- Haskell-Cafe - Haskell.org

Problems with threading?
by Louis Wasserman 08 Jun '10

08 Jun '10

While working on the Shootout, I noticed the following benchmarks: http://shootout.alioth.debian.org/u64/program.php?test=chameneosredux&lang=… <http://shootout.alioth.debian.org/u64/program.php?test=chameneosredux&lang=…> http://shootout.alioth.debian.org/u64q/program.php?test=chameneosredux&lang… The same program becomes almost 4 times slower when compiled with --threaded and run with +RTS -N5 -- even though the multi-core benchmark really only ever uses one processor. Other languages seem to have found a way of arranging these threads in a way such that parallelism actually happens, but as it stands, compiling this benchmark without --threaded actually makes Haskell competitive against the genuinely parallel alternatives in other languages...which is unusual by itself. I wanted to throw this out for people to discuss, because I'd like to see it improved. As it stands, I'm going to submit a version which asks not to be compiled with --threaded (and has a few other improvements). <http://shootout.alioth.debian.org/u64q/program.php?test=chameneosredux&lang…> Louis Wasserman wasserman.louis(a)gmail.com http://profiles.google.com/wasserman.louis

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Re: [Haskell-cafe] is there a way to prove the equivalence of these two implementations of (Prelude) break function?
by Alexander Solla 08 Jun '10

08 Jun '10

On Jun 8, 2010, at 2:38 AM, Alberto G. Corona wrote: > This is`t a manifestation of the Curry-Howard isomorphism? Yes, basically. If we rephrase the isomorphism as "a proof is a program, the formula it proves is a type for the program" (as Wikipedia states it), we can see the connection. The "characterization" of prelBreak I gave is a "type" for prelBreak. The type is richer than we can express in the Haskell type system ("prelbreak accepts a proposition p and a list xs, and returns a pair whose first element is the largest prefix of xs for which no x satisfies p, and whose second element is the complement of the first, taken in xs."), but we can still reason about the richer type mathematically, and the Curry-Howard isomorphism applies to it.

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Function to find a substring
by R J 08 Jun '10

08 Jun '10

What's an elegant definition of a Haskell function that takes two strings and returns "Nothing" in case the first string isn't a substring of the first, or "Just i", where i is the index number of the position within the first string where the second string begins? _________________________________________________________________ Hotmail has tools for the New Busy. Search, chat and e-mail from your inbox. http://www.windowslive.com/campaign/thenewbusy?ocid=PID28326::T:WLMTAGL:ON:…

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is there a way to prove the equivalence of these two implementations of (Prelude) break function?
by Thomas Hartman 08 Jun '10

08 Jun '10

Here's two implementations of break, a snappy one from the prelude, and a slow stupid stateful one. They are quickchecked to be identical. Is there a way to prove they are identical mathematically? What are the techniques involved? Or to transform one to the other? import Control.Monad.State import Test.QuickCheck tThis = take 5 . show . mybreak (>4000000) $ [1..10^7] tPrel = take 5 . show . prelbreak (>4000000) $ [1..10^7] prelbreak p xs = (takeWhile (not . p) xs,dropWhile (not . p) xs) -- fast, more or less as implemented in prelude iiuc mybreak p xs = evalState (brk p) ([],xs) -- stateful, slow brk p = do (notsat,remaining) <- get case remaining of [] -> return (notsat,remaining) (r:rs) -> if p r then return (notsat,remaining) else do put (notsat++[r],rs) -- ++ is probaby a major reason brk p

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Fwd: [Gtk2hs-users] Installation problem with cairo.
by Magicloud Magiclouds 08 Jun '10

08 Jun '10

Hi, I cannot subscribe to libraries maillist. So I forward this here. I cannot install gtk2hs-cairo by cabal using cairo 1.9.6 compiled myself. Cabal always said that the cairo library/devel files were missing. ---------- Forwarded message ---------- From: Axel Simon <Axel.Simon(a)in.tum.de> Date: Tue, Jun 8, 2010 at 7:15 PM Subject: Re: [Gtk2hs-users] Installation problem with cairo. To: Magicloud Magiclouds <magicloud.magiclouds(a)gmail.com> Cc: gtk2hs-users <gtk2hs-users(a)lists.sourceforge.net> Hi again, it's very difficult for me to say what is happening. Could you ask on the cabal mailing list to see if anybody there has an idea. Cheers, Axel On 08.06.2010, at 11:01, Magicloud Magiclouds wrote: > I've tried a little, the error was not thrown out in gtk2hssetup.hs. > And even I faked a version (1.8.10), it did not work. > > On Tue, Jun 8, 2010 at 3:47 PM, Axel Simon <Axel.Simon(a)in.tum.de> wrote: >> >> Hi, >> >> On Jun 8, 2010, at 9:21, Magicloud Magiclouds wrote: >> >>> Yes, seems like so. >>> Here is the output: >>> >>> # /usr/bin/pkg-config --modversion cairo-pdf >>> 1.9.6 >>> # /usr/bin/pkg-config --modversion cairo-ps >>> 1.9.6 >>> # /usr/bin/pkg-config --modversion cairo-svg >>> 1.9.6 >>> # /usr/bin/pkg-config --modversion cairo >>> 1.9.6 >>> >> >> Oh dear. >> >> Since cabal manages once to get the correct version and fails later on, I >> assume it's the magic Duncan added to out Gtk2HsSetup.hs file that requests >> the package version again. If you look for >> >> --FIXME: Cabal should tell us the selected pkg-config package versions in >> the >> -- LocalBuildInfo or equivalent. >> -- In the mean time, ask pkg-config again. >> >> in the cabal file and try to add some debugging output then maybe you can >> find out more. >> >> I suspect that either the LocalBuildInfo or the PackageDescription value is >> not the most up-to-date one but some default value that lack some path or >> some such. >> >> cheers, >> Axel >> >>> On Tue, Jun 8, 2010 at 2:56 PM, Axel Simon <Axel.Simon(a)in.tum.de> wrote: >>>> >>>> Hi, >>>> >>>> On Jun 8, 2010, at 8:54, Magicloud Magiclouds wrote: >>>> >>>>> /usr/bin/pkg-config --modversion cairo >>>>> setup: Missing dependency on a foreign library: >>>>> * Missing C library: cairo >>>>> 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. >>>> >>>> well, what's the output of >>>> >>>>> /usr/bin/pkg-config --modversion cairo >>>> >>>> ? Maybe cabal fails to parse the version for some reason. >>>> >>>> Axel >>>> >>>> >>> >>> >>> >>> -- >>> 竹密岂妨流水过 >>> 山高哪阻野云飞 >> >> > > > > -- > 竹密岂妨流水过 > 山高哪阻野云飞 -- 竹密岂妨流水过山高哪阻野云飞

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Updates in the regions library
by Bas van Dijk 08 Jun '10

08 Jun '10

Hi Arie (and others who are interested in the regions library), I would like to let you know that I'm working on a new version of my regions package and its reverse dependencies: regions-monadsfd, regions-monadstf, safer-file-handles, regional-pointers and usb-safe. The major change is that I removed the Resource class: class Resource resource where data Handle resource ∷ * open ∷ resource → IO (Handle resource) close ∷ Handle resource → IO () in favor of a much more simple interface, namely: -- | An 'IO' computation that closes or finalizes a resource. For example -- 'hClose' or 'free'. type CloseAction = IO () -- | A handle to a 'CloseAction' that allows you to duplicate the action to a -- parent region using 'dup'. newtype CloseHandle (r ∷ * → *) -- | Register the 'CloseAction' in the region. When the region terminates all -- registered close actions will be perfomed if they're not duplicated to a -- parent region. register ∷ MonadIO pr ⇒ CloseAction → RegionT s pr (CloseHandle (RegionT s pr)) Here's an example how to use this new interface from my updated regional-pointers package: import qualified Foreign.Marshal.Alloc as FMA -- | A regional handle to memory. This should provide a safer replacement for -- Foreign.Ptr.Ptr data RegionalPtr α (r ∷ * → *) = RegionalPtr (Ptr α) (CloseHandle r) {-| Allocates the given number of bytes and returns a regional pointer to them. This should provide a safer replacement for: Foreign.Marshal.Alloc.mallocBytes. -} mallocBytes ∷ MonadCatchIO pr ⇒ Int → RegionT s pr (RegionalPtr α (RegionT s pr)) mallocBytes size = block $ do ptr ← liftIO $ FMA.mallocBytes size let closeAction = free ptr ch ← register closeAction return $ RegionalPtr ptr ch And here's an example from safer-file-handles: -- | A regional handle to an opened file parameterized by the 'IOMode' in which -- you opened the file and the region in which it was created. data RegionalFileHandle ioMode (r ∷ * → *) = RegionalFileHandle (Handle ioMode) (CloseHandle r) openFile ∷ MonadCatchIO pr ⇒ FilePath → IOMode ioMode → RegionT s pr (RegionalFileHandle ioMode (RegionT s pr)) openFile = openNormal E.openFile -- | Opens a file in binary mode then yields a regional handle to it. This -- provides a safer replacement for System.IO.openBinaryFile. openBinaryFile ∷ MonadCatchIO pr ⇒ FilePath → IOMode ioMode → RegionT s pr (RegionalFileHandle ioMode (RegionT s pr)) openBinaryFile = openNormal E.openBinaryFile openNormal ∷ MonadCatchIO pr ⇒ (FilePath → IOMode ioMode → IO (E.Handle ioMode)) → FilePath → IOMode ioMode → RegionT s pr (RegionalFileHandle ioMode (RegionT s pr)) openNormal open filePath ioMode = block $ do h ← liftIO $ open filePath ioMode let closeAction = sanitizeIOError $ hClose h ch ← register closeAction return $ RegionalFileHandle h ch I haven't released it yet because I need to write some more documentation. However all the repositories contain the new code: darcs get http://code.haskell.org/~basvandijk/code/regions darcs get http://code.haskell.org/~basvandijk/code/regions-monadsfd darcs get http://code.haskell.org/~basvandijk/code/regions-monadstf darcs get http://code.haskell.org/~basvandijk/code/regional-pointers darcs get http://code.haskell.org/~basvandijk/code/safer-file-handles darcs get http://code.haskell.org/~basvandijk/code/usb-safe and some examples: darcs get http://code.haskell.org/~basvandijk/code/usb-safe-examples darcs get http://code.haskell.org/~basvandijk/code/safer-file-handles-examples darcs get http://code.haskell.org/~basvandijk/code/usb-safe-and-safer-file-handles-ex… Regards, Bas On Wed, Jun 2, 2010 at 3:13 PM, Bas van Dijk <v.dijk.bas(a)gmail.com> wrote: > On Wed, Jun 2, 2010 at 2:57 PM, Arie Peterson <ariep(a)xs4all.nl> wrote: >>> On Wed, Jun 2, 2010 at 2:28 PM, Bas van Dijk <v.dijk.bas(a)gmail.com> >> wrote: >>>> Before answering your questions I would like to make sure I understand >>>> your Resource type. When I want to create a memory Resource for >>>> example is the following what you have in mind? >>>> >>>> {-# LANGUAGE Rank2Types #-} >>>> >>>> -- from base: >>>> import Foreign.Ptr ( Ptr ) >>>> import Foreign.Marshal.Alloc ( mallocBytes, free ) >>>> >>>> -- from transformers: >>>> import Control.Monad.IO.Class ( liftIO ) >>>> >>>> -- from MonadCatchIO-transformers: >>>> import Control.Monad.CatchIO ( MonadCatchIO, bracket ) >>>> >>>> newtype Resource cap m = Resource { with :: forall a. (cap -> m a) -> m >>>> a } >>>> >>>> type Memory m a = Resource (Ptr a) m >>>> >>>> memory :: MonadCatchIO m => Int -> Memory m a >>>> memory size = Resource $ bracket (liftIO $ mallocBytes size) (liftIO . >>>> free) >> >> Yes, exactly. I also create type aliases for resources providing a >> specific capability. >> >> On Wed, 2 Jun 2010 14:45:08 +0200, Bas van Dijk <v.dijk.bas(a)gmail.com> >> wrote: >>> The previous can also be generalized using my Resource class: >>> >>> -- from regions: >>> import qualified Control.Resource as C ( Resource(..) ) >>> >>> resource :: (MonadCatchIO m, C.Resource resource) >>> => resource -> Resource (C.Handle resource) m >>> resource r = Resource $ bracket (liftIO $ C.open r) (liftIO . C.close) >> >> Yes, definitely. >> >> (This is not a literal generalisation of the 'memory' function, unless you >> make 'Int' an instance of 'C.Resource'; one would probably create a special >> type 'data Memory = Memory Int' instead. This is the difference I alluded >> to in my earlier email.) > > Indeed. > > My regional-pointers package provides this Memory type and an instance > for Resource: > http://hackage.haskell.org/packages/archive/regional-pointers/0.1.0.2/doc/h… > > Now I'm beginning to understand the problem with your 'fallback' > function. If I specialize the capability to Handles to Memory as in: > > -- from regional-pointers: > import Foreign.Ptr.Region ( Memory ) > > fallback :: Resource (C.Handle (Memory a)) IO > -> Resource (C.Handle (Memory a)) IO > -> Resource (C.Handle (Memory a)) IO > fallback (Resource primary) (Resource backup) = Resource l > where > l c = primary c `catch` (\(SomeException _) -> backup c) > > then the only way to create a value of type 'Resource (C.Handle > (Memory a))' is to apply my previously posted 'resource' function to > 'Memory nrOfBytes'. There's no other way to create Handles to Memory. > Is that your problem? > > The problem is that Handle is an associated _data_ type not an > associated _type synonym_: > > class Resource resource where > data Handle resource ∷ * > open ∷ resource → IO (Handle resource) > close ∷ Handle resource → IO () > > So 'Handle' is an injective type function which means that every > 'Handle resource' has only one 'resource'. > > I could try turning 'Handle' into an associated type synonym. > > Regards, > > Bas >

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PDF generation?
by Jim Tittsler 08 Jun '10

08 Jun '10

What is the easiest way to create PDF files from Haskell? Is gtk2hs's PDF output the preferred way?

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Re: [Haskell-cafe] is there a way to prove the equivalence of these two implementations of (Prelude) break function?
by Alberto G. Corona 08 Jun '10

08 Jun '10

> This isn`t a manifestation of the Curry-Howard isomorphism? > > 2010/6/8 Alexander Solla <ajs(a)2piix.com> > > >> On Jun 7, 2010, at 4:10 PM, Alexander Solla wrote: >> >> >>> You might note how much like evaluating the function generating the >>> analysis is. >>> >> >>

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haskell.org down?
by Ozgur Akgun 08 Jun '10

08 Jun '10

http://downforeveryoneorjustme.com/www.haskell.org -- Ozgur Akgun

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Haddock on HP failing
by Chris Dornan 08 Jun '10

08 Jun '10

Hi, I am trying to use Haddock on the Haskell Platform 2010.1.0.0 and getting haddock.exe: can't find a package database at E:\ghc\ghc-6.12.1\lib\package.conf.d I have tried uninstalling and re-installing HP (just in case) to no avail. Has anybody else seen this? Chris

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