- Haskell-Cafe - Haskell.org

Help with another Bird problem (3.3.4)
by Peter Hilal 25 Feb '09

25 Feb '09

Could someone provide a solution to do the following problem from Bird: The function "log" can be specified by the condition that log (2^m) = m for all m. Construct a program for log and prove that it meets the specification. Note that this problem doesn't specify a domain, unlike problem 3.3.3, which specified Nat as the domain. Thanks.

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Haskellers on Twitter!
by Daniel Peebles 25 Feb '09

25 Feb '09

Hi all, I liked Brian O'Sullivan's blog post on twitter (http://www.serpentine.com/blog/2008/12/05/functional-programmers-on-twitter/) so I moved the Haskell subset of his list (along with a couple of additions) onto the haskell wiki, to make it easier for people to update. You can find the page at http://haskell.org/haskellwiki/Twitter. Please update with yourself or any other Haskellers we may have missed. Cheers, Dan

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Hoogle and Network.Socket
by Thomas DuBuisson 25 Feb '09

25 Feb '09

I recall that Niel made sure hoogle doesn't search through non-portable libraries (a shame), but I thought Network.Socket could be used on Windows and yet Hoogle does not give any results for 'socket' or any other functions within Network.Socket. First, am I mistaken and Network.Socket is POSIX only? I could swear it wasn't. Secondly - is there any chance of lifting the non-portable libraries ban, Niel? From the stand point of an application developer it might not sound good, but even in Haskell some software is system level and bound to be single platform (case and point: XCB, xmonad, hsXenCtrl). Judging by the amount of research in systems level functional programming I wouldn't be surprised to see this collection grow and making functions hard to find isn't productive. Thomas

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New version of Hieroglyph released: Hieroglyph 1.1 is on hackage
by Jeff Heard 25 Feb '09

25 Feb '09

For those of you who don't read Reddit: Changes are minor right now. The main thing is that I'm now using Russell O'Connor's excellent Data.Colour library. The only other changes were to make H. compile with Gtk2Hs 0.10.x and to make it a bit easier to integrate Gtk2Hs guis with Hieroglyph and vice versa. Enjoy! -- Jeff

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package for algebraic structures
by Wolfgang Jeltsch 25 Feb '09

25 Feb '09

Hello, for Grapefruit’s incremental list signal support, I needed a type class of semigroups. A semigroup is similar to a monoid. The difference is that a semigroup doesn’t need to have a neutral element. So a semigroup type class would make a perfect superclass of Monoid, by the way. Since a semigroup class could be of more general interest, I decided to not include it in Grapefruit. Since I couldn’t quickly find an implementation of semigroups in Haskell, I put my own into a new package. Now, a package only for one class with one method seems like overkill. However, it could serve as a start for a package of all kinds of algebraic structures. So I called the package “algebra” and put it on Hackage. So if someone wants to implement rings, ideals, fields or whatever, I’d be happy to receive patches. Best wishes, Wolfgang

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Hac5 projects page
by Wolfgang Jeltsch 25 Feb '09

25 Feb '09

Hello, on <http://www.haskell.org/haskellwiki/Hac5/Projects>, you can list a project under “Project descriptions” and under “Experiences”. What’s the difference? Best wishes, Wolfgang

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ANN: bug fix for regex-tdfa, version 0.97.4 (and "regex-ast")
by ChrisK 24 Feb '09

24 Feb '09

Hello, The regex-tdfa package has had a series of bug fix releases (0.97.1 and 2 and 3 and now 4). This 0.97.4 releases finishes fixing the bug that was only mostly fixed in the 0.97.1 release. An example of the fixed bug: Apply the regex pattern (BB(B?))+(B?) to the text BBBB. The "BB" in the pattern should be used twice and both "B?" should match nothing. My code grouped the "+" wrong and matched the "BB" once and then both the "B?" matched a "B". The case fixed here was not initially caught because of how I search for unknown bugs. I use "Arbitrary" from QuickCheck to generate random patterns and strings to search, and compare regex-tdfa to another POSIX engine. Because I am on OS X, I am limited by the the native POSIX libraries bugs: this bug in regex-tdfa was triggered only when the native POSIX was also buggy. But the source of most of my unit tests is AT&T research [1], and they have a "libast" with a POSIX implementation. I have adapted my regex-* wrapper packages to make a "regex-ast" Haskell interface, but the difficulties with the AT&T headers prevent me from releasing this on hackage. This "regex-ast" has given me access to a less buggy POSIX back-end, and randomized testing has led to catching the bug fixed here (as well as a few bug reports back to AT&T). So while regex-tdfa will not win many speed contests, it is the only POSIX regular expression library I have running that passes all the unit tests. [1] http://www.research.att.com/sw/download/ http://www.research.att.com/~gsf/testregex/ http://www.research.att.com/~gsf/testregex/re-interpretation.html

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Looping after compiling with cabal
by Henk-Jan van Tuyl 24 Feb '09

24 Feb '09

L.S., I have updated wxFruit to compile with GHC 6.10.1, but when I compil using the commands: runhaskell Setup configure & runhaskell Setup build & runhaskell Setup install and run paddle.exe, I get the message: paddle: <<loop>> If I compile with: ghc --make paddle , the game starts normally. Any idea how I can solve this? Some more data: Using: Yampa-0.9.2.3 wxFruit-0.1.1 from Hackage, updated GHC 6.10.1 Windows XP Compile sessions: [...]\Haskell\GUI\wxHaskell\wxFruit-0.1.1.updated>ghc --make paddle [1 of 2] Compiling WXFruit ( WXFruit.hs, WXFruit.o ) [2 of 2] Compiling Main ( paddle.hs, paddle.o ) Linking paddle.exe ... This paddle.exe works fine [...]\Haskell\GUI\wxHaskell\wxFruit-0.1.1.updated>runhaskell Setup configure & runhaskell Setup build & runhaskell Setup install Configuring wxFruit-0.1.2... Preprocessing library wxFruit-0.1.2... Preprocessing executables for wxFruit-0.1.2... Building wxFruit-0.1.2... [1 of 1] Compiling WXFruit ( WXFruit.hs, dist\build\WXFruit.o ) C:\Programs\ghc\ghc-6.10.1\bin\ar.exe: creating dist\build\libHSwxFruit-0.1.2.a [1 of 2] Compiling WXFruit ( WXFruit.hs, dist\build\paddle\paddle-tmp\WXFruit.o ) Linking dist\build\paddle\paddle.exe ... Installing library in C:\Program Files\Haskell\wxFruit-0.1.2\ghc-6.10.1 Installing executable(s) in C:\Program Files\Haskell\bin Registering wxFruit-0.1.2... Reading package info from "dist\\installed-pkg-config" ... done. Writing new package config file... done. [...]\Haskell\GUI\wxHaskell\wxFruit-0.1.1.updated>cd dist\build\paddle [...]\Haskell\GUI\wxHaskell\wxFruit-0.1.1.updated\dist\build\paddle>paddle paddle: <<loop>> -- Regards, Henk-Jan van Tuyl -- http://functor.bamikanarie.com http://Van.Tuyl.eu/ --

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about gSoc ideas
by Li Feng 24 Feb '09

24 Feb '09

Hi all, I don't know if it is proper to ask about gsoc on this list, tell me if it's not. I find last couple year's gSoc ideas on http://hackage.haskell.org/trac/summer-of-code/report/1, which some of them labeled good/bad or something else. I don't know what's their status now, and I want to ask for advice about the project that really in need by the HASKELL and is suitable for a gSoc project. Any suggestion will be appreciate. Feng Li

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Need some advice on deploying an app
by Gü?nther Schmidt 24 Feb '09

24 Feb '09

Hi, I've just finished developing my haskell - windows app and am ready to ship it now. I'm using Inno Setup for the installation but need another tool that would wrap my app inside itself and check for valid keys or an expiration date on every start up. Can anyone recommend a good tool for that purpose? Günther

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Hac5: April 17-19, Utrecht -- Book Now!
by Sean Leather 24 Feb '09

24 Feb '09

Twelve days ago, we emailed you about a particular event... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The 5th Haskell Hackathon April 17 - 19, 2009 Utrecht, The Netherlands ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We have some updated information for you. If you don't want to read the details, then the important points are: * Hotel or hostel accommodation may be hard to come by, so book your room now! * Check out the website for lots of useful information. As I mentioned before, you can find out more about the Hackathon here: http://haskell.org/haskellwiki/Hac5 The site is a wealth of useful information gratefully provided by the Utrecht organizing team. If you haven't seen it recently, check again. In particular, however, we'd like to inform you of some newly obtained information. We unknowingly scheduled the Hackathon on the same weekend as a popular record and CD fair. http://www.recordplanet.nl/ So, not only do you get the chance to hack on projects involving your favorite purely functional programming language, you also have the opportunity to visit "the most impressive record fair of the world." However, this does have some drawbacks... Rooms in hotels and hostels in Utrecht are often notoriously difficult to come by. It's already a crowded city sometimes with too few places to stay (esp. if you want cheap). Therefore, if you've decided to join us or have already registered, we highly recommend booking a room at your earliest convenience. (If you haven't decided to visit Utrecht, then you should hurry up and agree to it already!) For this purpose, we have updated the main Hac5 page with information about accommodations. http://haskell.org/haskellwiki/Hac5#Accommodation We also have a Google map with information about places to stay and transportation. http://haskell.org/haskellwiki/Hac5#Map And finally, don't forget that you can use either the Attendees page, the Hackathon mailing list, or the IRC channel to communicate with other (potential) attendees or the organizers about sharing rooms, finding a place, or anything else. http://haskell.org/haskellwiki/Hac5/Attendees http://haskell.org/mailman/listinfo/hackathon #haskell-hac5 (on freenode) Good luck and happy hacking! == Organizers == Andres Löh, Utrecht University (UU) José Pedro Magalhães, UU Sean Leather, UU Eelco Lempsink, UU + Tupil Chris Eidhof, UU + Tupil ... and more ...

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Stacking StateTs
by Luis O'Shea 24 Feb '09

24 Feb '09

I've been experimenting with the state monad and with StateT, and have some questions about how to combine one state with another. This email is literate Haskell tested on GHCi, version 6.10.1. Also, sigfpe's post on monad transformers (http://blog.sigfpe.com/2006/05/ grok-haskell-monad-transformers.html) was very helpful. > import Control.Monad.State My question is basically whether the function modifyT (below) makes sense, whether some form of it already exists in a standard library, and (most importantly) whether it actually indicates that I'm thinking about StateT all wrong. > modifyT :: Monad m => > (s -> StateT t m s) > -> StateT t (StateT s m) () > modifyT f = do > x <- get > y <- lift get > (y',x') <- lift $ lift $ runStateT (f y) x > lift $ put y' > put x' Some context may be useful, so here is how I ended up thinking I needed modifyT. The state monad makes it easy to write stateful computations. For example here is a computation that has an Integer as its state and returns a String: > test1 :: State Integer String > test1 = do > modify (+ 1) > a <- get > return $ "foobar" ++ (show a) If the computation wants to do some IO then it makes sense to start with the IO monad and then apply the StateT transformer to it: > test2 :: StateT Integer IO String > test2 = do > modify (+ 1) > a <- get > lift $ print a > return $ "foobar" ++ (show a) So from now on I won't actually do any IO and will replace IO with an arbitrary monad m. Also instead of the fixed string "foobar" I'll have it take a String as a parameter: > test3 :: Monad m => String -> StateT Integer m String > test3 s = do > modify (+ 1) > a <- get > return $ s ++ (show a) A nice feature of all this is that it is easy to combine these computations: > test4 :: Monad m => StateT Integer m (String,String) > test4 = do > s1 <- test3 "foo" > s2 <- test3 "bar" > return $ (s1,s2) Now seeing as test3 takes a String and returns another String you can imagine using it to transform a String state. (I'm also going to assume that test3 is in another library so we don't want to alter how it's written.) So here is how you could use test3 in a computation that has (String,Integer) as its state: > test5 :: (Monad m) => m Integer > test5 = do > (s1,x1) <- runStateT (test3 "") 0 > (s2,x2) <- runStateT (test3 s1) (2*x1 + 1) > (s3,x3) <- runStateT (test3 s2) (x2*x2) > return x3 Then running test5 >>= print gives 17. The problem with test5, of course, is that we have manually threaded the state, with all the problems that implies. For example nothing prevents you from erroneously misthreading the state: > test5bad :: (Monad m) => m Integer > test5bad = do > (s1,x1) <- runStateT (test3 "") 0 > (s2,x2) <- runStateT (test3 s1) (2*x1 + 1) > (s3,x3) <- runStateT (test3 s1) (x2*x1) > return x3 Running test5bad >>= print gives 5. Obviously we want operate in a State monad with more state. One way to do this is to stack two StateTs on top of m. This is, finally, where I need the modifyT that we defined above -- it lets us "lift" test3 to a function that modifies the state of the top *two* StateTs. Now let's use it to rewrite test5: > test6 :: (Monad m) => StateT Integer (StateT String m) Integer > test6 = do > modifyT test3 > modify $ \x -> 2*x + 1 > modifyT test3 > modify $ \x -> x*x > modifyT test3 > x <- get > return x > > test7 :: (Monad m) => m Integer > test7 = evalStateT (evalStateT test6 0) "" As expected, running test7 >>= print gives 17. So, given that modifyT seems to be useful, does it, or something like it, already exists in the standard libraries? More likely, am I making a mountain of a molehill and is there a better way to structure all this? Thanks, Luis > main = do > test5 >>= print > test5bad >>= print > test7 >>= print

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advancePtr for ForeignPtr
by Henning Thielemann 24 Feb '09

24 Feb '09

Is still someone on haskell.org ? ---------- Forwarded message ---------- Date: Thu, 19 Feb 2009 21:40:08 +0100 (CET) From: Henning Thielemann <lemming(a)henning-thielemann.de> To: ffi(a)haskell.org Subject: advancePtr for ForeignPtr I want to have an advancePtr on ForeignPtr in order create a subarray. Is this reasonable and possible? Do I have to use 'touchForeignPtr' as finalizer of the subarray's ForeignPtr in order to assert that the superarray lives at least as long as the subarray? Anyway I'd prefer a function in the standard modules than doing such things by myself.

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looking for a 2d graphics package
by Martin DeMello 24 Feb '09

24 Feb '09

What 2d graphics library would be the best fit for this sort of thing? http://www.superliminal.com/geometry/tyler/gallery/circular/tiles060.html I took a look at diagrams but it seemed more geared towards things that fit on a rectangular layout. martin

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Semantic web
by gregg reynolds 24 Feb '09

24 Feb '09

Anybody implementing rdf or owl stuff in haskell? Seems like a natural fit. G

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Fwd: [plt-scheme] Vancouver Lisp Users Group meeting for March 2009 - Haskell for Lisp Programmers
by Tim Wawrzynczak 24 Feb '09

24 Feb '09

I thought you guys might find this interesting: Haskell for Lisp programmers ---------- Forwarded message ---------- From: Bill Clementson <billclem(a)gmail.com> Date: Mon, Feb 23, 2009 at 11:12 AM Subject: [plt-scheme] Vancouver Lisp Users Group meeting for March 2009 - Haskell for Lisp Programmers To: undisclosed-recipients Hi all, Haskell is a polymorphically statically typed, lazy, purely functional language based on the lambda calculus. As such, it shares some things in common with some dialects of Lisp but differs in other regards. Our March lispvan speaker will present an introduction to Haskell geared towards Lisp programmers. If you want to read up about Haskell before the meeting, a good starting point is the Haskell Wiki. Here's the "official" meeting notice: Topic: Haskell for Lisp Programmers Presenter: Erik Charlebois Date: Wednesday, March 4th, 2009 Time: 7pm - 10pm (or whenever) Venue: The Hackery, 304 Victoria Dr (entrance off Franklin), Vancouver (see map) Summary: Haskell is a lazy, pure, statically-typed functional programming language enjoying a lot of attention these days. Its strict approach to side effects is seen as one of the viable approaches to making parallel programming tractable. Erik will talk about the core differences between Haskell and Lisp, the actions the Haskell community is taking to manage this growth, and some neat applications of the language already in the wild. * Differences between Haskell and Lisp * Syntax * Static typing * Side effects with monads * The Haskell Platform * Build, Package, Distribute * Community * Haskell Dog and Pony Show Bio: Erik was a compiler developer for 3 years at IBM working on the XL Fortran and C/C++ compilers for the Cell processor. He is currently employed at Slant Six Games doing gameplay programming. For the past 2 years, he has been studying programming languages and databases in a search for smarter ways to build soft real-time applications like games. If possible, I will record the presentation and post it on my blog after the meeting for those who are unable to attend. Join us for a beer (bring your own - there's a fridge) and a chance to learn what static typing and monads are all about! Any updates will be posted on my blog entry for the meeting: http://bc.tech.coop/blog/090223.html -- Bill Clementson _________________________________________________ For list-related administrative tasks: http://list.cs.brown.edu/mailman/listinfo/plt-scheme

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Online GHC documentation
by Maurício 23 Feb '09

23 Feb '09

Just a small tip: I think it would be nice if GHC online documentation were built with links to the source code, like in hackage. Best, Maurício

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Fwd: cabal-install and bash scripts in windows- Was: Re: pkgenv - disposable, isolated pkg environments
by Alberto G. Corona 23 Feb '09

23 Feb '09

Forwarded to the list: By the way, there are important packages such are haskell plugins, that have also this same single obstacle for workining under Windows. Many have basically the same bash script that test the type of c compiler, which fails miserably under windows: example output: checking for C compiler default output file name... configure: error: C compiler cannot create executables See `config.log' for more details. cabal: Error: some packages failed to install: plugins-1.4.0 failed during the configure step. The exception was: exit: ExitFailure 77 Could be possible to check if this problem can be solved with cabal-install?. 2009/2/22 Duncan Coutts <duncan.coutts(a)worc.ox.ac.uk> > On Sun, 2009-02-22 at 18:38 +0100, Paolo Losi wrote: > > Duncan Coutts wrote: > > > > > Would it be useful to have cabal-install check a env var for its config > > > file? > > > > Definitely yes. > > This would allow dropping the dependency on bash aliasing and > > make porting to Windows fairly easy. > > Ok, I've filed a ticket so hopefully someone will pick it up. It should > be pretty easy. Just a few lines of code. > > http://hackage.haskell.org/trac/hackage/ticket/505 > > Duncan > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe >

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Practise of hiding contsructors and serialization
by Marc Weber 23 Feb '09

23 Feb '09

While working on extending scion I got some trouble and wonder which is the best way to do this? I have to pass a compilation result from a scion process instance to the scion daemon process. Of course I'd just like to use a simple Read Show for that. However I can't because two datatypes are NominalDiffTime and Bag ErrMsg: newtype NominalDiffTime = MkNominalDiffTime Pico deriving (Eq,Ord) data ErrMsg = ErrMsg { errMsgSpans :: [SrcSpan], errMsgContext :: PrintUnqualified, errMsgShortDoc :: Message, errMsgExtraInfo :: Message } Both are fine and both don't export all contstructors so you can't just let ghc derive instances for it? So the only way is to duplicate those datatypes in order to derive some Show, Read instances? On the one hand I do understand that you don't want users to access constructors directly. On the other hand it would be desirable to derive Read, Show instances here. Is there a way to get all? a) hiding constructors so that you don't have to expose implementation details to the user. b) still allow deriving serialization instances? Is there a better way than using toRational to get a type which can be serialzied quickly? I don't like Rational because the unit information 1e-12[s] is no longer included in the type.. Sincerly Marc Weber

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Error on instance of Control.Exception.Exception
by Maurício 23 Feb '09

23 Feb '09

Hi, I read here: www.haskell.org/ghc/docs/latest/html/libraries/base/Control-Exception.html that this is declared: --- class (Typeable e, Show e) => Exception e where toException :: e -> SomeException fromException :: SomeException -> Maybe e --- I understand this means Excepton is a class. But after I try: --- instance Exception DbError where --- GHC says: Type constructor `Exception' used as a class In the instance declaration for `Exception DbError' Isn't Exception a class? If it is, what is the proper way to have an Exception instance for my type? Thanks, Maurício

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ANNOUNCE: X Haskell Bindings 0.2
by Antoine Latter 23 Feb '09

23 Feb '09

I'd like to announce the 0.2.* series release of the X Haskell Bindings. This release, like the prior 0.1.* series focuses on making the API prettier. This does mean that there's a good chance this is a breaking release. Also, 0.2.* is based on the just-released version 1.4 of the XML descriptions of the X protocol. The goal of XHB is to provide a Haskell implementation of the X11 wire protocol, similar in spirit to the X protocol C-language Binding (XCB). On Hackage: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/xhb New this release: In the core protocol, a lot of the fields which previously were of type 'Word8' or 'Word16' now have appropriate higher-level types. For example, in the type GetWindowAttributesReply, the 'class' field was previously of type 'Word16', and is now of type 'WindowClass,' and the 'all_event_masks' field was of type 'Word32' and is now of type '[EventMask]'. These improvements haven't made their way out to the extensions yet, but the code-generation machinery is now in place for this to happen as the information makes its way into the XML protocol description. Related projects: X C Bindings: http://xcb.freedesktop.org/ -Antoine

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pkgenv - disposable, isolated pkg environments
by Paolo Losi 23 Feb '09

23 Feb '09

Hi all, I've been recently toying with a small tool inspired by the Python tool virtualenv [1]. What it basically allows to do is to setup isolated, disposable package environments. You can find a small session example in: http://www.haskell.org/haskellwiki/PkgEnv The main benefits should be: 1. allowing experimenting with package installations without "polluting" or breaking the default user package DB. When you're done you can simply remove the pkgenv directory => disposable 2. starting from a clean, fresh pkg "configuration" containing only system packages. This make cabal-install dependency analysis job much easier and predictable => isolated pkgenv now only runs on unix, even if it could be possible to port it to windows... To test it, download it from http://bitbucket.org/pao/pkgenv/raw/488bfe8e58dd/pkgenv chmod a+x and drop to an executable directory. Any feedback would be really appreciated. Is this useful at all? Are there better ways to reach the same goals? Pao 1. http://pypi.python.org/pypi/virtualenv

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Finding a PID in Windows
by Alexandru Scvortov 23 Feb '09

23 Feb '09

Quick question. In Linux, if you want to find the PID of a process, you use getProcessID from System.Posix.Process. How do you do the same under Windows? I cannot find the equivalent function in System.Win32 and searching Google does not yield any useful results. Thanks.

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instance MonadFix GenParser
by Paul Johnson 22 Feb '09

22 Feb '09

I want to write a parser for a Haskell-like type language. Amongst other things this means having a symbol table of top-level declarations. So for instance I want to be able to write in my type language: > type Foo = Bar Int > > data Bar a = Bar String a I can come up with a parser that identifies "Bar" in the type synonym as the name of another type. I could define a type to return from the parser which just has that as a string, but then I would have to write another data type which is essentially the same but replaces the string name with the actual data type, and a mapping function to use a symbol table to convert one into the other, like this: > data ParsedTypeExpr = ParsedTypeExpr {parsedBaseType :: String, parsedTypeArgs :: [String]} > > data TypeExpr = TypeExpr {baseType :: MyType, typeArgs :: [String]} > > convertTypeExpr :: (String -> MyType) -> ParsedTypeExpr -> TypeExpr I want to short-circuit this by looking up the definition of Bar in the parser. But that requires the symbol table to exist during the parse. I have to admit I haven't quite got my head around MonadFix yet, but if I understand it correctly I should be able to have a top level parser something like this: > parseDeclarations :: Parser [Declaration] > parseDeclarations = mdo > decls <- many ParseDeclaration symbols > let symbols = makeSymbolTable decls > return decls Unfortunately GenParser isn't an instance of MonadFix, so this won't work. Is there a good reason why GenParser can't be an instance of MonadFix? If not, what would the instance declaration be? Thanks, Paul.

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Re: Haskell-Cafe Digest, Vol 66, Issue 71
by David Yoffe 22 Feb '09

22 Feb '09

Hi D.R Plotkin, There are some nice mailing lists in haskell.org, include HUGS --- On Sat, 2/21/09, haskell-cafe-request(a)haskell.org <haskell-cafe-request(a)haskell.org> wrote: From: haskell-cafe-request(a)haskell.org <haskell-cafe-request(a)haskell.org> Subject: Haskell-Cafe Digest, Vol 66, Issue 71 To: haskell-cafe(a)haskell.org Date: Saturday, February 21, 2009, 7:01 PM Send Haskell-Cafe mailing list submissions to haskell-cafe(a)haskell.org To subscribe or unsubscribe via the World Wide Web, visit http://www.haskell.org/mailman/listinfo/haskell-cafe or, via email, send a message with subject or body 'help' to haskell-cafe-request(a)haskell.org You can reach the person managing the list at haskell-cafe-owner(a)haskell.org When replying, please edit your Subject line so it is more specific than "Re: Contents of Haskell-Cafe digest..." Today's Topics: 1. controlling timeout for Network.Socket.connect - how? (Belka) 2. Stacking StateTs (Luis O'Shea) 3. Haskellers on Twitter! (Daniel Peebles) 4. Fwd: Re: [Haskell-cafe] speed: ghc vs gcc (Khudyakov Alexey) 5. Re: Fwd: Re: [Haskell-cafe] speed: ghc vs gcc (Bulat Ziganshin) 6. Re[3]: [Haskell-cafe] Re: speed: ghc vs gcc (Bulat Ziganshin) 7. Re: Re[3]: [Haskell-cafe] Re: speed: ghc vs gcc (Louis Wasserman) 8. Re: Re: speed: ghc vs gcc (Daniel Fischer) 9. Re[5]: [Haskell-cafe] Re: speed: ghc vs gcc (Bulat Ziganshin) 10. Re: Stacking StateTs (David Menendez) 11. Re[2]: [Haskell-cafe] Re: speed: ghc vs gcc (Bulat Ziganshin) 12. Re: Re[5]: [Haskell-cafe] Re: speed: ghc vs gcc (Louis Wasserman) 13. Re: Re[5]: [Haskell-cafe] Re: speed: ghc vs gcc (Sebastian Sylvan) 14. Re: Help using catch in 6.10 (John Meacham) 15. Re: Re[5]: [Haskell-cafe] Re: speed: ghc vs gcc (Louis Wasserman) 16. The community is more important than the product (Don Stewart) 17. Re: Re[5]: [Haskell-cafe] Re: speed: ghc vs gcc (Sebastian Sylvan) 18. Re: Re: speed: ghc vs gcc (Daniel Fischer) 19. Re[7]: [Haskell-cafe] Re: speed: ghc vs gcc (Bulat Ziganshin) 20. Template Haskell compilation error on Windows (was Re: speed: ghc vs gcc) (Peter Verswyvelen) ---------------------------------------------------------------------- Message: 1 Date: Sat, 21 Feb 2009 11:26:51 -0800 (PST) From: Belka <lambda-belka(a)yandex.ru> Subject: [Haskell-cafe] controlling timeout for Network.Socket.connect - how? To: haskell-cafe(a)haskell.org Message-ID: <22139581.post(a)talk.nabble.com> Content-Type: text/plain; charset=us-ascii Hello, communion people! I have a problem and ask for an advice. I'm dealing with sockets on *Linux* platform (Network.Socket). The problem is that I can't fully control timeout for (connect :: Socket -> SockAddr -> IO ()) operation. On my system the timeout is - 3 seconds - I want to be able to change that in run-time. Well I managed to find out how to make it LESS THAN 3 seconds - using System.Timeout. But how to make timeout bigger (for example 9 seconds) is a mystery. (Notice: in order to achieve 9 seconds timeout - just repeating *connect* 3 times won't be effective for long-slow-way-connections. So it's not a solution.) The source code of Network.Socket.connect, taken from darcs: --------------------------------- -- Connecting a socket -- -- Make a connection to an already opened socket on a given machine -- and port. assumes that we have already called createSocket, -- otherwise it will fail. -- -- This is the dual to $bindSocket$. The {\em server} process will -- usually bind to a port number, the {\em client} will then connect -- to the same port number. Port numbers of user applications are -- normally agreed in advance, otherwise we must rely on some meta -- protocol for telling the other side what port number we have been -- allocated. connect :: Socket -- Unconnected Socket -> SockAddr -- Socket address stuff -> IO () connect sock@(MkSocket s _family _stype _protocol socketStatus) addr = do modifyMVar_ socketStatus $ \currentStatus -> do if currentStatus /= NotConnected then ioError (userError ("connect: can't peform connect on socket in status " ++ show currentStatus)) else do withSockAddr addr $ \p_addr sz -> do let connectLoop = do r <- c_connect s p_addr (fromIntegral sz) if r == -1 then do rc <- c_getLastError case rc of 10093 -> do -- WSANOTINITIALISED withSocketsDo (return ()) r <- c_connect s p_addr (fromIntegral sz) if r == -1 then (c_getLastError >>= throwSocketError "connect") else return r _ -> throwSocketError "connect" rc else return r connectBlocked = do #if !defined(__HUGS__) threadWaitWrite (fromIntegral s) #endif err <- getSocketOption sock SoError if (err == 0) then return 0 else do ioError (errnoToIOError "connect" (Errno (fromIntegral err)) Nothing Nothing) connectLoop return Connected --------------------------------- I know that controlling timeout is somehow connected to select(2) (I'm currently investigating this matter...), but it's not in the Network or Network.Socket libs (but in the libs that they FFI with). Hope I won't have to rewrite these low-level functions.... >__< Could anybody, please share some experience on how to adjust timeout for *connect*? Thanks in advance, Best regards, Belka -- View this message in context: http://www.nabble.com/controlling-timeout-for-Network.Socket.connect---how-… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ------------------------------ Message: 2 Date: Sat, 21 Feb 2009 15:33:28 -0500 From: Luis O'Shea <loshea(a)gmail.com> Subject: [Haskell-cafe] Stacking StateTs To: haskell-cafe(a)haskell.org Message-ID: <3636FA2B-5BB1-47CC-B20F-85491A55E4F7(a)gmail.com> Content-Type: text/plain; charset=US-ASCII; delsp=yes; format=flowed I've been experimenting with the state monad and with StateT, and have some questions about how to combine one state with another. This email is literate Haskell tested on GHCi, version 6.10.1. Also, sigfpe's post on monad transformers (http://blog.sigfpe.com/2006/05/ grok-haskell-monad-transformers.html) was very helpful. > import Control.Monad.State My question is basically whether the function modifyT (below) makes sense, whether some form of it already exists in a standard library, and (most importantly) whether it actually indicates that I'm thinking about StateT all wrong. > modifyT :: Monad m => > (s -> StateT t m s) > -> StateT t (StateT s m) () > modifyT f = do > x <- get > y <- lift get > (y',x') <- lift $ lift $ runStateT (f y) x > lift $ put y' > put x' Some context may be useful, so here is how I ended up thinking I needed modifyT. The state monad makes it easy to write stateful computations. For example here is a computation that has an Integer as its state and returns a String: > test1 :: State Integer String > test1 = do > modify (+ 1) > a <- get > return $ "foobar" ++ (show a) If the computation wants to do some IO then it makes sense to start with the IO monad and then apply the StateT transformer to it: > test2 :: StateT Integer IO String > test2 = do > modify (+ 1) > a <- get > lift $ print a > return $ "foobar" ++ (show a) So from now on I won't actually do any IO and will replace IO with an arbitrary monad m. Also instead of the fixed string "foobar" I'll have it take a String as a parameter: > test3 :: Monad m => String -> StateT Integer m String > test3 s = do > modify (+ 1) > a <- get > return $ s ++ (show a) A nice feature of all this is that it is easy to combine these computations: > test4 :: Monad m => StateT Integer m (String,String) > test4 = do > s1 <- test3 "foo" > s2 <- test3 "bar" > return $ (s1,s2) Now seeing as test3 takes a String and returns another String you can imagine using it to transform a String state. (I'm also going to assume that test3 is in another library so we don't want to alter how it's written.) So here is how you could use test3 in a computation that has (String,Integer) as its state: > test5 :: (Monad m) => m Integer > test5 = do > (s1,x1) <- runStateT (test3 "") 0 > (s2,x2) <- runStateT (test3 s1) (2*x1 + 1) > (s3,x3) <- runStateT (test3 s2) (x2*x2) > return x3 Then running test5 >>= print gives 17. The problem with test5, of course, is that we have manually threaded the state, with all the problems that implies. For example nothing prevents you from erroneously misthreading the state: > test5bad :: (Monad m) => m Integer > test5bad = do > (s1,x1) <- runStateT (test3 "") 0 > (s2,x2) <- runStateT (test3 s1) (2*x1 + 1) > (s3,x3) <- runStateT (test3 s1) (x2*x1) > return x3 Running test5bad >>= print gives 5. Obviously we want operate in a State monad with more state. One way to do this is to stack two StateTs on top of m. This is, finally, where I need the modifyT that we defined above -- it lets us "lift" test3 to a function that modifies the state of the top *two* StateTs. Now let's use it to rewrite test5: > test6 :: (Monad m) => StateT Integer (StateT String m) Integer > test6 = do > modifyT test3 > modify $ \x -> 2*x + 1 > modifyT test3 > modify $ \x -> x*x > modifyT test3 > x <- get > return x > > test7 :: (Monad m) => m Integer > test7 = evalStateT (evalStateT test6 0) "" As expected, running test7 >>= print gives 17. So, given that modifyT seems to be useful, does it, or something like it, already exists in the standard libraries? More likely, am I making a mountain of a molehill and is there a better way to structure all this? Thanks, Luis > main = do > test5 >>= print > test5bad >>= print > test7 >>= print ------------------------------ Message: 3 Date: Sat, 21 Feb 2009 16:14:15 -0500 From: Daniel Peebles <pumpkingod(a)gmail.com> Subject: [Haskell-cafe] Haskellers on Twitter! To: haskell-cafe(a)haskell.org Message-ID: <b1a8a5050902211314y74edbf39h97dcfa3188f80a60(a)mail.gmail.com> Content-Type: text/plain; charset=UTF-8 Hi all, I liked Brian O'Sullivan's blog post on twitter (http://www.serpentine.com/blog/2008/12/05/functional-programmers-on-twitter/) so I moved the Haskell subset of his list (along with a couple of additions) onto the haskell wiki, to make it easier for people to update. You can find the page at http://haskell.org/haskellwiki/Twitter. Please update with yourself or any other Haskellers we may have missed. Cheers, Dan ------------------------------ Message: 4 Date: Sun, 22 Feb 2009 00:58:59 +0300 From: Khudyakov Alexey <alexey.skladnoy(a)gmail.com> Subject: Fwd: Re: [Haskell-cafe] speed: ghc vs gcc To: haskell-cafe(a)haskell.org Message-ID: <200902220058.59198.alexey.skladnoy(a)gmail.com> Content-Type: Text/Plain; charset="iso-8859-1" Oh I've again sent mail to wrong address ---------- Forwarded Message ---------- On Saturday 21 February 2009 02:42:11 you wrote: > On Sat, Feb 21, 2009 at 12:22 AM, Bulat Ziganshin > <bulat.ziganshin(a)gmail.com > > > wrote: > > > > Hello Khudyakov, > > > > Saturday, February 21, 2009, 2:07:39 AM, you wrote: > > > I have another question. Why shouldn't compiler realize that `sum > > > > [1..10^9]' > > > > > is constant and thus evaluate it at compile time? > > > > since we expect that compilation will be done in reasonable amount of > > time. you cannot guarantee this for list-involving computation > > it would be nice to have a compiler that can run forever, incrementally > generating faster and faster versions of the same program, until you press > a key or a timeout is reached. > > then you just let it run before you get to bed ;-) > > you could even pass it in a test data set to which it must be optimized; > after the program is compiled, the compiler runs and profiles it, measures > the results, and does another pass to make it faster. > I've just remembered another but related approach to optimization. It uses genetic algorithm to determine close to the best set of optimization options. Alternatively it could be used to find badly interacting options, pessimizations. Implementation for gcc is here: http://www.coyotegulch.com/products/acovea/ In fact I didn't tried it but I liked the idea. -- Khudaykov Alexey ------------------------------ Message: 5 Date: Sun, 22 Feb 2009 01:09:23 +0300 From: Bulat Ziganshin <bulat.ziganshin(a)gmail.com> Subject: Re: Fwd: Re: [Haskell-cafe] speed: ghc vs gcc To: Khudyakov Alexey <alexey.skladnoy(a)gmail.com> Cc: haskell-cafe(a)haskell.org Message-ID: <528706754.20090222010923(a)gmail.com> Content-Type: text/plain; charset=us-ascii Hello Khudyakov, Sunday, February 22, 2009, 12:58:59 AM, you wrote: >> you could even pass it in a test data set to which it must be optimized; >> after the program is compiled, the compiler runs and profiles it, measures >> the results, and does another pass to make it faster. it supported in gcc4 and icl at least > I've just remembered another but related approach to optimization. It uses > genetic algorithm to determine close to the best set of optimization options. afaik it used widely for tuning parameters of compression algorithms -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com ------------------------------ Message: 6 Date: Sun, 22 Feb 2009 02:21:09 +0300 From: Bulat Ziganshin <bulat.ziganshin(a)gmail.com> Subject: Re[3]: [Haskell-cafe] Re: speed: ghc vs gcc To: Louis Wasserman <wasserman.louis(a)gmail.com> Cc: haskell-cafe(a)haskell.org Message-ID: <989437740.20090222022109(a)gmail.com> Content-Type: text/plain; charset=us-ascii Hello Louis, Saturday, February 21, 2009, 4:16:10 AM, you wrote: > In the meantime, a brief summary: a minor correction: the best gcc result shown in the thread was 50x faster than Don's one, so you need to miltiple all ratios by a factor of 50 > Straightforward and simple Haskell code, written by an individual > aware of issues with tail recursion and stream fusion, is frequently > within 3x the speed of GCC code when compiled with appropriate > optimizations in GHC. yes, within 150x margin > When performance is an absolute necessity, > Haskell code can sometimes be manually modified (e.g. with manual > loop unrolls) to equal GCC in performance. yes, to make it only 50x slower while being only 7 times larger (i mean source lines) > Can we move on? yes, we can! :) -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com ------------------------------ Message: 7 Date: Sat, 21 Feb 2009 17:30:23 -0600 From: Louis Wasserman <wasserman.louis(a)gmail.com> Subject: Re: Re[3]: [Haskell-cafe] Re: speed: ghc vs gcc To: Bulat Ziganshin <Bulat.Ziganshin(a)gmail.com> Cc: haskell-cafe(a)haskell.org Message-ID: <ab4284220902211530k1690103ay1a31f437a2c521f4(a)mail.gmail.com> Content-Type: text/plain; charset="iso-8859-1" Observation: The best gcc result shown in the thread, if I recall, precomputed the result of the full computation at compiletime and simply outputted it, when we looked at the assembly. While I will accept that this could be seen as an optimization GHC should have made, I do not accept that this will be the case with most everyday code a programmer writes, as most code is not used to simply compute arithmetic constants. For code that actively requires computation at runtime, I have seen no examples of an instance where well-optimized GHC is actually dozens or hundreds of times slower than GCC output. Louis Wasserman wasserman.louis(a)gmail.com On Sat, Feb 21, 2009 at 5:21 PM, Bulat Ziganshin <bulat.ziganshin(a)gmail.com>wrote: > Hello Louis, > > Saturday, February 21, 2009, 4:16:10 AM, you wrote: > > > In the meantime, a brief summary: > > a minor correction: the best gcc result shown in the thread was 50x > faster than Don's one, so you need to miltiple all ratios by a factor > of 50 > > > Straightforward and simple Haskell code, written by an individual > > aware of issues with tail recursion and stream fusion, is frequently > > within 3x the speed of GCC code when compiled with appropriate > > optimizations in GHC. > > yes, within 150x margin > > > When performance is an absolute necessity, > > Haskell code can sometimes be manually modified (e.g. with manual > > loop unrolls) to equal GCC in performance. > > yes, to make it only 50x slower while being only 7 times larger (i > mean source lines) > > > Can we move on? > > yes, we can! :) > > > -- > Best regards, > Bulat mailto:Bulat.Ziganshin@gmail.com > >

1 0

Array use breaks when I make it unboxed?
by Phil 22 Feb '09

22 Feb '09

Hi, The code below compiles fine as it is, but if I change the import statement to: import Data.Array.Unboxed I get the following error: philip-beadlings-imac-g5:MonteCarlo phil$ ghc -O2 --make test.hs [2 of 5] Compiling InverseNormal ( InverseNormal.hs, InverseNormal.o ) InverseNormal.hs:28:38: No instance for (IArray a1 Double) arising from a use of `!' at InverseNormal.hs:28:38-40 Possible fix: add an instance declaration for (IArray a1 Double) In the first argument of `(*)', namely `c ! 1' In the first argument of `(+)', namely `c ! 1 * q' In the first argument of `(*)', namely `(c ! 1 * q + c ! 2)' ....and so on My understanding is that I should just be able to use them like-for-like? Anyone seen this before? Thanks, Phil. module InverseNormal where import Array a = listArray (1,6) [-3.969683028665376e+01, 2.209460984245205e+02, -2.759285104469687e+02, 1.383577518672690e+02, -3.066479806614716e+01, 2.506628277459239e+00] b = listArray (1,5) [-5.447609879822406e+01, 1.615858368580409e+02, -1.556989798598866e+02, 6.680131188771972e+01, -1.328068155288572e+01] c = listArray (1,6) [-7.784894002430293e-03, -3.223964580411365e-01, -2.400758277161838e+00, -2.549732539343734e+00, 4.374664141464968e+00, 2.938163982698783e+00] d = listArray (1,4) [7.784695709041462e-03, 3.224671290700398e-01, 2.445134137142996e+00, 3.754408661907416e+00] invnorm :: Double -> Double invnorm p | p < 0.02425 = let q = sqrt ( -2*log(p) ) in (((((c!1*q+c!2)*q+c!3)*q+c!4)*q+c!5)*q+c!6) / ((((d!1*q+d!2)*q+d!3)*q+d!4)*q+1) | p > (1-0.02425) = let q = sqrt ( -2*log(1-p) ) in -(((((c!1*q+c!2)*q+c!3)*q+c!4)*q+c!5)*q+c!6) / ((((d!1*q+d!2)*q+d!3)*q+d!4)*q+1) | otherwise = let q = p-0.5 r = q*q in (((((a!1*r+a!2)*r+a!3)*r+a!4)*r+a!5)*r+a!6)*q / (((((b!1*r+b!2)*r+b!3)*r+b!4)*r+b!5)*r+1)

2 3

ANNOUNCE: wxFruit-0.1.2
by Henk-Jan van Tuyl 22 Feb '09

22 Feb '09

L.S., I have updated wxFruit to work with GHC 6.10; it can be downloaded from Hackage: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/wxFruit wxFruit is a graphical user interface that combines some of the power and versatility of wxHaskell with the elegance and simplicity of Fruit. The interface of wxFruit has a functional style, using arrows, whereas wxHaskell has an object oriented style. The package includes a demo game, PaddleBall: try to keep the ball in the game, using the mouse to move the paddle. The position of developer/maintainer is currently open. See also http://www.haskell.org/haskellwiki/WxFruit -- Regards, Henk-Jan van Tuyl -- http://functor.bamikanarie.com http://Van.Tuyl.eu/ --

2 1

Re[2]: [Haskell-cafe] Re: speed: ghc vs gcc
by Louis Wasserman 22 Feb '09

22 Feb '09

I am no longer sure that this conversation is producing useful information or a learning experience for any involved party, and suggest it ends. In the meantime, a brief summary: - Straightforward and simple Haskell code, written by an individual aware of issues with tail recursion and stream fusion, is frequently within 3x the speed of GCC code when compiled with appropriate optimizations in GHC. - When performance is an absolute necessity, Haskell code can sometimes be manually modified (e.g. with manual loop unrolls) to equal GCC in performance. - The amount of effort required for manually unrolling loops is greater than simply using standard GCC optimizations, and in practice few programmers will want to make this extra effort. For your everyday programmer, achieving that sort of performance is typically easier when writing in C. - If anybody wants a Haskell compiler to achieve GCC-level speeds while writing short and concise Haskell, it is preferable to add a ticket with examples already written out and exhaustively examined to minimize the effort Simon needs to make in working on the problem. GHC has had considerably fewer person-hours devoted to it than GCC, and only additional person-hours can improve it. - Even though it might not match with the amount of effort an average Haskell programmer would put into their code, it is *still* constructive to attempt to optimize Haskell code exhaustively and at a low level, if only to help us learn what sorts of transformations it would be useful for GHC to do automatically. This sort of information, I imagine, would be of significant use to Simon when attempting to improve GHC. Nobody is opining that everyday Haskell code will compile to code as speedy as GCC output. People *are* attempting to find out how Haskell code can be hacked at a low level to run as fast as GCC code, but not because they're claiming GHC output is as fast as GCC output. Rather, they're attempting to find out a) what sorts of approaches a really determined Haskell programmer can use to improve speed b) the sorts of optimizations a later version of GHC might be able to make, and c) what sort of code its optimizer might produce. This is not being reported as "fair Haskell vs C++ comparison" -- this is a collaborative effort to *improve* Haskell that was motivated by Bulat's original comparison. Can we move on? Louis Wasserman wasserman.louis(a)gmail.com

7 17

Template Haskell compilation error on Windows (was Re: speed: ghc vs gcc)
by Peter Verswyvelen 22 Feb '09

22 Feb '09

I tried to compile the template Haskell loop unrolling trick from Claus Reinke on my machine which is running Windows and GHC 6.10.1, and I got linker errors. (note that compiling *without* -fvia-C works fine) Compiling under Cygwin did not solve it. Any ideas how I could get this working? I have no experience with TH yet so I might be missing something essential... Thanks, Peter c:\temp>ghc -O2 -fvia-C -optc-O3 -fforce-recomp Apply.hs Apply.o:ghc6140_0.hc:(.text+0x7d): undefined reference to `templatezmhaskell_LanguageziHaskellziTHziSyntax_VarP_con_info' Apply.o:ghc6140_0.hc:(.text+0x10d): undefined reference to `templatezmhaskell_LanguageziHaskellziTHziSyntax_VarE_con_info' Apply.o:ghc6140_0.hc:(.text+0x19d): undefined reference to `templatezmhaskell_LanguageziHaskellziTHziSyntax_VarP_con_info' Apply.o:ghc6140_0.hc:(.text+0x571): undefined reference to `templatezmhaskell_LanguageziHaskellziTHziSyntax_VarP_con_info' Apply.o:ghc6140_0.hc:(.text+0x609): undefined reference to `templatezmhaskell_LanguageziHaskellziTHziSyntax_VarE_con_info' Apply.o:ghc6140_0.hc:(.text+0x6c9): undefined reference to `templatezmhaskell_LanguageziHaskellziTHziSyntax_VarE_con_info' Apply.o:ghc6140_0.hc:(.text+0x789): undefined reference to `templatezmhaskell_LanguageziHaskellziTHziSyntax_VarE_con_info' Apply.o:ghc6140_0.hc:(.text+0x82c): undefined reference to `templatezmhaskell_LanguageziHaskellziTHziLib_a23_closure' Apply.o:ghc6140_0.hc:(.text+0x868): undefined reference to `templatezmhaskell_LanguageziHaskellziTHziLib_a23_closure' Apply.o:ghc6140_0.hc:(.text+0x891): undefined reference to `templatezmhaskell_LanguageziHaskellziTHziSyntax_VarP_con_info' Apply.o:ghc6140_0.hc:(.text+0xd81): undefined reference to `templatezmhaskell_LanguageziHaskellziTHziSyntax_VarP_con_info' Apply.o:ghc6140_0.hc:(.text+0xe19): undefined reference to `templatezmhaskell_LanguageziHaskellziTHziSyntax_VarE_con_info' Apply.o:ghc6140_0.hc:(.text+0xed9): undefined reference to `templatezmhaskell_LanguageziHaskellziTHziSyntax_VarE_con_info' Apply.o:ghc6140_0.hc:(.text+0xf99): undefined reference to `templatezmhaskell_LanguageziHaskellziTHziSyntax_VarE_con_info' Apply.o:ghc6140_0.hc:(.text+0x103c): undefined reference to `templatezmhaskell_LanguageziHaskellziTHziLib_a23_closure' Apply.o:ghc6140_0.hc:(.text+0x1078): undefined reference to `templatezmhaskell_LanguageziHaskellziTHziLib_a23_closure' Apply.o:ghc6140_0.hc:(.text+0x10a1): undefined reference to `templatezmhaskell_LanguageziHaskellziTHziSyntax_VarP_con_info' Apply.o:ghc6140_0.hc:(.text+0x14d0): undefined reference to `__stginit_templatezmhaskell_LanguageziHaskellziTHziSyntax_' Apply.o:ghc6140_0.hc:(.text+0x292): undefined reference to `templatezmhaskell_LanguageziHaskellziTHziLib_lamE_info' Apply.o:ghc6140_0.hc:(.text+0x6ab): undefined reference to `templatezmhaskell_LanguageziHaskellziTHziLib_a23_info' Apply.o:ghc6140_0.hc:(.text+0x76b): undefined reference to `templatezmhaskell_LanguageziHaskellziTHziLib_a23_info' Apply.o:ghc6140_0.hc:(.text+0x9bc): undefined reference to `templatezmhaskell_LanguageziHaskellziTHziLib_lamE_info' Apply.o:ghc6140_0.hc:(.text+0xebb): undefined reference to `templatezmhaskell_LanguageziHaskellziTHziLib_a23_info' Apply.o:ghc6140_0.hc:(.text+0xf7b): undefined reference to `templatezmhaskell_LanguageziHaskellziTHziLib_a23_info' Apply.o:ghc6140_0.hc:(.text+0x11cc): undefined reference to `templatezmhaskell_LanguageziHaskellziTHziLib_lamE_info' C:\app\ghc-6.10.1/libHSrts.a(Main.o):Main.c:(.text+0x7): undefined reference to `__stginit_ZCMain' C:\app\ghc-6.10.1/libHSrts.a(Main.o):Main.c:(.text+0x36): undefined reference to `ZCMain_main_closure' collect2: ld returned 1 exit status >

2 2

Help using catch in 6.10
by Victor Nazarov 22 Feb '09

22 Feb '09

Hello, cafe. I whant to switch to GHC 6.10 My application compiled fine with 6.8.3, but after switchin to 6.10, I've got errors about usage of catch function: Main.hs:165:14: Ambiguous type variable `e2' in the constraint: `Exception e2' arising from a use of `catch' at Main.hs:165:14-38 Probable fix: add a type signature that fixes these type variable(s) Main.hs:261:17: Ambiguous type variable `e' in the constraint: `Exception e' arising from a use of `handle' at Main.hs:261:17-118 Probable fix: add a type signature that fixes these type variable(s) Relevant places in code are: ... getNSteps f = do text <- get entryNSteps entryText catch (readIO text >>= f) $ \_e -> do msgBox (Just window) [] MessageWarning ButtonsOk $ "Число шагов указано неверно: " ++ show text return () ... loadData :: IO ([Term], Map.Map String Term) loadData = do examples <- handle (\_e -> msgBox Nothing [] MessageWarning ButtonsOk "Ошибка чтения файла примеров" >> return []) $ do examplesLines <- fmap lines $ readFile "examples.txt" let parsings :: [Term] parsings = concatMap (fromEither . parse) examplesLines parse :: String -> Either ParseError Term parse = Parsec.parse (Lambda.parser >>= \t -> skipMany space >> eof >> return t) "" fromEither :: Either ParseError Term -> [Term] fromEither = either (const []) (\t -> [t]) return parsings ... -- Victor

4 3

Fwd: Re: [Haskell-cafe] speed: ghc vs gcc
by Khudyakov Alexey 22 Feb '09

22 Feb '09

Oh I've again sent mail to wrong address ---------- Forwarded Message ---------- On Saturday 21 February 2009 02:42:11 you wrote: > On Sat, Feb 21, 2009 at 12:22 AM, Bulat Ziganshin > <bulat.ziganshin(a)gmail.com > > > wrote: > > > > Hello Khudyakov, > > > > Saturday, February 21, 2009, 2:07:39 AM, you wrote: > > > I have another question. Why shouldn't compiler realize that `sum > > > > [1..10^9]' > > > > > is constant and thus evaluate it at compile time? > > > > since we expect that compilation will be done in reasonable amount of > > time. you cannot guarantee this for list-involving computation > > it would be nice to have a compiler that can run forever, incrementally > generating faster and faster versions of the same program, until you press > a key or a timeout is reached. > > then you just let it run before you get to bed ;-) > > you could even pass it in a test data set to which it must be optimized; > after the program is compiled, the compiler runs and profiles it, measures > the results, and does another pass to make it faster. > I've just remembered another but related approach to optimization. It uses genetic algorithm to determine close to the best set of optimization options. Alternatively it could be used to find badly interacting options, pessimizations. Implementation for gcc is here: http://www.coyotegulch.com/products/acovea/ In fact I didn't tried it but I liked the idea. -- Khudaykov Alexey

2 1

Haskell Weekly News: Issue 106 - February 21, 2009
by Brent Yorgey 22 Feb '09

22 Feb '09

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20090221 Issue 106 - February 21, 2009 --------------------------------------------------------------------------- Welcome to issue 106 of HWN, a newsletter covering developments in the [1]Haskell community. Announcements HWEB. Eric Macaulay, following a little [2]prodding by Neil Mitchell, has released version 0 of [3]HWEB, a small tool for producing literate Haskell programs. Cabal-1.6.0.2 and cabal-install-0.6.2. Duncan Coutts [4]announced point-releases of the Cabal library and the cabal-install command line tool. These releases include a number of fixes and minor improvements, and are expected to be included with ghc-6.10.2. Barrie 0.3.1. Fraser Wilson [5]announced a hackage release of [6]Barrie, an implementation of an idea for supporting state based, user-driven GUIs. Yogurt-0.3. Martijn van Steenbergen [7]announced the release of [8]Yogurt-0.3, a MUD client library for Haskell. This version improves over 0.2 in several ways, including support for GHC 6.10, no more unsafeCoerce needed, new support for forking threads, and various refactorings. wxFruit-0.1.2. Henk-Jan van Tuyl [9]announced an [10]update of [11]wxFruit, a graphical user interface that combines some of the power and versatility of wxHaskell with the elegance and simplicity of Fruit. The new version works with GHC 6.10, and also includes a demo game, PaddleBall. Interested parties, take note: the position of developer/maintainer for this library is currently open. Paper draft: "Denotational design with type class morphisms". Conal Elliott [12]announced a [13]draft of a new paper, "Denotational design with type class morphisms". Feedback is appreciated, especially if in time for the March 2 ICFP deadline. Crypto 4.2.0 & Related News. Creighton Hogg [14]announced the release of version 4.2.0 of the [15]Crypto library. Creighton will also betaking over maintenance of the library from Dominic Steinitz. The Typeclassopedia, and request for feedback. Brent Yorgey [16]announced a [17]first draft of an article entitled 'The Typeclassopedia', a "starting point for the student of Haskell wishing to gain a firm grasp of its standard type classes." Comments and feedback are encouraged! hslibsvm-2.88.0.1 - A FFI binding to LibSVM. S. Guenther [18]announced the [19]hlibsvm package, a set of Haskell bindings to the C++ [20]libsvm library. spacepart-0.1.0.0 (was called data-spacepart). Corey O'Connor [21]announced a new release of the [22]spacepart package, supporting space-partitioning data structures. The new release includes many bug fixes and some code cleanup. pqueue-mtl, stateful-mtl. Louis Wasserman [23]announced two new packages, [24]stateful-mtl and [25]pqueue-mtl. stateful-mtl provides an ST monad transformer, several useful operations on generic monad transformers, and a monad transformer intended to cleanly externally wrap operations on a mutable array (including resizing operations). pqueue-mtl provides implementations of several structures supporting a generic 'single-in, single-out' paradigm (encapsulated in a typeclass named Queuelike), including stacks, queues, and several implementations of priority queues. haha-0.1 - Animated ascii lambda. Sebastiaan Visser [26]announced [27]haha, a very minimal vector based ascii art library written just for fun. If you've always wanted to have a full-color rotating vector based ascii art lambda on your terminal, now is your chance! Discussion Darcs and Google Summer of Code. Eric Kow [28]floated the idea of having darcs apply to the Google Summer of Code as a separate mentoring organization, and discussed several ideas for student projects. Jobs Postdoctoral Research Position at Yale University. Paul Hudak [29]announced the availability of a postdoctoral research position at Yale University. The successful candidate will apply modern, high-level programming language ideas (such as embodied in Haskell) to help design and implement a language for the control of BGP-based network routers, with the goal of realizing high-level networking protocols for traffic engineering, security, and related networking concerns. Blog noise [30]Haskell news from the [31]blogosphere. * GHC / OpenSPARC Project: [32]Triage. * Manuel M T Chakravarty: [33]Mark your Haskell tweets with #haskell. * Gregg Reynolds: [34]Performance Economics. * Alex Mason: [35]AVar released (three times). * Sean Leather: [36]The strict danger of switching from pure to monadic Template Haskell. * Mads Lindstrom: [37]Using Mutable Arrays for Faster Sorting. * Conal Elliott: [38]Denotational design with type class morphisms. A draft of Conal's new paper. * Jesse Andrews: [39]Getting Tiled with XMonad. * happstack.com: [40]SOCALFP Presentation Slides: "Happstack is better than X". * Luke Palmer: [41]Dependent types are ridiculously easy. * GHC / OpenSPARC Project: [42]Thunderbirds are go. * Brent Yorgey: [43]Typeclassopedia---a generic response. * Alex Mason: [44]ASTM updates. * London Haskell Users Group: [45]Lemmih: LHC - past, present and future. * Eric Kow (kowey): [46]announcing: burrito tutorial support group. Laden with burrito tutorial guilt? The burrito tutorial support group can help. * Alex Mason: [47]ASTM: redundant STMish fun. * happstack.com: [48]Announcing the launch of the Patch-Tag blog. * Colin Ross: [49]XML parsing with Haskell. * Brent Yorgey: [50]The Typeclassopedia---request for feedback. * Sean Leather: [51]Incremental fold, a design pattern. * Manuel M T Chakravarty: [52]Comparison of type families with functional dependencies.. A nice summary comparison of these two Haskell language features. * Random permutations and sorting: [53]Heinrich Apfelmus. * A day with xmonad: [54]Colin Adams. * Antoine Latter: [55]MaybeT - The CPS Version. * Gregg Reynolds: [56]Intergalactic Telefunctors and Quantum Entanglement. * Gregg Reynolds: [57]In Praise of Elitism. * Dan Piponi (sigfpe): [58]Beyond Monads. A generalization of monads to parameterized monads. * Well-Typed.Com: [59]Cabal ticket #500. Quotes of the Week * KetilMalde: No, those are quite outdated by now. The new horsemen of the programming apocalypse are, of course, IO, MutableState, LazyMemoryLeak, and Bottom. * skorpan: i love the layout of lyah. makes me feel like having some chunky bacon. * lilac: * lilac looks forward to Cale explaining category theory by analogy to Call of Duty * byorgey: _|_ ... is a party pooper * idnar: enlarge your context in just seven days with all-natural herbal supplements! * mmorrow: gah, i'm so used to haskell i forgot a return stmt in C and was trying to figure out where the segfault was happening for 20 minutes About the Haskell Weekly News New editions are posted to [60]the Haskell mailing list as well as to [61]the Haskell Sequence and [62]Planet Haskell. [63]RSS is also available, and headlines appear on [64]haskell.org. To help create new editions of this newsletter, please see the information on [65]how to contribute. Send stories to byorgey at cis dot upenn dot edu. The darcs repository is available at darcs get [66]http://code.haskell.org/~byorgey/code/hwn/ . References 1. http://haskell.org/ 2. http://neilmitchell.blogspot.com/2009/01/small-scripts-with-haskell.html 3. http://mathmeth.com/eem/hweb/quickstart.shtml 4. http://www.haskell.org//pipermail/haskell-cafe/2009-February/056153.html 5. http://article.gmane.org/gmane.comp.lang.haskell.general/16882 6. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/barrie 7. http://article.gmane.org/gmane.comp.lang.haskell.general/16869 8. http://code.google.com/p/yogurt-mud/ 9. http://article.gmane.org/gmane.comp.lang.haskell.cafe/53341 10. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/wxFruit 11. http://www.haskell.org/haskellwiki/WxFruit 12. http://article.gmane.org/gmane.comp.lang.haskell.cafe/53166 13. http://conal.net/papers/type-class-morphisms/ 14. http://article.gmane.org/gmane.comp.lang.haskell.cafe/53029 15. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Crypto 16. http://article.gmane.org/gmane.comp.lang.haskell.cafe/52964 17. http://www.cis.upenn.edu/~byorgey/papers/typeclassopedia-draft-090216.pdf 18. http://article.gmane.org/gmane.comp.lang.haskell.cafe/52961 19. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hslibsvm 20. http://www.csie.ntu.edu.tw/~cjlin/libsvm/ 21. http://article.gmane.org/gmane.comp.lang.haskell.cafe/52951 22. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/spacepart 23. http://article.gmane.org/gmane.comp.lang.haskell.cafe/52920 24. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/stateful%2Dmtl 25. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/pqueue%2Dmtl 26. http://article.gmane.org/gmane.comp.lang.haskell.cafe/52865 27. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/haha 28. http://www.haskell.org//pipermail/haskell-cafe/2009-February/056057.html 29. http://article.gmane.org/gmane.comp.lang.haskell.cafe/53103 30. http://planet.haskell.org/ 31. http://haskell.org/haskellwiki/Blog_articles 32. http://ghcsparc.blogspot.com/2009/02/triage.html 33. http://justtesting.org/post/80211621 34. http://syntax.wikidot.com/blog:10 35. http://axman6.homeip.net/blog/2009/02/avar-released.html 36. http://feedproxy.google.com/~r/splonderzoek/~3/sD_bp8yKBxc/strict-danger-of… 37. http://lindstroem.wordpress.com/2009/02/19/using-mutable-arrays-for-faster-… 38. http://conal.net/blog/posts/denotational-design-with-type-class-morphisms/ 39. http://overstimulate.com/articles/why-xmonad 40. http://blog.happstack.com/2009/02/18/socalfp-presentation-slides-happstack-… 41. http://lukepalmer.wordpress.com/2009/02/18/dependent-types-are-ridiculously… 42. http://ghcsparc.blogspot.com/2009/02/thunderbirds-are-go.html 43. http://byorgey.wordpress.com/2009/02/17/typeclassopedia-a-generic-response/ 44. http://axman6.homeip.net/blog/2009/02/astm-updates.html 45. http://www.londonhug.net/2009/02/17/lemmih-lhc-past-present-and-future/ 46. http://koweycode.blogspot.com/2009/02/announcing-burrito-tutorial-support.h… 47. http://axman6.homeip.net/blog/2009/02/astm-redundant-stmish-fun.html 48. http://blog.happstack.com/2009/02/16/announcing-the-launch-of-the-patch-tag… 49. http://vcolin.com/2009/02/16/xml-parsing-haskell/ 50. http://byorgey.wordpress.com/2009/02/16/the-typeclassopedia-request-for-fee… 51. http://feedproxy.google.com/~r/splonderzoek/~3/tj_MkKqIlkQ/incremental-fold… 52. http://justtesting.org/post/78667708 53. http://apfelmus.nfshost.com/random-permutations.html 54. http://colina.demon.co.uk/?q=node/534 55. http://panicsonic.blogspot.com/2009/02/maybet-cps-version.html 56. http://syntax.wikidot.com/blog:9 57. http://syntax.wikidot.com/blog:8 58. http://blog.sigfpe.com/2009/02/beyond-monads.html 59. http://blog.well-typed.com/2009/02/cabal-ticket-500/ 60. http://www.haskell.org/mailman/listinfo/haskell 61. http://sequence.complete.org/ 62. http://planet.haskell.org/ 63. http://sequence.complete.org/node/feed 64. http://haskell.org/ 65. http://haskell.org/haskellwiki/HWN 66. http://code.haskell.org/~byorgey/code/hwn/

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Showing >100% CPU usage of parallel code
by Jim Burton 22 Feb '09

22 Feb '09

Hi, I copied the program below from a reddit post of dons'. I have a dual core laptop with ubuntu hardy and ghc 6.10.1. I can see the difference when I run the program with +RTS -N2 but CPU always says 100%. I'd like an example that shows >100 -- is it not showing >100 because of my timeformat or because of the program? If it's the latter can you point me to an example that will use more cpu? Here's the output: $ cat /proc/cpuinfo | grep processor | wc -l 2 $ export TIMEFORMAT="%E real,%U user,%S sys, %P cpu" $ ghc -O2 --make Par.hs -threaded $ time ./Par 1405006117752879898543142606244511569936384005711076 2.330 real,2.328 user,0.000 sys, 99.92 cpu $ time ./Par +RTS -N2 1405006117752879898543142606244511569936384005711076 1.504 real,2.316 user,0.016 sys, 100.00 cpu Here's the program: ---------------- import Control.Parallel main = a `par` b `par` c `pseq` print (a + b + c) where a = ack 3 10 b = fac 42 c = fib 34 fac 0 = 1 fac n = n * fac (n-1) ack 0 n = n+1 ack m 0 = ack (m-1) 1 ack m n = ack (m-1) (ack m (n-1)) fib 0 = 0 fib 1 = 1 fib n = fib (n-1) + fib (n-2) -------------------- Thanks, Jim -- View this message in context: http://www.nabble.com/Showing-%3E100--CPU-usage-of-parallel-code-tp22137081… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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A typeclass for Data.Map etc?
by Eugene Kirpichov 21 Feb '09

21 Feb '09

Greetings, Is there a typeclass for mappings with a Data.Map-like interface, with stuff like: empty, insert, insertWithKey, unionWith etc. ? And, probably, a similar typeclass for mutable mappings like Data.Hashtable. Looks like such a thing would be useful; as for now, I see at least two applications: Data.Map and Data.Trie (bytestring-trie) - it's a pity that they have rather similar interfaces, but the latter lacks many methods and some are named in a different way. Also, Data.Map has some inconsistensies, too: for instance, it has an insertWith' but lacks a unionWith'. "One typeclass for all" would eliminate these inconsistencies. I'm asking mainly because I've been wondering why noone has yet written a mutable hashtable package with a MArray-like interface, I wrote a small thing myself and I am unsure as to what interface it should have. -- Eugene Kirpichov

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RE: "first class" tuples?
by Brian Bloniarz 21 Feb '09

21 Feb '09

Wolfgang Jeltsch wrote: > Make , an infix operator. Then even the syntax (,) works without further ado. > Make , right-associative, for example. Then you can write (a1,...,an) which > means (a1,(a2,(...,an))). You just need one data declaration: > > data (a,b) = (a,b) > > However, this has the problem that it leads to more partially-defined values > than with today's tuples. For example, you could have a *triple* (a,_|_). > > So maybe we should treat tuple syntax completely as special syntax (as it is > today) and define our tuple types so that tuples don't end with the last > element (as above) but with an explicit empty tuple (like lists end in a > nil). This would also give use 1-tuples. We would need the unit type () for > empty tuples. Then we define a cons type which has a strictness annotation: > > data head :# tail = head :# !tail Lennart Augustsson wrote: > Look at the HList stuff by Oleg and others and you'll find the kind of > tuples you suggest. One thing about HList: the HCons type is lazy in its second element, so HList tuples can be more partially-defined than normal tuples. Anybody know the rationale for this? I'm curious whether it could be changed, or if any code depends on it. -Brian _________________________________________________________________ Access your email online and on the go with Windows Live Hotmail. http://windowslive.com/online/hotmail?ocid=TXT_TAGLM_WL_HM_AE_Access_022009

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Trying to install Cabal
by David 21 Feb '09

21 Feb '09

Hi! I've just installed ghc (v 6.10.1) for Windows, and it seems to be installed correctly, and now I'm trying to install Cabal (v1.6.0.2), but I'm getting the following error message (along with a lot of warnings about a deprecated something-or-other, which I assume I can ignore): C:\Temp>runghc Setup configure -p Distribution\Simple\Utils.hs:1:11: Warning: -fffi is deprecated: use -XForeignFunctionInterface or pragma {-# LANGUAGE ForeignFunctionInterface#-} instead Distribution\Simple\Utils.hs:4:15: Warning: -fffi is deprecated: use -XForeignFunctionInterface or pragma {-# LANGUAGE ForeignFunctionInterface#-} instead Distribution\Simple\InstallDirs.hs:1:11: Warning: -fffi is deprecated: use -XForeignFunctionInterface or pragma {-# LANGUAGE ForeignFunctionInterface#-} instead Distribution\Simple\InstallDirs.hs:4:15: Warning: -fffi is deprecated: use -XForeignFunctionInterface or pragma {-# LANGUAGE ForeignFunctionInterface#-} instead During interactive linking, GHCi couldn't find the following symbol: SHGetFolderPathA@20 This may be due to you not asking GHCi to load extra object files, archives or DLLs needed by your current session. Restart GHCi, specifying the missing library using the -L/path/to/object/dir and -lmissinglibname flags, or simply by naming the relevant files on the GHCi command line. Alternatively, this link failure might indicate a bug in GHCi. If you suspect the latter, please send a bug report to: glasgow-haskell-bugs(a)haskell.org Am I missing a dependency, or is ghc not installed properly, or am I doing something else wrong? Thanks, David.

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Error installing pkg 'HDBC-sqlite3'
by David 21 Feb '09

21 Feb '09

I've encountered another problem while trying to install 'HDBC-sqlite3'. I did the install "manually", instead of using Cabal, and during the build phase, received the following error message: D:\Apps\ghc\ghc-6.10.1\HDBC-sqlite3-2.1.0.0>runghc Setup build Preprocessing library HDBC-sqlite3-2.1.0.0... Database\HDBC\Sqlite3\Statement.hsc:41:21: sqlite3.h: No such file or directory Database\HDBC\Sqlite3\Statement.hsc: In function `main': Database\HDBC\Sqlite3\Statement.hsc:137: error: `SQLITE_NULL' undeclared (first use in this function) Database\HDBC\Sqlite3\Statement.hsc:137: error: (Each undeclared identifier is reported only once Database\HDBC\Sqlite3\Statement.hsc:137: error: for each function it appears in.) Database\HDBC\Sqlite3\Statement.hsc:148: error: `SQLITE_ROW' undeclared (first use in this function) Database\HDBC\Sqlite3\Statement.hsc:149: error: `SQLITE_DONE' undeclared (first use in this function) Database\HDBC\Sqlite3\Statement.hsc:150: error: `SQLITE_ERROR' undeclared (first use in this function) compiling dist\build\Database\HDBC\Sqlite3\Statement_hsc_make.c failed Is the file 'sqlite3.h' missing? Or am I doing something wrong? Thanks, David.

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foreign export space-leaks?
by James Ge 21 Feb '09

21 Feb '09

first I wrote a silly haskell program: --- a program to walk through very long list ---- data Silly = A !Int | B !Int deriving (Show) main = go [a + b | a <- [0..10000], b <- [0..10000]] where go [] = do putStrLn $ "completed." go (x:xs) = do case even x of True -> putStrLn $ show (A x) False -> putStrLn $ show (B x) go xs ---------- end of the program ----------- upper program ran well, and consumed fixed memory (2.8M watched by top). but when I exported the main to C and host the whole haskell program in C, memory consumption increased CONSTANTLY. what I did are: 1) explicit name the module to `Silly' and rename `main' to `call_me_back' 2) write a c wrapper following guildlines here(http://www.haskell.org/ ghc/docs/latest/html/users_guide/ffi-ghc.html#hs-exit): --- c wrapper code begins ---- #include <stdio.h> #include "HsFFI.h" #ifdef __GLASGOW_HASKELL__ #include "Silly_stub.h" #endif #ifdef __GLASGOW_HASKELL__ extern void __stginit_Silly ( void ); #endif int main() { hs_init(0, 0); #ifdef __GLASGOW_HASKELL__ hs_add_root(__stginit_Silly); #endif call_me_back(); hs_exit(); return 0; } ---- wrapper code ends ----- then I compiled them together: ---- Makefile section begins ----- ghc -O2 --make Silly.hs ghc -O2 --make Silly_wrapper.c ghc -O2 -o Silly.out *.o ./Silly -----Makefile sect ends ----------- this program consumed memory constantly until the process being terminated by OS because of `out of memory'. I guess this must have something to do with GC (although i tried import hs_perform_gc declared in HsFFI.h and called the function, but i didn't see any change), do you have ideas? Thanks in advance, jge

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Fwd: [Haskell-cafe] speed: ghc vs gcc
by Alberto G. Corona 21 Feb '09

21 Feb '09

I think that a higuer level language has better opportunities to optimize, specially if the compiler is coded in its own language. for example I guess that a good type dependent implementation would evaluate the sum[1..10^9::Int] at compilation time. I reality haskell is much much faster than c in some cases that now are not considered, but it is fair to remember that haskell outperfromed all the rest in those old benchmarks with did´t care to print the results. This may seem trivial now, but at the time surprised the benchmark people. 2009/2/21 Khudyakov Alexey <alexey.skladnoy(a)gmail.com> On Friday 20 February 2009 16:29:29 Bulat Ziganshin wrote: > > Hello haskell-cafe, > > > > since there are no objective tests comparing ghc to gcc, i made my own > > one. these are 3 programs, calculating sum in c++ and haskell: > > > > main = print $ sum[1..10^9::Int] > > > > ... skipped ... > > The discussion is mostly about low level optimizations such as loop > unrolling > etc. > > I have another question. Why shouldn't compiler realize that `sum > [1..10^9]' > is constant and thus evaluate it at compile time? > > -- > Khudakov Alexey > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe >

1 0

Paper draft: "Denotational design with type class morphisms"
by Conal Elliott 21 Feb '09

21 Feb '09

I have a draft paper some of you might enjoy, called "Denotational design with type class morphisms". Abstract: Type classes provide a mechanism for varied implementations of standard interfaces. Many of these interfaces are founded in mathematical tradition and so have regularity not only of *types* but also of *properties* (laws) that must hold. Types and properties give strong guidance to the library implementor, while leaving freedom as well. Some of the remaining freedom is in *how* the implementation works, and some is in *what* it accomplishes. To give additional guidance to the *what*, without impinging on the *how*, this paper proposes a principle of *type class morphisms* (TCMs), which further refines the compositional style of denotational semantics. The TCM idea is simply that *the instance's meaning is the meaning's instance*. This principle determines the meaning of each type class instance, and hence defines correctness of implementation. In some cases, it also provides a systematic guide to implementation, and in some cases, valuable design feedback. The paper is illustrated with several examples of type, meanings, and morphisms. You'll find the paper at http://conal.net/papers/type-class-morphisms/ . I'd sure appreciate feedback on it, especially if in time for the *March 2* ICFP deadline. Pointers to related work would be particularly appreciated, as well as what's unclear and what could be cut. This draft is an entire page over the limit, so I'll have to do some trimming before submitting. Enjoy, and thanks! - Conal

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parallelism or concurrency ? if they are different
by Paolino 21 Feb '09

21 Feb '09

When I came to haskell, I arrived with a small and only evolutionary background in programming. First monad I met was MonadState StdGen m. Everything was in someway acceptable, I had no problem in explicitating the need for the generator. The lesson was referential transparency. To me referential tranparency is still obscure as a feature. Not using the monad , my functions pass around a generator, then they are repeatable, same generator , same computation. Years pass by, now evolutionary algorithms need to scale multicores. But multicore can be used with threads or par, the difference is that par is pure, because it respects referential transparency. But threads not. They are always unrespectful ? Or it's an implementation issue of preemptive choice? Can I have a baton to pass around like I had for random generator, so that the computation ends without IO (unsafe performed) , without breaking tranparency, something like (runIOThreads :: ThreadsIO a -> ThreadsBaton -> a) ? >From Real World Haskell my algorithm have to be parallelized as they don't do some kind of IO, they don't deal with the world, but where is it stated that it is possible to write them with par (I couldn't) ? More , I'm not caring that my computation is unrepeatable, for me it's fine that the runtime system gives me the cached results for same arguments computation. The fact that it doesn't ,and recompute the function giving out something fuzzily different from before, is enough to coerce me to spit out IO values ? Finally, why and where the optimizer will substitute a value with its definition, so that it possibly get computed twice ? Thanks paolino

2 2

Haskell.org GSoC
by Daniel Kraft 20 Feb '09

20 Feb '09

Hi, I noticed last year Haskell.org was a mentoring organization for Google's Summer of Code, and I barely noticed some discussion about it applying again this year :) I participated for GCC in 2008 and would like to try again this year; while I'm still active for GCC and will surely stay so, I'd like to see something new at least for GSoC. And Haskell.org would surely be a very, very nice organization. Since I discovered there's more than just a lot of imperative languages that are nearly all the same, I love to do some programming in Prolog, Scheme and of course Haskell. However, so far this was only some toy programs and nothing "really useful"; I'd like to change this (as well as learning more about Haskell during the projects). Here are some ideas for developing Haskell packages (that would hopefully be of general use to the community) as possible projects: - Numerics, like basic linear algebra routines, numeric integration and other basic algorithms of numeric mathematics. - A basic symbolic maths package; I've no idea how far one could do this as a single GSoC project, but it would surely be a very interesting task. Alternatively or in combination, one could try to use an existing free CAS package as engine. - Graphs. - Some simulation routines from physics, though I've not really an idea what exactly one should implement here best. - A logic programming framework. I know there's something like that for Scheme; in my experience, there are some problems best expressed logically with Prolog-style backtracking/predicates and unification. This could help use such formulations from inside a Haskell program. This is surely also a very interesting project. What do you think about these ideas? I'm pretty sure there are already some of those implemented, but I also hope some would be new and really of some use to the community. Do you think something would be especially nice to have and is currently missing? Thanks for your comments, Daniel

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Re: Looking for pointfree version (Kim-Ee Yeoh) (02/12)
by Gene Arthur 20 Feb '09

20 Feb '09

>Kim-Ee Yeoh said: >On the same note, does anyone have ideas >for the following snippet? Tried the pointfree >package but the output was useless. >pointwise op (x0,y0) (x1,y1) = (x0 `op` x1, y0 `op` y1) First sorry for the delay in getting to this.. been behind on projects so had some days of mail piled up. Here is what I came up with, using one arrow operator, so you would have to import: Control.Arrow ((***)) at minimum to use this solution: pointfree :: forall t t1 c. (t -> t1 -> c) -> (t, t1) -> (t, t1) -> (c, c) pointfree op = curry $ (\(a,b) -> a `op` b) *** (\(a,b) -> a `op` b) examples of use, that were executed using: ghci -fglasgow-exts -farrows Control.Arrow *>pointfree (*) (3,5) (12,12) (15,144) *> pointfree (++) ("This ","That") ("Old"," Man") ("This That","Old Man") Hope that helps. -- gene ============================== website: http://haskblog.cloud.prohosting.com ============================== If Helen Keller is alone in a forest and falls, does she make a sound? ____________________________________________________________ Receive Notifications of Incoming Messages Easily monitor multiple email accounts & access them with a click. Visit http://www.inbox.com/notifier and check it out!

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Re: [Haskell-cafe] Re: [darcs-users] darcs and Google Summer of Code
by Wolfgang Jeltsch 20 Feb '09

20 Feb '09

Am Donnerstag, 19. Februar 2009 05:10 schrieben Sie: > Wolfgang Jeltsch wrote: > > I’ve put myself as a potential mentor on the old Haskell SoC ticket > > (<http://hackage.haskell.org/trac/summer-of-code/ticket/17>). However, > > one or two years ago I was told that mentoring is a very time-consuming > > thing (and to my knowledge, you don’t get any payments for that, at least > > for Haskell projects). So if some other person wants to mentor a > > Grapefruit-based GUI or patch viewer project, I’d be very happy and would > > support this person the best I can. > > Unless Google's changed things, the organization gets 500$ for each > project. What the Darcs organization does with that, who knows. Yes, who knows. The “Haskell orgainization” didn’t give a cent to the mentors, as far as I know. Am I wrong here? > It'd be a piddling amount as a stipend for the mentor, but... …it would be much better than nothing. :-) Best wishes, Wolfgang

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unresolved Liskell installation problems
by Benjamin L.Russell 20 Feb '09

20 Feb '09

I have been trying to install Liskell on top of GHC 6.10.1 on Windows XP Professional, Service Pack 2, since last month, but despite changes to the included Main.hs file and repeated exchanges on a related Weblog (see "CFruhwirth's Weblog: Liskell standalone" at http://blog.clemens.endorphin.org/2009/01/liskell-standalone.html) the problem is still unsolved. My last question was posted there on January 27, but there have been no further responses since then. In summary, here is a transcription of the related correspondence there: Posted by Clemens Fruhwirth on 9 January 2009 at 14:17: >[...] > >You can grab it with the usual > >darcs get http://code.haskell.org/liskell/ > > >This version has been tested with ghc 6.10.1 and should install like > >./Setup.lhs configure >./Setup.lhs build >./Setup.lhs install >cd LskPrelude >make install-inplace > >Optionally you can run make tests in the testsuite subdirectory. Posted by Benjamin Russell on 21 January 2009 at 23:27: >I just downloaded Darcs 2.2 and Liskell for Windows XP, Service Pack 2, but the following error message appeared when I ran: > >./Setup.lhs configure > >in Cygwin: > >Configuring liskell-0.1... >Setup.lhs: At least the following dependencies are missing: >ghc-paths -any > >How should I resolve this issue? Posted by ctnd on 23 January 2009 at 23:48: >[...] > >Perhaps install this package: >http://hackage.haskell.org/cgi-bin/hackage-scripts/package/ghc-paths Posted by ctnd on 24 January 2009 at 00:04: > Okay, I got Liskell running and compiling here with a couple of changes: > >In Main.hs, change: > >-- GHC.runGhc (Just "/home/clemens/deploy/ghc-6.10.1/lib/ghc-6.10.1/") $ do >GHC.runGhc (Just "/home/chris/.GHC/lib/ghc-6.10.1/") $ do > >To the appropriate value as I have. > >./Setup.lhs configure --user >./Setup.lhs build >./Setup.lhs install > >$ cd LskPrelude/ >$ make >$ make install-inplace > >Couldn't really get the tests working but I don't much care about that right now, just want to play with Liskell. > >Hope you guys figure it out! Posted by Benjamin Russell on 25 January 2009 at 20:51: >[...] > >Thanks for the advice, but: > >> In Main.hs, change: >> >> -- GHC.runGhc (Just "/home/clemens/deploy/ghc-6.10.1/lib/ghc-6.10.1/") $ do >> GHC.runGhc (Just "/home/chris/.GHC/lib/ghc-6.10.1/") $ do > >Done. However, the building step still fails: > >> $ ./Setup.lhs build >> Preprocessing library liskell-0.1... >> Setup.lhs: The program happy is required but it could not be found > >But "happy" is installed and listed in the PATH! > >> $ which happy >> /cygdrive/c/Program Files/Haskell/bin/happy > >> Perhaps install this package: >> http://hackage.haskell.org/cgi-bin/hackage-scripts/package/ghc-paths > >Already installed; _viz_: > >> $ cabal install ghc-paths >> Resolving dependencies... >> No packages to be installed. All the requested packages are already installed. >> If you want to reinstall anyway then use the --reinstall flag. > >How should I resolve this issue? Posted by ctnd on 27 January 2009 at 07:28: >[...] > >I had the same problem: > >Configuring liskell-0.1... >Setup.lhs: At least the following dependencies are missing: >ghc-paths -any > >I solved it by configuring as --user. I should've done this from the start as my GHC and cabal packages are all --user installed anyway. > >./Setup.lhs configure --user >./Setup.lhs build >./Setup.lhs install > >Hopefully it's the same for you. > >RE the `happy` problem, no idea. > [...] > >P.S. I saw your question on the mailing list but I'm unable to post to the list (despite asking for help from the admins) so I'll have to respond here. Posted by Benjamin Russell on 27 January 2009 at 21:59: >[...] > >Thanks again for the response. > >This time, a parse error occurs in the building phase: > >> Main.hs:218:0: parse error (possibly incorrect indentation) > >These are lines 218-19 of my Main.hs file: > >> partition_args :: [String] -> [(String, Maybe Phase)] -> [String] >> -> ([(String, Maybe Phase)], [String]) > >I tried merging line 219 into line 218, but the same error recurs. > >In addition, the following error occurs during the install phase: > >>Setup.lhs: dist\build\liskell\liskell.exe: copyFile: does not exist (No such file or directory) > >Sorry for the repeated questions, but would you happen to know how to resolve these issues? Does anybody know how to install Liskell successfully? -- Benjamin L. Russell -- Benjamin L. Russell / DekuDekuplex at Yahoo dot com http://dekudekuplex.wordpress.com/ Translator/Interpreter / Mobile: +011 81 80-3603-6725 "Furuike ya, kawazu tobikomu mizu no oto." -- Matsuo Basho^

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Overloading functions based on arguments?
by Daniel Kraft 20 Feb '09

20 Feb '09

Hi, I just came across a problem like this: Suppose I've got two related functions that do similar things, and I want to call them the same... Like in: foobar :: String -> Int -> Int foobar :: Int -> String -> Int (Bad example, but I hope you got the point.) Is this kind of overloading (instead of the polymorphism based overloading) possible in Haskell? Namely to have two functions with the same name but different signatures so they could be distinguished by a call's parameters? I fear not... So I guess I have to name the functions differently, right? Thanks, Daniel

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garbage collector woes
by Chris Waterson 20 Feb '09

20 Feb '09

I'm at wits end with respect to GHC's garbage collector and would very much appreciate a code review of my MySQL driver for HDBC, which is here: <http://www.maubi.net/~waterson/REPO/HDBC-mysql/Database/HDBC/MySQL/Connecti… > In particular, the problem that I'm having is that my "statements" (really, just iterators over a SQL query result set) are getting garbage collected prematurely. I've included the source for the relevant functions below. The first is newStatement, which creates a new HDBC Statement record (an elided version, below): > newStatement :: ForeignPtr MYSQL -> String -> IO Types.Statement > newStatement mysql__ query = withForeignPtr mysql__ $ \mysql_ -> do > stmt_ <- mysql_stmt_init mysql_ > ... > stmt__ <- newForeignPtr mysql_stmt_close stmt_ > ... > return $ Types.Statement > { > , Types.fetchRow = fetchRow mysql__ stmt__ results > } The mysql_stmt_init function is the MySQL C API that creates a new statement record. Its result must be freed by mysql_stmt_close, and therefore is wrapped with a ForeignPtr appropriately. The fetchRow function is part of the HDBC Statement API, and its signature is: > fetchRow :: IO (Maybe [SqlValue]) I.e., it retrieves the next row from the result set and returns the column values as a list. The "results" parameter is not relevant to this discussion: it maintains the buffers used for storage of the column values. The next function of interest is my implementation of fetchRow, copied in its entirety, below: > fetchRow :: ForeignPtr MYSQL -> ForeignPtr MYSQL_STMT -> [MYSQL_BIND] > -> IO (Maybe [Types.SqlValue]) > fetchRow mysql__ stmt__ results = > withForeignPtr mysql__ $ \_ -> > withForeignPtr stmt__ $ \stmt_ -> do > rv <- mysql_stmt_fetch stmt_ > case rv of > 0 -> row > #{const MYSQL_DATA_TRUNCATED} -> row > #{const MYSQL_NO_DATA} -> return Nothing > _ -> statementError stmt_ > where row = mapM cellValue results >>= \cells -> return $ Just cells It unwraps the ForeignPtrs and invokes the mysql_stmt_fetch C API with the native MYSQL_STMT structure, causing the column values for the next row to get bound into storage areas that we can convert to Haskell values. Typically, this code gets invoked in the generic HDBC layer by the fetchAllRows routine, which looks like this: > fetchAllRows :: Statement -> IO [[SqlValue]] > fetchAllRows sth = unsafeInterleaveIO $ > do row <- fetchRow sth > case row of > Nothing -> return [] > Just x -> do remainder <- fetchAllRows sth > return (x : remainder) The sth argument is simply an instance of the Statement record that I've returned from low-level MySQL driver. This all works, except... The behavior that I'm seeing is that the ForeignPtr to the native MYSQL_STMT struct has become unreachable after some number of iterations of the above loop. This causes mysql_stmt_close to be invoked, and subsequent calls to mysql_stmt_fetch fail with an error. Curiously, if I replace > stmt__ <- newForeignPtr mysql_stmt_close stmt_ with > stmt__ <- newForeignPtr_ stmt_ in my newStatement routine (i.e., so that mysql_stmt_close is never called), then fetchAllRows will merrily fetch all the rows from my statement handle. The down side, of course, being that I'll leak statement handles. So, I'm completely puzzled as to how I can continue to extract values from the apparently unreachable pointer! Using System.Mem.Weak, I've verified that: * The Statement record that I return from newStatement becomes unreachable. * The applied value of fetchRow becomes unreachable; e.g.: let r = fetchRow mysql__ stmt__ results addFinalizer r $ putStrLn "r is unreachable!" I'm not sure how this can be, given that fetchAllRows appears to be explicitly maintaining a reference to sth, which in turn ought to reference my fetchRow application. I've created a test program that directly invokes my driver code the same way that the generic HDBC layer does, and have verified that the lack of "-fno-cse" with unsafeInterleaveIO in the generic HDBC module is not relevant. I was similarly able to verify that this problem occurs with "-O0", so it's not due to any particular GHC optimization. Any thoughts on how to debug this would be greatly appreciated! Thanks in advance, chris

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Re: [Haskell-cafe] How to create an online poll
by gregg reynolds 20 Feb '09

20 Feb '09

See also www.surveymonkey.com Bulat Ziganshin <bulat.ziganshin(a)gmail.com> wrote: >Hello haskell-cafe, > >http://zohopolls.com/ > >-- >Best regards, > Bulat mailto:Bulat.Ziganshin@gmail.com > >_______________________________________________ >Haskell-Cafe mailing list >Haskell-Cafe(a)haskell.org >http://www.haskell.org/mailman/listinfo/haskell-cafe

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ANNOUNCE: Cabal-1.6.0.2 and cabal-install-0.6.2
by Duncan Coutts 20 Feb '09

20 Feb '09

I'm pleased to announce point-releases of the Cabal library and the cabal-install command line tool. If you are already using cabal-install then you can upgrade both using: $ cabal update $ cabal install Cabal cabal-install New users you can get it from: http://haskell.org/cabal/download.html For users on unix systems there is a source tarball with a bootstrap script. For users on Windows systems there is a pre-compiled cabal.exe. Release notes ============= Cabal-1.6.0.2 ------------- This is a point-release in the stable 1.6.x series. It is expected that this release will be included with ghc-6.10.2. It has a number of fixes and minor improvements. The most noticeable change is that Cabal now checks at configure time that C libraries and header files are available. This is known to break a small number of packages. The maintainers of these packages have been notified. Changes since 1.6.0.1: * New configure-time check for C headers and libraries * Added language extensions present in ghc-6.10 * Added support for NamedFieldPuns extension in ghc-6.8 * Fix in configure step for ghc-6.6 on Windows * Fix warnings in Path_pkgname.hs module on Windows * Fix for exotic flags in ld-options field * Fix for using pkg-config in a package with a lib and an executable * Fix for building haddock docs for exes that use the Paths module * Fix for installing header files in subdirectories * Fix for the case of building profiling libs but not ordinary libs * Fix read-only attribute of installed files on Windows * Ignore ghc -threaded flag when profiling in ghc-6.8 and older cabal-install-0.6.2 ------------------- This release contains a number of incremental improvements, including some new features. We expect to do another 0.6.x release in the not too distant future focusing on improvements in the way package dependencies are selected. Changes since 0.6.0: * The upgrade command has been disabled in this release * The configure and install commands now have consistent behaviour * Reduce the tendency to re-install already existing packages * The --constraint= flag now works for the install command * New --preference= flag for soft constraints / version preferences * Improved bootstrap.sh script, smarter and better error checking * New cabal info command to display detailed info on packages * New cabal unpack command to download and untar a package * HTTP-4000 package required, should fix bugs with http proxies * Now works with authenticated proxies. * On Windows can now override the proxy setting using an env var * Fix compatibility with config files generated by older versions * Warn if the hackage package list is very old * More helpful --help output, mention config file and examples * Better documentation in ~/.cabal/config file * Improved command line interface for logging and build reporting * Minor improvements to some messages Changes since 0.5.2: * Constraint solver can now cope with base 3 and base 4 * Allow use of package version preferences from hackage index * More detailed output from cabal install --dry-run -v * Improved bootstrap.sh Bugs and feature requests ========================= This is an excellent opportunity to make sure your favourite bug or feature request is properly described in our bug tracker: http://hackage.haskell.org/trac/hackage/ To help us guide development priorities please add yourself to the ticket's cc list and describe why that bug or feature is important to you. Credits ======= On behalf of the Cabal hackers and the community generally I'd like to thank the people who have contributed patches for these releases: * Gleb Alexeyev * Samuel Bronson * Thomas Schilling * Ganesh Sittampalam * Andrea Vezzosi Get involved ============ There's still a lot to do! We have big plans for Cabal-2.0, cabal-install and the Hackage website. So if you're interested in helping out with this core infrastructure project then: * subscribe to the cabal-devel mailing list: http://www.haskell.org/mailman/listinfo/cabal-devel * grab the source: http://haskell.org/cabal/code.html * read the guide to the source code: http://hackage.haskell.org/trac/hackage/wiki/SourceGuide * take a look at our list of bugs and feature requests: http://hackage.haskell.org/trac/hackage/report/12 especially the easy tickets: http://hackage.haskell.org/trac/hackage/report/13 Duncan

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Uses of `fix' combinator
by Khudyakov Alexey 19 Feb '09

19 Feb '09

Hello, While browsing documentation I've found following function > -- | @'fix' f@ is the least fixed point of the function @f@, > -- i.e. the least defined @x@ such that @f x = x@. > fix :: (a -> a) -> a > fix f = let x = f x in x I have two questions. How could this function be used? I'm unable to imagine any. Naive approach lead to nothing (no surprise): Prelude Data.Function> fix (^^2) <interactive>: out of memory (requested 2097152 bytes) Second question what does word `least' mean?`a' isn't an Ord instance. -- Khudyakov Alexey

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