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Hoogle and Network.Socket
by Thomas DuBuisson 24 Feb '09

24 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 24 Feb '09

24 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 24 Feb '09

24 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 24 Feb '09

24 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 23 Feb '09

23 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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