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serialize an unknown type
by Corentin Dupont 21 Oct '12

21 Oct '12

Hi the list! I have a simple question, how can I serialize/deserialize a structure like this: data InputChoice c deriving Typeable data Event a where InputChoice :: (Eq c, Show c) => [c] -> c -> Event (InputChoice c) (...) I'd like that the values of type "c" get serialized to a String... That's the easy part, but for deserializing, oops! Cheers, Corentin

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How do I specify language literals in hsparql?
by Andrew Pennebaker 21 Oct '12

21 Oct '12

If the raw SPARQL is rdfs:label "D (programming language)"@en, what would the hsparql <http://hackage.haskell.org/package/hsparql> syntax be? The docs<https://github.com/robstewart57/hsparql/blob/master/tests/DBPedia.hs> don't include any language literal examples. -- Cheers, Andrew Pennebaker www.yellosoft.us

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Blocking IO & FIFOs
by Jason Dusek 20 Oct '12

20 Oct '12

Hi all, I am developing a coroutine-like interface to Bash. http://hpaste.org/76523 The idea is that one can send multiple "queries" to an interpreter and then collect the results of each query. How do we know when Bash is done with each query? Waiting for "no more output" seems ambiguous; so the way CoBash works is: * Each query gets a tmp dir with two named pipes in it. * The query is wrapped in redirections to the pipes. * The pipes are removed when the query completes. This does work, sort of: +Prelude> :load CoBash.hs [1 of 1] Compiling CoBash ( CoBash.hs, interpreted ) Ok, modules loaded: CoBash. *CoBash> tuple@(i,o,e,p) <- start e :: Handle i :: Handle o :: Handle p :: ProcessHandle tuple :: (Handle, Handle, Handle, ProcessHandle) *CoBash> query tuple "for n in {1..4}; do sleep 1; echo $n; done" ("1\n2\n3\n4\n","") it :: (ByteString, ByteString) I say sort of because it is quite brittle. Many commands do not return at all, for example: *CoBash> query tuple "uname -a" The way I retrieve the output from the FIFOs seems dangerous: (,) <$> Bytes.hGetContents oh <*> Bytes.hGetContents eh Surely, the FIFO for STDERR can not be read from until the FIFO for STDOUT is finished; but if there is a great deal of error output then the process will fill the FIFO's buffer and get stuck. If we switch the order of the reads, the "for n in ..." example above blocks: (,) <$> Bytes.hGetContents eh <*> Bytes.hGetContents oh I have tried a few different ways to read from the two handles concurrently; for example, by giving each thread an MVar to put the contents in, or by using hGetNonBlocking on a list of handles in a loop. Using the latter method, I never get EOF; it just collects empty strings forever. For comparison's sake, the expect behaviour with FIFOs is: In the first terminal: :; mkfifo fifo :; cat > fifo a b c d ^D :; In the second terminal: :; cat < fifo a b c d :; Here I "open" the FIFO for reading with < while opening it for writing with >. As long as the writer writes, the reader reads; when the writer closes the write end of the pipe, the reader receives EOF. Trying to duplicate the read behaviour in Haskell, using hGetContents from GHCi while using cat to write to the FIFO, doesn't work; which seems a little bogus. There have a been a few past threads about FIFOs and their troublesome interaction with Haskell's async-by-default IO style. To switch to System.Posix for IO -- and deal with Ptr Word8, in order to handle binary data -- seems like an awful step down. -- Jason Dusek pgp // solidsnack // C1EBC57DC55144F35460C8DF1FD4C6C1FED18A2B {-# LANGUAGE OverloadedStrings , ScopedTypeVariables , ParallelListComp , TupleSections #-} module CoBash where import Control.Applicative import Control.Concurrent import Control.Concurrent.MVar import Control.Exception import Control.Monad import Data.Bits import Data.ByteString.Char8 (ByteString) import qualified Data.ByteString.Char8 as Bytes import Data.Maybe import Data.Monoid import qualified GHC.IO.Handle.FD import System.IO import System.IO.Error import System.Process import System.Posix.ByteString import System.IO.Temp import qualified Text.ShellEscape as Esc start :: IO (Handle, Handle, Handle, ProcessHandle) start = runInteractiveProcess "bash" [] Nothing (Just []) query :: (Handle, Handle, Handle, ProcessHandle) -> ByteString -> IO (ByteString, ByteString) query (i, _, _, _) query = withFIFOs query' where query' ofo efo = do Bytes.hPut i cmd hFlush i [oh, eh] <- mapM openFIFO [ofo, efo] (,) <$> Bytes.hGetContents oh <*> Bytes.hGetContents eh -- Works. -- (,) <$> Bytes.hGetContents eh <*> Bytes.hGetContents oh -- Blocks. where cmd = Bytes.unlines ["{", query, "} 1>" <> ofo <> " 2>" <> efo] shutdown :: (Handle, Handle, Handle, ProcessHandle) -> IO () shutdown (i, _, _, p) = () <$ hClose i <* waitForProcess p openFIFO path = GHC.IO.Handle.FD.openFileBlocking (Bytes.unpack path) ReadMode -- | Run an IO action with two FIFOs in scope, which will removed after it -- completes. withFIFOs :: (RawFilePath -> RawFilePath -> IO a) -> IO a withFIFOs m = withSystemTempDirectory "cobash." m' where m' = (uncurry m =<<) . mk . Bytes.pack mk d = (o, e) <$ (createNamedPipe o mode >> createNamedPipe e mode) where (o, e) = (d <> "/o", d <> "/e") mode = ownerReadMode .|. ownerWriteMode .|. namedPipeMode

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Monad.Reader #21 call for copy
by Edward Z. Yang 20 Oct '12

20 Oct '12

Call for Copy: The Monad.Reader - Issue 21 -------------------------------------------- Whether you're an established academic or have only just started learning Haskell, if you have something to say, please consider writing an article for The Monad.Reader! The submission deadline for Issue 21 will be: **Tuesday, January 1** The Monad.Reader ~~~~~~~~~~~~~~~~ The Monad.Reader is a electronic magazine about all things Haskell. It is less formal than journal, but somehow more enduring than a wiki- page. There have been a wide variety of articles: exciting code fragments, intriguing puzzles, book reviews, tutorials, and even half-baked research ideas. Submission Details ~~~~~~~~~~~~~~~~~~ Get in touch with me if you intend to submit something -- the sooner you let me know what you're up to, the better. Please submit articles for the next issue to me by e-mail (ezyang(a)mit.edu) Articles should be written according to the guidelines available from http://themonadreader.wordpress.com/contributing/ Please submit your article in PDF, together with any source files you used. The sources will be released together with the magazine under a BSD license. If you would like to submit an article, but have trouble with LaTeX please let me know and we'll work something out.

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Getting PID of a child process
by Jason Dusek 19 Oct '12

19 Oct '12

Hi All, Using `System.Process.runInteractiveProcess', I can start a process and get a handle to it: runInteractiveProcess :: FilePath -> [String] -> Maybe FilePath -> Maybe [(String, String)] -> IO (Handle, Handle, Handle, ProcessHandle) For diagnostic purposes, I'd like to print the PID of the process attached to this handle -- how best to do that? -- Jason Dusek pgp // solidsnack // C1EBC57DC55144F35460C8DF1FD4C6C1FED18A2B

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Release Candidate 2: HP 2014.4.0.0
by Mark Lentczner 19 Oct '12

19 Oct '12

Haskellistas - The second release candidate of HP 2014.4.0.0 is now available: - Source tarball: haskell-platform-2012.4.0.0-rc2.tar.gz<http://ozonehouse.com/mark/platform/haskell-platform-2012.4.0.0-rc2.tar.gz> - Mac 32-bit installer: Haskell Platform 2012.4.0.0 32bit rc2 signed.pkg<http://ozonehouse.com/mark/platform/Haskell%20Platform%202012.4.0.0%2032bit…> Mac notes: This version is now digitally signed by me, and so will install without fuss on OS X 10.8. I'll put up 64-bit version soon. - Mark Changes since RC1: TODO ---- [x] update vector and primitive versions (they had a point release to fix a bad bug, and the fix was very very simple) [x] remove Build.hs - it did all its work by shelling out anyway! [x] main .cabal file should not have versions commented out [x] this will require a way to extract the list of packages that need to be part of the source release [x] why not also extract the list of packages needed for core.packages [x] fix to build.hs (ticket #195) [x] bugs in build.sh (ticket #197) [x] build instructions in the tarball (ticket #207) [x] merge in shared library patch (ticket #198) MAC TODO -------- [x] mac cabal script needs to quote things with $HOME or ~ in them (ticket #192) [x] If the cabal command is "update" then the wrapper script shouldn't do an update the first time through! [x] sign Mac installers (ticket #203)

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acid-state audit trail
by Richard Wallace 19 Oct '12

19 Oct '12

Hey all, I've been looking at acid-state as a possible storage backend for an application. It looks like it fits my needs pretty damn well, but one thing that I'm curious about is if it is possible to get a list of "update events". You can obviously query for the current state, but it's not immediately apparent if you can see the history of your values state. This is useful in some things, like providing audit trails and debugging. As well as being able to re-create state in a different form. I was also curious if the createCheckpoint function eliminates the state history or does it just create a snapshot, it's not apparent from the docs. Thanks, Rich

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Adding custom events to eventlog
by Janek S. 19 Oct '12

19 Oct '12

Dear list, I'm using ThreadScope to improve performance of my parallel program. It would be very helpful for me if I could place custom things in eventlog (e.g. "now function x begins"). Is this possible? Janek

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Erroneous interaction between DataKinds and ExistentialQuantification?
by Stefan Holdermans 19 Oct '12

19 Oct '12

I am almost sure this is a known issue, but I noticed some erroneous (?) interaction between datatype promotion and existential quantification. Consider the following program: {-# LANGUAGE DataKinds #-} {-# LANGUAGE ExistentialQuantification #-} {-# LANGUAGE GADTs #-} {-# LANGUAGE KindSignatures #-} module Test where data K = forall a. T a -- promotion gives 'T :: * -> K data G :: K -> * where D :: G (T []) -- kind error! I would expect the type checker to reject it, but GHC (version 7.6.1) compiles it happily. Is this indeed a (known) bug? On a related note: is there a way to promote a type that involves an existential type variable of a kind other than *? Thanks, Stefan

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Build GHC to i386 platform represent an error after run command "make bootstrapping-files"
by Chatsiri Ratana 19 Oct '12

19 Oct '12

Hello All, I using GHC for x86_64 platform compiles the GHC source in order to port code to the i386 platform. Steps for building GHC to i386 platform at link[1]. Configure before initial other steps as completed follow by $./configure --enable-hc-boot --build=i386-unknown-linux --host=i386-unknown-linux --target=i386-unknown-linux --with-gcc=/usr/bin/gcc --with-ld=/usr/bin/ld --with-nm=/usr/bin/nm --with-ghc=/usr/lib/ghc/bin/ghc ---------------------------------------------------------------------- Configure completed successfully. Building GHC version : 7.7.20120806 Build platform : i386-unknown-linux Host platform : i386-unknown-linux Target platform : i386-unknown-linux Bootstrapping from HC files. Using GCC : /usr/bin/gcc which is version : 4.6.3 Building a cross compiler : NO Porting to foreign arch : NO Alien script : ld : /usr/bin/ld Happy : () Alex : () Python : /usr/bin/python Perl : /usr/bin/perl dblatex : xsltproc : HsColour was not found; documentation will not contain source links Building DocBook HTML documentation : NO Building DocBook PS documentation : NO Building DocBook PDF documentation : NO ---------------------------------------------------------------------- Next step for making executable file by command "make bootstrapping-files". It's show an error such as below. $ make bootstrapping-files make -r --no-print-directory -f ghc.mk bootstrapping-files /usr/bin/find: `libraries/ghc-prim/dist-install/build': No such file or directory /usr/bin/find: `libraries/ghc-prim/dist-install/build': No such file or directory /usr/bin/find: `libraries/integer-gmp/dist-install/build': No such file or directory /usr/bin/find: `libraries/integer-gmp/dist-install/build': No such file or directory /usr/bin/find: `libraries/base/dist-install/build': No such file or directory /usr/bin/find: `libraries/base/dist-install/build': No such file or directory /usr/bin/find: `libraries/filepath/dist-install/build': No such file or directory /usr/bin/find: `libraries/filepath/dist-install/build': No such file or directory /usr/bin/find: `libraries/array/dist-install/build': No such file or directory /usr/bin/find: `libraries/array/dist-install/build': No such file or directory /usr/bin/find: `libraries/deepseq/dist-install/build': No such file or directory /usr/bin/find: `libraries/deepseq/dist-install/build': No such file or directory /usr/bin/find: `libraries/bytestring/dist-install/build': No such file or directory /usr/bin/find: `libraries/bytestring/dist-install/build': No such file or directory /usr/bin/find: `libraries/containers/dist-install/build': No such file or directory /usr/bin/find: `libraries/containers/dist-install/build': No such file or directory /usr/bin/find: `libraries/old-locale/dist-install/build': No such file or directory /usr/bin/find: `libraries/old-locale/dist-install/build': No such file or directory /usr/bin/find: `libraries/old-time/dist-install/build': No such file or directory /usr/bin/find: `libraries/old-time/dist-install/build': No such file or directory /usr/bin/find: `libraries/time/dist-install/build': No such file or directory /usr/bin/find: `libraries/time/dist-install/build': No such file or directory /usr/bin/find: `libraries/unix/dist-install/build': No such file or directory /usr/bin/find: `libraries/unix/dist-install/build': No such file or directory /usr/bin/find: `libraries/directory/dist-install/build': No such file or directory /usr/bin/find: `libraries/directory/dist-install/build': No such file or directory /usr/bin/find: `libraries/process/dist-install/build': No such file or directory /usr/bin/find: `libraries/process/dist-install/build': No such file or directory /usr/bin/find: `libraries/hpc/dist-boot/build': No such file or directory /usr/bin/find: `libraries/hpc/dist-boot/build': No such file or directory /usr/bin/find: `libraries/hpc/dist-install/build': No such file or directory /usr/bin/find: `libraries/hpc/dist-install/build': No such file or directory /usr/bin/find: `libraries/pretty/dist-install/build': No such file or directory /usr/bin/find: `libraries/pretty/dist-install/build': No such file or directory /usr/bin/find: `libraries/template-haskell/dist-install/build': No such file or directory /usr/bin/find: `libraries/template-haskell/dist-install/build': No such file or directory /usr/bin/find: `libraries/Cabal/Cabal/dist-boot/build': No such file or directory /usr/bin/find: `libraries/Cabal/Cabal/dist-boot/build': No such file or directory /usr/bin/find: `libraries/Cabal/Cabal/dist-install/build': No such file or directory /usr/bin/find: `libraries/Cabal/Cabal/dist-install/build': No such file or directory /usr/bin/find: `libraries/binary/dist-boot/build': No such file or directory /usr/bin/find: `libraries/binary/dist-boot/build': No such file or directory /usr/bin/find: `libraries/binary/dist-install/build': No such file or directory /usr/bin/find: `libraries/binary/dist-install/build': No such file or directory /usr/bin/find: `libraries/bin-package-db/dist-boot/build': No such file or directory /usr/bin/find: `libraries/bin-package-db/dist-boot/build': No such file or directory /usr/bin/find: `libraries/bin-package-db/dist-install/build': No such file or directory /usr/bin/find: `libraries/bin-package-db/dist-install/build': No such file or directory /usr/bin/find: `libraries/hoopl/dist-boot/build': No such file or directory /usr/bin/find: `libraries/hoopl/dist-boot/build': No such file or directory /usr/bin/find: `libraries/hoopl/dist-install/build': No such file or directory /usr/bin/find: `libraries/hoopl/dist-install/build': No such file or directory /usr/bin/find: `libraries/transformers/dist-install/build': No such file or directory /usr/bin/find: `libraries/transformers/dist-install/build': No such file or directory /usr/bin/find: `libraries/xhtml/dist-install/build': No such file or directory /usr/bin/find: `libraries/xhtml/dist-install/build': No such file or directory /usr/bin/find: `libraries/terminfo/dist-install/build': No such file or directory /usr/bin/find: `libraries/terminfo/dist-install/build': No such file or directory /usr/bin/find: `libraries/haskeline/dist-install/build': No such file or directory /usr/bin/find: `libraries/haskeline/dist-install/build': No such file or directory /usr/bin/find: `libraries/integer-gmp/dist-install/build': No such file or directory /usr/bin/find: `compiler/stage1/build': No such file or directory /usr/bin/find: `compiler/stage1/build': No such file or directory /usr/bin/find: `compiler/stage2/build': No such file or directory /usr/bin/find: `compiler/stage2/build': No such file or directory /usr/bin/find: `libraries/haskell98/dist-install/build': No such file or directory /usr/bin/find: `libraries/haskell98/dist-install/build': No such file or directory /usr/bin/find: `libraries/haskell2010/dist-install/build': No such file or directory /usr/bin/find: `libraries/haskell2010/dist-install/build': No such file or directory /usr/bin/find: `libraries/random/dist-install/build': No such file or directory /usr/bin/find: `libraries/random/dist-install/build': No such file or directory /usr/bin/find: `libraries/primitive/dist-install/build': No such file or directory /usr/bin/find: `libraries/primitive/dist-install/build': No such file or directory /usr/bin/find: `libraries/vector/dist-install/build': No such file or directory /usr/bin/find: `libraries/vector/dist-install/build': No such file or directory /usr/bin/find: `libraries/dph/dph-base/dist-install/build': No such file or directory /usr/bin/find: `libraries/dph/dph-base/dist-install/build': No such file or directory /usr/bin/find: `libraries/dph/dph-prim-interface/dist-install/build': No such file or directory /usr/bin/find: `libraries/dph/dph-prim-interface/dist-install/build': No such file or directory /usr/bin/find: `libraries/dph/dph-prim-seq/dist-install/build': No such file or directory /usr/bin/find: `libraries/dph/dph-prim-seq/dist-install/build': No such file or directory /usr/bin/find: `libraries/dph/dph-prim-par/dist-install/build': No such file or directory /usr/bin/find: `libraries/dph/dph-prim-par/dist-install/build': No such file or directory /usr/bin/find: `libraries/dph/dph-lifted-base/dist-install/build': No such file or directory /usr/bin/find: `libraries/dph/dph-lifted-base/dist-install/build': No such file or directory /usr/bin/find: `libraries/dph/dph-lifted-boxed/dist-install/build': No such file or directory /usr/bin/find: `libraries/dph/dph-lifted-boxed/dist-install/build': No such file or directory /usr/bin/find: `libraries/dph/dph-lifted-copy/dist-install/build': No such file or directory /usr/bin/find: `libraries/dph/dph-lifted-copy/dist-install/build': No such file or directory /usr/bin/find: `libraries/dph/dph-lifted-vseg/dist-install/build': No such file or directory /usr/bin/find: `libraries/dph/dph-lifted-vseg/dist-install/build': No such file or directory /bin/sh: 1: Syntax error: Unterminated quoted string make[1]: *** [includes/dist-derivedconstants/build/tmp/mkDerivedConstants] Error 2 make: *** [bootstrapping-files] Error 2 Who have strategies or methods for solving build step at here? [1] http://hackage.haskell.org/trac/ghc/wiki/Building/Porting Thank in advance Chatsiri Rattana -- :--------------------------------------------------------

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