- Haskell-Cafe - Haskell.org

Re: [Haskell-cafe] Why 'round' does not just round numbers ?
by Janis Voigtlaender 28 Oct '08

28 Oct '08

Felipe Lessa wrote: > On Mon, Oct 27, 2008 at 8:15 AM, Janis Voigtlaender > <voigt(a)tcs.inf.tu-dresden.de> wrote: > >>That is of course true (and was the topic of heated discussion with my >>fourth grade math teacher), but does not explain 2.5 -> 2. > > > If you round to odd instead of round to even, then 4.5 rounds to 5, Well, of course I did not learn to round to odd. I learned to round .5 to above, but not to do repeated rounding. So we would never have either of > 2.45 -> 2.4 -> 2 > 2.45 -> 2.5 -> 3 as you suggest. Instead, always in one go: 2.45 -> 2 Because of the 4, whereas any digit following it would be ignored: 2.4x -> x In fact, by your explanation, you would have: 3.46 -> 3.5 -> 4 Which is most odd. 3.46 is definitely closer to 3 than to 4. -- Dr. Janis Voigtlaender http://wwwtcs.inf.tu-dresden.de/~voigt/ mailto:voigt@tcs.inf.tu-dresden.de

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Haskell on the JVM
by David Leimbach 28 Oct '08

28 Oct '08

Are there, or have there been Haskell ports to the JVM? Are any of them alive and well? Is there an interest in hosting GHC on the JVM (besides my own). I know I don't have time to tackle such a project but I'd be extremely interested in using such a thing. Especially in my day to day work. I currently do a lot of Java <-> Erlang via JInterface, and have been for months, yet there's many tasks I could do better in a language like Haskell.

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Re: [Haskell] Re: Current XML libraries status
by Uwe Schmidt 27 Oct '08

27 Oct '08

Hello David, > I tried to use HXT's readDocument with its tagsoup option for my > application. I couldn't find a way to construct the operation that > didn't run out of memory. I'll attach some code using HaXml's > saxParse so you can see what I want. Is that easy to do in HXT? > I simply want the text of <PMID> and <AbstractText> elements. here's an example, that reads the input in a lazy way. I ran this in ghci with a file containing 2^20 XML Elements. The file was about 18Mb in size. A normal parse with the standard parsec parser ran out of memory on my 1Gb box. This one used within ghci about 200Mb max. ------------------------------------ module Main where import Text.XML.HXT.Arrow import System main = do mapM_ main' names main = do (name:_) <- getArgs runX ( readDoc name >>> fromLA (deep (hasName "PIMD" -- select the nodes <+> hasName "AbstractText" ) >>> getChildren -- get the text >>> getText ) >>> arrIO putStrLn ) putStrLn "main finished" readDoc = readDocument [ (a_tagsoup, v_1) , (a_parse_xml, v_1) , (a_remove_whitespace, v_1) , (a_encoding, isoLatin1) , (a_issue_warnings, v_0) , (a_trace, "1") ] --------------------- Cheers, Uwe Schmidt -- Uwe Schmidt Web: http://www.fh-wedel.de/~si/

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External Sort: Sort a 10-million integer file with just 256M of ram.
by Thomas Hartman 27 Oct '08

27 Oct '08

Now on hackage: cabal install external-sort demo (included in distribution): thartman@thartman-laptop:~/external-sort>cat demo.hs {-# LANGUAGE PatternSignatures #-} import Algorithms.ExternalSort import Data.List import System.IO import System.Environment (getArgs) import System.Time import HSH -- to do: compare speed against unix sort util on a 10 million line file. -- pure in-memory prelude sort will crash your computer when the list gets over a million elements or so -- externalsort caches the sublists used in the sort algorithm on your hard drive, so you can sort a much larger list. {- The behavior below was on a demo executable, compiled. (In ghci, even last on a 10 million element list caused an out of memory error.) The test computer had 256M physical ram and was ulimited to 256M cache. *Main>:! ulimit -v 262144 For 10 million element list: *Main> :! time ./demo preludesort 7 demo: out of memory (requested 1048576 bytes) Command exited with non-zero status 1 4.88user 0.68system 0:21.11elapsed 26%CPU (0avgtext+0avgdata 0maxresident)k 0inputs+0outputs (0major+64817minor)pagefaults 0swaps *Main> :! time ./demo externalsort 7 10000000 73.87user 1.96system 1:24.25elapsed 90%CPU (0avgtext+0avgdata 0maxresident)k 792inputs+156280outputs (6major+16739minor)pagefaults 0swaps ./demo unixsort 7 wrote bigfile, time: Mon Oct 20 15:25:26 CEST 2008 demo: out of memory (requested 1048576 bytes) For 100 million element list, external sort failed. Can it be made to work? maybe in some future version. time ./demo externalsort 8 demo: out of memory (requested 1048576 bytes) real 10m14.061s user 8m26.712s sys 0m11.793s thartman@thartman-laptop:~/external-sort>ls -lh ExternalSort.bin -rw-r--r-- 1 thartman thartman 764M Oct 20 15:50 ExternalSort.bin The problem is not fitting a 10^8 element list in memory, the following works fine (when compiled, though not in ghci): t = putStrLn . show . last $ [1..10^8::Int] Maybe think about this more later. -} main = do [s,e] <- getArgs let exp = read e case s of "preludesort" -> sortwith exp $ return . sort "externalsort" -> sortwith exp externalSort "unixsort" -> unixsort exp _ -> let msg = "usage: ./demo preludesort 7 or ./demo externalsort 7 or ./demo unixsort 7 \ \(sort 10 million element list)" in fail msg sortwith exp s = putStrLn =<< return . show . last =<< s ([1..10^exp ::Int]) unixsort exp = do let fn = "bigfile" withFile fn AppendMode (\h -> (mapM_ (hPutStrLn h . show) ([1..10^exp::Int]) ) ) putStrLn . ( ("wrote " ++ fn ++ ", time: ") ++ ) . show =<< getClockTime run $ "time tail -n1 | sort " ++fn :: IO String return () t = putStrLn . show . last $ [1..10^8::Int]

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Instances of Lattice?
by Galchin, Vasili 27 Oct '08

27 Oct '08

Hi Henning, I am rereading my emails and I don't believe I got an examples of "instance Lattice". E.g. instance Lattice Bool. ?? Thanks, Vasili

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Examples of Mutually Recursive Types
by Hugo Pacheco 27 Oct '08

27 Oct '08

Hi all, I have been searching for examples of Haskell "real scenarios" that employ mutually recursive datatype definitions. Does anyone know some interesting libraries or structures that I could play with? Thanks, hugo -- www.di.uminho.pt/~hpacheco

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problem using ST monad
by Paul L 27 Oct '08

27 Oct '08

I'm have some trouble using the ST monad, and I think I'm confused about its use of existential type. > {-# OPTIONS -XRankNTypes #-} > import Control.Monad.ST > import Data.Array.ST I want to implement a map function that unfold all ST monads in a list: > mapST :: (a -> (forall s . ST s b)) -> [a] -> [b] > mapST f (x:xs) = runST (f x) : mapST f xs > mapST f [] = [] This is fine. However, it wouldn't typecheck if I had declared its type differently: mapST :: (a -> ST s b) -> [a] -> [b] I first thought the reason could be that runST has to take something of type (forall s . ST s b), but apparently this is not the case: > g :: (STArray s Int Int -> ST s a) -> ST s a > g f = newArray (0,0) 0 >>= f with this definition, runST (t (flip readArray 0)) happily returns me 0, despite the fact that the "s" in the type of "g" is not existentially quantified. Then when I try this one: mapST g [flip readArray 0] It fails to typecheck. Why? Is it possible, if at all, to implement a generic mapST? -- Regards, Paul Liu Yale Haskell Group http://www.haskell.org/yale

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Slavomir Kaslev has invited you to radiusIM.com
by Slavomir Kaslev 26 Oct '08

26 Oct '08

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Haskell Weekly News: Issue 90 - October 25, 2008
by Brent Yorgey 26 Oct '08

26 Oct '08

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20081025 Issue 90 - October 25, 2008 --------------------------------------------------------------------------- Welcome to issue 90 of HWN, a newsletter covering developments in the [1]Haskell community. One day a Haskell n00b asked the master coder, "Master, does (const 3 undefined) have the terminating nature, or not?" The master replied, "Of course." Cried the n00b, "But that changes everything! Why did you not tell me this before?" "You never asked." Immediately, the n00b was enlightened. Announcements Darcs hacking sprint. Eric Kow [2]announced that the [3]darcs hacking sprint is taking place this weekend! Lambdabot 4.2.2. Gwern Branwen [4]announced the release of [5]version 4.2.2 of lambdabot, the famous Haskell IRC bot. The new release has innumerable new features and bugfixes, trained suckling pigs, mermaids, etc. Autoproc Change of Maintainer (if you use procmail you should read this). Jason Dagit [6]announced that Gwern Branwen will be taking over the [7]autoproc project. Autoproc makes it quick and easy for Haskell programmers to make procmail recipes by using an embedded domain specific language. Once your recipes type check and compile, you simply run autoproc and it generates the corresponding procmail recipe. External Sort: Sort a 10-million integer file with just 256M of ram.. Thomas Hartman [8]announced the external-sort package. It implements an on-disk external sort algorithm in Haskell, which you can use to sort lists that will not fit in memory. IEEE-utils. Sterling Clover [9]announced the [10]IEEE-utils package, providing a number of bindings for anyone interested in doing hardcore floating-point programming. rewriting-0.1. Thomas van Noort [11]announced the release of [12]rewriting, a generic rewriting library for regular datatypes. Features include generic rewriting machinery, generic traversals, and rewrite rules defined as values instead of functions. REMINDER: Haskell Communities and Activities Report. Janis Voigtlaender [13]reminded everyone that the deadline for the November 2008 edition of the Haskell Communities and Activities Report (Friday, October 31) is approaching fast! If you haven't already, please write an entry for your new project, or update your old entry. For more information, see the original [14]call for contributions. lhs2tex-1.14. Andres Loeh [15]announced the release of [16]lhs2TeX version 1.14, a a preprocessor to generate LaTeX code from literate Haskell sources. colour 0.0.0. roconnor [17]announced an initial release of the [18]colour package. It is hoped that this library will become the standard colour library for Haskell. Discussion Hackage Improvement Ideas. Jason Dagit [19]suggested some improvements to Hackage and asked for others to contribute their ideas as well. Spine-lazy "multiqueue". Luke Palmer [20]asked for help implementing an efficient spine-lazy multiqueue. Jobs Functional programming job opening. Simon Peyton-Jones [21]announced a [22]job opening in functional programming at Microsoft. They are looking for "an experienced software development engineer who has mastered C/C++ and/or C# development and is now learning or is already an expert using F# (or Haskell)." Blog noise [23]Haskell news from the [24]blogosphere. * Eric Kow (kowey): [25]darcs hacking sprints - some pictures from Team Brighton. * Jason Dagit: [26]Understanding Darcs Commute. * Ketil Malde: [27]Optimization again: befuddled by bytestrings. * Creighton Hogg: [28]Revisiting old concepts. * Tupil: [29]On unit testing and type checking. * Eric Kow (kowey): [30]darcs weekly news #9. * >>> Alberto Corona: [31]Axioms and properties for haskell classes. Alberto demonstrates some code for adding checkable algebraic properties to type classes. * Creighton Hogg: [32]A serious problem. Creighton with some straight talk about typeclass abuse. * London Haskell Users Group: [33]Next meeting: Duncan Coutts on the Haskell Platform. * Manuel M T Chakravarty: [34]Keep those cores busy!. A comprehensive account of the full vectorisation transformation underlying the implementation of nested data parallelism in GHC. * Conal Elliott: [35]Simpler, more efficient, functional linear maps. * Conal Elliott: [36]Vector space bases via type families. * >>> Sebastian Fischer: [37]Constrained Monadic Computations. * Luke Palmer: [38]I know what I'm going to get for christmas. "I believe I have found a truly marvelous implementation of FRP which this blog post is too short to contain." * >>> codeflow: [39]On Haskell and C++. * >>> Simon Dobson: [40]Why Haskell will take over the world. Simon has some thoughts on functional programming and the future of programming languages. * >>> Falko: [41]Learning Haskell's Basics - Problems from Project Euler. Quotes of the Week * vixey: debugging code is admitting defeat * kaomoji: [on #haskell] man, you guys are really nerdy * sclv: I guess I'd believe the universe was lazy if the hubble looked at that stuff way at the edge of the big bang diaspora and when we magnified the picture we saw "stack overflow" * rwbarton: relational calculus? "DIFFERENTIATE TABLE users WITH RESPECT TO name" * heatsink: ban :: (BanContext no, UserIdentifer u) => u -> no u * rwbarton: I tried typechecking the value of unwords (replicate 125 "fmap") in ghci once, and it consumed all my memory * ghc: Step 3: Zonk the kinds About the Haskell Weekly News New editions are posted to [42]the Haskell mailing list as well as to [43]the Haskell Sequence and [44]Planet Haskell. [45]RSS is also available, and headlines appear on [46]haskell.org. To help create new editions of this newsletter, please see the information on [47]how to contribute. Send stories to byorgey at cis dot upenn dot edu. The darcs repository is available at darcs get [48]http://code.haskell.org/~byorgey/code/hwn/ . References 1. http://haskell.org/ 2. http://www.haskell.org//pipermail/haskell-cafe/2008-October/049775.html 3. http://wiki.darcs.net/index.html/Sprints 4. http://article.gmane.org/gmane.comp.lang.haskell.cafe/46842 5. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/lambdabot 6. http://article.gmane.org/gmane.comp.lang.haskell.cafe/46841 7. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/autoproc 8. http://article.gmane.org/gmane.comp.lang.haskell.cafe/46776 9. http://www.haskell.org//pipermail/haskell-cafe/2008-October/049760.html 10. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/ieee-utils 11. http://article.gmane.org/gmane.comp.lang.haskell.cafe/46750 12. http://www.cs.uu.nl/wiki/GenericProgramming/Rewriting 13. http://article.gmane.org/gmane.comp.lang.haskell.cafe/46696 14. http://www.haskell.org/pipermail/haskell/2008-October/020651.html 15. http://article.gmane.org/gmane.comp.lang.haskell.general/16538 16. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/lhs2tex 17. http://article.gmane.org/gmane.comp.lang.haskell.general/16524 18. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/colour 19. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/46764 20. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/46710 21. http://article.gmane.org/gmane.comp.lang.haskell.general/16511 22. http://members.microsoft.com/careers/search/details.aspx?JobID=E29D3886-A15… 23. http://planet.haskell.org/ 24. http://haskell.org/haskellwiki/Blog_articles 25. http://koweycode.blogspot.com/2008/10/darcs-hacking-sprints-some-pictures.h… 26. http://blog.codersbase.com/2008/10/24/understanding-darcs-commute/ 27. http://blog.malde.org/index.php/2008/10/24/optimization-again-befuddled-by-… 28. http://abstractabsurd.blogspot.com/2008/10/revisiting-old-concepts.html 29. http://blog.tupil.com/on-unit-testing-and-type-checking/ 30. http://koweycode.blogspot.com/2008/10/darcs-weekly-news-9.html 31. http://haskell-web.blogspot.com/2008/10/axioms-properties-for-haskell-class… 32. http://abstractabsurd.blogspot.com/2008/10/serious-problem.html 33. http://www.londonhug.net/2008/10/22/next-meeting-duncan-coutts-on-the-haske… 34. http://justtesting.org/post/55387637 35. http://feeds.feedburner.com/~r/conal/~3/425946113/ 36. http://feeds.feedburner.com/~r/conal/~3/425935010/ 37. http://www-ps.informatik.uni-kiel.de/~sebf/projects/constraint-monad.html 38. http://luqui.org/blog/archives/2008/10/19/i-know-what-im-going-to-get-for-c… 39. http://codeflow.wordpress.com/2008/10/18/on-haskell-and-c/ 40. http://www.simondobson.org/?p=179 41. http://informatikr.wordpress.com/2008/10/13/learning-haskells-basics-proble… 42. http://www.haskell.org/mailman/listinfo/haskell 43. http://sequence.complete.org/ 44. http://planet.haskell.org/ 45. http://sequence.complete.org/node/feed 46. http://haskell.org/ 47. http://haskell.org/haskellwiki/HWN 48. http://code.haskell.org/~byorgey/code/hwn/

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Hackage Improvement Ideas
by Jason Dagit 26 Oct '08

26 Oct '08

Hello, I was thinking of fun little projects people could work on to improve Hackage: 1) Popularity statistics -- like debian's popcon, gives stats on how many people have which packages from hackage installed 2) Per package ratings and feedback listed on the page for each package 3) A way to mark a package as "should be removed" 4) All the hackage pages should be wiki editable -- for example, the intro page refers to cabal-install as experimental but I think it's moved beyond that point but I'm not sure how to edit that sentence. What else should hackage do? Who wants to claim one of the above earn some serious karma? Jason

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duplicate instance declarations. Why?
by Alberto G. Corona 26 Oct '08

26 Oct '08

with: >{-# OPTIONS -fglasgow-exts -fallow-undecidable-instances #-} >class A a >class R a >class S a >instance R a => A a >instance S a => A a ---------- GHC gives *Duplicate instance declarations* * instance R a => A a * * instance S a => A a * ** *Why?*

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Crash!
by Andrew Coppin 26 Oct '08

26 Oct '08

Well what do you know? I have actually managed to write a pure Haskell program that generates an actual access violation when run! o_O I was under the impression that this is impossible, so I'm now slightly worried. The weird thing is, I spent 4 hours using the program without issue. However, when you feed it one specific input, it crashes. And I'm really not sure why. However, it appears to crash while asking GTK to save a PNG file. (??) That doesn't make a lot of sense, obviously. I do have some calls to unsafe array functions, but that doesn't appear to be where the crash is happening. Does anybody have any clue where I start with trying to diagnose this? I'm out of my depth...

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3-state, 2-symbol busy beaver
by Maurício 26 Oct '08

26 Oct '08

Hi, Just some easy fun: $> ghci Prelude> :l busyBeaver.hs Prelude> map snd busyBeaver [A,B,A,C,B,A,B,B,B,B,B,A,C,Halt] Best, Maurício -- | busyBeaver.hs data State = A | B | C | Halt deriving Show data Value = Blank | NonBlank type Tape = (Integer -> Value) moveRight tape = \n -> tape $ n - 1 moveLeft tape = \n -> tape $ n + 1 (write tape) n = if n == 0 then NonBlank else tape n table :: (Tape,State) -> (Tape,State) table (tape,state) = case (tape 0,state) of (Blank,A) -> ((moveRight . write) tape , B) (NonBlank,A) -> ((moveLeft . write) tape , C) (Blank,B) -> ((moveLeft . write) tape , A) (NonBlank,B) -> ((moveRight . write) tape , B) (Blank,C) -> ((moveLeft . write) tape , B) (NonBlank,C) ->((moveRight . write) tape , Halt) (_,Halt) -> (tape,Halt) busyBeaver = bb (const Blank,A) where bb t@(_,Halt) = t:[] bb t = t:(bb $ table t)

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hackage feature request: revision control location
by zooko 25 Oct '08

25 Oct '08

Hi folks: I'm trying to use hackage/cabal/cabal-install, and I have a feature request: it would be nice if the metadata about the package, which is displayed on e.g. "hackage-scripts/package/HTTP" had a field for the revision control tool that is used on that package (if any) and the publicly-readable repository for that package (if any). Thanks! Regards, Zooko --- http://allmydata.org -- Tahoe, the Least-Authority Filesystem http://allmydata.com -- back up all your files for $10/month

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Re: [Haskell] ANNOUNCE: colour 0.0.0
by Henk-Jan van Tuyl 25 Oct '08

25 Oct '08

On Wed, 22 Oct 2008 02:12:05 +0200, <roconnor(a)theorem.ca> wrote: > http://hackage.haskell.org/cgi-bin/hackage-scripts/package/colour-0.0.0 > > I hope for this library to become the standard colour library for > Haskell. Most software does not properly blend colours because they fail > to gamma-correct the colours before blending. Hopefully by using this > library, Haskell programs dealing with colour blending will avoid this > problem. > > I am making an early release of my colour library to get some feedback. > I am especially interested in getting feedback on the interfaces: should > functions be renamed, should functions be moved, etc. Should I put black > and white colours into Data.Colour? Which is better form making a > colour: (sRGB r g b) or (sRGB (r,g,b))? > > Bug reports and any patches are also welcome. Be warned, I haven't > extensively tested this library yet. > I think it would be nice to have conversion functions for wxHaskell and the like, to convert between the different color representations. -- Regards, Henk-Jan van Tuyl -- http://functor.bamikanarie.com http://Van.Tuyl.eu/ --

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Re: [Haskell] ANNOUNCE: colour 0.0.0
by roconnor＠theorem.ca 25 Oct '08

25 Oct '08

On Fri, 24 Oct 2008, Sebastian Sylvan wrote: > Another useful predefined space which I didn't see is the YCoCg space, which is used in lots of > compression schemes (like H.264 IIRC). YCoCg, like HLS and HSV, seems to not really be a colour space because it isn't well specified. A transformation is given from some unknown RGB space. Perhaps I should make a datatype for unknown RGB triple, and create HLS HSV, and YCoCg transforms from this type. I can have toRGB709 and toSRGB take and return this unknown RGB triple type. This would suggest changing sRGB and rgb709 from the type sRGB :: a -> a -> a -> Colour a to sRGB :: RGB a -> Colour a so the code "sRGB r g b" becomes "sRGB (RGB r g b)". That doesn't seem very nice. Also, I could add phantom type annotations to the RGB triple type, allowing it to be labeled as linear, or nonlinear, or other information. -- Russell O'Connor <http://r6.ca/> ``All talk about `theft,''' the general counsel of the American Graphophone Company wrote, ``is the merest claptrap, for there exists no property in ideas musical, literary or artistic, except as defined by statute.''

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ANN: Lambdabot 4.2.2
by Gwern Branwen 25 Oct '08

25 Oct '08

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA512 A quick note. Today was released the 4.2.2 version of the IRC bot Lambdabot. You can find it at <http://hackage.haskell.org/cgi-bin/hackage-scripts/package/lambdabot-4.2.2>, and the usual Darcs repository <http://code.haskell.org/lambdabot>. What is interesting about this release? * Less buggy. A few UTF-related bugs were fixed, some formatting bugs, etc. * Updated state (ever more @quote goodness) * New feature: Lambdabot can now be run in arbitrary directories like ~/. Before, one *had* to run in the darcs-gotten directory - Lambdabot had all sorts of hardwired constants like "./State/quotes" in it. Now the situation is such: Lambdabot first looks for a ./State/ and so on; if it finds a populated State/, it will read and write those files just like an old Lambdabot would. However, if State/ is not there, then Lambdabot will look for ~/.lambdabot/, and use the State/ hierarchy inside it, just as normal. Should there be neither a local directory, nor a ~/ directory, then Lambdabot will ask Cabal where all its State files were stuffed (presumably in /usr/share or wherever), and copy them to ~/.lambdabot, and try the sequence again. The upshot is that now you can be in ~/ or ~/bin/xmonad or anywhere, and type 'lambdabot' for a quick session. * No more dependency on BotPP and crazy pre-build processing, thanks to some Template Haskell contributed by sjanssen * those changes included in this classification * innumerable ones; * those drawn with a very fine camel's-hair brush; * etcetera * just broken the flower vase; * those that at a distance resemble flies - -- gwern -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (GNU/Linux) Comment: http://getfiregpg.org iEYEAREKAAYFAkkCfX4ACgkQvpDo5Pfl1oK/kQCeJAqdv4yNerXrhBQKaHjQlXWJ F4QAoJztlzLTFwHkFR5eRcrkFFmTcMe+ =lELz -----END PGP SIGNATURE-----

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ANN: Autoproc Change of Maintainer (if you use procmail you should read this)
by Jason Dagit 25 Oct '08

25 Oct '08

What is autoproc? ------------------------- Tired writing procmail recipes by hand? You're in luck! Autoproc makes it quick and easy for Haskell programmers to make procmail recipes by using an embedded domain specific language. Once your recipes type check and compile you simply run autoproc and it generates the corresponding procmail recipe on your screen. If you like the results, store it in ~/.procmailrc and enjoy! What's with this announcement? ------------------------------------------- I created autoproc a few years ago, but in that time I've farmed out my email to gmail and I'm no longer using procmail. In the meantime, Gwern Branwen has contributed nice features to the project to make it friendlier to use, cabalization and so on. With his permission, I am now declaring him the official maintainer and dictator for life. Long live Autoproc! Long live Gwern Branwen! Find it on Hackage: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/autoproc Find it on code.haskell.org: darcs get http://code.haskell.org/autoproc Note: We're using a darcs2 format repository, so to get the development version you'll need darcs 2.0 or newer. Thanks and enjoy your day! Jason

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The Haskell type inference feature I'd really like to see
by Dan Piponi 25 Oct '08

25 Oct '08

I'd like to be able to write something like > map zipWith ([1,2,3] >>= printMyInferredType) and have the compiler treat 'printMyInferredType' as undefined, but also produce the side effect of printing out its inferred type. What's the easiest way to simulate this with what we have now? -- Dan

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Re: [Haskell-cafe] Crash!
by Andrew Coppin 25 Oct '08

25 Oct '08

Thomas DuBuisson wrote: > So if you have such a specific portion of the code you think is to > blame, perhaps you could simple comment that out (return () instead of > write the file) and see if it crashes? I understand people avoidance > of brute force guess problem-compile-test cycles, but it seems you > have good evidence supporting this guess. Yeah, I can try different optimisation levels and so forth. I'm actually wondering if my code is writing off the end of an array and this "just happens" to hit some data structure used by GTK+? (In which case, minute changes in linkage, etc., would disturb the bug.) Does anybody know of any tools for definitely pinning down stuff like this? Surely C programmers have their code crash several hundred times a day due to bugs like this... > Also, be sure the thunks are evaluated - if the writing of the file > is what is forcing the evaluation (and thus triggering the condition) > then you need to separate these two cases. That's the fun part about Haskell, eh? ;-) However, in this instance, there's that much explicit mutation in the I/O monad on unboxed (and therefore strict) arrays that I'm pretty sure that isn't the problem. By the time the save-PNG function is called, the data already exists in the address space managed by GTK+. It has to, or GTK+ wouldn't be able to save it. Unless my *pure* code is somehow generating an access violation - which would surely indicate an actual compiler *bug*... (This seems laughably unlikely.)

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universal algebra "support" in Haskell?
by Galchin, Vasili 24 Oct '08

24 Oct '08

Hello, I see that there is a "Monoid" class from Data.Monoid. What other algebras like Group, Ring, etc. have support in Haskell? Thanks, Vasili

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RE: [Haskell] Current XML libraries status
by Mitchell, Neil 24 Oct '08

24 Oct '08

Redirected to haskell-cafe, since that's where all discussions should go (haskell = announcments only) > > Does some one have made performance tests on the different XML > > libraries for Haskell? I have a 20MB xml file that I want > to read. I > > remember from my earlier experiments (years ago) that all libraries > > were too slow and were consuming too much memory. > > For my XML needs, I ended up just using the TagSoup library > to extract the parts I wanted. At least this allows lazy > processing of large files (a typical file is in the 1 to 4 GB range). > > Performance is acceptable, and Neil is rumored to have a plan > to improve it further. I have a plan, I have the pseudo-code, and I have the notes. I currently don't have the time - but hopefully I'll find the time at some point. Thanks Nmeil ============================================================================== Please access the attached hyperlink for an important electronic communications disclaimer: http://www.credit-suisse.com/legal/en/disclaimer_email_ib.html ==============================================================================

1 0

darcs hacking sprint TOMORROW!
by Eric Kow 24 Oct '08

24 Oct '08

Hi all, Just pointing out that the darcs hacking sprint is taking place tomorrow (Saturday and Sunday 25-26 October)! Our Brighton and Portland venues are still open, so if you are thinking of dropping by, let us know :-) http://wiki.darcs.net/index.html/Sprints Cheers, -- Eric Kow <http://www.nltg.brighton.ac.uk/home/Eric.Kow> PGP Key ID: 08AC04F9

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distributed systems reading group
by Jason Dusek 24 Oct '08

24 Oct '08

I'm looking for good reading group for distributed systems. I've worked through a number of papers on my own and would like to work out some ideas with other folks who have an interest. I've read a little bit of Lynch, a bit more of Lamport and some of Chandra's work, as well as numerous slides, &c. * The impossibility results are sobering, but always leave a way out -- they make some assumption that one can dispense with in practice (for example, that processes start with different values). * The possibility results generally make untenable assumptions -- for example, that there is no link failure. I appreciate that this is not a matter of direct interest to the list, but I expect to find interested people here. -- _jsn

1 0

Sorry, but I'm in the mood (again)
by Achim Schneider 24 Oct '08

24 Oct '08

http://www.haskell.org/haskellwiki/?title=Special:Categories What are the mathematical properties of those Categories? Do they share common axioms? -- (c) this sig last receiving data processing entity. Inspect headers for copyright history. All rights reserved. Copying, hiring, renting, performance and/or quoting of this signature prohibited.

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Re: universal algebra "support" in Haskell?
by Galchin, Vasili 24 Oct '08

24 Oct '08

Hi Russell and others, Please "cc" me on all responses to my post 'universal algebra "support" in Haskell'. I am interested in algebras and non-algebras like pre-order, post-order, etc. support in Haskell! Thanks, Vasili

1 0

A heretic question
by Achim Schneider 24 Oct '08

24 Oct '08

What kind of things, barring coding on Haskell-less platforms and library interfaces would you choose to do in C++? I'm asking 'cos I'm learning C++ and can't get the proper motivation to do any program I can think of in it: If I need abstraction, I'm thinking Haskell or Scheme, and if I'm thinking performance, C itself more than suffices. Plus template programming makes me shudder because of its atrocities against clear and straightforward FP, but that's a different matter. Coming to think of it, a compiler from a clean syntax to C++ templates sounds like a fun project... which I'd do in Haskell. -- (c) this sig last receiving data processing entity. Inspect headers for copyright history. All rights reserved. Copying, hiring, renting, performance and/or quoting of this signature prohibited.

17 30

Linking and unsafePerformIO
by Mauricio 24 Oct '08

24 Oct '08

Hi, If I have a Haskell wrapper (with unsafe...) over a function that's never going to return different values and is always side-effect free, but can change depending on compile time options of its library; my program is running, and then the version of my library is updated by my distribution smart instalation system, which does update versions of libraries in use; is it possible that I get a wrong behavior of my program? I do not understand enough about package management to understand how running programs or libraries are updated, and less about how linking works between Haskelll and libraries on other languages, so I don't know if my program is guaranteed to stay with a single version of a library for each run. (Sure this is a weird situation, but I do like to think about worst cases.) Thanks, Mauríco

13 20

Pandoc questions
by Andrew Coppin 24 Oct '08

24 Oct '08

There doesn't seem to be any option to make Pandoc produce actual MathML output. Is there a reason for this? (The only option I can see is to spit out raw LaTeX plus a 70KB JavaScript program to transform this into MathML at the client end --- which seems a little silly to me. There's also no way to style the raw LaTeX differently in case JavaScript is unavailable.) Also, while Markdown *almost* does what I want, there are a few small constructs it doesn't have. For example, I'd like to have some way to denote a "term" the first time I use it. I could just use italics, but I'd prefer some way to visually indicate that this isn't just an emphasised word, it's a new technical term. In HTML, I'd use a style class, and in LaTeX I'd define a new command. But I can't see a way to do something that will still allow Pandoc to generate correct LaTeX *and* correct HTML from a single Markdown source... Any hints?

4 8

Re: External Sort: Sort a 10-million integer file with just 256M of ram.
by Ben 24 Oct '08

24 Oct '08

the problem with the current externalSort is that it is not recursive -- it tries to do everything in one pass. basically instead of attempting to merge all of the chunks together it should only merge chunksize chunks together, producing a new list of chunks. then those get merged, etc....there is a discussion of this in knuth i think. it shouldn't be hard to make this work, i just didn't have time when i wrote it. ben

1 0

Re: [Haskell-cafe] Fwd: enhancing type classes with properties
by Alberto G. Corona 24 Oct '08

24 Oct '08

It seems that some of the goals are not so hard. here I publised my progress. http://docs.google.com/Doc?id=dd5rm7qq_165rshp74gf&pli=1 I show how to define a Ring, such a mathematical structure in Haskell, how to instantiate the class Num as a Ring , how to (possibly in other moment of space-time) instantiate a new class as Num and how to test the axioms for the new class. All of then is something like a sophisticated "assert" mechanism, but , I think, much more flexible and elegant. 2008/10/22 Alberto G. Corona <agocorona(a)gmail.com> > I guess that the namespace thing is not necesary. Maybe it can be done in > template haskell. I never used TH however. it is a matter of inserting code > here and there and rewrite rules somewhere at compile time. It´s a nice > project. I´ll try. > > > 2008/10/22 Mitchell, Neil <neil.mitchell.2(a)credit-suisse.com> > >> Hi Alberta, >> >> It's a lot of work, but I wish you luck :-) Many of the underlying tools >> exist, but there definately needs more integration. >> >> Thanks >> >> Neil >> >> >> This material is sales and trading commentary and does not constitute >> investment research. Please follow the attached hyperlink to an important >> disclaimer >> *<www.credit-suisse.com/emea/legal>* >> >> >> ------------------------------ >> *From:* Alberto G. Corona [mailto:agocorona@gmail.com] >> *Sent:* 22 October 2008 4:23 pm >> *To:* Mitchell, Neil >> *Subject:* Re: [Haskell-cafe] Fwd: enhancing type classes with properties >> >> Hi Neil, >> >> I see the contract type mechanism and safety check techniques reflected >> in the above paper are a good step, But I think that something more >> general would be better. What I propose is to integrate directly in the >> language some concepts and developments that are already well know to >> solve some common needs that I thing can not be solved without this >> integration: >> >> To make use of: >> >> -Quickcheck style validation. By the way, Don Steward recommend to add >> quckcheck rules close to the class definitions just for better >> documentation >> >> - Implicit class properties defined everywhere in the documentation but >> impossible to reflect in the code (for example the famous monad rules: >> return x >>= f == f x etc ) >> >> - The superb ghc rewrite rule mechanism (perhaps with enhancements) >> >> - object style namespaces, depending on class names. >> >> To solve problems like >> >> - code optimization >> >> - code verification. regression tests for free!! >> >> - The need for safe overloading of methods and operators (making the >> namespaces dependent not only on module name but also in class names) . Why >> I can not overload the operator + in the context of a DSL for >> JavaScript generation if my operator does what + does? >> >> - strict and meaningful rules for class instances. >> - to make the rewrite rule mechanism visible to everyone >> >> >> >> 2008/10/22 Mitchell, Neil <neil.mitchell.2(a)credit-suisse.com> >> >>> Hi Alberto, >>> >>> Take a look at ESC/Haskell and Sound Haskell, which provide mechanisms >>> for doing some of the things you want. I don't think they integrate with >>> type classes in the way you mention, but I think that is just a question of >>> syntax. >>> >>> http://www.cl.cam.ac.uk/~nx200/ <http://www.cl.cam.ac.uk/%7Enx200/> >>> >>> Thanks >>> >>> Neil >>> >>> >>> This material is sales and trading commentary and does not constitute >>> investment research. Please follow the attached hyperlink to an important >>> disclaimer >>> *<www.credit-suisse.com/emea/legal>* >>> >>> >>> ------------------------------ >>> *From:* haskell-cafe-bounces(a)haskell.org [mailto: >>> haskell-cafe-bounces(a)haskell.org] *On Behalf Of *Alberto G. Corona >>> *Sent:* 22 October 2008 1:43 pm >>> *To:* haskell-cafe(a)haskell.org >>> *Subject:* [Haskell-cafe] Fwd: enhancing type classes with properties >>> >>> I´m just thinking aloud, but, because incorporating deeper mathematics >>> concepts has proven to be the best solution for better and more flexible >>> programming languages with fewer errors, I wonder if raising the type >>> classes incorporating axioms can solve additional problems. >>> >>> At first sight it does: >>> >>> >>> class Abelian a where >>> (+) :: a -> a -> a >>> property ((+))= a+b == b+a >>> >>> >>> >>> this permits: >>> 1- safer polimorphism: I can safely reuse the operator + if the type >>> and the property is obeyed. The lack of ability to redefine operators is a >>> problem for DSLs that must use wreid symbols combinations with unknow >>> meanings. To use common operators with fixed properties is very good. the >>> same aplies for method names. >>> >>> 2- the compiler can use the axions as rewrite rules. >>> >>> 3- in debugging mode, it is possible to verify the axiom for each >>> value a generated during execution. Thus, a generator is not needed like >>> in quickcheck. The logic to quickcheck can be incorporated in the debugging >>> executable. >>> >>> 3 guaranties that 1 and 2 are safe. >>> >>> >>> >>> >>> >>> a type class can express a relation between types, but it is not >>> possible to define relation between relations. >>> >>> ============================================================================== >>> Please access the attached hyperlink for an important electronic communications disclaimer: >>> http://www.credit-suisse.com/legal/en/disclaimer_email_ib.html >>> ============================================================================== >>> >>> >> ============================================================================== >> Please access the attached hyperlink for an important electronic communications disclaimer: >> http://www.credit-suisse.com/legal/en/disclaimer_email_ib.html >> ============================================================================== >> >> >

1 1

Re: [Haskell-cafe] Crash!
by Andrew Coppin 24 Oct '08

24 Oct '08

D.V. wrote: > On Thu, Oct 23, 2008 at 10:30 PM, Andrew Coppin > <andrewcoppin(a)btinternet.com> wrote: > >> Really? Well I've never ever seen GNOME crash. Hell, I run a GNOME desktop >> on a 0.01 GHz Amiga 1200 and it works! (Sure, it's slower than MS Vista on >> > > Now that's cool. I wish my Amiga still worked. > Hint: If you ever get it to work again... don't install Debian. Or rather, don't install Debian if you enjoy programs that open on the same calendar day as you click the icon. o_O It's really neat that you can make Linux run on anything, but that doesn't necessarily mean you _should_...

1 0

Re: [Haskell-cafe] Detecting unused read handles? (was: File handles and pipes)
by Thomas Hartman 24 Oct '08

24 Oct '08

>> Specifically I'm trying to concatenate the output of two system calls >> into the input of a third. The following code does not get the job Can the left-fold enumerator described by oleg in http://okmij.org/ftp/Haskell/fold-stream.lhs and with more references at http://okmij.org/ftp/Haskell/ be adapted for reading the output from arbitrary system calls? I.e., to deal with pipes? My intuition says yes but I'm still trying to wrap my head around the whole left fold enumerator approach to io. The text around "We can now test reading from two streams with interleaving:" in the first reference seemed particularly promising to me. > > > > > 2008/10/19 Stephen Hicks <sdh33(a)cornell.edu>: >> On Sun, Oct 19, 2008 at 1:44 AM, Brandon S. Allbery KF8NH >> <allbery(a)ece.cmu.edu> wrote: >>> On 2008 Oct 19, at 1:37, Stephen Hicks wrote: >>>> >>>> I'm trying to understand how to get pipes working in Haskell, in >>>> particular with the revamped System.Process (though I've tried similar >>>> experiments with System.Posix.IO and Control.Concurrent). >>>> Specifically I'm trying to concatenate the output of two system calls >>>> into the input of a third. The following code does not get the job >>>> done: >>> >>> Pipes are perhaps a bit misnamed: if you want to combine the output of two >>> pipes and funnel it into a third you can't simply "plumb them together", you >>> need to provide code which reads from the output pipes and writes into the >>> input pipe. If you don't care about order, forkIO a thread for each output >>> pipe which reads from the output pipe it's passed and writes to the input >>> pipe. If order is significant, use mapM/forM to run the output-to-input >>> code on each handle in turn. >> >> Thanks a lot - that seems to work very well, and even scales to large >> amounts of data nicely (and quickly, with Lazy ByteStrings). >> >> I've got one more question now. Suppose I want to do the same thing >> on the other side, with two processes *receiving* the data. Is there >> a way to tell whether the first process wants input, and if not, wait >> for the second process to do anything? >> >> That is, suppose I have something like >> >>> do (Just inh1, _, _, p1) <- createProcess (shell "echo 1") { std_in = CreatePipe } >>> -- wait for p1, possibly feeding it some input? >>> (Just inh2, _, _, p2) <- createProcess (shell "cat") { std_in = CreatePipe } >> >> Is there a way to figure out that the "echo 1" process never wanted >> any input, and therefore not give it any? I looked through all of >> System.IO and everything seemed to indicate that inh1 was open, even >> after the process ended. The only indication otherwise was that >> "hflush inh1" failed with "resource vanished". I guess what I'm >> asking is I want to "wait until the process p1 is waiting for input >> and/or terminates", and if it's the latter, move on to the next >> process in line, before actually doing any hPutStr into the read >> handles. Is that possible? >> >> Thanks, >> steve >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> >

2 1

any idea why cabal install cabal-install cant update itself in windows?
by Anatoly Yakovenko 24 Oct '08

24 Oct '08

C:\Documents and Settings\anatolyy>cabal install cabal-install Resolving dependencies... 'cabal-install-0.6.0' is cached. Configuring cabal-install-0.6.0... Preprocessing executables for cabal-install-0.6.0... Building cabal-install-0.6.0... ... Linking dist\build\cabal\cabal.exe ... Installing: C:\Documents and Settings\anatolyy\Application Data\cabal\bin C:\Documents and Settings\anatolyy>cabal --version cabal-install version 0.5.2 using version 1.4.0.2 of the Cabal library

3 4

building c2hs on Mac
by John Lato 23 Oct '08

23 Oct '08

Hello, I've been trying to build c2hs-0.15.1 on an Intel Mac (10.4), and am having some difficulty. It has dependencies on happy and alex, which would be fine, except that alex itself seems to require alex (using alex 2.2). Does anyone have any suggestions for how to get around this? I have ghc-6.8.3 and ghc-6.10 RC, and could use either. Last time I tried to build c2hs on a mac I think I used macports, which worked fine, except that's not an option this time because the computer in question isn't (and won't be) online. I'd have to rebuild ghc anyway, which I don't want to do. Thanks, John Lato

3 4

Plans for new System.Process?
by Stephen Hicks 23 Oct '08

23 Oct '08

Hi, I've been trying out the new System.Process and have found it to be very useful. I was wondering what the plans for it were - I'd rather not give up support for older versions of ghc just because I want to use createProcess. Are there plans of releasing process-1.0.1 so that it's compatible with older compilers too? Or does it depend on something internally that makes this impossible? Cheers, steve

2 1

Re: [Haskell-cafe] Re: universal algebra "support" in Haskell?
by Nathan Bloomfield 23 Oct '08

23 Oct '08

This question is relevant to a project I'm working on. I've been putting together an abstract algebra library for handling computations inside group rings, polynomial rings, and rings with adjoined elements. Once I've got it cleaned up a little I'll upload it to an appropriate place. (I forgot to cc haskell-cafe- sorry DavidA!) Nathan Bloomfield

1 0

Call for Papers: Workshop on Language Descriptions, Tools and Applications 2008
by Jurgen Vinju 23 Oct '08

23 Oct '08

LDTA: Workshop on Language Descriptions Tools and Applications ===Call For Papers 2009=== This is the Call For Papers for the Ninth Workshop on Language Descriptions, Tools and Applications (LDTA 2009) LDTA is a two-day satellite event of ETAPS which takes on the 28th and 29th of March 2009 in York, England. ==Scope== LDTA is an application and tool oriented forum on meta programming in a broad sense. A meta program is a program that takes other programs as input or output. The focus of LDTA is on generated or otherwise efficiently implemented meta programs, possibly using high level descriptions of programming languages. Tools and techniques presented at LDTA are usually applicable in the context of "Language Workbenches" or "Meta Programming Systems" or simply as parts of advanced programming environments or IDEs. The applications areas include, but are not limited to: * Program analysis, transformation, generation and verification * Implementation of Domain Specific Languages (both visual and textual) * Reverse engineering and reengineering * Refactoring and other source-to-source transformations * Application modelling (MDE, MDA, Software Factories, Software product lines) * Grammar engineering / Grammarware * Language definition and language prototyping * Debugging, profiling and testing * IDE construction * Compiler construction LDTA is a well-established workshop next to other conferences and workshops on (programming) language engineering topics such as SLE and GPCE.LDTA is traditionally a forum where computer science theories are put to the test of real-world software engineering issues, for example by applying: * context-free grammars to parser generation for real programming languages, * attribute grammars to static analyzer and compiler generation, * term rewriting to source-to-source transformation, * action semantics to programming language implementation, * model checking to software verification. Note that LDTA solicits submissions from any technological or theoretical domain, as long as the paper is within the application scope. ==Submission Procedure and Publication== Submissions in the following categories are admissible: * research papers, * tool papers, * experience papers The final versions of accepted papers will probably(*) be published in Electronic Notes in Theoretical Computer Science (ENTCS), Elsevier Science, and will be made available during the workshop. (*)Due to organizational changes at Elsevier, publication by ENTCS publication is provisional; another comparable venue will be found otherwise. Each submission must: * clearly and unambiguously state in which of the three categories it falls * be original, i.e. not published or submitted elsewhere, * contain a clear motivation, * contain a thorough analysis of the claimed contributions (for example by comparing to related work), * be written in less than 15 pages (research papers and experience reports), or less than 10 pages (tool papers) * use the ENTCS style. The authors of each submission are required to give a presentation at LDTA 2009. The authors of the tool papers are required to include an interactive demonstration in their presentations. The authors of the best papers will be invited to write a journal version of their paper which will be separately reviewed and, assuming acceptance, be published in journal form. As in past years, this will be done in a special issue devoted to LDTA 2009 of the journal Science of Computer Programming (Elsevier Science). The authors of the best tool papers will be invited to write a paper and submit the source of code of their tool, which will both be separately reviewed and, assuming acceptance, be published in the special issue on Experimental Software and Toolkits (EST) of the journal Science of Computer Programming (Elsevier Science). Please submit your abstract and paper using http://www.easychair.org/conferences/?conf=ldta2009 ==Program Committee== Jurgen Vinju, CWI, Amsterdam (co-chair) Torbjörn Ekman, Oxford, UK (co-chair) Erik Meijer, Microsoft, Redmond, USA Walid Taha, Rice University, Houston USA Bob Fuhrer, IBM TJ Watson, USA Susan Eisenbach, Imperial College, UK Jean-Marie Jacquet, FUNDP, Namur, Belgium Sibylle Schuppe, Chalmers, Sweden Elizabeth Scott, RHUL, UK Robert Grimm, NYU, USA Judith Bishop, Pretoria, South Africa Tudor Girba, Univ of Berne, Switzerland Marjan Mernik, University of Maribor, Slovenia Thomas Dean, Fondazione Bruno Kessler - IRST, Italy Martin Bravenboer, Univ. of Oregon, USA Pierre-Etienne Moreau, INRIA-LORIA, France Gabi Taentzer, Philipps-Universität Marburg, Germany Joao Saraiva, Universidade do Minho, Braga, Portugal Tijs van der Storm, CWI, The Netherlands Stephen Edwards, Columbia University, USA Peter Thiemann, Universität Freiburg, Germany ==Important Dates== Abstract submission deadline:Friday November 28th, 2008 Paper submission deadline:Friday December 5th, 2008 Notification of acceptance:Friday February 6th, 2009 Workshop date:28th and 29th of March, 2009

1 0

the Haskell notion of class vis-a-vis universal algebra?
by Galchin, Vasili 23 Oct '08

23 Oct '08

Hello, What is the relationship of a Haskell class to universal algebra? (a refresher ... http://en.wikipedia.org/wiki/Universal_algebra) ... it seems that all types that belong to a class are models? E.g. all "monads" have to satisfy the "monad laws" stated in the Monad class, i.e. equational axioms! Vasili

2 1

Help converting Perl to Haskell
by Jason Dagit 23 Oct '08

23 Oct '08

Hello, I'm not very perl literate, but I want to convert a perl script to Haskell. This bit of perl is part of darcs' test suite. I was hoping to make it "more portable" by writing it in Haskell. By more portable I mean, works in windows without cygwin/mingw/msys and avoids the need for perl also. Depending on a Haskell compiler seems reasonable since darcs is written in Haskell :) Correct me if I'm wrong, but if I want to make this work on windows I can't use System.Posix, right? If so, what is the portable way to set environment variables? I see[1] that getEnv exists in System.Environment, but setEnv is in System.Posix.Env. I looked in System.Win32 and I didn't see anything that looked like it would manipulate environment variables. Will I have to use System.Process.runProcess on Win32? I'd like this to work on ghc 6.6 and System.Process looks new? Another thing I noticed is that System.Directory doesn't give me a way to exactly emulate this bit of perl: mkdir 'test_output', 0750; If I use System.Directory.setPermissions, then I think the closest I can approximate those permissions is: setPermissions "test_output" (Permissions {readable = True, writable = True, executable = True, searchable = True}) Which just makes sure it has the 7 for user, but doesn't seem to change the other permissions. Maybe that won't matter in practice, but I wanted to make it as close as possible to minimize unforeseen problems. I guess I could write a function that uses setPermissions on win32 and uses the appropriate thing from System.Posix when not on windows. Below is the full perl script if you want to see what I'm starting from. I think most of it should be easy to replace. \begin{perl} #!/usr/bin/perl -w # Run each of the shell tests, capturing the output, and reporting passed # or failed. use Cwd; use File::Find; # Place to put test output to avoid cluttering test/ mkdir 'test_output', 0750; # Override the users default .darcs settings $ENV{HOME} = cwd(); mkdir '.darcs'; system 'echo ALL --ignore-times >> .darcs/defaults'; # Used for finding darcs, but may not be defined by the shell $ENV{PWD} = cwd(); # Put the right darcs first in PATH my $darcspath="$ENV{HOME}/.."; if ($ENV{DARCS}) { # User has asked for a particular darcs... my $actualdarcs=`which $ENV{DARCS}`; my $darcspath=`dirname "$actualdarcs"`; } $ENV{PATH} = "$darcspath:$ENV{PATH}"; # Some environment variables can act as defaults that we don't want $ENV{EMAIL} = $ENV{DARCS_EMAIL} = 'tester'; # These two environment variables will turn off darcs' "Christmas mode". # It will make the tests run a tad faster, and make darcs' output # independent of the testing systems locale and environment. $ENV{DARCS_DONT_COLOR} = 1; $ENV{DARCS_DONT_ESCAPE_ANYTHING} = 1; my $OK = 1; my @Failures; my @Passes; `which bash`; if( $? != 0 ) { die "You need bash to run the shell tests!" } for my $test (@ARGV) { my $test_out = "test_output/$test.out"; printf "Running %-40s", "$test ..."; my $output = `bash $test 2>&1`; if( $? == 0 ) { push @Passes, $test; print " passed.\n"; } else { $OK = 0; push @Failures, $test; print " FAILED!\n"; print "Output from failed $test:\n$output"; } # give ourselves write permissions to every file in a tmp dir # (in case a script sets permissions and fails to clean up # after itself) my @tmpdirs = glob("tmp* temp*"); if (@tmpdirs > 0) { find (sub { chmod 0755, $_; }, @tmpdirs); } } my $CWD = cwd(); if ($CWD =~ /bugs/ && $#Passes >= 0) { print "Some tests passed:\n"; print "\t$_\n" for @Passes; } if ($OK) { print "All tests successful!\n"; } else { print "TESTS FAILED!\n"; print "\t$_\n" for @Failures; } # Exit with non-zero if anything failed. exit !$OK; \end{perl} Thanks! Jason [1] http://www.haskell.org/ghc/docs/latest/html/libraries/

3 3

Cabal warning
by Henk-Jan van Tuyl 23 Oct '08

23 Oct '08

L.S., I keep getting the following warning for each "cabal install" command: Warning: Error parsing config file C:\Documents and Settings\[User]\Application Data\cabal\config: On line 1: GHC Warning: Using default configuration. The first line of this file is: compiler: GHC What can I do about this? -- Regards, Henk-Jan van Tuyl -- http://functor.bamikanarie.com http://Van.Tuyl.eu/ --

3 3

Spine-lazy "multiqueue"
by Luke Palmer 23 Oct '08

23 Oct '08

Hi, I need a rather strange data structure, and I can't find any existing implementations or think of a way to implement it. It's a "multiqueue", basically a map of queues. The trick is that it should be lazy in its spine and still support efficient access. For example, the following should hold: dequeue 1 (foldr (enqueue 1) empty [42..]) = Just (42, ...) (where dequeue :: k -> QMap k v -> Maybe (v, QMap k v), similarly for enqueue) I also need a unionWith :: ([v] -> [v] -> [v]) -> QMap k v -> QMap k v -> QMap k v. I realize that these might be some pretty tough requirements to meet. Any pointers or original ideas? Thanks, Luke

6 7

Template Haskell
by Andrew Coppin 23 Oct '08

23 Oct '08

If I'm understanding this correctly, Template Haskell is a way to auto-generate repetative Haskell source code. The thing that worries me is... if you need to write repetative Haskell source code, doesn't that mean that Haskell itself is broken in the first place?

4 5

ghc error: requested module name differs from name found in interface file
by Larry Evans 23 Oct '08

23 Oct '08

With a file containing: > module Main where > > import Array > import Control.Functor.Fix I get: > make > ghc -i/root/.cabal/lib/category-extras-0.53.5/ghc-6.8.2 -c catamorphism.example.hs > > catamorphism.example.hs:19:0: > Bad interface file: /root/.cabal/lib/category-extras-0.53.5/ghc-6.8.2/Control/Functor/Fix.hi > Something is amiss; requested module main:Control.Functor.Fix differs from name found in the interface file category-extras-0.53.5:Control.Functor.Fix > make: *** [all] Error 1 I used cabal to install category-extras: > /home/evansl/download/haskell/libs # cabal install category-extras > Resolving dependencies... > Downloading category-extras-0.53.5... > Configuring category-extras-0.53.5... > Preprocessing library category-extras-0.53.5... ... > /usr/bin/ar: creating dist/build/libHScategory-extras-0.53.5.a > Installing library in /root/.cabal/lib/category-extras-0.53.5/ghc-6.8.2 > Registering category-extras-0.53.5... > Reading package info from "dist/installed-pkg-config" ... done. > Saving old package config file... done. > Writing new package config file... done. > /home/evansl/download/haskell/libs # What should I do to import the Functor.Fix as shown here: http://comonad.com/reader/2008/recursion-schemes/ TIA. -Larry

3 6

Verifying a list of properties using QuickCheck
by Thomas van Noort 22 Oct '08

22 Oct '08

Hi, I would like to verify a list of properties using QuickCheck. Of course, I can test a single property using: quickCheck :: Testable prop => prop -> IO () Then, I can check a list of properties my mapping this function over a list: quickCheckL :: Testable prop => [prop] -> IO () quickCheckL = mapM_ quickCheck This gives me a result for each property: Prelude Test.QuickCheck> quickCheckL [1==1,2==2] OK, passed 100 tests. OK, passed 100 tests. However, I would like a single result for the complete list of properties instead of a result for each property. I realize that this restricts the properties to be of the same type, but that isn't a problem for my application. Did I miss a library function that provides me this functionality? Regards, Thomas

5 4

ANNOUNCE: rewriting-0.1
by Thomas van Noort 22 Oct '08

22 Oct '08

Generic rewriting library for regular datatypes =============================================== This package provides rewriting functionality for regular datatypes. Regular datatypes are recursive datatypes such as lists, binary trees, etc. This library cannot be used with mutually recursive datatypes or with nested datatypes. This library has been described in the paper: A Lightweight Approach to Datatype-Generic Rewriting. Thomas van Noort, Alexey Rodriguez, Stefan Holdermans, Johan Jeuring, Bastiaan Heeren. ACM SIGPLAN Workshop on Generic Programming 2008. More information about this library can be found at: http://www.cs.uu.nl/wiki/GenericProgramming/Rewriting Features -------- * Generic rewriting machinery * Generic traversals (top-down, bottom-up, etc.) * Rewrite rules are defined concisely as values instead of functions, which allows for better observability * Rewrite rules are defined in the original domain and do not require a manual extension for metavariables Requirements ------------ * GHC 6.10.1 (tested with 6.10.0.20081007) * Cabal 1.2.1 (or higher) Download & Source ----------------- Use cabal-install: cabal install rewriting Get the package: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/rewriting Get the source: svn checkout https://svn.cs.uu.nl:12443/repos/dgp-haskell/rewriting Bugs & Support -------------- Report issues, request features, or just discuss the library with the authors, maintainers, and other interested persons at: http://www.haskell.org/mailman/listinfo/generics

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Fwd: enhancing type classes with properties
by Alberto G. Corona 22 Oct '08

22 Oct '08

I´m just thinking aloud, but, because incorporating deeper mathematics concepts has proven to be the best solution for better and more flexible programming languages with fewer errors, I wonder if raising the type classes incorporating axioms can solve additional problems. At first sight it does: class Abelian a where (+) :: a -> a -> a property ((+))= a+b == b+a this permits: 1- safer polimorphism: I can safely reuse the operator + if the type and the property is obeyed. The lack of ability to redefine operators is a problem for DSLs that must use wreid symbols combinations with unknow meanings. To use common operators with fixed properties is very good. the same aplies for method names. 2- the compiler can use the axions as rewrite rules. 3- in debugging mode, it is possible to verify the axiom for each value a generated during execution. Thus, a generator is not needed like in quickcheck. The logic to quickcheck can be incorporated in the debugging executable. 3 guaranties that 1 and 2 are safe. a type class can express a relation between types, but it is not possible to define relation between relations.

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Build without install, using cabal
by Mauricio 22 Oct '08

22 Oct '08

Hi, I would like to include a few source files as 'executable' sections in a .cabal package description. However, although I do want to use main=mainDefault features, I do not want those packages to be installed when I run 'Setup.hs install'. Is it possible to do that? I believe there's no flag that indicates install step, since (I guess) flags are checked only at configure time. Thanks for your help, Maurício

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labels in HList
by roger peppe 22 Oct '08

22 Oct '08

hi, i'm trying to get labelled records working with the current version of HList. i've got code that looks like: >{-# language EmptyDataDecls #-} >module Tst where > import Data.HList > > data Foo; foo = proxy::Proxy Foo > data Bar; bar = proxy::Proxy Bar > rec1 = > foo .=. 1 .*. > bar .=. "hello" .*. > emptyRecord which gives me the error: Tst4.hs:8:2: No instance for (HEq (Proxy Foo) (Proxy Bar) HFalse) arising from a use of `.*.' at Tst4.hs:(8,2)-(10,12) Possible fix: add an instance declaration for (HEq (Proxy Foo) (Proxy Bar) HFalse) In the expression: foo .=. 1 .*. bar .=. "hello" .*. emptyRecord In the definition of `rec1': rec1 = foo .=. 1 .*. bar .=. "hello" .*. emptyRecord some discussion on #haskell suggesting importing Label4 and TypeEqGeneric1 but a) that's not possible because both are hidden inside the HList package and b) even when i get around that restriction, i still get a "No instance for (TypeCast HFalse HFalse)" error. thanks, rog.

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code generation
by z ghost 22 Oct '08

22 Oct '08

hello, im interested in using haskell to generate code and make little AI applications for fun.. is anyone already doing this sort of thing? it would be fun to collaborate with people on this. Here's some code as an example of the direction i'd like to go in. It builds up template haskell Exps and uses the Hint module to typecheck them. With some more work, it could be turned into a program that finds haskell programs (given a type as input).. http://www.sendspace.com/file/aj5r38 __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com

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