- Haskell-Cafe - Haskell.org

Re: [Haskell-cafe] Strange No instance error with cabal install
by Rune Harder Bak 21 Sep '11

21 Sep '11

Sorry, forgot to send to the list, But everything works today, and the commit was pulled from aeson to aeson-native, so that must have been it. Thanks! On Wed, Sep 21, 2011 at 8:20 AM, Rune Harder Bak <rune(a)bak.dk> wrote: > So you are saying, that this is basically because he has other version > of different packages, > not providing the same instances, that makes sense. > The other problem was no instance for Default (Request R) (Request > from Network.Wai) > It was provided by http-enumerator, but maybe not in his version of the package. > > I tried with aeson-native after you post without look, but I see a new > one has been released now. > Going to try it today. > Thanks! > > > On Tue, Sep 20, 2011 at 2:00 PM, Roel van Dijk <vandijk.roel(a)gmail.com> wrote: >> I see the aeson version with the stricter dependency on deepseq < 1.2 >> is now also released on hackage: >> >> http://hackage.haskell.org/package/aeson-0.3.2.12 >> >

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Typhoon
by Kazu Yamamoto 21 Sep '11

21 Sep '11

Hello, To those who are in Tokyo for ICFP: The typhoon is likely to come after 16:00 today. Many students and workers will go home earlier this afternoon. It's Japanse style. If typhoon comes, umbrella does not work. Please stay in your building. You should understand all traffic transportation will stop. Even blackout would happen. Please please don't underestimate the typhoon. Typhoon info: http://www.jma.go.jp/en/typh/ http://weathernews.jp/satellite/ Rain visual info: http://tokyo-ame.jwa.or.jp/en/index.html Please don't panic. Stay in your building for about two hours. Enjoy slow life. --Kazu

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Animas/Yampa - Using Zip as a Routing Function in a Parallel Switch with Feedback
by M. George Hansen 20 Sep '11

20 Sep '11

Greetings, I've been playing around with functional reactive programming using Animas/Yampa and ran into a strange situation. I'm using a parallel switch to route input to a collection of signal functions and using the output as feedback (to simulate state). Everything works as expected until I attempt to use zip as a routing function (i.e. pair each element of input with a signal function). Using zip as a routing function causes the program to enter an infinite loop when it evaluates the output from the parallel switch. Here is a minimal program that fails to terminate when using zip as a routing function: ----------------------------------------------------------------------------------------- {-# LANGUAGE Arrows #-} module LoopingTest ( ) where import Control.Arrow import FRP.Animas main = embed (process []) ([42], []) process :: [Activity] -> SF [InputEvent] SystemOutput process activities = proc inputEvents -> do rec let senses = map (\state -> (inputEvents, state)) states states <- par route activities -< senses returnA -< states route :: [Sense] -> [sf] -> [(Sense, sf)] -- route a sfs = fmap (\sf -> (head a, sf)) sfs route = zip type Activity = SF Sense State type InputEvent = Integer type State = [Integer] type Sense = ([InputEvent], State) type SystemInput = ([InputEvent], [State]) type SystemOutput = [State] ----------------------------------------------------------------------------------------- If you run the main function as-is the program will run forever, but if you change the route function to use the commented definition instead of zip the program terminates normally. I simply cannot wrap my brain around this issue - zip normally works just fine with infinite lists as long as one of the lists is finite, and in this case the number of Activity signal functions is known at compile time to be finite. I can't find anything conceptually wrong with using zip as a routing function either. If anyone has any thoughts I would be very grateful. -- M. George Hansen technopolitica(a)gmail.com

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Fwd: Klocwork eNews: Secure Coding for C/C++
by Vasili I. Galchin 20 Sep '11

20 Sep '11

Hello, I get so frustrated trying to convince managers and colleagues of the efficacy of FPLs. Below speaks volumes about the "type safety" of C and C++. It is a bandaid approach. Vasili --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- ---------- Forwarded message ---------- Date: Tue, Sep 20, 2011 at 9:14 AM Subject: Klocwork eNews: Secure Coding for C/C++ To: vigalchin(a)gmail.com ** [image: Klocwork eNewsletter - September 2011] eLEARNING Secure Coding for C/C++ When it comes to security attacks, the network used to be the prime target. But the attack profile has changed. Now security is a software problem too, with the number of software security vulnerabilities growing every year. As a result, the pressure on software developers to create secure software has never been greater. Brush up on the fundamentals of secure coding with this no charge, interactive eLearning course<http://mkto-d0052.com/track?type=click&enid=bWFpbGluZ2lkPWtsb2N3b3JrQmV0YWN…> : - Get the latest secure coding best practices - Learn nine tested secure coding techniques - See how to avoid common buffer overflows *This is a must-see course – view it today!*<http://mkto-d0052.com/track?type=click&enid=bWFpbGluZ2lkPWtsb2N3b3JrQmV0YWN…> SOCIAL MEDIA Follow Klocwork Do you know that Klocwork participates in all your favorite social media channels? Get quick updates from us and see what we're talking about by following us on Facebook, LinkedIn and Twitter. Check out our recent blog posts and links to our social media pages under the *Follow Us* section on www.klocwork.com<http://mkto-d0052.com/track?type=click&enid=bWFpbGluZ2lkPWtsb2N3b3JrQmV0YWN…> . BLOG Join the Discussion *Klocwork University consolidates learning resources into a single roster<http://mkto-d0052.com/track?type=click&enid=bWFpbGluZ2lkPWtsb2N3b3JrQmV0YWN…> * Your one stop for self-paced online learning. *Squeezing max from the 'try/finally' blocks<http://mkto-d0052.com/track?type=click&enid=bWFpbGluZ2lkPWtsb2N3b3JrQmV0YWN…> * Tips on handling resources in Java. *Importance of MISRA<http://mkto-d0052.com/track?type=click&enid=bWFpbGluZ2lkPWtsb2N3b3JrQmV0YWN…> * Klocwork's MISRA support is important to customers. Klocwork | 15 New England Executive Park | Burlington, MA 01803 1.866.556.2967 | www.klocwork.com<http://mkto-d0052.com/track?type=click&enid=bWFpbGluZ2lkPWtsb2N3b3JrQmV0YWN…> © 2011 Klocwork. All rights reserved. If you no longer wish to receive these emails, click on the following link: Unsubscribe<http://resources.klocwork.com/UnsubscribePage.html?mkt_unsubscribe=1&mkt_to…>

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Strange No instance error with cabal install
by Rune Harder Bak 20 Sep '11

20 Sep '11

Sometimes when one of our developers (using Arch-linux) tries to cabal install packages he gets a "no instance for" error. Code that compiles fine on my computer, and other computers I try it on. Even some packages on hackage (trying to install aeson-native for instance gives Data/Aeson/Types.hs:196:22: No instance for (NFData Object) arising from a use of `rnf' Possible fix: add an instance declaration for (NFData Object) In the expression: rnf o In an equation for `rnf': rnf (Object o) = rnf o In the instance declaration for `NFData Value') I tried removing the .ghc and .cabal folder, even reinstalled ghc-7.04 and cabal-install (most recent), but the problem persisted (might not have been a clean install though, I'm no Arch expert) I know this is kind of vauge, and not in she shape of filling a bug report, heck I can't even reproduce the error on my computer. But perhaps somebody else has run in to this strange behavior before? Best, Rune

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ANNOUNCE: lushtags, haskell ctags for Vim Tagbar plugin
by Bit Connor 20 Sep '11

20 Sep '11

I would like to announce the first release of my program lushtags. Available on hackage: cabal install lushtags At github: https://github.com/bitc/lushtags Screenshot: https://github.com/bitc/lushtags/raw/master/doc/screenshot-tagbar-2011-09-1… What is lushtags? From the README: lushtags ======== Create ctags compatible tags files for Haskell programs Similar programs are [hasktags][1], [gasbag][2], [hothasktags][3], and GHC's builtin ctags generation. lushtags differs from these by being designed to have smooth integration with the [Vim Tagbar][4] plugin. Tagbar is nice because it deals with creating tags automatically. There is no need to manually run commands or keep track of tag files. Just open any Haskell file in Vim and the Tagbar window will instantly show an interactive browsable list of all the functions and declarations in the file. This window also updates automatically as you edit the file. The tags created by lushtags are marked with several extensions, so that when used with Tagbar you get these features: - Type signatures are displayed for functions. - Tags are properly scoped so that, for example, data declarations appear as a tree with their constructors scoped as children. - Definitions that are exported from the module are marked as "public" and appear emphasized in Tagbar. - Tag locations are internally stored as patterns, not line numbers, so that you can correctly jump to tags even if they have moved in the source code during editing. ![screenshot](https://github.com/bitc/lushtags/raw/master/doc/screenshot-tagbar-2011-09-19.png) [1]: http://hackage.haskell.org/package/hasktags [2]: http://kingfisher.nfshost.com/sw/gasbag/ [3]: http://hackage.haskell.org/package/hothasktags [4]: http://majutsushi.github.com/tagbar/

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Data.Text.IO.hGetContents problem on windows
by David Virebayre 20 Sep '11

20 Sep '11

Bonjour Café, bonjour Bryan I have a program that works fine on linux, but doesn't on windows. On windows XP with the latest Haskell platform, I get: <socket: 1860>: hFileSize: invalid argument (Bad file descriptor) I think the problem is with hGetContents from Data.Text.IO, but my google-fu failed to help me find any information. Is there something I'm doing wrong ? David. The source code of the part that fails is as follows: -- Execute a command on a distant server using the rexec protocol. rexec :: HostName -- server to connect to -> Text -- user -> Text -- password -> TextEncoding -- server's text encoding -> Text -- command to execute -> IO (Maybe Text) rexec !ip !ru !rp !enc cmd = handle rexec_error $ do hdl <- connectTo ip (PortNumber 512) let end_param = T.singleton (chr 0) ctrl_string = T.concat [ "0", end_param, ru, end_param, rp, end_param, cmd, end_param ] hSetEncoding hdl enc TIO.hPutStr hdl ctrl_string -- make sure the control string is sent. hFlush hdl -- 1st char read is actually a error code which we ignore for now hGetChar hdl !res <- TIO.hGetContents hdl hClose hdl return (Just res) rexec_error :: SomeException -> IO (Maybe Text) rexec_error err = do putStrLn $ show err return Nothing

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Library support for sorting with Text.Data.ICU.Collate.MCollator?
by Richard Cobbe 19 Sep '11

19 Sep '11

I'm trying to sort a list of Text values using a collator obtained from the Text.Data.ICU.Collate module in the text-icu package on Hackage. Unfortunately, I can't use the normal Data.List.sortBy function with one of these collators, because the collators return (IO Ordering), not Ordering. It's easy to write sortWithCollator :: [Text] -> IO [Text], but I'd rather not have to. I haven't been able to find library support for this anywhere -- am I overlooking it, or do I need to write the sort function myself? Thanks, Richard

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The applicative instances for Either?
by Ketil Malde 19 Sep '11

19 Sep '11

Hi, I have a program that makes use of the applicative instance for Either String. I used to define these instances locally, but at some point, they became part of Control.Applicative. I have limited the dependencies to 'base >= 4', but apparently, some version 4s of base include this instance, some do not, and it causes problems for people trying to compile the program. Is there any information, or otherwise accessible source specifying exactly when this was changed, so that I can have more precise dependencies? And is there a simple way to handle this conditionally, either within cabal, or using CPP? -k -- If I haven't seen further, it is by standing in the footprints of giants

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Enumeratees are killing me
by tsuraan 18 Sep '11

18 Sep '11

I'm trying to write what I think should be a simple Enumeratee, but I'm just not having any luck getting it to typecheck, and I'm coming to the realization that I still have no idea what I'm doing. The essential thing I want to do is adapt Data.Enumerator.List.concatMapAccum so that the accumulator function has the type (s -> ao -> Either (ao, [ai]) (s, [ai]) ) . The accumulator returning Right (s, [ai]) behaves as normal, while returning Left (ao, [ai]) will cause the Enumeratee to call the upstream Iterator one last time with (Chunks ai) and then yield with the (ao : xs). I just can't make it work though. Here's the guts of my attempt: step _ k EOF = yield (Continue k) EOF step s k (Chunks xs) = loop s k xs loop s k [] = continue (step s k) loop s k (x:xs) = case decoder s x of Left (extra, ai) -> k (Chunks ai) >>== checkDone (\k' -> yield () $ Chunks (extra:xs)) Right (s', ai) -> k (Chunks ai) >>== checkDoneEx (Chunks xs) (\k' -> loop s' k' xs) At this point I've tried putting a bunch of random stuff into the part to the right of (>>==) in the Left case of loop, but without any luck. Any help would be much appreciated. It seems really weird to me that none of the built-in functions for Enumeratees let you stop before the Enumerator is done. That seems like a really common thing that a person would want; in my case, I'm parsing messages out of a byte stream, so I want to stop each Enumeratee as it finishes its message, but that doesn't seem possible without dropping down to this level.

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