- Haskell-Cafe - Haskell.org

Small Haddock question
by Andrew Coppin 04 Jul '09

04 Jul '09

This is irritating me now... Suppose I have something like the following: zero = 0 :: Int one = 1 :: Int two = 2 :: Int three = 3 :: Int How do I add Haddock comments to the end of each line? For some reason, Haddock doesn't like either of zero = 0 :: Int -- | Zero zero = 0 :: Int -- ^ Zero Either way it whinges about parse errors. How do I make it shut up and stop being so dense at me? :-} It's damned obvious what I want it to do...

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Haskell Weekly News: Issue 124 - July 4, 2009
by Brent Yorgey 04 Jul '09

04 Jul '09

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20090704 Issue 124 - July 04, 2009 --------------------------------------------------------------------------- Welcome to issue 124 of HWN, a newsletter covering developments in the [1]Haskell community. Announcements HLint 1.6. Neil Mitchell [2]announced the release of [3]HLint 1.6, a tool for automatically suggesting improvements to Haskell code. Haskell Implementers Workshop: accepted talks. Simon Marlow [4]announced that the list of talks at the [5]Haskell Implementers Workshop 2009 has now been posted. bloxorz clone. Patai Gergely [6]announced a [7]Haskell clone of the game "bloxorz", written by Viktor Devecseri. Fun with type functions. Simon Peyton-Jones [8]announced that he, Ken Shan, and Oleg have finished Version 2 of their [9]paper "Fun with Type Functions", which gives a programmer's tour of what type functions are and how they are useful. If you have a moment to look at, and wanted to help them improve it, leave comments on the linked wiki page. package Boolean: Generalized booleans. Conal Elliott [10]announced [11]Boolean, a new package for generalized booleans, which provides type classes with generalizations of Boolean values and operations, if-then-else, Eq and Ord. TernaryTrees-0.1.1.1 - An efficient ternary tree implementation of Sets and Maps. Alex Mason [12]announced the release of [13]TernaryTrees, a package that extends Data.Set ad Data.Map with some ternary tree structures, one of the more efficient ways of storing strings in a set. 6.12.1 planning. Simon Marlow [14]announced plans for a release of GHC 6.12.1, sometime around September. If you have the time and inclination to help with any of the listed features, please get involved! regular-0.1. José Pedro Magalhães [15]announced the release of the [16]regular library. Many generic programs require information about the recursive positions of a data type, such as generic fold, generic rewriting, and the Zipper data structure. Regular provides a fixed point view on data which allows these definitions for regular data types. It also serves as the basis for a [17]generic rewriting library. Google Summer of Code Progress updates from participants in the 2008 [18]Google Summer of Code. Haddock improvements. Isaac Dupree has made it easier to generate Haddock documentation [19]for non-exported functions, posted an [20]overview of the issues involved in getting proper cross-package documentation working, and his current [21]plan. EclipseFP. Thomas Ten Cate has done a lot of work on EclipseFP, including some [22]cosmetic updates and getting [23]error reporting to work better. space profiling. Gergely Patai is [24]working on a network protocol for his profiling grapher tool, so that other tools can monitor the profiling information. haskell-src-exts. Niklas Broberg has [25]released [26]haskell-src-exts version 1.0.0! fast darcs. Petr Rockai has completed [27]quite a bit of work on darcs, including a [28]beta release of darcs 2.3. Discussion Monoid wants a (++) equivalent. Bryan O'Sullivan [29]suggested adding a more concise operator to the Monoid class for 'mappend', leading to a long, bike-shed-ish (but hopefully still useful) discussion. Reflections on the ICFP 2009 programming contest. Justin Bailey began a [30]discussion on results and experiences from the ICFP 2009 programming contest. Blog noise [31]Haskell news from the [32]blogosphere. Blog posts from people new to the Haskell community are marked with >>>, be sure to welcome them! * Gergely Patai: [33]Playing and learning. * Ketil Malde: [34]A set of tools for working with 454 sequences. * Sebastian Fischer: [35]FP Overview. * Magnus Therning: [36]Making a choice from a list in Haskell, Vty (part 1). * David Amos: [37]Conjugacy classes, part 1. * Well-Typed.Com: [38]GHC and Windows DLLs. * Manuel M T Chakravarty: [39]Converting typed term representations: from HOAS to de Bruijn.. * >>> Ivan Uemlianin: [40]Haskell: sort and sortBy. * Gregory Collins: [41]Building a website with Haskell, part 3. * Michael Snoyman: [42]Hack sample- chat server. * Luke Palmer: [43]On the By functions. * Magnus Therning: [44]Dataenc finally making it into Debian. * Thomas ten Cate: [45]New build instructions. * Erik de Castro Lopo: [46]Three More for the Debian New Queue. * >>> Yuval Kogman: [47]What Haskell did to my brain. * Greg Bacon: [48]FFI: calling into kernel32.dll. * Greg Bacon: [49]Setting up a simple test with Cabal. * Ketil Malde: [50]Dephd updates. * Bryan O'Sullivan: [51]What's in a text API?. * Brent Yorgey: [52]2009 ICFP programming contest reflections. * Galois, Inc: [53]Galois, Inc. Wins Two Small Business Research Awards from Federal Agencies. * Greg Bacon: [54]Cleaning up your Haskell imports. * Douglas M. Auclair (geophf): [55]Realized Constants are Comonadic. Quotes of the Week * KF8NH: all monads are functors, but for Hysterical Raisins not all Monads are Functors. * lilac: lambda actually is just the greek letter l. it stands for lilac. * lilac: before mauke we all implemented map with a fold every time we needed it. * luqui: I'll just stick to my religion: I have a personal relationship with our lord and savior, the untyped lambda calculus. * copumpkin: I think I was implemented in haskell. I mean, my parents never used seq, ever. * Benjamin Russell: Haskell. "Avoid success at all costs." Made with dinosaur technology. About the Haskell Weekly News New editions are posted to [56]the Haskell mailing list as well as to [57]the Haskell Sequence and [58]Planet Haskell. [59]RSS is also available, and headlines appear on [60]haskell.org. To help create new editions of this newsletter, please see the information on [61]how to contribute. Send stories to byorgey at cis dot upenn dot edu. The darcs repository is available at darcs get [62]http://code.haskell.org/~byorgey/code/hwn/ . References 1. http://haskell.org/ 2. http://article.gmane.org/gmane.comp.lang.haskell.general/17332 3. http://community.haskell.org/~ndm/hlint/ 4. http://article.gmane.org/gmane.comp.lang.haskell.general/17331 5. http://haskell.org/haskellwiki/HaskellImplementorsWorkshop 6. http://article.gmane.org/gmane.comp.lang.haskell.cafe/60907 7. http://just-bottom.blogspot.com/2009/07/playing-and-learning.html 8. http://article.gmane.org/gmane.comp.lang.haskell.cafe/60846 9. http://haskell.org/haskellwiki/Simonpj/Talk:FunWithTypeFuns 10. http://article.gmane.org/gmane.comp.lang.haskell.cafe/60716 11. http://hackage.haskell.org/package/Boolean 12. http://www.haskell.org//pipermail/haskell-cafe/2009-June/063625.html 13. http://hackage.haskell.org/package/TernaryTrees 14. http://www.haskell.org//pipermail/haskell-cafe/2009-June/063681.html 15. http://www.haskell.org//pipermail/haskell/2009-July/021468.html 16. http://www.cs.uu.nl/wiki/bin/view/GenericProgramming/Regular 17. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/rewriting 18. http://hackage.haskell.org/trac/summer-of-code/wiki/SoC2008 19. http://haddock2009.wordpress.com/2009/06/23/how-to-navigate-your-code/ 20. http://haddock2009.wordpress.com/2009/06/24/cross-package-documentation-par… 21. http://haddock2009.wordpress.com/2009/06/25/cross-package-plan-a/ 22. http://eclipsefp.wordpress.com/2009/06/20/cosmetics/ 23. http://eclipsefp.wordpress.com/2009/06/30/compiling-and-error-reporting/ 24. http://just-bottom.blogspot.com/2009/06/short-term-hp2any-plans.html 25. http://nibrofun.blogspot.com/2009/06/gsoc-status-report-week-4.html 26. http://hackage.haskell.org/package/haskell%2Dsrc%2Dexts 27. http://web.mornfall.net/blog/soc_progress_5.html 28. http://web.mornfall.net/blog/darcs_2.3_beta_1.html 29. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/60754 30. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/60690 31. http://planet.haskell.org/ 32. http://haskell.org/haskellwiki/Blog_articles 33. http://just-bottom.blogspot.com/2009/07/playing-and-learning.html 34. http://blog.malde.org/index.php/2009/07/03/a-set-of-tools-for-working-with-… 35. http://www-ps.informatik.uni-kiel.de/~sebf/haskell/fp-overview.html 36. http://therning.org/magnus/archives/685 37. http://haskellformaths.blogspot.com/2009/06/conjugacy-classes-part-1.html 38. http://blog.well-typed.com/2009/07/ghcdlls/ 39. http://justtesting.org/post/134566537 40. http://llaisdy.wordpress.com/2009/07/03/haskell-sort-and-sortby/ 41. http://gregorycollins.net/posts/2009/07/02/building-a-website-part-3 42. http://blog.snoyman.com/2009/07/01/hack-sample-chat-server/ 43. http://lukepalmer.wordpress.com/2009/07/01/on-the-by-functions/ 44. http://therning.org/magnus/archives/672 45. http://eclipsefp.wordpress.com/2009/07/01/new-build-instructions/ 46. http://www.mega-nerd.com/erikd/Blog/CodeHacking/Debian/polyparse_dataenc_js… 47. http://nothingmuch.woobling.org/talks/takahashi.xul?data=yapc_na_2009/haske… 48. http://feedproxy.google.com/~r/gbacon/~3/o-lAJeIoUbk/ffi-calling-into-kerne… 49. http://feedproxy.google.com/~r/gbacon/~3/7rlf4Dd1JKU/setting-up-simple-test… 50. http://blog.malde.org/index.php/2009/06/16/dephd-updates/ 51. http://www.serpentine.com/blog/2009/06/30/python-and-haskell-text-apis-comp… 52. http://byorgey.wordpress.com/2009/06/29/2009-icfp-programming-contest-refle… 53. http://www.galois.com/blog/2009/06/29/galois-awarded-two-federal-sbirs/ 54. http://feedproxy.google.com/~r/gbacon/~3/AGNKaCB2-GI/cleaning-up-your-haske… 55. http://logicaltypes.blogspot.com/2009/06/realized-constants-are-comonadic.h… 56. http://www.haskell.org/mailman/listinfo/haskell 57. http://sequence.complete.org/ 58. http://planet.haskell.org/ 59. http://sequence.complete.org/node/feed 60. http://haskell.org/ 61. http://haskell.org/haskellwiki/HWN 62. http://code.haskell.org/~byorgey/code/hwn/

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Cont, ContT and IO()
by Günther Schmidt 04 Jul '09

04 Jul '09

Hi, I've got an IO action, some file system IO, traversing one level only and iterating over files found. I wish to build in an "early" exit, ie. if an IO action in the loop encounters a particular value I want it to abort the loop. Now so far, pls don't shoot, I have done this by throwing IO Exceptions and catching them. I'm trying to rewrite this using Continuatios / callCC but can't figure out where to place what. I certainly don't have the intuition yet and funny enough not even in RWH I could find some Cont/ContT examples. Would someone please draw me an example? Günther

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Half-integer
by Andrew Coppin 04 Jul '09

04 Jul '09

I just wrote a small module for dealing with half-integers. (That is, any number I/2 where I is an integer. Note that the set of integers is a subset of this; Wikipedia seems to reserve "half-integer" for such numbers that are *not* integers.) module HalfInteger where data HalfInteger i instance (Eq i) => Eq (HalfInteger i) instance (Ord i) => Ord (HalfInteger i) instance (Integral i) => Show (HalfInteger i) instance (Integral i) => Num (HalfInteger i) half :: (Num i) => HalfInteger i fromNum :: (Integral i, RealFrac x) => x -> HalfInteger i toNum :: (Integral i, Fractional x) => HalfInteger i -> x isInteger :: (Integral i) => HalfInteger i -> Bool Note carefully that the set of half-integers is *not* closed under multiplication! This means that for certain arguments, there are two reasonable products that could be returned. (E.g., 1/2 * 1/2 = 1/4, so 0 or 1/2 would be a reasonable rounding.) I haven't put a lot of effort into the rounding details of (*) or fromNum; which answer you get is kind of arbitrary. (However, addition and subtraction are exact, and for multiplications where an exact result is possible, you will get that result.) The Show instance outputs strings such as fromInteger 5 fromInteger 5 + half fromInteger (-5) - half depending on the isInteger predicate. Now, the question is... Is this useful enough to be worth putting on Hackage?

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ORM for haskell?
by Marc Weber 04 Jul '09

04 Jul '09

Some time ago I stumbled upon SQLAlchemy which is a great ORM wrapper library for python. It has a nice syntax I'd like to see in a haskell library as well. SQLAlchemy already provides some lazy features such as loading subitems on access etc. All haskell SQL libraries I know only let you run SQL statements but not much more. To start real business you no longer want to write many SQL commands. Example why it matters: schools - 1:n - teachers - 1:n - pupils If you want to list all schools which have a pupil with age > 3 you'd write an sql query like this: SELECT dictinct * FROM schools as s JOIN teachers t ON (t.school_id = s.id) JOIN pupils as p ON (p.teacher_id = t.id) WHERE p.age > 3 in SQLAlchemy it looks like this: session.query(School).join(School.teachers).join(Teacher.pupils).filter(Pupil.age > 3).all() difference? Because SQLAlchemy knows about the relations you don't have to remember alias names. So there is no chance to get that wrong. Another example: Updating the age of a pupil: row = SELECT * FROM pupils where age = 13; UPDATE pupils SET age = 14 WHERE id = <the id you got above> p = session.query(Pupil).filter(Pupil.age==13).one().age=14 session.commit() difference? You don't have to care about ids. you just assign a new value and tell the engine that it should commit. So again less chances to get something wrong. What about trees (eg web site navigation) id | title | parent_id 1 | top | null 2 | submenu | 1 3 | submenu2 | 1 should result in top - submenu - submenu2 using SQLAlchemy you can just do parent = session.query('nodes').filter(Node.id = 1) def print(node): print node.title print node.subnodes # this will run a subquery automatically for you returning submenu{,2} Again no sql. No chance to get something wrong? You can skim the manual to get a better idea how SQLAlchemy works http://www.sqlalchemy.org/docs/05/sqlalchemy_0_5_5.pdf I have to admit that I haven't used SQLAlchemy in a real project yet. However I can imagine doing so. Comparing this to what we have on hackage I'd say some work has to be done to get close to SQLAlchemy. The backend doesn't have to be a relational database. However I'd like to use this kind of abstraction in haskell. Is there anyone interested in helping building a library which a) let's you define kind of model of you data b) let's you store you model in any backend (maybe a relational database) c) does static checking of your queries at compilation time? Right now I'd say the best way to go is define the model in the application and not get the scheme from an existing database because there is not way to store all scheme details within a relational model. I think SQLAlchemy does it right by providing a way to define the model in python. Of course haskell doesn't have "objects" to store. But GADTs could be stored (data Foo = ...) So are there any volunteers who are interested in helping writing this kind of storage solution for haskell which could be used in real world business apps? Maybe this does already exist and I've missed it? Marc Weber

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space leak hints?
by Uwe Hollerbach 04 Jul '09

04 Jul '09

Good evening, all, I wonder if I could tap your collective wisdom regarding space leaks? I've been messing about with haskeem, my little scheme interpreter, and I decided to see if I could make it run reasonably space-efficiently. So far... no. Here's what I tried: I wrote a tiny scheme program to compute Collatz sequences for successive numbers, starting from 1 and incrementing forever (well, in principle). Because real scheme implementations are fully tail-call-optimized, this'll run in constant memory; I checked that with mzscheme, and it does indeed work. With my little interpreter, that's not the case: memory usage grows continually, although apparently less-than-linearly. I've built the interpreter with the profiling stuff described on the wiki and in RWH Ch 25 turned on and have made a few runs with that; I stuck the postscript plot that's the result of one of those runs onto my web site at http://www.korgwal.com/haskeem/run2.ps. The full source to the interpreter is a little large to paste into this message; it's available on my web site, and also on hackage. But according to the plot, there appear to be three main memory allocation issues, and they seem to all be related, if I'm reading stuff correctly. The core of the interpreter is a function, evalLisp, which evaluates scheme forms. There are of course a fair number of different forms, but the largest generic usage is "evaluate each of a list of forms, returning the value of the last of them as the overall result". In order to express that in a couple of different places, and to accomodate the possibility of an empty list, I have a really tiny function lastOrNil which just calls "last" on a (haskell) list, checking for the possibility of an empty list, and returning a haskeem LispVal object: > lastOrNil = liftM lON > where lON [] = List [] > lON l = last l (sorry, proportional fonting may be throwing this off). It's this function which is directly implicated in two of the top three memory pigs, and nearly directly in the third one as well. If I could eliminate the memory growth in these three cost centers, I would already capture over 90% of the growth in this benchmark, which would make me very happy indeed. But I don't really understand what is going on here. It seems entirely plausible, indeed likely, that the list which I'm traversing there is not fully evaluated. So I've tried adding 'seq' to this function. Uhhh... from memory, I dumped it after it didn't work, I had > lastOrNil = liftM lON > where lON [] = List [] > lON (l:[]) = l > lON (l:ls) = seq l (lON ls) (again, proportional fonting might mess me up here.) As I said, I dumped this after it made no difference whatsoever. I also tried bang-patterns in a couple of places, strictness annotation of my basic LispVal types... nothing. It all made exactly no difference, as far as I could tell. I've tried a couple of google searches, but haven't come up with anything better than what I've already described. So I'm a stumped chump! I'd be grateful for any suggestions... thanks in advance! Uwe

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How to present the commonness of some objects?
by Magicloud Magiclouds 03 Jul '09

03 Jul '09

Hi, I thought "class" was for this purpose. But it turns out not. Code as following could not compiled. 1 main = do 2 mapM_ (\(x, y, widget) -> do 3 a <- widgetRun widget 4 putStrLn $ show a 5 ) widgetList 6 7 widgetList :: (Widget w) => [(Integer, Integer, w)] 8 widgetList = [] 9 10 class Widget w where 11 widgetRun :: w -> IO () --- % ghc --make tmp/test.hs [1 of 1] Compiling Main ( tmp/test.hs, /tmp/Main.o ) tmp/test.hs:3:16: Ambiguous type variable `t' in the constraint: `Widget t' arising from a use of `widgetRun' at tmp/test.hs:3:16-31 Probable fix: add a type signature that fixes these type variable(s) -- 竹密岂妨流水过山高哪阻野云飞

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Help needed to pick a better name then "hack"
by Jinjing Wang 03 Jul '09

03 Jul '09

Hack is such an inconvenient name for a package, may I get some inspiration from renaming it? Also, is there an idiom to use when upgrading package name on hackage? Best, -- jinjing

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On the parallel between java annotations and monads
by Rafael Almeida 03 Jul '09

03 Jul '09

Hello, After an extensive search (5 minutes googling) I could not find any comparison between Java annotations (or Python annotations for that matter) and Monads. I think they are similar in various aspects and I want to discuss them here. I'm sure several of you have experience with Java programming and its annotation system. At first they seem like an extension to the typing system, by using annotations a single variable or method may have more than one type: the real type and all the annotations types. The way you declare them is not important for this discussion, but assume that you've created the annotations GreaterThanFive and LessThanTwenty, you could annotate a method like this (let's forget about all the class verbosity for a while): @GreaterThanFive @LessThanTwenty int doYourThing(); You could than use reflection to read those annotations and you could check if the returned integer is in the correct range. You could even make the compiler generate code that will do that checking automatically for you. Even though that was my first impression of them, that's not really how they are used in practice (at least the practice that I have experimented). People use them to implement Monad-like features to the language. Actually, you can forget monad and think of computation containers. On an EJB environment there's something called a container and it will do all sorts of computations when you call an annotated method or when you create a new annotated class. For instance, if, inside of an entity bean, you annotate a variable like this: @Column(name = "NAME") private String name; then, when you create a method like so: public String getName() { return name; } that name is actually something retrieved from the database, even though, it looks just like something in memory. As far as I know the interaction with monads for handling databases is not very different. There are other annotations which allows the container to "inject" some object on a variable, such as: @PersistenceContext private EntityManager entityManager; now you won't even create an EntityManager instance, but will use the object living inside the container. I compare that to getting a value from an State Monad. Like there, you'll do some computations using entityManager, but it will ultimately be returned to the container. While each computational container in Haskell is very rigid and well defined, in java there's nothing rigorous about the annotation. However, quite often the annotations in Java are used in a manner similar to the implementation of a Monad in Java. []'s Rafael

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hiding instance definitions in imported modules or redefining them, can it be done?
by John Lask 03 Jul '09

03 Jul '09

Is there a way to hide instance definitions when importing a module for instance I want to import Data.Monoid but wish to redefine the instance of Monoid for ( a->b) I don't suppose this is possible? Specifically, I wish to define a specialised instance of Monoid for String->Int, but it seems overlapping instances will not give me what I want, as this option seems to need to be applied at the definition site (aka Data.Monoid module, looking for confirmation of this?). The easy fix is just to do newtype M a b = M (a->b) etc..., but I was hopping to avoid this. I've encountered this issue several times. Why can't we redefine instances? I can't of thought that there are any seriouse technical issues in doing so? If so what are they? jvl

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Monad Input/Output and Monad Transformers
by Maciej Piechotka 03 Jul '09

03 Jul '09

1. Learning haskell I discovered that I/O should be avoided nearly 'at all costs'. The problem is that the IO monad is the only one which have more interactive work flow. There is Reader/Writer monad but in fact AFAIU first one is about the environment and second one is about logging. Implementation of Writer can be defined in terms of handles but it is rather limited (either non-full implementation which may be confusing or need of caching the result for pass etc.). I searched the hackage but I didn't find package with pure I/O. Such package may look like: class (Monad m, Monoid v) => MonadInput v m where -- | Gets an element from input (line of text [with \n], 4096 bytes, -- or something like that). mzero on end getChunk :: m v class (Monad m, Monoid v) => MonadOutput v m where -- | Puts an element putChunk :: v -> m () In similar way filters (for example buffered input) can be defined: class (MonadInput v m) => MonadBufferedInput m where -- | If not whole chunk has been consumed at once (for example only -- first 3 elements from list) rest can be returned. It will be -- returned as part of the input on next getChunk call. returnChunk :: v -> m () data (MonadInput v m, Monoid v) => BufferedInputT v m a = BufferedInputT a v Also pipes may be defined (as far as I understand but I'm not 100% sure) which probably will simplify the writing of network tests: -- | Evaluates the first argument. If the getChunk is called the -- evaluation is passed to second argument until the putChunk is -- called, which argument is returned in the first argument callPipeT :: (Monad m, Monoid v) => PipeInputT v m a -> PipeOutputT v m b -> m (a, b) I've started some tests but I'd be grateful for comments (well - probably I'm not the first who come to this idea so a) there is such package or b) my level of Haskell does not allow me to see the problems). 2. I find writing monad transformers annoying. Additionally if package defines transformer A and another transformer B they need to be connected 'by hand'. I find a simple solution which probably is incorrect as it hasn't been used: instance (MonadState s n, Monad (m n), MonadTrans m) => MonadState s (m n) where get = lift get put = lift . put (requires FlexibleInstances MultiParamTypeClasses FlexibleContexts UndecidableInstances - two last are not extensions used by mtl) Regards

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How to declare a Typeless Function
by Fernan Bolando 03 Jul '09

03 Jul '09

Hi I have a function that swaps rows of an array of double swap :: Array (Int,Int) Double -> [Int] -> Array (Int,Int) Double I then create a function that swaps rows of arrays of Complex Double swap :: Array (Int, Int) (Complex Double) -> [Int] -> Array (Int, Int) (Complex Double) In reality the function swap does not care whether its working on a double or a complex number. how do I declare swap so that it will work whether it's a complex or a double array. I tried googling but I wasn't sure what to google. fernan -- http://www.fernski.com

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Re: Monad Input/Output and Monad Transformers
by John Lato 03 Jul '09

03 Jul '09

> From: Maciej Piechotka <uzytkownik2(a)gmail.com> > > 1. Learning haskell I discovered that I/O should be avoided nearly 'at > all costs'. The problem is that the IO monad is the only one which have > more interactive work flow. There is Reader/Writer monad but in fact > AFAIU first one is about the environment and second one is about > logging. Implementation of Writer can be defined in terms of handles but > it is rather limited (either non-full implementation which may be > confusing or need of caching the result for pass etc.). > I'm not sure what you mean when you say that IO is the only monad with a "more interactive work flow". Do you mean that it allows interleaving of input and output? If so, I would ask what you're doing that makes this a concern. If it's for efficiency, don't worry about it. Haskell's laziness means that the language will take care of this for you. A good example is the bzlib[1] package; the "compress" function has type "ByteString -> ByteString" and automatically handles the chunking of data for you. If you need to partially process an input to determine how the rest of the input should be handled, there are many parser libraries (parsec[2], polyparse[3], etc.) that can either help with this directly or perhaps give ideas as to how you can handle it. You may also want to look at the iteratee[4] package. It sounds like it may accomplish what you're trying to do, although the interface is very different from what you specify. > > 2. I find writing monad transformers annoying. > Additionally if package defines transformer A and another transformer B > they need to be connected 'by hand'. > If this becomes onerous, I think the usual solution is to define custom lifting functions for the most commonly performed operations. However, my feeling is that you're probably trying to put together a monad stack to model what you're trying to do too soon, when you'd be better served trying to develop data structures and core functions that describe what you want to do. Of course, without more information this is just a guess. John Lato [1] http://hackage.haskell.org/package/bzlib [2] http://legacy.cs.uu.nl/daan/parsec.html, http://hackage.haskell.org/package/parsec [3] http://www.cs.york.ac.uk/fp/polyparse/, http://hackage.haskell.org/package/polyparse [4] http://okmij.org/ftp/Haskell/Iteratee/, http://hackage.haskell.org/package/iteratee

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Re: [Haskell-cafe] A Strict GCL Interpreter in Haskell
by Tillmann Rendel 03 Jul '09

03 Jul '09

Hi Hector, Hector Guilarte wrote: > I did that already, but it didn't work... Also, since this kind of error would be a run time error in my GCL Language, I don't want it to continue executing whenever an error is found, that's why I changed it back to just: > evalExpr:: Expr -> Tabla -> Int > > Instead of using the Either String Int... I think you misunderstand something. If you use (Expr -> Table -> Int), you are announcing: Whatever happens, I keep executing. If you use (Expr -> Table -> Either String Int), you are announcing: I may stop earlier because of some problem. Since may you want to stop earlier, you should use the second type. Let's look at a very small example, an interpreter for the following little language: data Expression = Literal Integer | Add Expression Expression | Divide Expression Expression Because of division by zero, an interpreter for this language may fail. So we have two kinds of return values: Sometimes we return a number, and sometimes we return an DivideByZero error. We can reflect that in a datatype: data Result = Number Integer | DivideByZeroError Now we can write our interpreter: eval :: Expression -> Result eval (Literal n) = Number n eval (Add a b) = case eval a of Number result_of_a -> case b of Number result_of_b -> Number (result_of_a + result_of_b) DivideByZeroError -> DivideByZeroError DivideByZeroError -> DivideByZeroError eval (Add a b) = case eval a of Number result_of_a -> case b of Number result_of_b -> if b == 0 then DivideByZeroError else Number (result_of_a + result_of_b) DivideByZeroError -> DivideByZeroError DivideByZeroError -> DivideByZeroError This interpreter will stop as soon as it encounters a division by zero, because we take care to return DivideByZeroError whenever we see a DivideByZeroError in one of the subterms. So you have to use an appropriate return type (like (Either String Int) or Result), and you have to pattern match on the result of "earlier" parts of your program, and propagate the error. Tillmann

2 1

Haskellers at University of Edinburgh? (hackathon)
by Eric Kow 03 Jul '09

03 Jul '09

Hi Haskellers, I'm looking for people at the University of Edinburgh who have a swipe card with access to the Informatics Forum and could hang around on 29 August (or perhaps 6 Sep). Thanks! PS. You may also be interested in some Hackathon news: we've reserved a room at the ICFP venue suitable for up to 50 people, but we can only have it for 30 August. I'm still holding out for a two-day space, but if I don't hear back by mid-week, we'll settle for a single Haskell Hack Day, preceded by a more informal Haskell Hacking Expedition the day before (for example, camping in in a wifi-enabled pub for the day). -- Eric Kow <http://www.nltg.brighton.ac.uk/home/Eric.Kow> PGP Key ID: 08AC04F9

7 7

[ghc] kind of the function arrow
by Dominic Orchard 03 Jul '09

03 Jul '09

I was just playing around and noticed that the kind of the function arrow in GHC is (?? -> ? -> *) when I (naively) expected it to be (* -> * -> *). After looking at (http://hackage.haskell.org/packages/archive/ghc/6.10.2/doc/html/Type.html#5) I see that the kind of (->) means that the parameter type cannot be an unboxed tuple, whilst the result type can be anything. Why is this? After reading this documentation I would expect the kind (? -> ? -> *). I'm now wondering if the kind of (->) could cause problems if the following style of declaration is requried: > type FunArg a b = (a -> b, a) *Main> :k FunArg FunArg :: * -> * -> * By using type variables, whose default kind is *, the function type is fixed to use only boxed types. But if one wanted to allow unboxed type parameters the kind would be wrong, and an explicit kind signature of # or ? can't be given as they are not part of Haskell's source language. I guess my question is why the (?? -> ? -> *) kind on (->) and what to do if synonyms or data types over (->) are required such as the example just stated. I'm just curious. Thanks, Dominic

2 1

Network.CGI -- practical web programming example.
by Edward Ing 02 Jul '09

02 Jul '09

I am somewhat new to haskell. It is amazing that I can actually write a CGI program using Network.CGI without really being comfortable with the Haskell type system. Especially when it involves monad transformations. So I decided that I better understand this. I looked at the Practical Web Programming examples to try to understand what is going on. I came up with a problem that might demonstrate my misunderstanding. I am wondering if you can answer questions I have. Code 1 is the example from PWP, Code 2 is my variation and it works so I am stumped by what the liftM is required. code 1>>> #!/usr/bin/runghc import Network.CGI import Text.XHtml import qualified Data.ByteString.Lazy as BS import Control.Monad (liftM) import Data.Maybe (fromJust) uploadDir = "../upload" fileForm = form ! [method "post", enctype "multipart/form-data"] << [afile "file", submit "" "Upload"] saveFile n = do cont <- (liftM fromJust) $ getInputFPS "file" let f = uploadDir ++ "/" ++ basename n liftIO $ BS.writeFile f cont return $ paragraph << ("Saved as " +++ anchor ! [href f] << f +++ ".") page t b = header << thetitle << t +++ body << b basename = reverse . takeWhile (`notElem` "/\\") . reverse cgiMain = do mn <- getInputFilename "file" h <- maybe (return fileForm) saveFile mn output $ renderHtml $ page "Upload example" h main = runCGI $ handleErrors cgiMain Code 2 (modifier) >>> import Network.CGI import Text.XHtml import qualified Data.ByteString.Lazy as BS import Control.Monad (liftM) import Data.Maybe (fromJust) uploadDir = "../upload" fileForm = form ! [method "post", enctype "multipart/form-data"] << [afile "file", submit "" "Upload"] saveFile n = do cont <- getInputFPS "file" let f = uploadDir ++ "/" ++ basename n liftIO $ BS.writeFile f (fromJust cont) return $ paragraph << ("Saved as " +++ anchor ! [href f] << f +++ ".") page t b = header << thetitle << t +++ body << b basename = reverse . takeWhile (`notElem` "/\\") . reverse cgiMain = do mn <- getInputFilename "file" h <- maybe (return fileForm) saveFile mn output $ renderHtml $ page "Upload example" h main = runCGI $ handleErrors cgiMain Questions === 1) Why did the author choose to insert "liftM" in function saveFile? It doesn't seem necessary in my version. 2) My background mainly is Java but here is my understanding of Monad Transforms. The CGIT m type carries around with it the CGI Request context and response contexts. The transformations (lifts) is similar to casting so that you can use the functions for specific manifestations but it also encapsulates the data. Is this correct? Edward

4 4

A Strict GCL Interpreter in Haskell
by Hector Guilarte 02 Jul '09

02 Jul '09

Hi everyone! (First of all, I don't know Monads!) I made a GCL (Guarded Command Language) Compiler and Interpreter for my Languages and Machines course in my University with alex, happy and ghc. I still have a doubt: 1) Since Haskell is Lazy, and my GCL program is being interpreted in Haskell then my GCL is Lazy too (I know is not as simple as that but believe me, somehow it is behaving lazy). The problem is that it can't be lazy (said to me by my teacher on monday) so I tried using seq, but it didn't work, I'll paste the code after this: Programs in GCL like: a) var i : value main i <- 1 / 0 end b) var i : value main i <- 1 / 0; show i end c) var i : value var foo : array of 2 main i <- foo[42] end d) var i : value var foo : array of 2 main i <- foo[42]; show i end act like this: a and c finish interpretation b throws division by zero error and finish interpretation d throws index out of bounds error and finish interpretation Now the code: (it is in Spanish. ListLValue is a List of L-Values for the assigments, ListExpr is the list of Expressions to be assigned, Tabla is the Symbol Table (Data.Map), actualizarVar updates a Variable in the Symbol Table with the new value "valor", ActualizarArray updates the position "indice" of an array in the Symbol Table. evalExpr evaluates an arithmetic Expression and returns an Int. Inside evalExpr are the verifications for division by zero of modulo by zero.) evalAsignacion:: ListLvalue -> ListExpr -> Tabla -> Tabla evalAsignacion [] [] tabla = tabla evalAsignacion ((Lid id):valueList) (expr:exprList) tabla = let valor = (evalExpr expr tabla) in valor `seq` evalAsignacion valueList exprList (actualizarVar id valor tabla) evalAsignacion ((LArrayPosition id exprArray):valueList) (expr:exprList) tabla = let valor = (evalExpr expr tabla) indice = (evalExpr exprArray tabla) in valor `seq` indice `seq` evalAsignacion valueList exprList (actualizarArray id indice valor tabla) evalExpr:: Expr -> Tabla -> Int evalExpr expr tabla = let salida = (snd (evalAritmetico expr tabla)) in salida `seq` if (isLeft salida) then error (getLeft salida) else getRight salida --((Int,Int) is the Line and Colum, that's for error reporting) evalAritmetico :: Expr -> Tabla -> ((Int,Int),(Either String Int)) --LET ME KNOW IF YOU NEED THIS PART TOO Thanks in advance, Hector Guilarte

3 2

Fun with type functions
by Simon Peyton-Jones 02 Jul '09

02 Jul '09

Friends Ken, Oleg, and I have finished Version 2 of our paper "Fun with Type Functions", which gives a programmer's tour of what type functions are and how they are useful. http://haskell.org/haskellwiki/Simonpj/Talk:FunWithTypeFuns If you have a moment to look at, and wanted to help us improve it, the above link goes to a wiki page where you can comment on the paper or discuss it. We still have time to improve it. Thanks Simon

1 0

ghc static linking on Windows
by Günther Schmidt 02 Jul '09

02 Jul '09

Hi, I tried to compile an app that uses sqlite3.dll with the -optl-static flag and the error message is: C:\ghc\ghc-6.10.3\gcc-lib\ld.exe: cannot find -lsqlite3 collect2: ld returned 1 exit status

2 1

Suggestions for simulating Object ID
by Hemanth Kapila 01 Jul '09

01 Jul '09

Hello all, Can some one please suggest something on simulating some sort of "object-Ids" in Haskell? I mean, something like the following relation will hold: > a1 == a2 = (objectID a1) == (objectID a2) Currently I have something like > import Data.Hash >import qualified Data.ByteString.Char8 as B > newtype UniqueID = UniqueID (Hash, B.ByteString) I have a type class called Identifiable, the instances of which are supposed to give a unqiue bytestring representation of the instance which can be arbitrarily long but should satisfy the condition mentioned earlier. > class Identifiable a where > instanceID :: a -> B.ByteString and finally, the required funtion objectID is defined as : > objectID :: (Hashable a, Identifiable a) => a -> UniqueID > objectID a1 = UniqueID (hash a1, instanceID a1) while comparing object Ids, I compare the hash values first (which can be faster for arbitrary values). Only if they are equal then I compare the instanceIDs and count on laziness for avoiding the construction of the bytestrings where they are not needed. Can you please suggest a better approach? I also toyed with the idea of storing all the data 'objects' in an array and use the index as the identifier but the trouble is I am not aware of all the number of instances before hand under all the circumstances. Many thanks Hemanth K

5 6

Happy GLR mode build failures
by Cetin Sert 01 Jul '09

01 Jul '09

Hi, It's not possible to build the Happy glr examples using GHC 6.10.3 and Happy 1.18.4: cetin@unique:~/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr$ make make loop CMD=run make[1]: Entering directory `/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr' for d in expr-eval expr-tree expr-monad hidden-leftrec highly-ambiguous packing nlp bio-eg; do (cd $d && make run); done make[2]: Entering directory `/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr/expr-eval' # might want to run happy with --ghc ghc -I../common -i../common -package data -O -cpp -fglasgow-exts -package lang -o expr --make Main.lhs <command line>: unknown package: data make[2]: *** [expr] Error 1 make[2]: Leaving directory `/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr/expr-eval' make[2]: Entering directory `/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr/expr-tree' # might want to run happy with --ghc ghc -I../common -i../common -package data -O2 -cpp -fglasgow-exts -package lang -o expr --make Main.lhs <command line>: unknown package: data make[2]: *** [expr] Error 1 make[2]: Leaving directory `/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr/expr-tree' make[2]: Entering directory `/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr/expr-monad' ghc -I../common -i../common -package data -cpp -fglasgow-exts -package lang -o expr --make Main.lhs <command line>: unknown package: data make[2]: *** [expr] Error 1 make[2]: Leaving directory `/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr/expr-monad' make[2]: Entering directory `/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr/hidden-leftrec' ghc -I../common -i../common -package data -cpp -fglasgow-exts -package lang -o expr --make Main.lhs <command line>: unknown package: data make[2]: *** [expr] Error 1 make[2]: Leaving directory `/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr/hidden-leftrec' make[2]: Entering directory `/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr/highly-ambiguous' ghc -I../common -i../common -package data -cpp -fglasgow-exts -package lang -o expr --make Main.lhs <command line>: unknown package: data make[2]: *** [expr] Error 1 make[2]: Leaving directory `/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr/highly-ambiguous' make[2]: Entering directory `/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr/packing' Makefile:8: warning: overriding commands for target `.y.hs' ../Makefile.defs:15: warning: ignoring old commands for target `.y.hs' ghc -I../common -i../common -package data -cpp -fglasgow-exts -package lang -o expr --make Main.lhs <command line>: unknown package: data make[2]: *** [expr] Error 1 make[2]: Leaving directory `/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr/packing' make[2]: Entering directory `/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr/nlp' ghc -I../common -i../common -package data -cpp -fglasgow-exts -package lang -o english --make Main.lhs <command line>: unknown package: data make[2]: *** [english] Error 1 make[2]: Leaving directory `/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr/nlp' make[2]: Entering directory `/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr/bio-eg' Making BioData.hs WITHOUT optimisation (for speed) ghc -I../common -i../common -package data -cpp -fglasgow-exts -package lang -funfolding-use-threshold0 -fno-strictness -c BioData.hs <command line>: unknown package: data make[2]: *** [BioData.hi] Error 1 make[2]: Leaving directory `/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr/bio-eg' make[1]: *** [loop] Error 2 make[1]: Leaving directory `/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr' make: *** [all] Error 2 cetin@unique:~/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr$ cabal update Downloading the latest package list from hackage.haskell.org cetin@unique:~/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr$ cabal install data cabal: There is no package named data cetin@unique:~/.cabal/packages/ hackage.haskell.org/happy/1.18.4/happy-1.18.4/examples/glr$ happy --version; ghc --version Happy Version 1.18.4 Copyright (c) 1993-1996 Andy Gill, Simon Marlow (c) 1997-2005 Simon Marlow Happy is a Yacc for Haskell, and comes with ABSOLUTELY NO WARRANTY. This program is free software; you can redistribute it and/or modify it under the terms given in the file 'LICENSE' distributed with the Happy sources. The Glorious Glasgow Haskell Compilation System, version 6.10.3 or GHC 6.10.1 and Happy 1.18.2: cetin@sweethome:~/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr$ makemake loop CMD=run make[1]: Betrete Verzeichnis '/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr' for d in expr-eval expr-tree expr-monad hidden-leftrec highly-ambiguous packing nlp bio-eg; do (cd $d && make run); done make[2]: Betrete Verzeichnis '/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr/expr-eval' # might want to run happy with --ghc ghc -I../common -i../common -package data -O -cpp -fglasgow-exts -package lang -o expr --make Main.lhs <command line>: unknown package: data make[2]: *** [expr] Fehler 1 make[2]: Verlasse Verzeichnis '/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr/expr-eval' make[2]: Betrete Verzeichnis '/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr/expr-tree' # might want to run happy with --ghc ghc -I../common -i../common -package data -O2 -cpp -fglasgow-exts -package lang -o expr --make Main.lhs <command line>: unknown package: data make[2]: *** [expr] Fehler 1 make[2]: Verlasse Verzeichnis '/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr/expr-tree' make[2]: Betrete Verzeichnis '/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr/expr-monad' ghc -I../common -i../common -package data -cpp -fglasgow-exts -package lang -o expr --make Main.lhs <command line>: unknown package: data make[2]: *** [expr] Fehler 1 make[2]: Verlasse Verzeichnis '/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr/expr-monad' make[2]: Betrete Verzeichnis '/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr/hidden-leftrec' ghc -I../common -i../common -package data -cpp -fglasgow-exts -package lang -o expr --make Main.lhs <command line>: unknown package: data make[2]: *** [expr] Fehler 1 make[2]: Verlasse Verzeichnis '/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr/hidden-leftrec' make[2]: Betrete Verzeichnis '/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr/highly-ambiguous' ghc -I../common -i../common -package data -cpp -fglasgow-exts -package lang -o expr --make Main.lhs <command line>: unknown package: data make[2]: *** [expr] Fehler 1 make[2]: Verlasse Verzeichnis '/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr/highly-ambiguous' make[2]: Betrete Verzeichnis '/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr/packing' Makefile:8: Warnung: Die Befehle für das Ziel ».y.hs« werden überschrieben ../Makefile.defs:15: Warnung: Alte Befehle für das Ziel ».y.hs« werden ignoriert ghc -I../common -i../common -package data -cpp -fglasgow-exts -package lang -o expr --make Main.lhs <command line>: unknown package: data make[2]: *** [expr] Fehler 1 make[2]: Verlasse Verzeichnis '/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr/packing' make[2]: Betrete Verzeichnis '/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr/nlp' ghc -I../common -i../common -package data -cpp -fglasgow-exts -package lang -o english --make Main.lhs <command line>: unknown package: data make[2]: *** [english] Fehler 1 make[2]: Verlasse Verzeichnis '/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr/nlp' make[2]: Betrete Verzeichnis '/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr/bio-eg' Making BioData.hs WITHOUT optimisation (for speed) ghc -I../common -i../common -package data -cpp -fglasgow-exts -package lang -funfolding-use-threshold0 -fno-strictness -c BioData.hs <command line>: unknown package: data make[2]: *** [BioData.hi] Fehler 1 make[2]: Verlasse Verzeichnis '/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr/bio-eg' make[1]: *** [loop] Fehler 2 make[1]: Verlasse Verzeichnis '/home/cetin/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr' make: *** [all] Fehler 2 cetin@sweethome:~/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr$ happy --version; ghc --version Happy Version 1.18.2 Copyright (c) 1993-1996 Andy Gill, Simon Marlow (c) 1997-2005 Simon Marlow Happy is a Yacc for Haskell, and comes with ABSOLUTELY NO WARRANTY. This program is free software; you can redistribute it and/or modify it under the terms given in the file 'LICENSE' distributed with the Happy sources. The Glorious Glasgow Haskell Compilation System, version 6.10.1 When I try to manually build something out of a .y file, I keep getting: cetin@sweethome:~/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr$ find | grep -E "y$" | xargs -n 1 echo happy -gcal happy -gcal ./packing/Expr.y happy -gcal ./highly-ambiguous/Expr.y happy -gcal ./expr-eval/Expr.y happy -gcal ./expr-monad/Expr.y happy -gcal ./nlp/English.y happy -gcal ./hidden-leftrec/Expr.y happy -gcal ./expr-tree/Expr.y happy -gcal ./bio-eg/Bio.y cetin@sweethome:~/.cabal/packages/ hackage.haskell.org/happy/1.18.2/happy-1.18.2/examples/glr$ find | grep -E "y$" | xargs -n 1 happy -gcal reduce/reduce conflicts: 2 happy: src/ProduceGLRCode.lhs:190:11-76: Irrefutable pattern failed for pattern (pre, drop_me : post) shift/reduce conflicts: 7 reduce/reduce conflicts: 1 happy: src/ProduceGLRCode.lhs:190:11-76: Irrefutable pattern failed for pattern (pre, drop_me : post) shift/reduce conflicts: 9 happy: src/ProduceGLRCode.lhs:190:11-76: Irrefutable pattern failed for pattern (pre, drop_me : post) shift/reduce conflicts: 9 happy: src/ProduceGLRCode.lhs:190:11-76: Irrefutable pattern failed for pattern (pre, drop_me : post) shift/reduce conflicts: 2 happy: src/ProduceGLRCode.lhs:190:11-76: Irrefutable pattern failed for pattern (pre, drop_me : post) shift/reduce conflicts: 4 reduce/reduce conflicts: 1 happy: src/ProduceGLRCode.lhs:190:11-76: Irrefutable pattern failed for pattern (pre, drop_me : post) shift/reduce conflicts: 9 happy: src/ProduceGLRCode.lhs:190:11-76: Irrefutable pattern failed for pattern (pre, drop_me : post) unused rules: 20 shift/reduce conflicts: 35 reduce/reduce conflicts: 68 happy: src/ProduceGLRCode.lhs:190:11-76: Irrefutable pattern failed for pattern (pre, drop_me : post) Does anyone have solution for this? The irrefutable pattern failure issue is especially bothersome for me as I ran into it in a Fortran grammar I'm writing and got stuck. Best Regards, Cetin Sert

1 0

List spine traversal
by Tony Morris 01 Jul '09

01 Jul '09

Is there a canonical function for traversing the spine of a list? I could use e.g. (seq . length) but this feels dirty, so I have foldl' (const . const $ ()) () which still doesn't feel right. What's the typical means of doing this? -- Tony Morris http://tmorris.net/

11 13

gtk2hs tray icon disappears when using GHCi
by Deniz Dogan 01 Jul '09

01 Jul '09

Hi I'm just trying out gtk2hs for the first time and I quite like it. However, for some reason my tray icon (...Gtk.Display.StatusIcon) disappears after a split second when I run my program using GHCi. What's the reason for this? Perhaps this is even a bug? It works just fine if I compile an .exe. I'm using Windows XP with GHC 6.10.3 and gtk2hs 0.10.1. import Graphics.UI.Gtk import Graphics.UI.Gtk.Display.StatusIcon main :: IO () main = do initGUI window <- windowNew tray <- statusIconNewFromFile "c:/Program Files/TortoiseHg/icons/commit.png" window `onDestroy` mainQuit widgetShowAll window mainGUI -- Deniz Dogan

1 0

Haskell on JVM
by Greg Meredith 01 Jul '09

01 Jul '09

Simon, et al, It might be interesting to look at CAL<http://labs.businessobjects.com/cal/>as a non-blank-slate beginning for Haskell on the JVM. To my mind there are three things that this needs to make it a real winner: - Much, much better Java interop. Basically, the bar to meet here is Scala/Java interop. - Better support for "std" Haskell syntax - and better support for some of the basic (semantic and syntactic) extensions - Figuring out what of Hackage it is reasonable to support Best wishes, --greg Date: Tue, 23 Jun 2009 15:16:03 +0100 > From: Simon Peyton-Jones <simonpj(a)microsoft.com> > Subject: RE: [Haskell-cafe] Haskell on the iPhone > To: Rick R <rick.richardson(a)gmail.com>, Haskell Cafe > <haskell-cafe(a)haskell.org> > Message-ID: > < > 638ABD0A29C8884A91BC5FB5C349B1C33F4BAAFA41(a)EA-EXMSG-C334.europe.corp.microsoft.com > > > > Content-Type: text/plain; charset="us-ascii" > > Good news about the iPhone port! > > There seems to be quite a bit more interest now in supporting platforms > other than win/*nix on x86 these days*. Maybe now there will be sufficient > motivation to make the fundamental changes required. Caveat: I have > absolutely no idea of the scope or complexity of said changes. I will look > through the LambdaVM code (and iPwn when available) to get an idea. > > There is definitely an opportunity here for someone to make an impact. > There is no reason in principle why Haskell can't run on a JVM or .net or > other platform. But it's not just a simple matter of absorbing some patch > or other. Here's a summary I wrote a little while ago: > > http://haskell.org/haskellwiki/GHC:FAQ#Why_isn.27t_GHC_available_for_.NET_o… > > The short summary is: > > * There is interesting design work to do; and then interesting > engineering work to make it a reality. > > * We (at GHC HQ) would love to see that happen, but are not likely > to drive it. > > * If someone, or a small group, wanted to take up the cudgels and > work on it, we'd be happy to advise. > > * We'd certainly consider folding the results into the HEAD, > provided the author(s) are willing to maintain it, and we feel that the > result is comprehensible and maintainable. > > * But another viable route might well be to use the GHC API, which > means that the result wouldn't be part of GHC at all, just a client of the > API. That would make it much easier to distribute upgrades etc, just as a > Cabal package. > > Simon > -- L.G. Meredith Managing Partner Biosimilarity LLC 1219 NW 83rd St Seattle, WA 98117 +1 206.650.3740 http://biosimilarity.blogspot.com

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ANN: package Boolean: Generalized booleans
by Conal Elliott 30 Jun '09

30 Jun '09

I just uploaded a new package [1] for generalized booleans, which provides type classes with generalizations of boolean values & operations, if-then-else, Eq and Ord. These values & types come up for me with every new deep DSEL, and I think they do for others as well. The design space has some tricky trade-offs, and I'm not positive I've found the optimum yet. Users & comments are very welcome. Please direct discussion to the haskell-cafe list (rather than haskell list). [1]: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Boolean - Conal

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Re: [Haskell-cafe] Monoid wants a (++) equivalent
by Bryan O'Sullivan 30 Jun '09

30 Jun '09

On Tue, Jun 30, 2009 at 9:50 AM, David Leimbach <leimy2k(a)gmail.com> wrote: > I actually worry that this will make people think, more incorrectly, that > Monoids are about appending stuff only. > I think that adding a graphical operator as a synonym for mappend would actually help to address that, since the magic word "append" would no longer be nearly as common in source code, and that textual name certainly is (unhelpfully) suggestive of a specific semantics.

3 2

Re: [Haskell-cafe] Making a strict (non-lazy) GCL Interpreter
by Hector Guilarte 30 Jun '09

30 Jun '09

Thanks Ketil, I'll try to give that a try, but as I said beforen, I don't know anything about monads, and since this project is for next monday and I have many other projects for the University for next week too I can't learn them right now... What I need to do is randomly select an element from a List... Any Ideas? Also, I had another question in my original e-mail... Any ideas about that? ------Original Message------ From: Ketil Malde To: Hector Guilarte Cc: haskell-cafe(a)haskell.org Subject: Re: [Haskell-cafe] Making a strict (non-lazy) GCL Interpreter Sent: Jun 30, 2009 05:00 Hector Guilarte <hectorg87(a)gmail.com> writes: > I need to randomly select ONE of the valid conditions and execute it's > instruction. I know there is a Random Monad, but it returns an IO > Int, No, this is not right. Values in the Random monad are computations that rely on randomness, but they can produce values of arbitrary type. (The 'a' in 'Random a', no?) > Is there anyway I can do some Random that doesn't involve IO? or any other > solution? Some options are: 1. Use the IO monad 2. Use the Random monad 3. Pass around a RandomGen explicitly 4. Generate an infinite stream of random values, and pass that around I think option 2 is the nicest, but option 4 may work if the use of randomness is limited. No. 3 does the same as 2 (I presume, I never looked) but with a lot more noise in your code, and no. 1 erases the separation between real IO, and computations -- which IME includes a lot of them -- that happen to depend on randomness (but require no other IO). -k -- If I haven't seen further, it is by standing in the footprints of giants

1 0

Reflections on the ICFP 2009 programming contest
by Justin Bailey 30 Jun '09

30 Jun '09

Anyone have thoughts to share? I'd love to read others' experiences but there isn't much coming up with searches or on redditt ... I was happiest with the VM I implemented. Sadly, I wasn't able to solve any of the scenarios, but my VM ran damn fast. That didn't seem to matter so much this year as it did two years ago - I think I am still scarred by Endo's DNA .. Anyways, for those who care, the heart of my VM implementation was a monadic fold over the program, with a mutable array representing the machine's memory, all inside ''runSTUArray.'' I used a simple data type to represent the machine: data Machine = Machine { instrs :: [OpCode] , dataMem :: UArray Int Val , outputs :: UArray Int Val , status :: !Int , inputs :: IntMap Val } where ''dataMem'' holds the data memory area. To execute a program, I folded over the ''instrs'' list and updated memory as I went: exec :: Machine -> Input -> Machine exec m@(Machine { instrs = instrs }) inps = let m' = m { inputs = readInputs inps } newMem = runSTUArray $ do mem' <- thaw (dataMem m) foldM (step m') mem' (zip instrs [0..]) I considered ''unsafeThaw'' in the above, but performance didn't hurt me much and it seemed safer. Since I was recording all output I was worried that would break referential integrity. In any case, when the fold was finished I just assigned ''newMem'' to the new machine and moved to the next iteration. ''step'' takes the mutable array and updates it while the program executes. I won't show the whole body, as it just a separate definition for each opcode, just the type: step :: Machine -> STUArray s Int Val -> (OpCode, Addr) -> ST s (STUArray s Int Val) The only downside to this approach was the machine had three mutuable states: memory, output, and status. runSTUArray only wants to return a single array so inside step I had to hold all values in one array. Not a big deal but a little ugly. I kept a diary of my experience over the weekend at http://icfp2009.codeslower.com. I started out with such optimism ... Stil, I'm glad to have done it. Lots of fun! My thanks to the organizers!

8 10

[help] Creating the simplest possible adhoc network
by lysgaard 30 Jun '09

30 Jun '09

Hi. I'm in the quest of exploring adhoc networks together with Haskell. Both are quite new to me. I found the http://hackage.haskell.org/package/adhoc-network-1.0.3 adhoc package in Hackage, it's made for the p2p chat client http://hackage.haskell.org/package/Barracuda Barracuda . I've tried to understand the barracuda client, but since my understanding of Haskell is not the best (yet!) the package becomes to massive for me to understand. I wondered if someone would be kind enough to help me build the simplest possible adhoc network peer using the http://hackage.haskell.org/package/adhoc-network-1.0.3 adhoc library What i want to make is just command line proof of concept code for the adhoc library. But since the documentation is rather sparse (German pdfs) I'm having real problems understanding how to achieve this. Have a nice summer! -Morten -- View this message in context: http://www.nabble.com/-help--Creating-the-simplest-possible-adhoc-network-t… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

1 0

6.12.1 planning
by Simon Marlow 30 Jun '09

30 Jun '09

Hi Folks, As usual, we're planning a major release of GHC around September. Here's our list of the main items currently scheduled for 6.12.1, and their status. If you have the time and inclination to help with any of these, please get involved! * Parallel performance. 6.12.1 will ship with the improvements to parallel performance described in our ICFP 2009 paper. Still to do: overhaul the +RTS GC settings, tune for good performance by default. * Parallel profiling: the new RTS tracing features will be included, and we hope to have a release of ThreadScope to coincide with GHC 6.12.1. ThreadScope is written using gtk2hs, and could benefit from someone with expertise in producing polished gtk2hs apps - if you can lend a hand, contact Satnam Singh <satnams(a)microsoft.com>. * Unicode I/O: the new Unicode I/O library is in, and will ship with 6.12.1. Still to do: decide on the public API for changing encodings and newline conversion. * Shared libraries: we intend to ship with shared library support on at least x86/Linux and x86-64/Linux. There are various tasks remaining to do here - Duncan, can we have a summary? * Data Parallel Haskell. Manuel, can you comment on the state of play? What can we expect in time for 6.12.1? * Plugin support in GHC. The patches are not yet in GHC, and as far as I know are awaiting review - Simon, can you say more? * The new backend code generator. At the moment, it seems unlikely that GHC 6.12.1 will ship with the new code generator enabled by default, although it may well be available for testing. Meanwhile, work on it continues. The smaller items are all embodied in tickets, here are the tickets currently in the 6.12.1 milestone (135): http://hackage.haskell.org/trac/ghc/query?status=new&status=assigned&status… and on the 6.12 branch (251): http://hackage.haskell.org/trac/ghc/query?status=new&status=assigned&status… I estimate there are 2 man years of work here - needless to say, we aren't going to fix all these tickets :) As usual, if you want to vote for something, add your email to the CC field of the ticket. Several of these tickets would make good tasks for a fledgling GHC hacker. e.g. http://hackage.haskell.org/trac/ghc/ticket/2362 (allow full import syntax in GHCi) has a lot of support, and is a nice self-contained task (but not a small one). Even if you're not a GHC hacker you can still help, e.g. by helping to narrow down the cause of a bug, or verifying a bug on your platform. Let me remind people that GHC HEAD has the new build system, and it's actually rather pleasant to work with. Even if you have no idea what you're doing, you can always say 'make' at the top level and the build system will figure out what needs doing (ok, so that's what build systems are supposed to do, but GHC's has never quite managed it until now!). Cheers, Simon

3 2

Breaking ghci
by Günther Schmidt 30 Jun '09

30 Jun '09

Hi folks, I would like to announce that I have not merely managed to make the RTS choke during runtime on stack overflows like lesser programmers, no, *I* have managed to write code that ghc is not even able to compile due to exhausting virtual memory! Top that! Günther

4 3

Re: BerkeleyDBXML linking problems.
by Sebastiaan Visser 30 Jun '09

30 Jun '09

(crosspost from haskell-libraries) Hello all, again. Meanwhile I've been able to install this package without too much trouble on a Linux system. Unfortunately MacOSX is still a problem. Both on Linux and Mac I installed the Berkeley DB and DBXML packages with `--prefix=/usr' so all include files and libraries end up in a standard place. Also both on Linux and Mac I installed the Haskell BerkeleyDB bindings just with: cabal install BerkeleyDB Because the DBXML include files are installed under /usr/include/dbxml/ *.hpp and the BerkeleyDBXML binding accesses them without this prefix I did: cabal install BerkeleyDBXML --extra-include-dirs=/usr/include/dbxml On both system installation is not a problem. Compiling the demo `adventure' included in de bindings distribution works fine on Linux but fails on MacOSX. The errors are the ones in my previous mail below. A full hpaste of it can be found here[1]. Any idea where the difference in behaviour comes from on these platforms and how to fix this? Unfortunately, my knowledge of the c++ toolchain and Haskell FFI bindings using these is _very_ limited. Thanks, Sebastiaan [1] http://www.hpaste.org/fastcgi/hpaste.fcgi/view?id=6389#a6389 On Jun 26, 2009, at 12:56 PM, Sebastiaan Visser wrote: > Hello all, > > After manually specifying where to find the appropriate include and > library directories for the dbxml distribution, I succeeded to > install both the BerkeleyDB and the BerkeleyDBXML Haskell bindings. > They both nicely show up in `ghc-pkg list'. > > But when I try to compile my own test or the demo program included > in the BerkeleyDBXML package it will kindly present me a dozen or so > pages of linking errors. The top lines are: > > Undefined symbols: > "std::basic_string<char, std::char_traits<char>, > std::allocator<char> >::_Rep::_M_destroy(std::allocator<char> > const&)", referenced from: > __xmlDocument_setContent in > libHSBerkeleyDBXML-0.6.2.a(dbxml_helper.o) > ... > > Do I have to tell GHC where to find the original dbxml libraries > when compiling my BerkeleyDBXML aware Haskell programs? > > Small system overview: > - Mac OS X 10.5.7 > - GHC 6.10.3 > - BerkeleyDB 0.7.1 > - BerkeleyDBXML 0.6.2 > - gcc/g++ 4.0.1 > > Any clue on how to fix this? > > Thanks, > > -- > Sebastiaan Visser

1 0

coding standard question
by Vasili I. Galchin 30 Jun '09

30 Jun '09

Hello, I am working with some existing code. "where/let" functions use the same name for function parameters as the outer function and hence there is a "shadow" warning from the compiler. To me it doesn't see totally unreasonable to code like this .... the downside is the nasty ghc warnings. Is there a coding consensus on this issue? Vasili

17 26

Wondering about c type in haskell.
by Magicloud Magiclouds 30 Jun '09

30 Jun '09

Hi, There are times, when we need to make some system calls, or call C library. So we have to deal with C data types. For example, CPid, which is an integer, actually. So we can do "fromIntegral pid". Then why do not we define "type CPid = Integer", and convert Haskell Integer with C Int internally. So the "user" does not have to care about the type convert (everywhere, which is ugly). And, specially, when doing something like serialisation, for Haskell Integer, the user does not have to do things with precision. But for CPid, without the fromIntegral, we have to specify its precision, well, on different machine/OS, the precision may not be the same. -- 竹密岂妨流水过山高哪阻野云飞

4 6

Making a strict (non-lazy) GCL Interpreter
by Hector Guilarte 30 Jun '09

30 Jun '09

Hi everyone! (First of all, I don't know Monads!) I made a GCL (Guarded Command Language) Compiler and Interpreter for my Languages and Machines course in my University with alex, happy and ghc. I asked about a week ago about the use of unsafePerformIO for that same project, now I have two new doubts: 1) When more than a Condition is true in a if cond1 -> instruction1 | cond2 -> instruction2 ... | condN -> instructionN fi I need to randomly select ONE of the valid conditions and execute it's instruction. I know there is a Random Monad, but it returns an IO Int, Is there anyway I can do some Random that doesn't involve IO? or any other solution? That part of the code is: (My code is in Spanish. TablaOutput is a type and it stands for the tupe of the Symbol Table (Data.Map) and the Output [String], obtenerValidos checks wich pair of (condition,instruction) are true and makes a list out of them, ejecutarUnoRand is the Instruction that executes one of the instructions randomly) evalSeleccion:: [(BoolY,Instruccion)] -> TablaOutput -> TablaOutput evalSeleccion lista tabla = let validos = obtenerValidos lista [] tabla in if (isEmpty validos) then error "Las guardias del If estan incompletas" else ejecutarUnoRand validos tabla obtenerValidos:: [(BoolY,Instruccion)] -> [(BoolY,Instruccion)] -> TablaOutput -> [(BoolY,Instruccion)] obtenerValidos [] validos tabla = validos obtenerValidos ((boolY,instruccion):bloqueIns) validos tabla = if (evalBoolY boolY (fst tabla)) then obtenerValidos bloqueIns (validos ++ [(boolY,instruccion)]) tabla else obtenerValidos bloqueIns validos tabla ejecutarUnoRand:: [(BoolY,Instruccion)] -> TablaOutput -> TablaOutput ejecutarUnoRand validos tabla = let rand = 0 --getStdRandom (randomR (0,(length validos))) HERE'S WHERE I'M SUPPOSED TO DO RANDOM, RIGHT NOW I'M JUST CHOSING THE FIRST in evalInstruccion (snd (validos !! rand)) tabla 2) Since Haskell is Lazy, and my GCL program is being interpreted in Haskell then my GCL is Lazy too (I know is not as simple as that but believe me, somehow it is behaving lazy). The problem is that it can't be lazy (said to me by my teacher today) so I tried using seq, I'll paste the code after this: Programs in GCL like: a) var i : value main i <- 1 / 0 end b) var i : value main i <- 1 / 0; show i end c) var i : value var foo : array of 2 main i <- foo[42] end d) var i : value main i <- foo[42]; show i end acts like this: a and c finish interpretation b throws division by zero error and finish interpretation d throws index out of bounds error and finish interpretation Now the code: (again, it is in Spanish. ListLValue is a List of L-Values for the assigments, ListExpr is the list of Expressions to be assigned, Tabla is the Symbol Table (Data.Map), actualizarVar updates a Variable in the Symbol Table with the new value "valor", ActualizarArray updates the position "indice" of an array in the Symbol Table. evalExpr evaluates an arithmetic Expression and returns an Int. Inside evalExpr are the verifications for division by zero of modulo by zero.) evalAsignacion:: ListLvalue -> ListExpr -> Tabla -> Tabla evalAsignacion [] [] tabla = tabla evalAsignacion ((Lid id):valueList) (expr:exprList) tabla = let valor = (evalExpr expr tabla) in valor `seq` evalAsignacion valueList exprList (actualizarVar id valor tabla) evalAsignacion ((LArrayPosition id exprArray):valueList) (expr:exprList) tabla = let valor = (evalExpr expr tabla) indice = (evalExpr exprArray tabla) in valor `seq` indice `seq` evalAsignacion valueList exprList (actualizarArray id indice valor tabla) evalExpr:: Expr -> Tabla -> Int evalExpr expr tabla = let salida = (snd (evalAritmetico expr tabla)) in salida `seq` if (isLeft salida) then error (getLeft salida) else getRight salida --((Int,Int) is the Line and Colum, that's for error reporting) evalAritmetico :: Expr -> Tabla -> ((Int,Int),(Either String Int)) --LET ME KNOW IF YOU NEED THIS PART TOO Thanks in advance, Hector Guilarte

2 1

[: Where the bracket things are? :]
by Paul Keir 30 Jun '09

30 Jun '09

I'd like to add my own custom list delimiters to ghc; such as the [: and :] of Data Parallel Haskell. The purpose is mainly to learn a little about GHC's internals. Any suggestions on the GHC files I should look at first? Alternatively, maybe this is actually possible from outside the compiler. Cheers, Paul

3 2

What's in a text API?
by Bryan O'Sullivan 30 Jun '09

30 Jun '09

I don't normally post blog links here, but this one is near and dear to my heart: what can we do to make Haskell a more hospitable language for text processing? http://www.serpentine.com/blog/2009/06/30/python-and-haskell-text-apis-comp… If you have comments or suggestions, please feel welcome to respond via the blog's comments or on this list. I'll be following both.

1 0

Reflections on Haskell and ICFP Contest 2009
by Rafael Gustavo da Cunha Pereira Pinto 30 Jun '09

30 Jun '09

Hi All, As the ICFP 2009 contest (http://www.icfpcontest.org) approaches its end, I decided to write down some thoughts I had while trying. On Friday I downloaded the task (http://www.icfpcontest.org/task-1.9.pdf) read it for a while, and, since my goal is to finish by Xmas, went to the swimming pool. :-D While swimming, I started to think on the problem, and realized that the task is almost too easy for Haskell. Actually the task was so easy, that they added a final, non-scoring, task for those who have finished early. This year's task is to build a VM that runs a (simple) program that simulates the physics of a satellite. The VM code has no branches, acting like a huge pocket calculator. The mission is to create a simulator that interact with this VM and maneuver the sattelite(s) on predefined patterns. Here is how it went: 1) Reading the orbiter data file: The orbiter data file is a stream of 32-bit unsigned integers, which are commands, and 64-bit double precision IEEE-754 floats, which are data, forming a 96-bit frame. For this part I decided to use the Data.Binary module from hackage. The module is great, and it is very simple to use. But that took me 3 hours to learn how to use it (which, with my "honey-do" list ended up to be in Sunday morning) By Saturday night I was cursing "The Binary Strike Force" because a) get :: Word32 reads it in little-endian b) get :: Double reads the result of an decodeFloat, which has no resamblance at all with IEEE-754 standards c) I spent the entire Saturday (2 hours, honey-do excluded) thinking I was doing something wrong!! I was really pissed of, until I found "getWord32le" and "getWord64le", which solved 80% of the problem. The final blow was to decode the Word64 encoded IEEE-754 float into a Haskell float, which took me another honey-do-free hour. First step solved. (BTW: I am attaching the first version to this e-mail. I will upload to Hackage upon completion, when getIEEE754float64le and putIEEE754float64le functions are done!) 2) Running the VM: This is the step I am working on. A really good and obvious approach to run the VM is to use a RWS monad, since: a) I have a fixed environment (the program and the input ports) b) I have a state (the program counter, the status register and the data memory contents) c) I have a monoid output (the output ports) This is my recurrent complaint (a rant, maybe): this really important monad is completely undocumented, left for the developer to figure out how to use it. Even each of the singular monads (Reader, Writer and State) is poorly documented. I will do some toy programs to understand each one. Let's hope I can create a hands-on tutorial on the RWS monad. 3) Controlling the sattelites This is going to be a piece of cake (aheeem! Just kidding!!). After computing the VM iteration, another computation will take the output data time series and estimate the next move. It will be a piece of cake, considering I would have learned enough of Haskell state monads on step 2 to have just to worry about the physics of the problem!!! I'll keep you updated as my tests go, and hopefully I will have a working demo of the task written in Haskell by Xmas... 2010! ;-) Best regards, Rafael Gustavo da Cunha Pereira Pinto

3 4

INAP 2009: DEADLINE EXTENSION and Final Call for Papers
by Pedro Salgueiro 29 Jun '09

29 Jun '09

------------------------------------------------------------------- (PLEASE DISTRIBUTE -- **DEADLINE EXTENDED** -- PLEASE DISTRIBUTE) ------------------------------------------------------------------- Final Call for Papers INAP 2009 18th International Conference on Applications of Declarative Programming and Knowledge Management November 5-7, 2009 Evora, Portugal http://www.di.uevora.pt/inap2009/ http://inap.dialogengines.com/ ------------------------------------------------------------ Organized by the Portuguese AI Society (APPIA), the INAP Committee and the Society of Logic Programming (GLP e.V.) == Overview == Declarative Programming is a family of advanced paradigms for the modeling and solving of complex problems. These specification and implementation methods have attracted more and more attention over the past years, e.g. in the domains of databases and natural language processing, for modeling and the processing of combinatorial problems, and for establishing systems for the web. == INAP 2009 == INAP is a communicative and dense forum for intensive discussion of applications of important technologies related to Prolog, Logic and Constraint Programming as well as closely related advanced software. It comprehensively covers the impact of programmable logic solvers in the Internet Society, its underlying technologies, and leading edge applications in industry, commerce, government, and societal services. INAP 2009 continues a tradition of successful workshops cast around the applications of declarative programming, which were held in Kobe (1997), Tokyo (1995, 1996, 1998 - 2001), Potsdam (2004), Fukuoka (2005) and Wuerzburg (2007). We invite the submission of high quality papers on the described topics, especially, but not exclusively, on different aspects of Declarative Programming, Constraint Processing and Knowledge Management as well as their use for Distributed Systems and the Web: - Knowledge Management, e.g. Data Mining, Decision Support, Deductive Databases - Distributed Systems and the Web, e.g. Agents and Concurrent Engineering, Semantic Web - Constraints, e.g. Constraint Systems, Extensions of Constraint (Logic) Programming - Theoretical Foundations, e.g. Deductive Databases, Nonmonotonic Reasoning - Systems and Tools for Academic and Industrial Use - Knowledge-based Web Services - Logic Solvers and Applications == Workshop Format == The technical program of the workshop will include invited presentations (to be announced), regular technical sessions with presentations of the accepted papers, system demonstrations and a panel discussion. == Conference Venue == The conference will be held at the University of Evora, Portugal in November 5-7, 2009. Evora is a nice and quiet historical city located in the south of Portugal that can be reached from Lisbon by train or coach in under 2 hours. It is a small city of 60.000 inhabitants, 120 km inland from Lisbon and classified by Unesco as World Heritage. The University of Evora was established in the 16th Century and is the 2nd oldest Portuguese University. The social program is promising since the region is very rich in historical sites (Stone Age, Roman, Medieval and Renaissance remains) and also offers a very special gastronomy. See http://en.wikipedia.org/wiki/%C3%89vora for more information. == Important Dates == Paper Submission Deadline: July 13, 2009 (EXTENDED!) Notifications to Authors: August 17, 2009 Camera-ready Version Deadline: September 14, 2009 INAP 2009 Workshop: November 5-7, 2009 == Submission Guidelines == Participants should submit a paper (maximum 15 pages, PDF format), describing their work in topics relevant to the workshop. Accepted papers will be presented during the workshop. At least one author of an accepted contribution is expected to register for the workshop, and present the paper. All submissions should include the author's name(s), affiliation, complete mailing address, and email address. Authors are requested to prepare their submissions, following the LNCS/LNAI Springer format. Please see: http://www.springer.de/comp/lncs/authors.html for further details. The submission should be submitted through the electronic submission site: http://www.easychair.org/conferences/?conf=inap2009 The deadline for receipt of submissions is July 13, 2009. Papers received after this date will not be reviewed. Eligible papers will be peer-reviewed by at least three members of the Program Committee. Authors will be notified via email of the results by August 17, 2009. Authors of accepted papers are expected to improve their paper based on reviewers' comments and to send a camera ready version of their manuscripts by September 14, 2009. Accepted papers will be included in the workshop proceedings, which will be distributed to the participants. As in previous editions, we plan to publish selected papers in a proceedings volume in the Springer Lecture Notes in Artificial Intelligence (LNAI) series. == Organizing Committee == Vitor Nogueira vbn AT di.uevora.pt Salvador Abreu spa AT di.uevora.pt Pedro Salgueiro pds AT di.uevora.pt Universidade de Evora Portugal == Program Committee == Salvador Abreu, University of Evora, Portugal (co-chair) Sergio Alvarez, Boston College, USA Philippe Codognet, CNRS/JFLI, Tokyo, Japan Vitor Santos Costa, University of Porto, Portugal Daniel Diaz, University of Paris I, France Ulrich Geske, University of Potsdam, Germany Gopal Gupta, UT Dallas, USA Petra Hofstedt, Technical University of Berlin, Germany Ulrich Neumerkel, Technical University of Vienna, Austria Vitor Nogueira, University of Evora, Portugal Enrico Pontelli, New Mexico State University, USA Irene Rodrigues, University of Evora, Portugal Carolina Ruiz, Worcester Polytechnic Institute, USA Dietmar Seipel, University of Wuerzburg, Germany (co-chair) Terrance Swift, CENTRIA, Portugal Hans Tompits, Technical University of Vienna, Austria Masanobu Umeda, Kyushu Institute of Technology, Japan Armin Wolf, Fraunhofer FIRST, Berlin, Germany Osamu Yoshie, Waseda University, Japan == Contact Information == inap2009(a)di.uevora.pt Universidade de Evora Departamento de Informatica Largo dos Colegiais, 2 7004-516 Evora - PORTUGAL

1 0

FFI and heap memory usage limit
by Marcin Kosiba 29 Jun '09

29 Jun '09

Hello, Recently I've come across a certain GC/FFI-related problem. I've googled a bit, but didn't find anything specific. I'm running certain simulations, which tend to allocate a lot of garbage in memory. Since this causes the OOM-killer to kill my simulation at 98% completion, I used the -M switch, and all was well. But because my simulation results are fairly big, I needed to compress them with bz2 before sending them over the network. So I used bzlib. Now this took an odd turn, because the simulation started crashing with out-of-memory errors _after_ completing (during bz2 compression). I'm fairly certain this is a GC/FFI bug, because increasing the max heap didn't help. Moving the bz2 compression to a separate process provided a reasonable solution. What I think is happening is that after the simulation completes, almost all of the available memory (within the -M limit) is filled with garbage. Then I run bzlib which tries to allocate more memory (from behind FFI?) to compress the results, which in turn causes an out-of-memory error instead of triggering a GC collection. I'm writing to ask if this is a known/fixed issue. I'm using ghc 6.10.3, bzlib 0.5.0.0. If this is something new then I'll try to come up with a small program which demonstrates the problem. -- Marcin Kosiba

5 5

Proper arrival of platform?
by Magnus Therning 29 Jun '09

29 Jun '09

When will the Haskell Platform arrive properly? With that I mean, when will GHC stop shipping with a set of base libraries (e.g. network)? /M -- Magnus Therning (OpenPGP: 0xAB4DFBA4) magnus＠therning．org Jabber: magnus＠therning．org http://therning.org/magnus identi.ca|twitter: magthe

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Haskell Weekly News: Issue 123 - June 29, 2009
by Brent Yorgey 29 Jun '09

29 Jun '09

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20090629 Issue 123 - June 29, 2009 --------------------------------------------------------------------------- Welcome to issue 123 of HWN, a newsletter covering developments in the [1]Haskell community. A bit late this week since over the weekend I was trying to get some unruly satellites to behave (with moderate success). Anyway, some fun stuff this week: Haskell on the iPhone; new libraries for 3D animation, web development, session types; new releases of haskell-src-exts and darcs; and more. Also, if it seems that there haven't been many quotes lately, it's because people haven't been @remembering very many in #haskell. I cannot telepathically sense (via the Haskell-force, hereafter known as the "Horce") when someone says something funny. Announcements Haskell Symposium call for participation. Stephanie Weirich [2]announced that [3]registration is now open for the [4]ACM SIGPLAN Haskell Symposium 2009, to be held on 3 September 2009 in Edinburgh, Scotland (co-located with ICFP). The purpose of the Haskell Symposium is to discuss experiences with Haskell and future developments for the language. The scope of the symposium includes all aspects of the design, semantics, theory, application, implementation, and teaching of Haskell. jhc 0.6.1. John Meacham [5]announced the release of [6]jhc 0.6.1, featuring a a much simplified cross-compilation mechanism. X Haskell Bindings 0.3. Antoine Latter [7]announced the 0.3.* series release of the [8]X Haskell Bindings. This release, like the prior 0.2.* series focuses on making the API prettier. happstack-0.3.2. Matthew Elder [9]announced the release of [10]happstack-0.3.2, with many changes, updates, and bug fixes. sendfile-0.1. Matthew Elder [11]announced the release of [12]sendfile, a library which exposes zero-copy sendfile functionality in a portable way. Right now it natively supports linux 2.6+ (maybe older too) and windows 2000+; on other platforms it will fall back seamlessly to a portable haskell implementation. Reusable Corecursive Queues via Continuations. Leon Smith [13]requested feedback on a draft of an upcoming article in Monad.Reader issue 14, "Lloyd Allison's Corecursive Queues: Why Continuations Matter", describing the implementation of the [14]control-monad-queue package. Haskell on the iPhone. Ryan Trinkle [15]announced that his company, iPwn Studios Inc., is currently preparing to release an open source patch to GHC that allows it to output binaries for iPhone OS. The patch will be released under a BSD license as soon as possible and hopefully integrated into the GHC main-line in the near future. Program to set the GNOME desktop background picture randomly. Colin Paul Adams [16]announced [17]gnome-desktop, a library which periodically picks a random picture from $HOME/Pictures, and sets it as the GNOME desktop background. loli: a minimal web dev DSL. Jinjing Wang [18]announced the release of [19]loli, a web development DSL built on top of [20]hack. It allows you to easily define routes, build your custom template backends through a simple Template interface, and integrate with other hack middleware. Cal3D animation library. Gregory D. Weber [21]announced the [22]Cal3D for Haskell project, which provides a partial binding to the [23]C++ Cal3D animation library, a platform- and graphics-API-independent C++ library for skeletal-based character animation. There are three packages available on hackage: [24]cal3d-0.1, a Haskell binding to the Cal3D library itself; as well as [25]cal3d-opengl-0.1 and [26]cal3d-examples-0.1. A Reader Monad Tutorial. Henry Laxen [27]announced a nice [28]Reader monad tutorial. full-sessions: yet another implementation of session types. Keigo Imai [29]announced the pre-release of [30]full-sessions, yet another implementation of session types in Haskell. Session types are used to statically check the safe and consistent use of communication channels according to protocols. A notable advantage of [31]this implementation is that it requires almost no type annotation or term annotations. and at the same time provides full functionality of session types including channel-generation and channel-passing. darcs 2.3 beta 1. Petr Rockai [32]announced the immediate availability of a first beta release of darcs 2.3. There are a number of improvements and bugfixes over the last stable release, 2.2 (see the announcement for a full list). Moreover, work has been done on performance of "darcs whatsnew" for large repositories. This has also introduced a slight risk of regressions, but please note that all of the disruptive changes are in read-only code paths: the new code will never touch your repository, so it is unable to cause permanent harm. The worst that could happen is that you get no or bad diff from "darcs whatsnew". Please help test it (cabal install [33]darcs-beta)! New release of ZeroTH. Robin Green [34]announced a new release (2009.6.23.3) of [35]ZeroTH, a tool for preprocessing Haskell code to run splices and remove Template Haskell dependencies. Major changes include support for more Haskell code via haskell-src-exts 1.0.0, better error messages, and librification. Emping-0.6 and Tests/Examples. Hans van Thiel [36]announced version 0.6 of [37]Emping, a (prototype) interactive tool for the discovery and analysis of (universal, not statistical) predictive rules in tables of nominal data. haskell-src-exts-1.0.0. Niklas Broberg [38]announced the first stable release of the [39]haskell-src-exts package, version 1.0.0! haskell-src-exts is a package for Haskell source code manipulation. In particular it defines an abstract syntax tree representation, and a parser and pretty-printer to convert between this representation and String. It handles (almost) all syntactic extensions to the Haskell 98 standard implemented by GHC, and the parsing can be parametrised on what extensions to recognise. HaRe (the Haskell Refactorer) in action - short screencast. Claus Reinke [40]linked to [41]a short video showing [42]HaRe, the Haskell refactorer, in action. HaRe still exists---but needs some love in the form of time and/or funding for maintenance and continued development. Trivial pivoting for the DSP lu decomposition. Fernan Bolando [43]announced the beginnings of a [44]simple circuit simulator using haskell, which uses a modified version of the haskell DSP library matrix, extended with a simple pivoting method. Discussion make some Applicative functions into methods, and split off Data.Functor. Ross Paterson [45]proposed moving several functions such as (<$), (*>), and so on into their respective classes with default definitions, to allow for specialized implementations. base library and GHC 6.12. Ian Lynagh began a [46]discussion about how to structure the base library in the future. Proposal: ExplicitForall. Niklas Broberg [47]proposed adding a new GHC extension, ExplicitForall, to be used for turning on explicit 'forall' syntax in types, and to help disentangle and simplify some existing extensions. Generic Graph Class. Ivan Lazar Miljenovic [48]proposed a generic graph class to serve as a common interface for the many Haskell libraries that deal with graph data structures. Type system trickery. Andrew Coppin [49]asked how to statically ensure certain properties of recursive data structures with the type system, generating varied suggestions involving GADTs. Blog noise [50]Haskell news from the [51]blogosphere. Blog posts from people new to the Haskell community are marked with >>>, be sure to welcome them! * Magnus Therning: [52]Making a choice from a list in Haskell, Vty (part 0). * The Gentoo Haskell Team: [53]Haskell in Gentoo. * Michael Snoyman: [54]Hack Introduction. * >>> Henry Laxen: [55]Reader Monad Confusion. * >>> Akshay: [56]Dynamic Programming in Haskell and why DP is useful. * David Amos: [57]Direct products revisited. * mightybyte: [58]Basic Happstack Blog App. * David Amos: [59]Some groups and some graphs. * Gergely Patai: [60]Short-term hp2any plans. * Isaac Dupree: [61]cross-package, Plan A. * >>> Oliver Reeves: [62]Data Crunching in Haskell. * Roman Cheplyaka: [63]Halting problem. * Petr Rockai: [64]darcs 2.3 beta 1. * Eric Kow (kowey): [65]Haskell syntax highlighting on Wikipedia and Wikibooks. * Greg Bacon: [66]Setting up a simple test with Cabal. * Isaac Dupree: [67]Cross-package documentation, part 1. * Sean Leather: [68]RFC: Extensible, typed scanf- and printf-like functions for Haskell. * >>> Akshay: [69]Foray Into Haskell. * >>> Ivan Uemlianin: [70]decorate-sort-undecorate in Haskell. * Isaac Dupree: [71]How To Navigate Your Code:. * Petr Rockai: [72]soc progress 5. * DEFUN 2009: [73]The tutorial schedule is now ready. * DEFUN 2009: [74]Last call for talk proposals!. * >>> Greg Bacon: [75]Setting up a simple test with Cabal. * The GHC Team: [76]New paper: Parallel Performance Tuning for Haskell. * Brandon Simmons: [77]Fun with Lazy Arrays: the LZ77 Algorithm. * >>> Keith: [78]Bird Tracks Through Math Land: Basic Matrix Ops. Quotes of the Week * gnuvince: Contributions to Hackage are measured in µConals. * DavidWheeler: Compatibility means deliberately repeating other people's mistakes. About the Haskell Weekly News New editions are posted to [79]the Haskell mailing list as well as to [80]the Haskell Sequence and [81]Planet Haskell. [82]RSS is also available, and headlines appear on [83]haskell.org. To help create new editions of this newsletter, please see the information on [84]how to contribute. Send stories to byorgey at cis dot upenn dot edu. The darcs repository is available at darcs get [85]http://code.haskell.org/~byorgey/code/hwn/ . References 1. http://haskell.org/ 2. http://article.gmane.org/gmane.comp.lang.haskell.general/17320 3. http://www.regmaster.com/conf/icfp2009.html 4. http://haskell.org/haskell-symposium/2009/ 5. http://www.haskell.org//pipermail/haskell/2009-June/021449.html 6. http://repetae.net/computer/jhc/ 7. http://www.haskell.org//pipermail/haskell/2009-June/021460.html 8. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/xhb 9. http://article.gmane.org/gmane.comp.lang.haskell.general/17317 10. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/happstack 11. http://article.gmane.org/gmane.comp.lang.haskell.general/17316 12. http://hackage.haskell.org/package/sendfile 13. http://article.gmane.org/gmane.comp.lang.haskell.general/17311 14. http://hackage.haskell.org/package/control-monad-queue 15. http://article.gmane.org/gmane.comp.lang.haskell.general/17307 16. http://article.gmane.org/gmane.comp.lang.haskell.general/17304 17. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/gnome%2Ddesktop 18. http://article.gmane.org/gmane.comp.lang.haskell.cafe/60675 19. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/loli 20. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hack 21. http://article.gmane.org/gmane.comp.lang.haskell.cafe/60596 22. http://haskell.org/haskellwiki/Cal3d_animation 23. http://home.gna.org/cal3d/ 24. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/cal3d 25. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/cal3d%2Dopengl 26. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/cal3d%2Dexamples 27. http://article.gmane.org/gmane.comp.lang.haskell.cafe/60591 28. http://www.maztravel.com/haskell/readerMonad.html 29. http://article.gmane.org/gmane.comp.lang.haskell.cafe/60511 30. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/full%2Dsessions 31. http://www.agusa.i.is.nagoya-u.ac.jp/person/sydney/full-sessions.html 32. http://article.gmane.org/gmane.comp.lang.haskell.cafe/60465 33. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/darcs%2Dbeta 34. http://article.gmane.org/gmane.comp.lang.haskell.cafe/60430 35. http://hackage.haskell.org/package/zeroth 36. http://article.gmane.org/gmane.comp.lang.haskell.cafe/60411 37. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Emping 38. http://article.gmane.org/gmane.comp.lang.haskell.cafe/60392 39. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/haskell%2Dsrc%2D… 40. http://article.gmane.org/gmane.comp.lang.haskell.cafe/60388 41. http://www.youtube.com/watch?v=4I7VZV7elnY 42. http://www.cs.kent.ac.uk/projects/refactor-fp/ 43. http://article.gmane.org/gmane.comp.lang.haskell.cafe/60590 44. http://plan9.bell-labs.com/sources/contrib/fernan/escomma.tar.bz2 45. http://thread.gmane.org/gmane.comp.lang.haskell.libraries/11428 46. http://thread.gmane.org/gmane.comp.lang.haskell.libraries/11413 47. http://thread.gmane.org/gmane.comp.lang.haskell.glasgow.user/17137 48. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/60460 49. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/60277 50. http://planet.haskell.org/ 51. http://haskell.org/haskellwiki/Blog_articles 52. http://therning.org/magnus/archives/664 53. http://gentoohaskell.wordpress.com/?p=3 54. http://blog.snoyman.com/2009/06/28/hack-introduction/ 55. http://www.maztravel.com/haskell/readerMonad.html 56. http://www.akrish.net/2009/06/28/dynamic-programming-in-haskell-and-why-dp-… 57. http://haskellformaths.blogspot.com/2009/06/direct-products-revisited.html 58. http://softwaresimply.blogspot.com/2009/04/basic-happstack-blog-app.html 59. http://haskellformaths.blogspot.com/2009/06/some-groups-and-some-graphs.html 60. http://just-bottom.blogspot.com/2009/06/short-term-hp2any-plans.html 61. http://haddock2009.wordpress.com/2009/06/25/cross-package-plan-a/ 62. http://buffered.io/2009/06/25/data-crunching-in-haskell/ 63. http://ro-che.blogspot.com/2009/06/halting-problem.html 64. http://web.mornfall.net/blog/darcs_2.3_beta_1.html 65. http://koweycode.blogspot.com/2009/06/haskell-syntax-highlighting-on.html 66. http://feedproxy.google.com/~r/gbacon/~3/7rlf4Dd1JKU/setting-up-simple-test… 67. http://haddock2009.wordpress.com/2009/06/24/cross-package-documentation-par… 68. http://feedproxy.google.com/~r/splonderzoek/~3/vO9VuXrFTCg/rfc-extensible-t… 69. http://www.akrish.net/2009/06/24/foray-into-haskell/ 70. http://llaisdy.wordpress.com/2009/06/24/decorate-sort-undecorate-in-haskell/ 71. http://haddock2009.wordpress.com/2009/06/23/how-to-navigate-your-code/ 72. http://web.mornfall.net/blog/soc_progress_5.html 73. http://www.defun2009.info/blog/2009/06/the-tutorial-schedule-is-now-ready/ 74. http://www.defun2009.info/blog/2009/06/last-call-for-talk-proposals/ 75. http://gbacon.blogspot.com/2009/06/setting-up-simple-test-with-cabal.html 76. http://ghcmutterings.wordpress.com/2009/06/22/new-paper-parallel-performanc… 77. http://coder.bsimmons.name/blog/2009/06/fun-with-lazy-arrays-the-lz77-algor… 78. http://blog.keithsheppard.name/2009/06/bird-tracks-through-math-land-basic.… 79. http://www.haskell.org/mailman/listinfo/haskell 80. http://sequence.complete.org/ 81. http://planet.haskell.org/ 82. http://sequence.complete.org/node/feed 83. http://haskell.org/ 84. http://haskell.org/haskellwiki/HWN 85. http://code.haskell.org/~byorgey/code/hwn/

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ANN: loli: a minimal web dev DSL
by Jinjing Wang 29 Jun '09

29 Jun '09

loli is a DSL built on hack. It allows you to easily define routes, build your custom template backends through a simple Template interface, and integrate with other hack middleware. * driver The simplest app looks like this import Network.Loli import Hack.Handler.Happstack main = run . loli $ get "/" (text "loli power") * route get "/hello" $ do text "hello" will route "/hello" to a controller that outputs hello. * middleware using a middleware is just as declaring middleware lambda * template the template interface is class Template a where interpolate :: a -> String -> Context -> IO String Context is just [(String, String)] After implementing your own template engine, you can use output $ your-engine-constructor "template-name" * demo I put the source of a dummy paste app on itself: <http://lolipaste.easymic.com/00000-lolipaste.haskell> loli is on hackage, lolipaste is in loli repo on github: * <http://github.com/nfjinjing/loli> happy hacking -- jinjing

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XMonad and NetworkManager?
by Ketil Malde 29 Jun '09

29 Jun '09

Hi, A bit off-topic, but this is the café, after all... Like many here, I run XMonad as my window manager on top of Linux. On - at least my brand of - Linux, networking is generally handled by NetworkManager, which really needs its associated applet (nm-applet) to work properly. While I discovered trayer, which at least let me run nm-applet without dragging in most of Gnome, it still drags in some of the bloat, and interacts a bit poorly with the rest of the system (temporarily locks up the screen, transparency doesn't work, positions itself awkwardly, needs gconfd at incovinient times..) So: has anybody tried better alternatives to NetworkManager and nm-applet? Wicd, say? Or something that can integrate with dzen? -k -- If I haven't seen further, it is by standing in the footprints of giants

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ANNOUNCE: X Haskell Bindings 0.3
by Antoine Latter 29 Jun '09

29 Jun '09

I'd like to announce the 0.3.* series release of the X Haskell Bindings. This release, like the prior 0.2.* series focuses on making the API prettier. This release is based on the XCB protocol descriptions version 1.5 This does mean that there's a good chance this is a breaking release for any code compiled against 0.2.*. The goal of XHB is to provide a Haskell implementation of the X11 wire protocol, similar in spirit to the X protocol C-language Binding (XCB). On Hackage: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/xhb Source: darcs get http://community.haskell.org/~aslatter/code/xhb/ New this release: * In 0.2, a lot of the core protocol requests, events and replies were updated to use prettier Haskell datatypes for the various enums and bitmasks. Thanks to Peter Harris's work on the protocol description XML files, these niceties have extended out to all of the extension requests, events and replies and such. * Due to name clashes, I the type-names for events and errors now include an "Event" or "Error" suffix. For example, the type "Notify" has become "NotifyEvent". * Now based on the protocol description version 1.5, from 1.4. Related projects: X protocol C-language Binding: http://xcb.freedesktop.org/

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[patch] lhaskell.vim update
by Nicolas Wu 29 Jun '09

29 Jun '09

I have made some modifications to the lhaskell.vim (v1.04) file to add a feature, and fix up some bugs. I don't know if this is the right place to post for patches, but the file I have claims that the haskell-cafe is the maintainer. First, I made it so that \begin{spec} and \end{spec} environments are recognised. This helps those of us who use lhs2TeX to document files. Second, I've fixed up the highlighting where inline Haskell between bars "|" used to be mistaken for verbatim text. There's also a small fix to handle \begin{code} \end{code} tags better. The modified file is attached.

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Haskell Platform + gtk2hs
by John Van Enk 29 Jun '09

29 Jun '09

List, Has any one managed to install gtk2hs on a Windows box running the Haskell Platform? I've had no luck; it seems the gtk2hs installer is unable to find the GHC installation. /jve

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How to convert CPid to Word32?
by Magicloud Magiclouds 29 Jun '09

29 Jun '09

Hi, I am trying to use Data.Binary with ProcessID. Well, how to convert between CPid and Word32? Thanks. -- 竹密岂妨流水过山高哪阻野云飞

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parallel haskell
by Kevin Smith 29 Jun '09

29 Jun '09

I'm interested in doing some research with parallel programming using Haskell (both multi-core on one machine and clusters using multiple machines) but in going through the various resources on the web (looking at GPH and others), it is not clear to me what the current state is as many of the resources/projects have out of date information in them. Any pointers ? What parallel extensions are available in the current version 6.10.3 ? Which parallel extensions support clustered networks ? Where to start ? Thanks

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