September 2004 - Haskell

Mixing monadic and non-monadic functions
by Sean E. Russell 17 Sep '05

17 Sep '05

Hello, I posted this question to comp.lang.functional, and someone suggested that I try this group instead. I'm struggling with monads. Well, not monads themselves, but mixing them with non-monadic functions. Here's my base case: someFunc :: String -> IO [a] ... ax <- someFunc a bx <- someFunc b assertBool "fail" $ length ax == length bx I don't like the assignments; the typing is redundant, if I have a lot of asserts like this, and the "variables" are temporary. What I'd much rather have is: ... assertBool "fail" $ (length $ someFunc a) == (length $ someFunc b) which is more readable, to my eye. The only solution which has been suggested that may work is liberal use of the liftM variants, but this gets *really* tedious and obtuse. Is there an elegant way to do what I want to do, or am I stuck with procedural-style assignments and bunches of temp vars? Thanks! -- ### SER ### Deutsch|Esperanto|Francaise|Linux|XML|Java|Ruby|Aikido ### http://www.germane-software.com/~ser jabber.com:ser ICQ:83578737 ### GPG: http://www.germane-software.com/~ser/Security/ser_public.gpg

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WS-FM 2004 Call For Participation
by Mario Bravetti 20 Jul '05

20 Jul '05

---------------------------------------------------------------------- We apologize if you receive multiple copies of this announcement. ---------------------------------------------------------------------- ====================================================================== 1st International Workshop on Web Services and Formal Methods (WS-FM 2004) February 23-24, 2004, Pisa, Italy Workshop affiliated to COORDINATION 2004, February 24-27, 2004 WS-FM 2004 homepage: http://www.cs.unibo.it/~lucchi/ws-fm04/ ====================================================================== - The technical program is available at: http://www.cs.unibo.it/~lucchi/ws-fm04/ - Information about registration, travel and accomodation can be found at the COORDINATION 2004 web site: http://www.di.unipi.it/Coordination2004/ If you intend to participate, we recommend you to register and book the hotel as soon as possible. The Coordination 2004 Organizing Committee informed us that hotels are going to be fully booked in short time.

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Announce: Cabal 0.1 (Library Infrastructure Project)
by Isaac Jones 01 Nov '04

01 Nov '04

Much thanks to all who've made this possible :) The Haskell Cabal The Common Architecture for Building Applications and Libraries. DOWNLOAD: The Haskell Cabal has reached pre-release stage, with a 0.1 version The community should use this release to evaluate the interfaces and explore the concepts of these tools. Download the Cabal here: http://www.haskell.org/cabal/download.html BUGS: Please report bugs and wish-list items here: http://sourceforge.net/tracker/?func=add&group_id=44807&atid=440922 Or email Isaac Jones: ijones(a)syntaxpolice.org ABOUT: The Haskell Cabal is meant to be a part of a larger infrastructure for distributing, organizing, and cataloging Haskell Libraries and Tools. It is an effort to provide a framework for developers to more effectively contribute their software to the Haskell community. Specifically, the Cabal describes what a Haskell package is, how these packages interact with the language, and what Haskell implementations must to do to support packages. The Cabal also specifies some infrastructure (code) that makes it easy for tool authors to build and distribute conforming packages. The Cabal is only one contribution to the larger goal. In particular, the Cabal says nothing about more global issues such as how authors decide where in the module name space their library should live; how users can find a package they want; how orphan packages find new owners; and so on. NOTES: This release is meant to provide the community with concrete information about how the interfaces are shaping up. This release does NOT fix the interfaces, we can't promise not to break anything that relies on these interfaces. We hope that Haskell authors will try to package their software using these tools, and let us know where they fall short. MORE INFORMATION: Please see the web site for the source code, interfaces, and especially the proposal, which will serve as documentation for this release: http://www.haskell.org/cabal/

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RE: [Haskell] optimisation of State monad
by Simon Peyton-Jones 29 Sep '04

29 Sep '04

I took a quick look. My bet is that profiling is interfering with optimisation (which it certainly does). I also used -G1 to force single-generation GC, which gives more accurate residency numbers. Without profiling, but all compiled with -O. iterR (take 100000 (repeat 1)) (Foo 0 0.0) ./test1 +RTS -K64M -sstderr -G1 Foo {foo = 0, bar = 0.0} 6,923,484 bytes allocated in the heap 3,288 bytes copied during GC 192 bytes maximum residency (18 sample(s)) iterL (take 100000 (repeat 1)) (Foo 0 0.0) ./test2 +RTS -K64M -sstderr -G1 Foo {foo = 0, bar = 0.0} 4,847,872 bytes allocated in the heap 22,032 bytes copied during GC 1,224 bytes maximum residency (18 sample(s)) iterR' (take 100000 (repeat 1)) (Foo 0 0.0) [iterR' is your iterR calling t1'] ./test3 +RTS -K64M -sstderr -G1 Foo {foo = -10, bar = 0.0} 41,046,244 bytes allocated in the heap 29,756 bytes copied during GC 212 bytes maximum residency (148 sample(s)) 148 collections in generation 0 ( 0.18s) These all seem reasonable to me. I didn't look at the state stuff. Simon | -----Original Message----- | From: haskell-bounces(a)haskell.org [mailto:haskell-bounces@haskell.org] On Behalf Of Georg Martius | Sent: 21 September 2004 11:15 | To: haskell | Subject: [Haskell] optimisation of State monad | | Hi folks, | | I have two questions to tail recursion, optimisation(ghc) and the State monad. Sorry about bothering | you with efficiency issues, but they become crusual to me since my programm needs more memory | than I have :-( | | I compiled the following small examples with | ghc -O6 -Wall -prof -auto-all -o test Test.hs (ghc 6.2.1) | and ran them with | ./test +RTS -K64M -sstderr | | > data Foo = Foo { foo :: !Integer , bar :: Double | > } deriving Show | > type Transformation a = a -> a | > | > addX :: Integer -> Transformation Foo | > addX x f = f { foo = (foo f) + x } | >t1 :: Integer -> Transformation Foo | > t1 x = (addX x . addX (-x)) | >iterR :: [Integer] -> Transformation Foo | > iterR list f = foldr t1 f list | > iterL :: [Integer] -> Transformation Foo | > iterL list f = foldl (\ f' i -> t1 i f') f listiterR (take 100000 (repeat 1)) (Foo 0 0.0) | 16,151,796 bytes copied during GC | 11,546,120 bytes maximum residency (5 sample(s)) | Productivity 20.3% of total user, 19.7% of total elapsed | | > iterL (take 100000 (repeat 1)) (Foo 0 0.0) | 3,020 bytes copied during GC | 25,904 bytes maximum residency (1 sample(s)) | Productivity 100.0% of total user, 80.0% of total elapsed | | | Okay, foldl is tail recursive and foldr not. Fine! | Now one weird thing: If I define t1 as: | > t1' :: Integer -> Transformation Foo | > t1' x f = let newfoo = foldr addX f (take 10 $ repeat x) | > in newfoo {foo = foo f - foo newfoo} | | > iterR (take 100000 (repeat 1)) (Foo 0 0.0) | 22,476 bytes copied during GC | 2,113,876 bytes maximum residency (3 sample(s)) | Productivity 60.0% of total user, 59.0% of total elapsed | | Why is the compiler able to optimise the call of t1' and not the one of t1? | | My second question belongs to the State monad: | > withFoo :: Foo -> State Foo (a) -> Foo | > withFoo state monad = execState monad state | >addXM :: Integer -> State Foo () | > addXM x = modify (\ f -> f { foo = (foo f) + x }) | >iterM :: [Integer] -> State Foo () | > iterM list = sequence_ $ map t1M list | >t1M :: Integer -> State Foo () | > t1M x = do addXM x | > addXM (-x) | | > withFoo (Foo 0 0.0) $ do iterM (take 100000 (repeat 1)) | 48,989,348 bytes copied during GC | 14,037,156 bytes maximum residency (7 sample(s)) | Productivity 15.5% of total user, 14.7% of total elapsed | | and if I define t1M as: | t1M' :: Integer -> State Foo () | t1M' x = do old <- get | sequence_ $ map addXM (take 10 $ repeat x) | modify (\ f -> f {foo = foo f - foo old}) | then the memory consumption is awfully high: | | > withFoo (Foo 0 0.0) $ do iterM (take 100000 (repeat 1)) | 172,468,996 bytes copied during GC | 48,522,520 bytes maximum residency (10 sample(s)) | Productivity 2.6% of total user, 2.5% of total elapsed | | Is there a way to optimise the State monad version? | | Any help would be appreciated. | | Georg | _______________________________________________ | Haskell mailing list | Haskell(a)haskell.org | http://www.haskell.org/mailman/listinfo/haskell

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[QCQ] Haskell-QuickCheck Questionnaire
by Koen Claessen 29 Sep '04

29 Sep '04

Dear Haskell-QuickCheck user, When John and I published the first paper about QuickCheck in 2000, we released a Haskell module that was cleary marked as DRAFT. Since then, a lot of things have happened; we and other people have made extensions and improvements to QuickCheck, but only very few of the extensions are part of the "standard" distribution of QuickCheck (included in GHC and Hugs), and none of the improvements. I am right now in the process of gathering all QuickCheck extensions and improvements I am aware of, and packaging them up in a nicely structured and concise way. At the same time, we are planning to write a new tutorial based on the new QuickCheck. In order to do this well, I would like to get your feedback. If you care about the future of QuickCheck, please take a moment to fill in the attached questionnaire. In particular, I would like to know what your typical use of QuickCheck is, so that I can avoid spending time on making things backwards compatible if it is not needed. List of intended includes: - testing monadic code - automatically shrinking counter examples - support for custom counter example callbacks - programmable test coverage warnings - dealing with exceptions - dealing with non-termination - automatic coarbitrary instance - generic predefined simple test data generators - generic default definitions for shrinking Thank you for your help! /Koen ---- QuickCheck Questionnaire ======================== Please fill in your answers like this: [ ] becomes [X] ... becomes <your answer> Multiple answers allowed where applicable. Please send your filled in questionnaires to koen(a)cs.chalmers.se. Please include the tag [QCQ] in the subject of your message. Don't send back your answers later than Friday, October 8th. == General ========================================================= *1. How often do you use / have you used QuickCheck? [ ] Never [ ] A few times [ ] Often [ ] I use it in almost all my projects *2. What Haskell system do you use it with? [ ] GHC [ ] GHCi [ ] Hugs [ ] NHC [ ] Other: ... *3. How often do you use the shell script "quickCheck"? [ ] Never [ ] A few times [ ] Often [ ] I use it in almost all my projects == Original QuickCheck module ===================================== (These are questions about functions that might be dropped from future versions.) *4. How often do you use the function "check" together with your own "Config"? [ ] Never [ ] A few times [ ] Often [ ] I use it in almost all my projects *5. How often do you use the functions "label", "classify", or "trivial"? [ ] Never [ ] A few times [ ] Often [ ] I use it in almost all my projects *5a. If so, which ones: ... *6. How often do you use the functions "two", "three", or "four"? [ ] Never [ ] A few times [ ] Often [ ] I use it in almost all my projects *7. How often do you use the function "vector"? [ ] Never [ ] A few times [ ] Often [ ] I use it in almost all my projects == Other QuickCheck modules ======================================= *8. How often do you use the module Debug.QuickCheck.Batch? [ ] Never [ ] A few times [ ] Often [ ] I use it in almost all my projects *9. How often do you use the module Debug.QuickCheck.Utils? [ ] Never [ ] A few times [ ] Often [ ] I use it in almost all my projects *10. How often do you use the module Debug.QuickCheck.Poly? [ ] Never [ ] A few times [ ] Often [ ] I use it in almost all my projects == Debugging tools ================================================ *11. How often do you use HOOD? [ ] Never [ ] A few times [ ] Often [ ] I use it in almost all my projects *12. How often do you use Hat? [ ] Never [ ] A few times [ ] Often [ ] I use it in almost all my projects *13. How often do you use Buddha? [ ] Never [ ] A few times [ ] Often [ ] I use it in almost all my projects == Suggestions =================================================== *14. Please write down if you find there are functions typically missing from the current QuickCheck distribution: ... *15. Please explain typical problems you have or have had with QuickCheck and did not know how to solve: ... *16. Please suggest any extension that you would like to see in QuickCheck (not already mentioned in the "indeded includes" list in the e-mail above): ... *17. How do you think we should distribute QuickCheck in the future? (As an independent library, in the standard library tree, ...): ... *18. Feel free to write any other comments (positive ones are welcome too :-): ... == The end ====================================================== Thanks! Please send your answers to koen(a)cs.chalmers.se with the tag [QCQ] in the subject, no later than Friday, October 8th.

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Call for Papers: Special Issue M4M
by Carlos Areces 29 Sep '04

29 Sep '04

Call for Papers for "Methods for Modalities" A Special Issue of the Journal of Applied Logic (http://www.sciencedirect.com/science/journal/15708683) The workshop `Methods for Modalities' (M4M) organized every two years aims to bring together researchers interested in developing proof tools and decision methods for modal logic broadly conceived, including description logic, hybrid logic, temporal logic, etc. During 2003 M4M-3, the third instance of the workshop was organized in Nancy, France. We have been invited by the Journal of Applied Logic to prepare a Special Issue containing selected publications from the workshop, in addition to other articles that might fit within the topics of interest of M4M. For that reason we are now distributing this Call for Papers. TOPICS OF INTEREST OF M4M The following list is provided as an example of suitable topics for the Special Issue. All topics should concern modal-like logics, broadly conceived. The list is by no means exhaustive and is given in an arbitrary order: * Automated theorem proving * Decision methods * Proof methods * Standard and non-standard inference problems * Model checking * Testing * Expressive power * Modelling * Applications * Successful uses of modal-like languages in other fields * Knowledge representation SUBMISSION DETAILS The final version of accepted papers has to follow the standard layout guidelines of the Journal of Applied Logic. Instructions for authors and the latex style files are available from http://staff.science.uva.nl/~m4m/SI/ Although not mandatory, we suggest to use the corresponding style files from that web-page also for your initial submission. The issue aims at high quality papers with a length around 20 to max. 30 pages. Please send your submission in postscript or pdf no later than October 31th, 2004 to areces(a)loria.fr. Notice that all papers will be refereed to ensure that their suitability for journal publication. IMPORTANT DATES Deadline for Submissions: October 31th, 2004 Reviews Due : November 21th, 2004 Final Versions Due : December 19th, 2004 GUEST EDITORS of the Special Issue Dr. Carlos Areces INRIA Lorraine 615, rue du Jardin Botanique 54602 Villers les Nancy Cedex, France phone : +33 (0)3 83 58 17 90 fax : +33 (0)3 83 41 30 79 e-mail : carlos.areces(a)loria.fr www : http://www.loria.fr/~areces ----- End forwarded message ----- -- Carlos Eduardo Areces ILLC, University of Amsterdam Nieuwe Achtergracht 166, 1018 WV, Amsterdam, The Netherlands phone : +31 20 525-6730 e-mail : carlos(a)science.uva.nl www : http://www.illc.uva.nl/~carlos visit : http://www.hylo.net -> The Hybrid Logic's Home Page

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hscpp
by Wolfgang Jeltsch 28 Sep '04

28 Sep '04

Hello, there was some discussion about a Haskell-friendly CPP a while ago. What happend to this project? I desperately need such a preprocessor. CPP 3.3.4, which I use now, is not usable for me because you cannot have such a simple thing like a \\ operator with it. How do others solve such problems? I cannot believe that there isn't a better way than living with all those terrible restrictions, using CPP imposes on you. Wolfgang

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Simple question about IO in hugs and ghc
by Vivian McPhail 26 Sep '04

26 Sep '04

Hi, When I run my main function I get an error: The prompt does not wait for user input and thus my parser fails with an empty head. Is there a switch to not echo to the console? Is this the problem? It happens in both Hugs and GHC main :: IO () main = do putStr "sentence? " input <- getLine case input of "quit" -> putStr "bye.\n" _ -> do let res = get_result $ proof $ do_proof $ getInput input in if res == Nothing then putStr ("-> Nothing\n") else putStr ("-> " ++ (show $ unJust res) ++ "\n") main ---- Sample output: START> $ mmccg.exe sentence? Fail: Prelude.head: empty list <END

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10th Est. Winter School in Comp. Sci., 1st call for partic.
by Tarmo Uustalu 25 Sep '04

25 Sep '04

[Lecturers: Danvy, Mehlhorn, Miltersen, Morrisett, Pinkas. Place/time: Palmse, Estonia, 27 Feb-4 March 2005. Deadline for registration and submission of abstracts for student talks/posters: ** 14 Jan 2005 **.] Call for Participation 10th Estonian Winter School in Computer Science EWSCS'05 Palmse, Estonia, 27 February-4 March 2005 http://www.cs.ioc.ee/yik/schools/win2005/ Background and objectives EWSCS is a series of regional-scope international winter schools held annually in Estonia. EWSCS are organized by CIDEC, a joint initiative of Institute of Cybernetics (Tallinn), Tallinn University of Technology and University of Tartu for the advancement of higher education in computer science and information technology. EWSCS'05 is the tenth event of the series. The main objective of EWSCS is to expose Estonian, Baltic, and Nordic graduate students in computer science (but also interested students from elsewhere) to frontline research topics usually not covered within the regular curricula. The subject of the schools is general computer science, with a bias towards theory, this comprising both algorithms, complexity and models of computation, incl. cryptography, and semantics, logic and programming theory. The working language of the schools is English. Programme The schools' scientific programme consists of short courses by renowned specialists and a student session. The course list for EWSCS'05 is the following: Olivier Danvy (University of Aarhus, Denmark: A Vade Mecum to Continuations Kurt Mehlhorn (MPI Saarbrücken, Germany): Implementing Algorithms Peter Bro Miltersen (University of Aarhus, Denmark: Universal Methods for Derandomization Greg Morrisett (Harvard University, Cambridge, MA, USA): Topics in Language-Based Security Benny Pinkas (HP Labs, Haifa, Israel): Privacy-Preserving Data Mining The purpose of the student session is to give students an opportunity to present their work (typically, thesis work) and get feedback. Registrants are invited to propose short talks (20 min) or posters. The selection will be based on abstracts of 150-400 words. The social programme consists of an excursion and a conference dinner. Venue Palmse is a small settlement 80 kms to the east from Tallinn in the county of Lääne-Viru. It is renowned for a large manor that used to belong to the von Pahlen family, today hosting the visitors' center of the Lahemaa National Park, a museum, and a hotel. Tallinn, Estonia's capital, is famous for its picturesque medieval Old Town, a UNESCO World Heritage site. There are direct flights to Tallinn from London, Paris, Milan, Amsterdam, Brussels, Frankfurt, Munich, Hamburg, Berlin, Prague, Warsaw, Moscow, Kiev, Copenhagen, Oslo, Stockholm, Gothenburg, Helsinki, Vilnius, Riga, ferries from Stockholm and Helsinki. From Vilnius, Riga, the Eurolines coach service is the practical travel option. Registration and cost The deadline for registration and submission of abstracts is 14 January 2005. All registrants will be notified of acceptance to school and acceptance of their talks/posters by 28 January 2005. The participation fee 4000 EEK (260 EUR) includes course materials, full boarding at Palmse, transportation from Tallinn to Palmse, excursion and conference dinner. For some students, we can partially waive the fee. Programme committee / organizing committee Tarmo Uustalu (IoC) (chair), Monika Perkmann (IoC) (secretary), Helger Lipmaa (Helsinki U. of Techn.), Peeter Laud (U. of Tartu), Jaan Penjam (IoC), Heli Uibo (U. of Tartu), Jüri Vain (Tallinn U. of Techn.), Varmo Vene (U. of Tartu) Sponsors Centers of Excellence in Research Programme of Ministry of Education and Research of Estonia, FP5 IST project eVikings II Further information Details on the submission of abstracts, registration procedure and cost, application for fee waiver are available from the school webpage, http://www.cs.ioc.ee/yik/schools/win2005/. Questions should be sent to ewscs05(a)cs.ioc.ee.

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Monadic pretty-printing
by Tomasz Zielonka 25 Sep '04

25 Sep '04

Hello! In my master's thesis I am dealing with a complicated case of pretty printing / unparsing. There are side effects, context dependency, unparsing to two different languages (two SQL dialects). To manage this complexity, I use a couple of ,,design patterns''. One of them is about giving a monadic interface to pretty printing library, to allow mixing it easily with various effects (IO, Reader, Cont). After some fiddling with a hand written pretty-printing monad, I realized that I can just use a Writer monad. HughesPJ.Doc can be trivially made an instance of Monoid - AFAIK all the needed laws hold. The only problem is to decide which one of document composition operators should be used as mappend. In my case I want <+> by default, but I arranged things so that I can have several different versions of Doc (newtyped). As I needed many other pretty-printing combinators beside <+>/mappend, I created a library of monadic pretty-printing combinators for separating (eg. with commas), vertical composition, nesting, putting in parentheses, <> composition, etc. In some cases it was necessary to use MonadWriter's "censor" method, but nothing more. I think it is quite elegant. The code written using this technique is also quite clear. Perhaps it would be worse, if it wasn't possible to choose a composition operator for Monoid doing the proper thing in 90% of cases. Below is a fragment of code that handles expression unparsing. unparse (Expr_BinaryOp op e1 e2) = parens $ do unparse e1 unparse op unparse e2 unparse (Expr_UnaryOp UnaryOp_Not (Expr_IsNull e)) = parens $ do unparse e kw IS kw NOT kw NULL unparse (Expr_UnaryOp op e) = parens $ do unparse op unparse e unparse (Expr_Constant cons) = do unparse cons unparse (Expr_In e inSpec) = parens $ do unparse e kw IN oneline (unparse inSpec) unparse (Expr_Between e1 e2 e3) = parens $ do unparse e1 kw BETWEEN unparse e2 kw AND unparse e3 unparse (Expr_Cast e datatype) = do kw CAST `catThen` parens (do unparse e kw AS unparse datatype) unparse (Expr_IsNull e) = parens $ do unparse e kw IS kw NULL ... As you can see, sometimes there is a need to use a different composition operator (catThen). I think that this technique, simple as it is, can be very useful for more complicated programs, especially if pretty-printing has to be interleaved with some computational effects. It also helps to achieve good modularity, by "dispatching on the monad type", which helps me to handle two different dialects of SQL with quite good code reuse. But getting to the point... I wonder if such a pattern was used or proposed before. I tried to find some mention of it, but with no luck (or luck :). Most examples of Writer monad use are about logging, etc. If there are no protests, I am going to claim I was the first to use such a technique. It may help me to rescue my poor master's thesis ;) Best regards, Tom -- .signature: Too many levels of symbolic links

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