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erratic behavior for System.Time.diffClockTimes
by Warren Harris 08 Apr '11

08 Apr '11

I'm trying out GHC-7.0.3-x86_64 for Mac OS X and see what seems to be a bug in System.Time.diffClockTimes. The TimeDiff tdPicosec field returns values that seem to jump around erratically: test = do startTime <- System.Time.getClockTime endTime <- System.Time.getClockTime let dt = diffClockTimes endTime startTime putStrLn $ show dt Prelude Test> test TimeDiff {tdYear = 0, tdMonth = 0, tdDay = 0, tdHour = 0, tdMin = 0, tdSec = 0, tdPicosec = 0} Prelude Test> test TimeDiff {tdYear = 0, tdMonth = 0, tdDay = 0, tdHour = 0, tdMin = 0, tdSec = 0, tdPicosec = 3000000} Prelude Test> test TimeDiff {tdYear = 0, tdMonth = 0, tdDay = 0, tdHour = 0, tdMin = 0, tdSec = 0, tdPicosec = -3329012246138323150000000} Prelude Test> test TimeDiff {tdYear = 0, tdMonth = 0, tdDay = 0, tdHour = 0, tdMin = 0, tdSec = 0, tdPicosec = 3000000} Prelude Test> test TimeDiff {tdYear = 0, tdMonth = 0, tdDay = 0, tdHour = 0, tdMin = 0, tdSec = 0, tdPicosec = -3329012246138322851000000} Prelude Test> I can file a bug, unless I'm overlooking something here. Warren

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fmap and LaTeX
by Mitar 08 Apr '11

08 Apr '11

Hi! Is there for <$> (fmap) operator some nice looking symbol in mathematics, LaTeX? I am looking here: http://www.soi.city.ac.uk/~ross/papers/Applicative.html http://www.haskell.org/ghc/docs/6.12.1/html/libraries/base/Control-Applicat… but only for other operators there are nice symbols, and <$> is left as it is. I have also tried \mathbin{<\$>} but it adds space around $ (at least in lhs2tex), so it looks ugly. Mitar

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FFI for a beginner
by Andrew Pennebaker 08 Apr '11

08 Apr '11

ncurses is proving too difficult to setup, so I'm working on a new library called charm. The C code works by itself, but I can't compile a Haskell wrapper for it. While the tutorials at HaskellWiki<http://www.haskell.org/haskellwiki/FFI_complete_examples>are helpful, they're outdated. Argh! The docs<http://www.haskell.org/ghc/docs/latest/html/users_guide/ffi-ghc.html#glasgo…>say that -#include pragmas no longer work, but fail to explain how to load code without them. Suffice to say I have no recourse but trial and error. GitHub: charm <https://github.com/mcandre/charm> and hscharm<https://github.com/mcandre/hscharm> <https://github.com/mcandre/charm>$ make cp /usr/include/charm.c . ghc --make -fforce-recomp -o hellocharm hellocharm.hs charm.hs charm.c -I/usr/include -dylib-install-name /usr/lib/libcharm.dynlib [1 of 2] Compiling Charm ( charm.hs, charm.o ) [2 of 2] Compiling Main ( hellocharm.hs, hellocharm.o ) Linking hellocharm ... ld: duplicate symbol _Charm_getWidth_info in charm.o and charm.o collect2: ld returned 1 exit status make: *** [hellocharm] Error 1 Cheers, Andrew Pennebaker www.yellosoft.us

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cab 0.1.2
by Kazu Yamamoto 08 Apr '11

08 Apr '11

Hello cafe, Let me announce "cab version 0.1.2". This version integrates "cabal-dev" as well as "cabal/ghc-pkg". So, you can use a sandbox for your development. http://www.mew.org/~kazu/proj/cab/en/ Here is the short explanation from the page above: ---- "cab" is a MacPorts-like maintenance command of Haskell cabal packages. Some parts of this program are a wrapper to "ghc-pkg", "cabal", and "cabal-dev". If you are always confused due to inconsistency of "ghc-pkg" and "cabal", or if you want a way to check all outdated packages, or if you want a way to remove outdated packages recursively, this command helps you. "cab" is designed to maintain user packages only assuming that users use a Haskell Platform and don't want to touch the global packages. ---- --Kazu

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DSL for task dependencies
by Serge Le Huitouze 07 Apr '11

07 Apr '11

Hi Haskellers! I think I remember reading a blog post or web page describing a EDSL to describe tasks and their dependencies "a la" make. Can anyone point me to such published material? Thanks in advance. --serge

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'Progress bar' enumeratee
by David Hotham 07 Apr '11

07 Apr '11

Hello, I've spent some time over the last couple of days trying to write an enumeratee that prints a "." every n bytes (with obvious intended use as a progress tracker). Seems like it oughtn't be hard, but it has been a steep learning curve... I have come up with something that seems to do the job but I don't know that I'm completely happy with it (or even that I completely understand it, to be honest). If anyone more expert would be kind enough either to reassure me that I'm doing it right or - more likely - to offer improvements / suggestions on what obvious simplifications I have overlooked, I'd be grateful. Thanks David import qualified Data.ByteString.Char8 as B import qualified Data.ByteString.Lazy.Char8 as BL import qualified Data.Enumerator as E import qualified Data.Enumerator.Binary as EB import Control.Monad.IO.Class (liftIO, MonadIO) import System.IO (hFlush, stdout) dotEvery :: MonadIO m => Integer -> E.Enumeratee B.ByteString B.ByteString m b dotEvery count = E.checkDone $ E.continue . dotIn count where dotIn need k E.EOF = E.yield (E.Continue k) E.EOF dotIn need k (E.Chunks []) = E.continue (dotIn need k) dotIn need k (E.Chunks xs) = iter where lazy = BL.fromChunks xs len = toInteger $ BL.length lazy iter = if len < need then k (E.Chunks xs) E.>>== E.checkDone (E.continue . dotIn (count - len)) else let (x1, x2) = BL.splitAt (fromInteger need) lazy s1 = E.Chunks $ BL.toChunks x1 s2 = E.Chunks $ BL.toChunks x2 enumee = E.checkDoneEx s2 (\k' -> dotIn count k' s2) in E.Iteratee $ do newStep <- E.runIteratee $ k s1 liftIO $ putStr "." >> hFlush stdout E.runIteratee $ enumee newStep PS Implementations which involve "EB.take count" seem to me unsatisfactory; one surely oughtn't need to have a large buffer to solve this problem PPS I did find an implementation via mapAccumM which I consider pleasing enough from an aesthetic point of view - but which runs 30x slower dotAt :: MonadIO m => Integer -> Integer -> Word8 -> m (Integer, Word8) dotAt n s w | s >= n = do liftIO $ putStr "." >> hFlush stdout return (1, w) | otherwise = return (s+1, w) dotEvery' :: MonadIO m => Integer -> E.Enumeratee B.ByteString B.ByteString m b dotEvery' n = EB.mapAccumM (dotAt n) 1

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parsec - source position information
by Ozgur Akgun 07 Apr '11

07 Apr '11

Hi, Is there a way to get source position[1] information from parsec while defining a parser? It surely knows about source positions, as they are used while reporting a parsing error. data Identifier = Identifier String SourcePos pIdentifier :: Parser Identifier pIdentifier = do pos <- ?? s <- pString return (Identifier s pos) [1] http://hackage.haskell.org/packages/archive/parsec/3.0.0/doc/html/Text-Pars… Thanks in advance, Ozgur

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Local copy of hackageDB
by José Pedro Magalhães 07 Apr '11

07 Apr '11

Hi all, I want to use cabal-install on a machine without internet access. I tried downloading http://hackage.haskell.org/cgi-bin/hackage-scripts/archive.tar, unpacking it and setting the local-repo field in the config file to this location but that doesn't work, as cabal-install says that it is missing the package list for the local repo. What should I do? Thanks, Pedro

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ANNOUNCE: swish 0.3.0.0
by Doug Burke 07 Apr '11

07 Apr '11

I am pleased to announce an update of the swish package to version 0.3.0.0 [1]. It is mainly meant to be a maintenance upgrade over the existing version on Hackage [2] by Vasili I. Galchin, but does add additional functionality in that it now supports the NTriples format and the N3 parser and formatter has been updated to better match the current specification. For those not aware of what Swish actually is, it is an experiment by Graham Klyne in writing a "Semantic Web" framework in Haskell [3]. I note that the wonderful machinery behind Hackage has already processed the documentation so you can read more about it at [1] as well as the very-sparsely-documented Wiki at [4]. [1] http://hackage.haskell.org/package/swish-0.3.0.0 [2] http://hackage.haskell.org/package/swish-0.2.1 [3] http://www.ninebynine.org/Software/swish-0.2.1.html [4] https://bitbucket.org/doug_burke/swish/wiki/Home Thanks for reading this far, Doug

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ANNOUNCE: DocTest-0.2.0
by Simon Hengel 07 Apr '11

07 Apr '11

I just uploaded a new version of DocTest[1] to Hackage. WHAT IS DocTest? ================ DocTest is a port of Python's doctest[2] to Haskell. It can be used to verify, that examples in Haddock comments[3] do still work. This also provides you with a simple mechanism to write unit test, without the burden of maintaining a dedicated test suite. A basic example of usage is at [4]. WHAT'S NEW IN THIS VERSION? =========================== Support for blank lines in the result of an expression (analogous to the <BLANKLINE>-feature of Python's doctest). Here is an example of usage: -- | -- Some example: -- -- >>> putStrLn "foo\n\nbar" -- foo -- <BLANKLINE> -- bar Currently this is implemented in DocTest, but we will move it to Haddock with the next release. Cheers, Simon [1] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/DocTest [2] http://docs.python.org/library/doctest.html [3] http://www.haskell.org/haddock/doc/html/ch03s08.html#id566093 [4] http://haskell.org/haskellwiki/DocTest _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

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