February 2009 - Haskell-Cafe

Help with another Bird problem (3.3.4)
by Peter Hilal 24 Feb '09

24 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 24 Feb '09

24 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 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 23 Feb '09

23 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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