January 2010 - Haskell-Cafe

ANN: bindings-DSL 1.0.4 (Category: FFI)
by Maurício CA 28 Jan '10

28 Jan '10

Hi, bindings-DSL is a mature and well documented preprocessor domain specific language you can use to generate bindings to a C API. It's based on functionality provided by hsc2hs. These are links to Hackage page and documentation: http://hackage.haskell.org/package/bindings-DSL http://bitbucket.org/mauricio/bindings-dsl New in this version: * Support for C unions. * Use of <inttypes.h> macros for wider portability. An example on the use of unions follow. Suppose you have: union example { int k; char c[4]; }; Then, using bindings-DSL, you'll write: #starttype union example #union_field k , CInt #union_array_field c , CChar #stoptype Here is a ghci session showing the resulting code: > let value = C'example 1 [] > u'example'k value (2^10) C'example {c'example'k = 1024, c'example'c = [0,4,0,0]} > u'example'c value [1,0,0,0] C'example {c'example'k = 1, c'example'c = [1,0,0,0]} > u'example'c value [0,0,0,1] C'example {c'example'k = 16777216, c'example'c = [0,0,0,1]} Peeking an uninitialized memory address: > v <- alloca $ \p -> peek p :: IO C'example > v C'example {c'example'k = 81842189, c'example'c = [13,-48,-32,4]} Hope it's useful to you. Best, Maurício

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ANNOUNCE: ThreadScope 0.1
by Satnam Singh 28 Jan '10

28 Jan '10

I've just released ThreadScope version 0.1 on Hackage. Threadscope is a graphical utility for viewing profiling information about Haskell threads. It was written jointly with Simon Marlow and Donnie Jones. It uses Gtk2HS so it works under Windows and the L-word operating system although there seem to be problems making it work with OS-X (due to Gtk2Hs issues I think). $ cabal install threadscope You may need to do cabal update to update your packages list. On Windows operating systems you may need to issue the command from a shell that is running with administrative privileges. Resources: * Web page: http://research.microsoft.com/threadscope * Parallel Performance Tuning for Haskell<http://research.microsoft.com/apps/pubs/default.aspx?id=80976> (paper at Haskell Symposium 2009) Please let me know if you have any problems. Also, please do let us know about your experience with ThreadScope and in particular about accounts of how you used ThreadScope to shed light on parallel performance bugs. If I get enough feedback I may collate the responses into an experience report or paper for ICFP or the Haskell Symposium. Thank you kindly. Enjoy! Cheers, Satnam ________________________________ Satnam Singh Microsoft 7 JJ Thomson Avenue Cambridge CB3 0FB United Kingdom Email: satnams(a)microsoft.com<mailto:satnams@microsoft.com> UK tel: +44 1223 479905 Fax: +44 1223 479 999 UK mobile: +44 7979 648412 USA cell: 206 330 1580 USA tel: 206 219 9024 URL: http://research.microsoft.com/~satnams Live Messenger: satnam(a)raintown.org<mailto:satnam@raintown.org>

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Re: [Haskell-cafe] scheduling an alarm
by Thomas DuBuisson 28 Jan '10

28 Jan '10

Brian Denheyer <briand(a)aracnet.com> wrote: > On Mon, 25 Jan 2010 23:19:53 -0800 > Thomas DuBuisson <thomas.dubuisson(a)gmail.com> wrote: > > > 1) Don't use System.Posix.Signals > > It isn't necessary and makes your code less portable > > > > 2) The POSIX SIGALRM is used/caught by the RTS and that is why you are > > seeing strange behavior. > > > > 3) Consider using Haskell exceptions from Control.Concurrent > > (throwTo). Not sure what you want to do but you can always > > "myThreadId >>= \tid -> forkIO $ threadDelay someDelayTime >> > > (throwTo tid someExceptionVal)" > > > > I just want a routine to run every 15 min. > You can still use Control.Concurrent: > import Control.Concurrent > > doEvent f usDelay = forkIO $ > threadDelay usDelay > doEvent f usDelay > f Or a wrapper around Control.Concurrent - Ex: The Control-Event package. > I'm not clear on why the throwTo is in you example. > It will give you an exception just like you were expecting from SIGALRM. Thomas

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ghc-core 0.5 build fails
by Brian Denheyer 28 Jan '10

28 Jan '10

Hi all, ghc-core.hs:263:13: Not in scope: data constructor `C.ExitException' Looks like this comes from the base control.exception ? When I go to the web page for control.exception, there is no exitexception. My reading of the hackage entry for ghc-core makes me think that I've got the correct version of everything. ghc is 6.10.4 Brian Creating dist/build/ghc-core (and its parents) Creating dist/build/ghc-core/ghc-core-tmp (and its parents) /usr/bin/ghc -o dist/build/ghc-core/ghc-core --make -hide-all-packages -i -idist/build/ghc-core/ghc-core-tmp -i. -idist/build/autogen -Idist/build/autogen -Idist/build/ghc-core/ghc-core-tmp -optP-include -optPdist/build/autogen/cabal_macros.h -odir dist/build/ghc-core/ghc-core-tmp -hidir dist/build/ghc-core/ghc-core-tmp -stubdir dist/build/ghc-core/ghc-core-tmp -package base-4.1.0.0 -package colorize-haskell-1.0.0 -package directory-1.0.0.3 -package filepath-1.1.0.2 -package pcre-light-0.3.1 -package process-1.0.1.1 -O -Wall -XPatternGuards ./ghc-core.hs

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UTF-16 to UTF-8
by Günther Schmidt 28 Jan '10

28 Jan '10

Hi, is there a library which converts from utf-16 to utf-8? Günther

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Map unionWith generalization
by Hans Aberg 28 Jan '10

28 Jan '10

I need ideally some generalizations of unionWith and unionWithKey, for efficiency matters (i.e. avoiding conversions and traversing the maps more than once). I could use a modification of the code in Map.hs, but then the problem is that the module Map interface does not export the constructors of data Map. So suggestions are welcome. For example, in Map String Integer (sparse representation of monomials) compute the minimum value of all associative pairs with the same key (the gcd); if only one key is present, the absent should be treated as having value 0. So unionWith min xs ys will not work, because unionWith will always apply the identity to the remaining value when one key is missing, whereas it should be sent to 0. So here, one would want: (a -> c) -> (b -> c) -> (a -> b -> c) -> Map k a -> Map k b -> Map k c where the two first functions are applied when the first or second key is missing. Hans

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Why no merge and listDiff?
by Will Ness 28 Jan '10

28 Jan '10

Hello cafe, I wonder, if we have List.insert and List.union, why no List.merge (:: Ord a => [a] -> [a] -> [a]) and no List.minus ? These seem to be pretty general operations. Brief look into haskell-prime-report/list.html reveals nothing. Could we please have them? On the wider perspective, is their a way to declare an /ordered/ list on the type level (e.g. [1,2,3] would be one, but not [2,3,1])? Non-decreasing lists? Cyclical, or of certain length? What are such types called? TIA!

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Supporting GHC 6.10 and 6.12 in HDBC-postgresql Setup.hs
by John Goerzen 27 Jan '10

27 Jan '10

Hi folks, I've gotten some reports (see below) of issues with building HDBC-postgresql on GHC 6.12. Its Setup.hs file [1] is the culprit. The problem is that AnyVersion needs to be removed to work with Cabal in GHC 6.12. But I still want to support older Cabal. Following the directions in the Cabal manual, I tried: #if MIN_VERSION_Cabal(1,8,0) pgconfigProgram (withPrograms lbi) #else pgconfigProgram AnyVersion (withPrograms lbi) #endif While of course adding the needed bits to invoke CPP. This didn't resolve it; apparently Cabal doesn't define macros for use in Setup.hs, only for use in the application. There also seems to be no conditional for use in the .cabal file to resolve this. I could check the GHC version, but that doesn't necessarily correspond to Cabal version. Any ideas? -- John [1] http://git.complete.org/hdbc-postgresql?a=blob;f=Setup.hs;h=0656cb41adc814d…

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wxHaskell - using XRC files
by Günther Schmidt 27 Jan '10

27 Jan '10

Hi, I'm looking for documentation on using XRC files with wxHaskell. I finally managed to cabal-install wxHaskell last night alas sans docs. Günther BTW: I'm using wxFormBuilder, any other good tools out there?

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custom widgets
by Andrew U. Frank 27 Jan '10

27 Jan '10

we used wx originally but switched to gtk. the great advantage is glade... which is very flexible and still you can add/change whatever you need to in gtk in your haskell code. we checked porting between linux (ubuntu) and windows (xp) and encountered no problems.

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