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Haskell-platform and ghc 7.4
by G 11 Mar '12

11 Mar '12

Am new to haskell, but one thing I wanted to try out was the performance of an app in haskel. Having issues getting it to compile under ghc 7.0.4. The owner recommend trying to upgrade to 7.2/7.4 I see a warning that the haskell-platform isn't compatible with with 7.4.1, or so my homebrew install says. Can it be made to compile ?? Can I remove the haskell-platform and then install the dev tools from the haskell-platform via cabal etc once I have moved to 7.4.x etc ? Thanks

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network-conduit proxy
by grant 11 Mar '12

11 Mar '12

I am trying to get a proxy working using the network-conduit package on windows. So I send a request to port 5002 and that gets forwarded to another port 5000 where I have a simple echo server running. I made a stab at it, but get intermittent send errors after the first connection Here is the code: {-# OPTIONS -Wall #-} import Data.Conduit import Data.Conduit.Network import Network (withSocketsDo) import Control.Monad.IO.Class (liftIO) import Control.Monad.Trans.Resource main::IO () main = withSocketsDo $ runTCPClient (ClientSettings 5000 "localhost") $ \src1 sink1 -> do liftIO $ print "in tcpclient section" liftIO $ withSocketsDo $ runTCPServer (ServerSettings 5002 Nothing) $ \src sink -> do liftIO $ print "in tcpserver section" _ <- liftIO $ runResourceT $ resourceForkIO $ do src1 $$ sink return () src $$ sink1 Thanks for any help, Grant

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haskell platform - mac lion - installation error
by Peter 11 Mar '12

11 Mar '12

Hello - I'm a new user, having some trouble installing the Haskell Platform (2011.4.0.0 64bit.pkg) on a Macbook Pro (10.7.3). I installed Xcode 4.3.1 (4E1019), then the Haskell Platform. When I double-click on the Platform package icon, I get an installation dialogue with an error message reading "Developer Tools Missing - Please install Xcode developer tools first." Are Xcode developer tools something distinct from Xcode itself? I'm mystified by this error message. Any assistance would be greatly appreciated - thank you.

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Haskell Java interoperability
by bartosz＠fpcomplete.com 11 Mar '12

11 Mar '12

I looked on haskell.org for solutions to Haskell/Java interop, but there doesn't seem to be any current project. What is the status of Lambada or its progeny (I asked Erik Meijer, but he lost track of it). Which project is closest to maturity? --Bartosz

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ANNOUNCE: diagrams 0.5
by Brent Yorgey 09 Mar '12

09 Mar '12

I am pleased to announce the release of version 0.5 of diagrams [1], a full-featured framework and embedded domain-specific language for declarative drawing. Check out the gallery [2] for examples of what it can do! [1] http://projects.haskell.org/diagrams [2] http://projects.haskell.org/diagrams/gallery.html Highlights of this release include: - A new diagrams-contrib [3] package of user-contributed modules, which so far contains code for tree drawing, Apollonian gaskets, planar tilings, "wrapped" layout, and turtle graphics. - Experimental support for animation, built on top of the new active [4] library. - Numerous small additions and improvements, including more general rounded rectangle shapes and better text support. - Much better performance in some common situations, such as laying out a very long list of diagrams using 'cat' and related combinators. - Added support for GHC 7.4. See the release notes [5] for complete details, and the diagrams wiki [6] for help migrating code from 0.4 to 0.5 (changes should be minimal). [3] http://hackage.haskell.org/package/diagrams%2Dcontrib [4] http://hackage.haskell.org/package/active [5] http://projects.haskell.org/diagrams/releases.html [6] http://www.haskell.org/haskellwiki/Diagrams/Migrate0.5 Try it out ---------- For the truly impatient: cabal install gtk2hs-buildtools cabal install diagrams Diagrams is supported under GHC 6.12, 7.0, 7.2, and 7.4. However, getting cairo to build can be tricky on some platforms; see the diagrams wiki [8] for more information and workarounds regarding specific platforms. (A new native SVG backend is in the works, targeted for the 0.6 release.) To get started with diagrams, read the quick tutorial [9], which will introduce you to the fundamentals of the framework. For those who are even less impatient but want to really dig in and use the power features, read the user manual [10]. [7] http://projects.haskell.org/gtk2hs/development/#development [8] http://www.haskell.org/haskellwiki/Diagrams [9] http://projects.haskell.org/diagrams/tutorial/DiagramsTutorial.html [10] http://projects.haskell.org/diagrams/manual/diagrams-manual.html Get involved ------------ Subscribe to the project mailing list [11], and/or come hang out in the #diagrams IRC channel on freenode.org for help and discussion. Make some diagrams. Fix some bugs [12]. Submit your cool examples for inclusion in the gallery or your cool code for inclusion in the diagrams-contrib package! [11] http://groups.google.com/group/diagrams-discuss [12] http://code.google.com/p/diagrams/issues/list Happy diagramming! Brought to you by the diagrams team: - Peter Hall - Ian Ross - Michael Sloan - Ryan Yates - Brent Yorgey with contributions from: - Sam Griffin - Claude Heiland-Allen - John Lato - Vilhelm Sjoberg - Luite Stegeman - Kanchalai Suveepattananont - Scott Walck

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ANNOUNCE: string-conversions-0.1
by Sönke Hahn 09 Mar '12

09 Mar '12

Hi all! string-conversions is a very simple package to facilitate dealing with different string types. It provides a simple type class that allows you to convert between values of different string types. It also provides type synonyms for these string types. Supported types are: - String - Strict ByteString - Lazy ByteString - Strict Text - Lazy Text http://hackage.haskell.org/package/string-conversions Any comments welcome. Cheers, Sönke

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If you'd design a Haskell-like language, what would you do different?
by Robert Clausecker 09 Mar '12

09 Mar '12

Image you would create your own language with a paradigm similar to Haskell or have to chance to change Haskell without the need to keep any compatibility. What stuff would you add to your language, what stuff would you remove and what problems would you solve completely different? Thanks in advance for all answers, yours Robert Clausecker

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The (!) operation
by Christopher Done 08 Mar '12

08 Mar '12

‘Ello. Is there a generalization of this operator? It's all over the place, it's basically (!) :: (Monad m, Indexed collection index value) => index -> container -> m value We have `(!!)` on lists, `(!)` on maps, vectors, json objects, … (doesn't seem there's one for bytestring) (Though I seem to recall the monadic return value being frowned upon but I don't recall why.) Thoughts? Ciao!

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GHCi fails to load C++ object files (missing symbol)
by Yves Parès 08 Mar '12

08 Mar '12

Hi, I'm trying to have GHCi load a haskell file that depends on a C++ object file, which causes GHCi to fail because of an unknown symbol (*and I did link with **libstdc++*), whereas the link into an executable with ghc works and runs perfectly. I've reduced my code to the smallest one that produces the problem: The C++ part defines a mere class and C externals that enable communication with Haskell: // Header Stuff.hpp class Base { public: Base(); ~Base(); } extern "C" { Base* mkthing(); void delthing(Base*); } ----------- // Source Stuff.cpp #include <iostream> #include "Stuff.hpp" using namespace std; Base::Base() { cout << "Base created" << endl; } Base::~Base() { cout << "Base deleted" << endl; } extern "C" { Base* mkthing() { return new Base(); } void delthing(Base* b) { delete b; } } Haskell code (just for reference, but I'm not sure it's relevant), Main.hs: {-# LANGUAGE ForeignFunctionInterface #-} import Foreign import Foreign.C foreign import ccall unsafe "mkthing" mkthing :: IO (Ptr ()) foreign import ccall unsafe "delthing" delthing :: Ptr () -> IO () main = do p <- mkthing delthing p I then compile it with: g++ -c Stuff.cpp ghci Main.hs Stuff.o -lstdc++ And then the error is: Loading object (static) Stuff.o ... done Loading object (dynamic) /usr/lib/i386-linux-gnu/gcc/i686-linux-gnu/4.5.2/libstdc++.so ... done final link ... ghc: Stuff.o: unknown symbol `__dso_handle' linking extra libraries/objects failed Whereas 'ghc Main.hs Stuff.o -lstdc++' works just fine. Does GHCi lacks a link directive that regular GHC has?

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Type classes for converting to Text and String
by Simon Hengel 08 Mar '12

08 Mar '12

Hi! When writing library code that should work with both String and Text I find my self repeatedly introducing classes like: class ToString a where toString :: a -> String class ToText a where toText :: a -> Text (I use this with newtype wrapped value types backed by Text or ByteString.) So I wonder whether it would be a good idea to have a package that provides those classes. Or maybe just ToText, and provide default implementations of toString and toText, like: class ToText a where toText :: a -> Text toText = Text.pack . toString toString :: a -> String toString = Text.unpack . toText How do you guys deal with that? Any thoughts? Cheers, Simon

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