November 2008 - Haskell-Cafe

Need machine for DPH benchmarking
by Roman Leshchinskiy 27 Nov '08

27 Nov '08

Hi all, we, the DPH team, are at the moment in the very unfortunate situation of not having a proper machine for running our benchmarks on. Could a kind soul maybe give us (i.e., me) access to a quadcore or 2xquadcore x86 Linux or OS X machine? I only need to build ghc on it and run small benchmarks which never take more than a couple of minutes, maybe once every couple of days or so. We do need to use all cores, though, so no other CPU-intensive processes can be running during benchmarking. This is only for a week or two, until we get our own machine. We would be eternally grateful and won't forget you when DPH takes over the world. Roman

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RE: [Haskell-cafe] followedBy parser in Parsec
by Paul Keir 27 Nov '08

27 Nov '08

'lookAhead' is exactly what I needed: try $ array_element >>= \ae -> lookAhead (reservedOp "(") >> return ae Many thanks, Paul Maybe you're looking for 'lookAhead'? > > [...] //Stephan -- Früher hieß es ja: Ich denke, also bin ich. Heute weiß man: Es geht auch so. - Dieter Nuhr

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Building QuickCheck 2 Under GHC 6.10.1
by Dominic Steinitz 27 Nov '08

27 Nov '08

Having been a happy user of QuickCheck 2 for many years, I now find it won't build under ghc 6.10.1. Before I investigate further, has anyone encountered this problem and has a fix? Thanks, Dominic. > C:\Users\Dom\QuickCheck>Setup build > Preprocessing library QuickCheck-2.0... > Building QuickCheck-2.0... > [2 of 9] Compiling Test.QuickCheck.Exception ( Test\QuickCheck\Exception.hs, dis > t\build\Test\QuickCheck\Exception.o ) > > Test\QuickCheck\Exception.hs:12:31: > Class `Exception' used as a type > In the type `Exception' > In the type `Either Exception a' > In the type `IO (Either Exception a)' > > Test\QuickCheck\Exception.hs:15:36: > Class `Exception' used as a type > In the type `Exception' > In the type `Either Exception a' > In the type `IO (Either Exception a)'

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followedBy parser in Parsec
by Paul Keir 27 Nov '08

27 Nov '08

Hi, Is there a way in Parsec to check what the next token is, and if it is what you're hoping for, leave it there. This is an example of something which doesn't work at all: testpar = try $ do ae <- array_element option [] $ try $ satisfy (\c -> c /= '(') >> unexpected "" return ae I'm finding this totally confusing by now %0 Can I invert "notFollowedBy" somehow, or maybe there's a "peek" function I don't know about? Help! Thanks, Paul

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HaskellWiki image upload fails because of - probably - the filesize.
by And1 27 Nov '08

27 Nov '08

Hey dear Haskell-Cafe-Readers, I tried several times to upload several images - screenshots that is - to my HaskellWiki/Xmonad site: http://haskell.org/haskellwiki/Image:And1_xmonad.png I always get the error, that the connection to the site/server was reset. I mailed both administrators of the HaskellWiki but I got, for about 2-4 weeks now, no reply. I tried to upload the following images, maybe that's important: http://and1.donnergurgler.net/misc/screen_2008-09-26.png http://and1.donnergurgler.net/misc/screen_2008-11-02.png http://and1.donnergurgler.net/misc/screen_2008-11-10.png I was told, that the problem is maybe the filesize of the new images, because it is bigger, then the filesize of the image already uploaded. Thanks for reading this and hopefully finding the problem, -- Regards, Andi R.

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Possible issue with Hoogle and Haddock?
by Stephen Hicks 27 Nov '08

27 Nov '08

Hi, I was noticing recently that there seems to be a problem with Hoogle and Haddock. In particular, I just hoogled "bracket" and got the following result: bracket :: IO a -> a -> IO b -> a -> IO c -> IO c Clearly this is the wrong type, as it should be bracket :: IO a -> (a -> IO b) -> (a -> IO c) -> IO c The Haddock-generated documentation at least has newlines to group the terms, but this is still far from correct. I noticed the same thing a while back in Parsec's documentation for token, token :: Stream s Identity t => t -> String -> t -> SourcePos -> t -> Maybe a -> Parsec s u a which again should have parens. Is this a bug? Is is something that's well-known? Cheers, steve

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haddock question
by allan 27 Nov '08

27 Nov '08

Dear all I'm trying to locally build the documentation for the haskell-src-exts package and running into a bit of bother. If I run: cabal haddock I get the error: haddock: parse error in doc string so: cabal haddock -v Doesn't really provide any extra information, it gives me the exact haddock command-line used but there is still no way (I can see) of obtaining the source file containing the parse error. So I downloaded via darcs the latest haddock source code and installed that but I get the exact same error message. I tried grepping in the haddock source code for that particular error message (and portions of it) but I couldn't find it. Finally I tried running haddock on a single source file: haddock Language/Haskell/Exts.hs and even this gets the exact same error message, which is somewhat bizarre since that file does not contain any documentation strings. Anyone have any ideas? regards allan -- The University of Edinburgh is a charitable body, registered in Scotland, with registration number SC005336.

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Philip Wadler video on Howard-Curry Correspondence ???
by Galchin, Vasili 27 Nov '08

27 Nov '08

Hello, I am reading re-reading Prof. Wadler paper Proofs are Programs: 19th Century Logic and 21st Century Computing but also want to re-read watch his video on same subject..... ??? Very kind thanks, Vasili

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Problem getting code from AFP08 parallel tutorial to run in parallel
by Olivier Boudry 27 Nov '08

27 Nov '08

Hi all, I'm reading the following tutorial: http://research.microsoft.com/~simonpj/papers/parallel/AFP08-notes.pdf "A Tutorial on Parallel and Concurrent Programming in Haskell" and have problems getting the expected speed improvement from running two tasks in parallel. With any version of the code present in pages 1-7 of the tutorial I keep getting the CPU stick to 50%. I did not forget to compile the code with `-threaded` and run it with `+RTS -N2` and it runs on a dual core machine on which I already used the Control.Parallel.Strategies.parMap function and got 100% CPU usage. The first version of the parallel function in the tutorial (page 6) is: parSumFibEuler :: Int −> Int −> Int parSumFibEuler a b = f 'par' (f + e) where f = fib a e = sumEuler b In the tutorial, swapping f and e on the 3rd line does the job, but in my case it doesn't change anything. C:\Temp\haskell>ghc --make -threaded SumEulerP6.hs [1 of 1] Compiling Main ( SumEulerP6.hs, SumEulerP6.o ) Linking SumEulerP6.exe ... C:\Temp\haskell>SumEulerP6 +RTS -N1 sum: 119201850 time: 36.890625 seconds C:\Temp\haskell>SumEulerP6 +RTS -N2 sum: 119201850 time: 36.859375 seconds Next page of the tutorial the tasks are explicitly sequenced so the code does not depend on the ordering of the two `+` operands: parSumFibEuler :: Int -> Int -> Int parSumFibEuler a b = f `par` (e `pseq` (f + e)) where f = fib a e = sumEuler b With once again a disappointing result: C:\Temp\haskell>ghc --make -threaded SumEulerP7.hs [1 of 1] Compiling Main ( SumEulerP7.hs, SumEulerP7.o ) Linking SumEulerP7.exe ... C:\Temp\haskell>SumEulerP7 +RTS -N1 sum: 119201850 time: 36.875 seconds C:\Temp\haskell>SumEulerP7 +RTS -N2 sum: 119201850 time: 36.75 seconds I tried this on a Windows XP Dell Dual Core with GHC 6.10.1 and on a iMac Dual Core with GHC 6.8.3 and got the same result on both. I'm probably missing something really stupid but I'm lacking the "parallel thinking" skills to understand how to look at the problem and resolve it. Any pointers? Thanks, Olivier.

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Need machine for DPH benchmarking
by Dominic Steinitz 27 Nov '08

27 Nov '08

> we, the DPH team, are at the moment in the very unfortunate situation > of not having a proper machine for running our benchmarks on. Could a > kind soul maybe give us (i.e., me) access to a quadcore or 2xquadcore > x86 Linux or OS X machine? I only need to build ghc on it and run > small benchmarks which never take more than a couple of minutes, maybe > once every couple of days or so. We do need to use all cores, though, > so no other CPU-intensive processes can be running during > benchmarking. This is only for a week or two, until we get our own > machine. We would be eternally grateful and won't forget you when DPH > takes over the world. > > Roman > Roman, Graeme can set you up on an 8 core machine if you email him. Dominic.

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