- Haskell-Cafe - Haskell.org

NewBinary: What is the license?
by Joel Reymont 08 Oct '05

08 Oct '05

Folks, NewBinary is based on nhc98's Binary and nhc98 is GPL. Does this mean that I cannot use NewBinary in commercial software? I'm afraid I just wasted a few days of work then :-(. Thanks, Joel -- http://wagerlabs.com/idealab

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Memoization
by Gerd M 08 Oct '05

08 Oct '05

Hello, I'm trying to use Data.Map to memoize computations. Unfortunately this didn't improve the runtime of f at all, so there must be something wrong with my implementation. Thanks in advance! f 1 s (HMM s0 _ sts) = s ??? sts s0 f t s hmm = memory hmm Map.! (t,s) memory hmm@(HMM s0 sss sts) = Map.fromList [ ((t,s),f' t s hmm) | t <- [1..100], s <- sss, s/=s0 ] f' 1 s (HMM s0 _ sts) = s ??? sts s0 f' t s hmm@(HMM s0 sss sts) = sum [ (memory hmm)Map.!(t-1,s') * (s ??? sts s') | s' <- sss, s' /= s0 ] _________________________________________________________________ Express yourself instantly with MSN Messenger! Download today it's FREE! http://messenger.msn.click-url.com/go/onm00200471ave/direct/01/

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runST
by Joel Reymont 08 Oct '05

08 Oct '05

Folks, Why use runST in the following example at http://www.n-heptane.com/nhlab/repos/NewBinary/Tests/BinDouble.hs ? doubleToInts d = runST ( do arr <- newDoubleArray (1,2) writeDoubleArray arr 1 d i1 <- readIntArray arr 1 i2 <- readIntArray arr 2 return (i1,i2)) Isn't it possible to do the same within the IO monad? Thanks, Joel -- http://wagerlabs.com/idealab

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Re: [Haskell-cafe] MutableByteArray as a Ptr
by Joel Reymont 08 Oct '05

08 Oct '05

This is no longer an issue as I found how to read and write Float and Double at the link below http://www.n-heptane.com/nhlab/repos/NewBinary/Tests/BinDouble.hs Originally, I was looking to get a chunk of memory using getByteArray from NewBinary.Binary and read a Storable after converting the array to a pointer. getByteArray :: BinHandle -> Int -> IO ByteArray getByteArray bh (I# sz) = do (MBA arr) <- newByteArray sz let loop n | n ==# sz = return () | otherwise = do w <- getByte bh writeByteArray arr n w loop (n +# 1#) loop 0# freezeByteArray arr Thanks, Joel On Oct 8, 2005, at 4:49 AM, Donald Bruce Stewart wrote: > Try it and see.. I think I have indeed done this in an old version of > Yi. However, it sounds a bit iffy, and there's no reason not to use a > ForeignPtr-ified malloc'd chunk of memory. -- http://wagerlabs.com/idealab

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Trouble understanding NewBinary
by Joel Reymont 08 Oct '05

08 Oct '05

Folks, In http://www.n-heptane.com/nhlab/repos/NewBinary/NewBinary/Binary.hs there's the following bit of code. What are the I#, S# and J#? instance Binary Integer where put_ bh (S# i#) = do putByte bh 0; put_ bh (I# i#) put_ bh (J# s# a#) = do p <- putByte bh 1; put_ bh (I# s#) let sz# = sizeofByteArray# a# -- in *bytes* put_ bh (I# sz#) -- in *bytes* putByteArray bh a# sz# get bh = do b <- getByte bh case b of 0 -> do (I# i#) <- get bh return (S# i#) _ -> do (I# s#) <- get bh sz <- get bh (BA a#) <- getByteArray bh sz return (J# s# a#) Thanks, Joel -- http://wagerlabs.com/idealab

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MutableByteArray as a Ptr
by Joel Reymont 07 Oct '05

07 Oct '05

Folks, http://www.haskell.org/hdirect/ffi-6.html "GHC's ByteArray and MutableByteArray primitive types are (im)mutable chunks of memory allocated on the Haskell heap, and pointers to these can be passed to foreign imported external functions provided they are marked as unsafe." Does this mean I can pass a MutableByteArray as an argument to Storable's peek and poke? Thanks, Joel -- http://wagerlabs.com/idealab

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Endian conversion
by Joel Reymont 07 Oct '05

07 Oct '05

Folks, Are there any endian conversion routines for Haskell? I'm looking to build binary packets on top of NewBinary.Binary but my data is coming in little-endian whereas I'll need to send it out big endian. Thanks, Joel -- http://wagerlabs.com/idealab

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Alternatives to hs-plugins?
by John Goerzen 07 Oct '05

07 Oct '05

I'm thinking of porting my OfflineIMAP program from Python to Haskell. In the configuration file for OfflineIMAP, I permit people to use a Python lambda expression for some things. For instance: folderfilter = lambda foldername: not re.search('(^Trash$|Del)', foldername) So I think it would be useful to be able to do something similar in Haskell. hs-plugins immediately occured to me. But there are several problems with it: 1. Only works with GHC (no Hugs) 2. Only as portable as ghci. So quite a few platforms that are important to me would be excluded (Alpha, ARM, AIX, etc.) I'm wondering if there are any alternatives? Can a Haskell program using Hugs call Hugs to evaluate an arbitrary hunk of code? Is there any portable Haskell interpreter written in Haskell? Thanks, -- John

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New to Monads
by Tom Hawkins 07 Oct '05

07 Oct '05

I'm just starting to feel comfortable working inside IO; now I am trying to wrap my head around Control.Monad.State. Looking at the implementation, I came across some unfamiliar syntax... class (Monad m) => MonadState s m | m -> s where What is the meaning of "| m -> s"? I found no mention of it in the tutorial. And slight logical dilemma... With IO, I understand one your in it, you can't get out. I.e., any function that conducts IO must have IO _ in the type signature. But this must not apply to all monads, otherwise the type signature for "main" would be rather messy (IO + State + every other monad used in a program). But I don't see how a monad could escape this fate since bind and return only produce more monads with the same type constructor. Thanks for your help! -Tom

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Working inside the fold
by Greg Buchholz 07 Oct '05

07 Oct '05

Recently I've been browsing some of Oleg Kiselyov's articles entitled "Towards the best collection traversal interface"... http://okmij.org/ftp/Computation/Continuations.html#enumerator-stream A programming language system gives us typically one of the two interfaces to systematically access elements of a collection. One traversal API is based on enumerators -- e.g., for-each, map, filter higher-order procedures -- of which the most general is fold. The second approach relies on streams, a.k.a. cursors, lazy lists. ...where he argues that (since they're both intraconvertible) a default enumerator/fold choice is better than the lazy-list approach. I was sufficiently intrigued I thought I'd take up the challenge and see what could be done working inside the fold. This message is literate Haskell source, for those of you playing at home. The first thing to do is define a few folds which will take the place of lists. I'll start out with a finite and infinite one... >numsTo10 f unit = foldr f unit [1..10] >nats f unit = foldr f unit [1..] If you want the sum of the first ten naturals you'd invoke it as... *Main> numsTo10 (+) 0 55 ...and to see that you can convert back to a list... *Main> numsTo10 (:) [] [1,2,3,4,5,6,7,8,9,10] That's nice, but the first thing you'll notice is that while there are numerous list processing functions in the prelude, there are none for specifically working inside a fold. Let's try and define a few... >map_ :: (a -> b) -> (b -> c -> d) -> a -> c -> d >map_ f g a b = g (f a) b ...so if we want the sum of the first ten squares... *Main> numsTo10 (map_ (^2) (+)) 0 385 ...or the actual list... *Main> numsTo10 (map_ (^2) (:)) [] [1,4,9,16,25,36,49,64,81,100] ...Filter is also a nice function... >filter_ p f a b = if p a then f a b else b *Main> numsTo10 (filter_ odd (:)) [] [1,3,5,7,9] ...and we can also play nice with infinity... >takeWhile_ unit p f a b = if p a > then f a b > else unit *Main> nats (takeWhile_ [] (<15) (:)) [] [1,2,3,4,5,6,7,8,9,10,11,12,13,14] ...That's a little bit ugly because you have to supply the unit value (in this case "[]") for the fold to takeWhile_. The dropWhile_ function is also a little quirky, since it uses the tupling trick from... "A Tutorial on the Universality and Expressiveness of Fold" http://citeseer.ist.psu.edu/hutton93tutorial.html >dropWhile_ p f a (ys, xs) =((if p a > then ys > else f a xs), f a xs) *Main> numsTo10 (dropWhile_ (<5) (:)) ([],[]) ([5,6,7,8,9,10],[1,2,3,4,5,6,7,8,9,10]) *Main> numsTo10 (dropWhile_ (<5) (+)) (0,0) (45,55) ...where the first member of the pair is the desired answer. If you want to do more than one thing inside the fold, "fork" might be the solution (is there a better name?) >fork f g z (x,y) = (f z x, g z y) *Main> numsTo10 (fork (:) (+)) ([],0) ([1,2,3,4,5,6,7,8,9,10],55) *Main> numsTo10 (fork (filter_ odd (:)) (fork (+) (*))) ([],(0,1)) ([1,3,5,7,9],(55,3628800)) ...And you can mostly compose these operations, although for infinite lists you'll hit bottom if anything other than takeWhile_ is the first function... >c = nats (takeWhile_ ([],(0,1)) (<20) > (filter_ even (map_ (^2) (fork (:) (fork (+) (*)))))) > ([],(0,1)) *Main> c ([4,16,36,64,100,144,196,256,324],(1140,34519618525593600)) ...So a few generic munging functions can be defined for inside the fold. I couldn't think of how to define "take" or "drop" or figure out what a zipWith would mean. Are there any other interesting functions that could be defined? Is there a better way define these functions? Is there anything other than curiosity which would motivate someone to use these functions? FWIW, Greg Buchholz

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Emacs Haskell Mode: Indenting after "where"
by Joel Reymont 07 Oct '05

07 Oct '05

Folks, Does anyone know how to make the Haskell mode (Emacs) indent the line after "where" for this type of look: peek = if be then peek0 else peekR where peek0 a = fmap BigEndian $ peek (castAway a) peekR a = peekByteOff a 0 instead of this: peek = if be then peek0 else peekR where peek0 a = fmap BigEndian $ peek (castAway a) peekR a = peekByteOff a 0 Thanks, Joel -- http://wagerlabs.com/idealab

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Re: [Haskell-cafe] New to Monads
by Wolfgang Jeltsch 07 Oct '05

07 Oct '05

Am Freitag, 7. Oktober 2005 06:32 schrieb Cale Gibbard: > That | m -> s reads "where m determines s", and means that there can > be at most one s (here, the state type) for a given m (the monad > type). This is used in type inference and checking to ensure that the > type of state being carried around by a monad in MonadState is well > defined, and to prevent you from having to annotate the operations in > MonadState with type signatures. (To tell which type s to use.) What you can express via this syntax is called functional dependencies (in analogy to functional dependencies in database theory). One should note that functional dependencies and even multi-parameter type classes are an extension to Haskell 98 and not part of Haskell 98 which is why you haven't read about them in the tutorial. > [...] Best wishes, Wolfgang

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Confused about types
by Lanny Ripple 06 Oct '05

06 Oct '05

I thought I was doing ok with haskell until I tried to program in it. :/ I figured the first thing to tackle was something easy so I hacked up newton's method. Worked great for Double's. Then I figured I would extend it to work with different types of Fractionals. What a pain. I finally got that working for Floats and Rationals but I'm drawing a blank on Complex. I've got: <Newton.hs> import Data.Complex import Data.Ratio import Debug.Trace main = putStrLn $ "answer = " ++ show (newton myd $ -5) newton :: (Fractional a, Ord a) => (a -> a) -> a -> a newton f x = newton_h f x 1.0e-6 newton_h, next_x_h, dy_h :: (Fractional a, Ord a) => (a -> a) -> a -> a -> a newton_h f x h = until ((<= h) . abs . f) (next_x_h f h) x next_x_h f h x = trace ("next_x = " ++ show foo) foo where foo = x - (f x) / (dy_h f x h) dy_h f x h = ( (f $ x + h) - f x ) / h -- roundTo :: Fractional a => a -> a -> a -- roundTo x eps = ((fromRational . toRational) (round $ x / eps)) * eps myd :: Double -> Double myd x = ((x/100 + 1) * x + 1) * x - 10 myf :: Float -> Float myf x = ((x/100 + 1) * x + 1) * x - 10 myr :: Rational -> Rational myr x = approxRational myr' 1e-6 where myr' = ((x/100 + 1) * x + 1) * x - 10 myc :: RealFloat a => Complex a -> Complex a myc x = x * x + 1 </Newton.hs> When I try newton myc 5 in ghci I get a warning about newton wanting Ords. Complex aren't ordered. I figure I need to specify a newton_h that can handle complex newton_h f (Complex x) h = until ((<= h) . realPart . abs . f) (next_x_h f h) x laughs at me. So does newton_h f (:+ r im) h = until ((<= h) .realPart . abs . f) (next_x_h f h) (:+ r im) although I sure thought I had read that constructors could be used in pattern matching. I've been working on this for too long and getting frustrated. Can someone clue me in? Thanks, -ljr -- Lanny Ripple <lanny(a)cisco.com> CC Tools / Cisco Systems, Inc.

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RE: [Haskell-cafe] Papers from the 2005 Haskell Workshop (Tallinn)?
by Simon Marlow 06 Oct '05

06 Oct '05

On 05 October 2005 17:11, Dimitry Golubovsky wrote: > The papers presented at the Workshop are already available in the ACM > library which requires membership/subscription to read full text PDFs. > Are there any plans to make those papers available anywhere else on > the Web without subscription? The papers I co-authored are available from my web page: http://www.haskell.org/~simonmar/bib/bib.html Cheers, Simon

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Re: [Haskell-cafe] Papers from the 2005 Haskell Workshop (Tallinn)?
by Dimitry Golubovsky 06 Oct '05

06 Oct '05

Nils Anders Danielsson wrote: > > Most authors do put their papers on their web pages nowadays. > In particular, I would like to read the paper on "halfs" (haskell filesystem). Googling for <halfs haskell filesystem> gave nothing but the Workshop's schedule and ACM Library TOC. Dimitry Golubovsky Middletown, CT

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Define a data structure of a predicate
by Sara Kenedy 05 Oct '05

05 Oct '05

Hello you all, I am a newbie in Haskell. Now I am working on datatype structure of Haskell, especially on predicate. Today I try to search on Internet to find the reference document but I did not find the specific. If any of you know how to define a data structure for the abstract syntax of predicate logicI , for example : x^2 + 3*x + 2 > 0, if you don't mind, please share with me. Thanks in advance.

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CFP: PAPP 2006
by Ch. A. Herrmann 05 Oct '05

05 Oct '05

--------------------------------------------------------------------- Please accept our apologies if you have received multiple copies. Please feel free to distribute it to those who might be interested. --------------------------------------------------------------------- ---------------------------------------------------------- CALL FOR PAPERS PAPP 2006 Third International Workshop on Practical Aspects of High-level Parallel Programming http://graal.ens-lyon.fr/~abenoit/conf/papp2006.html part of ICCS 2006 The International Conference on Computational Science May 28-31, 2006, University of Reading, UK ---------------------------------------------------------- AIMS AND SCOPE Computational Science applications are more and more complex to develop and require more and more computing power. Parallel and grid computing are solutions to the increasing need for computing power. High level languages offer a high degree of abstraction which ease the development of complex systems. Moreover, being based on formal semantics, it is possible to certify the correctness of critical parts of the applications. Algorithmic skeletons, parallel extensions of functional languages such as Haskell and ML, parallel logic and constraint programming, parallel execution of declarative programs such as SQL queries, etc. have produced methods and tools that improve the price/performance ratio of parallel software, and broaden the range of target applications. The PAPP workshop focuses on practical aspects of high-level parallel programming: design, implementation and optimization of high-level programming languages and tools (performance predictors working on high-level parallel/grid source code, visualisations of abstract behaviour, automatic hotspot detectors, high-level GRID resource managers, compilers, automatic generators, etc.), applications in all fields of computational science, benchmarks and experiments. Research on high-level grid programming is particularly relevant. The PAPP workshop is aimed both at researchers involved in the development of high level approaches for parallel and grid computing and computational science researchers who are potential users of these languages and tools. TOPICS We welcome submission of original, unpublished papers in English on topics including: * high-level models (CGM, BSP, MPM, LogP, etc.) and tools for parallel and grid computing * high-level parallel language design, implementation and optimisation * functional, logic, constraint programming for parallel, distributed and grid computing systems * algorithmic skeletons, patterns and high-level parallel libraries * generative (e.g. template-based) programming with algorithmic skeletons, patterns and high-level parallel libraries * applications in all fields of high-performance computing (using high-level tools) * benchmarks and experiments using such languages and tools PAPER SUBMISSION AND PUBLICATION Prospective authors are invited to submit full papers in English presenting original research. Submitted papers must be unpublished and not submitted for publication elsewhere. Papers will go through a rigorous reviewing process. Each paper will be reviewed by at least three referees. The accepted papers will be published in the Springer-Verlag Lecture Notes in Computer Science (LNCS) series, as part of the ICCS proceedings. Submission must be done through the ICCS website: http://www.iccs-meeting.org/iccs2006/papers/upload.php We invite you to submit a full paper of 8 pages formatted according to the rules of LNCS, describing new and original results, no later than December 2, 2005. Submission implies the willingness of at least one of the authors to register and present the paper. An early email to Anne.Benoit at ens-lyon.fr with your intention to submit a paper would be greatly appreciated (especially if you have doubts about the relevance of your paper). Accepted papers should be presented at the workshop and extended and revised versions will be published in a special issue of Parallel and Distributed Computing Practices, provided revisions suggested by the referees are made. IMPORTANT DATES December 2, 2005 Full paper due January 31, 2006 Referee reports and notification February 10, 2006 Camera-ready paper due May 2006 Journal version due June 2006 Referee reports July-October 2006 Revision of papers, final notification November 2006 Final paper due PROGRAM COMMITTEE Marco Aldinucci (CNR/Univ. of Pisa, Italy) Olav Beckmann (Imperial College London, UK) Anne Benoit (ENS Lyon, France) Alexandros Gerbessiotis (NJIT, USA) Stephen Gilmore (Univ. of Edinburgh, UK) Clemens Grelck (Univ. of Luebeck, Germany) Christoph Herrmann (Univ. of Passau, Germany) Zhenjiang Hu (Univ. of Tokyo, Japan) Frédéric Loulergue (Univ. Orléans, France) Casiano Rodriguez Leon (Univ. La Laguna, Spain) Alexander Tiskin (Univ. of Warwick, UK) ORGANIZERS Dr. Anne BENOIT Laboratoire d'Informatique du Parallélisme Ecole Normale Supérieure de Lyon 46 Allée d'Italie 69364 Lyon Cedex 07 - France Pr. Frédéric LOULERGUE Laboratoire d'Informatique Fondamentale d'Orléans Université d'Orléans Bâtiment IIIA - Rue Léonard de Vinci - BP6759 45067 Orléans Cedex 2 - France

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RE: [Haskell-cafe] Problem with sparc distribution?
by Simon Marlow 05 Oct '05

05 Oct '05

On 29 September 2005 10:37, Christian Maeder wrote: > I've repacked the distribution and put it at: > http://www.informatik.uni-bremen.de/agbkb/forschung/formal_methods/CoFI/ hets/solaris/ghc-6.4.1-sparc-sun-solaris2.tar.bz2 > > Can you copy it to http://www.haskell.org/ghc/dist/6.4.1/, Simon? Done. Simon

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Converting [Word8] to String
by Joel Reymont 04 Oct '05

04 Oct '05

Folks, How do I convert a list of bytes to a string? Cale has suggested a neat way of parsing binary packets in this thread: http://www.mail-archive.com/haskell-cafe@haskell.org/msg09413.html and I'm trying to create a packet reader for a Pascal-style string where the length is the first byte and the list of characters follows. I understand that I can take the first X bytes of the byte list but how do I make this into a string? I'll probably use fast packed strings to read from the socket handle and will unpack the fps into a list of bytes for parsing. Thanks, Joel -- http://wagerlabs.com/

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IRC for spreading information
by John Goerzen 04 Oct '05

04 Oct '05

I've got a bit of a concern to raise regarding reliance on IRC for spreading information important to the community. As I was preparing this week's HWN, I made the comment on #haskell that it's been a quiet week. Several people that were at ICFP and the workshops disagreed, saying there had been a lot of activity. But none of it appeared on the Haskell lists. With the help of some IRCers, I found information in Autrijus' blog and a link to some IRC logs. There *was* a lot going on. I would like to make a friendly request that important things like this be posted to the mailing lists. I don't have a problem with them being on IRC as well, but there are several problems with it being "IRC only" or "IRC mostly" or even "conference only": * The only way to participate effectively is to be in the IRC room at the exact same time as the other participants. Very difficult to include everyone in a global community such as that. * It is very cumbersome, and sometimes even impossible, to extract conversations from IRC logs, given that several conversations could have been happening at once in the channel. Mailing list archives, with support for threads, are much easier to read. As an aside, I will not be writing up summaries of IRC logs for HWN, though if someone else cares to do so and send them to me, I'd put them in. I simply don't have the time or the desire for a pounding headache that most people get from reading IRC logs ;-) -- John

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Short Cut / Rewrite Rules Problem in GHC
by Chris 04 Oct '05

04 Oct '05

Hi All. I am a student and a noob to Haskell. I am having some trouble with an example from the paper "Playing by the rules: Rewriting as a practical optimisation technique in GHC" by Simon Peyton Jones, Andrew Tolmach and Tony Hoare, specifically, the Short- cut Deforestation example in section 3.1. I was trying to compile the following using GHC version 6.4 on Mac OS X 10.4. The definition for build and the rule are from the paper (the rule also appears in the GHC online doc in section 7.10.1). ----------------------------------------------------- -- BOF -- File: Main.hs module Main where build :: (forall b. (a->b->b) -> b -> b) -> [a] build' g = g (:) [] {-# RULES "foldr/build" forall k z (g::forall b. (a->b->b) -> b -> b) . foldr k z (build g) = g k z #-} main :: IO () main = do putStr "" -- EOF ----------------------------------------------------- When I enable the extensions for GHC I get the following error: chris$ ghc -fglasgow-exts --make Main.hs Chasing modules from: Main.hs Compiling Main ( Main.hs, Main.o ) Main.hs:15:1: lexical error When I don't have them enabled it gives this error: chris$ ghc --make Main.hs Chasing modules from: Main.hs Compiling Main ( Main.hs, Main.o ) Main.hs:8:18: parse error on input `.' I have also tried moving the RULES option to the top of of the file above "module Main", but I still get the same errors. Also, should the definition of build be: build :: forall a. (forall b. (a -> b -> b) -> b -> b) -> [a] build g = g (:) [] If I try to load the Main.hs file in HUGS with the -98 option and the above version of build (with the forall a.), it works without a problem. However, it still gives the same errors in GHC. Additionally, I tried this on a different version of GHC, 6.2.2 on a x86 box running Gentoo Linux, and it yielded the same results. I am completely lost and would greatly appreciate any help. Thanks so much. - Chris.

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Re: [Haskell-cafe] Endian conversion
by Marc Ziegert 03 Oct '05

03 Oct '05

nice project. (except that winonly-closedsource-....thing. my condolence.) on which platform are you programming? mac? linux-ppc? i see that you understood most of that code. big-endian-test: the number 1234 has two ends (like a sausage), the end with the 1 is the big end (1000), the 4 is the little one. if you save he number 1 as int in little endian, then you write the bytes 01 00 00 00, and in big endian it is 00 00 00 01. so, if you read the first char, then it will either be ==1 (little) or /=1 (big). to write that LittleEndian stuff, you only need to replace Big with Little and "if be then" with "if not be then". it is the question wether to use he function xyz0(derived) or xyzR(reverse order of bytes). i hope, that the compiler optimizes "if True" away. to use the Storables, read the docu about the libs(functions) Network.Socket(sendBufTo) Foreign.Marshal.Utils(with) Foreign.Storable(peekThis,peekThat) you just need to read "LittleEndian CInt", remove that "LittleEndian"-constructor, work with that CInt, put the "BigEndian"-constructor at that CInt, write it... maybe you need to convert LE and BE enums, too. use "(toEnum . fromEnum)" to convert between any enum and CInt. good n8. - marc Joel Reymont wrote: > Well, I liked that bit of Template Haskell code that Marc sent. I'm > now stuck trying to adapt it to read Storables :-). > > It seems, on a second glance, that there's not that much to adapt. If > I read Marc's code correctly it "derives" Storable and uses the peek, > etc. methods to swap bytes around. Which means to me that so long as > the byte swapping methods are implemented and I try to store a > BigEndian or LittleEndian it would be stored correctly for me. > > Is this so? > > To recap, I'm trying to read binary packets from a socket and the > first thing I do is read the packet length. I then need to read the > packet body where the numbers are little or big endian. After > processing the packet I need to write it out and the numbers again > could be little or big endian. > > I could read a FastString from a socket since it has IO methods but I > don't know how to convert the FS into a pointer suitable for > Storable. So much to learn :-). > > Thanks, Joel > > On Oct 3, 2005, at 9:33 PM, Udo Stenzel wrote: > > > Why don't you pull out 4 bytes and assemble them manually? Three > > shifts, logical ors and fromIntegrals aren't that much of a burden > > after > > all. > > -- > http://wagerlabs.com/idealab > > > > > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe >

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14-queens Problem
by Yousry Abdallah 03 Oct '05

03 Oct '05

hi, is it fast to calculate all solutions for the 14-queens problem in 7 minutes? (searchspace size is 7,68E+031)

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NewBinary code for working with FastStrings
by Joel Reymont 02 Oct '05

02 Oct '05

Does anyone know why the FastString code in Binary.hs is commented out? -- http://wagerlabs.com/

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Reading Word16, Word32, etc. from a FPS
by Joel Reymont 02 Oct '05

02 Oct '05

Folks, How would I implement reading of big/little-endian shorts, longs, floats, etc. from a fast packed string? Thanks, Joel -- http://wagerlabs.com/

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how to break foldl' ?
by gary ng 30 Sep '05

30 Sep '05

Hi, say if I want to sum a list of numbers but only until it hits a max limit. Currently, I control it through the function and basically do nothing when the max is hit. However, if the list is very long, would this mean the same function would be called for the rest of the list which can be a waste of cycle ? In an imperative language, I just break/return in the middle of the loop. thanks for any help in advance. gary __________________________________ Yahoo! Mail - PC Magazine Editors' Choice 2005 http://mail.yahoo.com

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finally going on Solaris
by Brian McQueen 30 Sep '05

30 Sep '05

I've finally got a working ghc on Solaris. Its 6.4.1. I couldn't get the earlier, pre 6.4 versions going due to problems with my gcc. It seemed to be expecting a gcc shared library that my system didn't have, nor did any other gcc that I was able to compile. After loading a few prerequisites, and then reloading them with --enable-shared, its now going. I found a problem with a header file in the solaris distribution too - it expects stdint.h, which doesn't seem to be a part of Solaris anymore. I undef'd the HAVE_STDINT_H lines, and its working well now. Brian McQueen

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Problem with sparc distribution?
by Brian McQueen 29 Sep '05

29 Sep '05

I find there is a problem the binary distribution: http://www.haskell.org/ghc/dist/6.4.1/ghc-6.4.1-sparc-sun-solaris2.tar.bz2 But the older one seems to be OK. It seems that the tar file is corrupted or incomplete. If you untar it yu will find the ghc dir contains only the bin and lib dirs and none of the rest of the documentations and install scripts. Brian McQueen

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Neural networks and optimization in Haskell
by Joel Reymont 28 Sep '05

28 Sep '05

Folks, I got a project where I have a large number of variables and an outcome and I need to figure out which 20% of the variables has the largest effect on the outcome. Of course I also need to optimize the 20% of variables I end up with. This sounds like a job for a neural network to me, with arguments possibly optimized through genetic algorithms. I'm wondering, though, if I'm complicating things for myself and there's an easier approach to this. If not I'm wondering if there are ready-made NN or GA libraries for Haskell. Also, I'm curious if Haskell is really the best language for this type of problem and if lazy evaluation brings any specific advantages to the solution or would be a hindrance. I would welcome any pointers and feedback, yes, someone is actually paying me to do this :-). Thanks, Joel -- http://wagerlabs.com/

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newbe question
by feucht＠uni-koblenz.de 28 Sep '05

28 Sep '05

Hi i can not load program test1 into hugs, but test2 works. Am i missing some special syntax? greetings, Philip -------------- test1 ------------------ foo :: Maybe Int -> Int foo Nothing =-1 foo (Just a)= a -------------- test2 ------------------ foo :: Maybe Int -> Int foo Nothing = -1 -- ^ -- +-- note an extra space foo (Just a)= a

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Help wanted: Lazy multiway zipper with mismached intervals
by Rene de Visser 27 Sep '05

27 Sep '05

Hello, I need to zip together multiple lists. The lists are sorted by date, and each entry in the list represents data for a time interval. The time intervals between the lists may be missmatched from each other. This means that sometimes you don't need to move forward in list, while you move forward in other lists. It might also mean that you need to skip a number of entries foward. If the computation does not need part of the contents of one of the lists, then this list should be ignored until it is needed. As the lists are sorted you never need to go backwards. I found it fairly easy to write a zipper for two lists, where the items from both lists are needed (example binary operator on the payload of the list). However the combination of merging multiple lists together, and ignoring a list in the case it is not needed by the computation leads to very messy code. I though about if there was a away of encapsulating this in a monad, but haven't thought of any way to do this. Another idea is to have a mutable cursor for each list and move these forward as required. But I guess this might be worth avoiding? I think it would be good if somehow I could encapsulate each list, so on a per list basis, and can say given me the current head, or move one forward. But I haven't figured out how to pass the state of the other threads invisibly through. I guess the ony way might be to use the state monad? I guess there can be no simple recursive solution? Rene.

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XMLParse module
by Huong Nguyen 27 Sep '05

27 Sep '05

Hello all, I am reading XMLParse module http://www.germane-software.com/repositories/public/StatusReport/trunk/hxml… But, I am not clear about the purpose of this module and the function of two functions: parseInstance = unfoldr (pRun instanceItem) . pcdataMode parseDTD = foldl (\a b->b a) emptyDTD . unfoldr (pRun dtdItem) . markupMode parseDocument text = case pRun prolog (pcdataMode text) of Just (_, rest) -> unfoldr (pRun instanceItem) rest Nothing -> [ErrorEvent "Error parsing prolog"] -- can't happen. If any knows the meaning of those, please let me know. Thanks a lot. Best regards,

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Re: [Haskell-cafe] Typing problems with basic arithmetic - help!
by Marcin Tustin 26 Sep '05

26 Sep '05

For some reason the following code is producing an error message from ghci that the the patterns are non-exhaustive. Does anyone have any idea why that could be, given that the patterns are, at least in my meaning, provably exhaustive? choosenonuniqueset n (a:r) | (length r) > (n-1) = [ (sort (a:x)) | x <- (choosenonuniqueset (n-1) r)] `union` [ (sort (a:x)) | x <- (choosenonuniqueset n r)] | (length r) == (n-1) = [a:r] | (length r) < (n-1) = [] Error message is: *Main> :reload Compiling Main ( birthday.hs, interpreted ) Ok, modules loaded: Main. *Main> choosenonuniqueset 2 [1..5] *** Exception: birthday.hs:(22,0)-(27,29): Non-exhaustive patterns in function choosenonuniqueset *Main> choosenonuniqueset 5 [1..5] [[1,2,3,4,5]] *Main>

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Re: [Haskell-cafe] Typing problems with basic arithmetic - help!
by Marcin Tustin 26 Sep '05

26 Sep '05

Thanks for this: All I have to do now is fix the fact that my maths is stupidly screwed! On Fri, Sep 23, 2005 at 02:23:10PM -0400, J. Garrett Morris wrote: > Haskell doesn't do automatic numeric conversion for you - you need to > use fromIntegral to go from an integral type (like 2) to a floating > point type (as you'd need for division) and you can use round or trunc > to go the other direction. There's similarly a fromRational function > to convert from rational numbers to just about anything else you'd > need. A couple of applications of those functions - probably mainly > around your divisions - should fix things up. > > /g

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RE: [Haskell-cafe] Template Haskell and Types
by Simon Peyton-Jones 26 Sep '05

26 Sep '05

Hmm. Q is a monad, so I think fail :: Monad m => String -> m a will do the job. 'recover' should catch the exception, and let you try something else. Simon | -----Original Message----- | From: Gracjan Polak [mailto:gracjan@acchsh.com] | Sent: 20 September 2005 10:43 | To: Simon Peyton-Jones | Cc: haskell-cafe(a)haskell.org | Subject: Re: [Haskell-cafe] Template Haskell and Types | | Simon Peyton-Jones wrote: | > design note http://research.microsoft.com/~simonpj/tmp/notes2.ps | | | In the above paper there is something about 'giveUp'. Seems to quite | useful, but there is no such thing in ghc 6.4. | | Where did my giveUp go? And why? | | -- | Gracjan

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Failure and comonads
by Einar Karttunen 26 Sep '05

26 Sep '05

Hello With the resent discussion on comonads on #haskell (mostly due to Uustalo's excellent paper) I am wondering is it possible to model failure with comonads? It seems to me that Reader,Writer and State can be implemented with both monads and comonads. IO can be implemented as a monad but OI wants linear types. Streams make fine comonads. Is there anything corresponding to Maybe or List? - Einar Karttunen

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map in IO
by Tom Hawkins 25 Sep '05

25 Sep '05

What is the best way to perform a map inside IO? I defined the following function, but this must be common enough to warrant something in the standard library. What am I missing? -Tom mapIO :: (a -> IO b) -> [a] -> IO [b] mapIO _ [] = return [] mapIO f (x:xs) = do y <- f x ys <- mapIO f xs return (y : ys)

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RE: Typing problems with basic arithmetic - help!
by Scherrer, Chad 24 Sep '05

24 Sep '05

> For some reason the following code is producing an error > message from ghci that the the patterns are non-exhaustive. > Does anyone have any idea why that could be, given that the > patterns are, at least in my meaning, provably exhaustive? > You forgot to match against the empty list. Try adding choosenonuniqueset n [] = [] -Chad Scherrer

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Local quantification annotations
by Joel Reymont 24 Sep '05

24 Sep '05

Folks, What are the local quantification annotations they talk about here? http://www.cc.gatech.edu/~saswat/research/Summary.ps Thanks, Joel -- http://wagerlabs.com/

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Typing problems with basic arithmetic - help!
by Marcin Tustin 23 Sep '05

23 Sep '05

I'm trying to do some basic arithmetic code (in fact it calculates the probability of a birthday clash given year length and group size), and GHC and Hugs are both not liking the code: [marcin@ah-m2b2 ~]$ ghci burthday.hs ___ ___ _ / _ \ /\ /\/ __(_) / /_\// /_/ / / | | GHC Interactive, version 6.4, for Haskell 98. / /_\\/ __ / /___| | http://www.haskell.org/ghc/ \____/\/ /_/\____/|_| Type :? for help. Loading package base-1.0 ... linking ... done. Compiling Main ( burthday.hs, interpreted ) burthday.hs:14:37: No instance for (Fractional Integer) arising from use of `/' at burthday.hs:14:37 Probable fix: add an instance declaration for (Fractional Integer) In the definition of `pnorep': pnorep days n = (numeratorex days n) / (denominatorex days n) Failed, modules loaded: none. Prelude> :reload Compiling Main ( burthday.hs, interpreted ) Ok, modules loaded: Main. *Main> pnorep 365 30 <interactive>:1:0: Ambiguous type variable `a' in the constraints: `Fractional a' arising from use of `pnorep' at <interactive>:1:0-5 `Integral a' arising from use of `pnorep' at <interactive>:1:0-5 Probable fix: add a type signature that fixes these type variable(s) *Main> The first time is with the type annotations, the second without: import Ratio import Numeric numeratorex days n = (numdays days n) - (subtractex days n) -- :: Rational numdays days n = days * n --numdays :: Integer -> Integer -> Integer subtractex days n = (days * (days - 1)) / 2 --:: Rational denominatorex days n = (days^n) -- denominatorex :: Integer -> Integer -> Integer pnorep days n = (numeratorex days n) / (denominatorex days n) Help! Thanks!

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Re: [Haskell-cafe] Re: Network parsing and parsec
by Keean Schupke 23 Sep '05

23 Sep '05

Andrew Pimlott wrote: >On Tue, Sep 20, 2005 at 03:01:32PM +0100, Keean Schupke wrote: > > >> (see attachment for files) >> >> > >You didn't include all the used libraries (MonadControl, MonadState). > >Andrew > > Oops, here they are (it was extracted from a larger project), sorry about that... (Have posted this back to the mailing list incase anyone else is tying to use the libraries I posted) Regards, keean.

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RE: [Haskell-cafe] killing a running thread interactively
by Simon Marlow 23 Sep '05

23 Sep '05

Haskell doesn't, but the compilers all support a kind of global mutable variable. See various lengthy discussions on the topic on this list and the Haskell list in the past. Briefly, you do it like this: {-# NOILINE var #-} var :: IORef [ThreadId] var = unsafePerformIO (newIORef []) and if you're using GHC, compile the module with -fno-cse. Cheers, Simon On 22 September 2005 17:58, S. Alexander Jacobson wrote: > Ok, I didn't think Haskell had mutable global variables. > How would this work? > > -ALex- > > On Thu, 22 Sep 2005, Simon Marlow wrote: > >> There's no getAllThreadIds or similar right now. You have to save >> the ThreadIds yourself, perhaps in a global variable. Writing to a >> file doesn't work because there's no instance Read ThreadId. >> >> Cheers, >> Simon >> >> On 21 September 2005 21:14, S. Alexander Jacobson wrote: >> >>> More particularly, is there a getAllThreadIds function somewhere? >>> >>> -Ale- >>> >>> On Wed, 21 Sep 2005, S. Alexander Jacobson wrote: >>> >>>> Is the general pattern to write all threadIds to a file, and then >>>> have a separate function that takes the file and kills them? >>>> >>>> Or is there something more clever? >>>> >>>> -Alex- >>>> >>>> On Wed, 21 Sep 2005, Simon Marlow wrote: >>>> >>>>> On 16 September 2005 20:42, S. Alexander Jacobson wrote: >>>>> >>>>>> If I am running a server interactively. (using ghci). >>>>>> Is there any way to kill its running threads without terminating >>>>>> the interpreter? >>>>> >>>>> If you can get ThreadIds for the threads, yes. GHCi doesn't >>>>> (currently) create a new thread for each expression evaluation, so >>>>> attempting to kill that thread might kill your GHCi session (it >>>>> shouldn't but that's another story). >>>>> >>>>> Cheers, >>>>> Simon >>>>> >>>>> ** CRM114 Whitelisted by: simonmar(a)microsoft.com ** >>>>> >>>> >>>> ______________________________________________________________ >>>> S. Alexander Jacobson tel:917-770-6565 http://alexjacobson.com >>>> >>> >>> ______________________________________________________________ >>> S. Alexander Jacobson tel:917-770-6565 http://alexjacobson.com >> >> ** CRM114 Whitelisted by: simonmar(a)microsoft.com ** >> > > ______________________________________________________________ > S. Alexander Jacobson tel:917-770-6565 http://alexjacobson.com

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Network parsing and parsec
by John Goerzen 22 Sep '05

22 Sep '05

Hello, The recent thread on binary parsing got me to thinking about more general network protocol parsing with parsec. A lot of network protocols these days are text-oriented, so seem a good fit for parsec. However, the difficulty I come up time and again is: parsec normally expects to parse as much as possible at once. With networking, you must be careful not to attempt to read more data than the server hands back, or else you'll block. I've had some success with hGetContents on a socket and feeding it into extremely carefully-crafted parsers, but that is error-prone and ugly. Here's the problem. With a protocol such as IMAP, there is no way to know until a server response is being parsed, how many lines (or bytes) of data to read. Ideally, I would be able to slrup in more data as I go, but that doesn't seem to be very practical in Parsec either. Suggestions?

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Growing Trees
by Tom Hawkins 22 Sep '05

22 Sep '05

I'm porting an ML program to Haskell, but am having difficulty with particular data structure: a tree where each node has references to the children as well as the parent... data Tree a = TreeRoot { stuff :: a , children :: [Tree] } | TreeNode { stuff :: a , parent :: Tree , children :: [Tree] } But because of these bidirectional links, every time I add a node I must reconstructing the entire tree. There is also the add coding complexity of threading the tree through various functions to simulate state. What are my [monadic] options? -Tom

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RE: [Haskell-cafe] killing a running thread interactively
by Simon Marlow 22 Sep '05

22 Sep '05

There's no getAllThreadIds or similar right now. You have to save the ThreadIds yourself, perhaps in a global variable. Writing to a file doesn't work because there's no instance Read ThreadId. Cheers, Simon On 21 September 2005 21:14, S. Alexander Jacobson wrote: > More particularly, is there a getAllThreadIds function somewhere? > > -Ale- > > On Wed, 21 Sep 2005, S. Alexander Jacobson wrote: > >> Is the general pattern to write all threadIds to a file, and then >> have a separate function that takes the file and kills them? >> >> Or is there something more clever? >> >> -Alex- >> >> On Wed, 21 Sep 2005, Simon Marlow wrote: >> >>> On 16 September 2005 20:42, S. Alexander Jacobson wrote: >>> >>>> If I am running a server interactively. (using ghci). >>>> Is there any way to kill its running threads without terminating >>>> the interpreter? >>> >>> If you can get ThreadIds for the threads, yes. GHCi doesn't >>> (currently) create a new thread for each expression evaluation, so >>> attempting to kill that thread might kill your GHCi session (it >>> shouldn't but that's another story). >>> >>> Cheers, >>> Simon >>> >>> ** CRM114 Whitelisted by: simonmar(a)microsoft.com ** >>> >> >> ______________________________________________________________ >> S. Alexander Jacobson tel:917-770-6565 http://alexjacobson.com >> > > ______________________________________________________________ > S. Alexander Jacobson tel:917-770-6565 http://alexjacobson.com

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Newbie question: how to run HaXML in Unix
by Huong Nguyen 22 Sep '05

22 Sep '05

Hello everybody, This seems so simple question, but I did not find the solution. HaXML is installed. Do you know how I can run HaXML in Linux/Unix (which command I should write). Thank you.

2 1

mistake in Gentle Introduction
by Michael Vanier 22 Sep '05

22 Sep '05

On this page: http://www.haskell.org/tutorial/modules.html it refers to the process of hiding imported names from a module and gives the example: import Prelude hiding length whereas the correct syntax is import Prelude hiding (length) I spent nearly an hour beating my head against this. Can someone fix this in the documentation? Mike

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Really confused
by Mark Carter 22 Sep '05

22 Sep '05

I'm trying to define a type called Stream. For now, assume that that the type has 3 fields: uid, x, y. X and y represent a point in space that a stream occupies, and uid is a unique identifier for the stream. The uid should be "auto-generated". It's important that streams have an identity so that they can be referred to and manipulated. Streams will be put together into a list, and they'll eventually need to be able to point to one another. It would be nice to be able to print the uid, just to show that it works. Now it occured to me that what one might want to generate the uids is a monad, let's call it UID. It'll have a function get, which returns another identifier. I assumed that the best solution for the problem would be in terms of monads, because successive calls to get return different results; i.e. there's a bit of state going on inside. The values returned can start from 1, and increment by 1 each time. I had a look at some documentation at: http://www.haskell.org/tutorial/monads.html and I'm afraid my brain just froze. I get the idea that data SM a = SM (S -> (a,S)) maps a state to a result, and a new state. OTOH, looking at instance Monad SM where -- defines state propagation SM c1 >>= fc2 = SM (\s0 -> let (r,s1) = c1 s0 SM c2 = fc2 r in c2 s1) return k = SM (\s -> (k,s)) just confuses me no end. Any pointers, like am I taking completely the wrong approach anyway? I'm also puzzled as to how the initial state would be set. ___________________________________________________________ Yahoo! Messenger - NEW crystal clear PC to PC calling worldwide with voicemail http://uk.messenger.yahoo.com

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Re: [Haskell] Re: [Haskell-cafe] Haskell versus Lisp
by David F. Place 21 Sep '05

21 Sep '05

On Sep 20, 2005, at 3:43 PM, Glynn Clements wrote: > That, in a nutshell, is Lisp's key strength. It uses the same > structure for code as for data, which makes it very easy to add new > language features. > I assume that you refer to `eval' and the fact it operates on conses and symbols. Beyond the extremely contrived example of a metacircular interpreter, what are some examples of the benefits of this feature of lisp? What are some examples of language features that are easy to add? -------------------------------- David F. Place mailto:d@vidplace.com

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RE: [Haskell-cafe] killing a running thread interactively
by Simon Marlow 21 Sep '05

21 Sep '05

On 16 September 2005 20:42, S. Alexander Jacobson wrote: > If I am running a server interactively. (using ghci). > Is there any way to kill its running threads without terminating the > interpreter? If you can get ThreadIds for the threads, yes. GHCi doesn't (currently) create a new thread for each expression evaluation, so attempting to kill that thread might kill your GHCi session (it shouldn't but that's another story). Cheers, Simon

2 2