Integer' Expected type: Integer Inferred type: a In the application `op val1 val2' In the second argument of `($)', namely `op val1 val2' This makes no sense to me, since Integer is an instance of Num and op is defined as type Num a => a -> a -> a. Shouldn't the typechecker be able to instantiate 'a' with Integer and give the resulting type Integer -> Integer -> Integer, and then pass the final Integer to Number? Is my understanding of typeclasses off somehow? Any help would be appreciated. Regards, Jonathan

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Would someone explain this code to me?
by Justin Bailey 07 Dec '06

07 Dec '06

I'm reading Chris Okasaki's "Purely Functional Data Structures", and some of his Haskell is confusing me. He defines the type Color and RedBlackSet as: data Color = R | B data RedBlackSet a = E | T Color (RedBlackSet a) a (RedBlackSet a) and then later he defines a function insertSet: insertSet x s = T B a y b where ins E = T R E x E ... T _ a y b = ins s What I don't understand is his use of the "T" constructor, both at insertSet x s = T B a y b and in the where statement: T _ a y b = ins s Is "T" being redefined, so the "T" called in the first line is a new function that happens to be called "T" which is defined in the where statement? If that was the case, I would expect this to work: insertSet x s = foo B a y b where ins E = foo R E x E ... foo _ a y b = ins s but it does not. If anyone can explain what's going on here, I'd appreciate it. Thank you! Justin

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[Haskell] Defining Cg, HLSL style vectors in Haskell
by Slavomir Kaslev 07 Dec '06

07 Dec '06

Hello, I have to define a couple of float2, float3, float4 Cg, HLSL style vectors in Haskell. At first I was tempted to make them instances of Num, Floating, RealFrac, etc. but some of the functions defined in those classes have no sense for vectors. One such example is signum from class Num. There are several workarounds for this. One may come up with some meaning for vectors of such functions, for example: instance Num Float3 where ..... signum a | a == Float3 0 0 0 = 0 | otherwise = 1 This is silly. Other option, which I prefer, is to leave such functions undefined (that is signum=undefined, not just not defining them). Is this ok? Are there any other options? Another bugging thing is that some of the functions do have meaning for vectors but they need different signatures. For example (**) :: Floating a => a -> a -> a, for vectors should be (**) :: (Floating a, Vector v) => v -> a -> v, that is (**) applied for every component of the vector. Any workarounds for that? I know that I can scrap all those Num, Floating, RealFrac, etc. classes and define class Vector from scratch, but I really don't want to come up and use different names for +, -, etc. that will bloat the code. Last question: Does haskell have something like C++ templates? For example, some time in the future I may need types like int2, short3, etc., that behave just like float2, float3, but use different types for their components. I really, really wouldn't like to copy-paste the definitions of floatn and manually change their types to intn respectfully. Cheers. -- Slavomir Kaslev

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state updates and efficiency
by Tim Newsham 07 Dec '06

07 Dec '06

I am writing some code with complex nested state. I have a question about performance with respect to the State monad and the Reader monad. This is somewhat long, so a quick summary of the question up front: Can the compiler optimize out state updates that dont change the state? The question inline with the code: > module Test where > import Control.Monad.State > import Control.Monad.Reader I have some nested state. This is a simplified example where we have one record inside another. In my real-world example there is more nesting and there are lists and maps involved as well. > data T1 = T1 { f1 :: Int, f2 :: T2 } deriving(Show) > data T2 = T2 { f3 :: Int, f4 :: Int } deriving(Show) I want to build generic modifiers and reuse them often. A good example is modifying a numeric value: > adjNum :: (Num a) => a -> State a () > adjNum n = modify (+ n) I'm going to be writing state code for my T1 structure which is my master structure. If I'm going to be able to reuse adjNum I am going to have to run a nested state action inside an enclosing state monad. I can build a lifter that does this as long as I know how to extract the nested state and set it back in the enclosing state: > withInnerM :: (o -> i) -> (i -> o -> o) -> State i a -> State o a > withInnerM gettor settor act = do > outer <- get > let inner = gettor outer > (ret, inner') = runState act inner > outer' = settor inner' outer > put outer' > return ret Now we can make lifters for each of the fields: > withF1M = withInnerM f1 (\f r -> r {f1=f}) > withF2M = withInnerM f2 (\f r -> r {f2=f}) > withF3M = withInnerM f3 (\f r -> r {f3=f}) > withF4M = withInnerM f4 (\f r -> r {f4=f}) which lets us write some state code for T1 using building blocks like adjNum. For example, the following code will add a value to f1, add another value to f2's f3 and finally return the value of f2's f4: > tweakT1 :: Int -> Int -> State T1 Int > tweakT1 v1 v3 = do > withF1M $ adjNum v1 > withF2M $ withF3M $ adjNum v3 > withF2M $ withF4M $ get My question here has to do with efficiency. In order to update f2's f3 a new T2 had to be constructed and used to construct a new T1. There's no way around this (I assume). But when doing a mere get of f4, there's no reason why we should have to build a new T2 and then a new T1 since nothign changed. But that's how the code is written. We could write a different lifter that does not perform a state put on the return path. If we did this with the state monad then someone could accidentally use that non-modify version of the lifter and lose an update. So instead I chose to use the Reader monad and let the type system enforce the difference between lifters that modify (M) and those that just read (R). This involved two kinds of lifters. The first lifter runs a Reader action inside of a State monad: > withRead :: Reader s a -> State s a > withRead act = do > s <- get > return $ runReader act s The second lifter runs a nested Reader action inside of an enclosing Reader monad. It is similar in spirit to withInnerM: > withInnerR :: (o -> i) -> Reader i a -> Reader o a > withInnerR gettor act = do > i <- asks gettor > return $ runReader act i again we can generate lifters for each field: > withF1R = withInnerR f1 > withF2R = withInnerR f2 > withF3R = withInnerR f3 > withF4R = withInnerR f4 And finally we can use a reader monad to eliminate the extra state updates from our previous tweakT1 implementation: > tweakT1' :: Int -> Int -> State T1 Int > tweakT1' v1 v3 = do > withF1M $ adjNum v1 > withF2M $ withF3M $ adjNum v3 > withRead $ withF2R $ withF4R $ ask > > main = do > let x = T1 1 (T2 3 4) > print $ runState (tweakT1 5 6) x > print $ runState (tweakT1' 5 6) x My question here is: is it worth it? If I run > v1 = T2 1 1 > v2 = v1 {f3 = 1} is the compiler smart enough to notice that the record update doesn't result in a change, and avoid constructing an entirely new T2? If so, then I think the original implementation TweakT1 would be about as efficient as the more complicated TweakT1'. Otherwise, I think the latter would be a lot more efficient when the state is large and complex. Tim Newsham http://www.thenewsh.com/~newsham/

2 2

what GUI library should i select?
by Bulat Ziganshin 06 Dec '06

06 Dec '06

Hello haskell-cafe, afaik, there are just two good enough libs - wxHaskell and GtkHs. can anyone point (or write) detailed comparison of their features? i plan to write large GUI program in Haskell and want to select best one. the requirements that i can imagine at this moment is the following: * my main target is Windows but ability to compile the same code both for Windows and Linux would be a plus * the program developed is a sort of advanced file manager, so i need treeview, table view and tabbed view controls * user likes beauty, so various bells-and-whistles are welcomed. in particular, it would be great to have skinnable interface * use of resource file for all texts to make internalization easier -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com

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(a -> [b]) -> [a -> b] ?
by Joachim Breitner 06 Dec '06

06 Dec '06

Hi, while pondering over the four fours problem, I wondered: Is there a function of type (a -> [b]) -> [a -> b] It looks a bit like sequence when applied in the ((->) a) Monad: sequence :: [a -> b] -> a -> [b] but I was looking for the other direction. I came up with: \g -> map (\n a -> g a !! n) [1..] which has the desired type and functionality, but it looks rather inelegant and messy. Any better ideas? Thanks, Joachim -- Joachim "nomeata" Breitner mail: mail(a)joachim-breitner.de | ICQ# 74513189 | GPG-Key: 4743206C JID: joachimbreitner(a)amessage.de | http://www.joachim-breitner.de/ Debian Developer: nomeata(a)debian.org

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Beginner: IORef constructor?
by TJ 06 Dec '06

06 Dec '06

First of all, sorry if this is a really silly question, but I couldn't figure it out from experimenting in GHCi and from the GHC libraries documentation (or Google). Is there an IORef consturctor? Or is it just internal to the Data.IORef module? I want a "global variable", so I did the following: ------ module VirtualWorld where import Data.IORef theWorld = IORef [] -- This will be writeIORef'ed with a populated list as the user modifies the world. ----- It doesn't work. GHCi says that the IORef constructor is not in scope. I did a ":module Data.IORef" and then "IORef []" and it still gives me the same error. I'm using GHC 6.6 on Windows.

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There's nothing wrong with infinite types!
by Stefan O'Rear 06 Dec '06

06 Dec '06

I'm sure anyone who's used Haskell for any significant length of time has received this error message: Occurs check: cannot construct the infinite type: t = t -> t1 I for one took that as a challenge, and have implemented a type inference engine for infinite types. Expr> s (a -> b -> c) -> (a -> b) -> a -> c Expr> skk a -> a Expr> s(skk)(skk) (fix a . (a -> b)) Expr> Points of interest: * There are NO error conditions. it-unifier can assign a type to every syntactically valid expression of combinatory logic. * Typechecking is guaranteed to terminate in a linear number of steps, an (apparently) stronger guarantee than that provided by DHM. * (Mostly theoretical, since it-unify does not yet support sums or products): Fixpoint types subsume declared recursive datatypes. e.g: type List a = fix l . Either () (a,l) darcs get http://members.cox.net/stefanor/fixtypes/

2 1

Halp- haskell logic prover
by Dan Mead 06 Dec '06

06 Dec '06

Hey all, I've just finished my logic prover. I've been working on this as an undergraduate project with my advisor. Right now it only supports simple first order logic but in the spring I'll be adding predicates. Theres also a simple gui written in java 5 which is in the darcs repository. Comments are welcome! -Dan http://haskell.org/haskellwiki/Libraries_and_tools/Theorem_provers http://taz.cs.wcupa.edu/~dmead/code/halp/

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HOgg 0.2.0 Released
by Conrad Parker 06 Dec '06

06 Dec '06

HOgg 0.2.0 Released ------------------- The HOgg package provides a commandline tool for manipulating Ogg files, and a corresponding Haskell library. http://snapper.kfish.org/~conrad/software/hogg/ This is the initial public release. The focus is on correctness of Ogg parsing and production. The capabilities of the hogg commandline tool are roughly on par with those of the oggz* tools[0], although hogg does not yet provide an equivalent to oggz-validate. HOgg supports chained and multiplexed Ogg bitstreams conformant with RFC3533[1]. HOgg can parse headers for CMML, FLAC, OggPCM, Speex, Theora and Vorbis media codecs, and can read and write Ogg Skeleton bitstreams. [0] Oggz: http://www.annodex.net/software/liboggz/index.html [1] RFC3533: http://www.ietf.org/rfc/rfc3533.txt Installation ------------ I am very interested in hearing about problems with building or installing the package, particularly from people who are not yet familiar with building from Haskell source. You need ghc instead of gcc; it compiles to a binary: $ ./Setup.hs configure $ ./Setup.hs build $ sudo ./Setup.hs install Building of this release has been tested with: * GHC versions 6.4 and 6.6 [2] * The Haskell build system "Cabal" versions 1.1.3, 1.1.4, 1.1.6, and the current development trunk. [3] * fps (Data.ByteString.Lazy) version 0.7, and development trunk. [4] Note that if you are using the recently-released GHC 6.6 then you will not need separate installs of Cabal or fps. You will however need to remove the word "fps" from the hogg.cabal file; see the README for details. The GHC and Cabal versions listed above span the packages available in most current distributions. I've tested on Debian unstable, Ubuntu Dapper and Ubuntu Edgy. I'm particularly interested to hear reports of build success or failure on other distributions or operating systems. [2] GHC: http://www.haskell.org/ghc/ [3] Cabal: http://www.haskell.org/cabal/ [4] fps: http://www.cse.unsw.edu.au/~dons/fps.html Usage ----- $ hogg help Usage: hogg <subcommand> [options] filename ... Commands: help Display help for a specific subcommand Reporting: info Display information about the file and its bitstreams dump Hexdump packets of an Ogg file pagedump Display page structure of an Ogg file dumpraw Dump raw (unparsed) page data Extraction: rip Rip selected logical bistreams from an Ogg file (default: all) reconstruct Reconstruct an Ogg file by doing a full packet demux Editing: merge Merge, interleaving pages in order of presentation time addskel Write a Skeleton logical bitstream Source ------ Source code is available from the darcs repository at: darcs get http://snapper.kfish.org/~conrad/software/hogg/ cheers, Conrad.

1 0

Download locations for former-base libraries?
by John Goerzen 06 Dec '06

06 Dec '06

Hi, I am working on updating and splitting things out of MissingH. MissingH is going to depend on regex-compat, HUnit, QuickCheck, and FilePath, among others. For each such library, I need to be able to tell users where they can go to download the dependency. But I'm having a lot of trouble finding canonical download locations. For instance, the homepage of regex-compat, according to http://darcs.haskell.org/packages/regex-compat/regex-compat.cabal, is http://sourceforge.net/projects/lazy-regex. But the software available for download there doesn't even provide Text.Regex. Of course, just saying "download the latest version with darcs" isn't useful, either. People that want to use my package shouldn't have to have darcs, and they also shouldn't have to fight with broken development software. Or should I be telling people to download the GHC 6.6 extralibs source? That doesn't seem quite right either; it's packaged as a tar.bz2, but what would a Windows user with HUGS do? That person probably couldn't even unpack it. Thanks, -- John

3 4

Picking out elements of a heterogenous list
by Creighton Hogg 06 Dec '06

06 Dec '06

Hi Haskell-ers, So I think I understand the idea of creating a heterogenous list using typeclasses and existentials, but I don't see how to filter the list to retrieve elements of the list that are of only one type. More concretely, taking the example here<http://haskell.org/haskellwiki/Existential_type>how could we take a list of shapes [Shape] and pull out all objects that are Squares? I don't see an obvious way this makes sense. Is there a way of doing heterogenous lists that would make this possible?

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Re: haddock not finding base lib docs -- $topdir ?
by Simon Marlow 05 Dec '06

05 Dec '06

[ moving to haskell-cafe(a)haskell.org ] Claus Reinke wrote: >> This is due to the way GHC is installed on Windows, the package >> database doesn't have hardcoded pathnames, the idea being that you can >> move your GHC anywhere in the filesystem and it will still work. > > this is an essential feature (for instance, running GHC from a USB or > network drive, or just unpacking snapshots without using installers), > please do not start splicing in absolute paths! Don't worry, we don't intend to do that. >> Unfortunately this means that Haddock can't find the documentation for >> the packages. > > this part I do not understand - if GHC and ghc-pkg can find the > packages, why can't Haddock? wouldn't it just be a case of making > $topdir be in a fixed relationship to the output of "ghc --print-libdir"? well yes, but Haddock doesn't invoke 'ghc --print-libdir'. I think it would be better for ghc-pkg to hide $topdir from everyone by replacing it with its value in any ghc-pkg output. After all, $topdir is just a hack to make the GHC tree location-independent on Windows, it's not a documented feature of the package system. > or should there be a way to query ghc-pkg for the list of package > location roots? as you say, the main docs will be in a known location > relative to GHC, but perhaps docs in general should be be in a known > location relative to their packages, which ghc-pkg (or other tools for > other implementations) should be able to locate? > >> One workaround is to specify the paths by hand, using Haddock's >> --read-interface flag. You're using Haddock via Cabal though, so that >> doesn't work too well. The other workaround is to find GHC's >> package.conf file and replace the string $topdir with the literal path >> ("c:/ghc/ghc-6.6" in your case - perhaps you have to append "/doc" for >> the haddock fields, though). > > will all docs be moved into "`ghc --print-libdir`\\doc"? No. Docs can be installed wherever you like. Cabal has a policy for installation locations on Windows, which you can override if you want. > what about > local/user package databases? Same here, you can install things wherever you like. In fact, installing things inside the GHC tree isn't recommended. Cheers, Simon

1 0

unexpected compiler behavior
by jepalomar23＠ono.com 05 Dec '06

05 Dec '06

Hi, I am newbie in Haskell and do not understand why the interpreted mode differs from the compiled program. I run this code main = do putStr "line1" x<-getLine putStr "line2" y<-getLine return (x++y) either under runhugs or runghc or in a console under ghci and works properly, that is, first displays "line1" and then prompts for the corresponding inputs through the keyboard, and so on. However, if I compile the code with the command line ghc --make Main.hs -o main and launch the compiled program main, then at first prompts for the input lines through the keyboard and then displays the strings "line1" "line2". I have read in the tutorials that the command "do" implies an ordered execution and this only occurs in interpreted mode. Using the monadic notation >> , >>= occurs the same unordered behavior. ¿How can I avoid the unordered execution of this code in a compiled program? Thanks in advance. jepalomar

3 2

using greencard to write COM in haskell
by Anatoly Yakovenko 05 Dec '06

05 Dec '06

One of the goals for greencard ( http://www.cs.york.ac.uk/fp/nhc13/greencard.html#SEC2 ) is: A convenient way to write COM software components in Haskell, and to call COM components from Haskell. Are there any examples of the first goal. I would like to be able to write COM components in Haskell, so far I found this example of calling haskell form C: http://www.cs.york.ac.uk/fp/nhc13/CcallingHaskell.html >From what i understand form that example is that you register a bunch of haskell functions with your C program. So is there a way to start haskell form C? Ideally i would like something thats as easy to use as a dll, that the end use wouldn't be aware that they are using a component written in haskell. Also, I would like to have my haskell programs use my implementation of realloc which takes a context, is there an easy way to change ghc to use it? I guess I should start looking at the ghc source. Thanks, Anatoly

3 3

SYB, ext1Q, and deriving custom Typeable and Data instances
by Vyacheslav Akhmechet 05 Dec '06

05 Dec '06

Hi, I'm trying to use SYB to implement some basic relational persistance. I define a PKey datatype to represent primary keys like this: newtype PKey a = PKey a deriving (Show, Typeable, Data) I then define a sample data type like this: data User = User { id :: PKey Int, firstName :: String, lastName :: String, } deriving (Show, Typeable, Data) Finally, I try to iterate over the structure like this: test = gmapQ (gshow `ext1Q` aux) where aux :: PKey a -> String aux _ = "test" The problem is that for id gmapQ calls gshow instead of my customized version (aux). I've seen a discussion on this on haskell cafe at the following URL: http://www.opensubscriber.com/message/haskell-cafe@haskell.org/2167871.html I couldn't understand the following details: 1. Do I need to derive both Typeable and Data instances? 2. Do I need to derive them for both PKey and User or just PKey? 3. Where can I find sample code to derive these instances? Documentation shows a sample of how GHC derives Data, is that a good template to use? Also, what's a good example to derive Typeable (if in fact it needs to be done manually)? Thanks, - Slava.

1 0

'+++' and 'interleave'
by Greg Fitzgerald 05 Dec '06

05 Dec '06

Could ReadP's '+++' (symmetric choice) operator be implemented for all Monads with the 'interleave' function mentioned in Backtracking, Interleaving, and Terminating Monad Transformers<http://portal.acm.org/ft_gateway.cfm?id=1086390&type=pdf&coll=GUIDE&dl=GUID…>? This paper was a tough read for me, but it looks like they solve the same problem, but one interleaves computations within a monad and the other does it from the outside. Or am I just confused? Thanks, Greg

1 0

Four Fours problem in Haskell
by Joachim Breitner 05 Dec '06

05 Dec '06

Hi, This might be interesting for some of you (I hope): http://www.joachim-breitner.de/blog/archives/210-FourFours-in-Haskell.html Preview: An interesting programming puzzle appeard in the Blogosphere: To describe every integer from 1 to 100 as a calculation involving only and exactly four fours, and standard operations. There are solutions in C# (code) and in python (code), so I tried to do mine in Haskell. This seems to be meant for Haskell. The Type system makes the program really great to read. Functional programming allows me to conveniently create all possible associations of four operands with three binary operations. (I found five. Why are the other two sources using four?) And, in this program particular, the use of the list monad to quickly generate a list of all possible combination is really a programming-time-saver. The program is not too slow either: $ time ./fourfour>/dev/null real 0m0.917s user 0m0.852s sys 0m0.040s And it could probably be sped up by using some kind of hashing or similar stuffs. Note that the program has only 73 mostly quite short lines, while the python code has 119 and the C# code has 138 of relatively long lines (comments and empty lines not counted). I think this is impressive (unless you have worked with haskell a bit, then you are used to these kind of results). Comments welcome! Thanks, Joachim -- Joachim "nomeata" Breitner mail: mail(a)joachim-breitner.de | ICQ# 74513189 | GPG-Key: 4743206C JID: joachimbreitner(a)amessage.de | http://www.joachim-breitner.de/ Debian Developer: nomeata(a)debian.org

1 0

Re: help with threadDelay
by Neil Davies 05 Dec '06

05 Dec '06

Ian/Simon(s) Thanks - looking forward to the fix. It will help with the real time enviroment that I've got. Follow on query: Is there a way of seeing the value of this interval from within the Haskell program? Helps in the calibration loop. Neil

2 3

RE: Safe forking question
by Simon Marlow 04 Dec '06

04 Dec '06

[ duh, hit send by mistake, message continues... ] Chris Kuklewicz wrote: > forkInheritIO :: IO () -> IO ThreadId -- inherits parent's > block or unblock status > > forkBlockedIO :: IO () -> IO ThreadId -- starts the action in > "block" mode. Must manually "unblock" > Either of these is certainly possible, and I agree that forkBlockedIO is more generally useful than my forkCatchIO. One tantalising possibility is that we could make forkIO have the forkInheritIO behaviour without breaking much code, since I bet forkIO is almost never called inside block. Cheers, Simon

2 1

HaXml problem
by Alexis Hazell 04 Dec '06

04 Dec '06

Hi all, Say i have data of type Content, and i want to put that data into a type which is an instance of XmlContent, so that i can use it with hPutXml. How can i do so? Does it involve the List1 type and its NonEmpty constructor? Thanks in advance, Alexis.

2 1

Generate 50 random coordinates
by Huazhi (Hank) Gong 04 Dec '06

04 Dec '06

Hello,all My intention is to generate 50 random coordinates like (x,y). myrand :: Int myrand = randomRIO(1::Int, 100) rf=[(myrand, myrand) | a <- [1..50]] My short program is like this. However, GHCI say that the return type of randomRIO is IO a while the function defined by me is Int. Since I only need a integral type as my cooridinate, could you tell me how to fix this? Hank -- View this message in context: http://www.nabble.com/Generate-50-random-coordinates-tf2742242.html#a7651116 Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

8 8

complex state code
by Tim Newsham 04 Dec '06

04 Dec '06

I'm working on some code where I have some complex state. This is the first time I've dealt with anything like this in haskell. If anyone would review my code and let me know if there are ways I could do this better, cleaner, in a more idiomatic way, etc, I would greatly appreciate it. http://www.thenewsh.com/~newsham/Market.hs Tim Newsham http://www.thenewsh.com/~newsham/

1 0

compiler versus interpreter
by jepalomar23＠ono.com 03 Dec '06

03 Dec '06

I am programming an application with a lot of interactivity. When using x<-getChar the character corresponding to the pushed key is assigned to x immediately. Launching the module through runghc works properly. However, the compiled module through ghc requires to push return after the character key in order to complete the assignation procedure. It is a bug or there is some difference between compiler an interpreter? Thanks in advance. jepalomar

2 1

Functional GUI combinators for arbitrary graphs of components?
by Brian Hulley 03 Dec '06

03 Dec '06

Hi, I've been looking at the Fudgets research (http://www.cs.chalmers.se/ComputingScience/Research/Functional/Fudgets/ ) as an example of a purely functional gui. Afaiu a brief summary is that a Fudget can represent a GUI widget or some other object, which can have some internal state, and which receives and passes messages to the other Fudgets it is connected to. Fudgets are connected to each other by combinators eg: second >==< first -- sequential (first sends messages to second) a >*< b -- parallel There is a continuation passing implementation such that the messages are passed and internal states of Fudgets are updated (by replacing each fudget with an updated fudget) as these expressions are evaluated hence the message passing and maintenance of state doesn't involve any IORefs though interaction with external devices such as the OS uses IO. Anyway to get to my point, though all this sounds great, I'm wondering how to construct an arbitrary graph of Fudgets just from a fixed set of combinators, such that each Fudget (node in the graph) is only mentioned once in the expression. To simplify the question, assume we have the following data structure to describe the desired graph: data LinkDesc a = Series a a | Broadcast a [a] | Merge [a] a type GraphDesc a = [LinkDesc a] and a function to compute a combined object (eg Fudget) corresponding to an arbitrary graph would be: mkObj :: Ord label => Map label Obj -> GraphDesc label -> Obj mkObj = -- ??? The result of mkObj will be some expression, composed from a finite set of combinators applied to the named objects, but with the all important property that each named object appears no more than once in the expression (this is what allows Fudgets to correspond to notional objects which maintain internal state - during evaluation each fudget gets replaced by an updated fudget hence can only appear once in the whole expression). As a very simple example using existing Fudgets combinators, type Map label value = [(label, value)] mkObj [("A", objA), ("B", objB), ("C", objC)] [Series "A" "B", Series "B" "C"] === objC >==< objB >==< objA and mkObj [("A", objA), ("B", objB), ("C", objC)] [Broadcast "A" ["B", "C"]] === (objB >*< objC) >==< objA However: mkObj [("A", objA), ("B", objB), ("C", objC), ("D", objD)] [Broadcast "A" ["B", "C"], Series "B" "D", Series "A" "D"] === ??? The Fudgets library provides many combinators eg for looping, but even so, I don't think there are sufficient combinators to express the above graph (though possibly extra nodes and tagging/untagging would solve this example), or more heavily connected graphs such as: [Series "A" "B", Series "B" "C", Series "C" "D", Series "D" "B", Series "C" "A"] This problem is so general (ie converting a cyclic graph into an expression tree such that each node appears no more than once) that I'm sure someone somewhere must already have determined whether or not there can be a solution, though I don't know where to look or what to search for. Any ideas? Thanks, Brian. -- http://www.metamilk.com

3 5

Difficult memory leak in array processing
by Niko Korhonen 03 Dec '06

03 Dec '06

Hi everyone, I have the following code whose purpose is to add dither (noise) to a given array. The code looks very straightforward but apparently it has a memory leak somewhere. Here I try to run the algorithm for an array of 10,000,000 integers. Ten million unboxed strict integers should equal to 40MB which should pose no problems to any modern system. However, the program fails with a stack overflow error. I'm using GHC 6.6 on Windows with 1 GB of RAM. I've tried applying seq and some other strictness tricks (such as x == x) pretty much everywhere on the code with no results. Could you please help me understand what is going on here? Have I misunderstood something critical in how Haskell works? Here is the relevant portion of the code: module Main where import Data.Array.IO import System.Random type Buffer = IOUArray Int Int -- | Triangular Probability Density Function, equivalent to a roll of two dice. -- The number sums have different probabilities of surfacing. tpdf :: (Int, Int) -> IO Int tpdf (low, high) = do first <- getStdRandom (randomR (low, high)) second <- getStdRandom (randomR (low, high)) return ((first + second) `div` 2) -- | Fills an array with dither generated by the specified function. genSeries :: Buffer -> ((Int, Int) -> IO Int) -> (Int, Int) -> IO () genSeries buf denfun lims = let worker low i | i >= low = do r <- denfun lims writeArray buf i r worker low (i - 1) | otherwise = return () in do (lo, hi) <- getBounds buf worker lo hi main = do -- This should allocate a 40 MB array buf <- newArray_ (0, 10000000) :: IO Buffer -- Fill the array with dither genSeries buf tpdf (2, 12) -- niko.korhonen(a)gmail.com

10 18

Re: [Haskell] ANNOUNCE: Visual Haskell prerelease 0.2
by Krasimir Angelov 02 Dec '06

02 Dec '06

Hi Shelarcy, Could you check whether you have this registry key: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\VisualStudio\8.0\InstallDir and tell me its value? Typically its value should be such that the following script to work. Set shell = CreateObject("WScript.Shell") vstudioPath = shell.RegRead ("HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\VisualStudio\8.0\InstallDir") shell.Run ("""" & vstudioPath & "devenv.exe"" /Setup",0,true) Cheers, Krasimir On 11/30/06, shelarcy <shelarcy(a)gmail.com> wrote: > Hi Krasimir, > > > On 11/30/06, shelarcy <shelarcy(a)gmail.com> wrote: > >> But ... I can't install Visual Haskell prerelease 0.2. Near > >> the end of install process, Microsoft Development Environment > >> cause error. > On Thu, 30 Nov 2006 17:03:22 +0900, Krasimir Angelov <kr.angelov(a)gmail.com> wrote: > > Could you tell me what error message you see during the installation? > > If it is in Japan then translate it in English ;-). > > It's not good error message. Anyway, I translate it. > > Near the end of install process, error dialog opened and says: > > --- > The problem happende, so exit Microsoft Development Environment. > I'm sorry for causing inconvenience to you. > > (under its message, error dialog has form that send error report > for Microsoft or shows error detail. These messages are not > important, so I don't translate that.) > --- > > And click form that shows error detail, another dialog opened. > It shows: > > --- > :Error ditail: > An unhandled exception has been caught by the VSW exception filter. > :Error Signature: > AppName: devenv.exe AppVer: 7.10.6030.0 ModName: unknown > ModVer: 0.0.0.0 Offset: 00bbbacc > :Report Detail: > (Below meassage attetion to user that error report send what. > So these messages are not important, too.) > --- > > > Also it can help > > if you run the installer with logging: > > > > $ msiexec VSHaskell71.msi /l log.txt > > msiexec doesn't run its command. And error dialog noticed that > you forgot /i optio. So I used below command. > > $ msiexec /i VSHaskell71.msi /l log.txt > > I think log.txt is much more useful than previous messages. > log.txt also has Japanese messages. So I translated that part. > > --- > (snip) > > Action 20:38:17: CA_RegisterHelpFile.3643236F_FC70_11D3_A536_0090278A1BB8. > IHxRegisterSession::ContinueTransaction() returned 0. > Helpfile: C:\Program Files\Visual Haskell\doc\alex.HxS was successfully registered to namespace vs_haskell. > ????elpfile: C:\Program Files\Visual Haskell\doc\building.HxS was successfully registered to namespace vs_haskell. > Helpfile: C:\Program Files\Visual Haskell\doc\Cabal.HxS was successfully registered to namespace vs_haskell. > Helpfile: C:\Program Files\Visual Haskell\doc\haddock.HxS was successfully registered to namespace vs_haskell. > Helpfile: C:\Program Files\Visual Haskell\doc\happy.HxS was successfully registered to namespace vs_haskell. > Helpfile: C:\Program Files\Visual Haskell\doc\libraries.HxS was successfully registered to namespace vs_haskell. > Helpfile: C:\Program Files\Visual Haskell\doc\users_guide.HxS was successfully registered to namespace vs_haskell. > Helpfile: C:\Program Files\Visual Haskell\doc\vh.HxS was successfully registered to namespace vs_haskell. > Action 20:38:17: CA_RegisterPlugIn.3643236F_FC70_11D3_A536_0090278A1BB8. > IHxRegisterSession::ContinueTransaction() returned 0. > IHxPlugIn::RegisterHelpPlugIn() returned 0. > Namespace: vs_haskell was successfully plugged into namespace MS.VSCC.2003. > Action 20:38:17: CA_CommitHelpTransaction.3643236F_FC70_11D3_A536_0090278A1BB8. > Action 20:38:17: RegisterProduct. Registering product > RegisterProduct: {FEC3263A-9034-49C5-8C5D-902231009894} > Action 20:38:18: PublishFeatures. Publishing Product Features > PublishFeatures: Feature: Complete > Action 20:38:18: PublishProduct. Publishing product information > 1: {FEC3263A-9034-49C5-8C5D-902231009894} > Action 20:38:18: RollbackCleanup. Removing backup files > IHxRegisterSession::ContinueTransaction() returned 0. > Registration session: {FEC3263A-9034-49C5-8C5D-902231009894} was successfully committed. > RollbackCleanup: File: C:\Config.Msi\fc3d12.rbf > RollbackCleanup: File: C:\Config.Msi\fc3d13.rbf > RollbackCleanup: File: C:\Config.Msi\fc3d14.rbf > RollbackCleanup: File: C:\Config.Msi\fc3d15.rbf > RollbackCleanup: File: C:\Config.Msi\fc3d16.rbf > Action ended 20:38:18: InstallFinalize. Return value 1. > Action 20:38:18: CA_HxMerge_VSCC.3643236F_FC70_11D3_A536_0090278A1BB8. > Action start 20:38:18: CA_HxMerge_VSCC.3643236F_FC70_11D3_A536_0090278A1BB8. > ????tion ended 20:40:09: CA_HxMerge_VSCC.3643236F_FC70_11D3_A536_0090278A1BB8. Return value 1. > Action 20:40:09: CA_RemoveTempHxDs.3643236F_FC70_11D3_A536_0090278A1BB8. > Action start 20:40:09: CA_RemoveTempHxDs.3643236F_FC70_11D3_A536_0090278A1BB8. > Action ended 20:40:09: CA_RemoveTempHxDs.3643236F_FC70_11D3_A536_0090278A1BB8. Return value 1. > Action 20:40:09: VSHaskellInstall. Register Visual Haskell Plugin > Action start 20:40:09: VSHaskellInstall. > Error 1720. There is a problem with this Windows Installer package. A script required for this install to complete could not be run. Contact your support personnel or package vendor. Custom action VSHaskellInstall script error -2146828275, Microsoft VBScript Runtime Error: Couldn't match types.: 'Return' Line 55, Column 5, > MSI (s) (0C:D4) [20:51:43:359]: Product: Visual Haskell 0.2 for Visual Studio 2003 -- Error 1720. There is a problem with this Windows Installer package. A script required for this install to complete could not be run. Contact your support personnel or package vendor. Custom action VSHaskellInstall script error -2146828275, Microsoft VBScript Runtime Error: Couldn't match types.: 'Return' Line 55, Column 5, > > Action ended 20:51:43: VSHaskellInstall. Return value 3. > Action ended 20:51:43: INSTALL. Return value 3. > Action ended 20:51:43: ExecuteAction. Return value 3. > Action 20:51:43: FatalError. > Action start 20:51:43: FatalError. > Action 20:51:43: FatalError. Dialog created > Action ended 20:51:46: FatalError. Return value 2. > Action ended 20:51:46: INSTALL. Return value 3. > === Logging stopped: 2006/11/30 20:51:46 === > MSI (c) (B8:C4) [20:51:46:046]: Product: Visual Haskell 0.2 for Visual Studio 2003 -- Installation failed. > --- > > > > In the Visual Haskell\bin directory you can see one directory called > > 1033 with vs_haskell_ui.dll in it. vs_haskell_ui.dll contains various > > string resources used in Visual Haskell. For each supported language > > you need to have a different directory and 1033 is the code used for > > English. I don't know the code required for Japan but you can look at > > C:\Program Files\Microsoft Visual Studio 8\VC\bin directory and see > > what code VC++ is using. After that try to rename the 1033 directory > > to what is required for Japan. Tell me whether that works. > > Japanese diretory is 1041. > > After rename it, I tried to use Visual Haskell 0.2. But same error dialog > opened and exit Visual Studio, too. > > > -- > shelarcy <shelarcy capella.freemail.ne.jp> > http://page.freett.com/shelarcy/ >

3 12

Haskell source transformer?
by Dimitry Golubovsky 02 Dec '06

02 Dec '06

Hi, In order to automatize the creation of W3C DOM typesafe wrapper (this is needed for my Haskell->Javascript stuff) I am processing the OMG IDL files that contain interface definitions for DOM methods and attributes with HDirect. It works in general (for some reason it didn't like "boolean" type, so I used a preprocessor to redefine it as "Boolean"), and outputs some Haskell code full of foreign calls, yet it contains what I need: type signatures. For example, for the method "appendChild" it outputs: appendChild :: Node a1 -> Node a0 -> Prelude.IO (Node ()) appendChild newChild iptr = do o_appendChild <- Com.invokeIt (\ methPtr iptr -> Foreign.ForeignPtr.withForeignPtr newChild (\ new unmarshallNode o_appendChild (above lines of code may be truncated, they are just for illustration) This is almost it, but I need to replace the return type (using the JS monad instead of IO), and replace the method implementation with something else, based on unsafeJS. In some other cases I may need to modify type declarations, etc. I know there is a Haskell syntax parser around (maybe, more than one). Does anybody know of any utility based on such parser that does things I need, or rather a library on top of the parser? I just would like to avoid reinventing the wheel. Last thing I want to do is to change sources of HDirect. Thanks. -- Dimitry Golubovsky Anywhere on the Web

3 2

Parsec: Where's +++?
by Greg Fitzgerald 02 Dec '06

02 Dec '06

Koen Claessen's "Parallel Parsing Processes," suggests their parsing combinators have been integrated into Parsec. If so, where is the +++ operator hiding? If not, does anyone know of a parsing library with a choice operator that does breadth-first search? Also, how do I determine what instances a datatype supports? Is Parsec an instance of Applicative? Thanks, Greg

3 3

The Data.Array.* hierarchy is unsafe (or, Segfaulting for fun and profit)
by Spencer Janssen 02 Dec '06

02 Dec '06

I've discovered a problem in the array libraries that allows one to read arbitrary memory locations without the use of any unsafeFoo functions. Both GHC and Hugs are affected. > import Data.Array.IArray > import Data.Array.Unboxed Here is a poorly behaved instance of Ix: inRange and index ignore the bounds supplied. > newtype EvilIx = E Int deriving (Eq, Ord) > instance Ix EvilIx where > inRange _ _ = True > index _ (E i) = i > range (E x, E y) = map E $ range (x, y) One can read arbitrary memory locations, eventually indexing far enough to cause a segmentation fault. > main = print [a ! E (2^i) | i <- [0..]] > where > a :: UArray EvilIx Int > a = array (E 0, E 0) [] This problem is not specific to UArrays: > main' = print [a ! E (2^i) | i <- [0..]] > where > a :: Array EvilIx String > a = array (E 0, E 0) [] The issue is that the array operators trust the Ix instance to manage boundaries correctly. The solution is to double check the value returned by index with the actual length of the array. I volunteer to write the fix, if I can extract some hints from more knowledgeable folk. There's sizeOfByteArray#, is there an analog for an Array#? I need to know how to find the length of Hugs array primitives too. Cheers, Spencer Janssen

1 0

Command line utility that shrinks/simplifies functions applications ?
by Jason Dagit 02 Dec '06

02 Dec '06

On 11/30/06, Pepe Iborra <mnislaih(a)gmail.com> wrote: > > > On 30/11/2006, at 17:04, Spencer Janssen wrote: > > > I believe you're talking about the `pl' plugin for lambdabot. Lambdabot has > an offline mode, visit the homepage for the source: > > http://www.cse.unsw.edu.au/~dons/lambdabot.html > > > > > There is also a web interface to lambdabot, but I can't seem to find the > link. > http://lambdabot.codersbase.com/ > > It's really nice, I use it all the time. Thanks, we had fun putting lambdabot on the web (I have some other plans for it now too, but no time!). It had been a long time since I updated that instance of lambdabot but your email prompted me to do that today. The instance at that url now supports, redo, undo and unpl and has been synched with the official version of lambdabot 4p284. Thanks, Jason

1 0

why are implicit types different? (cleanup)
by S. Alexander Jacobson 02 Dec '06

02 Dec '06

Why do g and g' have different types? g x y = let ?f = \x-> x in ?f x ++ (show (?f y)) g :: [Char] -> [Char] -> [Char] g' :: (Show t) => [Char] -> t -> [Char] g' x y = let f = \x-> x in f x ++ (show (f y)) Is there a way I can use implicit types and let g be as general as g'? -Alex- ______________________________________________________________ S. Alexander Jacobson tel:917-770-6565 http://alexjacobson.com

4 6

First Call for Papers: TFP 2007, New York
by TFP 2007 02 Dec '06

02 Dec '06

CALL FOR PAPERS Trends in Functional Programming 2007 New York, USA April 2-4, 2007 http://cs.shu.edu/tfp2007/ OR http://tltc.shu.edu/tfp2007/ The symposium on Trends in Functional Programming (TFP) is an international forum for researchers with interests in all aspects of functional programming languages, focusing on providing a broad view of current and future trends in Functional Programming. It aspires to be a lively environment for presenting the latest research results through acceptance by extended abstracts. A formal post-symposium refereeing process then selects the best articles presented at the symposium for publication in a high-profile volume. TFP 2007 is co-hosted by Seton Hall University and The City College of New York (CCNY) and will be held in New York, USA, April 2-4, 2007 at the CCNY campus. SCOPE OF THE SYMPOSIUM The symposium recognizes that new trends may arise through various routes. As part of the Symposium's focus on trends we therefore identify the following five article categories. High-quality articles are solicited in any of these categories: Research Articles leading-edge, previously unpublished research work Position Articles on what new trends should or should not be Project Articles descriptions of recently started new projects Evaluation Articles what lessons can be drawn from a finished project Overview Articles summarizing work with respect to a trendy subject Articles must be original and not submitted for simultaneous publication to any other forum. They may consider any aspect of functional programming: theoretical, implementation-oriented, or more experience-oriented. Applications of functional programming techniques to other languages are also within the scope of the symposium. Articles on the following subject areas are particularly welcomed: o Dependently Typed Functional Programming o Validation and Verification of Functional Programs o Debugging for Functional Languages o Functional Programming and Security o Functional Programming and Mobility o Functional Programming to Animate/Prototype/Implement Systems from Formal or Semi-Formal Specifications o Functional Languages for Telecommunications Applications o Functional Languages for Embedded Systems o Functional Programming Applied to Global Computing o Functional GRIDs o Functional Programming Ideas in Imperative or Object-Oriented Settings (and the converse) o Interoperability with Imperative Programming Languages o Novel Memory Management Techniques o Parallel/Concurrent Functional Languages o Program Transformation Techniques o Empirical Performance Studies o Abstract/Virtual Machines and Compilers for Functional Languages o New Implementation Strategies o any new emerging trend in the functional programming area If you are in doubt on whether your article is within the scope of TFP, please contact the TFP 2007 program chair, Marco T. Morazan, at tfp2007(a)shu.edu. SUBMISSION AND DRAFT PROCEEDINGS Acceptance of articles for presentation at the symposium is based on the review of extended abstracts (6 to 10 pages in length) by the program committee. Accepted abstracts are to be completed to full papers before the symposium for publication in the draft proceedings and on-line. Further details can be found at the TFP 2007 website. POST-SYMPOSIUM REFEREEING AND PUBLICATION In addition to the draft symposium proceedings, we intend to continue the TFP tradition of publishing a high-quality subset of contributions in the Intellect series on Trends in Functional Programming. IMPORTANT DATES Abstract Submission: February 1, 2007 Notification of Acceptance: February 20, 2007 Registration Deadline: March 2, 2007 Camera Ready Full Paper Due: March 9, 2007 TFP Symposium: April 2-4, 2007 PROGRAMME COMMITTEE John Clements California Polytechnic State University, USA Marko van Eekelen Radboud Universiteit Nijmegen, The Netherlands Benjamin Goldberg New York University, USA Kevin Hammond University of St. Andrews, UK Patricia Johann Rutgers University, USA Hans-Wolfgang Loidl Ludwig-Maximilians Universität München, Germany Rita Loogen Philipps-Universität Marburg, Germany Greg Michaelson Heriot-Watt University, UK Marco T. Morazán (Chair) Seton Hall University, USA Henrik Nilsson University of Nottingham, UK Chris Okasaki United States Military Academy at West Point, USA Rex Page University of Oklahoma, USA Ricardo Pena Universidad Complutense de Madrid, Spain Benjamin C. Pierce University of Pennsylvania, USA John Reppy University of Chicago, USA Ulrik P. Schultz University of Southern Denmark, Denmark Clara Segura Universidad Complutense de Madrid, Spain Jocelyn Sérot Université Blaise Pascal, France Zhong Shao Yale University, USA Olin Shivers Georgia Institute of Technology, USA Phil Trinder Heriot-Watt University, UK David Walker Princeton University, USA ORGANIZATION Symposium Chair: Henrik Nilsson, University of Nottingham, UK Programme Chair: Marco T. Morazan, Seton Hall University, USA Treasurer: Greg Michaelson, Heriot-Watt University, UK Local Arrangements: Marco T. Morazan, Seton Hall University, USA ************************************************************************************ Dr. Marco T. Morazan TFP 2007 Program Committee Chair http://tltc.shu.edu/tfp2007/ http://cs.shu.edu/tfp2007/

1 0

Re: [Haskell] ANNOUNCE: Visual Haskell prerelease 0.2
by Johannes Waldmann 01 Dec '06

01 Dec '06

> > Not only the interfaces [Visual Studio vs. Eclipse] > > are completely different, but an entirely new > > set of interoperability problems would need to be solved. ... I still don't see what would be the fundamental difference. (Except perhaps that the Eclipse interfaces are easily available and well documented so it is at least possible to describe the interface problems...) The main advantage (Visual Haskell over eclipsefp) at the moment is that VH uses incremental (on-the-fly) typechecking/compilation while eclipsefp calls the compiler for whole modules? What source text transformations (refactorings) does VH support? Best regards, -- -- Johannes Waldmann -- Tel/Fax (0341) 3076 6479/80 -- ---- http://www.imn.htwk-leipzig.de/~waldmann/ -------

5 7

Re: How to get subset of a list?
by oleg＠pobox.com 01 Dec '06

01 Dec '06

Huazhi (Hank) Gong wrote: > Like given a string list s="This is the string I want to test", I want to get > the substring. In ruby or other language, it's simple like s[2..10], but how > to do it in Haskell? Quite simply, actually: > infixl 1 %% > str %% idxs = map (str !!) idxs That is it. Not the most efficient, but gets the job done. > tstring = "This is the string I want to test" > test1 = tstring %% [2..10] *Sub> test1 "is is the" > However, like I want to choose s[1,3,6,10] or something like this. > Are there some straightforward function or operator for doing this > job? Yes, see above. > test2 = tstring %% [1,3,6,10] *Sub> test2 "hsse" Indices don't have to be in the increasing order > test3 = tstring %% [10,6,3,1] *Sub> test3 "essh" or in any order... > test4 = tstring %% [10,6,3,1]++[2..10] *Sub> test4 "esshis is the" Of course if one cares about the overhead of running code (rather than the overhead of writing code), one would probably ask, as several posters did, if the list of characters is the right data structure and if the problem indeed calls for random access to the elements of the list.

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Building Binaries with Cabal
by John Goerzen 01 Dec '06

01 Dec '06

Hi folks, I'm in need of some Cabal assistance. I want to build the unit tests for MissingH using Cabal. According to the docs, this should require me to list all of the exposed modules from the library as other modules to the binary. Since there are dozens of these, I thought a simple hook could do the trick. I tried hooking into the confHook (which I have already used successfully to add "unix" as a build-dep on non-Windows platforms), and thought I could just pull the exposedModules list from the package and add those as otherModules to the executable. But it had no effect. So I tried hooking in to customBuildHook to do the same thing. Again, no effect. Here's the code I've tried. Suggestions appreciated. import Distribution.Simple import Distribution.PackageDescription import Distribution.Version import System.Info import Data.Maybe winHooks = defaultUserHooks {confHook = customConfHook} customConfHook descrip flags = let mydescrip = case System.Info.os of "mingw32" -> descrip _ -> descrip {buildDepends = (Dependency "unix" AnyVersion) : buildDepends descrip} in (confHook defaultUserHooks) mydescrip flags customBuildHook descrip lbi uh flags = let myexecutables = map bdfix (executables descrip) bdfix exe = exe {buildInfo = (buildInfo exe) {otherModules = exposedModules . fromJust . library $ descrip}} mydescrip = descrip {executables = myexecutables} in (buildHook defaultUserHooks) mydescrip flags main = defaultMainWithHooks winHooks

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New Name for MissingH?
by John Goerzen 01 Dec '06

01 Dec '06

Quick feedback time... One comment people made in the Future of MissingH thread was that the name isn't very suggestive of what the library does. I'm planning to follow the advice of many people and split the major MissingH components off into smaller bits (ConfigParser, HVFS, etc). MissingH itself will then contain any small utility functions (probably mainly string and list-related) that for whatever reason aren't suitable to go into base. What should it be called? Should it keep the MissingH name? The alternative I've been thinking of is something like Haskell Utility Library (HUL). Ideas?

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Command line utility that shrinks/simplifies functions applications ?
by Nicola Paolucci 01 Dec '06

01 Dec '06

Hi All! Haskell newbie here with a very simple question because google and hoogle are of no help. On the IRC channel #haskell (which I cannot access now from work) I saw somebody using a tool which automatically simplifies expressions,composition of multiple functions to the bare minimum. It was a query to lambdabot I think. Is that tool/library also standalone ? What's its name ? Where can I find it ? That really rocked ... Thanks, Nick

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[Redirect] polymorphism and existential types
by dons＠cse.unsw.edu.au 30 Nov '06

30 Nov '06

Redirected to haskell-cafe(a)haskell.org, the right list. -- Don ----- Forwarded message from Louis-Julien Guillemette <guillelj(a)iro.umontreal.ca> ----- Date: Mon, 27 Nov 2006 16:15:26 -0500 (EST) From: Louis-Julien Guillemette Subject: [Haskell] polymorphism and existential types Supposing a polymorphic value (of type, say, forall a . ExpT a t) is stored inside an existential package (of type, say, forall a . Exp a), I wonder how to recover a polymorphic value when eliminating the existential. The ``natural way'' to write this doesn't work: {-# OPTIONS -fglasgow-exts #-} data ExpT a t data Exp a = forall t . Exp (ExpT a t) f :: (forall a . ExpT a t) -> () f e = () g :: (forall a . ExpT a t) -> () g e = let e1 :: forall a . Exp a e1 = Exp e in case e1 of Exp e' -> f e' {- Test.hs:18:17: Inferred type is less polymorphic than expected Quantified type variable `a' is mentioned in the environment: e' :: ExpT a t (bound at Test.hs:18:11) In the first argument of `f', namely `e'' In the expression: f e' In a case alternative: Exp e' -> f e' Failed, modules loaded: none. -} In particular, the solution of pushing the forall inside doesn't work for me (it breaks other parts of my code...) : data Exp' = forall t . Exp' (forall a . ExpT a t) g' :: (forall a . ExpT a t) -> () g' e = let e1 :: Exp' e1 = Exp' e in case e1 of Exp' e' -> f e' Any help welcome! Louis-Julien _______________________________________________ Haskell mailing list Haskell(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell

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The Future of MissingH
by John Goerzen 30 Nov '06

30 Nov '06

Hi, Josef Svenningsson posted a comment on my blog today that got me to thinking. He suggested that people may be "intimidated by the size of MissingH, confused by the undescriptive name, and don't quite know what's in there." And I think he's right. I've been passively thinking about what MissingH should be for awhile now, and wonder if you all would have some suggestions. First, let me back up and describe a bit of what MissingH is. It gets its name because I think that it has useful functions that are "missing" from the standard Haskell libraries. But I can see how it's not very descriptive. The major features are: * A general-purpose modular logging infrastructure * A virtual filesystem component (similar to VFS in Gnome, but written in Haskell) * A configuration file parser, compatible with Python's and Perl's, which can also modify and generate config files and do variable interpolation * A bunch of tools for setting up pipes to/from processes * Tools to format numbers as quantities, with default configs for the SI system (1000-based) and binary system (1024-based) * Tools to track the progress of long-running actions and display a status bar on the terminal * Pure-Haskell un-gzip code, *DBM infrastructure, etc * Assorted list, string, regexp, bit, pointer, etc. utilities * MIME and email parsers. I wrote most of the code myself, but did pull some large chunks from others where licenses were compatible. The API reference is at http://gopher.quux.org:70/devel/missingh/html/index.html So, some of the questions are: Should this all be one library? I initially wrote it that way to make resolving dependencies easier for end users. Also, it still has utility because modules make use of each other's features. The list and string functions are used almost everywhere, for instance. HVFS support is also fairly pervasive. Should the module naming scheme be changed? Modules are currently named things like MissingH.List, MissingH.IO.HVFS, MissingH.ProgressMeter, etc. I guess these could go to System.ListExt, System.IO.HVFS, System.Console.ProgressMeter, etc. Could, and should, any of this be integrated into the Haskell libraries project? (That set of libraries formerly known as fptools) A few bits of code have already found their way into them. But I bet there could be a lot more. Maybe even the majority of it. How could greater community participation be encouraged, while still encouraging quality control? I have received some very good contributions to MissingH from people, and that's been great. I've also received some that just aren't that great -- they don't have Haddock docs, the code is opaque, they don't come with unit tests, etc. But by and large, I've been maintaining it mostly myself. Whenever I write some code, I think about whether this is generic code that could be useful in other projects. If so, I consider whether it would be appropriate for MissingH (and it usually is). It would be wonderful if others would be interested in contributing code that solves some need as well. There is a public darcs repo already, and I have received some darcs patches from people (thanks!) I'm not trying to rid myself of MissingH, but I think that it could be a nice resource for small tools from the entire community, if we can maintain a structure and QA footprint to it. What else should be done to make this a valuable resource for Haskell programmers? And a showcase for what is possible with Haskell? The floor's open... Thanks, -- John

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Lazy data from pipe using MissingH module
by Dougal Stanton 30 Nov '06

30 Nov '06

Newbie here working on a little program for fetching podcasts. I've been using the MissingH.Cmd module in concert with curl to download the RSS feeds like this: > fetchFeed :: Subscription -> IO (Either Error [Episode]) > fetchFeed sub = do > (pid, feed) <- pipeFrom "curl" (curlOpts ++ > ["--url", (slocation sub)]) > let eps = parseEpisodes (stitle sub) feed > forceSuccess pid > return eps According to the API docs I have to forceSuccess pid *after* I use the data. Will this construct do that, or does the compiler have free reign to move the line beginning 'let ...' wherever it feels? It seems to work occasionally for me but then just hangs, so I thought this might be the problem. Cheers, D. -- Dougal Stanton <ithika(a)gmail.com> <http://brokenhut.livejournal.com> Word attachments considered harmful.

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generating javascript
by jeff p 30 Nov '06

30 Nov '06

Hello, Are there any Haskell tools to generate javascript? Has anyone made a combinator library for javascript? thanks, Jeff

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SimonPJ and Tim Harris explain STM - video
by Bayley, Alistair 30 Nov '06

30 Nov '06

http://channel9.msdn.com/Showpost.aspx?postid=231495 The links to the video are a couple of yellow buttons at the bottom of the article: "Watch" or "Download". I haven't watched this yet (it's nearly an hour long, I think). Found via reddit (http://reddit.com) Haskeller's on TV (sort of...) woot woot! Alistair ***************************************************************** Confidentiality Note: The information contained in this message, and any attachments, may contain confidential and/or privileged material. It is intended solely for the person(s) or entity to which it is addressed. Any review, retransmission, dissemination, or taking of any action in reliance upon this information by persons or entities other than the intended recipient(s) is prohibited. If you received this in error, please contact the sender and delete the material from any computer. *****************************************************************

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