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ANNOUNCE: HakkuTaikai: Haskell Hackathon in Tokyo, 25th September 2011
by Liyang HU 25 Aug '11

25 Aug '11

You may have heard the rumours, and I can confirm that it's true: HakkuTaikai is happening! After spending a long week at ICFP 2011 talking about Haskell, why not relax by actually hacking some Haskell? Full details on the wiki page: http://www.haskell.org/haskellwiki/HakkuTaikai When: Sunday, 25th September 2011 Where: Room 1208 of the NII building; the same location as ICFP. Registration is free! See the wiki page above for details. Feel free to email or IRC or twit me with any questions. Many thanks to http://www.nii.ac.jp/ for hosting the event! Cheers, /Liyang

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How to make callCC more dynamic
by bob zhang 25 Aug '11

25 Aug '11

Hi, all I thought the right type for ContT should be newtype ContT m a = ContT {runContT :: forall r. (a-> m r) -> m r} and other control operators shift :: Monad m => (forall r . (a-> ContT m r) -> ContT m r) -> ContT m a reset :: Monad m => ContT m a -> ContT m a callCC :: ((a-> (forall r . ContT m r)) -> ContT m a) -> ContT m a unfortunately, I can not make callCC type check, and don't know how to do it. I managed to make shift, reset type check reset :: Monad m => ContT m a -> ContT m a reset e = ContT $ \ k -> runContT e return >>= k shift :: Monad m => (forall r . (a-> ContT m r) -> ContT m r) -> ContT m a shift e = ContT $ \ (k :: a -> m r) -> runContT ((e $ \ v -> ContT $ \c -> k v >>= c) :: ContT m r) return but still, I cann't use shift, reset in recursive jumpings like this? newtype H r m = H (H r m -> ContT m r) unH (H x) = x test = flip runContT return $ reset $ do jump <- shift (\f -> f (H f)) lift . print $ "hello" unH jump jump Have anyone tried this before? Best, bob

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Re: [Haskell-cafe] Lifting an enumerator
by John Lato 25 Aug '11

25 Aug '11

> Message: 17 > Date: Wed, 24 Aug 2011 17:02:49 +0300 > From: Michael Snoyman <michael(a)snoyman.com> > Subject: [Haskell-cafe] Lifting an enumerator > To: Haskell Cafe <haskell-cafe(a)haskell.org> > Cc: John Millikin <jmillikin(a)gmail.com> > Message-ID: > <CAKA2JgKF0dN4N8Ge1_q-zemLZM93bWg_FjMtbaZGzrC2Gqnq4w(a)mail.gmail.com> > Content-Type: text/plain; charset=ISO-8859-1 > > Hi all, > > Max asked earlier[1] how to create a new instance of a class in > Persistent using a monad transformer. Without getting into the > specific details of persistent, I wanted to pose a question based on a > much more general question: how can we lift the inner monad of an > enumerator? We can easily do so for an Iteratee[2], but there is > nothing to allow it for an Enumerator. > > At first glance, this problem looks very similar to the shortcomings > of MonadIO when dealing with callbacks. In that case, you cannot use > liftIO on a function that takes an `IO a` as a parameter. A solution > to this issue is monad-control[3], which can be used to allow > exception catching, memory allocation, etc. > > So I'm wondering: can we come up with a similar solution to this issue > with enumerators? I have a working solution for the specific case of > the ErrorT monad[4], but it would be great to be able to generalize > it. Bonus points if we could express this in terms of the typeclasses > already provided by monad-control. Based upon a similar problem I worked on in the past, I suspect this isn't possible in the general case, at least not safely. That is, any implementation (presuming it's possible at all) would violate the resource guarantees enumerators typically provide (an inner MonadCont is able to do this). Unfortunately I don't have a proof, so I'm open to counter-examples ;-) John L.

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haskell or lazy functional as procedure language
by Permjacov Evgeniy 25 Aug '11

25 Aug '11

Ok, I know, I want something strange. But consider situation, when one is starting a project and finds, that he need s 1) ACID relational storage 2) Power of good RDBMS system (postgresql for example) 3) Power of some very hight level language and compiled (haskell for example) for stored procedures 4) And all data processing MUST be performed inside RDBMS 5) And does not have enough money to by Oracle ore other commercial RDBMS. I already considered using ghc with postgresql. It could be very, very good pair, but.... ghc runtime cannot be re-initialized, and reqular way for stored procedures in postgresql is calling function from shared object (meaning, I have to shut down ghc runtime each time stored procedure ended). What other options do you see?

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Re: [Haskell-cafe] Existential question
by oleg＠okmij.org 25 Aug '11

25 Aug '11

> -- Is there a way to make this one work also? > data Kl i o = forall s. Kl (i -> s -> (s, o)) > iso :: (i -> Kl () o) -> Kl i o > iso f = Kl $ \i s -> (\(Kl kl) -> kl () s) (f i) Yes, if you move the quantifier: type Kl i o = i -> Kl1 o data Kl1 o = forall s. Kl1 (s -> (s,o)) iso :: (i -> Kl () o) -> Kl i o iso f = \i -> f i () iso1 :: Kl i o -> (i -> Kl () o) iso1 f = \i -> (\() -> f i) I'm not sure if it helps in the long run: the original Kl and mine Kl1 are useless. Suppose we have the value kl1 :: Kl Int Bool with the original declaration of Kl: data Kl i o = forall s. Kl (i -> s -> (s, o)) Now, what we can do with kl1? We can feed it an integer, say 1, and obtain function f of the type s -> (s,Bool) for an _unknown_ type s. Informally, that type is different from any concrete type. We can never find the Bool result produced by that function since we can never have any concrete value s. The only applications of f that will type check are \s -> f s f undefined both of which are useless to obtain f's result.

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Issue with lhs2TeX 1.17
by Arnaud Bailly 25 Aug '11

25 Aug '11

Hello, I recently reinstalled (using cabal) lhs2TeX v 1.17 (Haskell Platform installation 2011.2.0, Windows XP SP2, MiKTeX 2.8) and I cannot run latex anymore on the .tex files produced. Any clues about this ? Did I forgot to install some package ? This is not clear from the documentation which seems to imply cabal install does the right thing (TM). Thanks in advance for you help. Arnaud PS: Here is the beginning of the compilation output for latex Running `LaTeX' on `foo' with ``latex -interaction=nonstopmode "\input" "foo.tex"'' This is pdfTeX, Version 3.1415926-1.40.10 (MiKTeX 2.8) entering extended mode LaTeX2e <2009/09/24> Babel <v3.8l> and hyphenation patterns for english, dumylang, nohyphenation, german, ngerman, german-x-2009-06-19, ngerman-x-2009-06-19, french, loaded. (d:\projets\foo.tex ("D:\Program Files\MiKTeX 2.8\tex\latex\base\article.cls" Document Class: article 2007/10/19 v1.4h Standard LaTeX document class ("D:\Program Files\MiKTeX 2.8\tex\latex\base\size11.clo")) ("D:\Program Files\MiKTeX 2.8\tex\latex\ams\math\amstext.sty" ("D:\Program Files\MiKTeX 2.8\tex\latex\ams\math\amsgen.sty")) ("D:\Program Files\MiKTeX 2.8\tex\latex\amsfonts\amssymb.sty" ("D:\Program Files\MiKTeX 2.8\tex\latex\amsfonts\amsfonts.sty")) ("C:\Documents and Settings\abailly\Application Data\MiKTeX\2.8\tex\latex\stmaryrd\stmaryrd.sty") ("C:\Documents and Settings\abailly\Application Data\MiKTeX\2.8\tex\latex\polytable\polytable.sty" ("C:\Documents and Settings\abailly\Application Data\MiKTeX\2.8\tex\latex\lazylist\lazylist.sty") ("D:\Program Files\MiKTeX 2.8\tex\latex\tools\array.sty")) ("C:\Documents and Settings\abailly\Application Data\MiKTeX\2.8\tex\latex\a4wide\a4wide.sty" ("C:\Documents and Settings\abailly\Application Data\MiKTeX\2.8\tex\latex\ntgclass\a4.sty")) (d:\projets\foo.aux) ("D:\Program Files\MiKTeX 2.8\tex\latex\amsfonts\umsa.fd") ("D:\Program Files\MiKTeX 2.8\tex\latex\amsfonts\umsb.fd") ("C:\Documents and Settings\abailly\Application Data\MiKTeX\2.8\tex\latex\stmaryrd\ustmry.fd") Overfull \hbox (25.83325pt too wide) in paragraph at lines 116--186 $[][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][] Overfull \hbox (25.83325pt too wide) in paragraph at lines 116--186 [][][][] Overfull \hbox (25.83325pt too wide) in paragraph at lines 116--186 [][][] Overfull \hbox (25.83325pt too wide) in paragraph at lines 116--186 [][][][] Overfull \hbox (25.83325pt too wide) in paragraph at lines 116--186 [][][] Overfull \hbox (25.83325pt too wide) in paragraph at lines 116--186 [][][][] Overfull \hbox (25.83325pt too wide) in paragraph at lines 116--186 [][][][] Overfull \hbox (25.83325pt too wide) in paragraph at lines 116--186 [][][][][][][] Overfull \hbox (25.83325pt too wide) in paragraph at lines 116--186 [][][][][][][] Overfull \hbox (25.83325pt too wide) in paragraph at lines 116--186 [][][][][][][] Overfull \hbox (25.83325pt too wide) in paragraph at lines 116--186 [][][][][][][] Overfull \hbox (25.83325pt too wide) in paragraph at lines 116--186 [][][][][][][] Overfull \hbox (25.83325pt too wide) in paragraph at lines 116--186 [][][][][][][] Overfull \hbox (25.83325pt too wide) in paragraph at lines 116--186 [][][][][][][] Overfull \hbox (25.83325pt too wide) in paragraph at lines 116--186 [][][][][][][] Overfull \hbox (25.83325pt too wide) in paragraph at lines 116--186 [][][][][][] Overfull \hbox (25.83325pt too wide) in paragraph at lines 116--186 [][][][] Overfull \hbox (25.83325pt too wide) in paragraph at lines 116--186 [][][][][][][][][][] Overfull \hbox (25.83325pt too wide) in paragraph at lines 116--186 [][][][][][][] Overfull \hbox (25.83325pt too wide) in paragraph at lines 116--186 [][][][][][][] Overfull \hbox (25.83325pt too wide) in paragraph at lines 116--186 [][][][][][][] Overfull \hbox (25.83325pt too wide) in paragraph at lines 116--186 [][][][][][]$ ("D:\Program Files\MiKTeX 2.8\tex\latex\base\omscmr.fd") ! Missing $ inserted. <inserted text> $ l.609 \end{pboxed} ! Extra }, or forgotten $. <recently read> \egroup l.609 \end{pboxed} ! Missing $ inserted. <inserted text> $ l.609 \end{pboxed} ! Extra }, or forgotten $. <recently read> \egroup l.609 \end{pboxed} ! Missing $ inserted. <inserted text> $ l.609 \end{pboxed} ! Extra }, or forgotten $. \mbox #1->\leavevmode \hbox {#1} l.609 \end{pboxed} ! Missing $ inserted. <inserted text> $ l.609 \end{pboxed} ! LaTeX Error: \mathit allowed only in math mode.

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(Repa) hFlush: illegal operation
by Michael Orlitzky 25 Aug '11

25 Aug '11

I'm using Repa to process a ton of MRI data. The basic process is, * Read in the data * Create a big 'ol data structure (grid) from it * Compute the output in parallel using 'traverse' * Write the output to file However, during the last step, I'm getting, $ ./bin/spline3 +RTS -N4 spline3: output.txt: hFlush: illegal operation (handle is closed) Here's the entirety of my Main.hs: > module Main > where > > import Data.Array.Repa ( > DIM3, > Z(..), > (:.)(..), > ) > > import Values > import Grid(make_grid, zoom) > > mri_shape :: DIM3 > mri_shape = (Z :. 256 :. 256 :. 109) > > main :: IO () > main = do > mridata <- read_values_3d mri_shape "./data/mridata.txt" > let g = make_grid 1 mridata > let output = zoom g 1 > write_values_1d output "output.txt" And the two functions used from the Values module, > type Values1D = Array DIM1 Double > type Values3D = Array DIM3 Double > > read_values_1d :: FilePath -> IO Values1D > read_values_1d path = readVectorFromTextFile path > > > read_values_3d :: DIM3 -> FilePath -> IO Values3D > read_values_3d sh path = do > one_d <- read_values_1d path > return $ reshape sh one_d > > > write_values_1d :: Values3D -> FilePath -> IO () > write_values_1d v3d path = do > let size3d = size $ extent v3d > let shape1d = (Z :. size3d) > let v1d = reshape shape1d v3d > writeVectorToTextFile v1d path Am I doing something obviously wrong here? It takes about 45 minutes to run up to the point of failure, so I haven't attempted much trial & error. Packages: * ghc-7.2.1 * repa-2.1.1.6 * repa-io-2.1.0.1

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Using -> as both type and value constructor
by Armando Blancas 25 Aug '11

25 Aug '11

Studying the paper *A Simple Implementation for Priority Search Queues*, by Ralf Hinze, I came across the following syntax that I didn't understand and I couldn't use in GHCi 7.0.3 for defining a binding data type (page 3): Bindings are represented by the following data type: *data k -> p = k -> p* key :: (k -> p) -> k key (k -> p) = k prio :: (k -> p) -> p prio (k -> p) = p Note that we use '->' both as a type constructor and value constructor. [...] data PSQ k p The following page has these value constructors: *0 :: PSQ k p* *{.} :: (k -> p) -> PSQ k p* The paper says that's Haskell '98 code. I'll appreciate info on what kind of data declaration those are and any pointers to related documentation. Or maybe those are deprecated features. I'm stuck in this part. -armando www.cs.ox.ac.uk/people/ralf.hinze/talks/ICFP01.pdf

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Haskell Weekly News: Issue 196
by Daniel Santa Cruz 25 Aug '11

25 Aug '11

Welcome to issue 196 of the HWN, a newsletter covering developments in the Haskell community. This release covers the week of August 14 to 20, 2011. [1] http://goo.gl/8hDku New and Updated Projects * graphziz (Update - Ivan Lazar Miljenovic) Wraper around Graphviz. [2] http://goo.gl/gg30u * TKYProf (New - Mitsutoshi Aoe) A web-based interactive visualizer for GHC time and allocation profiling. [3] http://goo.gl/Inqze Quotes of the Week * accel: next time I'll read a few research papers before I start trolling hakell * jmcarthur: your opinions all suck. i'm going back to #haskell (...) oh shit, i'm already there Top Reddit Stories * Haskell For Kids: Week 1 Domain: cdsmith.wordpress.com, Score: 37, Comments: 13 On Reddit: [4] http://goo.gl/RY6li Original: [5] http://goo.gl/azAVz * New IBM CPU has transactional memory built in Domain: nextbigfuture.com, Score: 35, Comments: 4 On Reddit: [6] http://goo.gl/cbjvN Original: [7] http://goo.gl/JOpWx * [GSoC] Text/UTF-8: Aftermath Domain: jaspervdj.be, Score: 32, Comments: 7 On Reddit: [8] http://goo.gl/MTHNy Original: [9] http://goo.gl/esQNO * CamHac post-hackathon report Domain: haskell.org, Score: 31, Comments: 8 On Reddit: [10] http://goo.gl/RHpfF Original: [11] http://goo.gl/GkVaa * GHC 7.4 won't have top-level MonoPatBinds anymore! Domain: hackage.haskell.org, Score: 25, Comments: 5 On Reddit: [12] http://goo.gl/bS1VL Original: [13] http://goo.gl/SK2Tz * Ending GSoC (cabal repl) Domain: lambdasandwich.blogspot.com, Score: 25, Comments: 1 On Reddit: [14] http://goo.gl/Rrzmj Original: [15] http://goo.gl/chb8A * If one of Haskell's goals is concurrency, then why is it based on the λ-calculus and not on a process calculus? Domain: en.wikipedia.org, Score: 23, Comments: 39 On Reddit: [16] http://goo.gl/Qjcgc Original: [17] http://goo.gl/ZSwt1 * University of Reddit Class: "Fixing Imperative Programmers" Domain: reddit.com, Score: 22, Comments: 2 On Reddit: [18] http://goo.gl/1hYlf Original: [19] http://goo.gl/26Qxd * A Command Line Reddit Viewer written in Haskell : programming (xpost : /programming ) Domain: reddit.com, Score: 22, Comments: 0 On Reddit: [20] http://goo.gl/bT9q8 Original: [21] http://goo.gl/VmVfA * Web-Based Environment for Gloss (Early Alpha: READ WARNINGS!) Domain: cdsmith.wordpress.com, Score: 21, Comments: 1 On Reddit: [22] http://goo.gl/e4Tjo Original: [23] http://goo.gl/wVA9H Top StackOverflow Questions * What are practical uses of applicative style? votes: 21, answers: 9 Read on SO: [24] http://goo.gl/Ms6fs * Functional equivalent of decorator pattern? votes: 20, answers: 7 Read on SO: [25] http://goo.gl/o8FhO * Why do 3 and x (which was assigned 3) have different inferred types in Haskell? votes: 18, answers: 2 Read on SO: [26] http://goo.gl/cm9av * Haskell tuple constructor (GHC) and the separation between a language and its implementation votes: 15, answers: 1 Read on SO: [27] http://goo.gl/tFvtk * Polymorphism within higher-order functions? votes: 13, answers: 1 Read on SO: [28] http://goo.gl/hNvkE * What happens to missing type variables in Church-style core? votes: 12, answers: 2 Read on SO: [29] http://goo.gl/kb2TM * Trying to implement Data.Either votes: 12, answers: 1 Read on SO: [30] http://goo.gl/lguDh * How can I make file I/O more transactional? votes: 11, answers: 2 Read on SO: [31] http://goo.gl/BjGFV * Trying to understand the types produced by monad transformers votes: 11, answers: 2 Read on SO: [32] http://goo.gl/YHsRQ * Why doesn't Safe Haskell support Template Haskell? votes: 11, answers: 1 Read on SO: [33] http://goo.gl/E1NCS About the Haskell Weekly News To help create new editions of this newsletter, please send stories to dstcruz(a)gmail.com. Until next time, Daniel Santa Cruz References 1. http://haskell.org/ 2. http://permalink.gmane.org/gmane.comp.lang.haskell.general/18888 3. http://permalink.gmane.org/gmane.comp.lang.haskell.cafe/91743 4. http://cdsmith.wordpress.com/2011/08/16/haskell-for-kids-week-1/ 5. http://www.reddit.com/r/haskell/comments/jlrva/haskell_for_kids_week_1/ 6. http://nextbigfuture.com/2011/08/ibm-plants-transactional-memory-in-cpu.htm… 7. http://www.reddit.com/r/haskell/comments/jperf/new_ibm_cpu_has_transactiona… 8. http://jaspervdj.be/posts/2011-08-19-text-utf8-the-aftermath.html 9. http://www.reddit.com/r/haskell/comments/jo6cd/gsoc_textutf8_aftermath/ 10. http://www.haskell.org/haskellwiki/CamHac/PostHackathonReport 11. http://www.reddit.com/r/haskell/comments/jj5lw/camhac_posthackathon_report/ 12. http://hackage.haskell.org/trac/ghc/ticket/2357#comment:11 13. http://www.reddit.com/r/haskell/comments/jkeqp/ghc_74_wont_have_toplevel_mo… 14. http://lambdasandwich.blogspot.com/2011/08/ending-gsoc.html 15. http://www.reddit.com/r/haskell/comments/jn8nl/ending_gsoc_cabal_repl/ 16. http://en.wikipedia.org/wiki/Process_calculus 17. http://www.reddit.com/r/haskell/comments/jlipx/if_one_of_haskells_goals_is_… 18. http://www.reddit.com/r/uorfip/ 19. http://www.reddit.com/r/haskell/comments/jok49/university_of_reddit_class_f… 20. http://www.reddit.com/r/programming/comments/jorky/a_command_line_reddit_vi… 21. http://www.reddit.com/r/haskell/comments/jouql/a_command_line_reddit_viewer… 22. http://cdsmith.wordpress.com/2011/08/14/haskell-for-kids-a-web-based-enviro… 23. http://www.reddit.com/r/haskell/comments/jis8g/webbased_environment_for_glo… 24. http://stackoverflow.com/questions/7103864/what-are-practical-uses-of-appli… 25. http://stackoverflow.com/questions/7064389/functional-equivalent-of-decorat… 26. http://stackoverflow.com/questions/7055146/why-do-3-and-x-which-was-assigne… 27. http://stackoverflow.com/questions/7086668/haskell-tuple-constructor-ghc-an… 28. http://stackoverflow.com/questions/7061538/polymorphism-within-higher-order… 29. http://stackoverflow.com/questions/7076517/what-happens-to-missing-type-var… 30. http://stackoverflow.com/questions/7121257/trying-to-implement-data-either 31. http://stackoverflow.com/questions/7059223/how-can-i-make-file-i-o-more-tra… 32. http://stackoverflow.com/questions/7088085/trying-to-understand-the-types-p… 33. http://stackoverflow.com/questions/7107308/why-doesnt-safe-haskell-support-…

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Lifting an enumerator
by Michael Snoyman 24 Aug '11

24 Aug '11

Hi all, Max asked earlier[1] how to create a new instance of a class in Persistent using a monad transformer. Without getting into the specific details of persistent, I wanted to pose a question based on a much more general question: how can we lift the inner monad of an enumerator? We can easily do so for an Iteratee[2], but there is nothing to allow it for an Enumerator. At first glance, this problem looks very similar to the shortcomings of MonadIO when dealing with callbacks. In that case, you cannot use liftIO on a function that takes an `IO a` as a parameter. A solution to this issue is monad-control[3], which can be used to allow exception catching, memory allocation, etc. So I'm wondering: can we come up with a similar solution to this issue with enumerators? I have a working solution for the specific case of the ErrorT monad[4], but it would be great to be able to generalize it. Bonus points if we could express this in terms of the typeclasses already provided by monad-control. Michael [1] http://groups.google.com/group/yesodweb/browse_thread/thread/be2a77217a7f33… [2] http://hackage.haskell.org/packages/archive/enumerator/0.4.14/doc/html/Data… [3] http://hackage.haskell.org/package/monad-control [4] https://gist.github.com/1168128

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why the name lambda calculus?
by C K Kashyap 24 Aug '11

24 Aug '11

Hi, Can someone please tell me what is the root of the name lambda calculus? Is it just because of the symbol lambda that is used? Why not alpha or beta calculus? Regards, Kashyap

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Performance of concurrent array access
by Andreas Voellmy 24 Aug '11

24 Aug '11

Hi, I am getting my feet writing concurrent programs in Haskell with GHC for multicore machines. As a first step I decided to write a program that reads and writes concurrently to an IOArray, with no synchronization whatsoever. I'm doing this to establish a baseline to compare with the performance of other data structures that do use appropriate synchronization mechanisms. I ran in to some surprising results, namely that in many cases, I am not getting any speed up at all. Here are the details... I write a couple variations on a single program. The main idea is that I wrote a DirectAddressTable data structure, which is simply a wrapper around an IOArray providing insert and lookup methods: -- file DirectAddressTable.hs module DirectAddressTable ( DAT , newDAT , lookupDAT , insertDAT , getAssocsDAT ) where import Data.Array.IO import Data.Array.MArray import Data.Int (Int32) data DAT = DAT (IOArray Int32 Char) -- create a fixed size array; missing keys have value '-'. newDAT :: Int32 -> IO (DAT) newDAT n = do a <- newArray (0, n - 1) '-' return (DAT a) -- lookup an item. lookupDAT :: DAT -> Int32 -> IO (Maybe Char) lookupDAT (DAT a) i = do c <- readArray a i return (if c=='-' then Nothing else Just c) -- insert an item insertDAT :: DAT -> Int32 -> Char -> IO () insertDAT (DAT a) i v = writeArray a i v -- get all associations (exclude missing items, i.e. those whose value is '-'). getAssocsDAT :: DAT -> IO [(Int32,Char)] getAssocsDAT (DAT a) = do assocs <- getAssocs a return [ (k,c) | (k,c) <- assocs, c /= '-' ] I then have a main program that initializes a new table, forks some threads, with each thread writing and reading some fixed number of values to the just initialized table. The overall number of elements to write is fixed. The number of threads to use is a taken from a command line argument, and the elements to process are evenly divided among the threads. -- file DirectTableTest.hs import DirectAddressTable import Data.Int (Int32) import Control.Concurrent import Control.Parallel import System.Environment main = do args <- getArgs let numThreads = read (args !! 0) vs <- sequence (replicate numThreads newEmptyMVar) a <- newDAT arraySize sequence_ [ forkIO (doLotsOfStuff numThreads i a >>= putMVar v) | (i,v) <- zip [1..] vs] sequence_ [ takeMVar v >>= \a -> getAssocsDAT a >>= \xs -> print (last xs) | v <- vs] doLotsOfStuff :: Int -> Int -> DAT -> IO DAT doLotsOfStuff numThreads i a = do let p j c = insertDAT a j c >> lookupDAT a j >>= \v -> v `pseq` return () sequence_ [ p j c | (j,c) <- bunchOfKeys j ] return a where bunchOfKeys i = take numElems $ zip cyclicIndices $ drop i cyclicChars numElems = numberOfElems `div` numThreads cyclicIndices = cycle [0..highestIndex] cyclicChars = cycle chars chars = ['a'..'z'] -- Parameters arraySize :: Int32 arraySize = 100 highestIndex = arraySize - 1 numberOfElems = 10 * 1000 * 1000 I compiled this with "ghc --make -rtsopts -threaded -fforce-recomp -O2 DirectTableTest.hs". Running "time ./DirectTableTest 1 +RTS -N1" takes about 1.4 seconds and running "time ./DirectTableTest 2 +RTS -N2" take about 2.0 seconds! Using one more core than worker threads is a little better, with "time ./DirectTableTest 1 +RTS -N1" takes about 1.4 seconds and running "time ./DirectTableTest 1 +RTS -N2" and "time ./DirectTableTest 2 +RTS -N3" both taking about 1.4 seconds. Running with the "-N2 -s" option shows that productivity is 95.4% and GC is 4.3%. Looking at a run of the program with ThreadScope I don't see anything too alarming. Each HEC yields once per ms when a GC occurs. Running with 4 cores gives a time of about 1.2 seconds, which is at least a little better than 1 core. More cores doesn't improve over this. I found that changing the array type used in the implementation of DirectAddressTable from IOArray to IOUArray fixes this problem. With this change, the running time of "time ./DirectTableTest 1 +RTS -N1" is takes about 1.4 seconds whereas the running "time ./DirectTableTest 2 +RTS -N2" is about 1.0 seconds. Increasing to 4 cores gives a run time of 0.55 seconds. Running with "-s" shows a GC time of %3.9 percent. Under ThreadScope I can see that both threads yield every 0.4 ms, more frequently than in the previous program. Finally, I tried one more variation. Instead of having the threads work on the same shared array, I had each thread work on its own array. This scales nicely (as you would expect), more or less like the second program, with either IOArray or IOUArray implementing the DirectAddressTable data structure. I understand why IOUArray might perform better than IOArray, but I don't know why it scales better to multiple threads and cores. Does anyone know why this might be happening or what I can do to find out what is going on? Regards, Andreas

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Function composition in run-time?
by dokondr 24 Aug '11

24 Aug '11

Hi, What is the Haskell way to compose functions in run-time? Depending on configuration parameters I need to be able to compose function in several ways without recompilation. When program starts it reads configuration parameters from a text file. For example, I have three functions, f1, f2, f3, each doing some string processing. I need to support two configurations of string processors : if param1 then sp = f1 . f2 . f3 else sp = f1 . f3 I'd like to avoid 'if' somehow and instead use some declarative way to specify code to run in external configuration file. In other words I need some easy tools to create mini DSLs without all the efforts usually involved with implementing full-blown DSL. Thanks, Dmitri

5 7

different results after compilation
by Комар Максим 24 Aug '11

24 Aug '11

I have some script: $ runhaskell readfile.hs fromList [(Merchant {nick = "01010", location = "prontera", x = 184, y = 94},Shop {buy = ShopBuy {titleB = "AB> Green Salad=5k", itemsB = fromList [(Item {itemId = 12065, price = 5000, refine = "", card1 = 0, card2 = 0, card3 = 0, card4 = 0},(100,97))]}, sell = ShopSell {titleS = "", itemsS = fromList []}})] $ ghc --make readfile.hs Linking readfile ... $ ./readfile $ why results are different?

3 2

- Try to install ssh package by cabal.
by Loïc Maury 24 Aug '11

24 Aug '11

Hello, I try to install the ssh package with cabal, but unfortunately that doesn't work, I have this error : src/SSH/Crypto.hs:70:16: Couldn't match expected type `Data.ASN1.Types.ASN1t' with actual type `ASN1ConstructionType' I'am on Debian with ghc-7.0.1 I don't know how I can resolve this issue ? Thank you for help Loïc

2 2

Conflict with Network.CGI and System.Random
by william murphy 24 Aug '11

24 Aug '11

Hello all, I'm trying to write a program to be converted into a cgi file using Network.CGI and Text.Xhtml, and I want to have random numbers in it. Sounds simple, but I need to call the global random generator (I think) and I can't do that in the CGI block, i.e. cgiTMain = do gen <- getStdGen ... simply doesn't work, nor an variation of calling a function in the cgiTMainblock with a type of IO(), which is what I need to get the generator. Is it impossible both to write a program using Network.CGI and have random values? That seems very limiting, the people that wrote Haskell were smarter than that... Thanks, Will

2 1

Please take the State of Haskell, 2011 survey
by Johan Tibell 23 Aug '11

23 Aug '11

Hi all, I've put together a quick, 12-question State of Haskell, 2011 survey: http://blog.johantibell.com/2011/07/its-time-for-this-years-state-of.html The survey will hopefully give us some insight into how people use Haskell and perhaps also some ideas on how Haskell tools and libraries could be improved. This is the second year I run this survey. New from last year are specific questions on library support and reasoning about run-time performance. P.S. Please direct replies to this email to haskell-cafe(a)haskell.org. Cheers, Johan

4 5

Post-doc position
by Jacques Carette 23 Aug '11

23 Aug '11

People interested in (typed) code generation might be interested (or know people who are) in the following post-doc position. While the 'topic' is design for multiple visual scales, the tools used in practice will be DSLs and (typed) code generators. We use Haskell for implementing all of our DSLs (see [1] for details of part of the ongoing work). Feel free to contact me for further details. Jacques [1] http://www.cas.mcmaster.ca/~carette/SAGA/ [Sorry for the bad formatting, this 'ad' was unfortunately born as a Word document. Not my choice.] ============= Council on Library and Information Resources (CLIR) Postdoctoral Fellowship in Design for Multiple Visual Scales at McMaster University The Computing and Software Department and the University Library at McMaster University in Hamilton, Ontario, Canada invite applications for a two-year CLIR Postdoctoral Fellowship in software design, with an emphasis on games, for multiple visual scales, from the iPod Touch to 60inch high-resolution screen panels. The Fellowship is part of the Gaming Scalability Environment (G-ScalE) project involving Dr. Jacques Carette (Computing and Software, Faculty of Engineering), Dr. Andrew Mactavish (Multimedia, Faculty of Humanities), and Jeff Trzeciak (University Librarian). The fellow will start immediately and report to Dr. Carette but also work closely with the library on certain projects. Duties • Work with Dr. Carette and his students to identify all of the issues relating to usability at different scales, then help design (and implement) a set of domain-specific languages which capture the constraints of user-interface features with respect to scale. o From the psychology and user-interface literature, identify cognitive issues relating to scale perception, and capture these in a formal model. Examples: Fitts’ Law, Hick’s Law and the Steering Law; o Identify examples of such concerns, and pre-existing solutions, from existing software which works at multiple scales; put an emphasis on solutions concerning gaming software; o Relate these models and solutions to design constraints for features in software; o Embody these design constraint into a set of domain specific languages; and o Provide interpreters for these languages. • The above work will be done in conjunction with a number of other researchers and students, and is expected to lead to several peer-reviewed publications, as well as working software. • The candidate will be expected to teach one course (in the CAS department). • The candidate will be expected to work with the library to: o Identify the current and future library needs of Engineering faculty and students; o Assess current state of library resources, services and facilities in support of Engineering; o Make recommendations to the library administration for improvement; o Promote greater awareness of library resources, services and facilities within Engineering; o Promote greater awareness within the library of the faculty’s teaching and research priorities ; and o Provide support as needed to students and faculty within Engineering. Required Skills: • Ph.D. in Computer Science or Software Engineering is preferred, but a Ph.D. in psychology, human factors, or mathematics accompanied by a demonstrable expertise in software development and mathematical modelling. • Interest in multi-disciplinary work. • Capable of understanding the requirements of faculty and students in Engineering with regards to library resources, services and facilities. How to Apply If you have received your Ph.D. within the last five years and are interested in this fellowship, please email your curriculum vitae to abishop(a)clir.org. The Council on Library and Information Resources (CLIR) is an independent, nonprofit organization that forges strategies to enhance research, teaching, and learning environments in collaboration with libraries, cultural institutions, and communities of higher learning. CLIR promotes forward-looking collaborative solutions that transcend disciplinary, institutional, professional, and geographic boundaries in support of the public good.

1 0

Is there anyone interested in translating Haskell Report 2010 to Chinese?
by Qiuchi Jian 23 Aug '11

23 Aug '11

Hi, I am trying to read and translate the 2010 Haskell Report to Chinese for fun. I am wondering if anyone would like to join me. Cheers, Qiuchi

2 1

Why no Monoid, Num, Integral, or Floating RVarT instances?
by Barend Venter 23 Aug '11

23 Aug '11

It seems like you should be able to get instances for: (Monoid m) => Monoid (RVarT n m) (Num m) => Num (RVarT n m) and so forth for integral and floating Just wondering if I am missing something here or if there is any particular thing I'm missing. I am aware you would probably not be able to do an Eq or Show instance but me understanding was that in the case of the (Num b) => Num (a -> b) instance the solution was simply to leave those things undefined.

3 2

how long could it wait for an account on hackageDB?
by Qi Qi 23 Aug '11

23 Aug '11

Hello all, I wanted to have an account on hackageDB to upload a package. I followed http://hackage.haskell.org/packages/accounts.html, and sent an email to ross(a)soi.city.ac.uk for asking an account. It's been a couple days that I haven't heard back. Is this normal, or I have to do something else? Thanks, -- Qi Qi

2 1

Re: [Haskell-cafe] Question about data
by David Barbour 22 Aug '11

22 Aug '11

In addition to fixing 'Float', you should define the 'Fractional' instance for MathExpression. This would let you use: let pi = 3.14 :: MathExpression So your instance of Fractional would look like: instance Num MathExpression where (+) a b = Add a b (*) a b = Multiply a b (-) a b = Subtract a b negate b = Subtract 0 b fromInteger = MathFloat . fromInteger abs = undefined signum = undefined instance Fractional MathExpression where fromRational = MathFloat . fromRational (/) a b = Divide a b recip b = Divide 1 b That would give 'fromRational' and 'fromInteger' which are the main numeric conversion functions. Regards, Dave On Fri, Aug 19, 2011 at 1:40 PM, Paul Reiners <paul.reiners(a)gmail.com>wrote: > I've created a simple type declaration: > > data MathExpression = Float > | Add MathExpression MathExpression > | Subtract MathExpression MathExpression > | Multiply MathExpression MathExpression > | Divide MathExpression MathExpression > deriving (Show) > > Now how do I create an instance of MathExpression which is just a Float? >

1 0

ANN: Netwire 1.1.0 and instinct 0.1.0
by Ertugrul Soeylemez 22 Aug '11

22 Aug '11

Hello there, today I have released one new library 'instinct' for neural networks as well as a new revision of my AFRP library 'netwire', which comes along with many new features, but also with largely incompatible changes. Instinct is a library for neural networks, which currently features: * High performance, * arbitrary network models, as long as they don't loop, * reasonably compact memory representation, * backpropagation learning. Netwire is an arrowized functional reactive programming library written with networking applications in mind. Changes include: * Inhibiting signals now contain a SomeException value, * the Wire type has been generalized over the underlying monad. The second change brings up two new features: * Wires over arbitrary monads, hence * pure wires. I appreciate constructive feedback. Enjoy! Greets, Ertugrul -- nightmare = unsafePerformIO (getWrongWife >>= sex) http://ertes.de/

1 0

Is it written down somewhere what sort of things belong in Data.*?
by David Fox 22 Aug '11

22 Aug '11

I'm never quite sure what the distinction is that defines the modules under Data.*. Can anyone explain? -david

2 1

Problem with installing cabal-install on NetBSD.
by Loïc Maury 22 Aug '11

22 Aug '11

Hello, I try to install "cabal-install" on NetBSD. when I launch the installation (by booststrap.sh) and it come to Building cabal-install, it say : Distribution/Compat/FilePerms.hs:33:4 - Not in scope: `throwErrnoPathIfMinus1_' Do you know how I can fix this issue ? Thank you Loïc

1 0

QuasiQuotation with existing parsers
by Ivan Lazar Miljenovic 22 Aug '11

22 Aug '11

For graphviz [1], I'm thinking of adding in some quasi-quoting support for things like record labels [2], to make them easier to use and less verbose to define (i.e. by using actual Dot syntax [3] for them). If I wanted anti-quotation support in those though, what would be the preferable/recommended option? * Extend the current data types to also have the anti-quotation types (but don't export those constructors), adapt the parser accordingly and use that (though for quasi-quotation I'd need to convert the input String into a Text value, as that's what the existing parsers use). However, this means there's a chance that the anti-quotation types will leak through (and possibly cause problems when parsing real Dot code when the anti-quotation notation is found). This second complication could be relaxed with a Bool flag to the parser indicating whether or not anti-quotation should be supported, but it still feels a bit awkward to me. * Define new data types with anti-quotation support with new parsers for them, and after anti-quotation is evaluated convert them to the real data types. Requires duplicate work, etc. [1]: http://projects.haskell.org/graphviz/ [2]: http://hackage.haskell.org/packages/archive/graphviz/2999.12.0.3/doc/html/D… [3]: http://www.graphviz.org/doc/info/shapes.html#record -- Ivan Lazar Miljenovic Ivan.Miljenovic(a)gmail.com IvanMiljenovic.wordpress.com

1 0

custom SQL-to-Haskell type conversion in HDBC
by Henry House 22 Aug '11

22 Aug '11

Does there exist any sample code or other resources on writing a custom SQL-to-Haskell datatype converter instance for use with HDBC that would be accessible to someone just starting with Haskell? The reason I need this is because of this problem (using PostgreSQL): Prelude Database.HDBC.PostgreSQL Database.HDBC> res <- (quickQuery db "select 1::numeric(5,4);" []) Prelude Database.HDBC.PostgreSQL Database.HDBC> res [[SqlRational (1 % 1)]] Prelude Database.HDBC.PostgreSQL Database.HDBC> res <- (quickQuery db "select 1::numeric(5,0);" []) [[SqlRational (1 % 1)]] where db is a database connection. The SQL values 1::numeric(5,4) and 1::numeric(5,0) are supposed to be fixed-precision numbers having 4 and zero significant decimal figures after the decimal point, respectively. Both are offered by HDBC as the same SqlValue, SqlRational (1 % 1) but they are not really the same at all. The precision information has been lost. The native outputs of PostgreSQL, before HDBC's type conversion, are 1.0000 and 1 for 'select 1::numeric(5,4);' and 'select 1::numeric(5,0);', respectively. -- Henry House

4 14

Need help Very strange space behavior
by bob zhang 22 Aug '11

22 Aug '11

Hi all, I thought that Cont Monad is just equivalent to CPS Transformation, so if I have a monadic sum, if I run in Identity Monad, it will suck due to stackoverflow, and if I run it in Cont Monad, it will okay due to tail recursion. So I write a simple program to verify my idea. But to my surprise, the result is unreasonable due to my limited knowledge. All programs are compiled "ghc --make Test.hs -o test && ./test" Thank you in advance, the clearer the better!! (I am really confused) in the comments, suck means stackoverflow. sum0 n = if n==0 then 0 else n + sum0 (n-1) sum1 n = if n==0 then return 0 else sum1 (n-1) >>= \ v -> seq v (return (n+v)) sum2 n k = if n == 0 then k 0 else sum2 n (\v -> k (n + v)) sum3 n k = if n == 0 then k 0 else sum3 n (\ !v -> k (n + v)) sum4 n k = if n == 0 then k 0 else sum4 n (\ v -> seq v ( k (n + v))) sum5 n = if n==0 then return 0 else sum5 (n-1) >>= \ v -> (return (n+v)) -- main = print (sum0 3000000) -- suck reasonable -- main = print (flip runCont id (sum1 3000000)) -- rock 180M memory reasonable, but I am not clear why seq needed here, since its continuation is not applied until n goes to 0 -- main = print (flip runCont id (sum5 3000000)) -- suck -- why? -- main = print (flip runCont (const 0) (sum1 3000000)) -- rock 130M memory -- reasonable -- main = print (flip runCont (const 0) (sum5 3000000)) -- rock 118M memory -- reasonable -- main = print (sum2 3000000 (const 0)) -- a lot of memory (more than 1G) -- I thought sum2 is equivalent to sum5 (when sum5 is in Cont Monad), why? -- main = print (sum3 3000000 (const 0)) -- a lot of memory -- I thought sum3 is equivalent to sum1(Cont Monad), why? -- main = print (runIdentity (sum1 3000000)) -- suck -- exactly what I want -- main = print (sum3 3000000 id) -- a lot of memory -- equivalent to sum1 why? -- main = print (sum4 3000000 id) - - a lot of memory -- equivalent to sum1 why? -- main = print (sum [1 .. 3000000]) -- suck -- src sum = foldl (+) 0 -- reasonable -- main = print (foldl' (+) 0 [1 .. 3000000]) -- rock 1.5M memory -- reasonable -- Best, bob

1 0

Re: [Haskell-cafe] Failed link to mixed-language shared object
by David Banas 21 Aug '11

21 Aug '11

> ghc -dynamic -o ami_test -L. -lami ami_test.o > ./libami.so: undefined reference to `__stginit_haskell98_MarshalArray_' > ./libami.so: undefined reference to `__stginit_haskell98_MarshalError_' > collect2: ld returned 1 exit status I was able to solve this by changing these lines: import MarshalArray import MarshalError to read: import Foreign.Marshal.Array import Foreign.Marshal.Error I don't understand why this worked, since the available symbols in the 2 respective libraries appear totally similar: dbanas@dbanas-eeepc:/usr/lib/ghc-6.12.3$ nm -g haskell98-1.0.1.1/libHShaskell98-1.0.1.1.a | grep 'MarshalArray' MarshalArray__1.o: 00000030 T __stginit_haskell98_MarshalArray 00000000 T __stginit_haskell98_MarshalArray_ dbanas@dbanas-eeepc:/usr/lib/ghc-6.12.3$ nm -g -D haskell98-1.0.1.1/libHShaskell98-1.0.1.1-ghc6.12.3.so | grep 'MarshalArray' 00002b68 T __stginit_haskell98_MarshalArray 00002b24 T __stginit_haskell98_MarshalArray_dyn dbanas@dbanas-eeepc:/usr/lib/ghc-6.12.3$ nm -g base-4.2.0.2/libHSbase-4.2.0.2.a | grep '__stginit_.*Foreign.*Marshal.*Array' 0000006c T __stginit_base_ForeignziMarshalziArray 00000000 T __stginit_base_ForeignziMarshalziArray_ {Some output omitted.} dbanas@dbanas-eeepc:/usr/lib/ghc-6.12.3$ nm -g -D base-4.2.0.2/libHSbase-4.2.0.2-ghc6.12.3.so | grep '__stginit_.*Foreign.*Marshal.*Array' 003dc8cc T __stginit_base_ForeignziMarshalziArray 003dc834 T __stginit_base_ForeignziMarshalziArray_dyn Can anyone shed some light on this? Thanks!

1 0

Embedding Perl RegEx in Haskell
by C K Kashyap 21 Aug '11

21 Aug '11

Dear Haskell folks, I was attempting to do an EDSL that would allow me to describe regular expressions in Hakell and generate Perl as target - https://github.com/ckkashyap/LearningPrograms/blob/master/Haskell/edsl/rege… $ ghci regex.hs GHCi, version 7.0.3: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. Loading package ffi-1.0 ... linking ... done. [1 of 1] Compiling Main ( regex.hs, interpreted ) Ok, modules loaded: Main. *Main> let hello = stringToRegularExpression "hello" *Main> let world = stringToRegularExpression "world" *Main> :t hello hello :: RegularExpression *Main> :t world world :: RegularExpression *Main> let re = listToSequence [ hello, oneOrMore world, hello ] *Main> re hello(world)+hello *Main> :t re re :: RegularExpression I am looking for suggestions on how I could encode the anchors - ^ and $ and also how I could refer to captures. My goal is to be able to extend the idea to create an EDSL that could be used to build Perl tasks - such as filters, report generators etc Arguably this could be seen as a pointless exercise because I could chose to do the scripting in Haskell itself but I have a practical problem that I have to deal with clusters that have a little dated version of Linux where I could not really build the Haskell and where Haskell generated executables don't seem to run. When I started out with this idea, I was thinking of embedding Perl in Haskell but later I thought that perhaps that will sort of beat the point of "DS" bit in EDSL. So, I have started on this idea of trying to encode very precise "tasks". Regards, Kashyap

2 5

Existential question
by Tom Schouten 20 Aug '11

20 Aug '11

{-# LANGUAGE ExistentialQuantification #-} -- Dear Cafe, this one works. data Kl' s i o = Kl' (i -> s -> (s, o)) iso' :: (i -> Kl' s () o) -> Kl' s i o iso' f = Kl' $ \i s -> (\(Kl' kl') -> kl' () s) (f i) -- Is there a way to make this one work also? data Kl i o = forall s. Kl (i -> s -> (s, o)) iso :: (i -> Kl () o) -> Kl i o iso f = Kl $ \i s -> (\(Kl kl) -> kl () s) (f i) {- Couldn't match type `s0' with `s' because type variable `s' would escape its scope This (rigid, skolem) type variable is bound by a pattern with constructor Kl :: forall i o s. (i -> s -> (s, o)) -> Kl i o, in a lambda abstraction The following variables have types that mention s0 s :: s0 (bound at /home/tom/meta/haskell/iso.hs:11:17) In the pattern: Kl kl In the expression: \ (Kl kl) -> kl () s In the expression: (\ (Kl kl) -> kl () s) (f i) -}

2 2

Segfault in the libc malloc using FFI (occurs only in x86_64)
by Vincent Gerard 20 Aug '11

20 Aug '11

Hi cafe, I have been struggling with this issue for the past days. I have investigated at the Haskell, C and even at assembly level... Perhaps I'm missing something big ?? I hope someone familiar with FFI could help me on this Segfault. My env is: Linux Debian 3.0.0-1, SMP, GHC 7.0.4, x86_64, eglibc 2.13-10 (This issues occurs as well on others people with /= env, but only with x86_64 arch) The bug is in the hsmagick library (FFI bindings to GraphicsMagick), for which I am the maintainer. -- So here is a reproducer (Works fine in 32 bit, segfault in 64). You should have hsmagick + GraphicsMagick dev libs installed. import Graphics.Transform.Magick.Images main = do initializeMagick c <- readImage "image.jpg" putStrLn "End" -- Executing this program, compiled with standard options, a Segfault occurs at runtime. If I compile this small program with -threaded option an assertion error is thrown at runtime: main: malloc.c:3096: sYSMALLOc: Assertion `(old_top == (((mbinptr) (((char *) &((av)->bins[((1) - 1) * 2])) - __builtin_offsetof (struct malloc_chunk, fd)))) && old_size == 0) || ((unsigned long) (old_size) >= (unsigned long)((((__builtin_offsetof (struct malloc_chunk, >fd_nextsize))+((2 * (sizeof(size_t))) - 1)) & ~((2 * (sizeof(size_t))) >- 1))) && ((old_top)->size & 0x1) && ((unsigned long)old_end & >pagemask) == 0)' failed. This assertion error is cryptic for me... but it maybe could help someone here. However, having a C experience, investigating a Segfault is in my habits, so let's install debugs symbols on everything and dig with gdb. Here is the backtrace: Program received signal SIGSEGV, Segmentation fault. 0x00007ffff510292c in malloc_consolidate (av=0x7ffff540fe60) at malloc.c:5161 (this is inside the eglibc source) 5161 unlink(p, bck, fwd); (gdb) bt #0 0x00007ffff510292c in malloc_consolidate (av=0x7ffff540fe60) at malloc.c:5161 #1 0x00007ffff5104d64 in _int_malloc (av=0x7ffff540fe60,bytes=8520) at malloc.c:4373 #2 0x00007ffff5107420 in __libc_malloc (bytes=8520) at malloc.c:3660 #3 0x00007ffff67bf311 in CloneImageInfo (image_info=0x0) at magick/image.c:1012 #4 0x0000000000439dfa in hsmagickzm0zi5_GraphicsziTransformziMagickziFFIHelpers_mkNewImageInfo1_info () Yay, the Segfault is deep in the libc after a regular malloc (8520bytes) (I dug into the GraphicsMagick source starting from magick/image.c:1012) And this libc call is called by a call to CloneImageInfo(NULL) from Haskell, which is correct as it is graphicsMagick way to allocate an empty ImageInfo data structure. (http://www.graphicsmagick.org/api/image.html#cloneimageinfo) I tried in a C program to execute (after initializing ImageMagick) image_info=CloneImageInfo((ImageInfo *) NULL); And of course .... no Segfault... Let's look at the FFI call... This FFI call is the done by the mkNewImageInfo as shown in the trace. The Haskell FFI layer here has done the right job, calling the C function with the right args (NULL) Here is all the code related to mkNewImageInfo (the last Haskell part we see in the backtrace) --- mkNewImageInfo :: IO (ForeignPtr HImageInfo) mkNewImageInfo = mkFinalizedImageInfo =<< mkNewImageInfo_ mkFinalizedImageInfo :: Ptr HImageInfo -> IO (ForeignPtr HImageInfo) mkFinalizedImageInfo = newForeignPtr imageInfoFinalizer mkNewImageInfo_ :: IO (Ptr HImageInfo) mkNewImageInfo_ = clone_image_info nullPtr -- CALL before the Segfault destroyImageInfo :: Ptr HImageInfo -> IO () destroyImageInfo = destroy_image_info foreign import ccall "static magick/api.h &DestroyImageInfo" imageInfoFinalizer :: FunPtr (Ptr HImageInfo -> IO ()) foreign import ccall "static magick/api.h CloneImageInfo" clone_image_info :: Ptr HImageInfo -> IO (Ptr HImageInfo) -- To me, this code is right (and works perfectly in 32 bit). Furthermore, as the call is made with a nullPtr arg, no data structure is used ... I tried this code without using ForeignPtr Finalizers (hsmagick <= 0.4) and the Segfault occurs as well ... I even had a look at the generated assembly, which also looks right... It seems there is a real segmentation error, or an illegal access to a memory page... But I could not find the root cause of this error. And an additionnal piece to the puzzle, when running the program inside valgrind, there is no Segfault and the program works as expected. So if anyone have an idea on how only on 64bits arch an Haskell FFI call could led to a Segfault in the libc malloc, it would make my day, perhaps my week :) Thanks ! Vincent Gerard

3 2

Simon PJ in Australia
by Simon Peyton-Jones 20 Aug '11

20 Aug '11

This is a message for Australian FPers -- sorry to spam the rest of you. I'm crossing the planet to Australia for YOW (Melbourne Dec 1-2, Brisbane Dec 5-6). http://www.yowconference.com.au/YOW2011/ I'm committed for the conference dates of course, but I could spend a few days before or afterwards, hanging out with some of you guys. Hack on GHC, give a talk, eat pizza, university departments, Haskell users groups, surfing (on water, that is).... Do drop me (not the list) a line if any of that sounds fun. Simon PS: John Hughes is coming to Yow too, so you could try luring him into your lair too.

5 4

Question about data
by Paul Reiners 19 Aug '11

19 Aug '11

I've created a simple type declaration: data MathExpression = Float | Add MathExpression MathExpression | Subtract MathExpression MathExpression | Multiply MathExpression MathExpression | Divide MathExpression MathExpression deriving (Show) Now how do I create an instance of MathExpression which is just a Float? This doesn't work: *Main> let pi = 3.14 :: MathExpression <interactive>:1:10: No instance for (Fractional MathExpression) arising from the literal `3.14' Possible fix: add an instance declaration for (Fractional MathExpression) In the expression: 3.14 :: MathExpression In an equation for `pi': pi = 3.14 :: MathExpression

5 4

why is Random in System?
by Evan Laforge 19 Aug '11

19 Aug '11

I've noticed there's a convention to put modules having to deal with randomness into System.Random. I thought System was for OS interaction? Granted getting a random seed usually means going to the OS, but isn't the rest of it, like generating random sequences, distributions, selecting based on probability, shuffling, etc. all non-OS related algorithms? I'm not sure where I would expect Random to go, perhaps Math or maybe the toplevel, but under System seems, well, random... I notice random-fu puts it under Data, which is also not where I'd look, except that you always look in Data because everything goes into Data... but algorithms dealing with random numbers aren't really data structures either, are they?

8 14

Can I have a typeclass for topological spaces?
by Grigory Sarnitskiy 19 Aug '11

19 Aug '11

Hello! I just wonder whether it is possible to have a typeclass for topological spaces?

3 3

Failed link to mixed-language shared object.
by David Banas 19 Aug '11

19 Aug '11

Hi all, Does this trigger recollection in anyone: dbanas@dbanas-eeepc:~/prj/haskell/AMIParse/trunk$ make ghc -dynamic -o ami_test -L. -lami ami_test.o ./libami.so: undefined reference to `__stginit_haskell98_MarshalArray_' ./libami.so: undefined reference to `__stginit_haskell98_MarshalError_' collect2: ld returned 1 exit status make: *** [ami_test] Error 1 dbanas@dbanas-eeepc:~/prj/haskell/AMIParse/trunk$ ? Know what I need to do? Thanks, -db

2 2

Problem with types
by Anupam Jain 19 Aug '11

19 Aug '11

Hi all, Suppose I have a compound data type - data M o = M (String,o) Now, I can define a function that works for ALL M irrespective of o. For example - f :: M o -> M o f (M (s,o)) = M (s++"!", o) I can also use this function in an expression, applying it to different types without problem - p = (m1',m2') where m1 = M ("1", ()) m2 = M ("2", True) m1' = f m1 m2' = f m2 Main*> p (M ("1!",()),M ("2!",True)) However, if I try to parameterise over the function 'f' it does not work! - p f = (m1',m2') where m1 = M ("1", ()) m2 = M ("2", True) m1' = f m1 m2' = f m2 It doesn't even typecheck, producing the error - "Couldn't match expected type 'Bool' with actual type '()'" Is there a particular reason for this? How can I define a function like 'p' within Haskell? Thanks, Anupam Jain

4 3

Compilation error in Chapter 5 of "Real World Haskell"
by Paul Reiners 18 Aug '11

18 Aug '11

I'm trying to do the following from Chapter 5 of "Real World Haskell": Our choice of naming for the source file and function is deliberate. To create an executable, *ghc* expects a module named Main that contains a function named main. The main function is the one that will be called when we run the program once we've built it. 6 comments<comments:%20show%20/%20hide> *ghc -o simple Main.hs SimpleJSON.o* ---from http://book.realworldhaskell.org/read/writing-a-library-working-with-json-d… When I do that, I get this error: C:\ch05>ghc -o simple Main.hs SimpleJSON.o [2 of 2] Compiling Main ( Main.hs, Main.o ) Linking simple.exe ... SimpleJSON.o:fake:(.data+0x0): multiple definition of `SimpleJSON_getArray_closure' .\SimpleJSON.o:fake:(.data+0x0): first defined here SimpleJSON.o:fake:(.text+0x54): multiple definition of `SimpleJSON_getArray_info' .\SimpleJSON.o:fake:(.text+0x54): first defined here SimpleJSON.o:fake:(.data+0x4): multiple definition of `SimpleJSON_getObject_closure' .\SimpleJSON.o:fake:(.data+0x4): first defined here What's going wrong here?

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writing a good Setup.hs is *hard* (was: broken on install encoding 0.6.6)
by Rogan Creswick 18 Aug '11

18 Aug '11

On Wed, Aug 17, 2011 at 6:29 AM, Gang <yugang.bj(a)gmail.com> wrote: > > sorry to bother > Not in the least! I was trying to figure out what problem you were encountering, and I learned a lot. I never did recreate your problem, but in the process I ran into a whole host of other annoyances and strange situations relating to slightly broken cabal files and cabal build intricacies that confound our existing tools. I don't mean to pick on encoding or HaXml - I've seen the same kinds of issues in many, many Haskell packages (including most of the packages I've written myself) these are just the ones I ran into today. (and I am quite serious when I say that writing a good Setup.hs is very, very, difficult). My objective is just to motivate a minor change to cabal that would help to make this easier. On to the build problems: encoding-0.6.6 uses it's own source during the build process! It actually has to be partially compiled before the build tool can build encoding (!). I'm *amazed* that this actually works at all (impressed, too), and indeed, it doesn't work with cabal-dev, which is unfortunate: cabal-dev would have identified one of the dependency issues in HaXml 1.19 (pretty is an undocumented dependency, although I am unsure if that was true at the time 1.19 and encoding-0.6.6 were released. I haven't tracked the pretty dependency down to the exact source - it could be a transitive dep introduced by a recent version of something HaXml 1.19 needs. Per my subject line - this is amazingly difficult - keep in mind that we're not talking about building *packages*, this is just to build the *build tool*, and none of this is documented. How long before it is effectively impossible to recreate the circumstances that result in a successful encoding-0.6.6 build?). cabal-dev can't build encoding-0.6.6 because the encoding source that is referenced from encoding's Setup.hs depends on (at least) HaXml >= 1.19 && < 1.22.5; this is OK with cabal, since cabal-install installs a necessary HaXml into your user package db prior to building encoding's Setup.hs (modulo the missing upper version bound). Therefore HaXml "just happens" to be visible when cabal builds Setup.hs -- a build step that cabal-dev isn't capable of controlling (and probably never will be -- we could intercept system calls, but that's difficult when only supporting one OS, much less three). You can, of course, manually install HaXml to your local package db and then cabal-dev install encodings, but that's somewhat of a hack (and you'll find that the current HaXml won't work for the current encodings release, as Gang Yu did). Adding a section to the cabal file that specifies build dependencies for Setup.hs would make some very important parts of this process obvious - and it would *greatly* assist in debugging failing builds, not to mention allowing us to make use of the extensive libraries on hackage to write more expressive build systems. (We could actually use openshake in Setup.hs, once it's released, for example!) I've floated the idea past a number of Haskell programmers with positive responses, and there is a GSOC ticket that provides some more details (the project was not selected - no students proposed to work on it): http://hackage.haskell.org/trac/summer-of-code/ticket/1602 --Rogan > Regards > Gang > On 08/17/2011 04:59 PM, Gang Yu wrote: > > hi, cafe: > > I go through to the encoding package installation problem again. > > cabal install encoding > Resolving dependencies... > /tmp/encoding-0.6.68093/encoding-0.6.6/dist/setup/setup: 4: Syntax error: > ";" unexpected > > when I have a check on the this issue, I get: > > file > ~/.cabal/packages/hackage.haskell.org/encoding/0.6.6/encoding-0.6.6/dist/setup/setup > /home/gang/.cabal/packages/hackage.haskell.org/encoding/0.6.6/encoding-0.6.6/dist/setup/setup: > ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked > (uses shared libs), for GNU/Linux 2.6.27, not stripped > > My machine is: > > gang@gang-laptop:~$ uname -a > Linux gang-laptop 2.6.38-8-generic #42-Ubuntu SMP Mon Apr 11 03:31:50 UTC > 2011 i686 i686 i386 GNU/Linux > > is this related? How can I manually install the package from scratch? Any > helps or directs will be appreciated > > Thanks > Gang > > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > >

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Gaussian elimination
by Tobias Nipkow 18 Aug '11

18 Aug '11

Hi, I came up with the following extremely compact version of Gaussian elimination for matrices represented as functions. I searched the web but found nothing resembling it, probably because of its inefficiency. Has anybody seen something like it before? Thanks Tobias gauss :: Int -> (Int -> Int -> Rational) -> Maybe (Int -> Int -> Rational) gauss 0 a = Just a gauss (n+1) a = case dropWhile (\i -> a i n == 0) [0..n] of [] -> Nothing (k:_) -> let ak' j = a k j / a k n a' i = if i == k then ak' else (\j -> a i j - a i n * ak' j) in gauss n (swap k n a') swap :: Int -> Int -> (Int -> a) -> (Int -> a) swap k n f = g where g x | x == k = f n | x == n = f k | otherwise = f x

1 0

conditionally exposing modules in cabal
by Rogan Creswick 18 Aug '11

18 Aug '11

I would like to conditionally expose a number of internal modules in a library depending on a cabal flag - the idea is that new features could be implemented externally to the library without contaminating the source with undesirable changes. However, I've been unable to find a way to structure a cabal file that does not require repeating the list of modules. For example, this works: exposed-modules: Public.Stable.Module if flag(exposeInternals) exposed-modules: <long list of internal modules> else other-modules: <long list of internal modules, identical to above> But I don't want to maintain two identical lists of modules in the cabal file. I've tried putting the section headers in the if's, but this doesn't appear to work (cabal doesn't complain, but the modules to be exposed are not available as expected): exposed-modules: Public.Stable.Module if flag(exposeInternals) { exposed-modules: } else { other-modules: } <long list of internal modules> Does anyone have suggestions? Thanks! Rogan

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FFI question - FunPtrs to top-level functions
by Antoine Latter 18 Aug '11

18 Aug '11

Hi Haskell, I have a question about the Haskell FFI and creating FunPtrs to Haskell functions. Does anyone have any recommendations for when I have a top-level function that I would like to pass to a C function as a function pointer (that is called via a foreign import)? I know that the FFI provides the "wrapper" foreign import I can use to wrap Haskell functions, but then I would need to jump through hoops to manage the liefetime of of the FunPtr wrapper. If I were closing over interesting state I would want this - but the function (side-effectfully) operates only on its arguments (and the Haskell RTS, of course). Is it "okay" to place an "unsafePerformIO $ mkWrapper myFunc" as a top-level declaration, or am I journeying into uncharted lands? Is there something clever I can do with foreign exports and foreign imports, or is this just making things too complex? Thanks, Antoine

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Haskell Weekly News: Issue 195
by Daniel Santa Cruz 18 Aug '11

18 Aug '11

Welcome to issue 195 of the HWN, a newsletter covering developments in the Haskell community. This release covers the week of August 7 to 13, 2011. [1] http://goo.gl/8hDku You can find a HTML rendition of this newsletter at: http://contemplatecode.blogspot.com/2011/08/haskell-weekly-news-issue-195.h… Announcements Luite Stegeman created a nifty tool called hdiff, which shows code changes between different versions of hackage packages. [2] http://goo.gl/uqh97 New and Updated Projects * Netwire (New - Ertugrul Soeylemez) Arrowised FRP library. [3] http://goo.gl/tVlsH * Snap Riak Extensions (New - Edward Tate). [4] http://goo.gl/O0C2A * time (Update - Ashley Yakeley) Adds "instance RealFrac DiffTime". [5] http://goo.gl/Wm3UY * file-location (Update - Greg Weber) Error and debug information for haskell that gives file locations. [6] http://goo.gl/fTG4P * HTTP (Update - Ganesh Sittampalam) Bumps base dependency to work with GHC 4.2.1 [7] http://goo.gl/bydXi * hslogger, convertible, HDBC, HDBC-odbc, HDBC-postgresql, HDBC-sqlite3 (Update - John Goerzen) Update license to BSD3. [8] http://goo.gl/sD0Qg * taffybar (New - Tristian Ravitch) Slightly fancier status bar for xmonad. [9] http://goo.gl/SlNgi Quotes of the Week * Brend: Whoever chose the title "A Gentle Introduction to Haskell" is obviously accustomed to wrestling bears in piranha pits or something. * kmc: compare "trifecta" "parsec" --> GT * elliott: ... demonstrating C++ templates' wide range of expressivity in applications from stupid compile-time hacks to _really_ stupid compile-time hacks * solrize: "The last good thing written in C was Schubert's Ninth Symphony." * cmccann: [I] learned Haskell mostly by typing a lot of really dumb things into an editor window, then feeding them to GHC Top Reddit Stories * Simon Marlow: “[…] I think I finally understand how to track call stacks properly in a lazy functional language. If this pans out, we'll get backtraces in GHCi and more accurate profiling” Domain: plus.google.com, Score: 121, Comments: 15 On Reddit: [10] http://goo.gl/0DTba Original: [11] http://goo.gl/yIhnI * A Very General Method of Computing Shortest Paths (the Gauss-Jordan-Floyd-Warshall- McNaughton-Yamada algorithm) Domain: r6.ca, Score: 41, Comments: 8 On Reddit: [12] http://goo.gl/dgW4s Original: [13] http://goo.gl/e8ZBF * I'm reading http://www.cs.ru.nl/~wouters/Publications/ThePowerOfPi.pdf What is this syntax called and where can I learn it? Domain: imgur.com, Score: 36, Comments: 15 On Reddit: [14] http://goo.gl/FpFIu Original: [15] http://goo.gl/CE9Dz * Simon Marlow: "If you're using GHC 7.2.1 and find a performance loss relative to an earlier GHC, trying playing around with the new stack option" Domain: plus.google.com, Score: 25, Comments: 8 On Reddit: [16] http://goo.gl/2FTsH Original: [17] http://goo.gl/CJZsR * In your haskell-dreams, how does a shell look? Domain: self.haskell, Score: 23, Comments: 43 On Reddit: [18] http://goo.gl/jGyqH Original: [19] http://goo.gl/jGyqH * SO: Converting floating point between Word and Float/Double (my poor, unanswered question!) Domain: stackoverflow.com, Score: 21, Comments: 3 On Reddit: [20] http://goo.gl/csKRb Original: [21] http://goo.gl/JFDn2 * Current status of gtk2hs? Domain: self.haskell, Score: 18, Comments: 10 On Reddit: [22] http://goo.gl/HFwCR Original: [23] http://goo.gl/HFwCR * (Live from CamHac) ANN: fclabels-1.0: First class accessor labels. Domain: hackage.haskell.org, Score: 13, Comments: 19 On Reddit: [24] http://goo.gl/FXdY6 Original: [25] http://goo.gl/Ijl4H * PhD Position availalble at Strathclyde Domain: lists.seas.upenn.edu, Score: 12, Comments: 2 On Reddit: [26] http://goo.gl/FbdNs Original: [27] http://goo.gl/0R8Vi * [GSoC] Text/UTF-8: Studying memory usage of a simple web server Domain: jaspervdj.be, Score: 9, Comments: 1 On Reddit: [28] http://goo.gl/HkcJL Original: [29] http://goo.gl/EQn9h * Arrow = Category + Applicative? (Part IIa) Domain: cdsmith.wordpress.com, Score: 9, Comments: 21 On Reddit: [30] http://goo.gl/hB6YY Original: [31] http://goo.gl/dBSuA Top StackOverflow Questions * Lazy Evaluation vs Macros votes: 19, answers: 5 Read on SO: [32] http://goo.gl/28jcJ * Comparison of Priority Queue implementations in Haskell votes: 16, answers: 1 Read on SO: [33] http://goo.gl/MyMp4 * Converting IEEE 754 floating point in Haskell Word32/64 to and from Haskell Float/Double votes: 16, answers: 4 Read on SO: [34] http://goo.gl/2YaVC * Applicatives compose, monads don't votes: 15, answers: 5 Read on SO: [35] http://goo.gl/Ncdij * How can I speed up my Haskell program (to the level of Python) votes: 13, answers: 3 Read on SO: [36] http://goo.gl/jOXnL * How does ArrowLoop work? Also, mfix? votes: 12, answers: 1 Read on SO: [37] http://goo.gl/JrFRX * How could I remove the "if … then … else …" keywords in Haskell (GHC)? votes: 9, answers: 3 Read on SO: [38] http://goo.gl/gjNrm * how to use hoogle locally (like ctags)? votes: 8, answers: 1 Read on SO: [39] http://goo.gl/IGVEW * Would a type class "between" Category and Arrow make sense? votes: 8, answers: 2 Read on SO: [40] http://goo.gl/zgb7w * Can I avoid "rightward drift" in Haskell? votes: 8, answers: 4 Read on SO: [41] http://goo.gl/pc0Bn * Haskell Polyvariadic Function With IO votes: 8, answers: 4 Read on SO: [42] http://goo.gl/dfUVv * Why don't Haskell compilers facilitate deterministic memory management? votes: 8, answers: 4 Read on SO: [43] http://goo.gl/uhqw6 * Defining a function a -> String, which works for types without Show? votes: 7, answers: 3 Read on SO: [44] http://goo.gl/Mjcfs * Haskell: List Comprehension to Combinatory votes: 7, answers: 3 Read on SO: [45] http://goo.gl/tLryK * Applicative without a functor votes: 7, answers: 3 Read on SO: [46] http://goo.gl/UcXZ5 About the Haskell Weekly News To help create new editions of this newsletter, please send stories to dstcruz(a)gmail.com. Until next time, Daniel Santa Cruz References 1. http://haskell.org/ 2. http://permalink.gmane.org/gmane.comp.lang.haskell.cafe/91658 3. http://permalink.gmane.org/gmane.comp.lang.haskell.cafe/91525 4. http://permalink.gmane.org/gmane.comp.lang.haskell.cafe/91576 5. http://permalink.gmane.org/gmane.comp.lang.haskell.general/18880 6. http://permalink.gmane.org/gmane.comp.lang.haskell.cafe/91590 7. http://permalink.gmane.org/gmane.comp.lang.haskell.general/18883 8. http://permalink.gmane.org/gmane.comp.lang.haskell.cafe/91621 9. http://permalink.gmane.org/gmane.comp.lang.haskell.cafe/91672 10. https://plus.google.com/u/0/107890464054636586545/posts/XE4T6hHm3tK 11. http://www.reddit.com/r/haskell/comments/jdj2r/simon_marlow_i_think_i_final… 12. http://r6.ca/blog/20110808T035622Z.html 13. http://www.reddit.com/r/haskell/comments/jc7pb/a_very_general_method_of_com… 14. http://imgur.com/pPfjs 15. http://www.reddit.com/r/haskell/comments/jbfdc/im_reading/ 16. https://plus.google.com/107890464054636586545/posts/LqgXK77FgfV 17. http://www.reddit.com/r/haskell/comments/jfskp/simon_marlow_if_youre_using_… 18. http://www.reddit.com/r/haskell/comments/jce8q/in_your_haskelldreams_how_do… 19. http://www.reddit.com/r/haskell/comments/jce8q/in_your_haskelldreams_how_do… 20. http://stackoverflow.com/q/6976684/204932 21. http://www.reddit.com/r/haskell/comments/jd6wq/so_converting_floating_point… 22. http://www.reddit.com/r/haskell/comments/jgzcf/current_status_of_gtk2hs/ 23. http://www.reddit.com/r/haskell/comments/jgzcf/current_status_of_gtk2hs/ 24. http://hackage.haskell.org/package/fclabels-1.0 25. http://www.reddit.com/r/haskell/comments/jhoay/live_from_camhac_ann_fclabel… 26. http://lists.seas.upenn.edu/pipermail/types-announce/2011/002643.html 27. http://www.reddit.com/r/haskell/comments/jdjms/phd_position_availalble_at_s… 28. http://jaspervdj.be/posts/2011-08-09-text-utf8-memory-usage.html 29. http://www.reddit.com/r/haskell/comments/jdk6z/gsoc_textutf8_studying_memor… 30. http://cdsmith.wordpress.com/2011/08/13/arrow-category-applicative-part-iia/ 31. http://www.reddit.com/r/haskell/comments/ji8si/arrow_category_applicative_p… 32. http://stackoverflow.com/questions/7046950/lazy-evaluation-vs-macros 33. http://stackoverflow.com/questions/6976559/comparison-of-priority-queue-imp… 34. http://stackoverflow.com/questions/6976684/converting-ieee-754-floating-poi… 35. http://stackoverflow.com/questions/7040844/applicatives-compose-monads-dont 36. http://stackoverflow.com/questions/7003572/how-can-i-speed-up-my-haskell-pr… 37. http://stackoverflow.com/questions/6976944/how-does-arrowloop-work-also-mfix 38. http://stackoverflow.com/questions/6996286/how-could-i-remove-the-if-then-e… 39. http://stackoverflow.com/questions/6989668/how-to-use-hoogle-locally-like-c… 40. http://stackoverflow.com/questions/6997517/would-a-type-class-between-categ… 41. http://stackoverflow.com/questions/7008493/can-i-avoid-rightward-drift-in-h… 42. http://stackoverflow.com/questions/7030476/haskell-polyvariadic-function-wi… 43. http://stackoverflow.com/questions/7038811/why-dont-haskell-compilers-facil… 44. http://stackoverflow.com/questions/7005628/defining-a-function-a-string-whi… 45. http://stackoverflow.com/questions/7007222/haskell-list-comprehension-to-co… 46. http://stackoverflow.com/questions/7024788/applicative-without-a-functor

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Overloading in a sub-class
by Patrick Browne 17 Aug '11

17 Aug '11

Hi, Below are two questions concerning overloading in a sub-class. Thanks, Pat class Numb0 a where (+) :: a -> a -> a negate :: a -> a instance Numb0 Int where x + y = y negate x = x -- Are + and negate part of the signature of Numb1? class Numb0 a => Numb1 a where -- Is it possible to override these operations in instances of Numb1? -- Something like: -- instance Numb1 Float where -- x + y = y -- negate x = x -- Or even using Int as in the super class instance: -- instance Numb1 Int where -- x + y = y -- negate x = x This message has been scanned for content and viruses by the DIT Information Services E-Mail Scanning Service, and is believed to be clean. http://www.dit.ie

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ANNOUNCE: TKYProf
by Mitsutoshi Aoe 17 Aug '11

17 Aug '11

Hi, forks I'm glad to announce the alpha release of TKYProf. http://hackage.haskell.org/package/tkyprof https://github.com/maoe/tkyprof TKYprof is a web-based interacitve visualizer for GHC time and allocation profiling reports. It helps you to find the bottlenecks in your code quickly! Here is a blog post: http://blog.foldr.in/tkyprof-a-web-based-interactive-visualizer-fo It is still alpha and it have some bugs. I'm happy to hear your feedback. Thanks, -- Mitsutoshi Aoe maoe(a)foldr.in

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Haskell transformation of C code
by mukesh tiwari 17 Aug '11

17 Aug '11

Hello all I am trying implement this algorithm [ http://stackoverflow.com/questions/1621364/how-to-find-largest-triangle-in-… ] in Haskell but i am getting wrong answer for some test cases. A c++ implementation which is accepted for this problem [ http://www.spoj.pl/problems/MTRIAREA ] and i rewrote the C++ code in Haskell . Running both programs on some random test cases produce different result . For Haskell implementation , convex hull part is correct . Both codes [ c++ and Haskell ] produced same convex hull so i am skeptical about looPing :: ( Num a , Ord a , Eq a , Floating a ) => Int -> Int -> Int - > Int -> a -> Array Int ( Point a ) -> a and calArea :: ( Num a , Ord a , Floating a ) => Int -> Int -> Int -> Int -> a -> Array Int ( Point a ) -> ( Int , Int , Int , a ) function . Could some one please tell me what is wrong with these functions. I have posted both code on ideone . Haskell code [ http://ideone.com/IlwBv ] and accepted c++ for SPOJ problem [ http://ideone.com/vgNnt ] . For test case 20 886 9383 6915 2777 8335 7793 492 5386 1421 6649 27 2362 59 8690 3926 7763 3426 540 5736 9172 5368 5211 6429 2567 1530 5782 5123 2862 3135 4067 9802 3929 3058 4022 8167 3069 8456 1393 8042 5011 -1 Haskell produced the convex hull [P 27.0 2362.0,P 3426.0 540.0,P 8456.0 1393.0,P 9802.0 3929.0,P 8335.0 7793.0,P 5736.0 9172.0,P 886.0 9383.0,P 59.0 8690.0] and maximum triangle area 31466755.50 while C++ code produced the convex hull 27 2362 3426 540 8456 1393 9802 3929 8335 7793 5736 9172 886 9383 59 8690 and maximum area 33642111.00 . Based on these observation , I think my convex hull part is correct and I am stuck with looPing and calArea function . I tried to write Haskell code many ways but no success so it would be great if some one can tell me what is wrong with these two functions . Thank you

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ICFP Hotel Roommate
by Daniel Winograd-Cort 17 Aug '11

17 Aug '11

Hi, I'll be heading to ICFP in September, and I'm hoping to find someone to share a room with to save on hotel costs. Are there any other students looking for a roommate? Cheers, Dan

1 0

broken on install encoding 0.6.6
by Gang Yu 17 Aug '11

17 Aug '11

hi, cafe: I go through to the encoding package installation problem again. cabal install encoding Resolving dependencies... /tmp/encoding-0.6.68093/encoding-0.6.6/dist/setup/setup: 4: Syntax error: ";" unexpected when I have a check on the this issue, I get: file ~/.cabal/packages/ hackage.haskell.org/encoding/0.6.6/encoding-0.6.6/dist/setup/setup /home/gang/.cabal/packages/ hackage.haskell.org/encoding/0.6.6/encoding-0.6.6/dist/setup/setup: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.27, not stripped My machine is: gang@gang-laptop:~$ uname -a Linux gang-laptop 2.6.38-8-generic #42-Ubuntu SMP Mon Apr 11 03:31:50 UTC 2011 i686 i686 i386 GNU/Linux is this related? How can I manually install the package from scratch? Any helps or directs will be appreciated Thanks Gang

2 1

Getting segmentation fault when profiling, despite `-K100M'.
by David Banas 16 Aug '11

16 Aug '11

Hi all, I'm trying to profile a mixed language program, in which Haskell is NOT the top layer and does not contain the `main' function. (C is/does.) Is this effort doomed to fail? I'm getting a segmentation fault, as soon as the first Haskell function is called, despite having included `-K100M' in my list of +RTS args: 19 int argc = 5; 20 char* argv[] = {"ghcDll", 21 "+RTS", 22 "-hc", 23 "-p", 24 "-K100M", 25 NULL}; // argv must end with NULL 26 27 // Initialize Haskell runtime 28 char** args = argv; 29 hs_init(&argc, &args); Using gdb to trace through the C-code, up until the first call to Haskell, I get to here: 64 // Call the Haskell function. 65 res = amiInit( 66 impulse_matrix, 67 row_size, Here's the beginning of `amiInit': 41 -- Our Haskell implementation of `AMI_Init'. 42 amiInit :: Ptr CDouble -> CInt -> CInt -> CDouble -> CDouble -> 43 CString -> Ptr CString -> Ptr (StablePtr AmiModel) -> Ptr CString -> IO Int 44 amiInit impulse_matrix row_size aggressors sample_interval bit_time 45 ami_parameters_in ami_parameters_out ami_memory_handle msgHndl 46 | impulse_matrix == nullPtr = return 0 47 | otherwise = do 48 putStrLn "I'm here." I never see "I'm here." printed to my console, before I get the segmentation fault. Any thoughts? Thanks, -db

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