April 2011 - Haskell-Cafe

ANN: Hakyll 3.1
by Jasper Van der Jeugt 06 Apr '11

06 Apr '11

Hello all, I've just uploaded Hakyll 3.1.0.0 [1] to Hackage. It contains some backwards-incompatible changes (but they are really for the greater good). The most important change is the matching done in the rules DSL. What used to be written as: route "posts/*" someRoute compile "posts/*" someCompiler Is now written as: match "posts/*" $ do route someRoute compile someCompiler This new style is way more expressive, as you can define custom predicates such as: match (predicate (\i -> matches "foo/*" i && not (matches "foo/bar" i))) $ do ... For more information, see the Pattern documentation [2]. Another slight change is that the `Hakyll.Web.Tags` [3] module now uses an association list instead of a `Data.Map` -- in case you want to change the order in which tags are displayed. If you have any questions or trouble migrating, feel free to drop a mail to me or here [4] or visit us in #hakyll on Freenode. [1]: http://hackage.haskell.org/package/hakyll [2]: http://jaspervdj.be/hakyll/reference/Hakyll-Core-Identifier-Pattern.html [3]: http://jaspervdj.be/hakyll/reference/Hakyll-Web-Tags.html [4]: https://groups.google.com/forum/#!forum/hakyll Cheers, Jasper

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ncurses trouble
by Andrew Pennebaker 06 Apr '11

06 Apr '11

I'm having trouble using Haskell and ncurses Mac OS X (10.6.6 to be precise). GHC 6.12.3 gives me a lot of trouble, and GHC 7.0.2 even more. rogue.hs, is a text adventure game in the works. $ cat rogue.hs {-# LANGUAGE OverloadedStrings #-} import Data.Text import UI.NCurses main :: IO () main = runCurses $ do win <- defaultWindow updateWindow win $ do moveCursor 10 10 drawText "Hello world! Hit 'q' to exit" render waitForQ win waitForQ :: Window -> Curses () waitForQ win = do ev <- getEvent win Nothing case ev of Just (EventCharacter 'q') -> return () _ -> waitForQ win $ sudo port install ncurses ncursesw $ cabal install ncurses Resolving dependencies... Configuring ncurses-0.2... cabal: c2hs version >=0.15 is required but it could not be found. cabal: Error: some packages failed to install: ncurses-0.2 failed during the configure step. The exception was: ExitFailure 1 Hmm. Cabal couldn't find a solution to the c2hs dependency. So I install it manually. $ cabal install c2hs $ cabal install ncurses Resolving dependencies... Configuring ncurses-0.2... cabal: Missing dependency on a foreign library: * Missing C library: ncursesw This problem can usually be solved by installing the system package that provides this library (you may need the "-dev" version). If the library is already installed but in a non-standard location then you can use the flags --extra-include-dirs= and --extra-lib-dirs= to specify where it is. cabal: Error: some packages failed to install: ncurses-0.2 failed during the configure step. The exception was: ExitFailure 1 MacPorts' ncurses isn't detected by Haskell, so I use Homebrew's. $ brew install ncursesw $ ghc --make -o rogue rogue.hs [2 of 2] Compiling Main ( rogue.hs, rogue.o ) Linking rogue ... ld: warning: in /usr/local/lib/libncursesw.dylib, file was built for unsupported file format which is not the architecture being linked (i386) It appears that the Homebrew ncurses library is x86, and GHC is x86_64, or vice-versa. $ sudo port install ncurses +universal $ sudo port install ncursesw +universal $ brew install --universal ncursesw These don't visibly improve compilation in any way. I thought updating Haskell would fix the problem. $ wget http://lambda.galois.com/hp-tmp/2011.2.0.0/Haskell%20Platform%202011.2.0.0-… $ sudo installer -pkg "Haskell Platform 2011.2.0.0-i386.pkg" -target / $ ghc --version The Glorious Glasgow Haskell Compilation System, version 7.0.2 $ cabal --version cabal-install version 0.10.2 using version 1.10.1.0 of the Cabal library But it only made the problem worse. Now ncurses won't even build. $ cabal install ncurses Resolving dependencies... Configuring ncurses-0.2... Preprocessing library ncurses-0.2... Building ncurses-0.2... [1 of 4] Compiling UI.NCurses.Enums ( dist/build/UI/NCurses/Enums.hs, dist/build/UI/NCurses/Enums.o ) [2 of 4] Compiling UI.NCurses.Types ( UI/NCurses/Types.hs, dist/build/UI/NCurses/Types.o ) [3 of 4] Compiling UI.NCurses ( dist/build/UI/NCurses.hs, dist/build/UI/NCurses.o ) [4 of 4] Compiling UI.NCurses.Panel ( dist/build/UI/NCurses/Panel.hs, dist/build/UI/NCurses/Panel.o ) UI/NCurses/Panel.chs:49:1: Warning: The import of `UI.NCurses' is redundant except perhaps to import instances from `UI.NCurses' To import instances alone, use: import UI.NCurses() hsncurses-shim.c:5:29: error: ncursesw/curses.h: No such file or directory cabal: Error: some packages failed to install: ncurses-0.2 failed during the building phase. The exception was: ExitFailure 1 I'd settle for using hscurses, but it won't compile with GHC 7, and it has its own internal bugs besides. $ cabal install hscurses Resolving dependencies... Configuring hscurses-1.4.0.0... configure: WARNING: unrecognized options: --with-gcc checking for gcc... gcc checking for C compiler default output file name... a.out checking whether the C compiler works... yes checking whether we are cross compiling... no checking for suffix of executables... checking for suffix of object files... o checking whether we are using the GNU C compiler... yes checking whether gcc accepts -g... yes checking for gcc option to accept ISO C89... none needed checking for addnstr in -lcurses... yes checking for addnstr in -lncurses... yes checking for waddnwstr in -lncursesw... yes checking for iconv in -liconv... yes checking for libiconv in -liconv... yes checking for libiconv... yes checking how to run the C preprocessor... gcc -E checking for grep that handles long lines and -e... /usr/bin/grep checking for egrep... /usr/bin/grep -E checking for ANSI C header files... yes checking for sys/types.h... yes checking for sys/stat.h... yes checking for stdlib.h... yes checking for string.h... yes checking for memory.h... yes checking for strings.h... yes checking for inttypes.h... yes checking for stdint.h... yes checking for unistd.h... yes checking iconv.h usability... yes checking iconv.h presence... yes checking for iconv.h... yes checking curses.h usability... yes checking curses.h presence... yes checking for curses.h... yes checking ncurses.h usability... yes checking ncurses.h presence... yes checking for ncurses.h... yes checking ncursesw/ncurses.h usability... no checking ncursesw/ncurses.h presence... yes configure: WARNING: ncursesw/ncurses.h: present but cannot be compiled configure: WARNING: ncursesw/ncurses.h: check for missing prerequisite headers? configure: WARNING: ncursesw/ncurses.h: see the Autoconf documentation configure: WARNING: ncursesw/ncurses.h: section "Present But Cannot Be Compiled" configure: WARNING: ncursesw/ncurses.h: proceeding with the preprocessor's result configure: WARNING: ncursesw/ncurses.h: in the future, the compiler will take precedence checking for ncursesw/ncurses.h... yes checking locale.h usability... yes checking locale.h presence... yes checking for locale.h... yes checking langinfo.h usability... yes checking langinfo.h presence... yes checking for langinfo.h... yes checking wchar.h usability... yes checking wchar.h presence... yes checking for wchar.h... yes checking limits.h usability... yes checking limits.h presence... yes checking for limits.h... yes checking signal.h usability... yes checking signal.h presence... yes checking for signal.h... yes configure: creating ./config.status config.status: creating hscurses.buildinfo config.status: creating cbits/config.h configure: WARNING: unrecognized options: --with-gcc cabal: Missing dependency on a foreign library: * Missing (or bad) header file: HSCurses.h This problem can usually be solved by installing the system package that provides this library (you may need the "-dev" version). If the library is already installed but in a non-standard location then you can use the flags --extra-include-dirs= and --extra-lib-dirs= to specify where it is. If the header file does exist, it may contain errors that are caught by the C compiler at the preprocessing stage. In this case you can re-run configure with the verbosity flag -v3 to see the error messages. cabal: Error: some packages failed to install: hscurses-1.4.0.0 failed during the configure step. The exception was: ExitFailure 1 Cheers, Andrew Pennebaker www.yellosoft.us

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Using _ on the RHS of an equation?
by Jason Dagit 06 Apr '11

06 Apr '11

I think I got this idea from JHC, but I'm unable to find it documented in the JHC manual at the moment. The idea is that when _ appears on the RHS of an equation it is another name for undefined. Here is a hypothetical example, inspired by code I've seen in FFI definitions: \begin{code} {-# LANGUAGE EmptyDataDecls #-} data Bar instance Storable Bar where sizeOf _ = sizeOf #{size struct Bar} alignment _ = alignment (_ :: CDouble) -- here we could have just as succinctly said alignment (1 :: CDouble) data Foo -- the struct Foo on the C side contains a Bar instance Storable Foo where sizeOf _ = sizeOf #{size struct Foo} alignment _ = alignment (_ :: Bar) -- we can't instantiate a Bar \end{code} Is this something people would be interested in having as an extension in GHC? Or is it just too fluffy for anyone to really care? Thanks, Jason

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Re: [Haskell-cafe] ANN: stm-chans: Additional types of channels for STM.
by wren ng thornton 06 Apr '11

06 Apr '11

On 4/3/11 11:58 PM, Thomas DuBuisson wrote: > Wren, > Glad to see someone is doing a more complete packaging of STM helpers > and derivatives! > > I've done a little work on bounded TChans[1] (hackage "bounded-tchan" > package) and I think you should consider a few things: Ah, somehow I missed that in my searching. I'll give it a look and try to integrate things. > 1) Split the reader counter and writer counters as I've done in > bounded-tchan. This gives 2-5 times better performance (I benchmarked > using Criterion, a single reader, a single writer, and tested channels > with bounds of 10, 100, and 1000 elements). That's crazy. I wonder why... must be a contention issue... > 2) Implement a "tryWriteTBChan" for obvious reasons. Good idea. > 4) Help me figure out a good way to build dupTBChan [2]. It's not easy. I've yet to figure out a way of doing this that has the right semantics. Perhaps splitting the reader and writer counters will help, though it sounds like you haven't had much luck either. > [2] http://stackoverflow.com/questions/5446484/how-to-add-a-finalizer-on-a-tvar Have you taken a look at TwilightSTM? http://proglang.informatik.uni-freiburg.de/projects/syncstm/ http://hackage.haskell.org/package/twilight-stm Since I'm aiming to have stm-chans eventually incorporated into stm proper, that wouldn't work for me, though it sounds like it might solve the ideological question about adding finalizers to TVars -- Live well, ~wren

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Problems porting ghc6-6.10.1 to GNU/Hurd using 6.8.2
by Svante Signell 05 Apr '11

05 Apr '11

Hi, I'm currently trying to upgrade Debian GNU/Hurd ghc6.8.2 to 6.10.1 (and further from there, due to requirements of ghc and haddock versions), and get stuck on configuring the random-1.0.0.1 library in stage1. I have tried versions of ghc6 are 6.10.1+dfsg1-1 to 6.10.1+dfsg1-5 (the latest not requiring ghc6.10 due to haddock 2.4.2). The commands are shown below: (added the -verbose=3 parameter) cd ghc6-6.10.1+dfsg1/libraries (sorry for the missing \ due to cut-and-paste to the mailer) ( cd random && /home/srs/DEBs/ghc/ghc6-6.10.1+dfsg1/libraries/cabal-bin --verbose=3 /usr/bin/ghc6 /home/srs/DEBs/ghc/ghc6-6.10.1 +dfsg1/libraries/bootstrapping.conf configure --verbose=3 --prefix=/NONEXISTENT --bindir=/NONEXISTENT --libdir=/NONEXISTENT --libexecdir=/NONEXISTENT --datadir=/NONEXISTENT --docdir=/NONEXISTENT --haddockdir=/NONEXISTENT --htmldir=/NONEXISTENT --with-compiler=/home/srs/DEBs/ghc/ghc6-6.10.1 +dfsg1/ghc/stage1-inplace/ghc --with-hc-pkg=/home/srs/DEBs/ghc/ghc6-6.10.1 +dfsg1/utils/ghc-pkg/install-inplace/bin/ghc-pkg --libsubdir='$pkgid' --with-gcc=gcc --with-ld=/usr/bin/ld --with-hscolour=/usr/bin/HsColour --with-alex=/usr/bin/alex --with-happy=/usr/bin/happy --configure-option='--build' --configure-option='i486-gnu' --configure-option='--prefix=/usr' --configure-option='--with-ghc=/usr/bin/ghc6' --configure-option='build_alias=i486-gnu' --configure-option='CFLAGS=-g -O2' --configure-option='LDFLAGS=' --configure-option='CPPFLAGS=' --configure-option=--with-cc=gcc --with-hsc2hs=/home/srs/DEBs/ghc/ghc6-6.10.1 +dfsg1/utils/hsc2hs/install-inplace/bin/hsc2hs --haddock-options="--use-contents=../index.html --use-index=../doc-index.html" --enable-library-profiling --enable-split-objs ) && touch stamp/configure.library.build-profiling-splitting.random || touch random/unbuildable Output: ======= Creating dist (and its parents) ("/home/srs/DEBs/ghc/ghc6-6.10.1\ +dfsg1/ghc/stage1-inplace/ghc",["--numeric-version"]) /home/srs/DEBs/ghc/ghc6-6.10.1+dfsg1/ghc/stage1-inplace/ghc is version 6.10.1 ("/home/srs/DEBs/ghc/ghc6-6.10.1\ +dfsg1/utils/ghc-pkg/install-inplace/bin/ghc-pkg",["--version"]) /home/srs/DEBs/ghc/ghc6-6.10.1\ +dfsg1/utils/ghc-pkg/install-inplace/bin/ghc-pkg is version 6.10.1 ("/home/srs/DEBs/ghc/ghc6-6.10.1\ +dfsg1/ghc/stage1-inplace/ghc",["--supported-languages"]) Reading installed packages... ("/home/srs/DEBs/ghc/ghc6-6.10.1\ +dfsg1/utils/ghc-pkg/install-inplace/bin/ghc-pkg",["dump","--global"]) Hangs here! Running manually works OK!! /home/srs/DEBs/ghc/ghc6-6.10.1\ +dfsg1/utils/ghc-pkg/install-inplace/bin/ghc-pkg "dump" "--global" Gives a lot of output here... Below is the ghc-pkg script: cat /home/srs/DEBs/ghc/ghc6-6.10.1\ +dfsg1/utils/ghc-pkg/install-inplace/bin/ghc-pkg PKGCONF=/home/srs/DEBs/ghc/ghc6-6.10.1\ +dfsg1/inplace-datadir/./package.conf exec /home/srs/DEBs/ghc/ghc6-6.10.1\ +dfsg1/utils/ghc-pkg/install-inplace/libexec/ghc-pkg --global-conf\ $PKGCONF ${1+"$@"} I've tried changing the shell from dash to bash but no changes. I also tried to escape some of the variables in the gkc-pkg shell script but without any luck. Anybody can help me here??

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Encoding of Haskell source files
by Roel van Dijk 05 Apr '11

05 Apr '11

Hello, The Haskell 2010 language specification states that "Haskell uses the Unicode character set" [1]. I interpret this as saying that, at the lowest level, a Haskell program is a sequence of Unicode code points. The standard doesn't say how such a sequence should be encoded. You can argue that the encoding of source files is not part of the language. But I think it would be highly practical to standardise on an encoding scheme. Strictly speaking it is not possible to reliably exchange Haskell source files on the byte level. If I download some package from hackage I can't tell how the source files are encoded from just looking at the files. I propose a few solutions: A - Choose a single encoding for all source files. This is wat GHC does: "GHC assumes that source files are ASCII or UTF-8 only, other encodings are not recognised" [2]. UTF-8 seems like a good candidate for such an encoding. B - Specify encoding in the source files. Start each source file with a special comment specifying the encoding used in that file. See Python for an example of this mechanism in practice [3]. It would be nice to use already existing facilities to specify the encoding, for example: {-# ENCODING <encoding name> #-} An interesting idea in the Python PEP is to also allow a form recognised by most text editors: # -*- coding: <encoding name> -*- C - Option B + Default encoding Like B, but also choose a default encoding in case no specific encoding is specified. I would further like to propose to specify the encoding of haskell source files in the language standard. Encoding of source files belongs somewhere between a language specification and specific implementations. But the language standard seems to be the most practical place. This is not an official proposal. I am just interested in what the Haskell community has to say about this. Regards, Roel [1] - http://www.haskell.org/onlinereport/haskell2010/haskellch2.html#x7-150002.1 [2] - http://www.haskell.org/ghc/docs/7.0-latest/html/users_guide/separate-compil… [3] - http://www.python.org/dev/peps/pep-0263/

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Re: [Haskell-cafe] Using _ on the RHS of an equation?
by Paul Keir 05 Apr '11

05 Apr '11

Hi Jason, I like the idea. I've seen some code from Oleg Kiselyov which uses __ (two underscores) in this way. The thing that stops me though, is when I get it wrong, and undefined fires somewhere, but I don't know where. Something like you propose, but with a line number, would be sweet. Paul The University of Glasgow, charity number SC004401

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broken on build encoding
by Gang Yu 05 Apr '11

05 Apr '11

Hi, cafe, I always get the following build failure when I try to install encoding: Configuring encoding-0.6.4... Warning: This package indirectly depends on multiple versions of the same package. This is highly likely to cause a compile failure. package haskell98-1.0.1.1 requires random-1.0.0.2 package HaXml-1.20.2 requires random-1.0.0.2 package random-1.0.0.2 requires time-1.1.4 package random-1.0.0.2 requires time-1.2.0.4 Preprocessing library encoding-0.6.4... Building encoding-0.6.4... Data/Encoding/ByteSource.hs:124:0: warning: extra tokens at end of #ifndef directive Data/Encoding/ByteSink.hs:104:0: warning: extra tokens at end of #ifndef directive [ 1 of 65] Compiling Data.Static ( Data/Static.hs, dist/build/Data/Static.o ) [ 2 of 65] Compiling Data.Array.Static ( Data/Array/Static.hs, dist/build/Data/Array/Static.o ) Data/Array/Static.hs:14:35: Warning: Bindings containing unlifted types must use an outermost bang pattern: { (I# ri) = index (s, e) i } *** This will be an error in GHC 6.14! Fix your code now! In the expression: let (I# ri) = index (s, e) i in extract addr ri In the definition of `!': ! (StaticArray s e addr) i = let (I# ri) = index ... i in extract addr ri [ 3 of 65] Compiling Data.Map.Static ( Data/Map/Static.hs, dist/build/Data/Map/Static.o ) [ 4 of 65] Compiling Control.Throws ( Control/Throws.hs, dist/build/Control/Throws.o ) [ 5 of 65] Compiling Data.Encoding.Exception ( Data/Encoding/Exception.hs, dist/build/Data/Encoding/Exception.o ) [ 6 of 65] Compiling Data.Encoding.ByteSource ( Data/Encoding/ByteSource.hs, dist/build/Data/Encoding/ByteSource.o ) Data/Encoding/ByteSource.hs:151:17: Not in scope: data constructor `State' cabal: Error: some packages failed to install: encoding-0.6.4 failed during the building phase. The exception was: ExitFailure 1https://mail.google.com/mail/?shva=1#compose I manually installed a ghc-6.12.3, a ubuntu ghc-6.12.1, all the same? anybody can provide helps? thanks Gang

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ANN: Google Summer of Code student application period opens today
by Johan Tibell 05 Apr '11

05 Apr '11

Hi, The Google Summer of Code student application period starts today at 19:00 UTC. If you're a student and like to get paid to work on a Haskell project this summer I recommend you go find an interesting project [1] and start working on your application. You can find more information on the wiki [2]. Cheers, Johan 1. http://hackage.haskell.org/trac/summer-of-code/report/1 2. http://hackage.haskell.org/trac/summer-of-code/wiki/Soc2011

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lhs2tex and comment
by Mitar 05 Apr '11

05 Apr '11

Hi! I have problems with lhs2tex and nested (long) comments. It formats it all in one long line and does not wrap it. Is there a way to define those comments so that it would maybe automatically wrap them at the end of the page? (And still take into the account possible indentation of comments.) Or at least to not ignore newlines in comments? I am using poly mode. Mitar

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