- Haskell-Cafe - Haskell.org

cabal install time
by Ozgur Akgun 08 Feb '10

08 Feb '10

I hate sending such messages to cafe, but... When I try to install "time" I get the following error: > sudo cabal install time ld: duplicate symbol ___hscore_d_name in /Users/username/.cabal/lib/unix-2.4.0.0/ghc-6.10.4/libHSunix-2.4.0.0.a(dirUtils.o) and /Library/Frameworks/GHC.framework/Versions/610/usr/lib/ghc-6.10.4/base-4.1.0.0/libHSbase-4.1.0.0.a(PrelIOUtils.o) UsingSnow Leopard with the following versions of ghc and cabal > ghc --version The Glorious Glasgow Haskell Compilation System, version 6.10.4 > cabal --version cabal-install version 0.6.4 using version 1.6.0.3 of the Cabal library Thanks for any help. Best, -- Ozgur Akgun

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Haskell Weekly News: Issue 149 - February 08, 2010
by jfredett＠gmail.com 08 Feb '10

08 Feb '10

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20100208 Issue 149 - February 08, 2010 --------------------------------------------------------------------------- Welcome to issue 149 of HWN, a newsletter covering developments in the [1]Haskell community. Hello Haskellers, this week's HWN was delayed a bit in the hopes of making it a bit more substantial. I hate putting up thin HWNs, but of course this must occasionally happen. We have several new CFPs for workshops this week, a new benchmarking package, and some fun quotes. Till next week, Haskellers, your Haskell Weekly News! Announcements Call for Papers: Haskell Symposium 2010. Jeremy.Gibbons [2]announced a call for papers for the 2010 ACM SIGPLAN Haskell Symposium 2010 in Baltimore, Maryland; on 30th September. 2nd CfP: LOPSTR 2010. Temur Kutsia [3]announced a second call for papers for the 20th International Symposium on Logic-Based Program Synthesis and Transformation, being held in Hagenberg, Austria, July 23-25, 2010 (co-located with PPDP 2010). PAR 2010: First CFP. Koen Claessen [4]announced a first call for papers for PAR'10, the Workshop on Partiality and Recursion in Interactive Theorem Provers. data-ordlist-0.2. Leon Smith [5]announced a new release of ordlist, including a change to the module name and bug fixes. progression-0.1. Neil Brown [6]announced Progression, a metalibrary which consolidates various existing tools for Haskell optimization (notably Criterion). HList darcs repo. Oleg He who inhabits all types, but is not _|_, has [7]announced a new darcs repo for HList (and OOHaskell) on community.haskell.org. Discussion a beginner question: decorate-op-undecorate. Aran Donohue [8]asked about how to write a function which can 'inspect' inside a datatype. Translation of Haskell type classes. Enrique Martin [9]talked about some experiments he's done with type classes, and asked some questions regarding optimization related to them. Category Theory woes. Mark Spezzano [10]asked about resources for learning about category theory. Blog noise [11]Haskell news from the [12]blogosphere. Blog posts from people new to the Haskell community are marked with >>>, be sure to welcome them! * Dan Piponi (sigfpe): [13]The Categorification of the Naturals. * Roman Cheplyaka: [14]hledger. * Luke Palmer: [15]Associative Alpha Blending. * Neil Brown: [16]Progression: Supporting Optimisation in Haskell. * Holumbus: [17]Hayoo! Webservice API. * apfelmus: [18]The Operational Monad Tutorial. * Dan Piponi (sigfpe): [19]Tagging Monad Transformer Layers. * Darcs: [20]darcs weekly news #53. * JP Moresmau: [21]EclipseFP 1.110 released, with debugging support. Quotes of the Week * lispy|web: This curses binding appears to be terminally broken * lispy: I did, 'cabal install mage' and it complains about curses * lament: Just use fix to find the least funny joke * copumpkin: A monad is just a lax functor from a terminal bicategory, duh. fuck that monoid in category of endofunctors shit About the Haskell Weekly News New editions are posted to [22]the Haskell mailing list as well as to [23]the Haskell Sequence and [24]Planet Haskell. [25]RSS is also available, and headlines appear on [26]haskell.org. To help create new editions of this newsletter, please see the information on [27]how to contribute. Send stories to jfredett . at . gmail . dot . com. The darcs repository is available at darcs get [28]http://patch-tag.com/r/jfredett/HWN2/pullrepo HWN2 . References 1. http://haskell.org/ 2. http://article.gmane.org/gmane.comp.lang.haskell.general/17778 3. http://article.gmane.org/gmane.comp.lang.haskell.general/17770 4. http://article.gmane.org/gmane.comp.lang.haskell.general/17769 5. http://article.gmane.org/gmane.comp.lang.haskell.cafe/70035 6. http://article.gmane.org/gmane.comp.lang.haskell.cafe/69929 7. http://article.gmane.org/gmane.comp.lang.haskell.cafe/69898 8. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/69984 9. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/69914 10. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/69803 11. http://planet.haskell.org/ 12. http://haskell.org/haskellwiki/Blog_articles 13. http://blog.sigfpe.com/2010/02/decategorification-of-naturals.html 14. http://ro-che.blogspot.com/2010/02/hledger.html 15. http://lukepalmer.wordpress.com/2010/02/05/associative-alpha-blending/ 16. http://chplib.wordpress.com/2010/02/04/progression-supporting-optimisation-… 17. http://holumbus.fh-wedel.de/blog/?p=33 18. http://apfelmus.nfshost.com/articles/operational-monad.html 19. http://blog.sigfpe.com/2010/02/tagging-monad-transformer-layers.html 20. http://blog.darcs.net/2010/02/darcs-weekly-news-53.html 21. http://jpmoresmau.blogspot.com/2010/02/eclipsefp-1110-released-with-debuggi… 22. http://www.haskell.org/mailman/listinfo/haskell 23. http://sequence.complete.org/ 24. http://planet.haskell.org/ 25. http://sequence.complete.org/node/feed 26. http://haskell.org/ 27. http://haskell.org/haskellwiki/HWN 28. http://patch-tag.com/r/jfredett/HWN2/pullrepo%20HWN2

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Re: [Haskell-cafe] a beginner question: decorate-op-undecorate
by John Lato 08 Feb '10

08 Feb '10

Hi Stephen, > From: Stephen Tetley <stephen.tetley(a)gmail.com> > > Hi John > > I'm not sure about making Binding polymorphic to get Functor, > Traversable, Foldable... > > While I think you're correct that partitionEithers might not be a > useful example to draw from in this case, I'd assume that Binding > would be part of a larger syntax-tree, thus there might not be a > appropriate single leaf to make the tree polymorphic on. Felipe > Lessa's point - to use Uniplate or one of the Generics packages - > might be a better candidate for implementing traversals. I did not consider that, and hadn't seen any other replies when I first replied. If true, I would agree that one of the Generics packages would be the best option. Regardless, I think this is a valid approach. By thinking of data in terms of Functor, Traversable, etc., one can recognize these patterns. Even if Binding is part of a larger syntax tree and can't reasonably be made polymorphic, creating an fmap-like function to do what the OP requested is IMHO simple and idiomatic Haskell. Using Generics then simplifies the implementation. Cheers, John

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Number formatting
by Günther Schmidt 08 Feb '10

08 Feb '10

Hello, is there a function which will format a number with separators, something that will turn 14509.8674 into 14,509.86? Günther

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GUI programming
by Victor Nazarov 08 Feb '10

08 Feb '10

Hello, I've been writing some GUI application with Gtk2hs. It's an interpreter for lambda-calculus and combinatory logic, it's GPL and if you interested I can share it with cafe. The problem is that the GUI code has become very ugly and I'm tempted to rewrite it totally. I've been looking forward to the FRP stuff, but I've never seen a single definition of the term. Conal Eliot's "denotational programming" is too general to be definition. I want to try Grapefruit, but I got totally lost when I see arrow notation. I consider more lightweight and more imperative approach, something closer to CSP (Communicating Secuential Processes) then FRP. I've just crafted some sample program to illustrate my idea. The behaviour is a monad and it's IO monad so you can do any IO (Gtk2hs) programming you wish. The differences is that you don't attach static event handlers and tries to determine what to do dependent on application state. You attach and detach handlers as much as possible. Behaviour looks like a process that can stop execution and wait for some GUI event. When event arrived it continues execution. Do you see this approach viable. There are steel some details to emerge: * How to wait for several events * How to handle IO exceptions Here is the code: {-# LANGUAGE ExistentialQuantification #-} module Main where import Data.IORef import System.Glib import Graphics.UI.Gtk import Control.Monad.Trans type Event obj = IO () -> IO (ConnectId obj) data Behaviour a = forall b. BBind (Behaviour b) (b -> Behaviour a) | BIO (IO a) | forall obj. GObjectClass obj => BWaitEvent (Event obj) (Behaviour a) instance Monad Behaviour where action >>= generator = BBind action generator return a = BIO (return a) instance MonadIO Behaviour where liftIO action = BIO action runBehaviour :: Behaviour a -> IO a runBehaviour (BBind (BWaitEvent event after) f) = runBehaviour (BWaitEvent event (after >>= f)) runBehaviour (BBind (BIO a) f) = a >>= \x -> runBehaviour (f x) runBehaviour (BBind (BBind a f) g) = runBehaviour (a >>= (\x -> f x >>= g)) runBehaviour (BIO a) = a runBehaviour (BWaitEvent event after) = do sigIdRef <- newIORef (error "You can't access sigIdRef before signal is connected") sigId <- event $ do sigId <- readIORef sigIdRef signalDisconnect sigId runBehaviour after return () writeIORef sigIdRef sigId return (error "You can't expect result from behaviour") waitEvent :: GObjectClass obj => Event obj -> Behaviour () waitEvent event = BWaitEvent event (return ()) main :: IO () main = do initGUI window <- windowNew onDestroy window mainQuit set window [windowTitle := "Hello World"] button <- buttonNew let buttonB label = do liftIO $ set button [buttonLabel := label] waitEvent (onClicked button) buttonB (label ++ "*") runBehaviour (buttonB "*") set window [containerChild := button] widgetShowAll window mainGUI -- Victor Nazarov

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cabal fun (not)
by Johannes Waldmann 08 Feb '10

08 Feb '10

while trying to live with different versions of packages, I found cabal-install's behaviour strange because: you can "cabal install" a package without any complaint but the next "ghc-pkg list" is all red because of conflicts. and it's too late then - there's no way to get back. even if you re-install some package, it seems it is getting a different hashcode, so it's not recognized. if you were doing "cabal install --global" for some ghc package (e.g. old-locale), then ghc seems completely hosed and you've got to re-install the compiler. well that's not a big deal by itself but afterwards you have to re-install all packages ... so please please please have "cabal install" fail with some error message if (that is, before) the install would break anything. - J. $ ghc --version The Glorious Glasgow Haskell Compilation System, version 6.12.1 $ cabal --version cabal-install version 0.8.0 using version 1.8.0.2 of the Cabal library

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Darcs fundraising 2010 - send us to ZuriHac! ($792 more by 15 Feb)
by Eric Kow 08 Feb '10

08 Feb '10

Hi everybody, Only one more week of fundraising to go! We've raised $1208 so far, which gives us another $792 to go in our final push. Can we do it? I sure hope so. Even if we do not, we'll still have raised more than we did last year, so thanks to all! If you're still thinking of helping out, now is the perfect time :-) Otherwise, stay tuned at http://darcs.net/donations.html for our progress. Eric PS. If you send me an email telling me how much you donated, I can update the donations site immediately so that folks can watch our progress bar obsessively :-) Donating by Google Checkout ---------------------------------------------------------------------- Donating via Google Checkout puts more of your donation to work, since Google charges no Checkout fees to 501(c)(3) organizations. Please visit http://darcs.net/donations.html for more details. Donating by check (USA) ---------------------------------------------------------------------- The next best option is to donate by check if you have a US bank account. Checks should be made payable to "Software Freedom Conservancy, Inc.", with "Directed donation: Darcs" in the memo. They can be mailed to Software Freedom Conservancy 1995 BROADWAY FL 17 NEW YORK NY 10023-5882 USA Donating by Paypal ---------------------------------------------------------------------- Please visit http://darcs.net/donations.html for more details. -- Eric Kow <http://www.nltg.brighton.ac.uk/home/Eric.Kow> PGP Key ID: 08AC04F9

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ANN: data-ordlist-0.2
by Leon Smith 07 Feb '10

07 Feb '10

I have released data-ordlist 0.2, with a number of changes: 1. The module name is now Data.List.Ordered, instead of Data.OrdList 2. Three bugfixes: (ack!) insertSet and insertBag assumed reverse-ordered lists, nub failed to remove duplicates. Thanks to Topi Karvonen for reporting the first problem. 3. One semantic change: old_nubBy f == new_nubBy (not . f). The new version is better keeping with the spirit of the rest of the library, and makes the old nub bug much more obvious. Now nubBy is the greedy algorithm that returns a sublist such that for all binary predicates: isSortedBy pred (nubBy pred xs) == True 4. Improved documentation, I hope! Please consider taking a look and letting me know what you think. http://hackage.haskell.org/package/data-ordlist Cheers, Leon

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Re: [Haskell-cafe] a beginner question: decorate-op-undecorate
by John Lato 06 Feb '10

06 Feb '10

> From: Aran Donohue <aran.donohue(a)gmail.com> > > Hi Haskell-Cafe, > > Consider a data type such as > > data Binding = Binding Var (Either Value [Value]) > > representing a variable bound either to a fixed value or that has a list of > possible values. > > I'd like to perform an operation on say, the fixed-value members of a list > of bindings. Data.Either has "partitionEithers"---I'd essentially like to > use partitionEithers, but in a way that it "peeks" into the value field of > the binding. For the sake of argument, let's say I can't or can't modify > Binding to move the Either to the outside. I think that partitionEithers is leading you down the wrong trail. If what you want to do is modify some values inside the binding, I would start with this: > mapVal :: (Either Value [Value] -> Either Value [Value]) -> Binding -> Binding > mapVal f (Binding v e) = Binding v (f e) > > mapLeft :: (a -> b) -> Either a c -> Either b c > mapLeft f = either (Left . f) Right > > -- mapRight is just fmap, but for symmetry > mapRight :: (b -> c) -> Either a b -> Either a c > mapRight = fmap > > modifyFixed :: (Value -> Value) -> Binding -> Binding > modifyFixed f b = mapVal (mapLeft f) b > > modifyList :: ([Value] -> [Value]) -> Binding -> Binding > modifyList f b = mapVal (mapRight f) b > > -- note that modifyFixed and modifyList have very nice point-free representations > -- modifyFixed = mapVal . mapLeft > -- modifyList = mapVal . mapRight Now to apply this to a list: > modifyFixedBindings :: (Value -> Value) -> [Binding] -> [Binding] > modifyFixedBindings f binds = map (modifyFixed f) binds > -- or point-free > modifyFixedBindings' = map . modifyFixed In my opinion, this would be more idiomatic if Binding were polymorphic: > data Binding' k v = Binding' k v > > instance Functor (Binding' k) where > fmap f (Binding' k v) = Binding' k (f v) > > type Binding2 = Binding' Var (Either Value [Value]) now mapVal is just fmap, and these functions are: > modifyFixed2 :: (Val -> Val) -> [Binding2] -> [Binding2] > modifyFixed2 = fmap . fmap . mapLeft > > modifyList2 :: ([Val] -> [Val]) -> [Binding2] -> [Binding2] > modifyList2 = fmap . fmap . mapRight I've typed out all the steps for clarity, but to be honest, I wouldn't bother with the Fixed and List variants, unless you're going to use them frequently. I would do just: > mapVals :: (Either Value [Value] -> Either Value [Value]) -> [Binding] -> [Binding] > mapVals f = map (\(Binding var val) -> Binding var (f val)) and leave it at that, using "mapVals" with the "either" function when necessary. I would consider making Binding polymorphic, though, so you can write the Functor instance. You may also want to look at Data.Traversable. Cheers, John

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safe-lazy-io on GHC 6.12?
by Tom Tobin 06 Feb '10

06 Feb '10

After convincing myself the hard way that you can't be lazy across strict monadic results (by writing myself a "foldrM" -- yeah, I'm still a beginner), I noticed the recent discussion of safe-lazy-io vs. iteratee with interest. The safe-lazy-io package seems much easier to understand than iteratee, but it doesn't compile on GHC 6.12 (and I haven't had any luck in figuring out how to update it myself). The Hackage build log shows the same build result I'm getting [1]; is there any chance of it getting updated to work on 6.12? [1] http://hackage.haskell.org/packages/archive/safe-lazy-io/0.1/logs/failure/g…

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