March 2007 - Libraries

Ann: regex-base-0.91
by Chris Kuklewicz 13 Mar '07

13 Mar '07

I have updated the darcs repository and the hackage repository to have regex-base-0.91 Changes: GHC uses late instance overlap detection, whereas Hugs demands no potential overlap. Thus Hugs rejected some of the polymorphic results for matching given by RegexContext instances. The solution in version 0.91 of regex-base is to use newtypes. To this end there are 4 newtypes which are used to disambiguate some of the more complicated return types of match/matchM/=~/=~~. The new haddock documentation for Text.Regex.Base.Context has more details and lists all the instances. The 4 newtypes are: > newtype AllSubmatches f b = AllSubmatches {getAllSubmatches :: (f b)} > newtype AllTextSubmatches f b = AllTextSubmatches {getAllTextSubmatches :: (f b)} > newtype AllMatches f b = AllMatches {getAllMatches :: (f b)} > newtype AllTextMatches f b = AllTextMatches {getAllTextMatches :: (f b) } The 'f' parameters are containers types, such as [] or (Array Int). The two *Submatches types report all the captured (i.e. parenthesized) groups of the first match found. The two *Matches types report on the all the non-overlapping matches found. This clarifies the desires of the programmer and allows choice of either result to be made. The two *Text* version have the type of the searched text included in the type of the result 'b', unlike the other two types. This avoids overlapping. These newtypes are not used for all the instances, but only where they are needed to either avoid overlapping or remove possible confusion. Using this newtype schema has allowed a few new instances to be added. In particular all the instances should have a [] or (Array Int) option for the returned container. -- Chris Kuklewicz

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New I/O library
by Bulat Ziganshin 13 Mar '07

13 Mar '07

Hello libraries, i've further developed my idea of making new I/O library. look at http://haskell.org/haskellwiki/Library/IO Please edit it if you know how networking/async capabilities may be added to this design i've also added a proposal of developing it as SoC project: http://hackage.haskell.org/trac/summer-of-code/ticket/1113 -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com

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Re: [Haskell] Composing applicative functors?
by Ross Paterson 12 Mar '07

12 Mar '07

[redirecting to libraries] On Wed, Feb 21, 2007 at 04:23:50PM -0800, Conal Elliott wrote: > Is the composition instance of Control.Applicative defined somewhere? I see > it in the McBride & Paterson paper [1], but not in the library docs [2]. > I'd rather pull it in from a library than (re)define it myself. > > [1] http://www.soi.city.ac.uk/~ross/papers/Applicative.pdf > [2] > http://www.haskell.org/ghc/docs/latest/html/libraries/base/Control-Applicat… It's not defined in the libraries. The type (and the identity functor) should probably go in the module that defines Functor (currently Control.Monad) with a Functor instance, and an Applicative instance in Control.Applicative.

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Re: [Haskell-cafe] Program Command Line Arguments
by Ross Paterson 11 Mar '07

11 Mar '07

On Sun, Mar 11, 2007 at 12:51:16PM +1100, Donald Bruce Stewart wrote: > Dave: > > How are command line arguments to a ghc-compiled program > > accessed in Haskell? Or is that even possible? > > Simplest: System.Environment:getArgs > Complex: System.Console.GetOpt Which suggests that these belong in the same place in the module hierarchy. Certainly GetOpt doesn't belong with Readline and SimpleLineEditor. I'd suggest System.Console.GetOpt -> System.Environment.GetOpt, or to create a new node in the hierarchy.

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Re: Proposal: System.Timeout module for base (Trac #980)
by Andriy Palamarchuk 10 Mar '07

10 Mar '07

The documentation for the module is excellent. Could you add a few-lines example for an intended usage? Examples greatly shorten in a few ways time needed to start using some API. First, they are complementary explanation to other information. Second, someone can just copy an example to start playing with it. Another thing - in the header comments you mentioned that the module is "non-portable". Could you add an explanation why the module is non-portable? Thanks, Andriy ____________________________________________________________________________________ Yahoo! Music Unlimited Access over 1 million songs. http://music.yahoo.com/unlimited

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Applicative ((,) a)
by Conal Elliott 09 Mar '07

09 Mar '07

What was the motivation for providing the following Applicative instance? instance Monoid a => Applicative ((,) a) where pure x = (mempty, x) (u, f) <*> (v, x) = (u `mappend` v, f x) Is this instance described in "Applicative Programming with Effects<http://www.soi.city.ac.uk/%7Eross/papers/Applicative.html>"? I didn't spot a mention. Thanks, - Conal

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OpenGL and GLUT packages on Windows cause undefeined reference problem if build theirs myself
by shelarcy 09 Mar '07

09 Mar '07

Hello all, I tried to build OpenGL and GLUT packages on Windows by myself. Then runhaskell Setup.hs build cause below problem. $ runhaskell Setup.hs build Reading parameters from c:\home\ghc-6.7.20070305\libraries\GLUT\GLUT.buildinfo Preprocessing library GLUT-2.1... Building GLUT-2.1... (snip) c:\home\ghc-6.7.20070305\ghc-6.7.20070305\bin\ar.exe q dist\build\libHSGLUT-2.1.a dist\build\Graphics\UI\GLUT.o d (snip) dist\build\Graphics\UI\GLUT\Callbacks\Registration_stub.o Warning: resolving _hs_GLUT_getProcAddress@4 by linking to _hs_GLUT_getProcAddress Use --enable-stdcall-fixup to disable these warnings Use --disable-stdcall-fixup to disable these fixups This problem is already noticed by Pepe Gallardo. http://www.haskell.org/pipermail/hopengl/2006-December/000680.html And same problem cause if build GHC head snapshot myself, too. C:\home\ghc-6.7.20070305\libraries\GLUT\examples\OrangeBook\ogl2brick>C:\home\gh c-6.7.20070305\ghc-6.7.20070305\bin\ghc.exe --make Brick.hs [1 of 1] Compiling Main ( Brick.hs, Brick.o ) Linking Brick.exe ... C:/home/ghc-6.7.20070305/ghc-6.7.20070305/libHSGLUT.a(Extensions__3.o)(.text+0x1 4):fake: undefined reference to `hs_GLUT_getProcAddress@4' C:/home/ghc-6.7.20070305/ghc-6.7.20070305/libHSOpenGL.a(Extensions__3.o)(.text+0 x14):fake: undefined reference to `hs_OpenGL_getProcAddress@4' collect2: ld returned 1 exit status This problem doesn't occure Sigbjorn Finne's build snapshot ... http://www.haskell.org/ghc/dist/current/dist/ http://www.haskell.org/pipermail/cvs-ghc/2007-March/034396.html I don't know why .. but I know why reference is unresolved. CALLCONV is defined stdcall on Windows, but hs_**_getProcAddress (and other cbits's c functions) are build with ccall convention. Attached are darcs patch to fix these problem. But ... I don't know this patch doesn't cause any ptoblem Sigbjorn's next binary release. Because I don't know why OpenGL and GLUT can build correctly under his environment. Best Regars, -- shelarcy <shelarcy capella.freemail.ne.jp> http://page.freett.com/shelarcy/

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IO () as Monoid
by Conal Elliott 08 Mar '07

08 Mar '07

Is there a Monoid instance defined for IO () anywhere? I'm using the following, instance Monoid (IO ()) where { mempty = pure mempty; mappend = (*>) } This definition follows a general form mentioned in http://haskell.org/haskellwiki/TypeComposition, instance (Applicative f, Monoid a) => Monoid (f a) where mempty = pure mempty mappend = (*>) without the conflicts (overlapping instances) introduced by this definition. - Conal

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EnumSet and EnumMap
by Chris Kuklewicz 08 Mar '07

08 Mar '07

I could not quickly find anyone else writing this boiler plate, so I have posted this useful wrapper on the Haskell wiki at http://haskell.org/haskellwiki/EnumSet_EnumMap This uses a cheap newtype to wrap IntSet and IntMap so that you can store any Enum in them. It saves either writing many toEnum/fromEnum functions or using the slower and more generic Data.Set and Data.Map. The original motivation was to go from Map Char to IntMap. And as a bonus, the type signature of the newtype is the same kind as Data.Set and Data.Map (which matters when declaring instances...) > newtype EnumSet e = EnumSet {unEnumSet :: S.IntSet} > deriving (Monoid,Eq,Read,Show,Ord) > newtype EnumMap k a = EnumMap {unEnumMap :: M.IntMap a} > deriving (Eq,Read,Show,Ord,Monoid,Foldable,Functor) This has been quickly tested with GHC 6.6 and may contain typographical errors I have not caught yet. -- Chris

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Re: [Haskell-cafe] TVars & throw
by Chris Kuklewicz 08 Mar '07

08 Mar '07

Thomas Conway wrote: > On 3/8/07, Chris Kuklewicz <haskell(a)list.mightyreason.com> wrote: >> http://haskell.org/haskellwiki/New_monads/MonadAdvSTM > > Ah. Yes, I've independently discovered an equivalent technique. I'm > building external btree/hash table code, and need to handle the case > where you go to use a node that hasn't been paged in. My solution was > simply to throw an exception, catch it, do the IO, then rerun the > transaction. Which sounds *almost* equivalent. My onRetry is different in that it lets one create a sequence of actions that are contingent on retrying the whole transaction. If the transaction commits then these actions are not performed; the actions queued by onCommit will be performed instead. What happens in your throw/catch case if I have stm1 = do some_stm_code_that_throws_your_exception stm2 = return Foo and I run "atomically (stm1 `orElse` stm2)" ? Answer: The exception will prevent running stm2. So I think a mixture of the two would be interesting. Perhaps I will add a "forceRetry" command to the MonadAdvSTM code that uses such an exception to prevent any orElse code from running. > Um, is > unsafeIOToSTM $ atomically trans > going to run you into problems? YES! My code does not use "unsafeIOToSTM $ atomically" nor does it use "unsafePerformIO $ atomically". Both of those will kill the runtime system and thus the whole program. That fatal error is why there is the "*IO" functions like "newTVarIO" were added. My code uses "unsafeIOToSTM $ (IO code using MVar)" which is safe. -- Chris

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